Process, structure, and property relationships for carbon black-filled polylactic acid composite fabricated by fused filament fabrication: a mechanical performance study

Abstract

Carbon black-reinforced polylactic acid (CB-PLA) composites possess both mechanical and electrical properties suitable for fused filament fabrication (FFF). However, the correlation of various FFF process parameters with the mechanical properties and the microstructure of the fabricated parts still remains unexplored. In this study, the influence of important FFF parameters, namely infill density (ID), printing speed (PS), and layer thickness (LT), on the mechanical properties of CB-PLA (Young’s modulus (E), tensile yield strength (TYS), ultimate tensile strength (UTS), breaking strain (BS), strain energy density (SED), impact strength (IS), flexural modulus (FM), flexural yield strength (FYS)) is investigated systematically. The Box-Behnken design with response surface methodology (RSM), combined with ANOVA, was used for the quantification of main effects, nonlinearities, and interactions. ID showed the largest practical effect for seven of the eight mechanical responses, whereas LT showed the largest practical effect for FYS. Moreover, ID, PS, and LT showed linear, nonlinear, and interactive effects as well. Selected practical optimal conditions (ID = 80 %, PS = 60 mm/s, LT = 0.12 mm) yielded experimentally E  = 810.4 MPa, TYS = 14.9 MPa, UTS = 22.73 MPa, BS = 6.21 %, SED = 83.4 × 10 ⁴  J/m ³ , IS = 31.21 kJ/m ² , FM = 1,205.5 MPa, and FYS = 33.85 MPa. Under optimum parameters, scanning electron microscopy (SEM) showed improved layer adhesion and fewer visible defects. This study offers practical guidelines for optimizing the properties of FFF-printed CB-PLA composite, with balanced mechanical properties.