Tensile and impact behavior of drawn polystyrene and high-impact polystyrene

The tensile behaviors of drawn polystyrene (PS) and high-impact polystyrene (HIPS) were examined systematically in the wide range of strain rate, 1.7 × 10^?4–13.1 m/s, without changing the mode of deformation and the shape of the test pieces. It was found for both PS and HIPS that the flexion points of birefringence with increase of draw ratio are intimately correlated with the tensile properties. Especially, the breaking strain and energy of undrawn and drawn HIPS were assigned to the contributions of the following three toughening mechanisms: (a) the generation of large numbers of microcrazes from the equatorial zone of the dispersed rubber particles; (b) the extension of interfacial rubber phase around the circumpolar zone of the dispersed rubber particles and its disintegration from the matrix component; and (c) the shear band formation of the matrix component followed by cold drawing. These mechanisms were discussed in connection with the factors of stress concentration to the rubber particles, hydrostatic pressure effect arising from the difference in Poisson's ratio of rubber and matrix components, and heat generation due to the adiabatic deformation.     

Effects of the degree of crosslinking and test rate on the tensile properties of a crosslinked polyacrylic pressure-sensitive adhesive and vulcanized rubber

The effects of the tensile test rate on the properties of a pressure-sensitive adhesive (PSA) and of vulcanized rubber were ascertained and compared, using a poly(n-butyl acrylate-acrylic acid) random copolymer with varying degrees of crosslinking as the PSA. The 100% modulus of the PSA was found to increase along with the crosslinking degree and with faster tensile test rates. In contrast, the 100% modulus of the vulcanized rubber did not exhibit any test rate dependence. To assess this effect, the molecular weights between chemical and physical crosslinking points were determined via equilibrium swelling, dynamic mechanical analysis, and tensile tests. The proportion of physical crosslinking points was found to be far larger in the crosslinked PSA. Because these entanglement points can readily disentangle in response to slow deformation, variations in the test rate only affected the PSA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47272.     

Physico-mechanical and dynamic mechanical studies of nanographite reinforced chlorobutyl nanocomposites

Abstract

Nanographite reinforced chlorobutyl elastomer (CIIR) nanocomposites were prepared. The dispersion of the nanographite in the CIIR matrix has been investigated by scanning electron microscopy. The effect of increasing nanographite loadings (2, 4, 6 and 8 phr) on mechanical properties like tensile strength, hardness, elongation at break and modulus (100, 200 and 300%) has been studied. The study shows increase in tensile strength, hardness and modulus and decrease in elongation at break with nanographite loading, which can be attributed towards better CIIR–nanographite interaction. The above explanation was again verified from bound rubber measurements. It shows increase in bound rubber contents with nanographite loading. Dynamic mechanical analysis was used to study their relaxation behaviour as a function of temperature (?100 to 100°C) at frequency 1 Hz and 1% strain. The effect of increasing nanographite loadings on glass transition temperature was marginal in all the composites, and Tg value was in the range of ?10 to 10°C, which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. The effects of variation in nanographite loading and temperature on dynamic mechanical properties like loss tangent, storage and loss modulus have been reported. The effect of solvent (chloroform, benzene and tri-chloroethylene) on swelling properties at different periods of time (15, 30, 45 and 60 min) shows that the degree of swelling increases with time and decreases with concentration of nanographite loading.     

The effect of liquids on the dynamic properties of carbon black filled natural rubber as a function of pre-strain

A free oscillation technique has been adopted to measure the dynamic storage and loss moduli of carbon black filled natural rubber materials. These tests are conducted with small oscillations that are superimposed on a range of tensile pre-strains. In addition, the effect of temperature on the dynamic moduli is measured as well as the effect of swelling the materials to various extents by liquids with a range of viscosity. It is observed that the dynamic storage and loss moduli do not depend strongly on the pre-strain at small pre-strains. At higher pre-strains there is a marked increase in both the storage and the loss moduli. An increase in temperature causes a dramatic reduction in both the storage and loss moduli. The dynamic behaviour of the filled rubbers when swollen can be approximately ascribed to the combined effects of a reduction in the modulus of the rubber matrix (caused by the swelling action) and a reduction in the effective volume fraction of the filler. The liquids used had a range of viscosity of more than a factor of a thousand. Despite this, the loss moduli of the swollen rubbers varied by only about a factor of two. This insensitivity could be understood in terms of a previously developed theory, based on free volume considerations.     

