RESUMO
The aim of this research was to investigate the effect of functionalized cellulose nanocrystals (CNC) on the performance of urea-formaldehyde (UF) adhesive for the production of medium density fiberboard (MDF). Surface modification of CNC was performed using 3-Aminopropyltriethoxysilane (APTES). Some physical and thermal properties of reinforced and neat UF as well as formaldehyde emission and some mechanical (modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond strength (IB)) and physical properties (thickness swelling (TS) and water absorption (WA)) of the resulting MDF panels were determined. Based on the results, upon incorporation of modified CNC to the system, solid content, density, viscosity and free formaldehyde of UF adhesives decreased while gel time increased. Depending on addition of the modified CNC loading in the panels, the formaldehyde emission values varied from 11% to 17% lower than the panels made from neat UF. In comparison to the control samples, panels made with UF containing 2% modified CNC had 29.3% and 38.2% higher MOR and MOE respectively.
RESUMO
The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were fibrillated and compared to sugar beet pulp as a representative non-wood cellulose resource, and conventional microfibrillated cellulose produced from bleached pulp. An alkali pre-treatment of woody and sugar beet raw materials enhanced the degree of fibrillation achieved, same as TEMPO-mediated oxidation of microfibrillated cellulose. Nanopapers produced from fibrillated material showed highly variable density and mechanical performance, demonstrating that properties may be tuned by the choice of raw material. While nanopaper strength was highest for TEMPO-oxidated microfibrillated cellulose, fibrillated untreated sugar beet pulp showed the best adhesive performance. Different microscopic methods (AFM, SEM, light microscopy) examined the interface between wood and fibrillated material, showing particular distinctions to commercial adhesives. It is proposed that fibrillated material suspensions, which achieve bond strength up to 60% of commercial urea-formaldehyde adhesive, may provide a viable solution to bio-based adhesives in certain applications where wet-strength is not an issue.
