Wood-polymer composites from polylactide and coarse pine sawmill shavings: effect of filler content on structure, thermal behavior and flexural performance

Abstract Wood-based panels are still bonded predominantly with formaldehyde-releasing amino and phenolic resins, whereas commercial wood–plastic composites (WPCs) rely almost exclusively on petrochemical thermoplastic matrices. Consequently, a material that overcomes both limitations requires a bio-based, formaldehyde-free binder. Published polylactide (PLA)-based wood-polymer composites are, however, almost invariably produced from finely ground wood flour or purified cellulose and processed by extrusion or injection moulding. In contrast, studies on PLA composites reinforced with coarse, unmodified sawmill shavings and consolidated by simple hot pressing a processing route that may be suitable for small-scale manufacturing. In this work, pine planing shavings (25–30 mm long, 0.15 mm thick, aspect ratio ≈ 170–200), used as received without grinding or chemical modification, were hot-compounded with PLA 4032D and consolidated by hydraulic pressing at three shavings/PLA mass ratios (35/65, 25/75, and 20/80). The resulting composites were characterized by FTIR-ATR spectroscopy, X-ray diffraction (XRD), simultaneous thermogravimetry–differential scanning calorimetry (TG–DSC), optical microscopy, three-point bending, and water absorption tests. The 25/75 formulation exhibited the best overall performance, achieving a flexural strength of 42.0 ± 1.4 MPa (98% of neat PLA, 43.0 ± 1.5 MPa), along with the lowest water absorption (3.90 ± 0.18 wt%) and the most uniform filler distribution. Owing to the low density of the pressed boards (approximately 710 kg m −3 ), this formulation also achieved a specific flexural strength approximately 1.7 times that of neat PLA and several times greater than that of formaldehyde-bonded particleboard of comparable density. FTIR analysis showed that the composite spectrum was essentially a superposition of the constituent spectra, providing no evidence of covalent interaction. XRD and TG–DSC results were consistent with possible partial recrystallisation of the PLA matrix, while the glass-transition temperature increased by approximately 4–5 K. These findings demonstrate that coarse, untreated sawmill waste can be directly valorised into a low-toxicity, bio-based panel material through a simple manufacturing route.