Co-reporter:Shaojie Li;Guangjian He;Xia Liao;Chul B. Park;Qi Yang
RSC Advances (2011-Present) 2017 vol. 7(Issue 11) pp:6266-6277
Publication Date(Web):2017/01/18
DOI:10.1039/C6RA26457C
In this paper, long-chain branched polylactide (LCB-PLA) prepared by UV-induced reaction extrusion with trimethylolpropane triacrylate (TMPTA) was foamed by supercritical carbon dioxide (scCO2), and the effect of the long-chain branching structure on the cell morphologies of PLA foams was investigated. The LCB-PLA displayed higher complex viscosity, melting point and crystal nucleation potential under scCO2, and these factors could influence the foaming behavior of PLA which was proved by the different cell morphologies of samples foamed after various saturation times. The advantage of LCB-PLA on foaming was remarkable at high temperature and high pressure. LCB-PLA with more than 0.5% TMPTA showed nano-cells while the other samples showed micro-cells at 142 °C under 12 MPa, and the samples displayed elliptic cells with horizontal semimajor axis in linear PLA and circular cells or oval cells with vertical semimajor axis in LCB-PLA with increasing temperature. The improved cell morphology with reduced coalescence, no collapse and uniform cell distribution was also shown in LCB-PLA under higher pressure. All these results were due to the increasing matrix strength and higher crystal nucleation potential of LCB-PLA. The findings indicate that LCB-PLA possesses better foaming behavior at high temperature and high pressure. The wide foaming processing window of LCB-PLA would benefit the high temperature and high pressure foaming of PLA such as bead foaming and continuous extrusion foaming, thus broadening its application.
Co-reporter:Jian Xiong, Xia Liao, Jingjun Zhu, Zhu An, Qi Yang, Yajiang Huang, Guangxian Li
Polymer Degradation and Stability 2017 Volume 146(Volume 146) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.polymdegradstab.2017.10.012
•Isotatic polypropylene is investigated by exposing to different outdoor climates for four years.•PALS is used to investigate the mechanism of chemi-crystallization and free volume change.•The interaction between functional groups decreases the size of free volume holes.In order to explore the natural weathering mechanism of isotatic polypropylene (iPP) served in different outdoor climates, iPP samples were exposed to four typical climate conditions of China for four years. The microstructural changes of iPP were investigated by positron annihilation lifetime spectroscopy (PALS), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC) and wide-angle X-ray diffraction (WAXD). As the degradation processed, the molecular defects such as carbonyl and hydroxyl groups increased. Because of the formation of the new imperfect crystal caused by chemi-crystallization, the crystallinity increased initially and then reached a plateau. Due to the increase of crystallinity, the amounts of defects in crystalline-amorphous interfacial phase increased and the concentration of free volume holes decreased with exposure time. In addition, the interaction between functional groups constrained the mobility of molecular segments, which persistently decreased the size of free volume holes. The results showed that the freed molecule segments released by chain scission formed new crystals in the amorphous region during the degradation process. In addition, the similar microstructural changes of iPP weathered in different stations showed the similar degradation mechanism. Furthermore, the influence of the temperature on the degradation rate of iPP was more significant than other environmental factors.
Co-reporter:Yadong Lv, Yajiang Huang, Miqiu Kong, Qi Yang, Guangxian Li
Polymer Testing 2017 Volume 64(Volume 64) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.polymertesting.2017.09.040
•Evolution of structure-property correlation of polypropylene (PP) aging under six typical climate scenarios is uncovered.•Principal component analysis (PCA) is proved to be promising in establishing a comprehensive indicator for aging.•The degradation risk map of PP in China is established and the relative importance of weathering factors is evaluated.A full understanding on the relationships between weathering factors and deteriorations in the physical or mechanical properties of polymeric materials as well as their intercorrelations is critically important to forecast the durability of materials. In this work, the outdoor weathering behaviors of isotactic polypropylene (iPP) across a 1.5-year period under six typical climate scenarios in China are investigated. A wide sets of natural exposure conditions and test methods allow the establishment of the substantial correlations between chemical/physical structures and appearance/mechanical properties under simultaneous effects of multiple weathering factors (such as light, heat, oxygen etc.). The results under diverse natural environments suggest that the crystallinity and crack development depend largely on the molecular weight while the yellowing index correlates directly with the carbonyl index irrespective of the exposure conditions. The relationship between tensile strength and molecular weight is found to be in accord with an empirical linear model. Subsequently, using principal component analysis (PCA), a data reduction and visualization method, the degradation risk map of PP materials in China is established and the relative importance of relevant weathering factors is evaluated. Temperature is found to be the most dominant weathering factor on iPP aging under the climate scenarios investigated in the present work.
