Abstract
The electron beam (EB) induced polymerization of a typical epoxy acrylate (EP-AC) formulation designed for high performance fibre-reinforced composites has been investigated in order to quantify the influence of various processing parameters on polymerization kinetics. Crosslinking polymerization was first conducted on thin EP-AC films coated on a NaCl plate and irradiated in nitrogen with incremental EB-dose delivered by a 175 kV laboratory processor. In such conditions and with the particular geometry of the samples, thermal effects are small, inhibition by air is avoided and post-polymerization is reduced. The actual conversion vs. dose profiles can be reconstructed from discontinuous transmission FTIR measurements following each incremental dose application. Two limiting kinetic regimes were shown to be dependent on the square root of the dose rate (Ḋ) in the initial stage, and proportional to Ḋ in the final stage, as an expectable consequence of the change in chain termination mechanism. A second series of polymerizations was conducted with the reactive layer covered by a PET film that isolates the polymerizable medium from ambient air. The influence of the dose rate and of the temperature was examined under these conditions which allow some post-polymerization to take place. The activation energy determined from the Arrhenius plot drawn from the data recorded during the first regime was about 4 kJ mol–1. The polymerization that proceeds in the third kinetic regime was not significantly dependent on temperature, as expected for a process requiring segmental mobility that takes place in the glassy state. This kinetic study provides a useful set of information for developing a model based on the change of termination mechanism in a medium that is gradually solidifying upon simultaneous network densification and monomer consumption.
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