Difference in bound rubber formation of silica and carbon black with styrene‐butadiene rubber

Formation of bound rubber is affected by the physical structure and surface chemistry of filler and the property of rubber. Variation of the bound rubber formation in styrene‐butadiene rubber compounds filled with silica and/or carbon black was studied. Influence of temperature on extraction of loosely bound rubber was also investigated. For the both silica and carbon black‐filled compounds, the bound rubber content increases with increase in the silica content ratio. The bound rubber content decreases with increasing the extracting temperature. The loosely bound rubber content of the silica‐filled compound is higher than that of the carbon black‐filled one. Activation energy for the extraction of the unbound and loosely bound rubbers becomes higher as the total filler content increases. The activation energy of the silica‐filled compound is higher (almost double the value) than for the carbon black‐filled one. Copyright­© 2002 John Wiley & Sons, Ltd.     

Dynamic mechanical properties of epoxy/novolac system modified with reactive liquid rubber and carbon filler

This paper reports on the work carried out to evaluate the frequency dependent viscoelastic properties of epoxy/novolac compositons modified with a liquid reactive rubber and carbon filler. For epoxy systems modified with elastomer, three typical transitions were observed: the α-relaxation deeply related to the glass transition of epoxy, the β-transition of epoxy, and the glass transition of rubber appeared near to the β-relaxation of epoxy resin. Considering an Arrhenius equation, the activation energies of β-relaxation were estimated. In the region of glass transition and rubbery state the temperature dependence of the shift factor (α_T) was determined through Williams-Landel-Ferry (WLF) equation.     

Dynamic mechanical properties of epoxy resin/epoxidized rubber blends: Effect of phase separated rubber

The dynamic mechanical properties of blends of diglycidyl ether of bisphenol-A-based epoxy resin and internally epoxidized polybutadiene rubber have been studied. It is shown that the influence of the composition of the continuous phase and of the dispersed phase can be studied not only from the variations of the glass transition temperature but also from the changes in the apparent enthalpy of activation associated with this transition. As the initial rubber content increases, the composition of the dispersed phase remains practically constant while more rubber is able to dissolve in the continuous phase. Analysis of the rubbery plateau region reveals that the shear modulus of the blends is not much affected by the presence of dissolved rubber in the continuous phase but strongly depends on the volume fraction of dispersed phase. This volume fraction can be obtained from the relative drop in shear modulus after modeling the results with the Kerner equation. The results compares well with independent measurements by scanning electron microscopy. © 1994 John Wiley & Sons, Inc.     

Thermal expansion,free volume,and molecular mobility in a carbon black-filled elastomer

The thermal expansion of a butadiene–styrene copolymer filled with carbon blacks differing tenfold in mean particle size (HAF and MT) was investigated. The glass transition was unaffected by MT and was raised only 0.2°C for every 10 parts per hundred by weight of polymer of HAF black added. The coefficient of expansion of the polymer component of the composite in the rubbery region was substantially unaffected by either carbon black, but decreased markedly with increasing black loading in the glassy state. These results suggest that free volume is not altered appreciably by the presence of the filler in the rubbery state, but expands with decreasing temperature below T_g. The latter effect is explained by dilatation due to stresses set up around filler particles, arising from differences in the expansion coefficients of filler and polymer, which are not relieved in the glassy state. The near invariability of T_g and of the rubbery fected by adsorption of polymer segments on the carbon black surface. A conservative rough estimate indicates that restriction of segmental motion is confined to a 30 Å layer around the particles in which T_g is elevated by only 10°C.     

