PEB-g-MAN增韧SAN树脂的力学性能及增韧机理的研究

用悬浮接枝共聚合法合成了乙烯/1-丁烯共聚物（PEB）与甲基丙烯酸甲酯(MMA)/丙烯腈(AN)的接枝共聚物（PEB-g-MAN）,并用其增韧苯乙烯/丙烯腈共聚物（SAN）。研究了SAN/PEB-g-MAN共混物的力学性能、增韧机理和相结构。结果表明：PEB-g-MAN是SAN树脂的优良增韧剂,当PEB用量为25 %时,SAN/PEB-g-MAN的缺口冲击强度达63.3 kJ/m2,约为SAN树脂的60倍。SAN/PEB-g-MAN共混物在PEB含量为15 %-20 %时发生脆韧转变。脆韧转变前、脆韧转变过程中和脆韧转变后的冲击断面形态的SEM分析表明,共混物的增韧机理先是裂纹支化终止和空穴化,随后为高度空穴化,再为基体剪切屈服兼空穴化,最后转变为空穴化为主,剪切屈服为辅。TEM分析表明,PEB均匀分散于SAN连续相中,两相界面模糊,具有良好的相容性,且随着PEB含量的增加,共混物的相结构由"海-岛"结构转变为"双连续相"结构。     

细观结构参量对共混物银纹化倾向影响的数值模拟

银纹化、剪切屈服、空穴化是现今被广为接受的橡胶增韧塑料共混体系韧性得以增加的主要原因。进行了分散相颗粒形状较规则的单相连续两相共混物细观结构参量对共混物银纹的产生和发展影响的研究。借助有限元方法系统模拟了共混体系橡胶粒子的分布形式、添加比例、粒子尺寸、两相间界面层性能、粒子形状等细观结构参量的改变对共混物银纹化的影响规律。其规律可以加深对银纹化这一重要的共混物增韧机理的了解,并对改善共混物的细观结构形式,以期设计出有较好增韧效果的高聚物材料有一定指导意义。     

影响ABS树脂韧性的因素

通过收集相关资料,整理影响ABS树脂韧性的因素,讨论了接枝聚合物的接枝结构、基体SAN树脂结构、温度、共混条件等因素对ABS冲击强度的影响。接枝后的聚丁二烯橡胶增韧效果明显,不同粒径的橡胶粒子的最佳接枝层厚度相同,接枝层SAN与基体SAN树脂的组成相似时增韧效果好。基体SAN树脂的分子量或丙烯腈含量增加有利于ABS树脂的冲击强度。低温条件下ABS增韧机理以银纹机理为主。双螺杆挤出机拥有良好的剪切作用,能够将橡胶相分散更均匀,有利于冲击强度的提高。     

塑料/橡胶共混物的相结构与增韧作用(续)

塑料及其增韧材料在三维张应力作用下，基体可通过裂缝扩展、裂纹支化、多重银纹化、空穴化、剪切屈服等发生断裂。在聚合物断裂行为研究领域，裂缝、裂纹、银纹、空穴和剪切屈服都有其特定意义。裂缝是指材料断裂形成的两个表面之间的宏观缝隙，其特征是尖端应力高度集中，扩展速率极快，形成的断裂表面为光亮的镜面。银纹由纳米级空穴和纳米级聚合物微纤相间排列构成，即银纹是有许多微纤连接两表面的微裂纹。图13是裂缝及裂纹示意图。     

PS系列树脂的增韧机理及性能影响因素

综述了橡胶增韧PS系列树脂的原理及相关的增韧理论:微裂纹理论、多重银纹理论、剪切屈服理论、剪切带-银纹理论、空穴化理论和逾渗理论,阐述了各个理论的基本观点,分析了不同增韧理论的优缺点。详尽概述了橡胶增韧高抗冲聚苯乙烯(HIPS)和丙烯腈-丁二烯-苯乙烯共聚物(ABS)性能影响因素:增韧体系、增韧橡胶的种类及结构、增韧橡胶用量、橡胶粒径、橡胶离子接枝度,并重点介绍了采用低顺式聚丁二烯橡胶(LCBR)和线性丁苯嵌段共聚物(LBS)增韧体系的优点。此外,还简要介绍了聚苯乙烯(PS)系列树脂专用增韧橡胶LCBR和LBS的特征和性能。通过对PS系列树脂增韧改性的深入研究,为扩大其应用领域和生产发展提供理论基础。     

