From Biomass to Filament: Processing and Performance of a PLA Poly(lactic acid) Pine Cone-Filled Composite in Additive Manufacturing

This research evaluates the compounding, processing, and performance of a sustainable biocomposite filament for additive manufacturing, utilizing poly(lactic acid) (PLA) filled with raw pine cone (Pinus sylvestris) flour at 5 and 10 wt% filler contents. Tensile properties, surface topography, and processability of extruded filaments and 3D-printed specimens were systematically investigated. Incorporating pine cone flour yielded unprinted filament tensile strengths of 21.06 MPa (5 wt%) and 18.51 MPa (10 wt%), while 3D-printed specimens retained ~85% (5 wt%) and ~79% (10 wt%) of their corresponding unprinted composite filament tensile strength. This reduction in strength is hypothesized to stem from weak interfacial adhesion and polarity mismatch between the hydrophobic PLA and hydrophilic biomass, which is suggested to promote micro-void formation. Topographical analysis revealed surface anisotropy: top surface roughness increased (Ra up to 9.85 µm; Sz up to 100.2 µm), likely influenced by melt viscosity, whereas lateral roughness decreased (Ra down to 3.10 µm; Sz down to 45.4 µm), potentially associated with suppressed die swell. Printed ductility increased (>8%), a trend attributed to potential inter-layer re-melting during deposition. To overcome limited interfacial bonding, future work should incorporate coupling agents or chemical surface modifications. Overall, among the evaluated formulations, the composite with 5 wt% filler demonstrates a favorable balance of processability, mechanical integrity, and surface quality, showing high potential for non-load-bearing prototypes, indoor decorative elements, and light-duty packaging.