Crystallization kinetics of miscible thermosetting polymer blends of novolac resin and poly(ethylene oxide)

Results of an investigation of isothermal crystallization and melting behavior of both uncured and hexamine-cured novolac/poly(ethylene oxide) (PEO) blends were reported. The crystallization behavior of PEO in blends is strongly influenced by factors such as composition, crystallization temperature, and cross-linking. The time dependence of the relative degree of crystallinity deviated from the Avrami equation at high conversion. The addition of non-crystalline component into PEO caused a depression in both the overall crystallization rate and the melting temperature. The influence of curing on the crystallization and melting behavior of PEO is rather complicated. In general, curing led to increase of the overall crystallization rate of the blends, and enhanced the nucleation rate of PEO. The crystallization mechanism of PEO changed after curing. Curing also resulted in relatively slow depression of equilibrium melting point, and reduced the stability of PEO crystals in the blends. Experimental data on the overall kinetic rate constant Kn were analyzed according to the nucleation and growth theory. The surface free energy of folding σ(e) showed an increase with increase of novolac content for the uncured blends, whereas σ(e) displayed a maximum at 90/10 PEO/novolac composition for the cured blends.