Separability behavior in viscoelastic properties of EPDM gum vulcanizate

Dynamic mechanical properties of EPDM gum vulcanizates were studied using the dynamic viscoelastometer, Rheovibron. A small sinusoidal strain was superimposed on a static strain and its effect on dynamic mechanical properties were analyzed. The results are discussed in terms of total strain which takes the static strain into account. Separability of time and strain effects for loss modulus and the nonseparability for storage modulus are discussed. A critical strain was identified after which the stress dissipation mechanism changes. © 1994 John Wiley & Sons, Inc.     

Enhanced apparent payne effect in a gum vulcanizate at low temperature approaching glass transition

For a vuleanized elastomer compound containing no filler, variation of dynamic moduli with strain was examined in the transition zone approaching glass transition at 0.1, 1, 10, and 15 Hz. In the complete absence of filler‐filler/filler‐polymer interactions, the nonlinearity in dynamic moduli becomes enhanced upon approaching glass transition regardless of testing frequency. Under the test protocol employed, the extraordinary nonlinearity at 10 Hz and 15 Hz is shown to be associated with a spectacular shear‐heating event. At 10 Hz and ?19°C, a pronounced yielding‐like peak in the in‐phase stress component emerges at small strain (< 2%) during testing of increasing strain. However, the corresponding temperature rise here is only about 0.4°C. Interestingly, at or above 0°C, no such peak in the in‐phase stress component emerges for compounds filled with reinforcing filler above the percolation threshold. Discussion is also made relating the observations to the sliding friction of rubber materials.     

Dynamic properties of crosslinked epoxy resin at large cyclic and static deformation

Measurement of dynamic properties of crosslinked epoxy resin have been performed under torsional cyclic deformation with different amplitudes and frequencies and with extensional creep under different loads. It is found in both cases that the dynamic modulus decreases above a certain critical value of deformation. Truncation of the glassy state region and shifting of the transition zone to lower temperatures and higher frequencies have been observed as effects of large amplitude deformation. The maximum reduction in the modulus value and the minimum in the critical amplitude both occur in the region of T_g Shear fatigue of the material has been observed in the glassy state with a frequency- and temperature-dependent fatigue life. It is found that the loss modulus under extensional creep depends upon the values of the deformation and stress whereas the storage modulus depends solely upon the deformation. The ratio of energy expended during static and cyclic deformations is shown to depend only upon the extensional deformation.     

Elastic properties of real elastomers at small deformations

Elastic properties of real elastomers were examined by using partial derivatives of the strain energy density function (W) with respect to the invariant (I_i, i=1,2,3) of deformation tensor. The values of the derivatives at zero strain limit for styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR) and butadiene rubber (BR) were compared with those derived from the theory shown in the previous paper, where compressibility of the materials was taken into account. The asymptotic behavior of the derivatives for isoprene rubber (IR) and segmented polyurethaneurea (SPU) was also compared with those of the three types of rubbers. It was shown that the theoretical predictions for the limiting value agreed fairly well with the experimental values of the elastomers.     

EPDM的性能调节

研究了无机填料和软化剂用量对ＥＰＤＭ硫化胶力学性能的影响。结果表明,随轻质碳酸钙用量的增大,ＥＰＤＭ硫化胶的硬度增大,拉伸强度和扯断伸长率等性能下降;随环烷油用量的增大,ＥＰＤＭ硫化胶的硬度、拉伸强度等性能下降,拉断伸长率和压缩永久变形增大。利用等高线可预测胶料的性能,通过调整配方中轻质碳酸钙和环粽铀的用量,可选出能满足性能指标要求的胶料配方,达到调节ＥＰＤＭ硫化胶某些性能的目的。     

硫化压力对硫化胶性能的影响

试验研究了模压和注压硫化压力对硫化胶性能的影响。模压和注压硫化时型腔内压力变化趋势相同，硫化胶的300％定伸应力和拉伸强度随硫化压力的增大而增大。拉断伸长率、撕裂强度和压缩永久变形减小。减震橡胶垫实际对比试验表明，注压硫化最大压力为模压硫化的2倍以上，达到相同的静态刚度时硫化胶的硬度下降且压缩永久变形减小了42％，可提高制品的使用寿命。     

Elasticity at large deformations and high strain rates in injection molded polypropylene

