Thermal degradation of a phenolic resin, vegetable fibers, and derived composites

The thermal degradation behavior of resol, several vegetable fibers (two types of cotton fibers, sisal and sugar cane bagasse) and derived polymer composites have been investigated using thermogravimetric analysis (TGA). The initial thermal degradation temperature T-ONSET, the temperature at the maximum degradation rate TDM, and the char left at 500 degrees C corresponding to the crosslinked resol were higher than the values measured for the fibers and their composites. Thus, the addition of the fibers reduced the thermal resistance of the phenolic thermoset. The polymer and the fiber-composites showed a complex degradation involving different thermal decomposition processes. For that reason, the DTG curves were deconvoluted and a phenomenological kinetic expression was found for each individual peak. The overall thermal decomposition curve was recalculated adding each degradation process weighted according to its contribution to the total weight loss. An increase in the activation energy corresponding to the cellulose degradation was observed in the composites, highlighting the protective action of the resin encapsulating the fibers. (c) 2007 Wiley Periodicals, bic.