Crystallization of polyamide 11 during injection molding

The semicrystalline morphology of injection moldings of polyamide 11 (PA 11) prepared using mold temperatures of 25, 50, and 80°C was investigated. Regardless of the mold temperature, position-resolved X-ray diffraction (XRD) and polarized-light optical microscopy (POM) revealed presence of poor/imperfect α-crystals with an almost hexagonal arrangement of molecular stems in a nonspherulitic superstructure in the skin, and formation of α-crystals and spherulites in the core. With increasing mold temperature, the thickness of the skin layer decreased, and the perfection of α-crystals and the spherulite size in the core increased. The experimental observations are discussed in terms of predicted crystallization temperatures, with the prediction based on cooling-rate simulations for the various parts of the injection moldings using Moldflow^® and analysis of crystallization of the relaxed melt using fast scanning chip calorimetry, XRD, and POM. It is shown that the structure gradient in PA 11 injection moldings can be forecast without considering the effects of shear for this particular polymer. POLYM. ENG. SCI., 58:1053–1061, 2018.