具有高界面压应力的高分子共混物Ⅱ.拉伸过程中形态演化与增强机理

研究了聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)和聚碳酸酯(PC)/PE共混物在拉伸过程中形态的演化和增强机理.结果表明,高界面压应力是共混物在基体加工温度成型时,从成型温度冷却到室温过程中基体收缩比分散相大产生的;两种共混物在拉伸中有不同的形态演化过程:PC粒子原位形成了微纤,粒子与基体间没有明显的界面滑动,而PET粒子只产生较小的塑性变形,成为椭球状粒子,粒子与界面间存在滑动.PC对基体PE的增强效果比PET的更好,因为PC/PE共混物拉伸过程中形成了良好增强作用的原位微纤.在拉伸过程中,PET/PE试样的细颈在靠近非浇口端形成,并从此扩展开.部分拉伸后,PC/PE试样比PET/PE试样的弹性回复大,回复到平衡状态时间长,这是两种共混物分散相变形机理不同引起的.     

PET/PE原位微纤化共混物的形态与性能

用“熔融挤出—热拉伸—淬冷”方法制备了聚对苯二甲酸乙二醇酯(PET)／聚乙烯(PE)原位微纤化共混物(MCB)，研究了热拉伸比恒定时组成对MCB形态和力学性能的影响，形态观察发现，MCB形成了良好的纤维结构，热拉伸比恒定时，纤维的形态特征(如直径及其分布等)主要受PET含量影响，MCB拉伸模量和强度较通常共混物有显著提高，但太低和太高PET含量，增强效果有所减弱，随着PET含量的提高，MCB经历了从韧性拉伸断裂到脆性拉伸断裂的转变。     

具有高界面压应力的高分子共混物Ⅰ.制备和拉伸性能

考察了高界面压应力对不相容聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)和聚碳酸酯(PC)/PE共混物拉伸性能的影响.高界面压应力是共混物低温成型(PE的成型温度)时,分散相与基体从加工温度冷却到室温过程中基体的收缩比分散相粒子大产生的.尽管PET/PE和PC/PE共混物极不相容,但拉伸强度和模量随着PET和PC含量增加而增加.PET与PC含量相同时,PC/PE的拉伸强度和模量高于PET/PE的.采用Takayanangi方程计算共混物的拉伸模量时,具有高界面压应力的PC/PE共混物的拉伸强度高于界面有良好粘结的共混物的理论值,表明在不添加增容剂时,可通过控制加工条件改善共混物界面相互作用,提高共混材料的性能.     

导电原位微纤化复合材料的有机液体响应特性

通过熔融预混合-高温挤出热拉伸-淬冷-低温成型方法制备导电原位微纤化CB/PET/PE材料,CB选择性分布在PET微纤中,微纤相互搭接形成导电网络。将试样浸入二甲苯溶液测试其电性能对有机液体的敏感性,结果表明,原位微纤化CB/PET/PE材料的电阻率迅速升高,相对于普通CB/PE导电复合材料有更高的响应强度,这是由其特殊的微观结构和形态决定的;另外,材料电阻率的变化与其厚度相关,当试样厚度由140μm增加至500μm时,材料的电阻率对二甲苯的敏感程度降低。     

通过挤出-热拉伸制备CB/PET/PE导电复合材料

在前期热塑性塑料原位成纤研究基础上，尝试通过挤出-热拉伸制备原位微纤化炭黑(CB)／聚对幕二甲酸乙二醇酯(PET)／高密度聚乙烯(HDPE)导电复合材料。先将CB／PET熔融混合制成母料，再将母料和HDPE按一定的比例挤出一热拉伸。实验发现，体系成纤性能受母料的熔融粘度影响。在相对低的CB含量下，复合物能形成较好的原位微纤，从而具有较好的电性能．     

CB含量对微纤化导电复合材料CB/PET/PE非等温结晶的影响

采用差示扫描量热仪(DSC)研究了不同CB含量的原位微纤化复合材料CB/PET/PE在不同的冷却速率(2.5℃/min,5℃/min,10℃/min,20℃/min)的非等温结晶行为,采用扫描电子显微镜(SEM)观察微纤形态。结果表明,随CB含量增加,复合材料结晶起始温度降低,且相对结晶速率减小。SEM观察发现,CB的加入改变了微纤形态,随CB含量增加,CB粒子逐渐占据了微纤表面且纤维形态变差。     

