Valorização e caracterização de compósitos poliméricos biodegradáveis produzidos a partir de resíduo lignocelulósico da casca de castanha-do-Brasil

Abstract

Ecological and renewable composites made from lignocellulosic fibers are increasingly being used to replace conventional materials made from composites of synthetic materials to reduce the effect of greenhouse gas emissions. In this context, polymer composites with plant fibers are emerging as a promising alternative in the field of materials for various engineering applications. With this in mind, the aim of this study was to obtain and characterize three biodegradable composite materials made from lignocellulosic waste and modified through the chemical treatment of Brazil nut shells (Bertholletia excelsa) and castor oil-based polyurethane resin. The fibers underwent chemical modification (mercerization and bleaching) using NaOH and H₂O₂ solutions and were characterized together with the raw bark fibers in terms of their physicochemical, mechanical, and morphological properties. The preparation method was carried out in accordance with ABNT-NBR 14810-2, using the hot compression molding technique. Three composites were produced, one with in natura, mercerized and bleached fibres. The physical tests: moisture, density, and swelling; the mechanical tests: static bending, elasticity and the morphological test of these composites were evaluated and compared. When evaluating the cellulose content of fresh, mercerized and bleached chestnut shells and comparing them with those obtained in other studies, it was possible to highlight different and significant levels of 42.48%, 60.28% and 71.04% respectively, which is due to the partial or total removal of extractives and lignin. By XRF, for mercerized and bleached fibers. the residue is rich in Na with (43.36%) and (58.30%) respectively, followed by potassium (26.00%) and the highest percentage of calcium for the mercerized (19.03%). TGA analysis showed the stages of thermal degradation of the materials. The mechanical tests showed a significant increase in the tensile strength of the treated fibers. The composites are characterized as medium-density fibreboard (MDF) according to the standards. The micrographs of the composites obtained by SEM after the mechanical tests showed an improvement in fiber adhesion to the matrix with the chemical treatments. Thus, this study showed that composites made from Brazil nut shells and resin (PU) have great potential in the market, as they are made from renewable sources, at a low cost from a waste that is little used, adding value and giving the possibility of new applications compared to composites made from synthetic fibers.