Co-reporter:Xiao-Rong Sun, Zhi-Qiang Cao, Rui-Ying Bao, Zhengying Liu, Bang-Hu Xie, Ming-Bo Yang, and Wei Yang
ACS Sustainable Chemistry & Engineering September 5, 2017 Volume 5(Issue 9) pp:8334-8334
Publication Date(Web):August 14, 2017
DOI:10.1021/acssuschemeng.7b02121
A facile and green route to fabricate sustainable and biodegradable tridimensional interconnected hierarchically meso- and macroporous polylactide (PLA) monoliths was developed. The tunable morphologies and controllable pore sizes of the monoliths based on the stereocomplex (sc) crystallization of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) during the melt blending process were caused by the macro- and microphase separation between PLA and poly(ethylene oxide) (PEO). The proposed approach can be easily scaled-up and is environmentally sustainable, and it involves neither any toxic chemical reagents nor templates. The hierarchical morphologies of the porous materials contain mesopores regulated by the sc crystallite network formed during melt processing and macropores induced by macrophase separation. The porous structure was influenced by PDLA contents seriously, and the construction of interconnected pores made up of sc crystallite tridimensional network appears at a low PEO content of 20 wt %. The porous polymer monolith featured very good hydrophobicity with a water contact angle over 135°, as well as the strong lipophilicity, endowing the materials with potential applications in selective oil–water separation. Moreover, the much higher thermal and chemical resistance of the porous PLA monoliths based on sc crystallite network allowed us to significantly broaden the applications of the adsorbent in some harsh conditions and catalytic systems compared to those based solely on PLLA.Keywords: Hierarchical porous materials; Polylactide; Stereocomplex crystallization;
Co-reporter:Peng Yu, Rui-Ying Bao, Xiao-Jun Shi, Wei Yang, Ming-Bo Yang
Carbohydrate Polymers 2017 Volume 155() pp:507-515
Publication Date(Web):2 January 2017
DOI:10.1016/j.carbpol.2016.09.001
GO, HA and CS self-assemble into composites with an oriented microstructure.The self-assembly was performed under simultaneous crosslinking and reduction.HA was well loaded and fixed in the composite.The composite hydrogels show balanced strength and toughness.The composite hydrogels possess high porosity and large pore size.Graphene hydrogel has shown greatly potentials in bone tissue engineering recently, but it is relatively weak in the practical use. Here we report a facile method to synthesize high strength composite graphene hydrogel. Graphene oxide (GO), hydroxyapatite (HA) nanoparticles (NPs) and chitosan (CS) self-assemble into a 3-dimensional hydrogel with the assistance of crosslinking agent genipin (GNP) for CS and reducing agent sodium ascorbate (NaVC) for GO simultaneously. The dense and oriented microstructure of the resulted composite gel endows it with high mechanical strength, high fixing capacity of HA and high porosity. These properties together with the good biocompatibility make the ternary composite gel a promising material for bone tissue engineering. Such a simultaneous crosslinking and reduction strategy can also be applied to produce a variety of 3D graphene-polymer based nanocomposites for biomaterials, energy storage materials and adsorbent materials.
Co-reporter:Tao Gao, Yuan-Yuan Li, Rui-Ying Bao, Zheng-Ying Liu, Bang-Hu Xie, Ming-Bo Yang, Wei Yang
Composites Science and Technology 2017 Volume 152(Volume 152) pp:
Publication Date(Web):10 November 2017
DOI:10.1016/j.compscitech.2017.09.014
The performance of polymer blends greatly depends on the phase morphologies and the incorporation of nanofillers provides a low-cost but efficient strategy to tailor the morphology and performance of immiscible polymer blends. In this work, we obtained co-continuous like morphology in poly(l-lactide) (PLLA)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) blend with highly asymmetric composition (80/20, wt/wt) through the self-networking behavior of multi-walled carbon nanotubes (MWCNTs). It was found that the electrical conductivity and the ductility of PLLA/P(3HB-co-4HB)/MWCNTs composites were enhanced at the same time compared with PLLA/MWCNTs composites. The percolation threshold of the prepared PLLA/P(3HB-co-4HB)/MWCNTs composites was 0.58 wt%, 36% lower than that of PLLA/MWCNTs composites and the highest value of elongation at break for PLLA/P(3HB-co-4HB)/MWCNTs composites was 226.4% when the content of MWCNTs was 1 wt%. The results indicate that MWCNTs can contribute to the formation of co-continuous like structure and our work provides a new way to prepare biodegradable high-performance conductive polymer composites with excellent conductivity and mechanical properties.
Co-reporter:Jie Yang, Li-Sheng Tang, Rui-Ying Bao, Lu Bai, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Chemical Engineering Journal 2017 Volume 315(Volume 315) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.cej.2017.01.045
•Very low content of GNP is introduced into PEG/BN composite PCMs.•Thermal conductivity and photoabsorption ability of composite PCMs are enhanced.•GNP contributes to the perfect conductive network and sunlight harvesting ability.•Solar-to-thermal & solar-to-electric energy conversion and storage are realized.Phase change materials (PCMs) with high thermal conductivity and efficient solar energy conversion have recently attracted much attention. However, a facile strategy to enhance thermal conductivity and realize energy conversion and storage is still eagerly desired. In this work, a very low content of graphene nanoplatelets (GNP) is introduced into poly (ethylene glycol) (PEG)/boron nitride (BN) composite PCMs, resulting in great improvement in thermal conductivity and photoabsorption ability via a facile solution blending process. The presence of GNP contributes to enhancing thermal conductivity and realizing efficient solar energy conversion (including solar-to-thermal and solar-to-electric energy conversion) for the PEG/BN/GNP composite PCMs owing to the formation of improved BN/GNP thermally conductive network and the improvement of sunlight harvesting ability, respectively. Thermophysical properties demonstrate that compared with PEG/BN composite PCMs at the same BN content, PEG/BN/GNP composite PCMs containing a low GNP content maintain comparable energy storage density. The study sheds light on the realization of solar energy utilization and storage of the organic PCMs requiring high thermal conductivity.A kind of multifunctional composite PCMs with synergistic enhancement of thermal conductivity by introducing BN and very low content of GNP for light-thermal-electric energy conversion and utilization have been developed.Download high-res image (130KB)Download full-size image
Co-reporter:Tao Gong, Meng-Qi Liu, Hu Liu, Si-Piao Peng, Ting Li, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, Ming-Bo Yang, Zhanhu Guo
Polymer 2017 Volume 110(Volume 110) pp:
Publication Date(Web):10 February 2017
DOI:10.1016/j.polymer.2016.12.056
•MWCNTs can disperse homogeneously in PEO.•MWCNTs migrate from PEO phase to ORC phase during melt compounding.•MWCNTs maintain homogenous dispersion in ORC after etching PEO phase by water.•Such ORC/MWCNTs composites show drastically reduced percolation threshold and improved mechanical performance.A thermodynamic and kinetic method based on the selective distribution and migration of multi-walled carbon nanotubes (MWCNTs) in polyoxyethylene (PEO)/ethylene-α-octene random copolymer (ORC) composite system was reported to improve the dispersion of MWCNTs in ORC. Scanning electron micrographs and transmission electron micrographs confirmed that MWCNTs could almost completely migrate from the PEO phase to the ORC phase during melt compounding and lead to tremendously improved dispersion of MWCNTs in ORC, compared with traditional melt compounded ORC/MWCNT composites. Rheological analysis revealed that better MWCNTs network was developed at a lower content of MWCNTs with an improved dispersion of MWCNTs in ORC. The percolation threshold was drastically reduced from 3.82 to 0.35 vol % and the electrical conductivity was tremendously improved. The mechanical properties were also fully enhanced in comparison with traditional melt compounded ORC/MWCNT composites owing to the homogeneous dispersion of MWCNTs. These results manifest that, by proper selection of components with a selective distribution of MWCNTs and controlling the migration process of MWCNTs in the composites, the dispersion of MWCNTs in polymer matrix and resulting performance of the nanocomposites can be greatly improved.Download high-res image (233KB)Download full-size image
Co-reporter:Le Li, Zhi-Qiang Cao, Rui-Ying Bao, Bang-Hu Xie, Ming-Bo Yang, Wei Yang
European Polymer Journal 2017 Volume 97(Volume 97) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.eurpolymj.2017.10.025
•A novel macromolecular plasticizer, PLLA-PEG-PLLA triblock copolymer was synthesized.•PLLA-PEG-PLLA triblock copolymer was used to tailor the crystallization behavior of PLLA.•The structure of the copolymer determines the nucleation and plasticizing effect for PLLA.•The copolymer can suppress PEG crystallization-induced phase separation for PLLA matrix.Different from traditional small molecular plasticizers, poly(l-lactic acid) (PLLA)-polyethylene glycol (PEG)-PLLA triblock copolymers were synthesized by ring-opening polymerization of L-lactide on the end hydroxyls of PEG and blended with PLLA, to enhance the crystallization of PLLA. Non-isothermal and isothermal crystallization studies show that the triblock copolymer enhances the crystallization of PLLA due to the nucleation effect from PLLA segments and the plasticization effect from PEG segments, which strongly depends on the structure of copolymers. With shorter PLLA segment and longer PEG segment of the triblock copolymer, the glass transition temperature and cold crystallization temperature of the blends decrease, and the degree of crystallinity and spherulite growth rate increase owing to the higher content of PEG. However, triblock copolymers with relatively longer PLLA segment and shorter PEG segment show unique nucleation effects for PLLA, leading to the elevation of crystallization temperature of PLLA. The results confirm that the crystallization acceleration of PLLA can be ascribed to the nucleation and plasticization effect, and the plasticization effect is more significant. What’s more, the introduction of triblock copolymers improves the compatibility and durability due to the good interfacial interaction with PLLA matrix even at a high loading.Download high-res image (225KB)Download full-size image
Co-reporter:Qianyu Wang;Peng Yu;Lu Bai;Ruiying Bao;Ning Wang;Chuanbing Cheng;Zhengying Liu;Mingbo Yang;Zhanhu Guo
Nanoscale (2009-Present) 2017 vol. 9(Issue 46) pp:18194-18201
Publication Date(Web):2017/11/30
DOI:10.1039/C7NR06902B
Inspired by the leaf/vein structure of leaves which effectively supports the photosynthesis of green plants, a nano-leaf/vein bionic structure of self-assembled TiO2/MoS2 composites is applied to induce the reversible photochromic reactions of methylene blue (MB) for the first time. This reversible photochromic phenomenon gives a novel performance for the TiO2/MoS2 composites and expands their applications. Similar to the case where the natural vein network in leaves ensures the efficient material transfer and energy exchange for photosynthesis, the bionic internal MoS2 vein network in the composites ensures the efficient separation and directional transfer of photo-generated carriers to restrain the photocatalytic degradation reactions and to enhance the reversible photochromic reactions. Furthermore, the photosensitive applications of the TiO2/MoS2/MB systems with such a self-assembled nano-leaf/vein bionic structure are discussed with two typical photoelectric sensory models for both controllers and detectors.
Co-reporter:Xing Zhao;Lu Bai;Rui-Ying Bao;Zheng-Ying Liu;Ming-Bo Yang
RSC Advances (2011-Present) 2017 vol. 7(Issue 73) pp:46297-46305
Publication Date(Web):2017/09/26
DOI:10.1039/C7RA08074C
Two kinds of fumed SiO2 nanoparticles with the same average diameter but distinct surface characteristics (hydrophilic A200 and hydrophobic R974) were incorporated into an ethylene-α-olefin block copolymer (OBC) to prepare high-performance thermoplastic elastomeric nanocomposites via simple melt mixing. Hydrophilic A200 exhibits a particular chain-like distribution while hydrophobic R974 shows a homogenous dispersion in the nanocomposites. The rheological percolation threshold of OBC/A200 nanocomposites was much lower than that of OBC/R974 nanocomposites, showing a more developed nanoparticle network in OBC/A200 nanocomposites. Thermodynamic analysis revealed that the particular chain-like distribution of A200 and more developed network structure are due to the selective localization of hydrophilic A200 in the melt. The reinforcement effect of hydrophilic A200 in OBC/A200 nanocomposites is always higher than that of hydrophobic R974 in OBC/R974 nanocomposites at the same filler loading, and even better, the increments in the tensile modulus of OBC/A200 nanocomposites are almost four times higher than that of OBC/R974 nanocomposites at the same silica loading. Besides, the dielectric permittivity of the OBC/A200 composite at low frequency was also higher than that of the OBC/R974 composite with the same loading of filler at the same frequency. These results provide guidance for the preparation of high-performance elastomeric nanocomposites with both excellent mechanical performance and enhanced dielectric properties.
Co-reporter:Yang Liu;Xiaojie She;Xiaoni Zhang;Chenglu Liang;Jingjie Wu;Peng Yu;Yusuke Nakanishi;Banghu Xie;Hui Xu;Pulickel M. Ajayan
RSC Advances (2011-Present) 2017 vol. 7(Issue 87) pp:55269-55275
Publication Date(Web):2017/12/01
DOI:10.1039/C7RA10826E
Photocatalysis is one of the most promising technologies for solar energy conversion. With the development of photocatalysis technology, the creation of low-dimensional structure photocatalysts with improved properties becomes more and more important. Metallic 1T-TiS2 nanodots with a low-dimensional structure were introduced into environmentally friendly two-dimensional g-C3N4 (2D-C3N4) nanosheets by a solvothermal method. It was found that the ultrathin TiS2 nanodots were uniformly anchored on the surface of the 2D-C3N4. The effective suppression of electron–hole recombination was realized due to the addition of the intrinsic metallic property of 1T-TiS2 in the prepared nanocomposite. The 5 wt% TiS2/2D-C3N4 nanocomposite exhibited the best photocatalytic performance and the degradation rate towards RhB was ca. 95% in 70 min, which showed an improvement of ca. 30% in comparison with 2D-C3N4. The results indicate that the obtained TiS2/2D-C3N4 nanocomposite is a promising photocatalyst for practical applications.
