Co-reporter:FengYi Hou, DaShan Mi, Man Zhou, Jie Zhang
Polymer 2017 Volume 122(Volume 122) pp:
Publication Date(Web):28 July 2017
DOI:10.1016/j.polymer.2017.06.035
•The thickness and arrangement of shear layer and spherulites layer can be tuned.•A novel shear layer-spherulites layer alternated multilayer structure was prepared.•Such alternated structure is in favor of the improvement of impact strength.In general, the strength of injection molded objects increases with shear layer thickness or shish-kebab content. However, the effect of the change of the position of shear layer and spherulites layer on the mechanical properties is still unclear, when their thickness are fixed. To answer this question, a novel multilayer structure in which the shear layer mainly containing shish-kebab structure and spherulites layer consisted of spherulites stack alternatively was prepared by a self-designed multi-flow vibration injection molding (MFVIM) device. The results demonstrate that the impact strength can be enhanced significantly by such alternating structure, possibly because this structure is benefit for crack deflection and consequently induces more plastic deformation regions, through altering stress transfer direction and stress distribution. The tensile strength, however, is only affected little by such structure.Download high-res image (180KB)Download full-size image
Co-reporter:Dashan Mi;Renxi La;Wanwan Chen
Polymers for Advanced Technologies 2016 Volume 27( Issue 9) pp:1220-1227
Publication Date(Web):
DOI:10.1002/pat.3787
This study aims to investigate the interfacial crystallization between glass fiber (GF) and polypropylene (PP) by micro-injection molding. Three different kinds of transcrystallinity (TC) were formed at different conditions by different formation mechanisms. The virgin GF could form the TC by aligning the adjacent molecules to parallel with the GF surface, while the modified GF (M-GF) could induce the TC directly on its surface. Furthermore, the M-GF reduced the number of nano-voids between the GF and iPP, characterized by X-ray scattering technique. When β-nucleation agents (β-NA) were added, a novel net-coating layer was first discovered on the M-GF surface. This structure may be caused by the self-organization of β-NA and leads to some unique intensity streaks in SAXS patterns. Based on the experimental results, a schematic model was proposed. Copyright © 2016 John Wiley & Sons, Ltd.
Co-reporter:Man Zhou;Xin-peng Li;Ming Jin;Chao Xia
Chinese Journal of Polymer Science 2016 Volume 34( Issue 8) pp:1001-1013
Publication Date(Web):2016 August
DOI:10.1007/s10118-016-1814-4
In this article, crystalline morphology and molecular orientation of isotactic polypropylene (iPP), random copolymerized polypropylene (co-PP) and β-nucleating agent (β-NA) composites prepared by pressure vibration injection molding (PVIM) have been investigated via polarized light microscopy, scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Results demonstrated that the interaction between co-PP and iPP molecular chains was beneficial for the mechanical improvement and the introduction of β-NA further improved the toughness of iPP. In addition, after applying the pressure vibration injection molding (PVIM) technology, the shear layer thickness increased remarkably and the tensile strength improved consequently. Thus, the strength and toughness of iPP/co-PP/β-NA composites prepared by PVIM were simultaneously improved compared to those of the pure iPP prepared by conventional injection molding (CIM): the impact toughness was increased by five times and tensile strength was increased by 9 MPa. This work provided a new method to further enhance the properties of iPP/co-PP composites through dynamic processing strategy.
Co-reporter:Zhi-hao Zhao;Fei-fei Wang;Man Zhou;Kai-zhi Shen
Chinese Journal of Polymer Science 2016 Volume 34( Issue 12) pp:1479-1489
Publication Date(Web):2016 December
DOI:10.1007/s10118-016-1865-6
High density polyethylene (HDPE) with moderate content of crosslink network (CPE) was successfully prepared through chemical method. Specimens for structural characterization have been molded by conventional injection molding (CIM) and pressure vibration injection molding (PVIM). Influence of crosslink network on hierarchical morphology distribution and mechanical properties was systematically studied. Polarized light microscopy (PLM) revealed that both CIM and PVIM PE samples have a typical “skin-core” structure and the thickness of shear layer of CIM PE and PVIM CPE samples obviously increase. Scanning electron microscopy (SEM) showed that shish-kebab structures are clearly observed in shear layer of CIM CPE sample, indicating that the crosslink network can surely improve the formation of shish-kebab structures. Moreover, we suppose that shish-kebab structures emerged in shear and core layer of PVIM CPE sample. Wideangle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) confirmed that more orientation and shish-kebab structures form even in core layer of PVIM CPE sample, which demonstrated that the hierarchical morphology was apparently altered by periodical shear and crosslink network. Finally, the mechanical properties revealed that this oriented structure increase the tensile strength from 31 MPa of CIM PE sample to 46 MPa of PVIM CPE sample. However, the tensile behavior tended to change from ductile fracture to brittle fracture.