Co-reporter:Erbo Huang, Xia Liao, Chongxiang Zhao, Chul B. Park, Qi Yang, and Guangxian Li
ACS Sustainable Chemistry & Engineering 2016 Volume 4(Issue 3) pp:1810
Publication Date(Web):February 23, 2016
DOI:10.1021/acssuschemeng.6b00008
We used a high-pressure differential scanning calorimeter (HP-DSC) to study polymer plasticization by compressed gases at pressures of up to 30 MPa for polylactide (PLA), polycarbonate (PC), isotactic polypropylene (iPP), and polystyrene (PS). The pressure reached values twice as high as the previously published data. We found that the polymer/carbon dioxide (CO2) system’s heating curves have an unidentified endothermic peak above 5 MPa, which turns out to be from CO2’s phase transition. The HP-DSC could accurately determine the depression of the glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm) of various polymers at low pressures by simply starting at a higher temperature to avoid CO2’s phase transition; however, the increased plasticization effect of the dissolved CO2 lowered the Tg to the level of overlapping with CO2’s phase transition phenomena at elevated pressures, and therefore, the depressed Tg could not be measured above 6 MPa for PLA, PC, or PS. On the other hand, the Tc of iPP decreased with an increase in pressure, whereas Tm values of PLA and iPP decreased slightly with an increase in pressure and then remained almost unchanged above a certain pressure, which may indicate an increased hydrostatic pressure effect at elevated pressures.Keywords: Glass transition temperature; High-pressure differential scanning calorimeter (HP-DSC); Melting temperature; Phase transition; Supercritical carbon dioxide;
Co-reporter:Chenfei Jia, Xia Liao, Jingjun Zhu, Zhu An, Qiongwen Zhang, Qi Yang and Guangxian Li
RSC Advances 2016 vol. 6(Issue 37) pp:30986-30997
Publication Date(Web):16 Mar 2016
DOI:10.1039/C5RA26478B
β-Phase isotactic polypropylene (β-iPP) specimens with different contents of β-phase nucleating agent were employed to investigate the deformation-induced microstructure evolution during creep behavior. Morphological investigations by SEM showed that the crystalline morphologies of β-iPP were controlled by the content of the β-phase nucleating agent, namely, well-developed β-spherulites induced by low content of β-phase nucleating agent, bundle-like morphology with imperfect spherulites induced by medium content of β-phase nucleating agent and needle-like morphology induced by high content of β-phase nucleating agent. It was interesting to observe that all samples with different contents of β-phase nucleating agent showed a similar β/α transformation process. However, well-developed β-spherulites, which have integrated crystalline structure, showed poor creep resistance compared with the crystalline morphology nucleated by higher contents of β-phase nucleating agent. For bundle-like morphology, the crystalline phase was imperfect and obtained larger long spacing, resulting in better creep resistance. With respect to needle-like morphology, the crystalline phase was disordered and displayed largest long spacing, resulting in best creep resistance. The results of this work revealed that the creep resistance would be different with different crystalline morphologies. On the other hand, this work provided the evolution of microstructure during deformation to further explain the molecular mechanism of fatigue failure for creep.
Co-reporter:Yuwei Wang;Xia Liao;Shaojie Li;Yong Luo;Qi Yang
Polymer International 2016 Volume 65( Issue 10) pp:1195-1203
Publication Date(Web):
DOI:10.1002/pi.5175
The effects of oxygen functional groups and alkyl chains at the surface of graphene oxide (GO) on the thermal stability, mechanical properties and foaming behavior of poly(methyl methacrylate) (PMMA) nanocomposites were investigated. Alkyl-functionalized GO (GO-ODA) was prepared by grafting octadecylamine (ODA) on the surface of GO. PMMA/GO and PMMA/GO-ODA nanocomposite were obtained by solution blending and were foamed using supercritical carbon dioxide (scCO2). GO-ODA, with the presence of alkyl chains, showed a better dispersion capability in PMMA matrix than GO with a large amount of oxygen functional groups. In addition, the good dispersion capability increased thermal stability and mechanical strength. In comparison with PMMA/GO samples foamed at 70 °C, PMMA/GO-ODA nanocomposite foams displayed improved cell structures with higher cell density, smaller cell size and more homogeneous cell size distribution, which results from the strong heterogeneous nucleation due to alkyl chains on the GO surface. The foaming behaviors became more complicated at 80 °C as the GO might be intercalated and exfoliated with the aid of scCO2, thus further enhancing the heterogeneous nucleation during the foaming process. The results indicated that the surface chemistry of GO was closely related to the properties and foaming behavior of the nanocomposites. © 2016 Society of Chemical Industry
Co-reporter:Yadong Lv, Yajiang Huang, Junlong Yang, Miqiu Kong, Heng Yang, Jincan Zhao, Guangxian Li
Polymer Degradation and Stability 2015 Volume 112() pp:145-159
Publication Date(Web):February 2015
DOI:10.1016/j.polymdegradstab.2014.12.023
Co-reporter:Junsong Li, Guangjian He, Xia Liao, Hao Xu, Qi Yang and Guangxian Li
RSC Advances 2015 vol. 5(Issue 46) pp:36320-36324
Publication Date(Web):14 Apr 2015
DOI:10.1039/C5RA03682H
Poly(L-lactic acid) (PLLA) foams with unique nanocellular and needle-like morphology were successfully prepared by combining spherulite templating and supercritical carbon dioxide (CO2) foaming. The corresponding crystalline morphology formed under supercritical CO2 in PLLA was illustrated to investigate the foaming behavior of spherulites in detail. It was found that not only the degree of crystallinity but also the crystalline morphology played a vital role in cell nucleation and growth, thus the foam morphology. Nanocellular structure was primarily generated for the PLLA foamed at 100 °C and 12–24 MPa. Moreover, the morphological transition from approximate circular cells to needle-like cells occurred around 16 MPa at 100 °C because of the constraint of lamellae, and the two different structures coexisted at 100 °C and at pressures ranging from 16 to 24 MPa. The results indicated that the expansion ratio of spherulite was bigger than that of PLLA foam.
