Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical Technology, Beijing 100029, China.
Soft Matter. 2014 Mar 21;10(11):1816-22. doi: 10.1039/c3sm52375f.
The breakup of the rubber phase in an ethylene-propylene-diene monomer (EPDM)/polypropylene (PP) blend at the early stage of dynamic vulcanization is similar to that in an unvulcanized EPDM/PP blend because of the low crosslink density of the EPDM phase. In this work, the minimum size of the rubber phase in the unvulcanized EPDM/PP blend was first calculated by using the critical breakup law of viscoelastic droplets in a matrix. The calculated results showed that the minimum size of the rubber phase in the unvulcanized blend was in the nanometer scale (25-46 nm), not the micrometer scale as reported in many works. Meanwhile, the actual size of the rubber phase in the thermoplastic vulcanizate (TPV) at both the early stage and the final stage of dynamic vulcanization was observed by using peak force tapping atomic force microscopy (PF-AFM). The results indicated that the EPDM phase indeed broke up into nanoparticles at the early stage of dynamic vulcanization, in good agreement with the calculated results. More interestingly, we first revealed that the micrometer-sized rubber particles commonly observed in TPV were actually the agglomerates of rubber nanoparticles with diameters between 40 and 60 nm. The mechanism for the formation of rubber nanoparticles and their agglomerates during dynamic vulcanization was then discussed. Our work provides guidance to control the microstructure of the rubber phase in TPV to prepare high performance TPV products for a wide range of applications in the automobile and electronic industries.
在动态硫化的早期阶段，乙丙二烯单体（EPDM）/聚丙烯（PP）共混物中橡胶相的破裂与未硫化的 EPDM/PP 共混物相似，这是由于 EPDM 相的交联密度较低。在这项工作中，首先使用基体中粘弹性液滴的临界破裂规律计算了未硫化的 EPDM/PP 共混物中橡胶相的最小尺寸。计算结果表明，未硫化共混物中橡胶相的最小尺寸处于纳米级（25-46nm），而不是许多工作中报道的微米级。同时，使用峰值力敲击原子力显微镜（PF-AFM）观察了热塑性硫化胶（TPV）在动态硫化的早期和最终阶段的橡胶相的实际尺寸。结果表明，EPDM 相确实在动态硫化的早期阶段分裂成纳米颗粒，这与计算结果吻合较好。更有趣的是，我们首次揭示了在 TPV 中通常观察到的微米级橡胶颗粒实际上是直径在 40-60nm 之间的橡胶纳米颗粒的团聚体。然后讨论了在动态硫化过程中形成橡胶纳米颗粒及其团聚体的机理。我们的工作为控制 TPV 中橡胶相的微观结构提供了指导，以制备用于汽车和电子工业等广泛应用的高性能 TPV 产品。
