In this study, PA 66 and PA 6 fibers are heat set at temperatures between 25 and 200°C. Fractional recovery (f) depends on heat setting temperatures and crystallinity, which provides partial crosslinking that delays the onset of the flow regime and increases the time constant of relaxation at a given temperature. Mechanical properties are examined with an Instron tensile tester, and the effect of heat setting temperatures on mechanical properties is correlated with crystallinity changes. The terminal modulus and extension at break show a direct correlation with crystallinity, while there is no noticeable effect on initial modulus with crystallinity changes.
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