Morphological and mechanical properties of nylon 6 gel and melt films

Abstract

Nylon 6 films were prepared by gelation/crystallization from solutions and by molding from melt state. The resultant gel and melt films were elongated in a hot oven at 205°C under nitrogen. As co-solvent mixtures in preparing gel films, the formic acid/chloroform compositions studied were 100/0, 75/25, and 50/50. The mechanical properties of the gel films were hardly affected by composition but the gel film with the 75/25 composition could be readily elongated in comparison with those with the 100/0 and 50/50. The Young’s moduli and the tensile moduli for all the specimens are less than 5 and 0.15 GPa, respectively. The values of the Young’s moduli are much lower than the crystal lattice modulus (183 GPa) of nylon 6. To determine the reason for the poor mechanical properties of these specimens, the morphological properties of the gel film with the 75/25 composition, as an example, were investigated in comparison with those of the melt film by using wide angle X-ray diffraction, small angle X-ray scattering, and small angle light scattering. Deformation was found to be independent of a crystal transformation from a folded to a fibrous type and the preferential orientation of the crystal fiber axis (the b-axis) is mainly due to the rotation of crystallites leading to taut tie molecules. This mechanism hampers ultradrawing of nylon 6 films to realize high modulus and high strength. © 1988 The Society of Polymer Science, Japan.