Challenging the status quo: recyclability and performance of wood fiber thermoplastic composites

Abstract

We present a systematic study of thermoplastic polypropylene (PP) composites reinforced with wood fibers (WF) derived from Norway spruce industrial residues (FibraQ) as scalable, sustainable alternatives to conventional polymers. The wood fibers retain a characteristic softwood monosaccharide profile and display robust morphological integrity and uniform dispersion across loadings from 20 to 50 wt%. Mechanical characterization demonstrates a linear increase in tensile modulus and strength with increasing WF content, counterbalanced by reduced ductility and impact toughness due to increasing fiber network density. Thermal analyses confirm enhanced stability and elevated Vicat softening temperatures upon WF addition. Importantly, these composites exhibit outstanding closed-loop mechanical recyclability: after three industrially relevant processing cycles, PPWF retains >90% of initial stiffness and >94% tensile strength, significantly outperforming neat PP and previously reported biocomposite systems. Our study provides the first direct quantitative comparison of recyclability and structural retention for industrially relevant PPWF composites. These advances offer a pathway for integrating renewable residues into high-performance, durable, and circular materials platforms beyond the capabilities of conventional polymers.