Formation of Network by Carbon Black，Silica and Their Mixing Fillers in Isoprene Rubber北大核心CSCD

The network formed by fillers has great influence on the mechanical properties of rubber materials. To understand the formation of network by carbon black,silica,and carbon black/silica mixing fillers in rubber and its influence on the properties of rubber,isoprene rubber/filler composites with different filler loadings are prepared and their micromorphology,rheological and tensile properties are investigated. It is found that the dispersion of fillers is better in rubber after cure than that in rubber before cure for all three rubber systems,and the filler size of silica is smaller than that of carbon black,but the aggregation is more severe in silica filled rubber system. In mixed filler system,the two fillers tend to aggregate separately, leading to the low modulus at small strain than that in single filler system. With the increase of the filler loading,the tensile strength increases first and then decreases,the elongation at break decreases,and the temperature rise in compression flexometer tests increases. Moreover,the temperature rise in mixed filler system is higher than that in single filler system at high filler loading. © 2022, Science Press (China). All rights reserved.     

Structure of the carbon-black-particles framework in filled elastomer materials

Specific features of the structure of a rigid framework composed of aggregated carbon black particles in rubber were considered. The volume fractions of the main components of the material—the filler, the binder, the layer enveloping carbon black particles, and the polymer entrapped by aggregates—were calculated. It was found that the volume fraction of the polymer in the layer around filler particles can be very high. The average number of contacts between neighboring aggregates in rubber with a high filler content is six. During deformation, the structure undergoes strong changes, so that neighboring aggregates can move from each other or, conversely, the remote aggregates can approach each other.     

Free Volume of Montmorillonite/Styrene‐Butadiene Rubber Nanocomposites Estimated by Positron Annihilation Lifetime Spectroscopy

Summary: The size and concentration of free‐volume holes of two kinds of montmorillonite (MMT)/styrene‐butadiene rubber (SBR) nanocomposites were investigated by positron annihilation lifetime spectroscopy (PALS). Strong interfacial interaction caused an apparent reduction of the free‐volume fraction of rubber probably by depressing the formation of free‐volume holes in the interfacial region. Interfacial interaction in MMT/SBR nanocomposites was weaker than that in SBR filled with carbon black.

Dependence of normalized o‐Ps intensity of four kinds of composites on filler volume fraction.     

Electrical and mechanical behavior of filled elastomers 2: The effect of swelling and temperature

In this work the effect of swelling and temperature on the resistivity of highly carbon black filled elastomers under strain is investigated. This work shows that swelling, even to a modest extent of less than 10%, causes a marked increase in the electrical resistivity. The effect of a linear expansion due to swelling is much more marked than an equivalent linear tensile extension on the electrical resistivity. The increase in electrical resistivity with swelling is also much greater than the increase due to a reduction in the volume fraction of the carbon black alone. The increase in resistivity depends somewhat upon the chemical nature of the swelling agent. There is a relatively small effect of temperature induced volume change on resistivity, contrasting markedly with the large effect of a volume increase due to swelling. These observations suggest that on swelling there is a preferential migration of the solvent to the rubber/filler interfaces. This will push the carbon black aggregates apart and lead to a dramatic increase in the resistivity across the interface. There are also indications that at elevated temperatures the filler/rubber interactions are reduced. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2161–2167, 2004     

Effect of plasticizer concentration on the hysteresis,tear strength and stress-relaxation characteristics of black-loaded rubber vulcanizate

The effect of plasticizer concentration on the stress softening, tear strength and stress relaxation of black loaded bromobutyl rubber vulcanizate has been investigated. The stress softening in the rubber vulcanizate, an energy dissipative process at higher strain, may be explained primarily by changes that take place in the rubber phase of the filled vulcanizate. Increased plasticizer concentration leads to decrease in the equilibrium hysteresis. A quantitative relationship between energy density and hysteresis has been derived, which is applicable at and below the elongation at break. Increase in plasticizer concentration results in decrease in the effective diameter of the tip of the tear, which in turn decreases the tear strength. Rate of relaxation decreases with increase in the plasticizer concentration in the carbon-black-filled vulcanizate.     

Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

Dielectric relaxation processes in epoxy resin—ZnO composites

Polymer matrix‐ZnO microcomposites were prepared in different filler concentrations. The electrical relaxation dynamics of all samples was examined by means of broadband dielectric spectroscopy (BDS) over a wide temperature range. Two relaxation modes (namely β and γ), observed in the low temperature region, are attributed to the reorientation of small polar groups of the polymer matrix. Glass‐rubber transition (α‐mode) of the polymeric matrix and interfacial polarization phenomena are considered as responsible for the recorded relaxation processes in the high temperature region. An additional relaxation mode, named intermediate dipolar effect (IDE), is recorded at temperatures higher than ?30 °C in all composites. Its occurrence and dynamics are related to the presence and concentration of the filler. IDE and α‐relaxation are observed in the same frequency and temperature range, leading to a mutual superposition. The two processes were distinguished following a simulation procedure employing the simultaneous fitting of two Havrilliak‐Negami terms and a third term describing the contribution of DC conductivity to dielectric losses. The temperature dependence of relaxation times for α‐mode follows the Vogel‐Tamann‐Fulcher equation, whereas IDE relaxation times follow unusual temperature dependence. The latter is discussed under the assumption of intrinsic interfacial polarization phenomena within ZnO crystal domains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 445–454, 2009     

Effect of filler networking on the dynamic mechanical properties of crosslinked polymer solids

The strain amplitude dependence of the viscoelastic properties of eight different carbon blacks dispersed in two different rubbery networks is investigated and evaluated within the Cole-Cole approach for the complex elastic modulus at fixed temperature and frequency. This approach is based on the Kraus model of strain-dependent filler agglomeration-deagglomeration rates. We find a non-integer universal shape exponent of the Cole-Cole process that obviously depends only on the surrounding polymer matrix but is independent of the filler grade. The exponent can be related to the fractal dimension of the carbon black surface.     

The relaxation and deformational properties of a carbon-black filled elastomer in biaxial tension

Biaxial stress relaxation data acquired for a carbon-black-filled elastomer are analyzed. Consistent with previously published simple-tension and pure-shear results for this elastomer, the biaxial relaxation behavior is also found to be a separable function of time and strain effects. A departure from separability is observed at the larger strain; this might be a manifestation of strain-induced crystallization. An analysis of the biaxial results together with the earlier reported simple-tension and pure-shear data reveals that the deformational dependence of this elastomer obeys the Valanis—Landel hypothesis up to moderate deformations. The Ogden strain energy function is found to be an excellent analytical representation of all of the multiaxial data. Large relative errors found at small tensile strains between the data and the Ogden fit are attributed to carbon black structural effects.     

Hyperelasticity and stress softening of filler reinforced polymer networks

Starting from an analysis of filler networking in bulk polymers, a constitutive micro-mechanical model of stress softening and hysteresis of filler reinforced polymer networks is developed. It refers to a non-affine tube model of rubber elasticity, including hydrodynamic amplification of the rubber matrix by a fraction of hard, rigid filler clusters with filler-filler bonds in the unbroken, virgin state. The filler-induced hysteresis is described by an anisotropic free energy density, considering the cyclic breakdown and re-aggregation of the residual fraction of soft filler clusters with already broken, damaged filler-filler bonds. Experimental investigations of the quasi-static stress-strain behaviour of silica and carbon black filled rubbers up to large strain agree well with adaptations found by the developed model. The microscopic material parameters obtained appear reasonable, providing information on the mean size and distribution width of filler clusters, the tensile strength of filler-filler bonds and the polymer network chain density.     