Co-reporter:Jie Yang;Peng Yu;Li-Sheng Tang;Rui-Ying Bao;Zheng-Ying Liu;Ming-Bo Yang
Nanoscale (2009-Present) 2017 vol. 9(Issue 45) pp:17704-17709
Publication Date(Web):2017/11/23
DOI:10.1039/C7NR05449A
An ice-templating self-assembly strategy and a vacuum impregnation method were used to fabricate polyethylene glycol (PEG)/hierarchical porous scaffold composite phase change materials (PCMs). Hierarchically interconnected porous scaffolds of boron nitride (BN), with the aid of a small amount of graphene oxide (GO), endow the composite PCMs with high thermal conductivity, excellent shape-stability and efficient solar-to-electric energy conversion. The formation of a three-dimensional (3D) thermally conductive pathway in the composites contributes to improving the thermal conductivity up to 2.36 W m−1 K−1 at a relatively low content of BN (ca. 23 wt%). This work provides a route for thermally conductive and shape-stabilized composite PCMs used as energy storage materials.
Co-reporter:Hai-Yan Yin;Xin-Feng Wei;Rui-Ying Bao;Quan-Xiao Dong;Zheng-Ying Liu;Bang-Hu Xie;Ming-Bo Yang
CrystEngComm (1999-Present) 2017 vol. 19(Issue 12) pp:1689-1690
Publication Date(Web):2017/03/20
DOI:10.1039/C7CE90030A
Correction for ‘High-melting-point crystals of poly(L-lactic acid) (PLLA): the most efficient nucleating agent to enhance the crystallization of PLLA’ by Hai-Yan Yin et al., CrystEngComm, 2015, 17, 2310–2320.
Co-reporter:Sen-Qi Shen;Rui-Ying Bao;Zheng-Ying Liu;Bang-Hu Xie;Ming-Bo Yang
CrystEngComm (1999-Present) 2017 vol. 19(Issue 12) pp:1648-1657
Publication Date(Web):2017/03/20
DOI:10.1039/C7CE00093F
The morphology evolution of an organic nucleating agent (NA) in poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blends was investigated under a series of multi-step isothermal and nonisothermal processes at identical NA solubility achieved via the same NA concentration and final molten temperature of heating (Tf). It was found that the morphology of NA frameworks depended on the supercooling determined by the recrystallization temperature of the NA in the polymer melt, except for NA solubility. When the NA partly dissolved in the matrix, the residuum of the original flat-plate NA acting as a nucleus induced recrystallization at a low degree of supercooling, and small sheet-like NA particles formed in the melt. When the NA dissolved in the matrix absolutely, NA aggregation increased in the melt due to the low nucleation density of the NA itself. The shape of the NA aggregation depended on the recrystallization temperature. With the increase in the supercooling, the large aggregated sheet-like NA transformed into a dendritic-like framework accompanied by a decrease in the stem size of the NA frameworks. Moreover, the stereocomplex efficiency of the blend was influenced by the effective nucleation surface induced by the shape of the NA aggregation. For PLLA/PDLA blends with 1.0 wt% NA, the crystallization half time (t1/2) of stereocomplex (sc) crystallites at the crystallization temperature of 180 °C is as long as 79.8 min for the sample with a large aggregated sheet-like NA, with 1 order of magnitude reduction for that with a dendritic-like NA framework, leading to a t1/2 of 7.9 min. The morphological control of NA frameworks is of great significance to guide the formation of various crystal morphologies of sc crystallites. The established relationship between the self-assembled morphology of NA and NA concentration, NA solubility and supercooling affords guidance in practical processing to control the crystal morphology and polymorphic crystalline morphology of PLLA/PDLA blends via tuning the crystal morphology of NA in the polymer matrix.
Co-reporter:Tao Gong;Rui-Ying Bao;Zheng-Ying Liu;Bang-Hu Xie;Ming-Bo Yang
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 20) pp:12712-12719
Publication Date(Web):2017/05/24
DOI:10.1039/C7CP01278K
Polypropylene (PP) and five kinds of monodisperse polystyrene (PS) with different terminal relaxation times were used to explore the relationship between the mobility of polymer molecular chains and the coarsening process of immiscible polymer blends with a co-continuous morphology under quiescent melt annealing at different temperatures. The terminal relaxation time of all neat PP and PS was determined by a rheological approach to characterize the mobility of molecular chains. A selective dissolution experiment showed that all PP/PS (50/50) blends maintained a co-continuous structure during the whole annealing process. Significant coarsening behaviors were observed for all PP/PS blends under a scanning electron microscope. A linear time dependence of the size of the PS phase was found in all PP/PS blends and the coarsening phenomenon was more obvious with the decrease of the terminal relaxation time of the PS phase because of the increase of the mobility of the polymer molecular chains. A direct relationship between the phase coarsening rate and the terminal relaxation time of the PS phase was found for the first time and it satisfied the equation . According to this equation, the formulae and k ∝ Mw−1 can be derived, which can provide significant information for the control of the phase coarsening process of immiscible polymer blends with a co-continuous morphology.
Co-reporter:Peng Yu, Han-Qing Wang, Rui-Ying Bao, Zhengying Liu, Wei YangBang-Hu Xie, Ming-Bo Yang
ACS Sustainable Chemistry & Engineering 2017 Volume 5(Issue 2) pp:
Publication Date(Web):December 29, 2016
DOI:10.1021/acssuschemeng.6b02254
Sponge-like chitosan (CS)/reduced graphene oxide (rGO)/montmorillonite (MT) porous composite hydrogels were synthesized with a facile strategy of in situ reduction of graphene oxide (GO) without cross-linking of CS. Integral pore structure can be formed in the hydrogels when proper amount of MT was introduced. The composite hydrogel can restore to the original shape and dimension after compressive deformation like a sponge and show good stability in acid condition. Batch equilibrium measurements on the composite porous hydrogel were carried out to optimize the parameters for the removal of hexavalent chromium ions (Cr(VI)). The results reveal that the Cr(VI) ion sorption of the composite hydrogels is highly pH dependent and is the most effective at pH = 2. The sorption capacity increases with increasing temperature and the maximum Cr(VI) uptake of the composite hydrogel is 87.03 mg/g at 288 K. The sorption follows pseudo-second-order kinetic model and Langmuir isotherm. The composite porous hydrogels can be repeatedly used as adsorbent and a high sorption capacity after repeated usage can be maintained. Such an in situ GO reduction strategy can also be used to fabricate a variety of porous 3D polymer/rGO-based nanocomposites for biomaterials, energy storage materials, and adsorbent materials.Keywords: Chitosan/reduced graphene oxide/montmorillonite composite hydrogel; Cr(VI) sorption; In situ reduction of graphene oxide strategy; Porous structure; Repeated usage;
Co-reporter:Guoqiang Qi;Jie Yang;Ruiying Bao;Dongyun Xia;Min Cao
Nano Research 2017 Volume 10( Issue 3) pp:802-813
Publication Date(Web):2017 March
DOI:10.1007/s12274-016-1333-1
Recently, graphene foam (GF) with a three-dimensional (3D) interconnected network produced by template-directed chemical vapor deposition (CVD) has been used to prepare composite phase-change materials (PCMs) with enhanced thermal conductivity. However, the pore size of GF is as large as hundreds of micrometers, resulting in a remarkable thermal resistance for heat transfer from the PCM inside the large pores to the GF strut walls. In this study, a novel 3D hierarchical GF (HGF) is obtained by filling the pores of GF with hollow graphene networks. The HGF is then used to prepare a paraffin wax (PW)-based composite PCM. The thermal conductivity of the PW/HGF composite PCM is 87% and 744% higher than that of the PW/GF composite PCM and pure PW, respectively. The PW/HGF composite PCM also exhibits better shape stability than the PW/GF composite PCM, negligible change in the phase-change temperature, a high thermal energy storage density that is 95% of pure PW, good thermal reliability, and chemical stability with cycling for 100 times. More importantly, PW/HGF composite PCM allows light-driven thermal energy storage with a high light-to-thermal energy conversion and storage efficiency, indicating its great potential for applications in solar-energy utilization and storage.
Co-reporter:Li-Sheng Tang, Jie Yang, Rui-Ying Bao, Zheng-Ying Liu, Bang-Hu Xie, Ming-Bo Yang, Wei Yang
Energy Conversion and Management 2017 Volume 146(Volume 146) pp:
Publication Date(Web):15 August 2017
DOI:10.1016/j.enconman.2017.05.037
•GAs with diverse structure are fabricated by tuning the oxidation degree of GO.•The composite PCMs exhibits excellent shape-stability at high temperature.•The structure of GA plays a significant role in the shape-stability of composite PCMs.•Efficient light-to-thermal energy conversion and storage are realized.Polyethylene glycol (PEG)/graphene oxide aerogel (GA) composite phase change materials (PCMs) were prepared by introducing PEG into GAs from graphene oxide (GO) with different oxidation degree via vacuum impregnation. The structures of GAs were tuned by the oxidation levels of GO. A series of characterizations were used to analyze the chemical structure of GOs, including X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analysis. Structural analyses confirmed that the oxygenated functional groups increased and the hydroxyl groups were transformed into carboxyl and epoxy groups with increasing oxidation level. In addition, the graphitic nature of GO decreased while the sp3 domains of GOs increased owing to the disruption of the graphitic stacking order. Morphology analysis showed that the breakage of graphene sheet became more serious with the oxidation level increasing. When GAs prepared with GOs of higher oxidation levels were used, the composite PCMs showed excellent shape-stability during phase change and excellent thermal repeatability. The change of dimension for PGA6-40 heated from 35 °C to 150 °C was negligible under the load of a constant force (7 N). Efficient photo-to-thermal energy conversion and storage was realized in the composite PCMs.Effects of oxidation degree of GO on the structure and performance of shape-stabilized PCMs for an effective photo-to-thermal energy conversion and storage are examined.Download high-res image (96KB)Download full-size image
Co-reporter:Changping Feng, Haiying Ni, Jun Chen, and Wei Yang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 30) pp:19732-19738
Publication Date(Web):July 8, 2016
DOI:10.1021/acsami.6b03723
Thermally conductive polymer composites have aroused significant academic and industrial interest for several decades. Herein, we report a novel fabrication method of graphite/polypropylene (PP) composites with high thermal conductivity in which graphite flakes construct a continuous thermally conductive network. The thermal conductivity coefficient of the graphite/PP composites is markedly improved to be 5.4 W/mK at a graphite loading of 21.2 vol %. Such a great improvement of the thermal conductivity is ascribed to the occurrence of orientations of crystalline graphite flakes with large particles around PP resin particles and the formation of a perfect thermally conductive network. The model of Hashin–Shtrikman (HS) is adopted to interpret the outstanding thermally conductive property of the graphite/PP composites. This work provides a guideline for the easy fabrication of thermally conductive composites with network structures.
Co-reporter:Zhi-Qiang Cao, Xiao-Rong Sun, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, and Ming-Bo Yang
ACS Sustainable Chemistry & Engineering 2016 Volume 4(Issue 5) pp:2660
Publication Date(Web):April 5, 2016
DOI:10.1021/acssuschemeng.6b00176
Multiwalled carbon nanotube (CNT) grafted poly(l-lactide)-block-poly(d-lactide) copolymer (CNT-L-D) was synthesized by ring opening polymerization of d-lactide on the end hydroxyls of poly(l-lactide) (PLLA) prepolymers grafted on the surface of CNT. The stereocomplexation of solution cast and melt crystallized CNT-L-D, PLLA/CNT-L-D, and PDLA/CNT-L-D blends were investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and optical microscopic observation. Solution cast and melt crystallized CNT-L-D copolymer form exclusive stereocomplex (sc) crystallites. The melting temperature, normalized crystallinity, and the fraction of sc crystallites for both solution cast and melt crystallized PDLA/CNT-L-D blends are higher than those of PLLA/CNT-L-D blends, indicating distinct stereocomplexation mechanisms in both blends. The heterogeneous nucleating effect of CNT makes the PLLA block grafted directly on CNT always participate in sc crystallite formation. So, for PDLA/CNT-L-D blends, the stereocomplexation mainly occurs between PLLA blocks and free PDLA molecules, and for PLLA/CNT-L-D blends, the stereocomplexation mainly occurs between PLLA blocks and PDLA blocks. The nucleating effect of CNT enhances the sc formation of free PDLA molecules during solution casting and melt crystallization by the introduction of CNT-L-D, and the sc crystallites can reform after complete melting. However, the dilution effect of free PLLA molecules to PDLA blocks lowered down the stereocomplex efficiency of PLLA/CNT-L-D blends compared with that of PDLA/CNT-L-D blends, especially during melt crystallization, and the morphology transition of sc crystallites occurs from original well-rounded Maltese-cross spherulites for PDLA/CNT-L-D blends to dendritic form in PLLA/CNT-L-D blends.Keywords: CNT grafted poly(l-lactide)-block-poly(d-lactide); Poly(lactide)s; Stereocomplex behavior
Co-reporter:Li-Feng Ma, Rui-Ying Bao, Rui Dou, Shao-Di Zheng, Zheng-Ying Liu, Rui-Yan Zhang, Ming-Bo Yang, Wei Yang
Composites Science and Technology 2016 Volume 128() pp:176-184
Publication Date(Web):18 May 2016
DOI:10.1016/j.compscitech.2016.04.001
Conductive elastomeric materials of multi-walled carbon nanotube (MWCNT) filled thermoplastic vulcanizate (TPV) based on polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends were fabricated via different processing procedures, i.e., one-step and two-step methods, to control strain sensitivity aiming at applications from strain sensors to stretchable conductors. The phase size of cross-linked EPDM could be effectively tuned and the average diameter of EPDM particles was 550 nm for one-step TPV and 230 μm for two-step TPV. Uniform dispersion of MWCNTs in two-step TPV and serious aggregations of MWCNTs in one-step TPV were observed. Both TPVs showed excellent strain-resistance repeatability for 50 tensile and recovery cycles. The one-step-TPV showed a potential to be used as strain sensor due to a high gauge factor (GF) of 1004 at a strain of 100%, while the resistance for the two-step TPV composite was independent with strain even at a strain of 200%, resulting in a stretchable conductor with excellent resistance memory effect. The different strain sensitivity can be explained by the orientation of PP matrix. Moreover, the two-step TPV showed much lower electrical conductivity percolation threshold, 0.65 wt.%. This work provided a simple route to tune the strain sensitivity of MWCNTs filled TPVs based on PP/EPDM blends for applications from strain sensors to highly stretchable conductor through different processing procedures to control the morphologies and MWCNT dispersion.
