Fabrication and multi-scale mechanical characterisation of extruded PLA–tungsten carbide composites using fused filament fabrication

Ceramic-filled biodegradable polymer composites have attracted increasing interest in additive manufacturing research, yet the performance of polylactic acid (PLA) reinforced with tungsten carbide (WC) under realistic low-cost fabrication conditions remains poorly characterised. The aim of this research is to examine the mechanical and thermo mechanical properties of a composite consisting of 95 wt% (weight percent) of medical-grade PLA and 5 wt% micro-scale WC (tungsten carbide) (PW) particles (around 1 μm average diameter), fabricated using a single-screw extrusion process followed by Fused Filament Fabrication (FFF). Specimens conforming to ASTM standards (D638-22, D695-23, D790-17, D732-17) were subjected to tensile, compressive, flexural, and shear testing alongside Thermo-Mechanical Analysis (TMA) and Dynamic Mechanical Analysis (DMA), with results benchmarked against virgin PLA (vPLA). Compared with vPLA, the PW composite showed reduced average tensile strength (23% decrease, from 52.4 to 40.2 MPa), compressive strength (approximately 59% decrease, from 113.1 to 46.9 MPa), flexural strength (24% decrease, from 3.3 to 2.5 MPa), and shear strength (48% decrease, from 124.3 to 64.1 MPa). Prior research has suggested that the aforementioned reductions may be related to a number of variables, including the presence of large agglomerated WC particles, a lack of sufficient adherence between the WC and PLA materials, and/or increased viscosity of PLA melt; there is no way to separate these variables within this current experimental design therefore there is no means by which to obtain data concerning their respective impact on the mechanical and thermo mechanical properties of the current composite materials.. TMA tests show that WC inclusion lowers the coefficient of thermal expansion (CTE) by approximately 20% below the glass transition temperature, indicating improved dimensional stability. Reconfigured DMA results confirm increased stiffness through higher storage modulus (increased stiffness). The larger storage modulus value and the restricted mobility of the PLA producing composites provide evidence for improvements in many stiffness characteristics despite lower mechanical strength. The study confirms that PW sensitivity to processing method has been quantified for the first time. The tensile response for the PW composite produced with the same resin composition using either vertically/horizontally-oriented direct fused additive manufacturing versus an optimised twin screw compounding process had around 65 proportional-point difference in tensile properties.