Adesivo natural à base de cardanol modificado com nanopartículas de sílicas para produção de painéis MDP

Abstract

Medium Density Particle Boards (MDP) are widely used around the world for furniture and flooring. Urea formaldehyde (UF) is the synthetic adhesive commonly used for making these panels, due to its low cost, colorlessness and fast curing time. Despite these favorable properties, one of the main disadvantages of UF adhesive is the emission of free formaldehyde in wood panels, which causes health risks such as allergic, non-allergic and mucosal respiratory symptoms, as well as cancer. For the reduction of formaldehyde emissions, studies indicate that the insertion of silica nanoparticles in formaldehyde-based adhesives has shown significant results for its reduction. However, taking into account environmental issues and the sustainability of the raw material, the search for replacing the UF adhesive, which is of petroleum origin, drives the development of adhesives that are based on renewable or biological resources, and that present lower emission rates of formaldehyde. Therefore, the cardanol obtained from the cashew nut shell liquid, from the cashew tree, is considered a promising aromatic renewable source of petroleum-derived phenols, due to its high reactivity with formaldehyde both via resol and novalac. In this context, the objective of this study is to evaluate the potential use of cardanol-formaldehyde adhesive, modified with different percentages of silica nanoparticles and adhesive contents, for the production of MDP panels. For the production of the panels, Pinus oocarpa wood was used, with dimensions of 30 x 30 x 1.5 cm (length x width x thickness), nominal density of 0.70 g/cm3 and the parameters of the pressing cycle were 15 minutes, pressure of 4 MPa and temperature of 160ºC. The synthesis of the cardanol-formaldehyde adhesive occurred via resol. At the end, silica nanoparticles were added in the following mass proportions, based on the solids content of the adhesive: 0, 1 and 2%. The panels were produced with adhesive contents in proportions of 8, 10, 12 and 14% in relation to the dry mass of the particles. The physical, chemical and thermal properties of the adhesives, and the physical, mechanical properties, wood-adhesive interface, formaldehyde emission, thermal insulation and combustibility of the panels were evaluated. The analysis of the panel properties showed that the addition of 2% SiO2NPs to the adhesive with 8% content influenced the water absorption after 2 hours (WA2h), thickness swelling (TS) and thickness non-return rate (NTS). In the mechanical properties, the addition of nanoparticles had a negative impact, except for Janka hardness. All panels met the E1 class of low formaldehyde emission. From the joint analysis of the results, it is concluded that the addition of SiO2NPs was not favorable to the cardanol-formaldehyde adhesive in terms of mechanical properties, and the adhesive content from 11% reaches the standards established for the commercialization of the panels.