Valorização de resíduos de feijão na produção de materiais compósitos

Abstract

Bean agricultural production in Brazil is large-scale. Concomitant with high industrial production, there is a significant generation of waste. Given this context, this study aimed to analyze the use of bean (Phaseolus vulgaris) stems and pods in the production of three types of composite materials: agglomerates, gypsum composites, and polymeric composites. To this end, bean crop residues were first characterized in their natural state. Subsequently, these lignocellulosic elements were incorporated into wood panels produced with a urea-formaldehyde adhesive, through different levels of mass replacement (0%, 25%, 50%, 75%, and 100%) of Pinus oocarpa wood with particles of the byproduct. In gypsum composites with a constant water:gypsum ratio of 0.6, on the other hand, bean waste particles were embedded in the matrix through different mass substitution rates (0%, 2.5%, 5%, 7.5%, and 10%) of gypsum by waste. Finally, bean waste particles were also incorporated into polymeric composites through different mass substitution rates (0%, 10%, 20%, 30%, and 40%) of recycled low-density polyethylene (LDPE) by bean waste particles. The impacts of the presence of bean waste on the composites were analyzed based on the results of physical and mechanical tests. The bean waste presented an apparent density of 0.24 g/cm³, and lignin contents of 8.13%, holocellulose of 56.55%, extractives of 8.16%, and ash of 16.94%. In particleboards, the incorporation of such residues did not significantly influence the apparent density of the samples demonstrated. Furthermore, there was an increase in compaction ratio, water absorption, and thickness inchage properties, and a reduction in mechanical properties proportionally to the higher pine wood replacement rate by residues. On the other hand, in gypsum composites, there was an increase in thermal and acoustic insulation in composites with the presence of bean residues. Furthermore, in theoretical substitutions of up to 5.0% of gypsum by lignocellulosic material, there was a decrease in moisture content and an increase in most of the proven mechanical properties. In polymeric composites, the results showed that the lignocellulosic material caused a decrease in density and mechanical properties and an increase in water absorption properties after 24 h of experimentation and moisture content; these results were correlated with voids, cracks, and stress concentration points found in the micrographs. Furthermore, in the flammability test, the bean residues developed greater flame propagation. Thus, the research presented important results evolving in the propagation of processes with lower environmental impact and generation of products with higher added value, mainly in furniture, construction, and precast materials industries such as plates, decks, brise-soleils, among others.