嵌段共聚物相容剂对聚合物共混体系力学性能影响的连续介观模拟

结合介观动力学方法和三维弹簧格子模型,研究了嵌段共聚物相容剂对相容性较差的聚合物二元共混体系力学性能的影响.在适当范围内不断增加嵌段共聚物相容剂的用量,研究了相容剂含量对体系杨氏模数及拉伸强度的影响,同时也对不同体系材料的破碎位点进行了分析.结果表明,未加入相容剂的二元共混体系在拉伸模拟中表现出较低的拉伸强度,而适量添加相容剂可以显著提升材料的拉伸强度,随着相容剂含量的增加,共混体系的破碎位点会发生转移并最终改善材料的整体性能.而相容剂的加入对体系杨氏模数的影响较小.该连续模拟方法为关联聚合物复合体系的微观结构和宏观力学性能提供了一条高效的途径.     

相容剂对PP/POE共混体系脆韧转变行为的影响

采用熔融挤出法制备了不同相容剂含量的PP/POE共混体系,测试了不同体系的脆韧转变温度、热性能和力学性能.结果表明,乙烯-丙烯多嵌段共聚物相容剂的加入降低了PP/POE共混物的脆韧转变温度,提高了共混物的韧性.AFM和STEM照片显示相容剂的加入减小了橡胶分散相的临界粒子间距,PP和POE在两相界面结合处相互扩散或渗透,实现了POE弹性体在PP树脂中合适的尺度分布以及良好的形态分散.当相容剂含量达到10％时,POE分散相尺寸细小均匀,分散相粒子粒径为0.54μm,粒子间距为0.1 μm,PP结晶链段更多地插入到弹性体内部,弹性体POE分散相形成明显的“硬核-软壳”结构.DSC曲线中结晶峰和熔融峰的变化说明适量的相容剂对于材料结晶度的提高具有一定的促进作用.力学性能测试结果可以看出相容剂的加入在提高材料韧性,降低其脆韧转变温度的同时也保持了材料的刚性性能.     

三元聚合物共混体系的微观结构与力学性能模拟

建立一种构型模拟与力学性能模拟相结合的连续模拟方法研究了三元共混物(两种均聚物与一种共聚物)中交替共聚结构与嵌段共聚结构对力学性能的影响。通过蒙特卡罗模拟获得其构型,然后将该构型作为弹簧格子模型的数据输入,模拟三元共混体系的微观结构与力学性能。模拟结果表明:交替共聚物在体系中更倾向于在两种均聚物的界面处自我缠绕,而嵌段共聚物的两端分别渗透进与之相容的均聚物体相中;三元共混物的力学性能与其内部的两相界面结构相关;应变在交替共聚物体系中均匀分布,导致更多的断裂发生在体相中,交替共聚物体系比嵌段共聚物体系力学性能更强且更具韧性。这种连续模拟方法为研究材料组成与力学性能之间的关系提供了一种新方案。     

嵌段共聚物增容剂对不相容均聚物共混体系相行为和界面性质的影响

聚合物共混体系(又称聚合物合金)兼具其相应组分的均聚物和共聚物的多种特征,甚至具有新的理想性能,从而成为了一种具有极高经济价值的新材料.该材料的研发极大地丰富了高分子物理学、高分子化学和材料学的研究内容,拓宽了聚合物材料在现代工业中的应用,同时把聚合物材料研究推向了交叉科学的前沿.均聚物/嵌段共聚物/均聚物体系作为经典的三元聚合物共混体系,对其进行深入地研究,不仅可以促进人们对高分子科学中重要问题的理解,而且可为新型嵌段共聚物增容剂的改良和设计提供理论依据.近年来,有关聚合物共混体系的实验、理论和计算机模拟工作很多,并且取得了较大的进展,但是相关综述较少.本文以均聚物/嵌段共聚物/均聚物体系为例,综述该领域的基本概念和发展历史,并着重介绍两嵌段共聚物增容剂对该三元共混体系相行为和界面性质的影响.此外,还介绍了这一领域的关键科学问题、发展前景和研究方向.     

热致液晶／PEEK／嵌段共聚物共混体系的结构与性能

用ＷＡＸＤ、ＳＥＭ及力学性能测试等研究热致液晶／ＰＥＥＫ／嵌段共聚物三元共混体系形态、结构和性能。结果表明嵌段共聚物的加入，使体系具有一定的相容性和较好的界面粘接，共混物的强度、模量有一定的提高，对共混物的结晶行为具有明显的影响，当热致液晶含量高时，基材与液晶两相间出现明显的分离现象，即“皮－芯”结构．     

均聚物/两嵌段共聚物/均聚物三元聚合物共混体系界面性质的Monte Carlo模拟

利用格子Monte Carlo(MC)模拟方法研究了两嵌段共聚物增容剂AB的链长及浓度对不相容性均聚物A/B共混体系界面性质的影响.研究结果表明,当两嵌段共聚物的体积分数φC=0.05时,随着两嵌段共聚物分子链长NC从10增至20,界面厚度剧烈减小,而当两嵌段共聚物的分子链长NC进一步增加到60时,界面厚度轻微增加;两嵌段共聚物的取向参数q随着分子链长的增长而增加,即共聚物分子在垂直界面方向的拉伸程度增大.当两嵌段共聚物AB的分子链长NC固定为10时,随着链浓度增大,界面厚度增加,共聚物分子链取向参数q减小,共聚物分子在垂直界面方向的拉伸程度减小.     