温度对微孔发泡PP材料冲击性能的影响

研究了温度对微孔发泡PP材料冲击性能的影响。研究表明：发泡PP在高温及低温下均具有比未发泡PP高的冲击强度，其主要的增韧机理为：一是裂纹扩展时微孔周围的树脂变形消耗能量，二是微孔的存在松弛了裂纹尖端应力集中，并会诱使主裂纹分解成次生裂纹，使裂纹扩展的方向和方式都发生变化，表现为裂纹扩展的阻力。研究表明：高温和常温下两种机理都发挥作用，而低温下发泡PP韧性提高主要是第二种机理的作用。     

聚丙烯的冲击改性

本文比较了乙烯-辛烯（EO）共聚物和乙烯-丙烯-二烯三元共聚物（EPDM）橡胶提供的改性机理。在研究范围内，最高冲击强度在30％-40％橡胶含量间得到，与橡胶种类没有关系。橡胶熔体粘度的增加导致较高的整体冲击强度。在最佳配合量时，高粘性（MFI=1—5）EO橡胶主要通过银纹机理提供改性，而EPDM橡胶则通过和聚丙烯母体形成三维网络结构以能量耗散起作用。本文还讨论了加工条件对PP／EPR共聚物物理性能的影响。加工温度和螺杆速度的增加会导致离散橡胶粒子数目的减少，冲击强度几乎没有或有很小的增加，但拉伸强度和拉伸模量却有很大的减小。     

ABS的组成与性能研究进展(Ⅰ)

综述了苯乙烯-丙烯腈共聚物(SAN)和丙烯腈-丁二烯-苯乙烯共聚物(ABS)组成与性能的研究.不同丙烯腈含量SAN间的相容性与丙烯腈含量差值有关.SAN相对分子质量越低,保持相容性的丙烯腈含量差值可以越大.丙烯腈含量影响SAN的韧性.橡胶增韧时, SAN基体树脂中的丙烯腈含量高于SAN接枝物为佳,接枝率或界面黏结力适度为宜.橡胶相玻璃化转变温度的变化反映了SAN接枝橡胶和SAN基体树脂的相互作用.大粒径胶粒(大于1 μm)与小粒径胶粒(小于0.5 μm)组合增韧SAN产生协同效应.大粒径胶粒诱发银纹,小粒径胶粒终止银纹或改变银纹增长途径.     

EVA-g-MAH增韧阻燃ABS的研究

在ABS中加入乙烯/醋酸乙烯共聚物接枝马来酸酐(EVA-g-MAH)进行增韧改性,探讨了以银纹化增韧的弹性体的增韧机理以及EVA-g-MAH与ABS分散均匀性等问题。结果表明,添加10份EVA-g-MAH增韧的阻燃ABS冲击强度增幅达35%,热塑性弹性体增韧阻燃ABS主要以银纹化增韧机理进行增韧,但随着EVA-g-MAH用量的增加,其机械强度损失也越来越大。     

两种不同橡胶粒径的ABS树脂协同作用研究

采用两种不同橡胶粒径的丙烯腈-丁二烯-苯乙烯共聚物(ABS)掺混制备橡胶粒子尺寸双峰分布的ABS树脂。恒定ABS树脂的橡胶含量,通过调节不同粒径橡胶的质量比,考察其对ABS树脂力学性能的影响,并利用扫描电子显微镜和透射电子显微镜观察了ABS树脂的微观结构,分析了协同作用的增韧机理。结果表明,ABS树脂的冲击强度和屈服强度都随着大粒径橡胶粒子比例的减少而增大;当L-PB/S-PB为1/9时,ABS树脂的冲击强度和屈服强度最高,两种橡胶粒子发生了明显的协同作用。     