The deformation behavior of isotactic polypropylene (PP) as a function of strain rate was investigated at 50°C in uniaxial tension. Injection molded dogbone specimens were tested at high strain rates, ε = 10^?1 – 10² s^?1, and the local deformation in the neck was studied using fast tensile videometry. A strong elastic recoil was observed after fracture in this strain rate range with local elastic strains as high as ?_e = 2.0 – 3.2. The recoil is very fast and takes place within 1 ms. The elastic fraction of the strain at break was found to increase with the local strain rate. The elasticity further depends on strain and temperature. The elastic deformation behavior is part of the known transition from ductile cold drawing behavior to brittle fracture that occurs with strain rate or temperature. The elasticity in PP is thought to be due to a decrease in crystallinity, resulting in a discontinuous crystalline structure comparable to that of thermoplastic elastomers.     

A constitutive model for large multiaxial deformations of solid polypropylene at high temperature

Experiments on a blow‐molding grade of polypropylene have been performed at 135°C using a biaxial testing machine. Both simultaneous and sequential equibiaxial tests were performed at strain rates relevant to solid phase processing regimes. A constitutive model has been developed that includes a single Eyring process and two Edwards‐Vilgis networks. The effectiveness of this model for predicting the observed stress‐strain behavior is explored. Predictions of simultaneous stretching and the first stretch in sequential experiments are excellent. The second stretch in sequential experiments is less well predicted, but the model's performance is useful overall. The model is incorporated into a commercial finite element code and its practicality is demonstrated. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Viscoelastic properties of dilute aqueous solution of methylcellulose at ultrasonic frequencies

The viscoelastic properties of dilute aqueous solutions of methylcellulose at ultrasonic frequencies were investigated by a torsional method using quartz crystal resonators. The concentration dependences of G′ and G″ – ωη_s increased with increasing temperature at 13 kHz, but at higher frequencies G′ and G″ – ωη_s were simply proportional to the concentration irrespective of temperature. These results may be explained by the difference of corresponding viscoelastic mechanism at measuring frequencies. In order to examine the configuration of methylcellulose in water, which changes remarkably with temperature, the intrinsic values at various temperatures were experimentally obtained by extrapolation to zero concentration, and the frequency dependence of intrinsic dynamic viscosity was examined. The values of components of the complex intrinsic viscosity at various temperatures and their frequency dependences were quantitatively compared with those calculated from the Tschoegl theory. The values of hydrodynamic strength parameter in the Tschoegl theory for an aqueous solution of methylcellulose increased with increasing temperature, and an effect of the internal viscosity due to the aggregation of methylcellulose was observed at higher temperatures. However, on the whole, the viscoelastic behavior was relatively close to Rouse-like behavior.     

IIR耐热老化性能影响因素的研究

研究了不同硫化体系以及其它配方因素对IIR硫化胶耐热老化性能的影响.研究结果表明经过160℃×24h热老化后,树脂硫化IIR的力学性能保持率比硫黄硫化和硫给予体硫化IIR高;树脂用量为5～10份、氯化锡用量为5～9份、氧化锌的用量为5份时,IIR硫化胶的耐热老化性能最好;采用ISAF/GPF并用以及添加蓖麻油,可以获得较好的耐热老化性能.     

抗硫化返原剂对NR性能的影响

试验研究抗硫化返原剂PK900和HVA-2对NR硫化胶性能的影响。结果表明，加入抗硫化返原剂PK900或HVA-2可以增大NR硫化胶的回弹值和刚度，提高耐热性、耐甲苯性能及过硫后的耐压缩永久变形性能，其中抗硫化返原剂HVA-2的各项性能均优于PK900。     

甲基丙烯酸镁对EVM硫化胶性能的影响

将不饱和羟酸金属盐与乙烯-乙酸乙烯酯共聚物（EVM）共混制备硫化胶，研究了甲基丙烯酸镁（MDMA）对过氧化物硫化的EVM的硫化特性，物理机械性能以及耐热氧老化性能的影响。结果表明，MDMA能提高EVM胶料的硫化速度；MDMA显著地提高了EVM硫化胶的物理机械性能，其用量为20-50份时，硫化胶的拉伸强度保持在20MPa以上；与高耐磨炉黑增强的硫化胶相比，MDMA增强的EVM硫化胶具有较好的耐热氧老化性能。     