Deformation mechanisms in rubber toughened semicrystalline polyethylene terephthalate

The deformation mechanisms of rubber toughened polyethylene terephthalate (PET) are studied with fractography of impact fractured samples and tensile dilatometry. The dispersed phase consists of a mixture of an ethylene-co-propylene rubber (EPR) and a compatibilising agent (E-GMA8: copolymer of ethylene and 8 wt% of glycidyl methacrylate). It is found that the ductile fracture behaviour, above the brittle-ductile transition temperature (T_bd), consists of a high degree of rubber cavitation and extensive matrix shear yielding, both in the fracture plane and the stress whitened zone surrounding the crack. A steep increase in the volume strain upon tensile loading confirms the presence of the rubber voiding mechanism in the PET/(EPR/E-GMA8) blend system. It is seen that the stress whitened zone below the impact fracture surface consists of different zones, depending on the test temperature. Below T_bd, a layer of a highly deformed structure is followed by a cavitation layer containing only a limited number of cavitaties. Increasing the temperature, causes the deformation layer to be replaced by a zone lacking structure. It is believed that part of the fracture energy has been dissipated in the form of heat inducing a relaxation in the structure. Dynamical mechanical analysis under superimposed axial stresses reveals that the dispersed rubber particles internally cavitate in the presence of volume strain. At increased volume strains, the biaxial stress state in the cavitated particle is disturbed, resulting in the rupture of the rubber chains closest to the void by a tearing mechanism; revealing that the rubber particle is damaged upon cavitation.     

不同应变速率下橡胶混凝土损伤本构模型

为获得低应变速率下橡胶混凝土的力学性能,本文进行了不同应变速率下橡胶混凝土的轴压试验,分析了混凝土细骨料的橡胶颗粒体积替换率和应变速率对橡胶混凝土力学性能的影响规律。结果表明,随着应变速率的增加,橡胶混凝土的应力-应变关系曲线和抗压强度均呈现增大的趋势,橡胶混凝土初始损伤值呈现递减的趋势,但应变速率对橡胶混凝土的弹性模量影响不显著。当应变速率从3.3×10^-5/s增加至3.3×10^-3/s时,橡胶体积替换率为0%、20%和30%的橡胶混凝土抗压强度分别增加了31%、24%、10%。当橡胶体积替换率率从0%变化到30%时,承受应变速率为3.3×10^-5/s、3.3×10^-4/s和3.3×10^-3/s的橡胶混凝土抗压强度分别减少了17%、15%、30%;橡胶混凝土的耗能随着加载速率的增加,整体呈现增大的趋势。最后基于试验数据建立了不同应变率下橡胶混凝土的损伤本构关系模型,并采用试验数据验证了新建立模型的准确性。     

乙烯基含量对热硫化硅橡胶抗撕裂性能的影响

研究不同乙烯基含量对热硫化硅橡胶的力学性能尤其是抗撕裂性能的影响,采用平衡溶胀法测定硅橡胶的交联密度,研究不同乙烯基含量的硅橡胶并用胶的撕裂强度和交联密度的关系。结果表明,随着硅橡胶乙烯基含量的增大,硅橡胶硫化胶的断裂伸长率减小,300%定伸应力和硬度升高,当乙烯基摩尔分数为0.15%时,撕裂强度和拉伸强度较高。乙烯基摩尔分数为0.15%的硅橡胶和乙烯基摩尔分数为0.06%的硅橡胶并用,当并用比为50/50时,撕裂强度高达45.8 kN/m,乙烯基摩尔分数为0.30%的硅橡胶和乙烯基摩尔分数为0.06%的硅橡胶并用,当并用比为4/96时,撕裂强度可达42.9kN/m。乙烯基摩尔分数为0.30%的硅橡胶和乙烯基摩尔分数为0.15%的硅橡胶并用,并用比对硫化胶的撕裂强度影响不大。高乙烯基含量和低乙烯基含量的硅橡胶并用,有利于使硅橡胶的交联结构由"分散交联"转变为"集中交联",当并用胶的乙烯基摩尔分数在0.15%以内,硅橡胶并用胶的撕裂强度随乙烯基摩尔分数的增加而先增大后降低,而此时并用胶的交联密度与撕裂强度成反比。     

