In this work, we study the effect of microstructure of rubber particle aggregates on linear and nonlinear viscoelastic properties of olefinic thermoplastic vulcanizates (TPVs) based on ethylene‐propylene‐diene rubber (EPDM) and polypropylene (PP). TPVs samples with identical rubber content and different extent of rubber particle aggregation are prepared through dynamic vulcanization of PP/EPDM blends (conventional method) with different compositions as well as dilution of PP/EPDM 40/60 TPVs. Morphological observations show larger aggregates of cured rubber particles in the diluted samples (D) compared to the ones prepared by conventional method (B). The difference between the microstructures of the two series of samples decreases with increasing rubber content. Linear viscoelastic measurements demonstrate higher elastic modulus and dynamic viscosity at low frequency for D samples compared to B ones, representing the effect of aggregation of the dispersed rubber phase. The higher extent of aggregation in D samples also leads to a lower percolation threshold and smaller linear viscoelastic region. From fitting of a structure‐dependent model on the stress growth results, longer characteristic relaxation times are obtained for D samples due to the presence of rubber aggregates. Additionally, A higher degree of orientation and less contribution of rubber aggregate destruction are found under shear flow in D samples.

中文翻译：

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硫化橡胶颗粒的聚集对热塑性硫化橡胶流变学的影响

在这项工作中，我们研究了橡胶颗粒聚集体的微观结构对基于乙烯-丙烯-二烯橡胶（EPDM）和聚丙烯（PP）的烯烃热塑性硫化橡胶（TPV）线性和非线性粘弹性的影响。通过动态硫化具有不同组成的PP / EPDM共混物（常规方法）并稀释PP / EPDM 40/60 TPV，可以制备出具有相同橡胶含量和不同程度橡胶颗粒聚集程度的TPV样品。形态学观察表明，与通过常规方法（B）制备的那些相比，在稀释样品（D）中的固化橡胶颗粒的聚集体更大。两个系列的样品的微观结构之间的差异随着橡胶含量的增加而减小。线性粘弹性测量结果表明，与B样品相比，D样品在低频下具有更高的弹性模量和动态粘度，代表了分散橡胶相的聚集作用。D样品中较高的聚集程度也会导致较低的渗透阈值和较小的线性粘弹性区域。通过基于结构的模型对应力增长结果的拟合，由于存在橡胶聚集体，D样品获得了更长的特征弛豫时间。此外，在D样品的剪切流作用下，发现较高的取向度和较小的橡胶聚集体破坏贡献。D样品中较高的聚集程度也会导致较低的渗透阈值和较小的线性粘弹性区域。通过在应力增长结果上拟合结构相关模型，由于存在橡胶聚集体，D样品的特征弛豫时间更长。此外，在D样品的剪切流作用下，发现较高的取向度和较小的橡胶聚集体破坏贡献。D样品中较高的聚集程度也会导致较低的渗透阈值和较小的线性粘弹性区域。通过在应力增长结果上拟合结构相关模型，由于存在橡胶聚集体，D样品的特征弛豫时间更长。此外，在D样品的剪切流作用下，发现较高的取向度和较小的橡胶聚集体破坏贡献。