Co-reporter:C. P. Feng, L. Chen, F. Wei, H. Y. Ni, J. Chen and W. Yang
RSC Advances 2016 vol. 6(Issue 70) pp:65709-65713
Publication Date(Web):04 Jul 2016
DOI:10.1039/C6RA13921C
Polymer composites with segregated structures based on ultrahigh molecular weight polyethylene (UHMWPE) and graphite flakes were fabricated by a novel binder-mixing method and the traditional solvent-mixing method. Compared with the solvent-mixing method, the thermal conductivity of composites fabricated by the binder-mixing method improved on average by 26.27 percent at the volume fraction of graphite flakes from 2.22–18.83 vol%. Optical and SEM images showed that the binder-mixing method results in the formation of a more continuous and more homogeneous conductive network and wider thermally conductive paths, leading to the greatly improved thermal conductivity.
Co-reporter:Yang Liu, Cheng-Lu Liang, Jing-jie Wu, Rui-Ying Bao, Guo-Qiang Qi, Yu Wang, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2016 vol. 6(Issue 33) pp:27267-27271
Publication Date(Web):11 Mar 2016
DOI:10.1039/C6RA02942F
As a promising material with broad applications, reduced graphite oxide (rGO) hydrogels have attracted more and more great attention recently. However, most reports on rGO hydrogels focused on their applications, while the formation mechanism has not been paid enough attention. For the first time, we demonstrated the higher the ability of the solvents to form hydrogen bonds with the rGO sheets, the better the structural stability and properties of gel are. This study indicates that hydrogen bonding between solvent molecules and the oxygen-containing functional groups on rGO sheets is vital to achieve high-performance gels.
Co-reporter:Cheng-Lu Liang, Yang Liu, Rui-Ying Bao, Yong Luo, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Journal of Alloys and Compounds 2016 Volume 678() pp:80-86
Publication Date(Web):5 September 2016
DOI:10.1016/j.jallcom.2016.03.274
•Fe3O4 NPs with grain size of ca. 9 nm were coprecipitated and stabilized.•Fe3O4/rGO composites with different mass ratios were synthesized.•Fe3O4/rGO composites were used as anode material for LIB.•Optimum composition of the composites for improved cycling performance was explored.Well dispersed Fe3O4 nanoparticle suspensions with grain size of about 9 nm were coprecipitated and then compounded with different amount of GO (graphite oxide) followed by reduction of GO to obtain Fe3O4/rGO (reduced graphite oxide) composites with different component ratios. The as-obtained Fe3O4/rGO composites were used as anode materials for lithium ion batteries to investigate the best component ratio of the composite for the cycling performance. Fe3O4/rGO composite electrode containing 44.9 wt% Fe3O4 displayed the best cycling capacity of above 300 mA h g−1 at 1000 mA g−1 after 100 cycles and it was interesting to find that the trend of impedance spectra of Fe3O4/rGO electrodes after some cycles of electrochemical reactions can be well related to the overall cycling performances.
Co-reporter:Lifeng Ma, Ruiying Bao, Zhengying Liu, Wei Yang and Mingbo Yang
RSC Advances 2016 vol. 6(Issue 78) pp:74567-74574
Publication Date(Web):01 Aug 2016
DOI:10.1039/C6RA14731C
Thermoplastic vulcanizates (TPVs), as a special class of high-performance thermoplastic elastomers, have been widely used in the automotive industry, building, and electronics due to their good processability and recyclability. Here, the electrical performance and the formation of dual networks of TPV composites filled with carbon black (CB) based on isotactic polypropylene/ethylene–propylene–diene rubber (iPP/EPDM) blends was investigated by varying the content of the curing agent, phenolic resin (PF). With the incorporation of 6 wt% PF, the crosslinking degree of the EPDM phase reaches a high value of 47.4 wt% and the domains reach the smallest size. The electrical percolation threshold of TPV/CB composites decreases as the cross-linking degree increases and at last maintains a steady value of 13.9 wt%. The morphological structure, dynamic rheology behaviors and crystallization behaviors of TPV/CB composites were characterized to explain the selective dispersion of CB particles and the microstructure evolution of TPV/CB composites. With an increase in the curing degree of the EPDM phase, a denser dual network including the CB conductive network and the network of EPDM particles is formed in the iPP matrix. This study provides an effective strategy to realize the control of electrical properties and the formation of dual networks of TPV composites, and can be easily introduced into industrial applications.
Co-reporter:Zhi-Qiang Cao, Xiao-Rong Sun, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
European Polymer Journal 2016 Volume 83() pp:42-52
Publication Date(Web):October 2016
DOI:10.1016/j.eurpolymj.2016.08.005
•CNT-PLLA-b-PDLA copolymer was synthesized.•CNT-PLLA-b-PDLA was used to tailor the crystallization behavior of PLLA/PDLA blend.•Homocrystallization was suppressed in PLLA/PDLA blend.•Stereocomplex crystallization was enhanced in PLLA/PDLA blend.Self-nucleation is considered to be the ideal case for the nucleation of polymer crystallization; however, the nucleation effect of stereocomplex (sc) crystallites for sc crystallization of poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) blend is hard to be evaluated, due to that sc crystallites form through intermolecular packing of PLLA and PDLA molecular chains and sc crystallite is a good nucleating agent for the homocrystallization (hc) crystallization of PLLA or PDLA. In the current work, we proposed a facile strategy to tailor the sc crystallization behavior of PLLA/PDLA blend through in-situ preformed sc crystallites. Herein, Multi-walled carbon nanotube (CNT) grafted PLLA-block-PDLA copolymer (CNT-L-D) was synthesized and incorporated into an equimolar high-molecular-weight PLLA and PDLA blend to study its effect on the sc crystallites formation. The results manifested that, sc crystallization is highly enhanced by the addition of CNT-L-D, and sc crystallites can be formed exclusively in the blend with 10 wt% CNT-L-D during isothermal and nonisothermal melt crystallization. With the addition of CNT-L-D into the PLLA/PDLA blend, the sc crystallites formed preferentially between grafted PLLA-b-PDLA induced by CNT work as self-nucleation sites for sc crystallization. The nucleation densities are increased, and the competition between hc and sc crystallization which is the key factor influencing the exclusive formation of sc crystallites is tailored simultaneously. With significantly improved nucleation density and reduced sc spherulites size, sc spherulites cannot be entered by any other growing hc crystalline lamellae and the surface of sc spherulites cannot be covered with hc crystallites, leading to exclusive formation of sc crystallites.
Co-reporter:Tao Gong, Si-Piao Peng, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Composites Part B: Engineering 2016 Volume 99() pp:348-357
Publication Date(Web):15 August 2016
DOI:10.1016/j.compositesb.2016.06.031
A novel continuous segregated structure was constructed in polypropylene (PP)/carbon black (CB) composites, to improve the electrical conductive performance and achieve a balance of the electrical conductivity and mechanical properties. Compared with traditional segregated structures reported in literature, PP matrix maintained a continuous structure instead of being separated completely by the electrical conductive fillers and CB particles formed a thorough conductive network in the continuous segregated PP/CB composites. A percolation threshold as low as 0.37 vol%, which is significantly lower than the percolation threshold of melt compounded PP/CB composites (2.75 vol%) and PP/polystyrene (PS)/CB composites (3.23 vol%) with a double percolation structure, was obtained because of the formation of the two-dimensional conductive network of CB particles. The mechanical performance tests showed that the tensile modulus, strength and elongation of break could be maintained well at CB contents around the percolation threshold. That is, with this novel continuous segregated structure, a balance of strength, toughness and electrical conductivity property can be achieved in conductive polymer composites.
Co-reporter:Xiao-Ting Liu;Rui-Ying Bao;Yan-Mei Li
Journal of Polymer Research 2016 Volume 23( Issue 8) pp:
Publication Date(Web):2016 August
DOI:10.1007/s10965-016-1060-z
Chain entanglements and the entanglement degree determine many processes and behaviors of polymers. In this work, poly(l-lactide) acid (PLLA) samples with markedly decreased entanglements were obtained via a freeze extraction method and the kinetics of entanglement recovery process of freeze-extracted samples was monitored by dynamic rheology approach. The crystallization kinetics of freeze-extracted PLLA samples was further studied by polarized optical microscope, which revealed that the entanglement degree greatly influences the crystallization of PLLA and lower degree of entanglement or disentanglement was conducive to the melt-crystallization of PLLA. The spherulites grew faster in partially disentangled melt than in well entangled melt.
Co-reporter:Sen-Qi Shen, Rui-Ying Bao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Polymer 2016 Volume 95() pp:26-35
Publication Date(Web):11 July 2016
DOI:10.1016/j.polymer.2016.04.038
•β nucleating agent for iPP is grafted onto the surface of MWCNTs through chemical bonding.•The content of β crystals in iPP composite containing MWCNT-NA increase with increasing cooling rates.•The α and β nucleation competition becomes more intensive due to the dual nucleating ability of MWCNT-NA.Simultaneous improvement of stiffness and toughness of isotactic polypropylene (iPP) has caught tremendous effort for decades and previously we have shown that the modification of iPP with combined nanofillers and β-nucleating agent (β-NA) is an efficacious way to balance its stiffness and toughness. However, simultaneous introduction of reinforcing fillers and β-NA generates nucleation competition in the crystallization process and generally the formation of β crystals is depressed, while the nucleation competition induced by β-NA grafted onto the surface of reinforcing fillers was not clear yet. In this work, a kind of novel β-NA for iPP, N,N’-dicyclohexyl-1,5-diamino-2,6-naphthalenedi-carboxamide, was supported onto the surface of multi-walled carbon nanotubes (MWCNTs) through chemical bonds. The α and β nucleating competition among iPP nucleated by β-NA, physically mixed MWCNTs and β-NA (MWCNT + NA), and MWCNT supported β-NA (MWCNT-NA) was systematically investigated. Interestingly, in the presence of MWCNT-NA, iPP showed unique crystallization behaviors. The nucleation competition between α- and β-crystals became intensified and showed temperature dependence, and the relative content of β-crystals increased with increasing cooling rate, which is opposite to the general understanding of crystallization behaviors of semicrystalline polymers, but is highly desired in practical productions. A possible interpretation for this unusual crystallization behavior of iPP is provided.Download full-size image
Co-reporter:Ting Li, Li-Feng Ma, Rui-Ying Bao, Guo-Qiang Qi, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2015 vol. 3(Issue 10) pp:5482-5490
Publication Date(Web):02 Feb 2015
DOI:10.1039/C5TA00314H
Aiming at improved electrical conductive performance and simultaneously enhanced mechanical properties, a novel segregated structure was constructed for poly(ethylene-co-octene) (POE)/multi-walled carbon nanotube (MWCNT) elastomeric conductive composites with chemically cross-linked POE granules. Structural examination revealed the formation of unique phase morphologies with a stable segregated structure, in which the uncross-linked POE/MWCNT phase localized out of the cross-linked granules. With such a novel segregated structure, a percolation threshold as low as 1.5 vol% of MWCNTs was observed, which is significantly lower than the melt compounded POE/MWCNT composites; the stress at 100% and 300% stretching increased for more than 12% and 30%, respectively, and the tensile modulus inherent to the matrix elastomer was maintained. The elastic recovery of the composite with such a novel segregated structure was more than 85% and 65% after large strains up to 100% and 300%, respectively, always higher than the melt compounded POE/MWCNT composites. The Shore A hardness of the elastomeric conductive composites with cross-linked POE granules was also lower, showing better elasticity of POE/MWCNT composites with such a novel segregated structure. All these results demonstrated that the elastomeric POE/MWCNT conductive composites with such a novel segregated structure exhibited greatly reduced percolation thresholds with enhancement in mechanical properties, which provides a new way for the preparation of elastomeric conductive composites with simultaneously improved electrical performance and mechanical properties.
