Compatibilização química em compósitos de PLA reforçados com fibras de sisal

Abstract

Even though poly(lactic acid) (PLA) is fragile under impact and has low toughness, the polymer stands out for its stiffness and high tensile strength. This polymer is an interesting material not only for short-term applications, such as disposable products, but is also suitable for durable goods. Although PLA is a potential substitute for conventional polymers, its use is limited by high costs. Incorporation of vegetal fibers in PLA matrix has been evaluated as a manner of costs reduction and, consequently, raise the economic competitiveness of the polymer. Poor interfacial adhesion has been observed as consequence of chemical incompatibility of the phases in the composites, resulting in unsatisfactory mechanical performance. Addition of PLA grafted with maleic anhydride, PLA-g-MA, is a possible alternative to improve interfacial adhesion. Aiming costs reduction and, simultaneously, enhance or, at least, maintain PLA’s high mechanical performance, this project investigated the effects of addiction of two types of compatibilizers, prepared by reactive extrusion, with different chemical characteristics: one of them with higher molar mass and lower acidity content and the other with lower molar mass and higher acidity content. Composites containing 10 and 30% wt of sisal fibers were prepared by extrusion. Two levels of compatibilizers mass content, 2 and 6%, were used in formulations. Results of size exclusion chromatography analysis revealed intense molar mass reduction of the matrixes during processing, in presence of sisal fibers. In contrast, the presence and content of compatibilizer had no significant influence on matrixes degradation. Nucleating effect of sisal fibers to PLA crystallization on composites was verified. Were attained increases of 90 and 120% on impact strength and Young modulus in composites, respectively. The objective of maintaining the tensile strength of PLA in the composites was achieved. Meanwhile, no gains were reached on the property, even in presence of compatibilizers.