Co-reporter:Yuwei Wang, Xia Liao, Yong Luo, Qi Yang, Guangxian Li
Journal of Materials Science & Technology 2015 Volume 31(Issue 5) pp:463-466
Publication Date(Web):May 2015
DOI:10.1016/j.jmst.2015.01.010
The surface chemistry of filler is closely related to the structure and morphology of nanocomposite foams. Changing the property of filler is widely used to control the cell structures and functionalize the composite foams. Surface-functionalized graphene oxide (GO-ODA) was prepared by grafting octadecylamine (ODA) on the surface of graphene oxide (GO) to make the filler disperse better in the nanocomposites and have a strong interfacial interaction with polymer matrix. Poly(methyl methacrylate) (PMMA)/GO-ODA nanocomposite foams were obtained by solution blending and foamed using supercritical carbon dioxide (scCO2). Compared to neat PMMA and PMMA/GO samples, the PMMA/GO-ODA nanocomposite foams showed improved cell structures with smaller size, higher cell density and more homogeneous distribution, which should be attributed to the heterogeneous nucleation caused by well-dispersed GO-ODA nanosheets. This work not only improved the compatibility and interfacial interaction of GO with polymer matrix but also indicated that the modified GO sheets can act as ideal filler to control the cell density, size and size distribution efficiently.
Co-reporter:Shaojie Li;Ting He;Xia Liao;Qi Yang
Polymer International 2015 Volume 64( Issue 12) pp:1762-1769
Publication Date(Web):
DOI:10.1002/pi.4977
Abstract
The structural changes and crystallization kinetics of polylactide (PLA) during cold crystallization under CO2 at 80 °C were studied using in situ high-pressure Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra show that PLA can crystallize under air and CO2, and some differences are observed. In the second-derivative spectra, the 1220 cm−1 band is only found for PLA crystallized under CO2, and the tt conformer of PLA crystallized under CO2 is located at 1749 cm−1, while that of PLA crystallized under air is located at 1751 cm−1. From wide-angle X-ray diffraction, only the α′-crystal is observed when PLA is crystallized under air, whereas the α-crystal appears when crystallized under CO2. The crystalline-sensitive bands at 921 and 1458 cm−1 were used to analyze the crystallization kinetics of PLA. When PLA crystallizes under air, the 1458 cm−1 band changes faster than the 921 cm−1 one; when it crystallizes under CO2, the result reverses. This suggests that CO2 hinders interchain interactions while promoting the helix conformation. © 2015 Society of Chemical Industry
Co-reporter:Lingyun Wu;Jingjun Zhu;Xia Liao;Kai Ni;Qiongwen Zhang;Zhu An;Qi Yang
Polymer International 2015 Volume 64( Issue 7) pp:892-899
Publication Date(Web):
DOI:10.1002/pi.4862
Abstract
The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi-crystalline high-density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (Tg) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, Tg of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while Tg of the semi-crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of Tg of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry
Co-reporter:Kai Ni;Jingjun Zhu;Xia Liao;Yadong Lv;Lingyun Wu
Journal of Polymer Research 2015 Volume 22( Issue 6) pp:
Publication Date(Web):2015 June
DOI:10.1007/s10965-015-0753-z
The microstructure evolution of isotactic polypropylene (PP) exposed to subtropical humid climate of Guangzhou of China, were investigated by gel permeation chromatography, Fourier transform infrared spectroscopy, differential scanning calorimeter, dynamic mechanical analysis and positron annihilation lifetime spectroscopy. Positron data showed that the free volume of PP matrix decreased with involving a shrinking of the free volume hole sizes as the extent of weathering degradation of PP aggravated. The shrinkage of free volume hole sizes may be traced to the loss of mobility of molecules of PP matrix. The increase of the glass transition temperature substantiated undoubtedly the decrease of molecular mobility of PP chains. The increase in crystallinity might increase the amount of rigid amorphous fraction of PP matrix, which induced the loss of molecular mobility. Furthermore, the decrease of ortho-positronium formation ought to be correlated to the increase in crystallinity and the increasing amount of scavenchers which were in this work represented by the carbonyl groups.
Co-reporter:Chenfei Jia, Qiongwen Zhang, Xia Liao, Jingjun Zhu, Lingyun Wu, Kai Ni, Qi Yang, Zhu An, Guangxian Li
Polymer 2015 Volume 67() pp:92-100
Publication Date(Web):12 June 2015
DOI:10.1016/j.polymer.2015.04.057
•The molecular deformation mechanism of polypropylene during creep including three stages is proposed.•The mechanism explains the transition point during creep deformation.•Positron annihilation lifetime spectroscopy is a powerful microanalytical technique to explore the microstructure changes.•The disaggregation–recrystallization process would lead the free volume to increase in number while decrease in size.The hierarchical microstructure evolution of polypropylene during creep was explored via various methods, such as differential scanning calorimetry (DSC), scanning electron microscope (SEM), two-dimensional small-angle X-ray scattering (2D-SAXS), two-dimensional wide angle X-ray diffraction (2D-WAXD) and positron annihilation lifetime spectroscopy (PALS). The results revealed a correlation among the changes of micron-scale spherulites, nano-scale lamellae, crystalline blocks, atomic scale free volume and the deformation of polypropylene during creep. The elongation of micron-scale spherulites along the creep direction, accompanying with the increase of nano-scale lamellar long spacing, as well as the enlargement and amalgamation of atomic scale free volume were observed at ε below 17%; the imperfect fibrillar crystallites with polymer chains preferentially oriented along the creep direction, formed in the stress-induced crystalline block disaggregation–recrystallization process, were proved by SEM and 2D-SAXS results when ε was between 17% and 55%; the further orientation of polypropylene chains led to a higher degree of orientation and crystallinity. The molecular deformation mechanism of polypropylene during creep included three stages: the intralamellar slipping of crystalline blocks, accompanying with the enlargement and amalgamation of free volume, was activated at small strain (ε ≤ 17%); whereas the stress-induced crystalline block disaggregation–recrystallization process as well as the rearrangement and orientation of chains were proceeded at medium strain (17% < ε ≤ 55%); at last, orientation-induced crystallization occurred at larger strain (ε > 55%).
