Modified phenol formaldehyde resin with sodium silicate as a low-cure wood adhesive

Phenol-formaldehyde (PF) resin is a common adhesive in the plywood industry with the main advantage of its water resistance and high bonding strength. However, PF has unfavorable high curing temperatures which becomes of cost concern. In the present work, sodium silicate was used to modify the resin properties to lower its curing temperature. The amount of sodium silicate was varied in a range of 0% to 25% (w/w) in terms of sodium silicate to phenol. The thermal properties of the modified resin and its bonding strength were investigated. The experimental result showed that the presence of sodium silicate can increase crosslink density which leads to higher bonding strength. In addition, the presence of sodium silicate resulted in a lower curing temperature and reduced curing activation energy. The addition of 25% (w/w) sodium silicate could increase the bonding strength by more than 200% and decrease the curing temperature by about 35 degrees C. The improved processability and energy consumption offer advantages for the effective application of phenol-formaldehyde, particularly in the wood industry.