Filmes nanoestruturados desenvolvidos a partir de pseudocaule de bananeira e casca de café

Abstract

The objective of this work was to evaluate the physical, mechanical and optical characteristics of the nanostructured films obtained from post-harvest residues of banana (pseudocaule) and coffee (coffee husk). It was also used, for comparative purposes, the commercial pulp of eucalyptus previously treated through industrial processes of pulping and bleaching. In order to do so, the banana pseudocaule and coffee husk fibers underwent chemical pre-treatments (alkaline and bleaching / Alkaline) to remove the non-cellulosic constituents present in their structures, aiming at the production of cellulosic nanofibrils for later nanostructured films . The chemically pretreated banana pseudocaule and coffee bark fibers were transformed into cellulose nanofibrils using the mechanical defibrillation method using the Super Masscolloider Masuko grinder. Different passages (20 and 40) were evaluated. Nanofibrils were characterized by electron microscopy (SEM / FEG), crystallinity (XRD) and thermal stability (TG / DTG). The chemical pre-treatments were effective in the removal of the amorphous components of the fibers, increasing basic density, thermal stability and crystallinity, allowing the preparation of cellulose nanofibrils from these pretreated materials. The increase in the number of passages (from 20 to 40) by the grinder led to a decrease in the size of nanofibrils, with a decrease in the crystallinity index for banana pseudocaule nanofibrils and an increase in the crystallinity index for coffee bark nanofibrils and Commercial pulp of eucalyptus. The thermal stability was little altered by the increase in the number of passes through the grinder. In relation to the nanostructured films, the increase in the number of passes through the grinder promoted a decrease in the thickness, water absorption, solubility and water vapor permeability, leading to an increase in the apparent density, tensile strength and modulus of elasticity of the films. The banana pseudocaule films had higher values of tensile strength and apparent density when compared to the films of coffee husk and commercial eucalyptus pulp, but they presented high humidity and solubility. While the coffee husk films had a low apparent density, high water absorption and water vapor permeability, with low tensile strength and modulus of elasticity being justified by their poorly compacted structure in relation to the other films. The films produced from the pseudocaule of banana were the most affected by the soil degradation process due to its high moisture content in relation to the coffee husk and commercial eucalypt pulp films, presenting a mass loss of approximately 40% in 18 Weeks of soil inoculation. The results demonstrate the effectiveness of chemical pre-treatments as a procedure for the production of cellulose nanofibrils, demonstrating that it is possible to reuse the post-harvest residues of banana and coffee in the generation of nanostructured films.