高分子材料断裂力学评价方法研究进展

简要介绍了线弹性断裂力学、弹塑性断裂力学和基本断裂功这3种方法的理论背景和前提假设、材料参数的试验测试方法和计算过程、试样预制裂纹对测试结果的影响以及近些年在高分子材料上的应用研究进展，并对3种研究方法的应用范围和特点，具体实用效果进行了对比分析。     

Double cantilever beam fracture toughness measurement method for glass

A simple method of measuring Mode I fracture toughness, K_IC, of glass using the double cantilever beam (DCB) geometry is presented. An inert atmosphere is created at the crack tip to prevent subcritical crack growth and enable “pinning” the crack while the specimen is loaded to failure. This was achieved experimentally using liquid toluene or a glovebox with dry argon. K_IC values measured by this method showed good agreement with published literature values for selected glasses. Applicability of the analytical stress intensity factor solution based on crack length, crack front curvature, and the height of the crack guiding groove are confirmed through experimental data and finite element analysis. The experimentally observed crack front curvature, which leads near the edges for small groove heights and leads in the center for larger groove heights, is predicted from the geometry of the DCB specimen for a linear elastic solid through finite element modeling.     

Mechanical evaluation of propylene polymers under static and dynamic loading conditions

The present investigation is concerned with the evaluation of the impact toughness of commercial‐grade Propylene polymers. Conventional impact static stress–strain and static fracture experiments were carried out. Static stress–strain experiments revealed different pattern behaviors among the materials that were reflected in the fracture behavior. Under static conditions, all materials exhibited ductile behavior and crack grew under J‐controlled conditions displaying stress whitening through the whole fracture surface with the sole exception of the homopolymer, which displayed a ductile instability after some stable crack growth. Under dynamic conditions the homopolymer exhibited brittle behavior, the block copolymer exhibited some plastic deformation at the crack tip, and the random copolymer samples exhibited a whitening effect due to voiding and craze formation through the whole fracture surface, indicating that stable crack propagation was occurring. Fracture mechanics tests were analyzed by following different methods, depending on the mode of fracture presented by the polymer. The Normalization J‐method was used under static conditions. The elastic method, the corrected elastic method, and the essential work of fracture methodology were used to characterize brittle, semibrittle, and ductile behavior, respectively. Fracture mechanics parameters arisen from both static and dynamic conditions are compared. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2681–2693, 1999     

PP/POE/硅灰石复合材料性能的研究

用基本断裂功(EWF)方法研究聚丙烯(PP)/聚烯烃弹性体(POE)/硅灰石复合材料的断裂行为,研究不同硅灰石含量对复合材料断裂行为的影响,并把宏观断裂参数的变化与复合材料的微观结构联系起来,从物质结构上寻求断裂参数变化的原因.结果表明,当PP/POE/硅灰石质量比为62/8/30时,PP/POE/硅灰石复合材料的比基本断裂功为83 kJ/m2,PP/POE/硅灰石复合材料的断裂韧性主要取决于复合材料屈服后抵抗裂纹扩展的能力,PP/POE/硅灰石复合材料的塑性变形能力更依赖于屈服前的行为.相同大小的硅灰石制得的PP/POE/硅灰石复合材料的缺口冲击强度随着硅灰石含量的增加而降低.缺口冲击强度高的复合材料,比基本断裂功却较小,耐长期破裂性也较差,说明基本断裂功比缺口冲击强度更能揭示复合材料长期破坏行为的特征.     

