剪切塑性变形聚丙烯的形态和冲击断裂行为

Morphology and Impact Fracture Behavior of Plastically Shear Deformed Polypropylene

采用光学显微镜(ROM)、扫描电子显微镜(SEM)、广角X射线衍射(WAXD)、动态力学分析(DMA)和仪器化冲击仪对剪切塑性变形后等规聚丙烯(iPP)的结构和性能进行了研究。剪切塑性变形通过等通道转角挤压技术获得。结果表明,剪切塑性变形使iPP球晶变为近椭圆形,其长轴沿着剪切方向取向排列,iPP的结晶度降低,动态储能模量(E')增加,晶片间分子链活动性降低。根据微纤模型分析剪切变形后iPP的冲击断裂行为,表明取向微纤和系分子的存在使iPP的断裂需要更多的裂纹引发能和扩展能,并带来悬臂梁缺口冲击强度的增加,是未变形试样的4.8倍。

Reflected optical microscopy （ROM）, scanning electron microscopy （SEM） and wide angle X-ray diffraction （WAXD）, and dynamic mechanical analysis （DMA） and instrumented impact tester were utilized to study the structure and property of isotactic polypropylene （iPP） after plastically shear deformed. The equal channel angular extrusion technique was used to achieve the shear condition. The results show that the original spherulites are deformed into nearly ellipsoids with their long axis tilted along the shear direction, the degree of crystallinity decreases, the dynamic storage modulus （E＇） increases with reduced mobility of the molecular chains in the amorphous region. The impact fracture behavior of the shear deformed iPP was discussed according the fibrillar model, which suggested that the oriented fibrillar structure and the stretched molecular chains are responsible for the increase of energy required for crack initiation and propagation, resulting in the improvement of impact strength of iPP, as much as 4.8 times of that of the un-deformed sample.