Abstract
The development of wood-filled thermoset composites for extrusion-based processing requires formulations that combine suitable flow behavior, controlled curing, thermal stability, and adequate mechanical performance. This study examined the augmentation of phenol–resorcinol–formaldehyde (PRF) resin using three modifiers (ball-milled eggshells, gelatinized corn starch and sulfated castor oil) combined with waste wood fibers for extrusion-based manufacturing. Methods: The composite blends prepared by compression molding and extrusion processes were characterized by rheology, thermal analysis and flexural testing. Results: Modified and unmodified wet PRF–wood composite blends exhibited a good frequency-dependent decrease in complex viscosity indicating suitability for extrusion, while temperature-ramp measurements showed an increase in complex viscosity associated with progressive network formation and curing. A thermogravimetric analysis of cured blends showed decreased thermal stability of the modified PRF blends in the presence of wood. The flexural modulus (FM) and strength (FS) of the cured extruded composite blends were higher (FM: 4–6 GPa, FS: 45–68 MPa) than those of compression-molded samples (FM: 3.2–4.3 GPa, FS: 41–58 MPa). Statistically, two-way ANOVA identified significant formulation-dependent effects of modifier type and/or loading on flexural properties within the respective processing groups (compressed or extruded). Overall, the results demonstrate that these modifiers can be used to tailor the rheological, curing, thermal, and mechanical behavior of PRF-based composites while maintaining processability for extrusion. Conclusions: The findings provide a scientific basis for the continued development and optimization of renewable composite feedstocks for extrusion-based manufacturing of wood composite products.