共聚物在聚合物共混体系中的增容作用I.嵌段共聚物

随着高分子合金领域的研究发展，以共聚物作为增容剂对不相容的聚合物共混体系进行改性已得到了广泛的研究和应用。本文分为两篇，分别介绍利用嵌段共聚物、接枝共聚物和无规共聚物所做的增容改性研究。本篇着重讨论嵌段共聚物(包括两嵌段和三嵌段以及多嵌段共聚物)在聚合物共混体系中的增容作用和增容机理。     

含有机硅多嵌段及其接枝共聚物的表面组成

利用ＸＰＳ对聚二甲基硅氧烷与聚砜或／和聚对羟基苯乙烯组成的二元和三元多嵌段和接枝共聚物及其共混物进行了研究。结果表明溶液成果的聚合物样品的表面都存在有机硅富集，共混物的表面富集程度等于接枝共聚物，更高于多嵌段共聚物，讨论了有机硅含量和键接结构对有机硅表面富集的影响。     

桥连对嵌段共聚物自组装的调控

通过嵌段共聚物自组装形成“桥连”是制备具有优异力学性能的网络结构的有效途经, 具有重要的应用价值. 但是, 过去的研究工作很少讨论“桥连”对嵌段共聚物自组装行为本身的影响. 该研究评论主要总结了最近几年利用“桥连”对嵌段自组装行为进行调控的工作进展. 作者设计了BABCB三组分线性多嵌段共聚物, 当其自组装形成二元“介观晶体”(球、柱)结构时, 中间B嵌段连接A和C相区(嵌段聚集成的“大原子”), 自然地形成桥连; 减小中间桥连B嵌段的相对长度, 就可以增加其拉伸程度, 从而降低介观晶体的配位数; 另外, 两个末端B嵌段的相对长度可以直接调控A和C“大原子”之间的相对配位数. 基于这两个机理, 自洽场理论计算预测了各种配位数相等和不相等的二元介观晶体结构. 进一步, 将“拉伸桥连”概念拓展到AB型嵌段共聚物体系中, 并且通过多臂星型嵌段共聚物分子结构中的“组合构型熵效应”在AB型嵌段共聚物中形成高比率的桥连构型, 使传统的六角柱状结构转变为了四配位的四方柱状和三配位的石墨烯类柱状结构. 未来, 在ABC三组分嵌段共聚物体系的设计中引入拓扑结构以及使用共混等方法, 有望在介观尺度重铸大多数已知的原子/离子二元晶体结构, 甚至超越原子/离子晶体结构.     

iPS—b—iPP共聚物对iPS／iPP共混物的性能和形态影响的研究

报道了苯乙烯－丙烯等规嵌段共聚物增溶作用及ｉＰＳ－ｂ－ｉＰＰ／ｉＰＳ／ｉＰＰ三组分共混体系微观形态和力学性能的研究结果。ｉＰＳ－ｂ－ｉＰＰ的加入明显地改善了ｉＰＳ／ｉＰＰ二组分共混物的力学性能；共聚物含量超过１５％时，三组分共混物的抗冲击强度超过ＨＩＰＳ的抗冲击强度，并具有较高的耐热性。ＳＥＭ结果表明，ｉＰＳ－ｂ－ｉＰＰ在ｉＰＳ／ｉＰＰ共混中起到了相分散和相间“偶联”作用，并降低了共混体系的微相尺     

Reactive compatibilization of nylon copolymer/EPDM blends: experimental aspects and their comparison with theory

In situ reactive compatibilization was first time applied to a low melting nylon (nylon 6 and 66 copolymer) and EPDM blend system. The effects of in situ compatibilization and concentration of compatibilizer on the morphology and mechanical properties of nylon/EPDM blends have been investigated. The influence of EPM‐g‐MA on the phase morphology was examined by the scanning electron microscopy (SEM) after preferential extraction of the minor phase. The SEM micrographs were quantitatively analyzed for domain size measurements. The compatibilizer concentrations used were 0, 1, 2.5, 5, and 10 wt%. The graft copolymer (nylon‐g‐EPM) formed at the interface showed relatively high emulsifying activity. A maximum phase size reduction was observed when 2.5 wt% of compatibilizer was added to the blend system. This was followed by a leveling‐off at higher loadings indicating interfacial saturation. The conformation of the compatibilizer at the interface was deduced based on the area occupied by the compatibilizer at the blend interface. The experimental compatibilization results were compared with theoretical predictions of Noolandi and Hong. It was concluded that the molecular state of compatibilizer at interface changes with concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties. Measurement of tensile properties shows increased elongation as well as enhanced modulus and strength up on compatibilization. At higher concentrations of compatibilizer, a leveling‐off of the tensile properties was observed. A good correlation has been observed between the mechanical properties and morphological parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Future trends of plastic bottle recycling: Compatibilization of PET and PLA

