I am developing an adhesive for an application that requires heat resistance greater than 80°C. A formulation based on a waterborne polyurethane polymer currently provides the best adhesion to the substrate and is a fit for the application process. What approaches can be used to achieve the required level of elevated temperature performance?
A first approach—and an ideal situation—would be to identify a polyurethane dispersion that has the required property profile as supplied. Polyurethanes with excellent hydrolysis resistance are often based on a polyether polyol backbone. These polymers are often very soft with high elongation and show only moderate levels of heat resistance. Products based on polyester polyols can be either amorphous or crystalline, and film properties can vary widely from low modulus to high tensile strength, depending on the raw materials used in the polymer. The manufacturer of the adhesive raw materials can improve heat resistance by increasing the polymer’s molecular weight or by increasing the “hard block” content of the polymer. This is accomplished by including low-molecular-weight polyols or polyamines in the backbone of the polymer.