Large‐Format Fused Granulate Fabrication of Wood–Polypropylene Composites: The Role of Matrix Viscosity

ABSTRACT Large‐format fused granulate fabrication (FGF) directly processes pelletized wood–polymer composites, but the role of polymer matrix viscosity in printability and performance remains insufficiently defined. Two homopolymer polypropylene (PP) matrices of different melt viscosities were compounded with 10 or 20 wt.% wood flour (WF), with or without maleic anhydride‐grafted PP (MAPP). Rheology, differential scanning calorimetry, print observations, and mechanical tests of injection‐molded and FGF‐printed specimens evaluated flow, crystallinity, print quality, and performance. WF increased complex viscosity and extended relaxation in both matrices, whereas polymer‐normalized crystallinity changed only modestly. All formulations formed hollow hexagonal prisms; however, high‐WF formulations with the lower‐viscosity matrix had rougher surfaces and less uniform layers than corresponding higher‐viscosity formulations. WF generally increased stiffness; MAPP was associated with higher injection‐molded tensile and flexural strengths than corresponding non‐MAPP formulations, and WF reduced impact strength. Printed properties depended strongly on orientation, with horizontally extracted specimens generally outperforming vertically extracted specimens, particularly in tensile and flexural strength. Matrix viscosity was linked to melt flow, bead stability, surface quality, and mechanical anisotropy. The higher‐viscosity PP provided the more favorable balance of rheological stability, print quality, and printed mechanical performance.