Nonwoven rCF / PA6 Thermoplastic Composites: Hybrid Commingled Fibers vs. Powder Impregnation—Effects on Microstructure and Mechanical Properties

ABSTRACT Fiber‐reinforced thermoplastic composites are a promising sustainable alternative to thermoset‐based ones, combining recyclability with reduced cycle times. This study compares two impregnation strategies for polyamide 6 (PA6) composites reinforced with recycled carbon fiber (rCF) nonwoven fabrics: powder impregnation (PA6/rCF_p) and hybrid commingled fibers (PA6/rCF_hy). Four‐layer laminates were produced by compression molding at two temperatures (270°C and 285°C) and two pressures (5 and 10 bar). For PA6/rCF_p, pressure was the dominant processing variable: increasing it from 5 to 10 bar significantly improved both Young's modulus and tensile strength ( p < 0.01), reducing void content from ~11% to ~5%, while temperature had no significant effect. Optimal conditions (285°C, 10 bar) yielded E = 18.3 ± 1.7 GPa and σ _u = 286 ± 38 MPa. PA6/rCF_hy composites exhibited substantially lower performance ( E = 11.7 ± 1.2 GPa; σ _u = 119 ± 21 MPa) and persistently high void fractions (15%–26%), attributed to the spatial inhomogeneity of the hybrid precursor. A modified rule of mixtures with a quadratic void correction (1 − v _v ) ² accurately predicted powder composite modulus and tensile strength within ±6%, with orientation efficiency factors for stiffness ( η ₀ = 0.334) and strength ( η ₀ , _σ = 0.343) closely agreeing, confirming that the same fiber‐orientation architecture governs both responses. Applied to the hybrid system, the model captures the overall performance level but with larger scatter, indicating that the combination of high, pressure‐independent porosity and precursor inhomogeneity limits the predictive capacity of global mixture models. These findings identify precursor homogeneity as a critical prerequisite for effective consolidation of commingled nonwoven architectures.