橡胶增韧塑料机理

综述了橡胶增韧塑料机理研究的发展与现状,着重探讨了橡增韧机理中有关脆韧转变的定量研究,同时也讨论了分散相的形态参数、界面相容性和韧性测试条件以及分散相与基体的性能等因素对橡胶增韧塑料性能及增韧的影响,最后提出了橡胶增韧塑料研究的发展趋势。     

非弹性体增韧—聚合物增韧的新途径

本文是一篇关于非弹性增韧方法的综述。文章首先简要回顾了传统的橡胶增韧韧性聚合物材料的机理,然后着重介绍了最近在国外出现的刚性有机填料(ROF)增韧的基本概念、分析方法和增韧的冷拉机理,列举了脆性塑料粒子和韧性基体组成的合金体系的大量实验结果来说明以上内容,最后通过与传统橡胶增韧机理的对比指出非弹性体增韧是不同于后者的一种新增韧方法,并有可能成为制备高强度、高韧性工程塑料的一种新途径。     

Cavitation and cavity-free deformation of filled crystalline polymer systems

Main mechanisms of tough response of polymers are described. In heterogeneous polymer systems due to mechanical misfit between heterogeneities and the matrix a high negative pressure (tri-axial stress) is generated. The excessive negative pressure is the main reason of material cavitation. Cavitation appears to be another mechanism of tough response of the material to loading. Cavitation is a massive phenomenon in crystalline polymers and in all filled polymers. Cavitation itself does not consume much energy but allows for further toughening by activating other mechanisms. Examples of polypropylene filled with chalk modified by liquid, rubber and mineral filled polypropylene and syndiotactic polypropylene filled with chalk are described. Modes of deformation with significant compressive component of stress prevents for cavitation. Materials deformed in a cavity-free manner show much higher strength. It is pointed out that high polymer crystal anisotropy is necessary for the formation of a network of easy crystallographic slip in the unusual toughening of highly filled polymers observed recently. An example of syndiotactic polypropylene filled with submicro-chalk particles is presented.     

Ductile–brittle‐transition phenomenon in polypropylene/ethylene‐propylene‐diene rubber blends obtained by dynamic packing injection molding: A new understanding of the rubber‐toughening mechanism

For a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile–brittle (D–B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear‐induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D–B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler‐dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2086–2097, 2002     

聚合物共混物脆韧转变性能研究 Ⅳ橡胶粒子的分布对PVC/NBR共混物脆韧转变的影响

根据作者已建立的准网络形态模型和推导出的基体层厚度计算公式，从实验上研究了橡胶粒子的分布对聚氯乙烯（ＰＶＣ）／丁氰橡胶（ＮＢＲ）共混物脆韧转变的影响．结果表明，不仅无规形态ＰＶＣ／ＮＢＲ共混物存在脆韧转变主曲线，而且准网络形态ＰＶＣ／ＮＢＲ共混物也存在脆韧转变主曲线．但是两条主曲线明显不重合，表明橡胶粒子的分布对ＰＶＣ／ＮＢＲ共混物脆韧转变有显著影响．而且准网络形态ＰＶＣ／ＮＢＲ共混物的临界基体层厚度比无规形态ＰＶＣ／ＮＢＲ共混物的临界基体层厚度大得多，表明准网络形态比无规形态明显有利于增韧．因此临界基体层厚度不仅是基体的特征参数，还是界面粘结和橡胶粒子分布的函数．     

Structure-Property Relationships in Rubber-Modified Styrenic Polymers

Styrenic polymers and copolymers are often impact modified with rubber particles. The efficiency of rubber toughening depends mainly on the size of the rubber particles and the degree of cross-linking. The deformation rate, the temperature, the orientation of the polymer molecules and the efficiency of rubber grafting also influence rubber toughening. It is thought that on impact, cavitation inside the rubber particles occurs which reduces the detrimental dilatational stress in the bulk polymer without forming cracks in the brittle matrix or at the rubber-matrix interface. Crazing and shearing are facilitated if the rubber particles can easily cavitate. This can be achieved by either avoiding too much cross-linking or by adding oil (silicone oil in the case of ABS) into the rubber particles, which acts as nuclei for void formation. An electron spectroscopic imaging method is described which allows visualizing the location of the oil. Already after cooling silicone oil modified ABS samples down to liquid nitrogen temperature rubber cavitation is observed. This cavitation is caused by the thermal stress developing due to the differences in thermal expansion coefficient between the rubber phase and the SAN-matrix and is facilitated by silicone oil. Voiding also leads to an increase of light scattering, which can be detected by an optical microscope using dark field illumination.     

