Abstract
Commercial nylon 66 fiber was heated in N2 atmosphere or in vacuum to several temperatures below the melting point. ηsp/C of the polymer solution increased strikingly with heating in vacuum but little with heating in N2. The activation energy for the post-polymerization in vacuum is found to be 16.6 kcal/mol. Tensile strength, elongation and Young's modulus decreased with heating except the heating in vacuum at 253°C, by which the elongation was little influenced. The crystallinity measured by the density method increased with heating noticeably in comparison with that measured by X-ray method. The crystalline and amorphous orientations changed little with heating in vacuum. Superheating at the melting point measured by DTA method occurred slightly with heating in vacuum. The little decrease in the tensile elongation of the fiber heated in vacuum at 253°C could be explained by the formation of tie molecule and cross linkage during the post-polymerization. The formation of cross linkage is supported by the increased tensile properties upon moisture absorption.
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