The crystallization kinetics of polyamide 66 in non-isothermal and isothermal conditions: Effect of nucleating agent and pressure

The crystallization kinetics of virgin and nucleated polyamide 66 was inves tigated in non-isothermal and isothermal conditions, by use of DSC and high pressure dilatometry. In non-isothermal conditions, at atmospheric pressur e, the results were first analyzed using the Ozawa equation, leading to an Avrami exponent of 4 in the case of the virgin grade and 2.1 for the nuclea ted polyamide. However, experimental and calculated kinetics showed a diffe rence in the ending part of the crystallization, likely due to a large seco ndary crystallization phenomenon. Thus, the relative crystallinities were n ormalized to extract the primary crystallization from the whole signal and analyzed using the Douillard/Kim equation. In isothermal conditions, at atm ospheric pressure, the Avrami exponents were similar to the values obtained in non-isothermal conditions for both virgin and nucleated grades. Further more, the crystallization under pressure was examined in terms of crystalli zation supercooling. In non-isothermal conditions, the crystallization supe rcooling (Delta Tc) increases when the cooling rate increases, but it is no t affected by the pressure since the crystallization temperature increase i s due to the equilibrium melting temperature rise. In isothermal conditions , the supercooling (Delta T) rises according to the increase of the pressur e for the same crystallization temperature.