Electron Beam Processes

This chapter covers the chemical and physical processes involved in the electron beam radiation technology of polymeric materials. This includes cross-linking, degradation and grafting of polymers (thermoplastics and elastomers), and polymerization and copolymerization of monomers and oligomers. Radiation processing of monomers and polymers by electron beam such as polymerization and copolymerization of monomers, cross-linking, grafting, and degradation of polymers is induced by different chemically reactive species, including ionization, excitation, and capture of electrons. Besides these primary reactions, various secondary reactions arise in which ions or excited molecules take part. In curing applications, electrons have to penetrate the reactive solids and liquids with typical masses per unit area of one to several hundred g/m 2 (1 g/m 2 = 1 μm at unit density). In industrial practice, materials processed by electron beam machinery such as coatings, rubber compounds, and wire and cable compounds often contain mineral fillers and other ingredients that increase the density of the material. Such change of density requires correction in order to assess the appropriate voltage for the given application. The process of cross-linking is of particular practical importance and requires radiation promoters (prorads). These include a variety of compounds, including maleimides, acrylic, and allylic compounds. Opposite effects are promoted by radiation retardants. The major part of this chapter is dedicated to changes of general properties of polymeric substances resulting from their exposure to high-energy electrons.