Enhancing interlaminar adhesion in multi-material 3D printing: A study of conductive PLA and TPU interfaces through fused filament fabrication

In the rapidly expanding field of additive manufacturing, multi-material fused filament fabrication represents a frontier with vast potential for creating composite structures that blend the benefits of different material properties. Interlaminar adhesion between dissimilar materials remains a challenge for the realization of multifunctional structure for practical use. This study investigates the interlaminar adhesion between conductive polylactic acid and thermoplastic polyurethane, materials representative of rigid and flexible characteristics, respectively. We present a comparative analysis of two adhesion enhancement approaches: the incorporation of mechanical interlocking features and the modification of surface roughness at the interface. Through tensile testing, we evaluate the effectiveness of these methods against a benchmark coupon with unmodified interface. Micro-computed tomography analysis, surface morphology analysis, and mechanical performance assessments elucidate the failure modes and provide insights into the interfacial behavior of these interface designs. We found that the interface design with top infill modification showed the highest interlaminar adhesion strength, with an improvement of at least 25% compared to the benchmark coupon. Our findings aim to inform the design and manufacturing practices in multi-material 3D printing and to open new avenues for the development of multifunctional, composite 3D-printed systems.