Analysis of nylon 66 solidification process

A methodology capable to describe the relationship between heat transfer from the melt, during the cooling process, and the development of crystallinity for a thermoplastic like Nylon 66 have been developed. To simulate the crystallization process two kinetics model were used: the Avrami model for isothermal processes and the Kamal equations for non-isothermal ones, both associated with a non-stationary balance of energy. For Nylon 66, both models studied were found to fit very well experimental values within the whole range of studied temperatures and cooling rates. In the case of isothermal crystallization, that is when outer surfaces are kept at constant temperatures, the temperature profile changes from the initial melt temperature to the final one, with a rate that gets lower as the crystallization zone moves away from the external surface. Otherwise, temperature profiles obtained by the non-isothermal crystallization process, showed three zones: two of transition and one intermediate where all points are cooled at some rate. Crystallinity profiles show a plateau shape when crystallization is isothermal, being plain in case of non-isothermal one. Experimental temperature and crystallinity profiles are theoretically simulated by means of the proposed procedure. Finally, tensile and impact properties do not show significant dependence with the used cooling rates (5-20 degreesC min(-1)). (C) 2001 Elsevier Science Ltd. All rights reserved.