Effect of addition of microfibrillated cellulose to urea-formaldehyde on selected adhesive characteristics and distribution in particle board

Several studies demonstrate that the addition of microfibrillated cellulose (MFC) to urea-formaldehyde (UF) wood adhesive improves the mechanical bond strength of wood particle board. In order to elucidate potential underlying mechanisms, the distribution of unmodified UF as well as MFC-modified UF (UF-MFC) in particle board was studied by means of light microscopy. The viscosity and cure characteristic of the adhesive systems were also characterised. UF-MFC showed high viscosity and shear thinning compared to UF. Both chemical and mechanical cure of adhesive were delayed in the presence of MFC. In UF-MFC, the size distribution of adhesive particles shifts towards larger particles compared to UF. More adhesive is directly available for adhesive bonding, and a larger part of the wood is covered with adhesive. This may be the cause for the better mechanical performance of particle board bonded with UF-MFC compared to UF.