Closing the loop of polyurethane adhesives: Acidolysis process optimization

Polyurethane adhesive (PUA) are a specialized application of polyurethanes. Acidolysis of PUA waste yield a recycled polyol with tunable properties. This process was optimized by response surface methodology to predict the domain of parameters where the lowest of viscosity, hydroxyl, and acid values could be achieved. Relationships between temperature, polyurethane-to-polyol, and polyurethane-to-acid ratios, and viscosity, molecular weight, hydroxyl and acid values were established and optimal conditions were validated for a robust process. The polyurethane-to-acid ratio had the most significant influence on the acid value of the product. Hydroxyl value, viscosity and molecular weight were primarily affected by the polyurethane-to-polyol ratio. Using a recycled polyol obtained at 205 °C, a polyurethane-to-polyol ratio of 1.4 kg/kg, and a polyurethane-to-acid ratio of 50 kg/kg, we successfully produced a new adhesive incorporating up to 28 % recycled material. This demonstrated adhesion properties for wood applications on par with those of virgin adhesives, without experiencing crash phenomena.