高抗冲聚苯乙烯的增韧机理

概述了以高抗冲聚苯乙烯（ＨＩＰＳ）为中心的有关橡胶增韧机理的理论，并且总结了界面，性能、粒子尺寸、粒 距及缠结密度等因素对橡胶／高分子共混体系性能的影响。     

高聚物拉伸形变中的声发射

对一系列高聚物进行了单轴拉伸过程中声发射的观察,包括玻璃态高聚物、结晶高聚物、共聚物、共混高聚物和一种交联橡胶。非晶态高聚物拉伸时声发射次数很少,伴随银纹和微裂缝的产生而出现。结晶高聚物在屈服成颈时出现强的声发射,在颈部拉伸的初期声发射较少或不出现,拉伸到接近试件断裂前声发射强烈,次数急剧增多。相同高聚物但试件加工成形历史不同会在声发射上得到反映。交联的顺丁橡胶拉伸时声发射很弱,但可以观察到,在拉力-形变曲线开始偏离线性后出现,没有Kaiser效应。共混高聚物拉伸时声发射很多。高耐冲击共混接枝塑料在断裂前不出现强烈的声发射。如试样和试件加工成形条件相同,声发射现象的重演性是相当好的。     

ACOUSTIC EMISSION DURING STRETCHING OF POLYMERS

Acoustic emission has been studied for a wide range of polymers including amorphous glasses, semi-crystalline polymers, copolymers, polymer blends and a crosslinked rubber during the course of uni-axial stretching at room temperature. For non-crystalline polymers acoustic emission occurred in rather small number of events accompanied by crazing and micro-crack formation. Strong acoustic activity appeared during yielding and necking of crystalline polymers. Rather small number or none of acoustic bursts occurred during the initial stage of neck drawing but numerous strong bursts appeared when drawing proceeded approaching specimen break. Specimens of the same polymer but of different fabrication history may be reflected in their acoustic emission behavior. Acoustic emission during stretching crosslinked polybutadiene rubber was very weak but observable when the force-elongation curve started to deviate from the linear region. No Kaiser effect was observed for the rubber. Very strong and numerous acoustic emission was observed during stretching specimens of polymer blends. High impact resistant polymer modifications showed no sharp increase of acoustic activity before specimen break. So long as the polymer and conditions of specimen fabrication are the same quite reproducible acoustic emission behavior could be observed.     

Toughness Enhancement of Nanostructured Amorphous and Semicrystalline Polymers

An overview is given of different micromechanical deformation processes leading to an enhancement of toughness in heterophase polymers. The well-known mechanism of rubber or particle toughening of semicrystalline polymers was studied in HDPE and PP blends. In particular, the micromechanical processes in the semicrystalline polymer strands between modifier particles were investigated in detail, revealing processes of separation, yielding, breaking and twisting of lamellae. These processes are compared with lamellae forming amorphous SBS block copolymers with alternating soft (polybutadiene) and hard (polystyrene) layers. Depending on the deformation direction, the mechanism of thin layer yielding or chevron formation appears. In both polymeric systems, the initial stage of deformation is characterized by a plastic yielding of the soft phase with a reorganization of the hard (glassy or crystalline) lamellae. The second stage is determined by the alignment of the hard phase towards the deformation direction and the plastic yielding. Detailed comparison of these similar mechanisms in very different polymers with similar nanostructured morphology should help to improve toughening of amorphous as well as semicrystalline polymers.     

A novel staining technique for studying toughening mechanisms in saturated acrylic rubber-modified polymers

A novel technique which utilizes a two-stage staining approach, (i.e., styrene absorption followed by osmium tetraoxide staining) is introduced for staining saturated polyacrylate rubbers. This novel staining approach, which stains and hardens polyacrylate rubber, is found to be useful for room temperature microtomy of polyacrylate rubber-modified polymers. Therefore, both the morphology and the crack tip toughening mechanisms of polyacrylate rubber-modified systems can be studied. Details concerning staining time, staining media, and use of solvents are discussed.     

