Green coconut husk and curaua fibers were submitted to different chemical treatments—acid or alkaline followed by reaction with a silane compound—to improve compatibility between fiber and polypropylene (PP) matrix, in order to obtain composites with better properties than those of pure PP matrix for use as engineering materials. Fiber samples were analyzed before and after treatments to study the effects on thermal stability and morphology. The results showed that the crystallinity index and heat resistance significantly increased when the alkaline treatment followed by silane reaction was applied to both fibers. In this case, the crystallinity index increased from 53% in the coconut fiber in natura to 67% in the treated fiber. Regarding curaua fiber, the increase was from 61% to 81%. The degradation onset temperature of coconut fiber increased from 255℃ to 272℃ and of curaua fiber from 275℃ to 314℃. The treated fibers were mixed with a commercial PP matrix in a twin-screw mini-extruder at 180℃. The composites were analyzed by SEM to observe the compatibility between cellulose fibers and PP matrix.
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