Co-reporter:Ting Li, Jun-Hong Pu, Li-Feng Ma, Rui-Ying Bao, Guo-Qiang Qi, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Polymer Chemistry 2015 vol. 6(Issue 40) pp:7160-7170
Publication Date(Web):26 Aug 2015
DOI:10.1039/C5PY01236H
Ethylene-α-octene copolymers with different chain architectures (ethylene-α-octene random copolymer (ORC) and ethylene-α-octene block copolymer (OBC)) were adopted to prepare elastomeric composites with multi-walled carbon nanotubes (MWCNTs) through melt mixing. Extremely uniform dispersions of MWCNTs in OBC and serious aggregations of MWCNTs in ORC were observed. The percolation threshold of OBC composites was 2.5 vol%, much lower than that of ORC composites. Rheological measurements and thermodynamic analysis revealed that the uniform dispersion of MWCNTs in OBC is due to the selective localization of the nanotubes in the molten state, and the stronger volume exclusion effect of OBC crystals in nanoscopic dimensions towards nanotubes also accounts for the developed MWCNT network after crystallization. Although OBC itself showed lower stress at a certain stretching and tensile modulus than that of ORC, the percentages of reinforcement in stress at a certain stretching and tensile modulus of OBC composites were almost twice as much as that of ORC composites at the same content of MWCNTs. Elongations of OBC composites were all higher than 1600% (even when the MWCNT content was as high as 7.84 vol%) and were always at least 200% larger than that of ORC composites at the same content of MWCNTs. The results provide significant guidance for the preparation of conductive elastomeric materials with both excellent electrical performance and mechanical properties by utilizing thermoplastic polyolefin copolymers with blocky chain architectures.
Co-reporter:Guo-Qiang Qi, Jie Yang, Rui-Ying Bao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Carbon 2015 Volume 88() pp:196-205
Publication Date(Web):July 2015
DOI:10.1016/j.carbon.2015.03.009
The design and preparation of high comprehensive performance composite phase change materials (PCMs) via a straightforward route were pioneered. Graphene oxide (GO) nanosheets were introduced as supporting materials to keep the shape of polyethylene glycol (PEG) stable during the phase change process and graphene nanoplatelets (GNP) were used as conductive fillers to improve the thermal conductivity and electrical conductivity. The comprehensive performance and structure–property relationships of composite PCMs with hybrid graphene nanomaterials were investigated by means of various characterization techniques. The PEG/GO/GNP composite PCM with only 2 wt% GO and 4 wt% GNP hybrid fillers exhibited superior comprehensive performance: thermal energy storage density as high as 98.2% of pure PEG, shape stabilization effect, high thermal conductivity of 1.72 W/mK (more than 490% increase over pure PEG), high electrical conductivity of 2.5 S/m and excellent thermal reliability after thermal cycling. The incorporated GO and GNP were proved to be effective supporting materials and conductive materials respectively, and also played an important role in improving the phase change enthalpy of PEG. Furthermore, GO also contributed to the enhancement of thermal conductivity but acted as barriers in the conductive path. The present study represents an important step toward developing high comprehensive performance composite PCMs.
Co-reporter:Hai-Yan Yin, Xin-Feng Wei, Rui-Ying Bao, Quan-Xiao Dong, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, and Ming-Bo Yang
ACS Sustainable Chemistry & Engineering 2015 Volume 3(Issue 4) pp:654
Publication Date(Web):March 13, 2015
DOI:10.1021/sc500783s
In this work, a novel, effective and simple approach to largely improve the thermomechanical properties and heat distortion resistance of biodegradable poly(l-lactide) (PLLA) by using a new nucleating agent (NA), i.e., itself high-melting-point homocrystallites (hPLLA crystallites) is reported. Specially, hPLLA crystallites with a melting temperature (Tm) of 187 °C were introduced into the PLLA matrix with a lower Tm, i.e., 168 °C via simply melt blending at 170 °C which is between the Tms of the two PLLAs. Nonisothermal and isothermal crystallization results reveal that hPLLA crystallite is an efficient nucleating agent for PLLA. Also, hPLLA crystallites show much more prominently promoting effect on the crystallization rate of PLLA in comparison with two widely reported NAs for PLLA, talc and stereocomplex crystallites. Most importantly, this promoting effect is still efficient at very high cooling rate, leading to a crystallinity of 39.1% at a cooling rate of 100 °C/min, which can help to obtain high-crystallinity PLLA products in conventional manufacturing processes. The optical microscopic observation reveals that the remarkable crystallization promotion can be attributed to the outstanding heterogeneous nucleation effect, as a result of both identical chemical constitution and lattice constitution between hPLLA crystallites and PLLA matrix. Further characterizations indicate that the enhancement of PLLA crystallinity by using such a new efficient NA can enhance the thermomechanical properties and heat distortion resistance of PLLA remarkably. For instance, at 80 °C (above Tg of PLLA), the elastic modulus increases by 60 times from 8 to 477 MPa with the incorporation of 5 wt % hPLLA.Keywords: Biodegradable polylactides; heat distortion resistance; high crystallinity; nucleating agent; thermomechanical properties;
Co-reporter:Hai-Yan Yin, Xin-Feng Wei, Rui-Ying Bao, Quan-Xiao Dong, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
CrystEngComm 2015 vol. 17(Issue 23) pp:4334-4342
Publication Date(Web):30 Apr 2015
DOI:10.1039/C5CE00645G
In the present work, a new approach to significantly accelerate the crystallization of poly(L-lactide) (PLLA) by utilizing poly(D-lactide) (PDLA) crystallites is presented. In particular, a PDLA with a high melting point (25 °C higher than that of PLLA) and high crystallinity (hPDLA) was introduced into the PLLA matrix via melt blending at a temperature between the melting points of PLLA and hPDLA. It was proved that the hPDLA crystallites were not melted and were instead reserved in the PLLA matrix. Results showed that a small amount of hPDLA crystallites can largely elevate the crystallization temperature, reduce the crystallization half-time and promote the crystallization rate of PLLA. In situ polarizing microscope observations showed that the great improvement of the crystallization rate was caused by the excellent nucleation effect of the hPDLA crystallites. Wide-angle X-ray diffraction results showed that the crystalline structures of the PLLA crystallites and hPDLA crystallites showed very good lattice match, which results in a largely reduced energy barrier for nucleation and increased crystallization kinetics.
Co-reporter:Hai-Yan Yin, Xin-Feng Wei, Rui-Ying Bao, Quan-Xiao Dong, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
CrystEngComm 2015 vol. 17(Issue 11) pp:2310-2320
Publication Date(Web):06 Feb 2015
DOI:10.1039/C4CE02497D
Even though self-nucleation is considered to be the ideal case for polymer nucleation, it has rarely been used to enhance polymer crystallization in practical processing techniques. Inspired by self-nucleation theory and by utilizing the large difference in melting points of various poly(L-lactide) (PLLA) resins, we introduced high-melting-point PLLA (hPLLA) crystallites into a low-melting-point PLLA (lPLLA) matrix via melt blending at a processing temperature between the two melting points of the selected PLLA resins. The hPLLA crystallites turn out to be efficient nucleating agents (NAs) for lPLLA and high crystallinity (>40%) PLLA samples with a greatly accelerated crystallization rate can be easily obtained. The results of non-isothermal crystallization show that the crystallization process is remarkably accelerated with a small amount (0.1 wt%) of hPLLA. With a further increase of hPLLA content, the crystallization temperature of the blends continues to shift to higher temperature. This crystallization promoting effect results from the excellent nucleation ability of the hPLLA crystallites, as revealed by in situ optical microscopy observation. Furthermore, an incredibly high nucleation efficiency of 103.0% (exceeding 100%) was obtained for the PLLA sample with 5.0 wt% hPLLA. The nucleation mechanism for hPLLA was studied systematically. It was found that the lPLLA matrix and hPLLA crystallites possess an absolutely identical crystal structure of α-form crystals and an excellent interfacial interaction between the nucleating agent, i.e., hPLLA crystallite, and the lPLLA matrix is achieved, resulting in the reduction of the energy barrier for heterogeneous nucleation and acceleration of crystallization kinetics. Therefore, by using high-melting-point polymer crystals as NAs, the crystallization rate of their low-melting-point polymer matrix can be improved largely, thus providing a simple way to obtain high crystallinity products for semicrystalline polymers with very low crystallization rates.
Co-reporter:Jian-Ming Feng, Xi-Qiang Liu, Rui-Ying Bao, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2015 vol. 5(Issue 91) pp:74295-74303
Publication Date(Web):25 Aug 2015
DOI:10.1039/C5RA13637G
The morphologies of polymer blends generated during processing are usually unstable and phase coarsening often occurs in the melt state, so suppressing the morphology coarsening is crucial to obtain polymer blends with tailored and stable structure and properties. The effect of nano-silica particles located at the interface on the phase coarsening of a polypropylene (PP)/polystyrene (PS) blend was studied in this work. In co-continuous 50/50 PP/PS blend, the particles at the interface can effectively suppress the coarsening process even at a very low particle loading. Real-time observation conducted by using an optical microscope equipped with a camera and a hot stage showed that a small loading of particles has little effect on the retraction process but can suppress the coalescence and at high loading of particles, both the retraction and coalescence process can be significantly suppressed. The suppressing effect towards the coalescence was confirmed in 70/30 blend with PS phase as the dispersed phase. The stabilization mechanism used in particle stabilized emulsions was adopted to explain the suppressing effect of nano-silica particles located at the interface towards the phase coarsening of PP/PS blends.
Co-reporter:Rui-Ying Bao, Wen-Rou Jiang, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2015 vol. 5(Issue 44) pp:34821-34830
Publication Date(Web):09 Apr 2015
DOI:10.1039/C5RA02575C
Polylactide (PLA) is strong and stiff but brittle while poly(ethylene terephthalate glycol) (PETG) is flexible. In view of their complementary properties, PETG was blended with PLA via reactive melt blending to overcome the drawbacks of PLA, aiming at applications in the packaging industry. During reactive blending, crosslinking reaction between PLA chains and methylene diphenyl diisocyanate (MDI) led to improved melt elasticity, viscosity and molecular mass evaluated by various rheological plots including storage and loss modulus, viscosity, loss tangent, weighted relaxation spectra, and molecular weight distribution curves. Interfacial compatibilization occurred between PLA and PETG through the reaction of free isocyanate groups on the crosslinked PLA chains with the terminal hydroxyl groups of the PETG chains. The variation of viscoelasticity of the PLA matrix and interfacial compatibilization resulted in fine phase morphology and enhanced interfacial adhesion of the blends. Thus, the failure mode of the blends changed from brittle fracture of neat PLA to ductile fracture. The resulting PLA-MDI/PETG blends displayed a significant improvement in the elongation at break and a simultaneous improvement of tensile strength, maintaining the high tensile modulus.
Co-reporter:Rui-Ying Bao, Wei Yang, Zheng-Ying Liu, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2015 vol. 5(Issue 25) pp:19058-19066
Publication Date(Web):09 Feb 2015
DOI:10.1039/C5RA00691K
The effect of melt blending with poly(methyl methacrylate) (PMMA), a miscible polymer with polylactide (PLA), on the crystallization and melting behaviors and crystalline structure of high-molecular-weight poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blend was investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Due to the decreased segmental mobility of PLA chains and the dilution effect of the introduced PMMA, the crystallization of PLA is hindered. The polymorphic crystallization of the PLLA/PDLA blend can be tailored by the amount of PMMA and dynamic and isothermal crystallization conditions. The formation of stereocomplex (sc) crystallites is favored for the blends containing PMMA lower than 50 wt% during cold crystallization. During isothermal melt crystallization, the formation of sc crystallites is always accompanied by the generation of homochiral (hc) crystallites at a crystallization temperature (Tc) ranging from 110 to 160 °C for neat PLLA/PDLA blend, while the crystallization window for exclusive sc crystallites is widened to 160 °C, 140–160 °C, and 110–150 °C for PLLA/PDLA blends containing 10, 25, and 50 wt% PMMA, respectively. Especially, the formation of sc crystallites can be enhanced over the entire Tc range of 110–160 °C when the PMMA content is lower than 25 wt%. The enhanced sc crystallite formation can be ascribed to the reduced crystallization competition resulting from highly restricted hc crystallization. With the PMMA content increasing to 75 wt%, the inhibition effect on the crystallization of PLA suppresses either hc or sc crystallization.
Co-reporter:Yang Liu, Cheng-Lu Liang, Rui-Ying Bao, Guo-Qiang Qi, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2015 vol. 5(Issue 1) pp:10-15
Publication Date(Web):19 Nov 2014
DOI:10.1039/C4RA13309A
The three-dimensional (3D) architecture of reduced graphite oxide (rGO) hydrogels is of interest in applications such as supercapacitors, soft machines and regenerative medicine, etc. The structural stability of the rGO hydrogel is the foundation for these applications. However, little attention has been paid to this issue. Here, the structural and performance stabilities of rGO hydrogels prepared at different temperatures were investigated in detail. It was found that 40 °C was the most effective condition for the reduction of graphite oxide, as the reducibility of vitamin C was embodied successfully and the network of the rGO hydrogel was formed. The rGO hydrogel prepared at 40 °C showed the best structural stability with time, the lowest electrical resistance and the highest mechanical strength. These results provide guidance for the synthesis of structurally stable rGO hydrogels and their further applications in electrical devices.