炭黑填充聚苯乙烯熔体流变行为

研究了炭黑(CB)填充聚苯乙烯(PS)熔体的稳态和动态流变行为. CB/PS复合体系在CB体积分数φ=0.06时发生逾渗转变. 结果表明, 低应变区熔体模量降低主要归因于粒子-粒子及粒子-高分子间作用力的破坏, 高应变下模量的急剧下降则主要与高分子链间解缠结有关. 采用“两相”模型拟合线性动态流变行为, 发现应变放大因子A_f(φ)、填充相模量及松弛指数与温度有关. A_f(φ)~φ关系符合Guth方程和扩散控制的粒子簇聚集模型. “粒子相”形状参数与聚集体分维度均随温度升高而有所降低, 说明CB粒子聚集体因团聚而趋于各向同性, 应变放大效应减弱. “粒子相”特征模量G'_f1(φ)和G"_f0(φ)与φ关系满足标度律. 当φ > 0.06时, G'_f1(φ)和G"_f0(φ)及其标度指数均随温度升高而明显降低, 其G'_f1(φ)变化幅度略大于G"_f0(φ), 说明“粒子相”弹性与黏性组分具有不同的温度依赖性. 随着温度升高, 扩散控制的CB粒子团聚过程加快, 应变放大效应减弱.     

CB/HDPE导电复合体系中Kerner-Nielson方程修正及电渗流与粘弹渗流的相关性

随着导电填料含量的增加,聚合物导电复合材料的电导率呈现非连续的递增.当填料含量达到渗流阈值并导致渗流现象出现时,导电填料相互聚集并形成网络,体系电导率急剧增大,关于此类电渗流现象已有很多报道^[1～4].填充类导电复合材料的结构和性能与其粘弹性密切相关.近年来,由于炭黑填充使得许多光学方法失效,流变学方法受到了广泛重视.最新的研究发现,非均相结构的出现和演化对浓度的依赖性有着特征流变响应,是一种粘弹渗流现象^[5～7].     

A new relaxation process in the high-elastic state at low temperatures

A new relaxation process, explaining the change of elasticity in rubberlike polymers at critical stress (0.1?0.5 kgf/cm²) has been discovered. This process is characterized by the low value of activation energy (weak temperature dependence of relaxation times) and large sizes of kinetic units (strong dependence of relaxation time on stress). Critical stress depend on temperature and for rubberlike polymers turns to zero at 40°?60°C. Mechanism of the phenomena can be explained by the existence of the ordered molecular microregions, creating additional crosslinking points of nonchemical nature with free chains of the network, breaking up at critical stress. Observed phenomena is analogous to the process of forced rubber elasticity of those polymers in glassy state. Critical stress is analogous to the limit of forced rubber elasticity below glass transition temperature.     

Effect of solvent and carbon black species on the rubber–carbon black interactions studied by pulsed NMR

The spin–spin relaxation time T₂ and the fraction of short T₂ component for composites of natural rubber with carbon black prepared under various conditions have been measured by pulsed NMR. Effect of swelling with a solvent (CCl₄), carbon black species (SAF, HAF, SRF) with different surface areas, and different initial carbon black loadings (35, 50, 70 phr) have been determined. Molecular motion in the rubber phase not in the immediate vicinity of the carbon black surface increases rapidly with increasing solvent concentration, yet it is still slightly restricted compared to rubber with solvent alone. On the other hand, molecular motion in the immobilized layer around carbon black and the fraction rubber in that layer are not affected by the solvent. This indicates strong restriction of molecular motion of polymers at the surface. For estimation of the thickness of the immobilized layer, the necessity of using an appropriate measure of surface area accessible to polymer molecules is pointed out. The degree of immobilization in the layer and the thickness of the layer do not vary appreciably with the nature of carbon black or the initial loading of carbon black.     

Bulk viscoelastic contribution to the wet‐sliding friction of rubber compounds

The wet‐sliding friction characteristics of rubber compounds made of high cis‐polybutadiene were examined with a British pendulum skid tester at room temperature. Three series of compounds were prepared—unfilled or filled with carbon black at two different levels. The bulk viscoelastic properties as characterized by the bulk glass‐transition temperature for the compounds were systematically adjusted by changing the crosslinking density via sulfur vulcanization. In fact, the dynamic mechanical glass‐transition temperature for the compounds ranges between approximately ?100 and 20 °C. Consequently, the wet‐sliding friction of these rubber compounds is dramatically affected. With increasing compound glass‐transition temperature, the wet‐sliding friction increases to a maximum and then decreases. However, the rate of increase or decrease varies with the amount of filler in the compounds. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 757–771, 2003