Co-reporter:Bi-qiang Jin;Xin-peng Li;Ming Jin;Da-shan Mi
Chinese Journal of Polymer Science 2016 Volume 34( Issue 2) pp:164-173
Publication Date(Web):2016 February
DOI:10.1007/s10118-016-1747-y
The crystallization behavior, rheological behavior, mechanical properties and microstructures of injection molded isotactic polypropylene (iPP), polypropylene random copolymer (co-PP) and iPP/co-PP blends were investigated. Differential scanning calorimetry (DSC) and dynamic rheological analysis illustrated that iPP and co-PP were compatible in the blends and co-PP uniformly dispersed in the iPP phase. Polarizing optical microscope (POM) was adopted to observe the crystal size and morphology evolution. The results of mechanical properties and scanning electron microscopy (SEM) indicated that the crystal size of iPP in iPP/co-PP blends (10 wt% co-PP + 90 wt% iPP and 30 wt% co-PP + 70 wt% iPP) radically decreased after the incorporation of co-PP. During crystallization, the molecular chain segments of co-PP could penetrate iPP spherulites and form a network-like crystalline structure. The network-like crystal structure could effectively transmit stress and consume more energy to overcome intermolecular forces to resist stretching. In this way, the strength would improve to a certain degree. The impact fracture mechanism of iPP/co-PP blends is quasi ductile fracture by multiple crazes. Our work discovered that the blends containing 10 wt% and 30 wt% of co-PP exhibited prominent toughness and reinforcement.
Co-reporter:Dashan Mi, Chao Xia, Ming Jin, Feifei Wang, Kaizhi Shen, and Jie Zhang
Macromolecules 2016 Volume 49(Issue 12) pp:4571-4578
Publication Date(Web):June 20, 2016
DOI:10.1021/acs.macromol.6b00822
Oriented “shish-kebab” structure can enable remarkable mechanical enhancement in polymers. Therefore, the formation mechanism and practical application of this structure have been extensively studied. However, the effect of shish-kebab content on mechanical properties is still uncertain. Knowledge of this effect is crucial in the academic and industrial fields but remains elusive because shish-kebab content is difficult to control. In this work, a self-developed multiflow vibrate-injection molding was used to produce samples with different shear layer thicknesses. The content of shish-kebab was represented by R, i.e., the thickness ratio of shear layer (composed by shish-kebab) to the whole sample. Results showed that with increased R impact/tensile strength exponentially increased, whereas elongation at break exponentially decreased. Based on the results, a modified model was proposed to interpret the strengthening and toughening mechanism. This study established a new method of predicting and controlling the mechanical properties of samples with shish-kebab and spherulite structures.
Co-reporter:Chao Xia, Hailan Du, Feifei Wang, Renxi La, Dashan Mi, Xinpeng Li, Jie Zhang
Materials Letters 2015 Volume 153() pp:66-69
Publication Date(Web):15 August 2015
DOI:10.1016/j.matlet.2015.04.005
•A novel crystal morphology (α banded spherulite) of iPP is achieved in this study.•The spherulite morphology is correlation with pressure fluctuation.•No rings could be found in the exterior of the spherulite.•The pressure vibration is indispensable to the formation of banded spherulites.•The formation mechanism of α banded spherulite is proposed.This article reports the novel crystal morphology of isotactic polypropylene (iPP) called α banded spherulites, which were induced by a pressure vibration field and investigated through polarized light microscopy, scanning electron microscopy and atomic force microscopy. Results showed that the height profile of banded spherulite along the radius corresponded to the pressure fluctuation in the cavity. No rings were found in the exterior of the spherulites, indicating that pressure vibration with a specific intensity was indispensable for the formation of banded spherulites. This work provided a new insight into the formation mechanism of banded spherulites induced by a mechanical field.
