On the Description of the Phenomenon of Filled Elastomer Strengthening

Relations invariantly relating the matrix deformation to the composite deformation have been derived. A model that permits obtaining a Mullins effect and explains the multiple increase in the strength characteristics of the composite compared to the matrix is proposed. At the basis of the model is the presence at the matrix–filler boundary of a hard rubber layer. This layer is formed due to the interaction between the active surface of the filler and the rubber macromolecules. The quantitative form of the tension distribution function density of active chains of the mesh explaining the strengthening phenomenon has been substantiated.     

纳米石墨/天然橡胶复合材料的应力软化与动态性能

以不同尺寸的纳米石墨为原料,制备了纳米石墨/天然橡胶(NR)复合材料.研究不同尺寸(30、80、150 nm)的纳米石墨对复合材料的应力软化效应(Mullins效应)、Payne效应、动态生热和损耗因子的影响.结果表明:随着纳米石墨尺寸的增大,纳米填料对纳米石墨/NR复合材料体系的补强作用明显,应力软化效应增大、动态损耗因子增加,但Payne效应降低;纳米石墨/NR复合材料动态损耗因子越大,其动态生热越高;动态生热还与填料粒子网络形成紧密相关.SEM观察及Payne效应分析结果表明:采用不同尺寸的纳米石墨材料填充天然橡胶,大尺寸石墨在橡胶基体中易于分散均匀,片层的聚集程度小,而小尺寸纳米片层表现出较明显的团聚.     

不同维数填料对橡胶Payne效应的影响

在变外力作用下,填充橡胶的动态模量会随着应变的增加而急剧下降的现象称为Payne效应。研究填充橡胶的Payne效应可以保证橡胶制品在使用过程中的安全性和可靠性,同时获得具有良好力学性能的橡胶制品。文中通过胶乳-双辊连用法制备了炭黑/天然橡胶复合材料(RCB)、碳纳米管/天然橡胶复合材料(RCNT)和石墨烯/天然橡胶复合材料(RGE)。扫描电镜和透射电镜图像显示,该方法可以将填料均匀分散在橡胶基体中。Mooney-Rivlin曲线和动态力学性能测试显示RGE复合材料的Payne效应最强,RCB复合材料的Payne效应最弱。     

Control of the structure and properties of barium sulphate-filled blends of polypropylene and ethylene propylene copolymers

The structure and properties of polypropylene (PP) and ethylene propylene copolymer (EPR) blends filled with BaSO₄ have been investigated. The aspect of structure control concerned was the separate dispersion of filler and rubber in the PP matrix or encapsulation of the filler in the rubber phase. The former structure prevails in the PP/EPR/BaSO₄ systems, and addition of maleic anhydride-grafted polypropylene (MAPP) enhances the adhesion between the PP matrix and the filler. Encapsulation of the filler particles into the elastomer takes place when maleated EPR-rubber (EPMA) is used, and the encapsulated structure prevails even under the severe shearing conditions of injection molding. The improved matrix/filler adhesion resulted in increased yield stress and tensile strength, but decreased impact resistance. The particle size of the filler proved to be a crucial factor; below a certain particle size aggregation becomes a dominating factor. Extensive aggregation leads to the deterioration of all mechanical properties, especially to decreased impact strength.     

Synthesis, structure and properties of a novel hybrid bimodal network elastomer with inorganic cross-links: The case of silicone–nanocrystalline titania

We describe an innovative concept of synthesizing a novel hybrid bimodal network elastomer with high strength–high ductility combination involving utilization of functionalized nanocrystalline titania as short-chain cross-links between neighboring elastomer chains. This subject is germane both fundamentally and from an application viewpoint. Silicone rubber is selected as the model elastomer. The short-chain cross-links are acrylic acid functionalized nanocrystalline titania that are an integral component of bimodal network structure of the elastomer. To delineate and separate the effects of functionalization from nanoparticle effects, a relative comparison is made between silicone rubber–titania nanocomposite (i.e. containing dispersion of titania as a reinforcement filler) and silicone rubber–titania hybrid network elastomer (i.e. titania as short chain cross-links). An important finding is that the effect of functionalized titania present as short chain cross-links is far more significant than non-functionalized titania present as reinforcement filler, on mechanical behavior. This is presently ascribed to the double bonds introduced to nanocrystalline titania via functionalization with acrylic acid that provide active sites for the cross-linking reaction resulting in inorganic bridging chains. The basic physical mechanisms that govern elastic recovery in hybrid bimodal network elastomer with short chain cross-links of functionalized nanocrystalline inorganic particles are discussed. The hypothesis of the study described here is that the hybrid bimodal network elastomer with short chain cross-links of functionalized nanocrystalline inorganic particles modifies the unimodal long chain network elastomer with consequent increase in modulus and high strength–ductility combination.     

