Isothermal crystallization kinetics of nylon 6, blends and copolymers using simultaneous small and wide-angle X-ray measurements

Crystallization behavior in a number of blends and copolymers of nylons (polyamides) was investigated using time-resolved X-ray scattering data obtained simultaneously in the small- and wide-angle regimes. The following samples studied were: nylon 6 homopolymers (N6) of different molecular weights, copolymers of N6 and nylon 6,6 (N6/66), and blends of these with an amorphous nylon (N6I/T), which is a 70:30 random copolymer of poly(hexamethylene isophthalamide) and poly(hexamethylene terephthalamide). Addition of comonomers and blending with the N6I/T reduces the crystallinity of N6. Isothermal crystallization data obtained at several temperatures showed the expected faster crystallization kinetics at higher degrees of supercooling. Comonomer units in the N6 backbone reduce the rate of crystallization. N6I/T affects the crystallization (lamellar growth) behavior of N6/N66: the rate is higher at temperatures above the T_g of N6I/T (120 °C) where the crystallization is nucleation-driven, and lower below the T_g of N6I/T where it is growth-driven. Lamellar spacing decreases with an increase in the degree of supercooling, and this decrease is smaller in the blends than in the homopolymer. Larger lamellar spacing in N6I/T blends is due not to the insertion of N6I/T segments into the interlamellar regions but to an increase in the lamellar thickness. Blending seems to change the morphology by affecting the crystallization behavior rather than by thermodynamic phase separation. Residual monomers, which act as plasticizers, dramatically reduce the crystallization rate, whereas shear or similar mechanical history of the resin considerably accelerate the crystallization rate.