Co-reporter:Feifei Wang, Hainan Du, Hong Liu, Yu Zhang, Xiongwei Zhang, Jie Zhang
Polymer Testing 2015 Volume 45() pp:1-11
Publication Date(Web):August 2015
DOI:10.1016/j.polymertesting.2015.04.014
The mechanical properties of isotactic polypropylene (iPP) and ethylene–octene copolymer (POE) blends with or without β-nucleating agent (β-NA) were systematically studied. Results demonstrated that, after β-NA and POE were separately added, the impact strength of injection molded iPP samples increased. β-NA and POE were also found to have a synergistic toughening effect on iPP matrix, and the effect was significant. When the contents were 0.05 wt% β-NA and 10 wt% POE, the impact strength reached the maximum, i.e., almost 15 times that of neat iPP. SEM further revealed that POE in skin and core layers existed as long and narrow strips along the flow direction and throughout crystals. The tensile strength did not deteriorate because of the special phase morphology and tight interfacial interaction between POE phase and matrix. WAXD and DSC revealed that POE addition had negligible influence on crystal form, and a considerable number of β crystals was generated by adding β-NA. SEM results also confirmed a critical β-NA content. When β-NA content was lower than the critical value, perfect β sphaerocrystals were generated. When β-NA was higher, “bundle-like” crystal structures formed. Perfect β sphaerocrystals were more efficient for dissipating energy because of the looser stacking pattern, thus showing better toughness.
Co-reporter:Ming Jin, Biqiang Jin, Xiang Xu, Xinpeng Li, Tao Wang, Jie Zhang
Polymer Testing 2015 Volume 46() pp:41-49
Publication Date(Web):September 2015
DOI:10.1016/j.polymertesting.2015.06.018
The effects of ultrahigh molecular weight polyethylene (UHMWPE) and mould temperature (Tmould) on an isotactic polypropylene (iPP) matrix moulded via micro-injection were investigated via polarized light microscopy, scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray diffraction and small-angle X-ray scattering. Results showed that the complex viscosity of the system increased significantly when the UHMWPE content was more than 5%; however, this viscosity decreased when the UHMWPE content was less than 5%. In addition, the addition of UHMWPE increased the onset of crystallisation temperature and the relative crystallinity of the β-form crystals in micro-injection moulded specimens. Moreover, the UHMWPE phase induced the formation of fan-shaped β crystals in iPP/UHMWPE blends. When mould temperature was 50 °C, the degree of orientation of microparts increased and the crystalline structures were highly compact. However, the relative crystallinity of the β-phase form (Kβ) was lower than those prepared at 130 °C Tmould. Most importantly, well-oriented, bundle-like β crystals have been discovered for the first time in 5 wt.% UHMWPE/iPP blends obtained at 130 °C Tmould owing to the “orientation-maintenance” and “shear-amplification” effects of UHMWPE.
Co-reporter:Ming Jin, Renxi La, Yu Zhang, Kejun Liu, Xinpeng Li, Jie Zhang
Polymer Testing 2015 Volume 42() pp:135-143
Publication Date(Web):April 2015
DOI:10.1016/j.polymertesting.2015.01.010
The crystalline and oriented morphologies of isotactic polypropylene (iPP), ultrahigh molecular weight polyethylene (UHMWPE) and β-nucleating agent (β-NA) blends molded by micro-injection were investigated via polarized light microscopy, scanning electron microscopy, differential scanning calorimetry and wide-angle X-ray diffraction. The results showed that the addition of β-NA raised the onset crystallization temperature and the relative crystallinity of the β crystals of the micro-injection molding (MIM) specimens because of its strong heterogeneous nucleating effect in the iPP matrix. The introduction of UHMWPE, because of its “maintaining-orientation” effect, increased the thickness of the shish–kebab structure in the skin layer and induced the formation of perfect β cylindrulites that are epiphytic and symmetrical on the surface of long fibrous crystals. Furthermore, stratiform β crystals induced by the combined effects of strong shear flow field and addition of UHMWPE and β-NA were observed and investigated. Such a unique structure provides an effective way to tune the mechanics of MIM parts.
Co-reporter:Ren-xi La;Qi-xiong Zhou;Chao Xia;Da-shan Mi
Chinese Journal of Polymer Science 2015 Volume 33( Issue 11) pp:1625-1632
Publication Date(Web):2015 November
DOI:10.1007/s10118-015-1708-x
Isotactic polypropylene (iPP) samples obtained by pressure vibration injection molding (PVIM) and conventional injection molding (CIM) were studied by polarized-light microscopy (PLM), respectively. It was found that the alternating bright and dark banded spherulites were generated in the transitional region of PVIM parts. It is the first time that the banded spherulites of isotactic polypropylene were observed in polymer processing. What’s more, the banded spherulites were proved to be constituted of α-form crystal by hot stage polarized-light microscopy (HT-PLM) and wide angle X-ray diffraction (WAXD). Morphology of the banded spherulites was also studied by scaning electronical microscopy (SEM).
