Castor oil based polyurethane adhesives for wood-to-wood bonding

Most adhesives are polymeric adhesives and if made from renewable sources they will have low cost and biodegradability which are of importance. In view of these properties we synthesized polyurethane (PU) adhesives from three different polyester polyols, obtained by reacting a castor oil derivative and diols (glycols) with diisocyanate adducts, where different NCO/OH ratios were used to give various compositions. The polyols and PUs were characterized by FTIR spectroscopy. The effect of NCO/OH ratios, types of isocyanate adducts and chain length of glycols were studied, by determining wood-to-wood adhesion strength, i.e. by lap shear strength measurement. The change in lap shear strength after being placed in cold water, hot water, acid or alkali solutions was tested. Thermal stability of these PU adhesives was determined by thermogravimetric analysis.