Morphology of gamma-irradiated polypropylene gels crystallised from xylene solution—2. Kinetics of melting and crystallisation

Abstract

The kinetics of melting and the non-isothermal crystallisation of PP gels obtained through irradiation in bulk, boiling in xylene and subsequent drying was investigated by means of DSC. When the irradiation dose increases the melting temperatures decrease, the enthalpies are low and do not depend on the dose applied. At constant temperature the melting rate increases with the dose. The viscosity of the superheated crystals and the activation energy for transport through the phase boundary crystal-melt decrease with the dose. The temperatures of non-isothermal crystallisation decrease when the irradiation dose increases. The crystallisation rate decreases with dose at constant temperature. The viscosity of the supercooled melts increases sharply with dose. The dependences described confirm the suggestion that the primary nucleation during the gel formation and their subsequent recrystallisation does not depend on the dose. The general crystallisation rate includes both the secondary nucleation rate and the growth rate of the lamellae, which depends on the diffusion of crystallisable molecules in the viscous melt. The data obtained prove the validity of the previously defined rate of non-isothermal processes and further the possibility for application of the equations of kinetics of melting and non-iosthermal crystallisation.