Yarn-Based Aligned Recycled Carbon Fiber/PA11 Composites: Yarn Development, Coupon Characterization, Initial Structural Demonstration, and Screening Life-Cycle Assessment

Re-aligned recycled carbon fiber (rCF) yarns provide a complementary architecture to aligned rCF tapes, enabling load-path-oriented reinforcement placement with potential for automated near-net-shape preforming and three-dimensional formability. This study investigates hybrid rCF/polyamide 11 (PA11) wrap yarns produced through roller carding, hollow-spindle wrap spinning, tailored fiber placement (TFP), and consolidation. Two rCF/PA11 yarn formulations with nominal fiber/matrix mass ratios of 72/28 and 80/20 were developed, yielding fiber volume fractions of 54.4 and 58.5 vol.%, respectively. Mechanical characterization focused on UD coupon testing under axial tensile, transverse tensile, and shear loading. For the rCF/PA11 72/28 and 80/20 formulations, longitudinal tensile testing yielded moduli of 57.8 ± 4.2 and 64.3 ± 6.3 GPa and strengths of 920 ± 41 and 815 ± 86 MPa, respectively. The 72/28 material additionally exhibited an in-plane shear modulus of 1.87 ± 0.03 GPa and shear strength of 48.7 ± 1.4 MPa. Relative to the previously reported aligned rCF/PA11 tape laminates at a comparable fiber volume content, albeit with distinct processing machinery, the 72/28 yarn laminate showed higher longitudinal modulus and longitudinal strength but substantially lower transverse and shear properties, suggesting a possible architectural trade-off associated with discrete yarn lanes, helical wrapping, and TFP preforming. A conrod-shaped preliminary structural benchmark manufactured from rCF/PA11 72/28 sustained 11.3 ± 0.5 kN at a mass of 23.0 ± 1.0 g, corresponding to a 71% higher specific load capacity than the aluminum reference. Proof-of-concept thermoforming of three double-curved shell demonstrators confirmed the capability of the yarn-based preforms to form complex three-dimensional geometries, although local fiber alignment defects highlighted the need for improved draping control. A screening life-cycle assessment estimated 0.42 kg CO2-eq per rCF/PA11 benchmark part, representing reductions of approximately 63% relative to the virgin-CF/PA12 stretch-broken yarn route and 52% relative to virgin-CF/epoxy routes. The results demonstrate the potential of rCF/PA11 wrap yarns as high-fiber-content textile intermediates for load-path-oriented TFP preforming and subsequent three-dimensional thermoforming.