Property enhancement of PP-EPDM thermoplastic vulcanizates via shear-induced break-up of nano-rubber aggregates and molecular orientation of the matrix
Property enhancement of PP-EPDM thermoplastic vulcanizates via shear-induced break-up of nano-rubber aggregates and molecular orientation of the matrix
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通过纳米橡胶聚集体的剪切诱导破碎和基体的分子取向增强 PP-EPDM 热塑性硫化橡胶的性能
DOI：
10.1016/j.polymer.2015.03.011
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发表时间：
2015-04
期刊：
影响因子：
4.6
通讯作者：
Tian, Ming
中科院分区：
文献类型：
--
作者：
Chen, Feng;Fu, Qiang;Ning, Nanying;Tian, Ming
为了研究熔体剪切对PP/EPDM热塑性硫化橡胶（TPV）相形态和力学性能的影响，采用动态保压注射成型装置，在PP/EPDM热塑性硫化橡胶注射成型保压过程中，对TPV熔体连续施加振荡剪切。为了清楚的比较，还使用了常规的注射成型。结果表明，常规注射成型可在PP基体中形成尺寸约为1.5 μm的大尺寸EPDM橡胶聚集体。令人惊讶的是，当引入振荡熔体剪切时，首次实现了尺寸为约40 nm的分散良好的纳米级EPDM颗粒，此外还大大增强了PP基体的分子取向。结果表明，动态填充注射成型样品的拉伸强度和伸长率同时得到提高。此外，步进循环测试显示出典型的“Mullins效应”的常规注塑成型样品和动态填充注塑成型样品，但改善了动态填充注塑成型的耐疲劳性。为了分离PP基体取向和纳米级EPDM粒子对PP/EPDM热塑性弹性体拉伸性能的影响，对注塑样品进行热退火处理以消除PP基体的取向。结果表明，动态保压注射成型试样退火后拉伸强度有所下降，但断裂伸长率基本保持不变。通过比较热处理前后的性能变化，得出PP基体的取向有利于提高弹性模量和拉伸强度，而断裂伸长率的提高与橡胶粒径的减小和在TPV中分散性的改善直接相关。我们的工作表明，熔体剪切对橡胶颗粒的破碎和TPV的基体取向以及强烈的影响。分离出PP基体取向和橡胶粒径对TPV拉伸行为的贡献，为制备新型高性能TPV提供了指导。
In this study, in order to investigate the influence of melt shearing on the phase morphology and mechanical performance of PP/EPDM thermoplastic vulcanizates (TPVs), the oscillatory melt shear was successively applied on the TPV melt in the mold cavity during the packing stage of injection molding by a modified facility, called dynamic-packing injection molding. For a clear comparison, conventional injection molding was also used. It is shown that conventional injection-molding results in large EPDM rubber aggregates with dimensions of ∼1.5 μm dispersed in the PP matrix. To our surprise, well-dispersed nanoscale EPDM particles with dimensions of ∼40 nm have been achieved for the first time when introducing oscillatory melt shearing, in additional to a largely enhanced molecular orientation for PP matrix. As a result, a simultaneous improvement of tensile strength and elongation has been achieved for dynamic packing injection molded samples. In addition, step cycle tests showed typical “Mullins effect” for both conventional injection-molded samples and dynamic packing injection molded samples but improved fatigue resistance for dynamic packing injection molded ones. To isolate the contribution of PP matrix orientation and nanoscale EPDM particle on the tensile behavior of PP/EPDM TPVs, thermal annealing of injection molded samples were carried out to eliminate the orientation of PP matrix. It was found that the tensile strength is decreased but the elongation at break is maintained after annealing of dynamic packing injection molded samples. By comparing the property change before and after annealing, it is concluded that the orientation of PP matrix is in great favor of Young's modulus and tensile strength while the enhanced elongation at break is directly corresponding to the decreased rubber size and improved dispersion in TPVs. Our work demonstrates the strong effect of melt shearing on the breakup of rubber particles and matrix orientation of TPVs as well. The isolation of the contribution of PP matrix orientation and rubber particle size on the tensile behavior of TPVs provides guidance for the preparation of new TPVs with high performance.
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