Co-reporter:Xi-Qiang Liu, Rui-Ying Bao, Xiao-Jun Wu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2015 vol. 5(Issue 24) pp:18367-18374
Publication Date(Web):05 Feb 2015
DOI:10.1039/C4RA16261G
The effect of temperature on the rheological behaviors of a shear thickening fluid (STF) prepared by dispersing fumed silica (SiO2) particles into polyethylene glycol (PEG) under mechanical stirring and ultrasonication was investigated using a rotational rheometer. Under steady shear, the system showed an obvious shear thickening behavior due to the formation of “hydroclusters” of SiO2 particles driven by hydrodynamic lubrication forces. The value of the critical shear rate at which the shear thickening begins grows monotonically with temperature. Dynamic temperature sweeps show that elevating the temperature induces a gelation transition of the SiO2/PEG system when the concentration of SiO2 exceeds a critical value, which is found to be lower for the system consisting of higher average molecular weight PEG. The gelation process also becomes more remarkable at a higher concentration of SiO2 particles. It is found that the temperature induced gelation of SiO2/PEG sol is essentially related to the disappearance of the solvation layer on the surface of SiO2 particles as well as the change of hydrogen bonds.
Co-reporter:Yang Liu, Guo-Qiang Qi, Cheng-Lu Liang, Rui-Ying Bao, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2014 vol. 2(Issue 19) pp:3846-3854
Publication Date(Web):21 Feb 2014
DOI:10.1039/C3TC32586E
As a novel tissue engineering material and transistor, reduced graphite oxide (rGO) hydrogel is attracting more and more attention, and a stable and highly electrical conductive rGO hydrogel is the cornerstone for these applications. We controlled the structures of graphite oxides (GOs) with three different methods and the corresponding assembled rGO hydrogels were obtained using Vitamin C (VC) as the reducing agent and the stability and electrical resistance of the rGO hydrogel were studied. The results showed that the appropriate interlayer distance and grain size of GO prepared by two-step oxidation were beneficial for VC molecules to insert in the interspace between layers for the reduction. After reduction, the loose and tangled network structure was well assembled, which determines the stability and electrical conductivity of the resulted rGO hydrogel.
Co-reporter:Rui-Ying Bao, Jun Cao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2014 vol. 2(Issue 9) pp:3190-3199
Publication Date(Web):20 Dec 2013
DOI:10.1039/C3TA14554A
Balanced stiffness and toughness is always the goal of high-performance general plastics for engineering purposes and the interfacial crystalline structure control has been proved to be an effective way to approach this goal. In this work, a kind of novel β-nucleating agent (β-NA) for isotactic polypropylene (iPP), one of the most rapidly developing general plastics, was supported onto the surface of octadecylamine functionalized graphene oxide (GO-D), and the effects of functionalized graphene oxide (GO) on the crystallization behavior, crystalline structures and mechanical properties of iPP composites were studied. The presence of the octadecyl chain changes the hydrophilic GO to be hydrophobic, and further supporting of β-NA onto GO-D (GO-N) does not change its solubility in xylene. The hydrophobic nature of octadecyl chains on the GO-D and GO-N surfaces leads to improved interfacial adhesion with the non-polar iPP matrix. At the same time, GO-N exhibits high efficiency in inducing the formation of β-crystals of iPP. The relative content of β-crystals, kβ, reaches a value as high as 73.6% at a loading of 0.1 wt% GO-N, resulting in a maximum increase in impact strength by almost 100% and a simultaneous improvement of the tensile strength by about 30%. This work provides a potential industrializable technique for high-performance iPP nanocomposites.
Co-reporter:Li-Feng Ma, Rui-Ying Bao, Rui Dou, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang and Qiang Fu
Journal of Materials Chemistry A 2014 vol. 2(Issue 40) pp:16989-16996
Publication Date(Web):21 Aug 2014
DOI:10.1039/C4TA03833A
A conductive elastomeric composite of carbon black (CB) filled thermoplastic vulcanizate (TPV) based on polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends was fabricated via phenolic resin (PF)-induced dynamic vulcanization in an effort to prepare temperature sensitive elastomeric materials with balanced properties. Fourier transformed infrared spectroscopy and gel content analysis revealed that the EPDM was effectively cured by PF and the degree of crosslinking reached 38.7 wt%. Morphology observation revealed that CB particles distributed in the EPDM phase in uncrosslinked thermoplastic elastomer composites, whereas CB particles were almost completely located in the PP matrix in TPV composites. For TPV composites, the morphological characteristic combined the temperature sensing properties of the PP/CB composite with the excellent resilience of the cured EPDM phase, resulting in an excellent balance in electrical and mechanical properties. Compared with the contrast composite, the TPV composite showed the lowest percolation threshold of electrical conductivity, significant enhancement of tensile stress at 300% stretching, ultralow negative temperature coefficient (NTC) effect, outstanding positive temperature coefficient (PTC) effect and repeatability. This study offers an example of high-performance temperature sensitive elastomeric materials with balanced properties.
Co-reporter:Rui-Ying Bao, Wei Yang, Xin-Feng Wei, Bang-Hu Xie, and Ming-Bo Yang
ACS Sustainable Chemistry & Engineering 2014 Volume 2(Issue 10) pp:2301
Publication Date(Web):August 18, 2014
DOI:10.1021/sc500464c
Melt processing of polymers is preferable in industry. Unfortunately, for high molecular weight (Mw) poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends, exclusive formation of stereocomplex (sc) crystallites from the melt has never been achieved. We proposed a new and simple approach to enhance the melt crystallization of sc crystallites from high Mw PLLA/PDLA by using poly(ethylene glycol) (PEG). The crystallizability of the PLLA/PDLA blend is greatly enhanced by PEG during crystallization from the melt. The resulted crystalline structures depend on the Mw and content of PEG, and the crystallinity of sc crystallites increases with increasing content or decreasing Mw of PEG. More importantly, exclusive formation of sc crystallites is achieved in the blends with 10% PEG having Mw values of 1000 or 2000 g mol–1. Polarized optical microscopy (POM) observation shows that the spherulitic growth rates of sc crystallites are accelerated. The results demonstrate that segmental mobility of polylactides (PLA) chains plays a dominant role on the formation of sc crystallites from melt and provide a simple way to prepare sc crystallites from high Mw PLA by melt blending and enlarge the applications of PLA.Keywords: Biodegradable enantiomeric polylactides; Chain mobility; Stereocomplex crystallites;
Co-reporter:Guo-Qiang Qi, Cheng-Lu Liang, Rui-Ying Bao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Solar Energy Materials and Solar Cells 2014 Volume 123() pp:171-177
Publication Date(Web):April 2014
DOI:10.1016/j.solmat.2014.01.024
•The highest stabilized PEG content is 96 wt% in the PEG/GO composites.•The shape-stabilized PEG presents a high heat storage capacity of 142.8 J g−1.•The shape-stabilized PCM exhibits an excellent thermal reliability up to 200 melting/freezing cycles.Graphene oxide (GO) sheets are introduced to stabilize the shape of the most widely studied phase change material for thermal storage, polyethylene glycol (PEG) during the solid–liquid phase change process. In this composite, a maximum weight percentage of PEG as high as 96% without any leakage up to a temperature as high as 150 °C, far above the melting temperature of PEG, has been achieved. Such a weight percentage of PEG is the highest value among PEG based shape-stabilized PCMs to the best of author׳s knowledge. The shape-stable PCM presents a high heat storage capacity of 142.8 J g−1 and excellent thermal reliability within at least 200 melting/freezing cycles. The thermal properties of the PEG/GO composite PCMs with various GO contents are also investigated. The present study provides a highly potential shape-stabilized composite PCM with a high content of PEG for thermal energy storage as well as a way to enhance the heat storage density of PEG based shape-stabilized PCM.
Co-reporter:Xi-Qiang Liu, Ruo-Han Li, Rui-Ying Bao, Wen-Rou Jiang, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Soft Matter 2014 vol. 10(Issue 20) pp:3587-3596
Publication Date(Web):11 Feb 2014
DOI:10.1039/C3SM53211A
The properties of polymer blends greatly depend on the morphologies formed during processing, and the thermodynamic non-equilibrium nature of most polymer blends makes it important to maintain the morphology stability to ensure the performance stability of structural materials. Herein, the phase coarsening of co-continuous, immiscible polyamide 6 (PA6)–acrylonitrile-butadiene-styrene (ABS) blends in the melt state was studied and the effect of introduction of nano-silica particles on the stability of the phase morphology was examined. It was found that the PA6–ABS (50/50 w) blend maintained the co-continuous morphology but coarsened severely upon annealing at 230 °C. The coarsening process could be divided into two stages: a fast coarsening process at the initial stage of annealing and a second coarsening process with a relatively slow coarsening rate later. The reduction of the coarsening rate can be explained from the reduction of the global curvature of the interface. With the introduction of nano-silica, the composites also showed two stages of coarsening. However, the coarsening rate was significantly decreased and the phase morphology was stabilized. Rheological measurements indicated that a particle network structure was formed when the concentration of nano-silica particles was beyond 2 wt%. The particle network inhibited the movement of molecular chains and thus suppressed the coarsening process.
Co-reporter:Xi-Qiang Liu, Zhen-Yi Sun, Rui-Ying Bao, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2014 vol. 4(Issue 77) pp:41059-41068
Publication Date(Web):12 Aug 2014
DOI:10.1039/C4RA04380D
The effect of nano-silica particles on the shape relaxation of dispersed droplets in polypropylene/polystyrene (PP/PS) blend was investigated. The nano-silica particles were controlled to be distributed in PS phase, which presented dispersed droplets in the blends. By using an optical microscope equipped with a camera and a hot stage, the shape relaxation of the deformed droplets in the blends after application of a big strain was observed in melt state. The shape relaxation process of PS droplets from highly elongated fibers towards spheres was observed. The nano-silica particles were found to retard the relaxation process of the deformed PS droplets, especially when a particle network was formed. It was showed that the shape relaxation of the droplets was essentially related to the movement of the molecular chains and the relaxation of the oriented chains. These results provide a new understanding of the evolution of morphology for nanoparticles filled polymer blends, based on the slow movement of molecular chains.
Co-reporter:Xi-Qiang Liu, Qian-Yu Wang, Rui-Ying Bao, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
RSC Advances 2014 vol. 4(Issue 90) pp:49429-49441
Publication Date(Web):29 Sep 2014
DOI:10.1039/C4RA09138H
The morphologies of polymer blends generated during processing are usually unstable and morphology coarsening often occurs in the melt state, so suppressing the morphology coarsening is crucial to obtain polymer blends with tailored and stable structure and properties. Here, we report the morphology coarsening behavior of a co-continuous polypropylene/polystyrene (PP/PS) blend, with and without nano-silica particles, subjected to quiescent annealing in the melt state. The filled nano-silica particles were controlled to selectively distribute in the PS phase and formed a rheological particle network at a concentration of 8 wt% relative to the mass of the PS phase. A significant coarsening, which can be divided into two stages with different coarsening rates, was observed for the pure blend. Real-time monitoring of the coarsening process showed that the morphology coarsening process proceeded via retraction of elongated domains first and then coalescence of the retracted domains. The filled nano-silica particles were found to be able to suppress the coarsening process, which was demonstrated to be achieved by slowing down the retraction process of elongated domains. It was also found that the suppression effect of nano-silica particles heavily depended on the particle concentration and when a particle network formed, the suppression effect was more prominent. A stabilization mechanism, based on the phase deformation being closely related to the movement of polymer molecular chains, was proposed to expound the role of the introduced particles. When a particle network structure was formed, the movement of polymer molecular chains was significantly retarded and the corresponding phase deformation became difficult, leading to suppressed retraction process of the elongated domains and the whole phase coarsening phenomenon.
Co-reporter:Kai Ke, Xin-Feng Wei, Rui-Ying Bao, Wei Yang, Yong Luo, Bang-Hu Xie, Ming-Bo Yang
Polymer Testing 2014 Volume 34() pp:78-84
Publication Date(Web):April 2014
DOI:10.1016/j.polymertesting.2013.12.012
Poly (vinylidene fluoride) (PVDF) films or membranes are generally produced using solution media, and this process raises two interesting questions which deserve to be explored, i.e., whether residual solvent exists and what is the effect of any residual solvent on the structure and properties of the PVDF matrix. Samples with residual N-N-dimethylformamide (DMF) were prepared via a solution precipitation method followed by different drying times. Fourier transform infrared spectroscopy results demonstrated that residual solvent existed in the PVDF matrix even although the samples were dried for 72 h at 60 °C. This can also be verified by energy dispersive X-ray spectroscopy results. Results of differential scanning calorimetry revealed that the residual solvent promotes the nucleation of PVDF markedly during its crystallization. Both dynamic mechanical and melt rheology tests showed that elastic moduli are greatly increased owing to the reinforcement in samples containing DMF residual.
