Cationic Curing of Epoxy–Aromatic Matrices for Advanced Composites: The Assets of Radiation Processing

Abstract

Cross-linking polymerization of multifunctional aromatic monomers initiated by exposure to high energy radiation continues to be explored as a promising alternative to thermal curing for the production of high-performance composite materials. High-energy radiation processing offers several advantages over thermosetting technology by allowing for fast and out-of-autoclave curing operations and for its adaptability in the manufacturing of large and complex structures at reduced energy costs. The present article covers the basic aspects of radiation curing by cationic polymerization of epoxy resins, providing a status report on recent investigations conducted in our group to improve the properties of epoxy matrices and gain better control over the process for producing composites. A selection of results based on blends prepared with different composition of epoxy aromatics, transfer agents, thermoplastic toughening agents and onium salt initiators exemplifies the importance of the composition on polymerization kinetics and on the properties of resulting materials. The superiority of radiation-triggered polymerization-induced phase separation of thermoplastic additives is emphasized by the obtained morphology of toughened materials. The low initial temperature and fast curing of the reactive blends limits the expansion of phase-separated thermoplastic domains, resulting in an enhancement of the toughness.

Radiation-induced cross-linking polymerization: Recent developments for coating and composite applications

“…The polymerization mechanism in industrial processes is mainly free radical, with acrylate or methacrylate monomers. Cationic curing of epoxy-or vinylether-based formulations are also used in specifi c applications [5].…”

“…After dimerization and protonation, the formed radical initiates the polymerization. In the case of cationically polymerizable formulations, such as epoxies, the presence of an onium salt is necessary to obtain active initiator centers in suffi cient amounts [5].…”