Kinetic study of polymerization/curing of filament‐wound composite epoxy resin sytems with aromatic diamines

The kinetics of the polymerization/curing of an 80/20 blend of a diglycidyl ether of bisphenol A (DGEBA) and a diglycidyl ether of 1,4‐butanediol (DGEBD) with a commercial mixture of methylene dianiline and m ‐phenylene diamine (Tonox 60/40) was studied, at amine/epoxy ratios ranging from 1.1 to 4.4. Fourier transform infrared (FT‐IR) measurements were used to follow the extent of epoxy conversion at 18–122°C, and bulk viscosity measurements were used to define the working range of the resin. For an amine/epoxy ratio of 1.1, the activation energy for the polymerization/curing reaction (based on time to 50% epoxy conversion in the S‐shaped conversion‐time plots) was 11.9 kcal/mole by FT‐IR. This value compared favorably with the corresponding value of 12.7 kcal/mole obtained by Moroni and co‐workers in a complementary differential scanning calorimetry (DSC) study of the same system. The FT‐IR conversion‐time plots were fitted to a kinetic expression that can be accommodated by an autocatalytic mechanism; the expression contains two rate constants with activation energies of 13.7 and 10.0 kcal/mole, respectively. The viscosity of the curing epoxy resin was found to obey the Williams‐Landel‐Ferry equation, with a Di Benedetto expression for the glass transition temperature.