Co-reporter:Tian Xia, Yajiang Huang, Xiaolian Jiang, Youbing Li, Xuanlun Wang and Guangxian Li
RSC Advances 2014 vol. 4(Issue 63) pp:33431-33434
Publication Date(Web):24 Jul 2014
DOI:10.1039/C4RA05478D
With increasing temperature, a transition from fracture phase separation (FPS) to viscoelastic phase separation (VPS) was found in dynamically asymmetric PS/PVME blends with LCST behavior. Typical morphology formed via VPS disappeared under large quench depths, indicating some other specification might control the morphological evolution during VPS besides the dynamic asymmetry.
Co-reporter:Yifan Zhang, Xia Liao, Xianglin Luo, Suilin Liu, Qi Yang and Guangxian Li
RSC Advances 2014 vol. 4(Issue 20) pp:10144-10150
Publication Date(Web):31 Jan 2014
DOI:10.1039/C3RA47503D
Birefringent Maltese-cross concentric ring-banded spherulites with radial periodic variation of thicknesses grown from six-arm star-shaped poly(ε-caprolactone) (PCL) under the condition of subcritical CO2 were observed in this study. The structure of unique unclassical ring-banded spherulites was found to be different from that of traditional ring-banded spherulites which formed by periodic twisting of lamellar crystals along the spherulite radial direction. Laser scanning confocal microscopy, atomic force microscopy and scanning electronic microscopy images revealed that the ring-banded structure consisted of alternating periodically ridge and valley bands with continuous edge-on lamellae. A two-steps growth mechanism of ring-banded spherulites has been proposed to explain the development of central crystals and periodic ring-bands via CO2.
Co-reporter:Xia Liao, Haichen Zhang, Yuwei Wang, Lingyun Wu and Guangxian Li
RSC Advances 2014 vol. 4(Issue 85) pp:45109-45117
Publication Date(Web):23 Sep 2014
DOI:10.1039/C4RA07592G
In this study, a typical immiscible system, a poly(lactic acid) (PLA)/polystyrene (PS) bioblend is used to investigate the effect of interface and phase structure on bubble nucleation and porous morphologies using supercritical carbon dioxide as a physical foaming agent. A unique microcellular skin-core structure with a porous core and surface, and a nonporous skin layer which is embedded in a solid PLA phase are observed. The involved possible mechanism of the interfacial nucleation and confined foaming behavior in multi-phase systems has been discussed. Because of the higher gas concentration and lower activation energy barrier, bubble nucleation preferentially occurs at the interface of the PS and PLA phases. Due to the constrained effect of the crystalline PLA phase, smaller space could be provided for the expansion of the PS phase during the foaming process, hence gas bubbles in the interior are restrained from further growth. The porous structures of the PS phases are similar when the blends have comparable phase morphology. The results indicated that the confinement effect on the foam behavior is not only related to the crystalline PLA phase but also the phase structure of the blend.
Co-reporter:Y. J. Huang, M. Q. Kong, G. L. Chen, Q. Yang and G. X. Li
RSC Advances 2014 vol. 4(Issue 81) pp:43150-43154
Publication Date(Web):05 Sep 2014
DOI:10.1039/C4RA07229D
Two possible mechanisms of generating core–shell droplets, namely the rupture of blend films and the disintegration of compound threads, were identified in immiscible polymer blends with high viscosity. The deformation and relaxation behavior of the core–shell droplets was shown to be intimately related to the core-to-shell diameter ratio (Rcs).
Co-reporter:Shuting Xi, Yajiang Huang, Qi Yang, and Guangxian Li
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 14) pp:5916-5924
Publication Date(Web):March 13, 2014
DOI:10.1021/ie5001407
The efficiency of tin(II) 2-ethylhexanoate catalyst and hydrophilic silica nanoparticles in compatibilizing polycarbonate/poly(methyl methacrylate) (PMMA/PC) blends were compared in terms of the morphological, thermal, and mechanical properties. Both the catalyst and nanoparticles were found to refine the morphology of PMMA/PC blends. Although the blends with catalyst exhibited smaller phase size, they possessed more deteriorated mechanical performance and worse thermal properties than those of nanoparticle-filled ones due to the significant degradation during transesterification reactions. The addition of nanoparticles refined the morphology of PMMA/PC blends kinetically to a lesser extent. However, the thermal and mechanical properties of blends were improved noticeably upon the addition of nanoparticles. Finally, the mechanisms, advantages, and disadvantages of catalyst and nanoparticles in compatibilizing PMMA/PC blends were discussed and compared.