Co-reporter:Cheng-Lu Liang, Zhong-Hai Mai, Qi Xie, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, and Ming-Bo Yang
The Journal of Physical Chemistry B 2014 Volume 118(Issue 30) pp:9104-9111
Publication Date(Web):July 10, 2014
DOI:10.1021/jp504938f
The “ion–dipole” interaction has been the most widely accepted mechanism for the direct formation of polar phases (β, γ) of poly(vinylidene fluoride) (PVDF), which have been widely used as transducers, actuators, and sensors. However, the type of charged ions is still controversial. In order to throw light upon this issue, two types of charged small organic molecules that are in different physical states (melt or solid) during the crystallization of PVDF were melt-blended with PVDF resin. Results revealed that only the incorporation of positive charged molecules can lead to the formation of polar phases. Additionally, it is interesting to find that during the crystallization of PVDF, molten positively charged molecules resulted in β-phase dominating, while solid positively charged molecules exclusively induced γ-phase. These results lead to the understanding that the induced formation of polar phases of PVDF is due to the “positive ion–CF2 dipole” interaction.
Co-reporter:Xin-Feng Wei, Rui-Ying Bao, Zhi-Qiang Cao, Wei Yang, Bang-Hu Xie, and Ming-Bo Yang
Macromolecules 2014 Volume 47(Issue 4) pp:1439-1448
Publication Date(Web):February 14, 2014
DOI:10.1021/ma402653a
Stereocomplex (SC) crystallites, formed between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA), show a melting point 50 °C higher than that of PLLA or PDLA homocrystallites, which makes it possible for SC crystallites to be reserved in the melt of PLLA in asymmetric PLLA/PDLA blends and to act as a rheological modifier and a nucleation agent for PLLA. Herein, by a rheological approach, a transition from the liquid-like to solid-like viscoelastic behavior was observed for the SC crystallites reserved melt, and a frequency-independent loss tangent at low frequencies appeared at a PDLA concentration of 2.0 wt %, revealing the formation of SC crystallite network. By a delicately designed dissolution experiment, the structure of the formed network was explored. The results indicate that the network are not formed by SC crystallites connected directly with each other or by bridging molecules, but by the interparticle polymer chains which are significantly restrained by the cross-linking effect of SC crystallites. Nonisothermal and isothermal crystallization show that the reserved SC crystallites can accelerate remarkably the crystallization rate of PLLA due to heterogeneous nucleation effect. Besides, a special PDLA concentration dependence, e.g., the overall crystallization rate is almost independent of PDLA content for the blends with PDLA content higher than PDLA percolation concentration (2.0 wt %), was also observed. The increase of nuclei density for the blends containing PDLA from 2 to 5 wt % was estimated from POM observations. The result of an enhanced nucleation but an unchanged overall crystallization rate reveals the confining effect of the SC crystallite network on PLLA crystallization. This confining effect can be ascribed to the restrained diffusion ability of PLLA chains owing to the SC crystallite network.
Co-reporter:Cheng-Lu Liang;Qi Xie;Rui-Ying Bao;Bang-Hu Xie
Journal of Materials Science 2014 Volume 49( Issue 12) pp:4171-4179
Publication Date(Web):2014 June
DOI:10.1007/s10853-014-8112-8
Poly(vinylidene fluoride) (PVDF) has been widely used as transducers, actuators,and sensors due to its exceptional electroactive properties among polymer materials and the electroactive properties of PVDF heavily depend on its polymorphs. The effects of cetyl trimethyl ammonium bromide (CTAB) on the crystallization behavior of PVDF during isothermal crystallization and annealing process were studied, and the results showed that the polar phases (β, γ) were induced by CTAB when PVDF was isothermally crystallized at 145–160 °C. Increasing the isothermal crystallization temperature resulted in an increased γ-phase formation with a concomitant decrease of α and β phases. A 100 % γ-phase formation occurred when the sample isothermally crystallized at 155 and 160 °C. The crystalline phase transition of the sample annealed at 160 °C for various time revealed that CTAB induced the transformation from α to γ′ phase and a higher concentration of CTAB resulted in shorter transformation time, as well as higher transformation degree.
Co-reporter:Wen-Rou Jiang, Rui-Ying Bao, Wei Yang, Zheng-Ying Liu, Bang-Hu Xie, Ming-Bo Yang
Materials & Design 2014 59() pp: 524-531
Publication Date(Web):
DOI:10.1016/j.matdes.2014.03.016
Co-reporter:Xin-Feng Wei;Rui-Ying Bao;Zhi-Qiang Cao;Liang-Qing Zhang
Colloid and Polymer Science 2014 Volume 292( Issue 1) pp:163-172
Publication Date(Web):2014 January
DOI:10.1007/s00396-013-3067-x
Stereocomplex crystallite (SC) between enantiomeric poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA), with largely improved thermal resistance and mechanical properties compared with PLLA and PDLA, is a good nucleating agent for poly(lactic acid) (PLA). The effects of SC and/or polyethylene glycol (PEG) on the crystallization behaviors of PLA were investigated. The non-isothermal and isothermal crystallization kinetics revealed that SC and PEG can separately promote the crystallization rate of PLA by heterogeneous nucleation and increasing crystal growth rate, respectively. However, their promoting effect is limited when used alone, and the modified PLA cannot crystallize completely under a cooling rate of 20 °C/min. When SC and PEG are both present, the crystallization rate of PLA is greatly accelerated, and even under a cooling rate of 40 °C/min, PLA can crystallize completely and get a high crystallinity owing to the excellent balance between simultaneously improved nucleation and crystal growth rate.
Co-reporter:Cheng-Lu Liang;Zhong-Hai Mai;Qi Xie;Rui-Ying Bao
Journal of Polymer Research 2014 Volume 21( Issue 12) pp:
Publication Date(Web):2014 December
DOI:10.1007/s10965-014-0616-z
The γ phase of poly(vinylidene fluoride) (PVDF) was induced by tetrabutylammonium bisulfate and the kinetics of isothermal and non-isothermal crystallization of the induced γ-PVDF in the absence of α phase were investigated with differential scanning calorimeter. The crystallization kinetics were evaluated on the basis of the theory of Avrami and those modified by Jeziorny, Ozawa, Liu and Mo. The Avrami exponent n of the induced γ-PVDF was evaluated and was found to be in the range of 2.4–2.9 for isothermal crystallization and in the range of 3.1−4.5 for non-isothermal crystallization, much higher than those of γ-PVDF homogeneously nucleated at high temperatures as reported in literature. Moreover, the accelerated crystallization rate of the induced γ-PVDF, even faster than the kinetically most favored α phase, was demonstrated by the drastically shortened half-time of crystallization t1/2 and enhanced crystallization rate constant K. It is shown that dominating γ-PVDF could be melt crystallized with a drastically enhanced crystallization rate with the incorporation of tetrabutylammonium bisulfate.
Co-reporter:Guo-Qiang Qi, Jun Cao, Rui-Ying Bao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2013 vol. 1(Issue 9) pp:3163-3170
Publication Date(Web):14 Jan 2013
DOI:10.1039/C3TA01360J
The structure of graphene oxide (GO) was tuned by controlled ultrasonication (40 kHz, 400 W). It was found that one hour of sonication was the critical point. Under ultrasonication, GO was exfoliated gradually in one hour and further treatment led to a reverse trend. The size of GO sheets decreased sharply in the first hour and then remained almost unchanged with the extension of sonication. In other words, once the GO sheets were cut into pieces small enough, they tended to restack together. Defects on the surface of GO were easily generated even within a short period of ultrasonication and the chemical structure was also changed. GO treated with different sonication times was incorporated into poly(vinyl alcohol) (PVA), and the structure and properties of PVA/GO nanocomposites were also discussed. The hydrogen bonding between the GO and PVA matrix increased before the critical point and then decreased, which was the key factor influencing the glass transition temperature. Meanwhile, the mechanical strength of the nanocomposites was improved before the critical point. The reinforcing mechanism is believed to be the effective load transfer between the PVA matrix and GO via strong hydrogen bonding interactions caused by the exfoliation effect.
Co-reporter:Yuan An, Rui-Ying Bao, Zheng-Ying Liu, Xiao-Jun Wu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
European Polymer Journal 2013 Volume 49(Issue 2) pp:538-548
Publication Date(Web):February 2013
DOI:10.1016/j.eurpolymj.2012.10.020
The introduction of ultrahigh molecular weight polyethylene (UHMWPE) leads to very rich and unusual hierarchical crystalline morphologies in mini-injection molded isotactic polypropylene (iPP) based materials and the role of UHMWPE in the formation of the hierarchical structures has been studied. The hierarchical structures, including the shish-kebab-like structure, β-cylindrite, β-spherulite and α-spherulite, in the injection molded samples were characterized by wide-angle X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Results indicated that the content of crystal modifications and the distribution of the crystal morphologies formed are closely related to the density and arrangement of the row nuclei formed, which can be tuned by the content of UHMWPE and its dispersion in the matrix. The density and arrangement of the row nuclei are determined by the hydrodynamic interaction, melt adsorption, and interdiffusion between iPP and UHMWPE. With the distance between the row nuclei increasing, the corresponding dominating crystals are shish-kebab-like structure, β-cylindrite, β-spherulite and α-spherulite in sequence.Graphical abstractHighlights► Rich and unusual hierarchical structures of mini-injection molded blends were disclosed. ► Relationship between the density of row nuclei and crystal morphologies was obtained. ► Influences of UHMWPE on the formation of the hierarchical structures were discussed.
Co-reporter:Xi-Qiang Liu, Rui-Ying Bao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Polymer Testing 2013 Volume 32(Issue 1) pp:141-149
Publication Date(Web):February 2013
DOI:10.1016/j.polymertesting.2012.09.003
The phase inversion behavior of immiscible polyamide 6/acrylonitrile-butadiene-styrene (PA6/ABS) blends and the effect of hydrophobic nano-silica particles were studied. The phase morphology was characterized by scanning electron microscopy and selective extraction. The feasibility of rheological measurements to detect the co-continuity and phase inversion composition in the melt state was evaluated. The evolution of the storage modulus of the blends at a constant low frequency with composition showed a great enhancement of the elasticity when PA6 was the dispersed phase, and the maximum of the storage modulus at the evaluated frequency was definitely related to the phase inversion in pure blends. It was found that the PA6 was more likely to form the continuous phase, and a complete co-continuous composition range did not exist. The nano-silica particles showed selective distribution in the blends and a network-like structure of the nano-silica particles in the ABS phase was formed when ABS was the matrix, which invalidated the rheological technique to detect the phase inversion composition. A non-isothermal rheological procedure was designed to verify the phase inversion composition obtained by selective extraction measurement. Several models were employed to predict the phase inversion composition. It was confirmed that the viscosity ratio was the most important factor influencing the phase inversion. The introduction of hydrophobic nano-silica particles led to a shift of the phase inversion composition to higher ABS content due to the enhanced viscosity ratio.
Co-reporter:Rui-Ying Bao, Wei Yang, Wen-Rou Jiang, Zheng-Ying Liu, Bang-Hu Xie, and Ming-Bo Yang
The Journal of Physical Chemistry B 2013 Volume 117(Issue 13) pp:3667-3674
Publication Date(Web):March 11, 2013
DOI:10.1021/jp311878f
The crystallization and melting behaviors and crystalline structure of melt and cold crystallized poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blend were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), respectively. The isothermal crystallization kinetics during the melt and cold crystallization process were analyzed using the Avrami equation. The overall crystallization rate constant (k) of cold crystallization is much higher than that of melt crystallization. Moreover, k as a function of crystallization temperature shows different trends in melt and cold crystallization, indicating different crystallization mechanisms in the melt and cold crystallization. The polymorphic crystallization of homocrystallites (the transition crystallization temperature from δ to α form) is not altered by either the equimolar blending of PLLA and PDLA or the type of crystallization procedures, while the crystallization window for exclusive stereocomplex crystallites is widened from 170 °C for melt crystallization to 170–200 °C for cold crystallization. The stereocomplex crystallites are hard to form in both melt and cold crystallization at crystallization temperatures of 90 and 100 °C, and the crystallinity of stereocomplex crystallites for cold crystallization is higher than that of melt crystallization at temperatures above 110 °C. Especially, a pure and significantly higher crystallinity of stereocomplex crystallites can be achieved at 170–200 °C by cold crystallization. The results provide a huge possibility to control stereocomplex crystallization to enlarge its applications.
Co-reporter:Kai Ke;Rui-Ying Bao;Xi-Qiang Liu;Zheng-Ying Liu
Journal of Materials Science 2013 Volume 48( Issue 24) pp:8509-8519
Publication Date(Web):2013 December
DOI:10.1007/s10853-013-7669-y
Poly(vinylidene fluoride) (PVDF) nanocomposites containing homogeneously dispersed multi-walled carbon nanotubes (MWCNTs) and carbon black (CB) were fabricated by a small melt mixer. The uniform dispersion of the nanofillers in PVDF was confirmed by both scanning electron microscopy and transmission electron microscopy. Both the heterogeneous nucleation efficiency and crystallization half-time show that MWCNTs exhibit higher nucleation efficiency than CB for the crystallization of PVDF. Meanwhile, MWCNTs show greater contribution to the reinforcement of the storage modulus of PVDF as revealed by dynamic mechanical analysis, especially at low temperatures. However, the enhancement of the storage modulus in the melt state is reversed due to the network formed by serious agglomeration of CB. This study provides some insights into the nucleating and reinforcing efficiency of MWCNTs and CB in polymers.
