Different toughening strategies for UV-cured epoxy resins

Owing to their outstanding properties, epoxy resins are widely used in different industries and recently used in novel applications such as semiconductors and lithographic inks. Due to their low fracture toughness, Toughening of epoxy is widely discussed in literature during last decades. Many toughening agents including organic and inorganic materials are used to accomplish this purpose. The objectives of this research are to synthesize and use different toughening agents and study the influence of these modifiers on the mechanical and thermal properties in general and the fracture toughness in particular of the UV-cured cycloaliphatic epoxy resins. Particularly, we desired to improve the fracture toughness of modified epoxies cured via UV light without sacrificing their thermal and other mechanical properties. Polymeric molecules or ceramic nanoparticles have been introduced; (1) Hyperstar polymers based on hyperbranched polyester core with or without hydroxyl reactive groups in their arms (2) reactive core/shell polymeric nanoparticles prepared by seeded emulsion polymerization (3) reactive or nonreactive diblock copolymer prepared via ATRP and based on polyethylene oxide and (4) commercial alumina nanoparticles as inorganic particles. The effect of the addition of these toughening agents on the rate of UV-curing process and glass transition temperature, Tg, have been investigated. Subsequently, the morphology of the facture surfaces has been studied carefully using FE-SEM. The stress intensity factor, KIC, measurements which is an indicator for fracture toughness was evaluated in terms of single-edge-notch three-point-bending (SENB). Cationic UV-curing technique was utilized for the preparation of the modified epoxy composites. Specifically, the cationic photopolymerization of cycloaliphatic epoxy is known to proceed through nucleophilic attack of neutral monomer to oxonium cation, which is active chain end of the polymerization. The UV induced polymerization technique is a solvent free method occurring at room temperature which is eco-friendly. It is indeed a polymerization process used for industrial applications because of the high production rate and the low energy consumption compared to thermal processes. The rapid UV-curing process helps to maintain good dispersion of modified particles avoiding further aggregation that could occur during longer thermal treatment