Blends of polypropylene resins with a liquid crystalline polymer. I. Isothermal crystallization

The isothermal crystallization kinetics of blends of different polypropylene (PP) resins and a liquid crystalline polymer (LCP) after two different melting conditions (200 and 290°C) were studied by DSC and polarized light optical microscopy. The resins were a homopolymer (hPP), a random copolymer with ethylene (cPP), and a maleic anhydride grafted PP (gPP). The LCP was Vectra A950, a random copolymer made of 75 mol % of 4‐hydroxybenzoic acid and 25 mol % of 2‐hydroxy,6‐naphthoic acid. It was observed that the overall crystallization rates of all the blends after melting at 200°C were higher than those after melting at 290°C. The LCP acted as a nucleating agent for all the PP resins; however, its nucleating effect was stronger for the hPP than for the cPP and gPP resins. After both melting conditions, an increase was observed in the overall crystallization rate of the hPP and gPP resins with the increase in the amount of LCP, but not in the cPP crystallization rate. The fold surface free energy σe of hPP and cPP in the blends decreased, but increased in the gPP blends. Finally, all the PP resins formed transcrystallites on the LCP domain surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 916–930, 2003