Polyamide 6-wheat straw composites: Degradation kinetics

Degradation kinetics of ground wheat straw (WS), polyamide 6, and a WS-polyamide 6 composites obtained from extrusion were investigated. 15 wt% of ground WS was melt blended with other additives naming; lithium chloride salt (LiCl) and N-butylbenzenesulfonamide plasticizer (N-BBSA) as matrix treatments. The additives were added to reduce the melting point of polyamide 6 and ease of composite processing (reduction in processing temperature and time). Two commonly used non-isothermal kinetic models were used to investigate the degradation kinetics of WS and the composite. Thermal gravimetric analysis was utilized to measure the thermal stability and degradation kinetics of different composite formulation. The activation energy of WS was identified by iso-conversional Friedman kinetic method. Through this method, WS activation energy was found to be around 141.4 kJ/mol. Composite kinetic studies were based on the Coats and Redfern procedure. It was concluded that the composite activation energy was correlated to the residual weight percentage of the composite at the maximum thermal degradation temperature. The onset of degradation of WS was dictated by the thermal stability of its lignin content and was found to be around 188 degrees C. WS, however, did not go through a major degradation up to 245 degrees C at which drastic decomposition starts. This temperature range overlaps with processing temperature of Polyamide 6 and required matrix/WS treatments. Addition of salt and plasticizer individually or with each other at any level decreased the onset of degradation temperature. Addition of plasticizer at 4 wt% level, however, shifted the degradation peak to higher temperature representing a more thermally stable composite. POLYM. COMPOS., 2012. (C) 2012 Society of Plastics Engineers