Recycled carbon fiber heavy tows for thermoset composites part I: A novel twist-free approach

The recycling of carbon fiber (rCF) is critical for sustainable manufacturing in industries such as aerospace, automotive, and sporting goods. Recently, thermoplastic composites have been developed using rCF hybrid yarn structures, where rCF serves as the reinforcing fiber and thermoplastic support fibers (e.g., PA 6 staple fibers) act as the matrix, blended in a 50/50 volume ratio using modified short staple fiber technology. However, the majority of carbon fiber reinforced plastics (CFRP) are still based on thermoset matrix systems. This study presents a novel mechanical recycling technology for rCF with the goal of producing twist-free heavy tows with high fiber orientation using a minimum of 90 vol.-% carbon fiber. The process adapts conventional yarn formation techniques - fiber opening, blending, carding and drawing - ultimately leading to the development of heavy tows suitable for load-bearing thermoset composite applications. Two innovative concepts were explored to improve fiber cohesion: Concept I involved blending rCF with hot melt adhesive fibers (≤10% by volume), followed by thermal activation to fuse the adhesive into the fiber structure. Concept II used 100% rCF slivers sprayed with a binder-based solvent. Both methods produced reproducible heavy tows with high fiber orientation, achieving fineness-related strengths of approximately 1 to 5 cN/tex, suitable for subsequent fabric-forming processes. The study highlights the potential of these rCF heavy tows for use in sustainable, resource-efficient materials and lightweight load-bearing composite construction.