Thermal stability of blends of polyolefins and sisal fiber

This paper deals with the effect of acetylated and non-acetylated fiber on thermal degradation of blends of PP and polyolefins, specifically: PP/HDPE, PP/HDPE/functionalized EPR and PP/HDPE/non-functionalized EPR. To determine activation energy, the thermograms were analyzed through the Horowitz-Metzger (H-M), Coats-Redfern (C-R), and Reich-Stivala (R-S) integral methods. The studies have shown that the starting temperature of the decomposition of the fiber, whether treated or not, is maintained almost at the same level. Acetylated fiber stability was also found to increase, because activation energy ranged between 119 and 171 kJ/mol, depending on the method used; for non-acetylated fiber it was between 98 and 148 kJ/mol. This could be attributed to the fact that the fiber was fibrilized when it was treated with alkali, which resulted in a rough surface. This phenomenon can be the result of the substitution of OH groups by more voluminous ones, which brings about restrictions in the segmental mobility, thus increasing rigidity in the main cellulose chain. Activation energy of PP and PP/HDPE and PP/HDPE/functionalized and nonfunctionalized EPR blends ranges between 250 and 180 kJ/mol. When they are mixed with treated and non-treated fiber, a sudden decrease in activation energy is observed and this effect is slightly clearer with the untreated filler. This could be explained because mixing acetylated fiber with polymers results in higher polymer-filler interaction, which favors thermal stability of the compounds. These results let us infer that a satisfactory profit/cost relation justifies treating fiber for adding it to PP and to PP/HDPE and PP/HDPE/EPR blends. (C) 1999 Elsevier Science Ltd. All rights reserved.