Physical Aging and Young's Modulus of Polyamide 11 Containing Different Crystal Polymorphs

Variation of the conditions of melt‐crystallization of polyamide 11 (PA 11) yields largely different semicrystalline morphologies, including spherulitically arranged triclinic α‐crystal lamellae on slow cooling and a nodular pseudo‐hexagonal mesophase not arranged in a higher‐order µm‐scale superstructure on fast cooling. For samples of a similar fraction of the ordered phase, Young's modulus of PA 11 containing α‐crystals is almost twice than that of PA 11 containing mesophase. Specific annealing experiments allowed reorganization of the mesophase to α‐crystals without a qualitative change of the overall semicrystalline morphology but a significant increase of Young's modulus, which scales with the maximum annealing temperature and suggests that the modulus of elasticity of crystals is significantly higher than that of the mesophase. Long‐term annealing of high‐temperature crystallized PA 11 containing α‐crystals in a space‐filled spherulitic superstructure at ambient temperature does not cause a change of Young's modulus. For rapidly cooled, low‐temperature crystallized PA 11, containing mesophase, the modulus increases over a period of days and weeks, with the increase scaling with the fraction of initially available crystallizable amorphous structure, allowing for glass relaxation and continuation of crystallization. The performed study allows precise adjustment of Young's modulus of polyamide 11 in a wide range.