Raman investigation of thermoplastic vulcanizates based on hydrogenated natural rubber/polypropylene blends

Raman spectroscopy including mapping technique appears as a powerful technique for the characterization of polymer blends like thermoplastic elastomers (TPEs) and thermoplastic vulcanizates (TPVs). The Raman spectra of polymers blends such as natural rubber/polypropylene (NR/PP) and 65% hydrogenated natural rubber/polypropylene (65%HNR/PP) were identified and the phase distribution was determined. The study was driven for the same type of blends in TPEs state and TPVs state obtained after to 2 different processes, either peroxide cure or sulfur cure. The morphology of TPEs and TPVs obtained by Raman spectroscopy were compared and confirmed using scanning electronic microscopy.Raman mapping shows that the phase morphology of NR/PP, 65%HNR/PP, were characterized as continuous rubber phase morphology of the thermoplastic elastomers (TPEs) and a fine dispersion of cross-linked rubber phase in a continuous matrix of the thermoplastic vulcanizates (TPVs). Raman spectroscopy is demonstrated to be a reference to determine the content ratio of each component in the TPVs. Moreover, Raman mapping could be used to calculate the phase size of cross-linked rubber phase dispersed in the thermoplastic vulcanizates (TPVs).     

Processing,properties and morphology of polypropylene-epdm blends

Blends of polypropylene and an elastomer (ethylene propylene diene terpolymer, EPDM) are systematically investigated to determine the effect of the rubber on the polymer properties. Five compositions on the complete range of blend compositions are analyzed. The study reported here is a first of a series which main objective is to analyze in a systematic way the influence of the different factors that determine the effectiveness of EPDM as an impact modifier for PP. In this first part of the study, the processing behavior of the PP-EPDM blends are analyzed and the mechanical properties of the processed blends (tensile, flexural and impact resistance) are examined. Halpin-Tsai and porosity models successfully represent the mechanical behavior of the blends. The model results allow a physical interpretation of the role of the dispersed phase in terms of the aspect ratio and of the stress concentration factors associated to the dispersed particles. Moreover, the mechanical properties are correlated with the morphology of the blends studied by scanning electron microscopy, where two phases are clearly observed in the complete range of compositions. The results show that PP-EPDM blends with at low rubber content present a good processability, without significant deterioration with respect to neat PP and with a considerable improvement of the room and low temperature performance.     

Crazing and shear deformation of polymer alloys

Crazing and/or shear yielding mechanisms in multiphase polymer alloys play a critical role in toughening. The present paper describes the use of finite element models (FEM) to simulate the crazing and shear deformation behaviour around the particles embedded in brittle or ductile matrices. The FEM simulation results on the stress distribution reveal that the dilatational stress within the rubber particles is high enough to cavitate. The stability of craze growth can be reached when the compliant particle is incorporated in a brittle matrix. On the other hand, shear yielding around the particle occurs in the equator of the particle/matrix interface when the stress locally exceeds the yield stress of the matrix. This yield-initiation stress increases with the increase in the elastic modulus and Poisson's ratio of the particles. The toughening mechanism, that cavitation occurs first followed by shear yielding to form a neck between the particles, is discussed based on the simulation results for the two-particle model.     

J-integral analysis of ductile fracture of PP/EP rubber blends

The use of J-analysis to describe the ductile behaviour of PP/EP rubber blends is investigated. Two fundamental approaches are discussed and tested at low and high strain rate as a function of temperature.The results are presented with particular emphasis on the sensitivity of the parameters obtained by J-analysis to rubber content and particle size.     

Mechanical and fracture behavior of polypropylene/poly(ethylene-co-vinyl alcohol) blends compatibilized with ionomer Na

In this work the deformation and fracture behavior of PP/EVOH blends compatibilized with ionomer Na⁺ at room and low temperature was studied. Uniaxial tensile tests on dumb-bell samples and fracture tests on single-edge notched bending (SENB) specimens were performed for 10 wt.% and 20 wt.% EVOH blends with different ionomer content at 23 °C and −20 °C. The incorporation of EVOH to PP led to less ductile materials in tension as judged by the lower values of the ultimate tensile strain displayed by all PP/EVOH blends in comparison to neat PP. In contrast, the ionomer Na⁺ addition partially counteracted this effect. The compatibilizing effect of ionomer Na⁺ was also evident in fracture results since higher values of the fracture parameter were obtained for the ternary blends. SEM observations also confirmed this effect. On the other hand, PP/EVOH blends exhibited different fracture behavior with test temperature. All blends showed “pseudo stable” behavior at room temperature characterized by apparently stable crack growth that could not be externally controlled. On the contrary, blends behaved as semi-brittle at −20 °C with some amount of stable crack growth preceding unstable brittle fracture. Finally, irrespectively of the temperature or the ionomer content all PP/EVOH blends exhibited more ductile fracture behavior with a higher tendency to stable crack propagation than neat polypropylene.     

