Nanoindentation studies on polymorphism of nylon 6

In the present study, a nanoindentation technique is used to probe the hardness and modulus of the two crystal forms (i.e. γ-phase and α-phase) of nylon 6, which were formed by isothermal annealing at 60 and 200 °C, respectively. The crystal structures of nylon 6 were evidenced by X-ray diffraction. By nanoindentation, the hardness and elastic modulus of the γ-form crystals were found to be 53 and 50%, respectively, lower than those of the α-form crystals of nylon 6. The much higher stiffness and hardness of the α-form crystals may be related to the higher packing density of polymer chains originated from the stronger hydrogen bonding interchain interactions in the α-phase crystals.