Toughening Modification of Epoxy Resins Using Polyurethanes: A Review

Thermoset polymers have excellent properties of high dimensional stability at elevated temperatures, low creep and good resistance against solvents due to their three-dimensional crosslinking structure. Proper thermal-mechanical properties for these polymers are based on such cured structures with high crosslink density. Due to its excellent mechanical properties, epoxy resin has been widely used in coatings, adhesives and composites. In recent years, a variety of modification procedures have been introduced for toughening of cured resin structure in order to minimize crack formation and improve their impact resistance. Chemical modification of epoxy resins with polyurethanes is one of the most efficient procedures to achieve this goal. Polyurethanes have unique properties including good abrasion resistance, ease of processing and high rupture strength. After a brief introduction of epoxy and polyurethane resins, the procedures and the mechanisms of fracture toughness in polyurethane-modified epoxy are reviewed in present article. Different polyurethanes with wide range of chemical structures are able to toughen the epoxy structure efficiently and provide improved resins for use indifferent applications.