The effect of dispersed paint particles on the mechanical properties of rubber toughened polypropylene composites

The influence of dispersed paint particles on the mechanical properties of rubber toughened PP was investigated. The matrix was basically a hybrid of PP, rubber and talc. Model systems with spherical glass bead filled matrix were also studied to examine the effect of filler shape and size. Properties like tensile strength, strain at break, impact strength, and fracture toughness were influenced by the dispersed inclusions. Tensile strength at yield decreased linearly according to Piggott and Leinder's equation. Strain at break decreased more drastically with paint particles than glass beads, revealing that irregularly shaped particles offered greater stress concentrations. The tensile strength and strain at break were less influenced by the size of paint particles whereas a slight decrease in the modulus values was observed with decreasing particle size. Impact strength and fracture toughness also decreased with increasing filler fraction. Lack of stress transfer between filler and matrix aided in reduction of impact strength. Decrease in fracture toughness was influenced by volume replacement and constraints posed by fillers. The size of paint particles had little effect on the impact strength and fracture properties at the filler concentration levels used in this investigation.     

Micromechanical analysis of an elastomer filled with particles organized in chain-like structure

Organization of iron filler particles inside an elastomer is obtained by curing the polymer in presence of a magnetic field. We have studied the effect of structuring the particles in chains on the quasistatic behavior in elongation in the absence of magnetic field. The effect of a coupling molecule between the surface of the particles and the elastomer is also analyzed. It is shown that the modulus of the first loading curve is strongly increased by structuring the particles, and also by the use of a coupling agent. Using an effective medium approach we well reproduce the experimental behavior of the elastic modulus and we deduce that a thick layer of elastomer is still present between the particles. A finite element calculation allows to distinguish between two modes of rupture at high strains, depending on the strength of the coupling between the particles and the matrix.     

橡胶相尺度对亚微米或纳米橡胶颗粒填充环氧复合材料性能的影响

对比研究了由液体橡胶在环氧树脂中原位形成的亚微米橡胶/环氧复合材料和在环氧树脂中直接添加纳米橡胶颗粒形成的纳米橡胶/环氧复合材料的性能。研究表明：未固化混合物的黏度随着纳米橡胶相的加入逐渐增加,但随着亚微米橡胶相含量的增加而降低;橡胶/环氧复合材料的玻璃化转变温度随着纳米橡胶颗粒的加入逐渐增加,但随着亚微米橡胶相含量的增加而降低;两种橡胶相的添加均使复合材料的弹性模量降低,断裂延伸率增加;在较低含量时,纳米橡胶颗粒可以提高环氧的拉伸强度;两种橡胶填充的橡胶/环氧复合材料均显示出明显的增韧效果。微观形貌分析表明,两种橡胶均可以在应力作用下脱粘并促进裂纹尖端的塑性变形。     

Mechanical behavior of the alumina-filled silicone rubber under pure shear at finite strain

The mechanical behavior of filler-reinforced rubber was investigated under pure shear at large deformation. Nanocomposites were composed of silicone rubber with different volume fractions of aluminum oxide nanoparticles, ranging from 0% to 5.0%. Thin sheet specimens were manufactured and submitted to monotonic tensile loading. The Digital Image Correlation method was employed to obtain displacement fields and consequently the stress–stretch responses were achieved. The experimentally measured stress–stretch curves were fitted to Yeoh and Lopez-Pamies models in order to estimate material parameters of the neat silicone rubber. Using this information, Mullins–Tobin and Bergstrom–Boyce approaches were employed to evaluate the strain amplification factor of the nanocomposites with different volume fractions of nanoparticles. The results indicate that a significant increase in the stiffness of filled rubber is obtained by small concentrations of nanoparticles. The effect of nanoparticles on mechanical behavior of reinforced rubber can be described using Yeoh and Lopez-Pamies models with Mullins–Tobin and Bergstrom–Boyce approaches. However, the strain amplification factor expression proposed by Bergstrom–Boyce was not suitable to describe the obtained results. In the case, the Guth model was more indicated.     

