Optimizing In-Situ Adhesive Bonding for Multi-Material Additive Manufacturing: Mechanistic Comparison of Solvent-Assisted and Thermal Methods for ABS-PLA Joints

The robust joining of dissimilar polymers, such as acrylonitrile butadiene styrene (ABS) with polylactic acid (PLA) is essential to promote multi-material additive manufacturing (AM). This work systematically compares acetone assisted solvent bonding at 25 and 75°C to direct thermal bonding at 100–160°C for ABS-PLA lap-shear joints, by use of ABS as an in-situ adhesive and according to ISO 4587, as standard. The optimal thermal bonding temperature was 140°C as it yielded the highest shear strength of 2.2.96 ± 0.02 MPa, which was a 92% improvement compared to acetone bond temperature of 25°C (1.54 ± 0.02 MPa) and one-way ANOVA showed that there are trends that differ significantly between conditions (p < 0.001).There was a mechanistic shift between the brittle adhesive failure in solvent-bonded joints to the ductile cohesive failure in thermally-bonded joints by temperature-enhanced molecular interdiffusion (zone widths up to 0.475 mm at 160°C). The use of scanning electron microscopy proved the occurrence of filament tear, plastic deformation and degradation in the specimens after heating (e.g., void density was about 23.6% at 160 C), whereas finite element analysis provided confirmation of stress distributions and mechanisms of failure. Such results offer the basis to optimize joining parameters towards reliable, repairable and sustainable multi-material AM structure via efficient, high-performance approach.