The objective of the activity is the development of low-temperature curing resins with extended process/pot life suitable for CFRP manufacturing applications.

Curing of polymers resins for CFRP composites is for the vast majority of cases stimulated through temperature, whereas the curing temperature is a trade-off between required pot-life, thermal properties, hardware compatibility, and mechanical performance. For example, a high curing temperature leads to very good thermal properties and allows long pot-life, but causes increased internal stress and distortion. Ideally the adhesive is processed as well as cured near room temperature (practically < 100?C), typically followed by a short post-cure. Such resins provide the additional benefit of lower energy consumption, but have a fundamental drawback of reduced pot-life. For manufacturing of large and/or complex shaped hardware, a long processing time or pot-life is required that cannot be achieved with preferred low-temperature curing adhesives. Advanced resin systems, so-called latent systems, show essentially no activity around room temperature, but react very fast after external stimulation, so-called cure on demand. The latter can be achieved by heating, photo irradiation, ultrasonic exposure, electron beam exposure, etc. Even with thermally induced latent systems, a storage stability at room temperature of several months can be achieved with curing temperatures as low as 80?C. Another attractive solution is the use of UV induced polymerisation by introducing the concept of frontal polymerisation. In this case the polymerisation is initiated on the surface of the adhesive, and the exothermic reaction creates a propagation front through the bulk material. The following tasks are encompassed in this activity : - Revision of state of the art for cure on demand with various external stimuli, including temperature and radiation. - Requirement definition for low-temperature curing adhesives for composite manufacturing. - Resin development for two different initiation systems and performance optimisation following a trade-off materials performance, processing constraints, and hardware requirements. - Performance demonstration on small demonstrator concepts for the two initiator systems.