Preparation and Characterization of Polypropylene Homocomposites: Exploiting Polymorphism of PP Homopolymer

In this study, the properties of polypropylene (PP) homocomposites, prepared by film-stacking followed by hot pressing, were investigated. Alpha- and beta-PP served as matrices, whereas highly oriented PP tapes of the alpha form acted as reinforcement in the homocomposites. Tapes with different draw ratios (DR = 6-12) have been produced and characterized by mechanical and wide-angle X-ray scattering measurements. Tapes with a DR = 8 were incorporated in a cross-ply (CP) manner in the corresponding homocomposite laminates. Specimens were subjected to static (tensile, flexural) and dynamic (instrumented falling weight impact, IFWI) tests. The thermal and thermomechanical properties of the PP tapes and homocomposites were studied by differential scanning calorimetry and dynamic mechanical thermal analysis. The homocomposite morphology was probed by polarized light microscopy, which gave evidence of transcrystalline layer at the interface between tape and matrix. The storage modulus of the CP homocomposites was improved prominently by the tape reinforcement. In static tensile tests, the homocomposites exhibited much higher stiffness and strength when compared with the neat PP specimens. However, this was accompanied with a marked reduction in the ultimate elongation. The IFWI tests showed that both alpha- and the beta-PP failed in macroscopically brittle manner, whereas the corresponding homocomposites failed in semiductile way. The homocomposite laminates prepared with beta-PP matrix exhibited higher resistance to penetration than those with alpha-PP. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 684-691, 2010.