Co-reporter:Kewei Xiang;Siduo Wu;Guangsu Huang;Jing Zheng;Jingyun Huang
Macromolecular Research 2014 Volume 22( Issue 8) pp:820-825
Publication Date(Web):2014 August
DOI:10.1007/s13233-014-2106-x
In this work, styrene-butadiene rubber (SBR) was thermally aged at 130 °C with ageing period up to 4 days. The relaxation behavior was studied by dynamic mechanical analysis (DMA) in temperature scanning mode at multifrequencies and the crosslinking network was characterized by swelling method. Glass transition temperature (Tg) and activation energies (Ea) during transition evaluated by Starkweather method were found to increase after ageing. Time-temperature superposition (TTS) procedure was performed to obtain master curve and shift factors (αT). The derived αTs were fitted by William-Landel-Ferry (WLF) and Vogel-Fulcher-Tamman (VFT) equations. WLF fitting parameters confirmed decreased free volume fraction (f) and thermal expansion coefficient (αf) near Tg versus ageing time. Temperature dependent relaxation properties were examined by VFT fitting parameter D. It was found that the aged SBR displayed more brittle behavior, becoming more and more deviated from Arrhenius fashion. This phenomenon was illustrated by the enhanced intermolecular coupling and severe crosslinking during ageing.
Co-reporter:Junlong Yang, Yajiang Huang, Yadong Lv, Pengfei Zhao, Qi Yang and Guangxian Li
Journal of Materials Chemistry A 2013 vol. 1(Issue 37) pp:11184-11191
Publication Date(Web):24 Jul 2013
DOI:10.1039/C3TA11989K
The antioxidative effect of chemically reduced graphene oxide (rGO) on the thermal-oxidative stability of polypropylene (PP) was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). rGO was prepared by reduction of graphene oxide (GO) and characterized by atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. PP/rGO nanocomposites were then prepared without using a compatibilizer by melt blending. It was found that the thermal-oxidative degradation of PP was retarded noticeably by the rGO. The stabilization mechanism of rGO was discussed in terms of the changes in carbonyl bands and oxygen diffusion. It was proposed that the improved thermal-oxidation stability of PP/rGO nanocomposites can be attributed to the decline in both the concentration of peroxy radicals and oxygen permeability. The acceptor-like electronic property afforded by the long conjugated CC bonds and the barrier effect of rGO were suggested to be responsible for the improved thermal-oxidation stability of PP.
Co-reporter:Yadong Lv, Yajiang Huang, Miqiu Kong, Guangxian Li
Polymer Testing 2013 Volume 32(Issue 2) pp:179-186
Publication Date(Web):April 2013
DOI:10.1016/j.polymertesting.2012.10.008
Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA.
Co-reporter:Tian Xia, Yajiang Huang, Xiaolian Jiang, Yadong Lv, Qi Yang, and Guangxian Li
Macromolecules 2013 Volume 46(Issue 20) pp:8323-8333
Publication Date(Web):October 11, 2013
DOI:10.1021/ma4011582
The morphology change and the corresponding molecular mechanism of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends induced by hydrophilic or hydrophobic nanoparticles were studied. It was found that there was a threshold of hydrophilic silica loading for the occurrence of network–droplet morphological transition in PS/PVME blends. On the contrary, the viscoelastic network could sustain for a much longer time in the blends with higher loading of hydrophobic silica. Rheological measurements suggested that the networking of hydrophilic silica nanoparticles in the PVME-rich phase would significantly reduce the dynamic asymmetry of two phases and make the compositional asymmetry the dominant factor in controlling the morphology development during phase separation. However, adding the hydrophobic silica fillers would result in an increase of dynamic asymmetry and a decrease in compositional asymmetry because of their selective dispersion in the PS-rich phase, both stabilizing the continuous network structure.
Co-reporter:Ting He, Xia Liao, Yunchuan He, Guangxian Li
Progress in Natural Science: Materials International 2013 Volume 23(Issue 4) pp:395-401
Publication Date(Web):August 2013
DOI:10.1016/j.pnsc.2013.06.006
In this paper, novel electric conductive polylactide/carbon nanotubes (PLA/CNTs) foams were fabricated by a pressure-quench process using supercritical CO2 as a blowing agent. The morphology of PLA/CNTs nanocomposites prepared by solution blending was characterized using SEM and the results indicate that CNTs well dispersed in PLA matrix. The introduction of CNTs improved the thermal stability of PLA. The morphology and electrical properties of PLA/CNTs foams were characterized and discussed. Depending on the process parameters, such as saturation temperature and pressure, nanocellular or microcellular structure of PLA/CNTs nanocomposites were obtained. The volume resistivity of PLA/CNTs foams was from 0.53×103 Ω cm to 15.13×103 Ω cm, which was affected by cell structure and crystallization of foams oppositely. Foaming reduced the electrical conductivity due to the decrease of CNTs volume content and the break of conductive pathways. However, crystallization increased the electrical conductivity possibly because of the CNTs structural change in which the CNTs were less curled and more connected.
