The effect of pressure and clay on the crystallization behavior and kinetics of polyamide-6 in nanocomposites

The crystallization kinetics of polyamide-6 (PA-6) and its nanocomposite (PNC) with 2% clay were studied, using a pressure dilatometer (50 Mpa to 200 Mpa) to. follow the volume changes associated with the crystallization process. Isobaric experiments were carried out to evaluate the effect of pressure and clay on melting temperature (T-m) and crystallization temperature (T-c) of PA-6. The melting temperatures of PA-6 in the PNC were very close to those of PA-6 alone at comparable pressures, but the crystallization temperatures in the PNC were lower than those of PA-6 alone. The materials exhibited two crystallization zones in isothermal/isobaric experiments. The initial zone involved both the gamma-form and the alpha-form of PA-6, while in the latter zone the alpha-form was dominant. The Avrami equation was used to fit the isothermal/isobaric crystallization data. The Avrami exponent n was between, 1.0 and 3.2 for the gamma-form of unfilled PA-6, between 0.9 and 2.6 for the gamma-form in PNC and for the a-form of PA-6 alone, n was between 1.0 and 2.1 and in PNC between 1.2 and 2.6. The Avrami rate constants (K) for PA-6 and PNC depend on the experimental crystallization temperature as well as pressure. The rate of crystallization under similar conditions was higher for PNC. Infrared studies on compression molded PA-6 and PNC samples, cooled from melt at different rates, confirm the formation of the gamma-form in the initial stages of crystallization, as well as its transformation into the a-form at later stages. In the case of PNC, the gamma-form stabilized when the sample was quenched from melt.