ANALYSIS OF LAMELLAR STRUCTURE IN SEMICRYSTALLINE POLYMERS BY STUDYING THE ABSORPTION OF WATER AND ETHYLENE-GLYCOL IN NYLONS USING SMALL-ANGLE NEUTRON-SCATTERING

Preferential diffusion of deuterated solvents into the amorphous regio ns of a semicrystalline polymer enhances the contrast between the crys talline and amorphous regions measurable by small-angle neutron scatte ring. This scattering in nylons from the diffusion of D2O and deuterat ed ethylene glycol (d-EG) is analyzed by identifying the distinct cont ribution to scattering From the two amorphous regions, one in the inte rlamellar spaces and the other outside the lamellar stacks. The centra l diffuse scattering (I-d) is the non-Bragg, liquidlike, or independen t scattering, and is attributed to the solvents (D2O/d-EG) in the amor phous domains outside the lamellar stacks. The lamellar scattering (I- l) is the interference peak from the lamellae in the stacks and is use d to evaluate the distance between the lamellae, the thickness of the interlamellar spaces, and the coherence length of the lamellar stacks. The invariant calculations show that 70%-80% of the lamellar stack is crystalline. About one-third of the amorphous material in a highly cr ystalline nylon is in the interlamellar space, and two-thirds is outsi de the lamellar stacks. The thickness of the interlamellar amorphous r egions into which solvent molecules diffuse varies from 10 to 60 Angst rom depending on the thermal history and is a major contributor to the observed increase in lamellae spacing. Structural changes in nylon 6 immersed in water are accelerated at 125 degrees C, and this temperatu re could be the hydrated-equivalent of the Brill transition observed a t 160 degrees C in dry nylon 6. Water or EG diffuses into the fold sur faces of nylon lamellae at elevated temperatures, and subsequent struc tural changes are accompanied by hydrolysis of the nylon chains. EG be ing a stronger solvent reduces the lamellar thickness at elevated temp eratures.