A solventless castor oil-based PU adhesive for wood and foam substrates

Solventless adhesives from renewable sources are greatly appreciated by the researches since they can be produced at low prices and can be biodegradable, as compared to those produced from petrochemical sources. In this work, solventless castor oil-based polyurethane (PU) adhesives were prepared to evaluate the influence of the NCO/OH molar ratio and the chemical nature of the substrates (wood/wood and foam/foam) on the adhesive force. The solventless castor oil-based PU adhesives were prepared with NCO/OH molar ratios of 1, 2, or 3 having dibutyltin dilaurate (DBTL) and triethylenediamine (TEDA) as catalysts. The adhesives were characterized by FT-IR spectroscopy, differential scanning calorimetry, and thermogravimetric analyses. The tack-free time of the solventless PU adhesives was dependent on the catalyst concentration, and their mechanical properties were influenced by the NCO/OH molar ratio. The solventless PU adhesive foam joints showed peeling strength values 75% higher than that of a solvent-based commercial adhesive currently applied in the mattress industry. The solventless PU adhesive wood joints showed lap shear strength values 20% higher than that of a commercialized solvent-based adhesive used for wood.