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.