JOURNAL OF COMPOSITE MATERIALS Article Reuse and upcycling of thermoset prepreg scrap: Case study with out-of-autoclave carbon fiber/epoxy prepreg Gaurav Nilakantan and Steven Nutt Abstract A large amount of uncured thermoset prepreg scrap is generated during manufacturing, including both ply cutter trim waste and out-of-spec material. While techniques to recycle end-of-life cured composite waste and reclaim carbon fiber are well established and commercialized, there is little effort made presently towards reusing uncured scrap prepreg. Here, we present a viable and scalable technique to process scrap prepreg into intermediate forms that can be readily manufactured into commercial end-products. Using out-of-autoclave carbon fiber/epoxy prepreg as an example, we report the mechanical properties, microstructure, and performance of composite laminates fabricated with scrap pre- preg under various processing conditions. Demonstrator parts manufactured with scrap prepreg are also presented. Keywords Prepreg, reuse, carbon fiber, thermoset, recycling, mechanical properties, compression molding Introduction There has been a significant increase in the global demand for carbon fiber (CF) and CF composites from several industries, notably aerospace and automo- tive. The global prepreg industry is expected to grow to an estimated USD 6.1 billion by 2019, 1 while the global demand for CF composites is projected to reach USD 20.1 billion by 2018 with an annual growth rate of 6.4%. 2 Newer aircraft from Boeing (e.g., 787, 777X) and Airbus (e.g., A380, A350) exemplify the increasing use of composites in aircraft structures. Boeing’s market outlook (2015–2035) projects a doubling of the world aircraft fleet size from approximately 23 k in 2015 to 45k in 2035, valued around USD 5.9 trillion. Within the fleet, single aisle aircraft are projected to grow from 15k in 2015 to 32k in 2035. In the automo- tive industry, increased mileage requirements for US passenger cars of 23.1 km/l by 2025 has led automotive manufacturers to increasingly explore using CF to help reduce vehicular weight. Similarly, the sporting and recreation industry is also increasingly using carbon and other polymeric fibers (e.g., aramids) to produce lighter and stronger sports equipment. Thermoset composite prepreg waste can be broadly classified into uncured waste generated during the manufacturing operation and cured waste from end- of-life parts. Techniques to handle these material streams can therefore be classified as ‘‘reuse’’ and ‘‘recycle,’’ respectively. Recycling efforts seek to reclaim CFs from cured waste by removing the matrix through various techniques such as burn-off (pyrolysis), matrix digestion (acids and supercritical fluids), or depolymer- ization. Individual reclaimed CFs demonstrate excellent moduli and strength retention properties compared to virgin fibers. However, they lose their continuous and aligned configuration and instead often appear as tangled arrays of fibers that must be reprocessed (realigned via carding, and often resized) before they can be processed into new CFRP parts. More informa- tion on composites recycling technologies, their impact, and market outlook can be obtained from earlier works. 3–7 There are only a handful of companies glob- ally that have commercialized recycling processes, such as Adherent Technologies and Carbon Conversions M.C. Gill Composites Center, University of Southern California, Los Angeles, CA, USA Corresponding author: Gaurav Nilakantan, Teledyne Scientific Company, 1049 Camino Dos Rios, Thousand Oaks, CA 91360, USA. Email: gaurav.nilakantan@teledyne.com Journal of Composite Materials 2018, Vol. 52(3) 341–360 ! The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0021998317707253 journals.sagepub.com/home/jcm