Influence of sample thickness on fracture behaviour of a polyketone and a polyketone-rubber blend

The influence of sample thickness on the fracture behaviour of an aliphatic polyketone and a blend of this polymer and 10 wt% core-shell rubber was studied. The sample thickness was varied from 0.1 to 8 mm. The skin morphology was studied by SEM. The fracture behaviour was studied on single edge notch specimen at a high strain rate (30 s⁻¹) in the temperature range of −40 to 120 °C. The fracture stress, fracture strain and fracture energies were determined. The temperature development in the notch area was followed with an Infra Red camera. The cavitation of the rubber particles was studied on tensile bars with a laser setup.With decreasing specimen thickness the fracture energies increased strongly and the brittle-ductile transition shifted to lower temperatures this both for the aliphatic polyketone and the polyketone-rubber blend. The deformation in these materials in accompanied with a strong temperature increase in the deformation zone. The addition of rubber particles decreases the sensitivity towards the thickness. However, in very thin samples the cavitation of the rubber particles is more difficult and the rubber toughening effect decreases. The strong thickness effects on the fracture toughness indicate for both the homo polymer and the blend indicate that data from a standard test with 4 mm thick samples are not representative for thin walled applications.     

不同应变率下橡胶混凝土抗压性能及能量特性研究

对四种橡胶体积掺量(0%、5%、10%、20%)的级配良好橡胶混凝土开展单轴抗压试验,对力学性能和破坏形态方面进行分析,得到了橡胶混凝土综合性能最优时的橡胶掺量,进而对最优掺量组进行不同应变率下的单轴压缩试验,并分析了不同应变率下橡胶混凝土的能量特性。试验结果表明,橡胶混凝土表现为裂而不散的类延性破坏,而非普通混凝土的脆性破坏。随着橡胶掺量的增加,抗压强度大幅降低,但变形能力得到增强,在掺量为10%时,橡胶混凝土的抗压强度达标,变形能力最好。橡胶混凝土受压时能量演化和转化过程是输入能先大量转化为弹性能并储存;接着耗散能转化率开始增加,使试件表面产生大量微裂纹;最后弹性能快速释放,耗散能转化率占比明显提高,从而导致试件整体破坏。另外随着应变率增大,橡胶混凝土的抗压强度和初始弹性模量明显提高,而峰值应变降低,同时输入总能量、弹性能与耗散能均呈现上升趋势,其中弹性能增加更明显。     

Filler/matrix-debonding and micro-mechanisms of deformation in particulate filled polypropylene composites under tension

Volume strain measurements of particulate filled polypropylene (PP) composites containing different glass beads and talc as filler were carried out in tension as a function of temperature and strain rate to determine the micro-mechanisms of deformation. While local cavitation mechanisms (micro-voiding, crazing, and micro-cracking) and subsequent debonding of the particles dominated as failure mechanisms at high strain rates and at room temperature, a more significant contribution of local shear yielding was observed with a reduced contribution of cavitational mechanisms at low strain rates or at 80 °C. This change in the dominating micro-mechanisms of deformation resulted in smaller volume strains during the tensile loading of the composites than for the respective neat matrix. Moreover, a novel approach is introduced for the detection of debonding using volume strain measurements, which takes into account the dilatational and deviatoric behavior of the neat matrix polymer and the composite. The results are supported by acoustic emission measurements carried out simultaneously on the same specimens.     

Evaluation of kinetics and transport mechanism of solvents through natural rubber composites containing organically modified gadolinium oxide

The solvent transport properties of the prepared composites were analysed using solvents of varying cohesive energy density and the effect of both modified as well as unmodified filler on the sorption and diffusion behaviour of NR vulcanisates has been investigated. It is found that the equilibrium uptake decreases with increase in filler content, as anticipated owing to the restrictions offered by the filler for solvents to diffuse into the polymer matrix. The mechanism of transport in natural rubber composites was carefully tracked and it was found to exhibit an anomalous mode of solvent transport where the polymer relaxation is in par with the rate of diffusion. Theoretical modelling of the swelling parameters was done and the results were found to be in agreement with existing models. The excellent swelling resistance coupled with the simultaneous improvement in mechanical properties would definitely pave way for the utilisation of these composites as barrier membranes.     

