Chemical or physiochemical changes induced by exposure to various types and intensities of radiation. (1) Synthesis of ethyl bromide from hydrogen bromide and ethylene, using α-radiation from cobalt-60. (2) Cross-linking of such polymers as polystyrene and polyethylene with either β- or γ- radiation. (3) Vulcanization of rubber with ionizing radiation. (4) Polymerization of methyl methacrylate monomer with cobalt-60 as source of γ-rays. Free radical formation is involved in both cross-linking and polymerization reactions. This technique is also being applied in the textile finishing field for grafting and cross-linking fibers with chemical agents for durable-press fabrics. (5) Processing of various foods (cooking, drying, pasteurizing, etc.) by electromagnetic energy in the microwave region of the spectrum; preservation and sterilization of food products by ionizing radiation (γ- and X-rays). The dosage of radiation is strictly controlled, and FDA approval is required. Irradiation is also effective in inhibiting sprouting and preventing insect infestation of stored grains. (6) Curing or hardening of organic protective coatings (paints, inks) by exposure to infrared, UV, or electron-beam radiation. Required are a monomer or oligomer and a photoninitiator, which induces polymerization by free radical formation.See “Electrocure.”