Co-reporter:Kejun Liu, Ming Jin, Renxi La, Jie Zhang, Tao Wang, Xiongwei Zhang
Materials Letters 2014 Volume 125() pp:209-212
Publication Date(Web):15 June 2014
DOI:10.1016/j.matlet.2014.03.169
•A feasible way to prepare transcrystallization of β-form iPP without flow field.•Nucleating agents can form the network throughout the transcrystallization via self-assembly.•The adhesion between fiber and matrix is probably to be improved and the crack propagation in the matrix is restricted.The transcrystallization of isotactic polypropylene (iPP) containing a network of nucleating agents (NAs) is investigated. The iPP transcrystallization exhibits abundant β-modification crystallization with slight orientation. Throughout the transcrystallization, a network comprising self-assembled NAs is formed during the diffusion of NAs from the poly(l-lactic acid) fiber to the iPP matrix. The self-assembled network of NAs is formed in binary, phase-separated mixtures. The network provides continuous reinforcing structures, which could be used to improve fiber-matrix adhesion and resist crack propagation. These results are beneficial in understanding the self-assembly process and transcrystallization.
Co-reporter:Ming Jin, Kejun Liu, Hong Liu, Yu Zhang, Hainan Du, Xinpeng Li, Jie Zhang
Polymer Testing 2014 Volume 39() pp:1-11
Publication Date(Web):October 2014
DOI:10.1016/j.polymertesting.2014.07.008
Co-reporter:Yu Zhang, Chengling Wang, Hainan Du, Xinpeng Li, Dashan Mi, Xiongwei Zhang, Tao Wang, Jie Zhang
Materials Letters 2014 Volume 117() pp:171-174
Publication Date(Web):15 February 2014
DOI:10.1016/j.matlet.2013.12.005
•Crosslinking bundles can promote the crystallization of PLA samples.•Increasing crosslinking degree can raise onset crystallization temperature.•The perfection of crystal lamellas with higher crosslinking degree is inferior.In this study, the influence of crosslinking structures on the crystallization of polylactide (PLA) samples was investigated. Chemical-induced crosslinking method was adopted and crosslinking structures were successfully achieved in the presence of dicumyl peroxide (DCP) and triallyl isocyanurate (TAIC). Originally it was commonly suggested that crosslinking would block the motion of chains, thus hindering the crystallization process. However, our results indicate that low or moderate crosslinking bundles (not complete polymer network) can promote the crystallization of PLA samples to some extent. With further increasing crosslinking degree (from 12.1% to 41.2%), although the onset crystallization temperature can be increased as well, the perfection of crystal lamellas is inferior. Based on the experimental results, a schematic model is proposed.
Co-reporter:Peng Deng, Ben Whiteside, Feifei Wang, Keith Norris, Jie Zhang
Polymer Testing 2014 Volume 34() pp:192-201
Publication Date(Web):April 2014
DOI:10.1016/j.polymertesting.2014.01.006
This study investigates the influence of length scale effects (micro- and macro-injection molded parts) and mold temperature on the epitaxial growth and morphological characteristics in injection-molded bars of isotactic polypropylene (iPP)/high-density polyethylene (HDPE) blends. After preparing the blends with an iPP content of 70 wt% via melt extrusion, the injection-molded bars were formed using both micro and conventional injection molding. Samples were subsequently prepared from the moulded components to allow investigation of the internal morphology using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarized light microscopy (PLM). The results indicated that the matching of micro scale and appropriate mold temperature was most favorable for epitaxial crystallization. The micro-parts had a large fraction of shear layer compared with macro-parts. The SEM observations showed that the shear layer of the former consisted of a highly oriented shish-kebab structure. Moreover, the effects of different methods of injection molding on the morphological characteristics of the micro-parts and macro-parts in different layers were elucidated in detail using PLM and SEM.
