Co-authors​ :

 David LEACH (UNITED STATES) 

The first modern composites in the early 1900s used thermosetting resins such as phenolic, polyester, and epoxy. The resins were readily available, simple to formulate and more importantly had low viscosities and so were easy to impregnate into high fiber volume composites. The resins had high mechanical strength and met the required service temperature, but were brittle. Thermoplastic polymers were developed from the 1930s to 1970s with increasing thermal and mechanical performance. These included semi-crystalline polymers with glass-rubber transition temperature (Tg) in excess of 90°C, and amorphous polymers with Tgs over 200°C. In the early 1980s a major step forward was the commercialization of poly(aryl-ether-ketones), PAEKs. These polymers, and notably PEEK, combine the benefits of crystalline polymers, increased service temperature (Tg of 140-150°C), and high toughness. Thermoplastic polymers displaced thermosetting resins in unreinforced and short fiber applications due to the ease of molding and short cycle times, but the viscosity of thermoplastic polymers presented a major challenge to wetting out highly reinforced composites. By the early 1980s there was a demand for composites with high toughness and ease of fabrication. This led to the development and commercialization of thermoplastic composites (TPC) in the form of unidirectional tapes by ICI (now Solvay) and fabric reinforced materials by TenCate (now Toray). To realize the processing benefits of TPCs it was necessary to move from thermoset fabrication technologies, such as autoclave, to rapid fabrication and assembly methods including stamp-forming, fiber placement and welding. Initial work to develop these technologies was performed in the 1990s. During this same period the toughness of epoxy-based composites was increased, using thermoplastic toughening mechanisms. Some TPC applications emerged, but widespread adoption of high-performance TPCs was not realized. Further opportunities came in the 2000s with increased use of composites in commercial aircraft, notably the Boeing 787 and Airbus A350, which drove many detailed parts to TPCs. This provided a platform for development of cost-effective fabrication methods and material databases, although adoption of TPCs was limited to smaller, secondary components. Moving into the 2020s there is again great interest in TPCs for structural applications. Transportation is committed to achieve net-zero by 2050 which requires lightweight materials, TPCs are sustainable in that materials and parts can be recycled or downcycled, and applications demand high volume and high-rate. These include electric vehicles, the next generation of commercial aircraft, advanced air mobility and unmanned air vehicles. This is driving the readiness of high-rate manufacturing for large scale parts and assemblies for example through the Clean Aviation program in Europe, and in the NASA High Rate Composites Manufacturing program in the USA.