Crystallization kinetics of impact modified polypropylene

Abstract

Non-isothermal crystallization kinetics of PP homopolymer (PPHP), PP copolymer (PPCP) and nucleated PP copolymer (PPCPN) were studied using differential scanning calorimetry (DSC) at different cooling rates. Various kinetic models, namely, Avrami equation modified by Jeziorny, Ozawa method and the method developed by Mo were employed to describe non-isothermal crystallization kinetics of the samples. The Ozawa analysis failed to provide an adequate description of the crystallization process; however, the method developed by Mo was successful in describing the non-isothermal crystallization of PP samples. Different kinetic parameters such as Avrami exponent n, kinetic crystallization rate constant kc, another kinetic parameter F(T), crystallization temperature Tc, half life of crystallization t1/2 etc. were determined at various cooling rates. The difference in the values of Avrami exponent n in PPCPN indicated a heterogeneous nucleation and tridimensional spherulitic growth, whereas both PPHP and PPCP showed different nucleation and growth trends. The values of t1/2, kc and F(T) showed that in all samples crystallization rate increased with increase in cooling rate. Moreover, the crystallization rate of PPCPN was faster than that of other two samples at a given cooling rate. The activation energy for the transport of macromolecular segments to growing crystal surface was determined by using the Kissinger method. The lowest activation energy (ΔE) of PPCPN indicated a highest crystallization tendency than that of other two samples.