Combined electromechanical dynamic fracture behavior of lead zirconate titanate (PZT)

Coupon specimens of poled and depoled lead zirconate titanate (PZT) are examined under combined stress wave and electric loading conditions. Mode-I crack initiation and fracture behavior is examined using ultrahigh-speed imaging and two-dimensional digital image correlation. The dynamic critical stress intensity factor () is extracted using measured displacement fields ahead of the impulsively loaded crack tip, and compared between poled and depoled plates that were either under no electric field, positive 0.46 kV/mm electric field, or negative 0.46 kV/mm electric field. Poled specimens had a poling direction and applied electric field direction normal to the crack front. The addition of an electric field resulted in a crack-enhancing effect, where the dynamic fracture toughness of poled specimens under 0.46 kV/mm was almost half that of samples with no electric field. Depoled samples experienced almost no change in dynamic fracture toughness with the addition of an electric field.     

Fracture energy release rate in nylon fibers

The effect of relative humidity on the fracture energy release rate, G_Ic, for single nylon 6,6 fibers has been determined previously. In this article, it is shown that G_Ic is independent of relative humidity for moisture contents of > 2.3% once the plastic zone correction is made. G_Ic is compared with various proposed mechanisms to account for fracture energy. It is shown that the energy required to disrupt or “melt” the crystals in the plastic zone accounts for the majority of the energy required to break the specimen, and should be considered explicitly in future analyses of fracture in semicrystalline polymers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1541–1544, 1998     

油气储层裂缝描述综述

随着勘探程度的提高,裂缝型油气藏在新增储量中将会占有更大的比重,储层裂缝的研究日益受到重视。在大量文献调研的基础上,研究了国内外关于储层裂缝描述研究的现状以及存在的问题,分析论述了相似露头区描述、岩心镜下观测、人工压裂实验等目前储层裂缝描述的主要技术方法,简要总结了储层裂缝的特征分类、成因以及对后期开发注水的影响。     

裂缝性储层水力裂缝扩展规律数值模拟研究

天然裂缝与水力裂缝的相互作用形成复杂裂缝的关键,采用耦合孔隙水压力的内聚力单元,模拟了天然裂缝存在下水力裂缝的扩展情况,探讨了逼近角及天然裂缝起裂应力对水力裂缝扩展及天然裂缝开启范围的影响。为保证缝内压力的连续性,在预置天然裂缝与水力裂缝的相交处耦合孔隙压力,裂缝位置采用变密度进行网格划分以提高收敛性。数值分析结果表明:水力裂缝的诱导应力场使得天然裂缝提前开启,天然裂缝的破坏形式以剪切破坏为主导;水平主应力差一定时,逼近角越小天然裂缝越易开启且开启长度越长;天然裂缝起裂应力增加,水力裂缝最大缝宽增加天然裂缝开启范围缩小。     

地层裂缝的研究

本文以偶极子声波测井理论为依据,根据物理模型相似性原理,用水泥、细砂和水为主要材料制作了无裂缝、水平裂缝和竖直裂缝三种模拟井。使用一发双收,6cm,8cm,10cm,12cm四种源距的偶极子声系分别在三种模拟井中进行实验并得出结论。     

Relationships between microstructure,fracture–surface morphology,and mechanical properties in ethylene and propylene polymers and copolymers

The fracturing of four different polyolefin materials (a polypropylene homopolymer, a propylene–ethylene copolymer, a polyethylene homopolymer, and an ethylene–hexene copolymer) was studied with the objective of developing a better understanding of the relationships between the morphology of semicrystalline polymers, the morphology and growth kinetics of their fracture surfaces, and their mechanical properties. A scanning electron microscope and an optical microscope were used to obtain images of the fracture surfaces. The samples were injection‐molded or hot‐pressed to generate different microstructures. Fracture experiments were performed at 23, 0, and −20°C to generate fracture surfaces with different morphologies from the same supermolecular structure. It appears that the fracture propagates through the spherulites in a brittle manner. The macroscopic aspect of the fracture surfaces is temperature‐independent and changes are visible only at the microscopic scale. Over the range of temperatures studied, the rms roughness [root mean square roughness decreased by only about 20%, while the fracture energy of all but one of the materials (a high‐density ethylene–hexene copolymer) decreased by about 60% as the temperature was reduced. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2370–2382, 2000