ISOTHERMAL CRYSTALLIZATION KINETICS OF COMPATIBILIZED BLENDS OF POLYOLEFINS WITH A SEMIFLEXIBLE LIQUID-CRYSTALLINE POLYMER

A study of the isothermal crystallization behaviour and an analysis of the kinetic parameters of compatibilized blends of polyolefines (isot actic poly(propylene) (iPP) and high density polyethylene (HDPE)) with a semiflexible liquid crystalline polymer (LCP) SBH 1 : 1:2 of Eniric erche, Italy are presented in this work. The compatibilizers are ad ho c synthesized graft copolymers of the liquid crystalline polymer graft ed to functionalized poly(propylene) (PPAA) or polyethylene (PEox) - P P-g-SBH and PE-g-SBH copolymers, respectively. It has been established that the LCP dispersed phase in the blends plays a role in nucleation for the polyolefine matrix crystallization. This effect is more prono unced in the poly(propylene) matrix than in the polyethylene matrix, d ue to the lower crystallization rate of the former. The addition of PP -g-SBH copolymers (2.5-10 wt.-%) to 90/10 and 80/20 iPP/SBH (w/w) blen ds provokes a drastic increase of the overall crystallization rate of the iPP matrix and of the degree of crystallinity. Contrarily, the add ition of PE-g-SBH copolymers (2.5-8 wt.-%) to 80/20 HDPE/SBH (w/w) ble nds almost does not change or only slightly decreases the PE overall c rystallization rate. Moreover, the interpretation of the Avrami expone nts indicates that the iPP crystallization mechanism in the compatibil ized iPP/SBH blends remains unchanged only until a degree of conversio n of 0.7 and changes above this value; the PE crystallization mechanis m and the degree of crystallinity in the compatibilized HDPE/SBH blend s do not alter. The results were interpreted in terms of some differen ces in the compatibilization mechanism and efficiency of both types of graft copolymers (PP-g-SBH and PE-g-SBH). The relationships between b lend morphology and nucleation phenomena are discussed.