LaRC-IA polyimide fibers were extruded from the melt and drawn. The fibers were characterized by sonic pulse propagation, polarized optical microscopy, calorimetric analysis, X-ray diffraction, and tensile testing. When the amorphous, essentially isotropic, as-extruded filaments were heated slowly in a calorimeter, no “cold” crystallization could be detected. However, when these filaments were drawn at temperatures above the Tg of the polymer, they crystallized rapidly to produce oriented semicrystalline structures. The consequent increases in modulus and strength were significant, with the properties reaching the levels of commercial fibers of intermediate tenacity.
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Dorsey et al. (1999) studied this question.
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