Fracture mechanisms in rigid core-shell particle modified high performance epoxies

The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT _g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed.     

高聚物声发射的一些观察

对高聚物的声发射做了进一步的实验观察。玻璃态高聚物在拉伸屈服以前的声发射有Kaiser效应,但在高弹态则不然。非晶态高聚物从玻璃态到高弹态的转变,玻璃态拉伸时在屈服附近出现声发射,高弹态时声发射要少而弱得多,只在高弹拉伸的断裂前出现声发射。非晶态、晶态高聚物或共混高聚物在突然升温到100℃时有声发射,但在突然降温到-60℃时却不出现声发射,这可能也说明声发射与高聚物试样内形成空洞有关。一种聚丙烯树脂在不同注射成形工艺条件下所得试件,在拉伸时的声发射行为可反映加工成形的好坏,成形好的声发射少得多。     

Structure and properties of blends of isotactic polypropylene with ethylene-propylene oil

The structure of blends of isotactic polypropylene with ethylene-propylene oil was studied by light and atomic force microscopy, X-ray diffraction, and DSC. It was shown that the blends are heterogeneous systems which contain semicrystalline PP and oil crystallizing at low temperatures. An increase in the oil content leads to a change in the spherulite size; a decrease in the lamella size; and, accordingly, to a drop in the melting temperature of PP. The PP-oil blends are thermodynamically compatible in melt. The mechanism of PP deformation gradually varies from the ductile to the quasi-brittle mode with a significant deterioration of mechanical characteristics of the material with an increase in the oil content. The experimental results are described satisfactorily by a model of deformation of the polymer matrix alone.     

Viscoelastic behavior of polypropylene/nitrile rubber thermoplastic elastomer blends: Application of Kerner's models for reactively compatibilized and dynamically vulcanized systems

The viscoelastic properties of binary blends of nitrile rubber (NBR) and isotactic polypropylene (PP) of different compositions have been calculated with mean‐field theories developed by Kerner. The phase morphology and geometry have been assumed, and experimental data for the component polymers over a wide temperature range have been used. Hashin's elastic–viscoelastic analogy principle is used in applying Kerner's theory of elastic systems for viscoelastic materials, namely, polymer blends. The two theoretical models used are the discrete particle model (which assumes one component as dispersed inclusions in the matrix of the other) and the polyaggregate model (in which no matrix phase but a cocontinuous structure of the two is postulated). A solution method for the coupled equations of the polyaggregate model, considering Poisson's ratio as a complex parameter, is deduced. The viscoelastic properties are determined in terms of the small‐strain dynamic storage modulus and loss tangent with a Rheovibron DDV viscoelastometer for the blends and the component polymers. Theoretical calculations are compared with the experimental small‐strain dynamic mechanical properties of the blends and their morphological characterizations. Predictions are also compared with the experimental mechanical properties of compatibilized and dynamically cured 70/30 PP/NBR blends. The results computed with the discrete particle model with PP as the matrix compare well with the experimental results for 30/70, 70/30, and 50/50 PP/NBR blends. For 70/30 and 50/50 blends, these predictions are supported by scanning electron microscopy (SEM) investigations. However, for 30/70 blends, the predictions are not in agreement with SEM results, which reveal a cocontinuous blend of the two. Predictions of the discrete particle model are poor with NBR as the matrix for all three volume fractions. A closer agreement of the predicted results for a 70/30 PP/NBR blend and the properties of a 1% maleic anhydride modified PP or 3% phenolic‐modified PP compatibilized 70/30 PP/NBR blend in the lower temperature zone has been observed. This may be explained by improved interfacial adhesion and stable phase morphology. A mixed‐cure dynamically vulcanized system gave a better agreement with the predictions with PP as the matrix than the peroxide, sulfur, and unvulcanized systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1417–1432, 2004