Optimization of Additive Manufacturing Process Parameters for Locally Sourced Polymer Composites in Nigeria's Small-Scale Production Industries

Fused deposition modelling (FDM) holds considerable promise for small-scale manufacturing enterprises across sub-Saharan Africa, yet the high cost of imported filament materials continues to obstruct widespread adoption. Nigeria's agricultural economy generates substantial quantities of agro-waste byproducts — notably cassava starch and palm kernel shell (PKS) — whose conversion into printable polymer composites has received limited systematic investigation, particularly with respect to print parameter optimisation. This study investigated the combined effects of three critical FDM process parameters — nozzle temperature (190–230 °C), infill density (40–100%), and layer thickness (0.1–0.4 mm) — on the tensile strength and surface roughness (Ra) of cassava starch-reinforced polylactic acid (CS/PLA) and palm kernel shell/PLA (PKS/PLA) composite filaments fabricated from locally sourced Nigerian materials. A central composite design (CCD) under response surface methodology (RSM) was employed, yielding 20 experimental runs per composite system. Tensile specimens were prepared in accordance with ASTM D638 Type I geometry, and surface roughness was measured using a contact profilometer. For the CS/PLA composite (10 wt% cassava starch), optimum tensile strength of 47.3 MPa was achieved at 215 °C, 80% infill, and 0.15 mm layer thickness — representing a 23.4% improvement over non-optimised baseline conditions. For the PKS/PLA composite (15 wt% PKS), optimum tensile strength reached 44.8 MPa under comparable parameter settings. Surface roughness was minimised at Ra = 2.14 µm for CS/PLA and Ra = 2.87 µm for PKS/PLA at the lowest layer thickness tested (0.1 mm). Analysis of variance (ANOVA) confirmed that layer thickness exerted the most statistically significant influence on surface roughness (p < 0.001), while infill density was the dominant factor governing tensile performance (p < 0.001). These results demonstrate that agro-waste polymer composites sourced entirely within Nigeria can achieve mechanical and surface quality properties that are broadly comparable to commercial PLA grades, offering a viable cost-reduction pathway for local small-to-medium enterprises (SMEs).