Effects of functionalization and annealing in enhancing the interfacial bonding and mechanical properties of 3D printed fiber-reinforced composites

Abstract The properties of 3D printed polymer composites depend significantly on the fiber-matrix bonding, inter-bead bonding between each layer, and process-induced void contents. This study focuses to determine the effects of acid-based oxidation treatment of fibers on fiber-matrix interfacial bonding. The effects of nozzle geometry and post-manufacturing vacuum annealing on microstructure, inter-bead bonding, and mechanical properties of fused filament fabrication (FFF) based composites are also studied. The surface treatment of fibers had a profound impact on the chemical compositions of the fibers. A significant increase in – C O O H sites from 0.22 m m o l / g to 0.98 m m o l / g was observed with 30 minutes oxidation treatment. The energy dispersion spectroscopy (EDS) also showed the evidence of increased oxygen content on the fibers. Such treated fibers were found to improve both the tensile properties, short beam shear strength, and fracture toughness. The vacuum annealing almost doubled the degree of crystallinity of the composite and gave rise to a chain rearrangement in the polymer-crystalline phase, studied through Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The overall increase in tensile strength, tensile modulus, and short beam shear strength were about 20.58%, 73%, and 7%, respectively in comparison to the baseline. The fracture toughness of the vacuum-annealed sample with functionalized fibers was 23% higher than the un-annealed-untreated fiber-reinforced composite. Such increment in structural properties was further explained through the SEM analysis of the fracture surfaces. Evidence of crack deflection due to increased surface roughness, fiber alignment, pullouts, fiber-matrix debonding, and crystallinity of the matrix was observed from the analysis.