Tannin-phenolic hybrid biomacromolecular resins for extrusion-based biocomposite manufacturing

The surging demand for environmentally benign alternatives to petroleum-based resins has sparked interest in bio-derived phenolic systems for biocomposites and additive manufacturing. This study reports the development of an extruded tannin-PRF (phenol-resorcinol-formaldehyde) resin-wood composites using ponderosa pine bark tannins (PT) and commercial maritime pine bark tannins (CT) as renewable phenolic substitutes. The hybridization of tannins with PRF aimed to enhance renewable content while retaining the mechanical and thermal performance essential for extrusion-based manufacturing. All resin-wood blends exhibited shear-thinning behavior with consistent complex viscosity, confirming their processability for extrusion. Thermogravimetric (TGA) and dynamic mechanical (DMA) analyses revealed that tannin incorporation delayed degradation onset and increased glass transition temperature (T_g) due to enhanced aromatic condensation and crosslink formation. Among the formulations, the PT-PRF wood composite achieved the most balanced thermal performance, combining moderate T_g of 211 °C, delayed decomposition, and higher char yield. Mechanical testing demonstrated that tannin-PRF hybrid composites achieved flexural strength (40-47 MPa) and modulus (4.0-4.3 GPa) comparable to neat PRF, whereas neat tannin composites exhibited lower values due to reduced crosslink density. Water absorption studies showed that hybrid systems maintained low equilibrium uptake ranging from 19 to 24% and Fickian diffusion behavior, indicating improved dimensional stability and interfacial cohesion. Overall, these findings establish tannin-PRF hybrid resins as promising, high-performance, and partially bio-based alternatives for cleaner extrusion manufacturing of structural wood composites, advancing the transition toward renewable materials and circular bioeconomy applications.