LOW-TEMPERATURE CURING EPOXIES FOR ELEVATED-TEMPERATURE COMPOSITES

A low curing temperature epoxy formulation was characterized as a matrix material for glass-fibre-based composites for elevated temperature use. The formulation comprised a blend of tetra- and trifunctional epoxies and a two-part curing system including a high functionality active amine and an amino-terminated elastomer that, in addition, imparted high toughness to the high aromaticity epoxy matrix. Curing conditions and cross-linking states were studied and optimized using dielectric loss factor (DLF) measurements and differential scanning calorimetry (DSC) analysis in addition to Fourier transform infra-red (FTIR), hardness and molecular weight between cross-links (M(c)) calculations. Results indicated that ambient curing conditions resulted in optimal molecular network development. However, curing was incomplete and a curing temperature of 60-degrees-C or preferentially 120-degrees-C was required to obtain high cross-linking levels. DLF results showed that curing at room temperature proceeds quickly and that the main polymerization peak occurs at 48-degrees-C, with an additional peak at 120-degrees-C and a glass transition temperature at 160-180-degrees-C. Glass fibre-reinforced composites prepared from the preferred epoxy formulation displayed better flexural strength and comparable interlaminar shear strength, compared with a commercial, 120-degrees-C curing, prepregged glass composite based on a modified epoxy matrix.