Co-reporter:Li-Feng Ma, Wei-Kang Wang, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Materials & Design 2013 51() pp: 536-543
Publication Date(Web):
DOI:10.1016/j.matdes.2013.04.066
Co-reporter:Rui-Ying Bao, Zhi-Tian Ding, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Polymer 2013 Volume 54(Issue 3) pp:1259-1268
Publication Date(Web):5 February 2013
DOI:10.1016/j.polymer.2012.12.050
β phase isotactic polypropylene (β-iPP) with the β phase lamellae oriented parallel to the melt extrusion direction, was employed to investigate the deformation-induced structure evolution at various temperatures (25, 80, 110, 130 and 140 °C). The orientation change of β phase during deformation greatly influences the β to α phase transformation and its temperature dependence. At temperatures lower than 110 °C, the orientation of β phase is almost unchanged during deformation, and void or crack forms before fragmentation and reorientation of β phase. The crystal size change of β phase is small, and the defolding of the β lamellae triggers the β to α phase transformation. As the deformation temperature rises to 130 and 140 °C, the reorientation of β phase occurs gradually upon stretching, and the size of micro-voids decreases due to the fact that less β crystal fragmentation takes place at high draw temperature than that at low temperature. The β to α phase transformation is mainly induced by intra-lamella slip, and the trend of crystal size change of β phase is larger. The chains orientation changes from perpendicular to the stretching direction in β phase to parallel to the stretching direction in α phase is achieved by the chains defolding of β phase along the stretching direction at temperatures lower than 110 °C, and it is through the chains reorientation of β phase along the stretching direction at temperatures of 130 and 140 °C. The crystal size of α phase of the deformed β-iPP during deformation depends on the dynamic balance of the breakage of existing α crystal and the formation of new crystal through phase transformation. Specially, at draw temperature of 25 °C, the slippage of β phase relieves the breakage of α phase crystal, which indicates that the high content of β phase crystal really accounts for the toughening effect on iPP.
Co-reporter:Xiao-Jun Wu, Yu Wang, Wei Yang, Bang-Hu Xie, Ming-Bo Yang and Wei Dan
Soft Matter 2012 vol. 8(Issue 40) pp:10457-10463
Publication Date(Web):31 Aug 2012
DOI:10.1039/C2SM25668A
The effect of temperature on colloid systems of hydrophobic and hydrophilic fumed silica in dodecane was investigated mainly by means of dynamic rheology. Dynamic frequency sweeps showed frequency-independent elastic modulus (G′), indicating the presence of gel networks in both dispersions. Dynamic temperature sweeps consisting of a heating and cooling cycle were also conducted. For the hydrophobic fumed silica gel, G′ slowly decreased with rising temperature owing to the increased particle mobility and decreased strength of hydrogen bonds due to the higher thermal energy. However, the hydrophilic fumed silica gel showed a rather unusual temperature dependent behavior involving a transition temperature (Tc) and an irreversible increase in G′ during the cooling cycle. This unusual behavior was believed to be related to the restructuring of nanoparticle chain aggregates (NCA) of fumed silica in gels as also revealed by FTIR results. Further analysis on this behavior showed that elevated temperature tended to increase the fractal dimension (Df) of aggregates, resulting in more compact NCAs and thereby a denser gel network with a higher G′. These results suggest that temperature is an important external variable that can be regarded as an optional simple way to tailor the viscoelastic properties and to control the microstructure of colloidal systems such as fumed silica dispersions in dodecane.
Co-reporter:Kai Ke;Yu Wang;Kai Zhang;Yong Luo;Bang-Hu Xie;Ming-Bo Yang
Journal of Applied Polymer Science 2012 Volume 125( Issue S1) pp:E49-E57
Publication Date(Web):
DOI:10.1002/app.36293
Abstract
The melt viscoelasticity, electrical conductivity, and crystallization of poly(vinylidene fluoride)/multiwalled carbon nanotubes (MWCNTs) composites prepared by melt blending with different shear effects were examined. Rheological characterization indicated that the incorporation of MWCNTs substantially affected the viscoelastic behavior of the composites. A visible rheological network of CNTs was detected in the composites with relatively high content of MWCNTs. The electrical conductivity of the composites differed substantially for the composites prepared with different shear effects because of the different dispersion states of the MWCNTs in the composites. The nonisothermal crystallization of the composites revealed that the samples prepared with high shear intensity and long shear time exhibited a higher crystallization peak temperature and crystallinity. Besides, the heterogeneous nucleation effect of the MWCNTs was found to be significantly dependent on the dispersion state, which dominated the crystallization even when the confinement effect of the nanotube network existed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Jun Cao;Yu Wang;Kai Ke;Yong Luo;Bang-Hu Xie;Ming-Bo Yang
Polymer International 2012 Volume 61( Issue 6) pp:1031-1040
Publication Date(Web):
DOI:10.1002/pi.4177
Abstract
The effect of three kinds of graphitic fillers with distinct morphologies, natural graphite sheets (NGs), chemically reduced graphite oxide sheets (CRGs) and thermally reduced graphite oxide sheets (TRGs), on the crystallization, rheological behavior and mechanical properties of poly(vinylidene fluoride) (PVDF)-based composites has been investigated comparatively. NGs exhibit smooth surface and multilayer-stacked structure; most CRGs are in the form of aggregates that are restacked during reduction; while TRGs show a wrinkled topography of relatively thin graphene sheets. The introduction of these graphitic fillers into the PVDF matrix contributes differently to the crystallization, rheological behavior and mechanical properties of the composites. Among them, TRGs show the greatest strengthening effect, as revealed by rheological and dynamic mechanical responses. Compared with chemical reduction technology, thermal reduction is a more economical, environmentally friendly and scalable approach to prepare functionalized graphene sheets. Copyright © 2012 Society of Chemical Industry
Co-reporter:Kai Ke, Yu Wang, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Polymer Testing 2012 Volume 31(Issue 1) pp:117-126
Publication Date(Web):February 2012
DOI:10.1016/j.polymertesting.2011.10.005
The effect of high molecular weight resin and multi-walled carbon nanotubes (MWCNTs) on the crystallization, rheological and dynamic mechanical properties of poly (vinylidene fluoride) (PVDF) composites was investigated. A synergetic effect of the high molecular weight resin and MWCNTs on the nucleation in the crystallization process of the matrix has been observed, and their contributions to the crystallization of the matrix are two-sided. The composites containing both the high molecular weight resin and MWCNTs have much higher crystallization peak temperatures but lower crystallinity, especially for samples with high MWCNT content. For the isothermal crystallization at relative high temperatures, higher Avrami exponent and shorter half-time of crystallization are observed for the composites containing both the high molecular weight resin and MWCNTs. The introduction of the high molecular weight resin not only reinforces the matrix, but also promotes the dispersion of MWCNTs. The reinforcement and synergetic nucleation effects of the high molecular weight resin and MWCNTs were also confirmed by dynamic mechanical analysis.
Co-reporter:Jia-lin YAN, Gui-jiao CHEN, Jun CAO, Wei YANG, Bang-hu XIE, Ming-bo YANG
New Carbon Materials 2012 Volume 27(Issue 5) pp:370-376
Publication Date(Web):October 2012
DOI:10.1016/S1872-5805(12)60022-5
Graphene oxide (GO) obtained by Hummers method was functionalized by ethylenediamine (EA) and 1,6-hexanediamine (HA) in N, N-dimethyl formamide using 1, 1, 3, 3-tetramethy-luronium hexafluorophosphate as a coupling agent. The functionalized GO was characterized by elemental analysis, FT-IR, XRD, XPS, TGA, SEM and TEM. Results showed one carbon atom in nine to ten of the carbon atoms in GO was functionalized by an amine group. The thermal stability of the GO functionalized by HA was much higher than the one functionalized by EA. However, the former was less dispersible in N, N-dimethyl formamide than the latter.
Co-reporter:Rui-Ying Bao, Wei Yang, Wen-Rou Jiang, Zheng-Ying Liu, Bang-Hu Xie, Ming-Bo Yang, Qiang Fu
Polymer 2012 Volume 53(Issue 24) pp:5449-5454
Publication Date(Web):9 November 2012
DOI:10.1016/j.polymer.2012.09.043
A low temperature approach to prepare stereocomplex of high-molecular-weight poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) at temperatures much lower than those adopted in conventional melt blending, is presented in this paper. Wide-angle X-ray diffraction and differential scanning calorimetry results verified that complete stereocomplex crystallites without any evidence of the formation of homocrystallites can be achieved not only at equimolar PLLA/PDLA blends, but also at non-equimolar PLLA/PDLA (60:40) blends using such an approach. Furthermore, stereocomplex formation is more efficient for non-equimolar blends than for the equimolar one. Significant improvements in the crystallinity and melting temperature of stereocomplex crystallites and the thermal stability are achieved by this low temperature approach compared with either conventional melt blending or solution casting method. More interesting, fine powder form of stereocomplex can be obtained directly. The process takes advantage of the temperature window at which only the stereocomplex can grow and the homopolymers can no longer crystallize, and develops a feasible way to overcome the molecular diffusion issue in the stereocomplex growth. Thus this novel process provides a unique low temperature, solvent free processing route of preparing high degree stereocomplex crystallites using high-molecular-weight polylactides that has not previously been reported.
Co-reporter:Li-Feng Ma, Xin-Feng Wei, Qi Zhang, Wei-Kang Wang, Li Gu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Materials & Design 2012 33() pp: 104-110
Publication Date(Web):
DOI:10.1016/j.matdes.2011.07.017
Co-reporter:Yuan An, Li Gu, Yu Wang, Yan-Mei Li, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Materials & Design 2012 35() pp: 633-639
Publication Date(Web):
DOI:10.1016/j.matdes.2011.10.017
Co-reporter:Xi-Qiang Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Materials & Design 2012 34() pp: 355-362
Publication Date(Web):
DOI:10.1016/j.matdes.2011.08.028
Co-reporter:Jie Li, Rui-Ying Bao, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Materials & Design 2012 40() pp: 392-399
Publication Date(Web):
DOI:10.1016/j.matdes.2012.04.022
Co-reporter:Xi-Qiang Liu;Yu Wang;Zheng-Ying Liu;Yong Luo
Journal of Materials Science 2012 Volume 47( Issue 11) pp:4620-4631
Publication Date(Web):2012 June
DOI:10.1007/s10853-012-6327-0
The roles of nano-silica particles in the morphology, rheological, crystallization, and melting properties of polyamide 6/acrylonitrile–butadiene–styrene (PA6/ABS) blends were investigated. With the addition of nano-silica particles possessing different surface characteristics (hydrophilic or hydrophobic), the blends showed a notable difference in the morphology of the dispersed ABS phase in the melt or solid state, which is mainly caused by different distribution states for the two kinds of nano-silica particles. Particularly, it was found that the hydrophilic nano-silica particles tended to distribute in PA6 matrix, whereas the hydrophobic nano-silica particles were almost located at the PA6/ABS interface. Besides, the shear thinning behavior of the composites was significantly changed with the incorporation of hydrophobic nano-silica particles and the contribution from the interface was regarded as the dominated one to influence the rheological properties. Finally, with different surface characteristics and their distribution states, it was found that nano-silica particles can play different roles in crystallization and melting properties.
Co-reporter:Jun Cao;Guo-Qiang Qi;Kai Ke;Yong Luo
Journal of Materials Science 2012 Volume 47( Issue 13) pp:5097-5105
Publication Date(Web):2012 July
DOI:10.1007/s10853-012-6383-5
The effect of thermal reduction temperature and time on the structure and composition change of reduced graphite oxide sheets was studied. The results show that the exfoliation degree increased with the elevation of temperature, as evidenced by the decreased layers in the defected nanocrystallites formed by the collapse of graphite oxide sheets. Although, the exfoliation degree shows reverse trend with the extension of time studied. As for the de-oxygenation, both the elevation of temperature and the extension of time favor the reduction process, evidenced by the increasing atomic ratio of carbon to oxygen, and a quite marked de-oxygenation effect was obtained with atomic ratio of 499 by heating at 1000 °C for 2 h. A structural schematic of thermally reduced graphite oxide sheets was proposed for the understanding of the reduction process.
Co-reporter:Ruiying Bao;Zhitian Ding;Ganji Zhong;Banghu Xie
Colloid and Polymer Science 2012 Volume 290( Issue 3) pp:261-274
Publication Date(Web):2012 February
DOI:10.1007/s00396-011-2550-5
The effects of draw temperature on the deformation-induced morphology evolution of isotactic polypropylene in terms of crystal orientation, degree of crystallinity, crystal size in the direction normal to chain axis, long spacing, and the deformation behavior at the crystal lattice and lamellae scale were investigated using differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering, respectively. The results revealed that the thermal behaviors are associated with the deformation-induced morphology evolution, and the morphology evolution is strongly temperature dependent. At low strain, crystal fragmentation takes place at all the draw temperature range studied; at high strain, after crystal fragmentation the draw temperature shows different effects on the morphology evolution: at low temperature (25 °C), fragmentation of the crystal blocks continues; at medium temperatures (80 and 110 °C), the broken crystal blocks remain stable and the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks with crystal size almost identical to that of the original broken ones; at high temperatures (130 and 140 °C), not only the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks, but also these small broken crystal blocks melt and recrystallize and the new crystal blocks formed possess larger crystal size than those of the original broken ones.
