The Study Of Orientation And Crystallization Of The Polypropylene Prepared By Melt Stretching

Polypropylene (PP) as the second largest plastics, widely used, has its own shortcomings of poor impact performance. So to improve the performance of the PP has been the research focus. During processing polymer melts are generally subjected to different types of flow field. Flow field affects the crystallization of polymer through inducing orientation and stretch of chain, whose effects show up in different ways such as accelerating crystallization kinetics, modifying the morphology from spherules to shish-kebab, and inducing new crystal forms. Consequently, the performance of the resulting product depends strongly on the flow field during processing.In this thesis, the melt iPP was stretched to prepare the fiber and sheet, by changing the stretching rate, (β-nucleating agent content and crystallization temperature. The small angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry heat (DSC) were carried out to study the morphological structure of iPP fiber and sheet. The main results are as follows:(1) The degree of crystallization of iPP sheet is at the same level under different SRs. These results can be attributed to the higher level stretching and the content ofβ-NA. The processing of stretch and temperature field has led to the different orientation of the crystal structure. The stretch field andβ-NA could increase the content of (3 phase, which has the same trend of pure iPP.(2) Pure iPP fibers are affected by stretching very strongly. The higher the stretching rate, the greater the density ofα-row nuclear is. The growth rate of a phase is very fast, limited space in the fiber will soon be covered with a phase, which is collided with each other soon. Thus the formation of the p-crystal was inhibited.(3) When a small amount of p-NA was added, the degree of orientation of the molecular chain was not high under low stretch rate. When the stretch rate was further enhanced, the degree of orientation can be significantly improved at the same content ofβ-NA. The degree of orientation could be improved under higher lower stretch rate (50cm/min) and higher contentβ-NA. When the stretch rate was further improved, the molecular orientation degree of iPP fiber with low content ofβ-NA was at the same level. When theβ-NA was added in iPP, the surface free energy of the conformational change required was reduced.