硫化剂DCP对NBR/木质素硫化胶性能的影响

研究了用DCP作硫化剂时木质素的用量对NBR胶料硫化特性和硫化胶物理性能的影响,并与硫黄硫化体系进行了对比。试验结果表明,随着木质素用量的增大,NBR胶料的ML和MH增大,t10保持不变,t90有所延长;当木质素用量为50份时,NBR硫化胶的综合物理性能最佳,拉伸强度、定伸应力和撕裂强度均明显高于硫黄硫化胶。动态粘弹特性分析表明,木质素与NBR具有良好的相容性,DCP硫化胶的玻璃化转变温度比硫黄硫为胶约低4℃。综合性能分析认为,硫化剂DCP对NBR／木质素体系具有原位反应相容作用。     

Viscoelastic properties of alkyd ceramers

The viscoelastic behavior of three alkyd ceramers was studied using dynamic mechanical thermal analysis (DMTA). A commercial product was compared to model alkyds. The model alkyds were prepared from phthalic anhydride, glycerol, and linseed or sunflower seed oil. Three sol–gel precursors, titanium tetra-i-propoxide, titanium di-i-propoxide diacetylacetonate, and zirconium tera-n-propoxide were investigated. The alkyd ceramers were evaluated as a function of both alkyd type and a sol–gel precursor content. The viscoelastic data showed that both E′ and T_g were affected by sol–gel precursor content. Both the crosslink density and T_g demonstrated a minimum at low sol–gel precursor contents. After this minimum, both the crosslink density and the T_g increased substantially. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2017–2028, 1999     

Viscoelastic properties of tire cords

The viscoelastic properties of commercial rayon, nylon 66, and poly(ethylene terephthalate) tire cords have been investigated by dynamic mechanical techniques using the Vibron viscoelastomer DDV-II. The effect of temperature, humidity, and geometric structure on the viscoelastic response has been determined for the tire cord assemblies. Subsequently, the underlying mechanisms and the polymer and fiber structural factors which influence them are discussed. Also, the consequences of the cord properties on tire hysteretic characteristics are discussed. This enables tires to be designed to meet specific service requirements. Characterization of materials in this way is becoming more important, particularly as the performance demands on tires become more stringent.     

配合剂对NBR硫化胶性能的影响

试验研究促进剂和炭黑的品种和用量对要求较高硬度和强伸性能的NBR硫化胶整体性能的影响。结果表明，与促进剂CZ和DM相比，促进剂TMTD硫化胶的300％定伸应力、拉伸强度、撕裂强度和耐油性能较高，而硬度变化不大，促进剂TMTD的最佳用量为1．2份；与炭黑N660、N770和喷雾炭黑相比，填充炭黑N330硫化胶的硬度和拉伸强度较大，而拉断伸长率、拉断永久变形和压缩永久变形较小，炭黑N330的用量以75份为宜。     

Viscoelastic properties of stereocomplex polymers

Sterecomplex polymers were synthesized by radical polymerization of mixtures of isotactic and syndiotactic poly(methyl methacrylate) (PMMA) in some vinyl monomers under the conditions of stereocomplex formation. The viscoelastic properties of stereocomplex polymers were studied by a sinusoidal vibration method and compared with those of the usual blended polymers. It was found that the network structure resulting from the stereocomplex association between isotactic and syndiotactic PMMA prevents a phase separation of the newly created polymers from the matrix of PMMA during the polymerization process, and that makes the viscoelastic properties and optical transparency of stereocomplex polymers very different from those of the usual blended polymers without stereocomplex formation.     

Morphological evolution and properties of thermoplastic vulcanizate/organoclay nanocomposites

Nanocomposites composed of organoclay and thermoplastic vulcanizates (TPVs) based on uncompatibilized or compatibilized polypropylene (PP)/ethylene–propylene–diene rubber (EPDM) blends were prepared in this study. The morphology of the nanocomposites was studied with wide‐angle X‐ray diffraction and transmission electron microscopy, which suggested that the addition of the compatibilizer played a key role in determining the morphology of the composites because of their interaction with the clay surface. Scanning electron microscopy study indicated the changes in the morphology of the rubber particles. Dynamic mechanical analysis was also applied to the analysis of these phenomena. Moreover, for nanocomposites with uncompatibilized PP/EPDM blends as the matrix, the samples showed tensile enhancement compared with neat TPV. Although the addition of the compatibilizer changed tensile properties of the composites in a rather different trend, the tensile modulus increased dramatically when the compatibilizer was added. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40618.