Influence of accelerated aging on clay-reinforced polyamide 6

Organically modified clay-reinforced polyamide 6 was subjected to accelerated heat aging to estimate its long-term thermo-oxidative stability and useful lifetime compared to the virgin material. Changes in molecular weight, and thermal and mechanical properties were monitored and connected to the polymer modification encountered during aging. The incorporation of the clay filler was found to result in moderate polymer degradation during processing, which became more pronounced with aging time at elevated temperature, imparting discoloration. Post-crystallization was favoured by short periods of heat exposure, leading to an increase of crystalline content. Conversely, extended chain scission occurring after prolonged residence time negatively affected crystallites' size, lowering the degree of crystallinity. The aging-induced transformations of crystal structures correlated well with materials' mechanical performance, yielding initially hard and brittle specimens which gradually adopted a softening behavior. Relative to the unfilled polymer, the loss of ductility during aging was milder in the case of nano-composite, indicating that the clay filler restricted degradation, prolonging durability. (C) 2008 Elsevier Ltd. All rights reserved.