Co-reporter:Hainan Du, Yu Zhang, Hong Liu, Kejun Liu, Ming Jin, Xinpeng Li, Jie Zhang
Polymer 2014 Volume 55(Issue 19) pp:5001-5012
Publication Date(Web):15 September 2014
DOI:10.1016/j.polymer.2014.08.012
•PP blends with different phase morphologies and crystalline structures are achieved.•Elongated domains transmit stress better, spherical ones induce larger stress field.•Only blend of elongated POE and well-developed β-spherulite achieve highest toughness.In the work, ethylene–octene copolymer (POE) toughened isotatic polypropylene (PP) blends with different phase morphologies and crystalline structures were successfully fabricated and their influence on the toughness of PP blends was discussed. POE domains not only played the role of stress concentration to induce stress field around them, but also acted as stress deliverer to transmit stress to the deep into the PP matrix. Elongated domains transmitted stress better, but spherical ones induced a larger stress field. As for the crystalline structure of PP matrix, compared with the “bundle-like” β-crystals, well-developed β-spherulites could induce a larger stress field. The toughness of the blends with different combinations of phase morphology and crystalline structure was also discussed. Only the blend with elongated POE domains and well-developed β-spherulites could achieve super-high toughness. To achieve this goal requires simultaneous optimization of nucleating agent content, POE content and composition, and processing conditions. This work provides a good example to better understand the influence of phase morphology of rubbers and crystalline structure of matrix in rubber-toughed polymer system.
Co-reporter:Yu Zhang;Hong Liu;Lei Zhang;Xiongwei Zhang
Journal of Applied Polymer Science 2013 Volume 128( Issue 5) pp:3382-3389
Publication Date(Web):
DOI:10.1002/app.38552
Abstract
To study the interaction between β-nucleation agent and nano-CaCO3 in iPP matrix, the dynamic rheology properties, crystallization and melting behaviors, impact fracture surface of β-nucleation agent (β-NA) nucleated and nano-CaCO3 filled iPP were investigated in details in this study. Under suitable conditions, the β-NA has a “promoting dispersion effect” on the dispersion of nano-CaCO3 in PP matrix. However, 0.2 wt % β-NA nucleated sample has a worse “promoting dispersion effect” than 0.05 wt % β-NA nucleated sample at relatively high nano-CaCO3 content (7.5 wt %). The reason is that 0.2 wt % β-NA aggregates on the surface of nano-CaCO3 agglomerations. The α crystals induced from β-crystals grow more regular and perfect than conventional α crystals. For the relative fraction of β crystals (Kβ), the nano-CaCO3 content has little influence on 0.05 wt % β-NA nucleated samples, but obvious effect on 0.2 wt % β-NA nucleated samples. Based on the investigated results, a mechanism model about the interaction between β-nucleation agent and nano-CaCO3 in iPP matrix is proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Yu Zhang;Hong Liu;Lei Zhang;Xinpeng Li;Hainan Du
Journal of Applied Polymer Science 2013 Volume 129( Issue 5) pp:2744-2753
Publication Date(Web):
DOI:10.1002/app.38987
Abstract
In this study, the influence of β-nucleation agent (β-NA) on the morphology and properties of multi-walled carbon nanotube (MWCNT) filled isotactic polypropylene (iPP) composites was explored in details. The results show that the incorporation of β-NA has promoted the dispersion of MWCNT in the iPP matrix, which is profitable for improving the thermal stability and conductivity properties of MWCNT-iPP composites. Besides, the 0.05 wt % β-NA nucleated samples exhibit higher impact toughness than that of un-β-NA-nucleated ones. Further SEM observations show that the morphology of MWCNT changes from large agglomerations to small clusters with doping of β-NA. The main reason is that the incorporation of β-NA (TMB-5) in MWCNT filled iPP matrix has led to the formation of a charge-transfer complex. Some of these clusters act as nucleation sites for inducing crystallization of α spherulites, which have a compete growth with β-NA induced β crystals. Meanwhile, other clusters exist in the inter-lamella amorphous phase of β crystals, some of them even combine two adjacent β spherulites. Accordingly, a large conductive network comes into being. Based on the investigated results, a mechanism model is proposed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Yu Zhang, Lei Zhang, Hong Liu, Hainan Du, Jie Zhang, Tao Wang, Xiongwei Zhang
Polymer 2013 Volume 54(Issue 21) pp:6026-6035
Publication Date(Web):4 October 2013
DOI:10.1016/j.polymer.2013.08.024
In this study, a novel approach has been developed to introduce orientation to bundle-like β spherulite in iPP samples. The addition of UHMWPE phase, which plays the role of maintaining orientation of iPP chains, into β-nucleation agent nucleated iPP samples leads to the formation of oriented β spherulite in the inner region of injection molded samples. Accordingly, both the tensile strength and impact strength of the sample have been improved. It proves that the arrangement of crystallites is another important factor to determine the toughness in addition to β-crystal content, especially when the content is relatively high. Based on the investigated results, a schematic model about the formation of orientated β crystals via the addition of UHMWPE is proposed. It's the first time that oriented β spherulite is observed and investigated. Our study suggested an alternative approach to achieve good mechanics in polypropylene via introducing orientation to β spherulite.
