Polymer, Vol.72, 104-112, 2015
Highly oriented microstructures and surface mechanical properties of polypropylene (PP) molded by ultra-high shear rate
Raman spectroscopy and wide-angle X-ray diffraction (WAXD) were used to evaluate microstructures, i.e. molecular orientation, crystalline orientation and the relative amount of beta-phase crystal (K), near the surface of injection molded polypropylene (PP). It was found that highly ordered structure near the surface (0-30 mu m) was formed when ultra-high injection speed (1000 mm/s or (gamma) over dot = 1670 s(-1)) was utilized. Subsequently, increase of relative amount of beta-phase crystal near the surface was achieved. The relationship between the microstructures and surface mechanical properties measured by micro-cutting method and progressive load scratch tests was investigated. The highly oriented PP showed higher surface mechanical properties due to the increase in degree of molecular and crystalline orientation. The increased scratch properties were considered to be also affected by higher beta-phase crystal content. (C) 2015 Elsevier Ltd. All rights reserved.
Keywords:Polypropylene;Ultra-high speed injection molding;Scratch behavior;Highly oriented micro-structure