Co-reporter:Peng Li;Yajiang Huang;Miqiu Kong;Yadong Lv;Yong Luo
Colloid and Polymer Science 2013 Volume 291( Issue 7) pp:1693-1704
Publication Date(Web):2013 July
DOI:10.1007/s00396-013-2904-2
The fractionated crystallization behavior of polypropylene (PP) droplets in its 20/80 blends with polystyrene (PS) in the presence of hydrophilic or hydrophobic fumed silica nanoparticles was studied by using differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It was found that the fractionated crystallization of PP droplets in the PS matrix was promoted by adding a low content of hydrophobic or hydrophilic nanoparticles due to their morphological refinement effect. However, discrepancies in the fractionated crystallization behavior of PP droplets occurred as the nanoparticle content increased. The crystallization became dominated by the heterogeneous nucleation effect of high content of hydrophilic nanoparticles, which possibly migrated into PP droplets during mixing and significantly suppressed their fractionated crystallization. In contrast, the morphological refinement effect still played a dominated role in promoting the fractionated crystallization of PP droplets in PP/PS blends filled with higher content hydrophobic nanoparticles as a result of the efficiently morphological refinement effect.
Co-reporter:Daofei Bao;Xia Liao;Ting He;Qi Yang
Journal of Polymer Research 2013 Volume 20( Issue 11) pp:
Publication Date(Web):2013 November
DOI:10.1007/s10965-013-0290-6
Polymer foams with nanoscale cell structure were prepared from polycarbonate (PC)/poly (lactic acid) (PLA) blends. The immiscible blends with PLA as the dispersed phase were foamed through using batch foaming process and CO2 as the physical foaming agent. Nanoscale cells emerged in both PLA domain and PC matrix of blend with 25 wt.% PLA content under an appropriate foaming condition. In the PLA domain, the formation of nanoscale pores was related to the confined foaming, blend and the crystallinity of PLA component. A transition from closed nanoscale cells to open nanoscale cells emerging in the PLA domain was in connection with the foaming condition. In the PC matrix, the cell property of the nanoscale cells was affected by the PLA phase. Moreover, the average cell sizes of nanocellular foams of both phases could be controlled within 40–130 nm by manipulating the size of PLA domain and saturation pressure.
Co-reporter:Yadong Lv;Yajiang Huang;Miqiu Kong;Hong Zhu;Qi Yang
Rheologica Acta 2013 Volume 52( Issue 4) pp:355-367
Publication Date(Web):2013 April
DOI:10.1007/s00397-013-0696-4
Stress relaxation probing on the immiscible blends is an attractive route to reveal the time-dependent morphology–viscoelasticity correlations under/after flow. However, a comprehensive understanding on the stress relaxation of co-continuous blends, especially after subjected to a shear strain, is still lacking. In this work, the stress relaxation behavior of co-continuous polystyrene/poly(methyl methacrylate) (50/50) blends with different annealing times, strain levels, and temperatures was examined under step shear strain and was correlated with the development of their morphologies. It was found that co-continuous blends display a fast relaxation process which corresponded to the relaxation of bulk polymer and a second slower relaxation process due to the recovery of co-continuous morphology. The stress relaxation rates of co-continuous blends tend to decrease due to the coarsening of instable co-continuous structure during annealing. Furthermore, the stress relaxation of the co-continuous blends is strongly affected by the change of viscosity and interfacial tension caused by the temperature. The contribution of morphological coarsening, viscosity, and interfacial tension variation on the stress relaxation behavior of co-continuous blends was discussed based on the Lee–Park model and time–temperature superposition principle, respectively.
Co-reporter:Yuan Mei, Yajiang Huang, Qi Yang, Guangxian Li
Polymer 2012 Volume 53(Issue 23) pp:5413-5422
Publication Date(Web):26 October 2012
DOI:10.1016/j.polymer.2012.09.028
The effect of hydrophilic silica nanoparticles (SiO2) on the shape stability of crystallizable polybutylene terephthalate (PBT) fibrils in polystyrene (PS) matrix under quiescent and shear conditions was investigated using optical-shear technique, differential scanning calorimetry (DSC) and rheometry. The contributions of the crystallization and viscoelasticity to the improved stability of molten PBT fibrils with different nanosilica contents were discussed based on their rheology data and polarized microphotographs. Upon the addition of only 0.05 wt.% SiO2 nanoparticles, the shape stability of PBT fibrils during quiescent annealing increased noticeably due to the rapid crystallization in these filled PBT droplets. With increasing nanoparticle content, the enhanced viscoelasticity of PBT droplets due to the addition of nanoparticles also began to play a role in improving the shape stability of droplets. The addition of silica nanoparticles was also found to suppress the development of nodular morphology on PBT fibrils under shear flow caused by heterogeneous crystallization. It has been suggested that the loading of a relative high content of silica nanoparticles, the application of a rapid quenching and low rate shear flow are in favor of the shape stability of PBT fibrils under shear flow.Graphical abstract
Co-reporter:Xiaojuan Peng, Yajiang Huang, Tian Xia, Miqiu Kong, Guangxian Li
European Polymer Journal 2011 Volume 47(Issue 10) pp:1956-1963
Publication Date(Web):October 2011
DOI:10.1016/j.eurpolymj.2011.07.008
The morphology of immiscible fluid mixtures under confined environment usually displays different scenarios compared with those presented in bulk systems. In this work, the influence of confinement and component ratio on the droplet morphology of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends in confined steady shear flow was investigated. While increasing the degree of confinement, the morphology of dispersed phase experienced a transition from the bulk behavior toward the confined behavior. Increasing the concentration of PIB phases in confined blends resulted in more coarsened structure under low shear rate and generated pearl necklace or string-like structures under a higher shear rate. The maximum aspect ratio of PIB droplets increased while increasing PIB concentration. The width and the aspect ratio of PIB droplets obtained experimentally were compared to the predictions of a single droplet MM model for bulk flow and an M model considering confinement. The experimental droplet width agreed well with the predictions of these two models only in the small droplet zone, large deviations appeared for the degree of confinement up to 0.36 and higher, whereas constant droplet width was found. The M model decreased the deviation between the experimental aspect ratio and the prediction of MM model in the high Ca zone. Good agreement between the prediction of M model and experiment results was found when the orientation angles of the droplets were corrected by using the M model.Graphical abstractHighlights►The effect of confinement and component ratio on the morphology of PIB/PDMS blends in confined shear flow was investigated. ► The experimental width and aspect ratio of PIB droplets were compared to the predictions of MM model and M model. ► The prediction of M model agreed well with the experiment results when the orientation angles were corrected.
