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.
Abstract. Malva fiber was submitted to alkali treatments with NaOH aqueous solutions at different concentrations, times and temperatures. Fiber samples were analyzed before and after treatments to study their effects on crystallinity, thermal stability and morphology. The results showed that the crystallinity index and thermal resistance significantly increased when the alkaline treatment was conducted with 7 % NaOH solution. Higher concentrations of NaOH, such as 10, 15 and 20 %, did not considerably increase the fiber crystallinity index. By X-ray diffraction, it was observed that defibrillation occurred in mercerized fibers, which is expected to be advantageous for use as fiber reinforcement in polymer matrices. The same fiber samples were mixed with a poly(3-hydroxybutyrate) matrix in a twin-screw miniextruder at 453 K. The composites were analyzed by TGA and DMA to evaluate the influence of fiber addition in mechanical and thermal properties of the polymer.
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