Elastic Behaviour of Ternary Rubber-filled Vulcanizates

Near-equilibrium stress–strain measurements have been carried out on ternary rubber vulcanizates. The effect of variation of the butyl rubber content on the elastic behaviour of the ternary rubber vulcanizates has been studied. It has been found that butyl rubber (IIR) is less sensitive to the vulcanization system used than either natural rubber (NR) or styrene–butadiene rubber (SBR). One can obtain a partially crosslinked system with an IIR phase embedded in the crosslinked matrix of NR and SBR. The role played by carbon black during mixing of the ternary blend has been investigated. The Mooney–Rivlin relationship was used to describe the behaviour of the ternary rubber matrix. The constants 2C₁ and 2C₂ have been calculated by use of the strain-amplification factor and the total crosslink density of the ternary rubber–carbon black systems has been investigated. The data have been evaluated in terms of the molecular theories of rubber elasticity. The elastic behaviour was found to be intermediate between the affine and phantom limits of the theory. © of SCI.     

Natural rubber composites reinforced with sisal/oil palm hybrid fibers: Tensile and cure characteristics

Natural rubber was reinforced with untreated sisal and oil palm fibers chopped to different fiber lengths. The influence of fiber length on the mechanical properties of the hybrid composites was determined. Increasing the fiber length resulted in a decrease in the properties. The effects of concentration on the rubber composites reinforced with sisal/oil palm hybrid fibers were studied. Increasing the concentration of fibers resulted in a reduction in the tensile strength properties and tear strength but an increase in the modulus of the composites. Fiber breakage analysis was evaluated. The vulcanization parameters, processability characteristics, and stress–strain properties of these composites were analyzed. The extent of fiber alignment and the strength of the fiber–rubber interface adhesion were analyzed from the anisotropic swelling measurements. Scanning electron microscopy studies were performed to analyze the fiber/matrix interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2305–2312, 2004     

Prediction of the twisting moment and axial force in a circular rubber cylinder for combined extension and torsion based on the logarithmic strain approach

The scope of the present work is the application of a particular class of strain energy function, based on the logarithmic strain, for the prediction of the twisting moment and axial force of a rubber circular cylinder under combined extension and torsion. The strain energy function involves four material parameters three of which are determined by fitting published experimental data from simple tensile and compression tests of natural rubber. One of the parameters of the proposed model has physical meaning, and it is equal to one ninth of the initial modulus of elasticity of the material. Hence, the number of unknown parameters is reduced to three. The logarithmic strain energy function is then applied to a combined extension and torsion problem of a rubber circular cylinder to check its performance for more complicated deformations. The results are compared with corresponding experimental and theoretical solutions available in the literature to validate the proposed model. It is found that the proposed strain energy function apart from predicting the common modes of deformations is also capable to determine more complicated types of deformation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

测定柔性橡胶应变和泊松比的新方法

通过采用以电荷耦合装置为核心的变形测量系统测定了大变形条件下胎冠胶BIVE，三角胶TRI和带束层胶AMET等3种橡胶材料的应变和泊松比，实验结果表明，将橡胶材料的单轴拉伸实验结果以时间－位移的形式输入计算机，经过专用软件处理后就可以得到橡胶在任意时刻的反变和泊松比。     

ABS树脂拉伸性能及形变机理的研究

研究了丙烯腈丁二烯苯乙烯共聚物（ABS）树脂在不同温度和不同拉伸速率时的拉伸行为以及物理老化对其拉伸行为的影响。结果表明,屈服强度随测试温度的升高而下降,断裂伸长率并不随着测试温度的升高而提高,直到测试温度升高到接近ABS树脂塑料相的玻璃化转变温度时,断裂伸长率才显著提高;断裂伸长率随拉伸速率的增加而降低,在不同的拉伸速率下,ABS的形变区内均可观察到银纹现象;在较高的拉伸速率下,形成的银纹数量较多,但银纹较短,银纹的扩展得到了有效抑制;ABS树脂经物理老化后断裂伸长率明显降低,银纹数量增加并出现了空洞成串现象。     

Improved mechanical properties and special reinforcement mechanism of natural rubber reinforced by in situ polymerization of zinc dimethacrylate

