When it comes to commercial epoxy adhesives, adding a polyurethane segment into epoxy polymers can improve heat resistance and strength.
Generally, epoxy adhesives are suitable for applications that demand solvent resistance, resistance at very high temperatures and rigidity. Polyurethane adhesives are suitable for applications that require adjustable cure rates, low-temperature cure and adhesion, toughness and flexibility.
Hybridization of adhesives can help reduce brittleness. This is usually done by creating a second phase in the epoxy matrix or adding reactive diluents or plasticizers to the epoxy resin. Adding polyurethane segment into an epoxy polymer can also toughen the adhesive.
Tests revealed that modified adhesives that added a blocked polyurethane prepolymer and diamine were stronger. The tests also surprisingly found that blocked polyurethane prepolymers could improve an adhesive’s heat resistance.
Blocked polyurethane prepolymer improves an adhesive’s strength by increasing the reactivity of the epoxy resin. It also increases resistance to tearing through the phase separation of the polyurethane segment from the epoxy matrix, and also allows for full polymerization of the epoxy resin before the onset of vitrification.
Source: Toughening Epoxy Adhesives
