HIGH-MODULUS POLYPROPYLENE - EFFECT OF POLYMER AND PROCESSING VARIABLES ON MORPHOLOGY AND PROPERTIES

The morphology and properties of high modulus polypropylenes (PP) are characterized over a wide range of material variables. These variables include the tacticity, room temperature xylene solubles (XSRT), molec ular weight, melt flow rate (MFR), and polydispersity index (PI). Flex ural modulus in quench-cooled compression moldings of propylene homopo lymer can be correlated to the volume fraction crystallinity, phic, by an empirical logarithmic dependence. The quantitative zero orientatio n results for the quench-cooled compression moldings provide an approx imate crystallinity normalization for oriented moldings. WAXS analyses of crystalline orientation were determined over a range of melt tempe ratures and mold locations and correlated to the skin area fraction by optical microscopy. WAXS analysis of the balance of orientations for the crystallographic axes suggest that the orientation balance is prim arily determined by the ''melt orientability'' of the resin type. An e mpirical description of flexural modulus in injection molded PP is dev eloped for the range of material variables and molding conditions stud ied. This description is represented as a function of crystallinity-no rmalized modulus vs. the frozen-in crystalline orientation.