We improved the recyclability of mixed poly(ethylene-terephthalate) (PET) and poly(lactic acid) (PLA) bottle waste. We made uncompatibilized and compatibilized PET/PLA blends of different weight ratios with a twin-screw extruder. Then, we analysed the mechanical properties, the miscibility and the thermal stability of the blends with and without compatibilizers. From the change in intrinsic viscosities (IV), we concluded that different reactions occur between the polymer chains due to the compatibilizers. We observed that when ethylene-butyl acrylate-glycidyl methacrylate (E-BA-GMA) as compatibilizer was added, the blends became tougher; elongation at break and Charpy impact strength increased, but Young's modulus of the blends decreased. In addition, the compatibilizers improved the thermal stability of the blends and this may have been caused by a number of mechanisms.     

Effects of the compatibilizer PE‐g‐GMA on the mechanical,thermal and morphological properties of virgin and reprocessed LDPE/corn starch blends

The effects of the compatibilizer polyethylene grafted with glycidyl methacrylate (PE‐g‐GMA) on the properties of low‐density polyethylene (LDPE) (virgin and reprocessed)/corn starch blends were studied. LDPE (virgin and reprocessed)/corn starch blends containing 30, 40 and 50 wt% starch, with or without compatibilizer, were prepared by extrusion and characterized by the melt flow index (MFI), tensile test, dynamic mechanical analysis (DMTA) and light microscopy. The addition of starch to LDPE reduced the MFI values, the tensile strength and the elongation at break, whereas the modulus increased. The decreases in the MFI and tensile properties were most evident when 40 and 50 wt% starch were added. Blends containing 3 wt% PE‐g‐GMA had higher tensile strength values and lower MFI values than blends without compatibilizer. Light microscopy showed that increasing the starch content resulted in a continuous phase of starch. Copyright © 2005 John Wiley & Sons, Ltd.     

Novel elastomeric polyurethane fibers modified with polypropylene microfibers

Extrusion of immiscible polymer biphasic blends to form in situ microfibers of the minor component in the matrix of the major component is an elegant way to create composites with new properties. The process was used to obtain thermoplastic polyurethane elastomers modified with polypropylene microfibers. The effect of phase interaction on blend morphology and properties was studied by running a series of blends with and without a maleated polypropylene compatibilizer. Six different blends were prepared: three with compatibilizer and three without the compatibilizer. All blends contained polypropylene as a minor component (80/20; 90/10 and 95/5). Extrusion spinning of polyurethane/polypropylene blends with and without compatibilizer resulted in polyurethane fibers modified with highly-oriented polypropylene microfibrils at all component ratios. Increasing polypropylene concentration in the thermoplastic polyurethane matrix increased hardness and modulus, but did not affect tensile strength and lowered elastic recovery.     

Preparation and cryogenic mechanical properties of epoxy resins modified by poly(ethersulfone)

A thermoplastic, poly(ethersulfone) (PES) was used to modify a bisphenol‐F based epoxy resin cured with an aromatic diamine. The initial mixtures before curing, prepared by melt mixing, were homogeneous. Scanning electron microscopy (SEM) micrographs of solvent‐etched fracture surfaces of the cured blends indicated that phase separation occurred after curing. The cryogenic mechanical behaviors of the epoxy resins were studied in terms of tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding behaviors at room temperature (RT). The addition of PES generally improved the tensile strength, elongation at break, and impact strength at both RT and 77 K except the RT tensile strength at 25 phr PES content. It was interesting to observe that and the maximum values of the tensile strength, elongation at break, and impact strength occurred at 20 phr PES content where a co‐continuous phase formed. Young's modulus decreased slightly with the increase of the PES content. Moreover, the tensile strength and Young's modulus at 77 K were higher than those at RT at the same composition, whereas the elongation at break and impact strength showed the opposite results. Finally, the differential scanning calorimetry analysis showed that the glass transition temperature (T_g) was enhanced by the addition of PES. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 612–624, 2008     

Morphological,rheological, and mechanical properties of ethylene propylene diene monomer/carboxylated styrene-butadiene rubber/multiwall carbon nanotube nanocomposites

