High energy radiation cure of resin systems for structural adhesives and composite applications

Radiation cure polymerisation of a commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using a 60Co irradiation source, compounding the monomer with few percentage of an onium salt catalyst. The cure process has been monitored by a gamma-calorimetric technique and systems irradiated at doses corresponding to different positions in the gamma-calorimetric curve have been characterised via solubility tests and dynamic mechanical torsion analysis. Changes in both the measured gel fractions and tan δ values were associated with the progress of polymerisation and crosslinking reactions and these were dose dependent. Furthermore, systems irradiated at lower doses exhibited a latent thermal reactivity, undergoing further crosslinking by high temperature treatments, thus suggesting that synergy by the combination of radiation and thermal cure can help to achieve the desired applicative properties of these systems. These results have been discussed in the light of the most accredited radiation-induced polymerisation mechanisms for epoxy resins.