The development of a low temperature cure modified epoxy resin system for aerospace composites

It has been recognised within the composites industry that there are economic advantages in moving away from a conventional autoclave cure at high temperature. A low temperature cure (LTC) resin system has been developed that can be cured at 85 °C initially then subsequently further cured at 175 °C, for a short period. For such resins there is a requirement to achieve the same toughness properties as conventional thermoplastic toughened high temperature cured (HTC) material. The development of an LTC resin system has required a special catalyst systems and appropriate choice of a poly(ethersulphone) co-polymer, in terms of molecular structure, molecular weight and chain ends. Toughness development in thermoset–thermoplastic blends requires an appropriate development of phase morphology during cure. Morphology control has been achieved in LTC materials. Application of linear elastic fracture mechanics measurements of toughness in association with transmission electron microscopy and scanning electron microscopy of the fracture surface has demonstrated links between the toughness and the phase morphology and the chemistry. Small angle neutron scattering has enabled the development of the phase morphology during the low temperature curing process to be monitored. The presence of phase morphology in the resin means that the influence of phase or interface boundaries on the environmental stress cracking (ESC) properties might be a critical issue. This issue has been addressed and investigated for three environments, namely air, demineralised water and dichloromethane at 23 °C. The LTC material is shown to perform in a similar manner to a comparable conventional HTC resin system.