Interação de nanocristais de celulose com o adesivo ureia-formaldeído em juntas coladas de Eucalyptus sp

Abstract

The aim of this study was to evaluate the potential use of cellulose nanocrystals (CNC) as a reinforcing agent in urea-formaldehyde adhesive for bonded joints of Eucalyptus sp. The CNCs were added to the urea-formaldehyde adhesive in the proportions T0 (0%), T1 (2%), T2 (4%), T3 (6%) and T4 (8%). For bonding 200 g.m-2 amount of adhesive was used, 8 minutes for bonding time, 10 kgf.cm-2 of pressure, and 150°C for adhesive curing temperature. CNC's used in this study were characterized by using transmission electron microscopy techniques (TEM), and zeta potential was measured. The shear strength was determined according to ASTM D 2339-98 standard. The CNC had a cylindrical feature and were about 85 nm long and 10 nm wide with a zeta potential of -56.96 mV. The viscosity of the adhesives was significantly increased by the addition of cellulose nanocrystals. However the addition of CNCs did not change the pH, the gel time and the solid content of the adhesives, for which values of 7.3 ± 0.5; 165 seconds and 66% respectively were found. The addition of CNCs increased the shear strength of the adhesive, both in dry and wet tests. Thus, the CNC's are characterized as effective reinforcing agents, due to the creation of hydrogen bonds between the wood-adhesive and adhesive-CNC's interface. Its application as an additive is recommended in order to improve the shear strength of the urea formaldehyde adhesive, as well as its resistance to moisture.