Abstract

A hybrid nanocomposite based on ethylene propylene diene monomer/carboxylated styrene-butadiene rubber (EPDM/XSBR) blend with different concentrations (0–7 phr) of multiwall carbon nanotube (MWCNT) was prepared on a two-roll mill. The role of grafted maleic anhydride (EPDM-g-MA) as compatibilizer and the effect of different concentrations of MWCNT on mechanical properties, morphology, rheological and curing characteristics of nanocomposites were investigated. The curing behavior of the prepared nanocomposites was studied using a rheometer. Also, the microstructure of nanocomposites was observed using TEM. By increasing the MWCNT concentration in the compatible blends, the curing time and scorch time of the blends decreased, while the maximum and minimum torque increased. Failure surface morphology studies showed that the existence of EPDM-g-MAH compatibilizer improved the distribution of MWCNT within the polymer matrix and uniform distribution of MWCNT with a small amount of aggregation was obtained. On the other hand, the presence of MWCNT in the matrix led to a sharper surface of the fracture. Also, mechanical properties such as modulus, tensile strength, hardness, fatigue, resilience and elongation-at-break for compatible EPDM/XSBR nanocomposite showed better results than those for incompatible composite.     

The compatibilizing effect of epoxy resin (EP) on polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr) blends

A new method was used to prepare thermoplastic elastomers based on polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr) with improved mechanical properties. An epoxy resin (EP) was used as a compatibilizing agent. The effect of EP on mechanical properties, swelling percentage and morphological characteristics of the blends was investigated with different blend compositions. The results showed that the incorporation of EP has improved the tensile strength, Young's modulus and elongation at break of PP/NBRr-EP blends compared with PP/NBRr blends. The enhancement of tensile properties of PP/NBRr-EP blends is due to the better adhesion between the two phases with the incorporation of EP. This is quite evident by scanning electron microscopy of tensile fractured surfaces. PP/NBRr-EP blend exhibits lower stabilization torque and swelling percentage than PP/NBRr blends. The lower stabilization torque is an indication of better processing characteristics.     

Properties of immiscible and ethylene-butyl acrylate-glycidyl methacrylate terpolymer compatibilized poly (lactic acid) and polypropylene blends

Poly(lactic acid) (PLA) and polypropylene (PP) blends of various proportions were prepared by melt-compounding. The miscibility, phase morphology, thermal behavior, and mechanical and rheological properties of the blends were investigated. The blends were immiscible systems with two typical morphologies, spherical droplet and co-continuous, and could be obtained at various compositions. Complex viscosity, storage modulus and loss modulus depend on the PP content. Thermal degradation of all blends led to two weight losses, for PLA and PP. The incorporation of PP improved the thermal stability of the blend. The effect of compatibilizer (ethylene-butyl acrylate-glycidyl methacrylate terpolymer, EBA-GMA) on the morphology and mechanical properties of 70/30 w/w PLA/PP blends was investigated. The tensile strength of these blends reached a maximum for 2.5 wt% EBA-GMA, and impact strength increased with increasing EBA-GMA content, suggesting that EBA-GMA is an effective compatibilizer for PLA/PP blends.     

Cold‐drawn induced microstructure in PVC‐bentonite nanocomposites

The mechanical properties and cold drawn‐induced micro and nanostructure of polyvinyl chloride (PVC)‐bentonite nanocomposites have been investigated. Molded sheets with 5 wt% concentration of bentonite and two processing additives were melt extruded and two‐roll‐milled processed. The flame retardant additive promoted polymer intercalation whereas a pigment dispersant promoted clay exfoliation, the polymer matrix showed isotropic orientation. The intercalated nanocomposite exhibited nanoplates oriented with their planes parallel to the molded sheet surface and the Young's modulus and yield stress were significantly enhanced relative to neat PVC. The strain at fracture (～144%) was slightly reduced relative to the matrix (～167%). Cold drawing induced molecular chain orientation along the tensile axis and preserved the orientation of the intercalated nanoclays. The fracture mechanism, as investigated via scanning electron microscopy (SEM) revealed plastic fracture mechanism (similar to neat PVC). On the other hand, the exfoliated nanocomposite did not show any improvement in mechanical properties but rather a significant decay of strain at fracture (～44%). The fractured region, as examined by SEM, exhibited microvoid morphology. Analysis of the fractured region showed PVC macromolecules oriented along the tensile axis but no preferred orientation of the nanoclays. The limited strain at fracture found for this material appears to be associated with the initially randomly oriented nanoclays being unable to orient under the tensile deformation. The nanoclays would act as stress concentrators leading to rapid material's failure due to loss of adhesion with the polymer matrix. The results suggest that exfoliated nanoclays could play a detrimental role when the nanocomposite is subjected to large deformations at temperatures well within the glassy regime. Copyright © 2009 John Wiley & Sons, Ltd.