Toughening of phenolic resins

Reduced brittleness and increased fracture toughness are ongoing desirable improvements in cured resole or novolac-type (PR) systems. This chapter discusses various strategies for toughening the polymeric networks. Both chemical modification and physical reinforcement are examined. Chemical modifications include using monomers to introduce flexible polymer segments into the phenolic backbone and/or adding a second polymer that is compatible with the PRs and capable of co-curing. Physical reinforcement is achieved by adding high-molecular-weight polymers or inert fillers, such as nanostructures and fibers. The different types of toughening agents, the timing of adding modifiers, the structure-property relationships and their underlying mechanisms, as well as the relative benefits and drawbacks of these systems, will all be thoroughly discussed. Their application potential is also taken into account.