Co-reporter:Kejun Liu, Lei Zhang, Hong Liu, Peng Deng, Hainan Du, Xinpeng Li, Jie Zhang
Materials Letters 2013 90() pp: 145-147
Publication Date(Web):
DOI:10.1016/j.matlet.2012.09.032
Co-reporter:Chao Guo;Fang Hui Liu;Xian Wu;Hong Liu
Journal of Applied Polymer Science 2012 Volume 126( Issue 2) pp:452-462
Publication Date(Web):
DOI:10.1002/app.36698
Abstract
To compare the difference of morphological evolution of HDPE micropart and macropart, micropart with 200 μm thickness and macropart with 2000 μm thickness were prepared. The PLM images of micropart and macropart exhibited a similar “skin–core” structure, but the micropart showed a much larger fraction of orientation layer. The SEM observation of core layer of micropart featured an unoriented lamellae structure and shear layer of micropart showed a highly oriented shish-kebab structure. The 2D-WAXD patterns of shear layer of macropart indicated twisted oriented shish-kebab (KM-I) structures, however that of micropart indicated untwisted oriented shish-kebab (KM-II) structures which was firstly found in microinjection molding. The diffraction pattern of the micropart exhibited stronger azimuthal dependence than the shear layer of macropart, indicating the most pronounced orientation of HDPE chains within lamellae. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Xinyuan Qian;Hong Liu;Fanghui Liu;Xueqin Gao
Journal of Applied Polymer Science 2012 Volume 123( Issue 2) pp:682-690
Publication Date(Web):
DOI:10.1002/app.34499
Abstract
The injection-molded specimens of neat HDPE and the PET/HDPE blends were prepared by conventional injection molding (CIM) and by pressure vibration injection molding (PVIM), respectively. The effect of oscillation pressure and PET phase with different shapes on superstructure and its crystal orientation distribution of injection molded samples were characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and two-dimension wide-angle X-ray diffraction techniques (2D-WAXD). Hermans' orientation functions were determined from the wide-angle X-ray diffraction patterns. With the PET particles added, the shear viscosity of blend increase and crystallization rate of HDPE phase is enhanced. For the neat HDPE samples, with the promotion from oscillation shear, the orientation parameter experienced a large increase, moreover, the PVIM can induce transverse lamellae (kebabs) twisting in growth direction. Because of the redefined flow field and nucleation effect of PET particles, the crystal orientation of blend is also increased. So the tensile strength of vibration samples enhanced and elongation at break declined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Yu Zhang, Jie Zhang, Xinyuan Qian, Peng Deng, Kaizhi Shen
Polymer 2012 Volume 53(Issue 19) pp:4318-4327
Publication Date(Web):31 August 2012
DOI:10.1016/j.polymer.2012.07.013
It has been well established that periodical shear stress can improve the mechanical performance of isotactic polypropylene during injection molding. In the current study, Polarized Light Microscopy (PLM), two-dimensional Wide-Angle X-ray Diffraction (2D-WAXD), Scanning Electron Microscopy (SEM) were employed to investigate the morphology evolution of vibration sample. Compared with static sample, the morphology of vibration one, which is derived from periodical shear field, exhibits different hierarchy structure: there is an additional fiber layer containing cylindrulites between the shear layer and the core layer, and the orientation is enhanced obviously. Through etching technique, it is found that there exists non-crystalline component in the fibril (core) of cylindrulite, and it may induce the growth of β crystals directly regardless of its non-crystalline nature. Based on the investigated results, a model of formation of cylindrulite is proposed.Graphical abstract
Co-reporter:Jie Zhang;Hong Liu;Lei Zhang;Qixiong Zhou;Xueqin Gao;Kaizhi Shen
Polymer Bulletin 2012 Volume 68( Issue 1) pp:239-251
Publication Date(Web):2012 January
DOI:10.1007/s00289-011-0627-4
In this study, isotactic polypropylene (iPP) samples were prepared by self-made pressure vibration injection device, in which a periodical shear field was imposed on the iPP melt during the filling and packing stages. The crystal structures and orientation of samples were investigated by wide-angle X-ray diffraction and polarizing light microscopy (PLM). The β form and γ form were found in vibration injection molding samples. Compared with the static samples, the orientation of iPP chains within lamellae was observed in the transition layer (at the depth of 1.5 mm from the surface) of the vibration injection molding samples, and the orientation was found even in the core layer. The PLM observation indicates the β form exists in the transition and core region of the vibration sample. Besides, two types of β-PP could be observed simultaneously in the core region under high magnification. The bright β crystallites (βIII) are fan-shaped and lie perpendicularly to the flow direction. In the other hand, the ringed β crystallites (βIV) almost remain their spherulite shape. Moreover, fiber crystal was observed in vibration sample, even in the core region. Some fiber crystals in the transition region reappeared in the cooling circle after the sample was held at 180 °C for 2 min. This could be explained in structure memory effect and its high thermal stability.