GEP/PO原位微纤化共混物的制备

利用“熔融挤出-热拉伸-淬冷”方法制备了几种通用工程塑料(GEP)／聚烯烃(PO)原位微纤化共混物，研究了加工设备(挤出机、注塑机、HAAKB流变仪附属单螺杆挤出机)和口模结构(窄缝状、片状、棒状)对聚对苯二甲酸乙二醇酯(PET)／聚乙烯(PE)共混物原位成纤的影响，发现带矩形窄缝状口模的挤出机挤出能产生更好的纤维结构，而有高剪切作用的对空注塑不能形成纤维结构。观察PET／PE，PET／聚丙烯(PP)，聚碳酸酯(PC)／PE及PC／PP共混物的成纤情况，发现通常认为不利于成纤(粘度比大于1)的PC／PE和PC／PP体系也形成了较好的纤维形态。总体上，PET／PE的成纤效果好于其它的体系。     

可降解型聚丁二酸丁二醇酯/聚乳酸原位成纤增强复合材料

采用"熔融挤出-冷拉伸-微注成型"方法成功制备了可降解型高分子——聚丁二酸丁二醇酯(PBS)/聚乳酸(PLA)的原位成纤复合材料,其中PBS为基体连续相而PLA为微纤增强相;并从组分黏度比、组分含量比以及拉伸形变比三方面分析讨论了微纤化结构的形成条件。扫描电子显微镜观察结果表明,所采用的可降解型高分子原料的黏度比并不在最适宜成纤的范围内,但提高拉伸比以及高的PLA含量都可以增加PLA微纤的数量和长径比。研究发现PLA相部分形成微纤化结构后,由于自身力学性能的提高并且增加了两相间的界面作用,对PBS/PLA复合材料体系有显著增强作用。拉伸强度与拉伸模量分别比纯PBS提高了55%和140%,优于文献报道的几种天然纤维对PBS的增强效果。     

增容对LLDPE/PET微纤增强复合材料形态和结晶的影响

采用熔融挤出、拉伸和退火制备了线性低密度聚乙烯(LLDPE)和聚对苯二甲酸乙二醇酯(PET)质量比为80/20的增容和未增容微纤增强复合材料(MFC)。利用扫描电镜(SEM)和差示扫描量热仪(DSC)分别研究了增容剂LLDPE-g-MAH对微纤复合材料中LLDPE的结晶、熔融以及分散相PET形态变化的影响。结果表明,增容剂LLDPE-g-MAH的加入,影响了PET粒子成纤的连续性,减小了分散相尺寸,当增容剂用量为10份时影响最为明显;PET微纤对基体LLDPE的结晶有异相成核作用,这种作用受增容剂用量的影响,增容剂用量为10份时,对LLDPE结晶有促进作用,而PET的熔点却随增容剂增加而降低。     

炭黑填充PET/PE导电原位微纤化复合材料

根据炭黑（CB）粒子在聚合物中的选择性分布理论,通过工艺控制,使CB粒子主要分布在微纤表面。本工作将CB粒子首先与聚乙烯（PE）共混,再与聚对苯二甲酸乙二醇酯（PET）熔融混合-挤出-热拉伸-淬冷。形态观察表明,CB粒子可以良好地分布于PET微纤表面。电性能测试表明,分布于微纤表面的CB粒子有助于微纤之间的电子传导,该复合材料的正温度系数（PTC）较强,而负温度系数（NTC）较弱。     

PET/PE原位微纤化共混物的非等温结晶

通过挤出、热拉伸及淬冷制备了聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)原位微纤化共混物。采用差示扫描量热仪(DSC)研究了PET/PE原位微纤化共混物的非等这结晶特性,为了比较,同时考察了纯PE和PET/PE通常共混物的结晶特性。结果表明,PET微纤对PE有良好结晶异相成核作用,可提高结晶温度、缩短结晶时间、增大结晶速率,但使PE的结晶度和熔点降低;增加降温速率,结晶峰变宽且向低温方向移动。     

Effects of stretching on mechanical properties of aligned multi-walled carbon nanotube/epoxy composites

