Production of fiber reinforced epoxy matrix composites via photopolymerization

Fiber reinforced epoxy matrix composites, which are high performance engineering materials, have limited use due to long curing times and high energy needs. Photopolymerization is a fast, economic and environmentally friendly polymerization technique that transforms liquid resin systems into crosslinked solid polymers with lower energy requirement at room temperature. From this point of view, the idea has emerged that the photopolymerization technique can be used in the production of fiber reinforced epoxy matrix composites. In this study, industrial type epoxy resin (diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F (DGEBA/F)) cured in a short time at room temperature with visible lights was developed and used in the production of fiber reinforced composites. For this purpose, the radical induced cationic frontal polymerization (RICFP) technique based on the use of heat produced during the photopolymerization was chosen for the deep curing of industrial type epoxy resin. In this technique, the heat released as a result of the photopolymerization reaction on the surface activates the radical initiator in the formulation and curing occurs throughout the thickness. The developed formulation contained DGEBA/F epoxy as base resin, iodonium salt as photoinitiator, thioxantone as sensitizer, oxethane as accelerator and 1,1,2,2-tetraphenyl-1,2-ethanediol as radical initiator. Firstly, the optimization study was done for the curing formulations in terms of thickness, hardness, curing speed and mechanical properties, and the most effective cured one via visible lights was selected. This formulation was characterized by FT-IR, DSC, TGA and three-point bending tests and its properties were determined. Then, the fiber reinforced composites were prepared by hand lay-up, vacuum bagging and vacuum infusion methods using glass and carbon fibers in different forms (mat, multiaxial, woven) and optimized epoxy resin formulation. These composites were obtained in a very short time, such as 15 minutes, at room temperature upon visible light irradiation. It was determined that the glass fiber reinforced composites prepared by hand lay-up method showed better curing performance than the other composites. Mechanical characterizations of these composites such as bending, tensile, and shear tests were made according to the relevant international standards and compared with the reference composites that were thermally cured with amine based hardener via conventional route. The photocured composites showed similar mechanical properties with the reference composites. Morphological analyzes of the fracture surfaces of the composites showed that a good fiber-matrix adhesion was formed and that the fractures occurred from the interface. In addition, a prototype was produced with the developed system and a process comparison was made with the traditional method. Thus, it has been proven that fiber reinforced composites can be produced in a short time with less energy consumption, competitive cost, and investment without losing performance by curing industrial type epoxy resins via photopolymerization. Keywords: Photopolymerization, Epoxy resin, Composites, Fast curing, Prototype