Real-Time X-Ray Scattering Study of Processing of Thermoplastic Polymers: Effects of Stress

摘要

During the course of this research program we have contributed significantly to the understanding of structure/processing relationships in thermoplastic polymers crystallized from the melt. We concentrated efforts in metallocene- synthesized polyolefins, viz., polypropylene and polyethylene. Real-time wide and small angle X-ray scattering were performed to study the development of different crystallographic phases in PP and PE. Multiple crystallographic forms crystallize in PP, including the orthorhombic gamma and monoclinic alpha phases. Kinetics of crystallization were measured for each phase. We demonstrated that gamma crystallizes at higher temperature than alpha, but melts at lower temperature. Gamma does not convert into alpha upon heating. We showed that nucleation and growth is the mechanism of crystal formation (not spinodal decomposition, as suggested by others) Stress was incorporated into a study of effects of zone-drawing on the structure of PE. Structure was studied using molecular retraction, X-ray scattering and thermal analysis as functions of drawing stress and temperature.