Electron-beam initiated polymerization of acrylate compositions, 2 - Simulation of thermal effects in thin films

The thermal effects taking place during the electron beam-induced polymeriz ation of acrylate type formulations were numerically simulated on the basis of the general heat equation applied to a one-dimensional system. The natu re, the dimensions and the environment, of the polymerizing medium were def ined for representing the actual conditions of kinetic experiments performe d with a 175kV laboratory accelerator and FTIR monitoring. The modeled syst em was constituted of a polymerizable position coated onto a NaCl plate, in itially at 20 degreesC in gaseous nitrogen at the same constant temperature , with or without a PET film covering the reactive layer. Polymerization pr ofiles describing the progress of the reaction as a function of dose were m odeled on a phenomonological basis from actual data obtained by discontinuo us FTIR monitoring of typical epoxy acrylate or polyurethane acrylate compo sitions. The influence of the reactive layer thickness (10/100 mum), dose r ate (10-110 kGy . s(-1)), maximum polymerization heat (200-400 J . g(-1)) o n the temperature-time variations was examined :For continuous irradiation. In spite of the relatively small thickness of the reactive layer, signific ant temperature rise is simulated when heat production is large and fast co mpared to energy dissipation at the reactive layer boundary, nj, obtained d ata substantiate the fact that upon fractionated EB-treatment with small do se increments (down to 0.6 kGy per pass) at low dose rate (down to 10 kGy . s(-1)) the heat release can be considered weak and without noticeable infl uence on the conversion data processed for a detailed kinetic analysis. For example, a maximal temperature rise of 6 degreesC was calculated for a fra ctionated irradiation of 2 kGy increments at 19 kGy . s(-1) applied to a po lymerizable formulation releasing a maximum enthalpy of 300 J . g(-1).