Co-reporter:Miqiu Kong, Yajiang Huang, Guangling Chen, Qi Yang, Guangxian Li
Polymer 2011 Volume 52(Issue 22) pp:5231-5236
Publication Date(Web):13 October 2011
DOI:10.1016/j.polymer.2011.08.052
The effect of hydrophilic silica nanoparticles (SiO2) on the relaxation and breakup dynamics of selectively filled polyamide (PA6) droplets with different degrees of deformation in polystyrene (PS) matrix during quiescent annealing were in situ investigated. It was found that, with the increase of silica content, the relaxation process of PA6 droplets was slowed down gradually and the relaxation mode was changed correspondingly. The critical break aspect ratios (ARcr) of PA6 droplets were also improved with the increase in SiO2 nanoparticle contents. Comparisons of the experimental values of ARcr, characteristic relaxation time (τd) and breakup time (tb) of the SiO2-filled PA6 droplets with corresponding theoretical values were made. The results of comparison were discussed in terms of viscoelasticity and interfacial tension. It was proposed that the alternation of the viscoelastic properties of PA6 droplets in stead of the interfacial tension change of the blends was responsible for the phenomena observed.
Co-reporter:Tian Xia;Yajiang Huang;Xiaojuan Peng
Macromolecular Chemistry and Physics 2010 Volume 211( Issue 20) pp:2240-2247
Publication Date(Web):
DOI:10.1002/macp.201000237
Co-reporter:Wei Tong;Yajiang Huang;Chenglei Liu;Xiaolian Chen
Colloid and Polymer Science 2010 Volume 288( Issue 7) pp:753-760
Publication Date(Web):2010 May
DOI:10.1007/s00396-010-2201-2
The influence of surface nature (hydrophobic and hydrophilic) and concentration of silica nanoparticles on the coalescence behavior of immiscible polydimethylsiloxane (PDMS)/polyisobutylene (PIB) (90/10) blends under simple low-rate shear flow were investigated via optical shear technique. It was found that the coalescence of PIB droplets in PDMS matrix was suppressed efficiently by incorporating hydrophobic silica nanoparticles, and a constant droplet size was obtained at high particle contents. The addition of a small amount (<0.4 wt.%) of hydrophilic silica nanoparticles also decreased the size of PIB droplets. Clusters of small PIB droplets were formed at low filler concentration. When the filler concentration exceeded 0.8 wt.%, the clusters of PIB drops disappeared and elongated PIB threads with large size were formed, which suggest that the coalescence of PIB droplets was promoted. The results indicate that the discrepancy in the morphology evolution of PDMS/PIB blends upon the addition of silica nanoparticles is controlled not only by the surface chemistry of nanoparticles but also by their concentration in the blends.
Co-reporter:Xiaolin Liu;Yajiang Huang;Cong Deng;Xiaojun Wang;Wei Tong;Yuxin Liu;Jianqian Huang;Qi Yang;Xia Liao
Polymer Engineering & Science 2009 Volume 49( Issue 7) pp:1375-1382
Publication Date(Web):
DOI:10.1002/pen.21330
Abstract
The creep behavior and creep failure law of polypropylene (PP) were investigated by using a multifunctional stress-aging testing machine under different aging environmental conditions (temperature, UV, and stress). Photoinduced changes in samples were studied using gel permeation chromatography and X-ray photoelectron spectrometer. Surface morphologies were also observed by scanning electron microscopy. It was found that there is a critical failure strain (εcrit) for PP during the creep course. Once the creep deformation exceeds the εcrit, creep failure of PP takes place very rapidly. The value of εcrit is independent of the tensile stress and UV irradiation, whereas it is only affected by the temperature and the nature of the PP, such as molecular weight and molecular structure. With increasing temperature, the value of εcrit increases gradually. In addition, the creep rate of PP increases rapidly with increasing tensile stress and temperature as well as under irradiation with UV light. This study may provide a new way to predict the service lifetime of PP. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Co-reporter:Yuxin Liu;Qi Yang
Journal of Applied Polymer Science 2008 Volume 109( Issue 2) pp:782-788
Publication Date(Web):
DOI:10.1002/app.27707
Abstract
The nonisothermal crystallization behavior of linear low-density polyethylene (LLDPE)/glass fiber (GF) composite was investigated by differential scanning calorimetry (DSC). It was observed that the crystallization temperature peak (Tp) of LLDPE composite containing 5.0 wt % GF (LLDPE/GF5) was higher than that of the pure LLDPE at various cooling rates. The half-time of crystallization (t1/2) of LLDPE/GF5 composite was shortened under the effect of GF. The nonisothermal crystallization kinetics of LLDPE and LLDPE/GF5 composite were analyzed through the Avrami, Ozawa, and Mo equations. The results indicated that the data of the nonisothermal crystallization for LLDPE and LLDPE/GF5 composite calculated based on the Ozawa equation did not have the good linear relationship, but the nonisothermal crystallization behaviors of LLDPE and LLDPE/GF5 composite could be successfully described by the modified Avrami and Mo methods. The crystallization rate Zc of the modified Avrami parameter of LLDPE/GF5 composite was higher than that of pure LLDPE at the same cooling rate. The Mo parameter F(T) of LLDPE/GF5 composite was lower than that of LLDPE at the same degree of crystallinity. Through the Kissinger equation, the activation energies Ed of LLDPE and LLDPE/GF5 composite were evaluated, and their values were 312.3 and 251.2 kJ/mol, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Co-reporter:Qi Yang;Ying Zhang;Peng Zhang;Kun Yang
