Viabilidade técnica de produção de compósitos de polietileno (HDPE) reforçados com resíduos de madeira e derivados das indústrias moveleiras

Abstract

The objective of this work was to analyze the production variables of polymeric composites reinforced with different type of wood and wood composites residues, generated by the furniture industries of Serra Gaúcha. Firstly, a diagnostic of wood residues generation was performed in the cities of Bento Gonçalves, Caxias do Sul, Flores da Cunha and Lagoa Vermelha. Three experiments of residue incorporations in composites with polyethylene were done with material supplied by the furniture industries (processed with a Drais mixer). The quality of the mixtures done with virgin and recycled HDPE, the efficacy of coupling agents and the influence of three different types of residues in the physical-mechanical properties of composites were analyzed. Wood sawdust of Pinus taeda and Apuleia leiocarpa, as well as medium density fiberboard (MDF) sawdust were utilized. Finally, a main experiment for the analysis of variables that influence extrusion process was performed. In this experiment, sawdust of Eucaliptus grandis and Pinus taeda wood was used with HDPE. It was also used MDF and particleboard sawdust. The mixtures were processed in two types of extruders: a 35mm single-screw, with rotation of 150 rpm and a co-rotational 30mm double-screw. After mixing, test specimens were injection molded. Four types of sawdust in proportions of 20, 30 and 40% and two processing methods were tested, in an incomplete factorial experiment that totalized 16 treatments. For material properties evaluation, mechanical tests of tensile strength, flexural strength and impact resistance were done, as well as composites chemical and physical characterization. The results showed influence of all analyzed variables in composites properties. The use of recycled HDPE did not affected composites quality, and the use of a commercial coupling agent improved tensile and flexural strength properties. The use of different types of sawdust in Drais mixer showed significant influence in density, tensile and flexural strength of the specimens. Sawdust proportion influenced average values of density and flexural modulus. In this experiment, elastic modulus expressed flexural properties in a better way than ultimate strength. There was the formation of bubbles in the pressing that caused increase in the porosity of the composite, affecting the tensile and flexural properties, mainly in the composites confectioned with Apuleia leiocarpa wood. In composites manufactured by extrusion, sawdust acted as a reinforcement filler and nucleation agent. The sawdust proportion showed significant correlation with all mechanical properties and with density of test specimens. Therefore, it was considered as parameter of importance in the determination of the composites HDPE/wood properties. There was better filler-matrix adhesion in composites fabricated by extrusion in relation to the confectioned in the Drais mixer. In this experiment, tensile and flexural strength were influenced by all studied variables and all interactions between variables were significant. In a general analysis, best results were obtained in double-screw extrusion process and for higher proportions of sawdust. MDF sawdust resulted in the largest while pine sawdust, the lowest mechanical properties values of the composites. The type of sawdust showed interaction with the process and proportion employed. It was confirmed the technical viability of furniture industry residue utilization in the production of wood-polymer composites. The control of sawdust type is fundamental for final product quality, being its choice dependent on the desirable quality and availability.