Composites based on epoxy resin and differently aligned multi-walled carbon nanotube (MWCNT) sheets have been developed using hot-melt prepreg processing. Aligned MWCNT sheets were produced from MWCNT arrays using the drawing and winding technique. Wavy MWCNTs in the sheets have limited reinforcement efficiency in the composites. Therefore, mechanical stretching of the MWCNT sheets and their prepregs was conducted for this study. Mechanical stretching of the MWCNT sheets and hot stretching of the MWCNT/epoxy prepregs markedly improved the mechanical properties of the composites. The improved mechanical properties of stretched composites derived from the increased MWCNT volume fraction and the reduced MWCNT waviness caused by stretching. With a 3% stretch ratio, the MWCNT/epoxy composites achieved their best mechanical properties in this study. Although hot stretching of the prepregs increased the tensile strength and modulus of the composites considerably, its efficiency was lower than that of stretching the MWCNT sheets.     

Polyethylene-polyethylene microfibrillar composites

Solid-state drawing of melt-crystallized, or gel(solution)-crystallized, polyethylene (PE) is well established as a means of producing high modulus high-strength fibres. Here, an alternative route, based on melt-processing, is reviewed and its merits are assessed. Contrary to expectation, melt processing of flexible chain polymers can directly yield oriented products with good mechanical properties, without the need for post-drawing in the solid state. The melt-processed PE can give a special microfibrillar composite morphology which results in good mechanical properties. The paper also reviews aspects of composites design by comparing these microfibrillar composites with traditional fibre composites and molecular composites.Dedicated to professor Andrew Keller, FRS, after retirement, as a mark of appreciation for his contributions to the understanding of polymer crystallization, and for allowing us to learn about the subject and encouraging our investigations in a general research environment at Bristol.     

In—situ Composite Based on Poly （ethylene terephthalate）,Polyamide and Polyethylene with Microfibres Formed through Extrusion and Hot Stretching

In-situ composites based on dispersed poly (ethylene terephthalate) (PET) or polyamide (PA),and continuous Polyethylene (PE) were prepared through a single screw extruder of Haake rheometer system with a rod-die relatively small in diameter.The extrudate was drawn at a drawing ratio of 3.1,and then quickly cooled in cold water.The specimens were obtained by injection molding at processing temperatures less than 190℃，far below the melting temperature of PET (265℃) and PA (230℃),which can maintain the solid state of PET and PA microfiber phase in the composites.Morphological observation with scanning electron microscopy (SEM) indicated that PET and PA can more or less form in-situ microfibers at compositions studied (0-20 wt pct PET or PA),and especially,PET and PA were almost deformed into fibers at the concentration of 15wt pct.Eensile strength and especially.PET and PA were almost deformed into fibers at the concentration of 15wt pct.Tensile strength and modulus of the blends reinforced by PET or PA microfibers showed to be increased from the tensile test results.The most noticeable improvement of the tensile properties occurred at 15wt pct of PET in PET/PE system,corresponding to the highest microfiber content,where the tensile strength reached 32.5 MPa,whereas only 19.5 MPa for the pure PE.     

Morphology of in situ poly(ethylene terephthalate)/polyethylene microfiber reinforced composite formed via slit-die extrusion and hot-stretching

This article introduced the morphologies of in situ microfiber reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The PET/PE MRC was prepared through slit-die extrusion and hot-stretching, followed injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the microfibers. Morphological observation indicated that the PET microfibers could be achieved by the way used in this study, and the microfiber characteristics, such as diameter, diameter distribution, were mainly dominated by PET content at a fixed hot-stretching ratio (HSR) of 19.17. Increasing the PET content the fiber diameter became bigger and the diameter distribution wider, but the minimum fiber diameter always remained constant.     

固相挤出制备回收PET基复合材料的研究

采用一种新的固相双螺杆挤出法制备回收PET基复合材料与传统的熔融挤出法进行对比,所用的无机填料为片状的滑石粉及球状的碳酸钙。通过考察熔体流动速率的变化评价回收PET的降解程度,DSC考察结晶性能,SEM观察填料分散情况,并测定弯曲、冲击性能及热变形温度。研究发现,相对于熔融挤出,固相挤出制备rPET复合材料有效缓解rPET降解程度,无机填料分散更细微,结晶度提高,力学性能改善。并且发现用C aCO3填充rPET时,材料性能的改善则不如T alc显著。