Composites of Poly(Acrylate) Copolymer filled with diatomaceous earth: morphology and mechanical behaviour

Failure mechanisms of poly(acrylate) (PA) copolymer system filled with a diatom filler have been studied. The natural diatom filler is characterised by the original skeletal structure which allows high "inner" porosity and thus matrix penetration inside the filler particles and agglomerates of various shapes in PA composite. High diatom filler crystallinity influences the matrix re-structurization by changing the intensity ratio of matrix amorphous halos indicating the increased composite film inhomogeneity. Interactions at the interface between diatom filler and PA copolymer matrix, specially for coarse cylindrical-shaped particles are low, showing low adhesion in the composite. We see composite weakening with the increased filler volume fraction, i.e. lowering the composite strength at break as a consequence of lower degree of interactions. On the other hand, the composite modulus and the yield strength increased as a result of matrix hardening due to the pronounced matrix penetration inside the porous diatom filler. The mechanisms of failure depend on the location with the lowest product of composite module and break energy. Because dewetting occurred, it is the product EG in the interfacial region between PA matrix and diatom filler particles that was relevant. The effects of filler characteristics, may be followed through an interaction coefficients calculated from a model equations. The numerical values of coefficients in the model are only comparative, but the relative values can be connected with changes at the interface. Electronic Publication     

Effect of morphology on the behaviour of ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO₃ or Mg(OH)₂) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (_y) for the two limiting morphologies over an interval of elastomer volume fractions (V _e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.     

不同改性白炭黑填充天然橡胶的流变性能EI北大核心CSCD

通过橡胶加工分析仪和毛细管流变仪分别研究了添加偶联剂KH560、Si69、NXT和不加偶联剂的白炭黑填充天然橡胶的填料网络结构,考察了不同偶联剂对白炭黑填充NR的流变形为的影响。结果表明,3种偶联剂均改善了白炭黑的表面特性,使白炭黑填料网络化程度减轻,储能模量和损耗模量变小,Payne效应大大减弱,改善了加工性能。其中偶联剂NXT的改性综合效果最佳。     

Effect of elastomer interfacial agents on tensile and impact properties of CaCO3 filled HDPE

This work focuses on the modification of the tensile yield strength of CaCO3 filled HDPE brought about by the incorporation of SEBS elastomers. Two types of SEBS elastomers were used, grafted and ungrafted with maleic anhydride functions. The grafted elastomer encapsulates the filler particles in-situ and creates an adhesive interphase. The tensile yield stress was increased with increasing content of grafted elastomer until a maximum value. The influence of the interfacial area and the volume fraction of filler were studied. It was shown that the relative increase in tensile yield stress when increasing amount of interfacial agent was added, both depends on the volume of filler and the interfacial area.     

微悬浮法CaCO3表面接枝PMMA及其在PVC中的应用

在水介质中,超声作用下用油酸对纳米碳酸钙进行表面修饰,再以微悬浮原位聚合法用PMM A进行接枝包覆,成功制备了PMM A/C aCO3复合粒子。借助透射电镜(TEM)、红外光谱(FT-IR)、热失重(TG)等分析手段对复合粒子的形态结构进行了表征。实验结果表明,油酸可通过羧酸盐的形式吸附于碳酸钙粒子表面,一定量PMM A通过油酸分子的不饱和双键接枝于碳酸钙粒子表面。将所得PMM A/C aCO3复合粒子与PVC共混制得PVC/PMM A/C aCO3复合材料。复合材料的TEM照片表明,C aCO3粒子非常均匀地分散在PVC基体中,两相界面模糊。随着PMM A/C aCO3纳米复合粒子用量的增加,复合材料的强度和韧性同时提高。当复合粒子用量高于12%时,复合材料的冲击强度可提高3倍,而拉伸强度下降很少。     