Polymer Engineering & Science 2007 Volume 47(Issue 2) pp:95-102
Publication Date(Web):17 JAN 2007
DOI:10.1002/pen.20677
Three types of polypropylene (PP) with different intrinsic toughness were used to study the mechanical properties and morphologies of the PP composites filled with single-filler and hybrid-filler of calcium carbonate particles. The calcium carbonate particles used were with average particle sizes of 25 μm (CC25), and 0.07 μm (CC0.07), respectively. A hybrid-filler CaCO3 named CC25/CC0.07 was used as a mixture of CC25 and CC0.07 (CC25/CC0.07 weight ratio = 1:1). It was found that the type of PP and the particle size of inorganic filler were the two important factors for the determination of mechanical properties of the composites. And the general mechanical properties of the composites filled with hybrid-filler CaCO3 were better than those of the composites filled with single-filler CaCO3, but the synergistic hybridization effect of the hybrid-filler CaCO3 did not exist. The major toughening mechanism of the PP/CC25 composites was the cavitation of the matrix caused by CC25, and the major toughening mechanism of the PP/CC0.07 composites was the pinning effect introduced by CC0.07. For the PP/CC25/CC0.07 composites, the cavitation of the matrix caused by CC25 and the pinning effect introduced by CC0.07 existed simultaneously. And when the intrinsic toughness of the matrix was large enough, the major factor to toughen PP was the pinning effect introduced by CC0.07, otherwise the major factor to toughen PP was the cavitation of the matrix caused by CC25. POLYM. ENG. SCI., 47:95–102, 2007. © 2007 Society of Plastics Engineers
Co-reporter:Guojun Luo, Wenze Li, Wenbin Liang, Guogang Liu, Yi Ma, Yanhua Niu, Guangxian Li
Composites Part B: Engineering (15 February 2017) Volume 111() pp:
Publication Date(Web):15 February 2017
DOI:10.1016/j.compositesb.2016.12.016
High performance polypropylene/glass fiber (PP/GF) composites were prepared by treating GF with a film former (GFf) containing a certain ratio of maleic anhydride grafted polypropylene (MPP) and a kind of β-nucleating agent (TMB-5) via impregnation method, and meanwhile introducing different amount of MPP in the matrix. The coupling effects of GF treatment and the matrix modification on the mechanical properties and interfacial microstructures were investigated in detail. It is found that the film former can efficiently facilitate both the interfacial adhesion and β-transcrystallinity with the aid of appropriate MPP in the matrix. Addition of small amount of MPP (2 wt%) to the matrix in GFf system could significantly improve the mechanical properties with ca. 100% and 178% enhancements in tensile and impact strength, respectively, compared to the commercial GF reinforced PP (PP/GFc). With further increase of MPP content, the tensile strength of the composite increases slightly, accompanied by deterioration of the impact strength. The dramatically improved mechanical properties can be attributed to the simultaneously enhanced interfacial adhesion and β-form transcrystallinity through the coupling effects of nucleating agent locked by MPP on the surface of GFf and those MPP in both the film former and matrix. A schematic mechanism of interfacial microstructure formation is depicted, in which the diffusivity of MPP and PP, the nucleating agent and the molecular interactions are considered as key factors influencing the formation of β-transcrystallinity and interfacial adhesion.
Co-reporter:Junlong Yang, Yajiang Huang, Yadong Lv, Pengfei Zhao, Qi Yang and Guangxian Li
Journal of Materials Chemistry A 2013 - vol. 1(Issue 37) pp:NaN11191-11191
Publication Date(Web):2013/07/24
DOI:10.1039/C3TA11989K
The antioxidative effect of chemically reduced graphene oxide (rGO) on the thermal-oxidative stability of polypropylene (PP) was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). rGO was prepared by reduction of graphene oxide (GO) and characterized by atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. PP/rGO nanocomposites were then prepared without using a compatibilizer by melt blending. It was found that the thermal-oxidative degradation of PP was retarded noticeably by the rGO. The stabilization mechanism of rGO was discussed in terms of the changes in carbonyl bands and oxygen diffusion. It was proposed that the improved thermal-oxidation stability of PP/rGO nanocomposites can be attributed to the decline in both the concentration of peroxy radicals and oxygen permeability. The acceptor-like electronic property afforded by the long conjugated CC bonds and the barrier effect of rGO were suggested to be responsible for the improved thermal-oxidation stability of PP.
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