The peroxide‐cured natural rubber (NR) was reinforced by in situ polymerization of zinc dimethacrylate (ZDMA). The experimental results showed NR could be greatly reinforced by ZDMA. The tensile strength and the hardness of NR/ZDMA composites increased with the content of ZDMA. The reinforcement mechanism was studied further. Both high crosslinking density provided by ionic crosslinking and strain‐induced crystallization improved the mechanical properties. The crosslinking density was determined by an equilibrium swelling method and the crystallization index was measured by Wide‐angle X‐ray diffraction (WXRD). When the amount of ZDMA was high, the ability of strain‐induced crystallization decreased, due to the strong interactions between the rubber phase and the hard poly‐ZDMA (PZDMA) nanodispersions. At the moment, the increasing ionic crosslinking density made up for the effect of the drop of the strain‐induced crystallization, and played a more important role in the reinforcement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of uniaxial tensile strain on the release of small molecules from silicone rubber

Silicone rubber materials may be subject to mechanical strains which can affect the transport properties of small molecules loaded in the materials such as plasticizers and active molecules, hence deteriorating their intended mechanical properties or affecting their performance as carriers of active molecules. Therefore, it is important to understand the effects of mechanical strains on transport of small molecules in the silicone rubber matrix. In this work, silicone rubber sheets loaded with 2 wt% triacetin were stretched and held at four different lengths up to 125% engineering strain. The mass transfer coefficients and diffusion coefficients of triacetin in the strained silicone rubber were determined by monitoring the release of triacetin using headspace gas chromatography–mass spectrometry. It was found that there was no significant change of diffusion coefficient as the applied strain increased, which might result from two microstructure changes that had conflicting effects on diffusion: chain orientation and free volume deformation.     

Preparation,morphology and properties of natural rubber composites filled with untreated short jute fibres

Green composites were obtained by incorporation of short jute fibres in natural rubber matrix using a laboratory two-roll mill. The influence of untreated fibre content (1, 2.5, 5, 7.5 and 10 phr) on the mechanical properties, dynamic mechanical properties, swelling properties was examined. The behaviour of prepared green composites under cyclic compression was also investigated. Fibre dispersion in rubber matrix was studied by scanning electron microscopy. The highest tensile strength (21.1 MPa) and highest tear strength (39.9 N/mm) were found for composites containing 2.5 and 5 phr of short jute fibres, respectively. The results also suggested that increasing fibrous filler content resulted in increasing of tensile moduli 100, 200 and 300 % of elongation and hardness, and decreasing of rebound resilience and abrasion resistance of prepared jute/natural rubber composites. The cyclic compression test showed that increasing the amount of short jute fibres in the rubber matrix is related to increase of the energy dissipated in the composite. The incorporation of short jute fibres into the rubber matrix improves the stiffness of the composites, and it is related to the interaction between fibre surface and rubber matrix. The application of short fibres in higher amounts leads to formation of fibre agglomerates reducing the mobility of the rubber polymer chains. The mentioned agglomerates act as defects in rubber matrix, which caused decreasing of some properties, e.g. relative elongation at break.     

Diffusional Creep and Cavitational Strains in High-Purity Alumina under Tension and Subsequent Hydrostatic Compression

Diffusional creep and cavitation in pure alumina prepared with three different fabrication processes are compared under tension and subsequent hydrostatic compression. The deformation rates are separated into a volume-conserving creep rate and cavitational rate by measuring the longitudinal and transverse strains intermittently during deformation. Concurrent grain growth causes the volume-conserving strain rate to decrease in a manner consistent with Nabarro-Herring creep. The creep stress index of n = 1.3 and the average activation energy of Q = 480 kJ/mol are also consistent with Nabarro-Herring creep controlled by aluminum lattice diffusion. Anelastic loading and unloading transients are also identified and separated from the creep strains. High-voltage electron microscopy indicates that cavities nucleate at grain edges early and continuously in the creep process. The surfaces of these cavities tend after some growth to exhibit negligible curvature and various dihedral angles. The activation energy of Q = 450 kJ/mol and stress dependence of the cavitation rate of n = 1.3 are consistent with a grain boundary diffusional growth mechanism. The loading mode is found to have no significant effect on the cavitation rate during tensile creep and the subsequent decavitation rate during hydrostatic compression. The cavitation and decavitation rates are in good agreement with the model proposed by Speight and Beere when the effects of grain growth on cavity accumulation on grain boundaries are included. Exaggerated grain growth in high-density specimens can lead to early cavity coalescence and failure.