Co-reporter:Liangbo Yang, Fanghui Liu, Hesheng Xia, Xinyuan Qian, Kaizhi Shen, Jie Zhang
Carbon 2011 Volume 49(Issue 10) pp:3274-3283
Publication Date(Web):August 2011
DOI:10.1016/j.carbon.2011.03.054
An isotactic polypropylene/multi-wall carbon nanotube (iPP/MWCNT) composite was prepared by a vibration injection moulding technique. The effect of the vibration field on the electrical conductivity property of samples was investigated. The results show that the electrical conductivities of the samples prepared by vibration injection moulding was far higher than those of samples prepared by conventional injection moulding when the CNT concentration are above 2 wt.% and below 6 wt.%. Besides the electrical conductivity of vibration injection moulded samples are a little higher than those of the compression moulded samples. The higher conductivity was resulted from the MWCNT movement induced by the periodical shear during vibration injection moulding. The agglomerates or individual MWCNT were disentangled, stretched and oriented along the flow direction, resulting in better conducting paths thus greatly increased the electrical conductivity. The electrical conductivity increased with increasing vibration frequency. The difference in the voltage–current relationships among the samples prepared at different vibration frequencies suggests that the mechanism of electrical conductivity of iPP/MWCNT composite changed from a tunnel to an ohmic effect. Compared with conventional injection moulded samples, there was no loss of mechanical properties.
Co-reporter:Qixiong Zhou, Fanghui Liu, Chao Guo, Qiang Fu, Kaizhi Shen, Jie Zhang
Polymer 2011 Volume 52(Issue 13) pp:2970-2978
Publication Date(Web):8 June 2011
DOI:10.1016/j.polymer.2011.05.002
In this study, isotactic polypropylene (iPP) samples were prepared by conventional injection molding (CIM) and pressure vibration injection molding (PVIM), in which a periodical shear field was imposed on the iPP melt during the cooling solidification. The distribution of supermolecular structures of samples was investigated by Polarized Light Microscopy (PLM) and Scanning Electron Microscopy (SEM). Results show that the through-the thickness-morphology of sample prepared by CIM features a typical skin-core structure, as a result of general shear-induced crystallization. This structure can be divided into three layers, including a skin layer in which the shish–kebab structure was found, a transition region with deformed spherulite structure and a core layer with spherulitic structure. However, the morphology of the sample prepared by PVIM, as a result of periodical shear-induced crystallization, features a richer and fascinating supermolecular structure and can not be roughly divided into three layers. A region full of shish–kebab-like cylindrulite structures was found between the transition region and the core layer, which is rare to be seen in conventional injection molding. Based on their various core structures, two kinds of shish–kebab-like cylindrulites were defined: one is multi-fibril-core cylindrulite of which core is an assembly of multiple fibrils, and the other is single-fibril-core cylindrulite of which the core just contains a single fibril. Based on the investigated results, a schematic illustration is proposed to depict the through-the thickness-distribution of supermolecular structure of iPP sample prepared by PVIM. The mechanism of the formation of the two kinds of shish–kebab-like cylindrulite structures is also depicted by a schematic illustration, and it was discussed in terms of periodical shear-induced crystallization.
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