Bonding CompositesPart 4: Various types of Adhesives for Composites: Polyurethanes, Heat stable adhesives, Syntactics, etc…

In previous chapters we have studied several types of adhesives for composites: epoxies, polyesters, structural acrylics... We are now studying other types available. Polyurethane chemistry is a very wide subject, PU enjoy a very versatile chemistry: there are one and 2 components PU, chemically curing, humidity curing, PU reactive hot melts, they may be flexible or rigid adhesives, thermoplastic or thermosetting adhesives, adhesives and/or sealants, semi-structural or non structural adhesives. These different products depend on the formulation, by using various polyols, prepolymers, isocyanate terminated polymers, various isocyanates... Therefore we must define here the types of PU adhesives which are used for composite bonding: these adhesives are usually 2 components, semi-structural, high performances adhesives. They may cure at room temperature or provide accelerated curing by mild temperature heat curing, at temperature ranging from 60 to 100°C.Isocyanate terminated prepolymers can react with water, alcohols, amines and other reactive chemicals.