The effect of supercooling of the melt on the semicrystalline morphology of PA 66

•FSC was used to prepare isothermally crystallized samples of PA 66.•XRD, AFM, and POM were used to characterize the morphology.•High temperatures produced lamellar α-crystals arranged in spherulitic superstructure.•Low temperatures produced the γ-mesophase which is non-lamellar, particle-like shape.•A change in the crystallization mechanism occurs at a temperature of about 115°C.