Model filled rubber Part V Mechanical properties of rubbery composites

Monodisperse size crosslinked polymeric particles of specific chemical compositions, synthesized by emulsifier-free emulsion polymerization, were used as model fillers to study the effect of filler chemical composition on stress-strain behavior of rubbery composites. The modulus, E or G of filled composites increased while the stress and the strain at break decreased with increasing filler-matrix interactions. Physical crosslinking, either due to particle clustering or a network of filler particles with an adsorbed polymer layer supplemented chemical crosslinking. As a result, the overall crosslink density(chemical and physical) was effectively enhanced. The strength of the physical networks, and hence the stiffness of the composites increases with increasing particle-matrix interactions. However, excessively strong matrix-filler interaction would cause a loss of polymer flexibility at the particle-matrix interface, resulting in a decreased stress and elongation at break of the particle filled composites in the order PS > PMMA > PSVP.     

A micromechanics-based incremental damage model for carbon black filled rubbers

This paper is to develop a simple micromechanics-based model taking account of progressive damaging for carbon black (CB) filled rubbers. The present model constitutes of the instantaneous Young's modulus and Poisson's ratio characterizing rubber-like material, a double-inclusion (DI) configuration considering the absorption of rubber chains onto CB particles, and the incremental Mori-Tanaka formula to compute the effective stress–strain relations. The progressive damage in filled rubbers is described by the DI cracking, which is represented by the remaining load–carrying capacity. The present predictions are capable of embodying the well-known S-shaped response of filled rubbers, and also verified by the comparison with the experimental and analytical results. Moreover, strain localization effect is clearly demonstrated by finite element method (FEM) simulations, and reaches a decisive interpretation to the complicated synergic micro-mechanisms between hard fillers and soft phase in such flexible composites.     

Morphology/behaviour relationship of nanocomposites based on natural rubber/epoxidized natural rubber blends

In order to analyze the effect of an epoxidized natural rubber (ENR) and filler treatment on the morphology and behavior of natural rubber (NR) nanocomposites, blends of these polymers have been prepared. The nature and extent of the clay dispersions in the filled samples were evaluated by X-ray diffraction. In the presence of ENR, an exfoliated structure was obtained which suggests that enough rubbery polymer was incorporated into the interlayer spacing. The effect of clay in rubber compounds was analyzed through rheological, mechanical and swelling characterization. A sensible improvement in the nanocomposite properties was observed by the addition of organoclay. It has been deduced that the properties of the compounds strongly depend on the extent of the silicate nanolayers dispersion into the rubber matrices as well as on the organoclay type and elastomer compatibility.     

全氟辛基季胺碘化物改性碳纳米管对天然橡胶胶乳性能的影响

用水溶性的阳离子表面活性剂全氟辛基季胺碘化物FC-134对碳纳米管进行非共价键改性,并用液相法制备改性碳纳米管/天然橡胶复合材料,研究了改性碳纳米管对天然橡胶复合材料的影响。结果表明,改性碳纳米管在水介质中具有很好的稳定性。佩恩效应表明,碳纳米管经过表面修饰增强了与橡胶的相互作用,降低了碳纳米管之间的相互作用。橡胶加工分析仪的结果表明,碳纳米管均匀地分散到复合材料中。与未改性碳纳米管/天然橡胶胶乳复合材料相比,改性碳纳米管/天然橡胶胶乳复合材料硫化胶的撕裂强度提高了65%,拉伸强度提高了29%。     

基于链化分析的磁流变弹性体剪切模量模型

磁流变弹性体是一种磁流变材料,由高分子橡胶基体掺杂微米级的铁磁性颗粒固化而成.基于磁性物理学理论,从磁流变弹性体在磁场作用下铁磁性固体颗粒极化成链的微观结构出发,探讨磁流变流体中固体颗粒间的相互作用机理,分析研究颗粒间的相互作用力,建立了一种微观力学模型,可用于分析磁流变流体在外加磁场作用下剪切模量及其影响因素的作用效果,揭示磁流变效应的微结构机理,为磁流变弹性体的性能优化、工程开发及应用提供理论依据.