Co-reporter:Xiao-Jun Wu;Yu Wang;Min Wang;Bang-Hu Xie
Colloid and Polymer Science 2012 Volume 290( Issue 2) pp:151-161
Publication Date(Web):2012 January
DOI:10.1007/s00396-011-2535-4
The structure and viscoelastic properties of fumed silica gels in dodecane were studied by means of dynamic rheology. With increasing the specific surface area of fumed silica nanoparticles, the plateau elastic modulus (G′), which is frequency-independent and shows the characteristic of a network of the fumed silica gels, decreases. Such networks of fumed silica gels show a significant temperature-dependent behavior and a transition temperature (Tc) related with the restructuring of nanoparticle chain aggregates of fumed silica in gels. Under oscillatory shear, the fumed silica gels experience disorganization and reorganization and present strong structural recovery ability after adjusting oscillatory shear (AOS) at small strain amplitudes (1–10%), and a more perfect network structure than that in origin gels can be induced. Elevated temperature (above Tc) improves the network structure to be more compact and stronger than that at a lower temperature, as a result, the deformation resistance during the AOS period and the structural recovery after AOS are enhanced. These results indicate that the network structure and viscoelastic properties of fumed silica gels can be tailored and optimized by performing small-amplitude oscillatory shear at a properly selected temperature.
Co-reporter:Kai Ke, Yu Wang, Xi-Qiang Liu, Jun Cao, Yong Luo, Wei Yang, Bang-Hu Xie, Ming-Bo Yang
Composites Part B: Engineering 2012 Volume 43(Issue 3) pp:1425-1432
Publication Date(Web):April 2012
DOI:10.1016/j.compositesb.2011.09.007
Multi-walled carbon nanotube (MWCNT)/poly(vinylidene fluoride) (PVDF) composites were prepared by two frequently-used approaches, melt and solution mixing. The dispersion state of MWCNTs in the PVDF matrix was evaluated by rheological properties and confirmed by optical microscope, scanning electron microscope and transmission electron microscope images. It was found that the dispersion state of MWCNTs was dependent not only on the concentration of MWCNTs but also the mixing method. Specifically, solution mixing led to a much better dispersion of MWCNTs than melt mixing at low concentrations of MWCNTs (less than 5 wt.%), while the situation was reversed at higher concentrations. The dispersion mechanisms of MWCNTs for the two mixing methods were also discussed.
Co-reporter:Shi-Wei Wang;Rui-Ying Bao;Ben Wang;Bang-Hu Xie
Colloid and Polymer Science 2010 Volume 288( Issue 6) pp:681-688
Publication Date(Web):2010 April
DOI:10.1007/s00396-010-2194-x
A kind of β-nucleating agent, calcium pimelate, for polypropylene (PP) was chemically supported onto the surface of multi-wall carbon nanotubes, and the effect of the multi-wall carbon nanotube-supported β-nucleating agent on the mechanical properties and morphology of isotactic polypropylene composites was investigated. The composites of isotactic polypropylene and multi-wall carbon nanotube-supported β-nucleating agent exhibited excellent impact toughness compared with pure isotactic polypropylene and β-nucleated isotactic polypropylene, being more than seven times over that of pure isotactic polypropylene and more than three times over that of β-nucleated isotactic polypropylene. The excellent impact behaviors of the composites were also evidenced by the fracture morphology based on scanning electron microscopy observations. Differential scanning calorimetry and wide-angle X-ray diffraction results verified the enhanced nucleating ability of the multi-wall carbon nanotube-supported β-nucleating agent, which greatly improved the impact toughness without significantly deteriorating the strength and stiffness of the polypropylene composites.
Co-reporter:Xiang-Jun Zha, Ting Li, Rui-Ying Bao, Lu Bai, Zheng-Ying Liu, Wei Yang, Ming-Bo Yang
Composites Science and Technology (8 February 2017) Volume 139() pp:17-25
Publication Date(Web):8 February 2017
DOI:10.1016/j.compscitech.2016.12.011
Co-reporter:Yuanming Zhai, Rongchun Zhang, Wei Yang, Mingbo Yang
Polymer (7 April 2017) Volume 114() pp:44-53
Publication Date(Web):7 April 2017
DOI:10.1016/j.polymer.2017.02.076
Co-reporter:Li-Feng Ma, Rui-Ying Bao, Rui Dou, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie, Ming-Bo Yang and Qiang Fu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 40) pp:NaN16996-16996
Publication Date(Web):2014/08/21
DOI:10.1039/C4TA03833A
A conductive elastomeric composite of carbon black (CB) filled thermoplastic vulcanizate (TPV) based on polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends was fabricated via phenolic resin (PF)-induced dynamic vulcanization in an effort to prepare temperature sensitive elastomeric materials with balanced properties. Fourier transformed infrared spectroscopy and gel content analysis revealed that the EPDM was effectively cured by PF and the degree of crosslinking reached 38.7 wt%. Morphology observation revealed that CB particles distributed in the EPDM phase in uncrosslinked thermoplastic elastomer composites, whereas CB particles were almost completely located in the PP matrix in TPV composites. For TPV composites, the morphological characteristic combined the temperature sensing properties of the PP/CB composite with the excellent resilience of the cured EPDM phase, resulting in an excellent balance in electrical and mechanical properties. Compared with the contrast composite, the TPV composite showed the lowest percolation threshold of electrical conductivity, significant enhancement of tensile stress at 300% stretching, ultralow negative temperature coefficient (NTC) effect, outstanding positive temperature coefficient (PTC) effect and repeatability. This study offers an example of high-performance temperature sensitive elastomeric materials with balanced properties.
Co-reporter:Yang Liu, Guo-Qiang Qi, Cheng-Lu Liang, Rui-Ying Bao, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2014 - vol. 2(Issue 19) pp:NaN3854-3854
Publication Date(Web):2014/02/21
DOI:10.1039/C3TC32586E
As a novel tissue engineering material and transistor, reduced graphite oxide (rGO) hydrogel is attracting more and more attention, and a stable and highly electrical conductive rGO hydrogel is the cornerstone for these applications. We controlled the structures of graphite oxides (GOs) with three different methods and the corresponding assembled rGO hydrogels were obtained using Vitamin C (VC) as the reducing agent and the stability and electrical resistance of the rGO hydrogel were studied. The results showed that the appropriate interlayer distance and grain size of GO prepared by two-step oxidation were beneficial for VC molecules to insert in the interspace between layers for the reduction. After reduction, the loose and tangled network structure was well assembled, which determines the stability and electrical conductivity of the resulted rGO hydrogel.
Co-reporter:Jie Yang, Li-Sheng Tang, Rui-Ying Bao, Lu Bai, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 48) pp:NaN18851-18851
Publication Date(Web):2016/11/09
DOI:10.1039/C6TA08454K
Latent heat energy storage and release media of organic phase change materials (PCMs) are promising to utilize thermal energy coming from solar radiation for effective thermal management. However, the inherently low thermal conductivity and poor photoabsorption of organic PCMs lead to slow thermal charging/discharging rates, hindering the direct thermal energy conversion and storage. Here, we demonstrate that multifunctional PCMs with high thermal conductivity, improved shape-stability and efficient light–thermal–electric energy conversion can be fabricated by introducing polyethylene glycol (PEG) into graphene oxide (GO)/boron nitride (BN) hybrid porous scaffolds (HPSs) constructed via an ice-templated assembly strategy. Owing to the self-assembly of thermally conductive fillers during ice-growth, the obtained PCMs exhibit a high thermal conductivity (as high as 1.84 W m−1 K−1 at 19.2 wt% of BN), which is much higher than that of the composites fabricated by the solution blending method. Furthermore, the obtained composite PCMs with high energy storage density and excellent thermal stability can also be utilized to realize efficient light-to-thermal and light-to-electric energy conversion and storage, providing promising application potential in advanced energy-related devices and systems for solar energy utilization and storage.
Co-reporter:Tao Gong, Rui-Ying Bao, Zheng-Ying Liu, Bang-Hu Xie, Ming-Bo Yang and Wei Yang
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 20) pp:NaN12719-12719
Publication Date(Web):2017/04/20
DOI:10.1039/C7CP01278K
Polypropylene (PP) and five kinds of monodisperse polystyrene (PS) with different terminal relaxation times were used to explore the relationship between the mobility of polymer molecular chains and the coarsening process of immiscible polymer blends with a co-continuous morphology under quiescent melt annealing at different temperatures. The terminal relaxation time of all neat PP and PS was determined by a rheological approach to characterize the mobility of molecular chains. A selective dissolution experiment showed that all PP/PS (50/50) blends maintained a co-continuous structure during the whole annealing process. Significant coarsening behaviors were observed for all PP/PS blends under a scanning electron microscope. A linear time dependence of the size of the PS phase was found in all PP/PS blends and the coarsening phenomenon was more obvious with the decrease of the terminal relaxation time of the PS phase because of the increase of the mobility of the polymer molecular chains. A direct relationship between the phase coarsening rate and the terminal relaxation time of the PS phase was found for the first time and it satisfied the equation . According to this equation, the formulae and k ∝ Mw−1 can be derived, which can provide significant information for the control of the phase coarsening process of immiscible polymer blends with a co-continuous morphology.
Co-reporter:Ting Li, Li-Feng Ma, Rui-Ying Bao, Guo-Qiang Qi, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 10) pp:NaN5490-5490
Publication Date(Web):2015/02/02
DOI:10.1039/C5TA00314H
Aiming at improved electrical conductive performance and simultaneously enhanced mechanical properties, a novel segregated structure was constructed for poly(ethylene-co-octene) (POE)/multi-walled carbon nanotube (MWCNT) elastomeric conductive composites with chemically cross-linked POE granules. Structural examination revealed the formation of unique phase morphologies with a stable segregated structure, in which the uncross-linked POE/MWCNT phase localized out of the cross-linked granules. With such a novel segregated structure, a percolation threshold as low as 1.5 vol% of MWCNTs was observed, which is significantly lower than the melt compounded POE/MWCNT composites; the stress at 100% and 300% stretching increased for more than 12% and 30%, respectively, and the tensile modulus inherent to the matrix elastomer was maintained. The elastic recovery of the composite with such a novel segregated structure was more than 85% and 65% after large strains up to 100% and 300%, respectively, always higher than the melt compounded POE/MWCNT composites. The Shore A hardness of the elastomeric conductive composites with cross-linked POE granules was also lower, showing better elasticity of POE/MWCNT composites with such a novel segregated structure. All these results demonstrated that the elastomeric POE/MWCNT conductive composites with such a novel segregated structure exhibited greatly reduced percolation thresholds with enhancement in mechanical properties, which provides a new way for the preparation of elastomeric conductive composites with simultaneously improved electrical performance and mechanical properties.
Co-reporter:Rui-Ying Bao, Jun Cao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2014 - vol. 2(Issue 9) pp:NaN3199-3199
Publication Date(Web):2013/12/20
DOI:10.1039/C3TA14554A
Balanced stiffness and toughness is always the goal of high-performance general plastics for engineering purposes and the interfacial crystalline structure control has been proved to be an effective way to approach this goal. In this work, a kind of novel β-nucleating agent (β-NA) for isotactic polypropylene (iPP), one of the most rapidly developing general plastics, was supported onto the surface of octadecylamine functionalized graphene oxide (GO-D), and the effects of functionalized graphene oxide (GO) on the crystallization behavior, crystalline structures and mechanical properties of iPP composites were studied. The presence of the octadecyl chain changes the hydrophilic GO to be hydrophobic, and further supporting of β-NA onto GO-D (GO-N) does not change its solubility in xylene. The hydrophobic nature of octadecyl chains on the GO-D and GO-N surfaces leads to improved interfacial adhesion with the non-polar iPP matrix. At the same time, GO-N exhibits high efficiency in inducing the formation of β-crystals of iPP. The relative content of β-crystals, kβ, reaches a value as high as 73.6% at a loading of 0.1 wt% GO-N, resulting in a maximum increase in impact strength by almost 100% and a simultaneous improvement of the tensile strength by about 30%. This work provides a potential industrializable technique for high-performance iPP nanocomposites.
Co-reporter:Guo-Qiang Qi, Jun Cao, Rui-Ying Bao, Zheng-Ying Liu, Wei Yang, Bang-Hu Xie and Ming-Bo Yang
Journal of Materials Chemistry A 2013 - vol. 1(Issue 9) pp:NaN3170-3170
Publication Date(Web):2013/01/14
DOI:10.1039/C3TA01360J
The structure of graphene oxide (GO) was tuned by controlled ultrasonication (40 kHz, 400 W). It was found that one hour of sonication was the critical point. Under ultrasonication, GO was exfoliated gradually in one hour and further treatment led to a reverse trend. The size of GO sheets decreased sharply in the first hour and then remained almost unchanged with the extension of sonication. In other words, once the GO sheets were cut into pieces small enough, they tended to restack together. Defects on the surface of GO were easily generated even within a short period of ultrasonication and the chemical structure was also changed. GO treated with different sonication times was incorporated into poly(vinyl alcohol) (PVA), and the structure and properties of PVA/GO nanocomposites were also discussed. The hydrogen bonding between the GO and PVA matrix increased before the critical point and then decreased, which was the key factor influencing the glass transition temperature. Meanwhile, the mechanical strength of the nanocomposites was improved before the critical point. The reinforcing mechanism is believed to be the effective load transfer between the PVA matrix and GO via strong hydrogen bonding interactions caused by the exfoliation effect.
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