Interfacial behavior between thermoplastics and thermosets fabricated by material extrusion-based multi-process additive manufacturing

Multi-material additive manufacturing (MMAM) allows one to fabricate objects using dissimilar materials with different material properties. However, most of the existing MMAM processes are limited to the fabrication of either dissimilar thermoplastics or thermosets. To address this issue, a multi-process additive manufacturing (MPAM) technique combining two different material extrusion-based processes is developed to fabricate both thermoplastics and thermosets in a single print. To understand the interfacial behavior between a thermoplastic, polylactic acid (PLA), and a thermoset, polydimethylsiloxane (PDMS), the effect of process parameters on the surface morphology of PLA and PDMS is evaluated using an in-line 3D surface profiler. The intra-layer and interlayer adhesion between PLA and PDMS are analyzed under tensile and bending loads, respectively. The morphology of PLA and PDMS at the failure surface after mechanical tests is examined to understand the interfacial failure mechanism. Experimental results have shown that a flow rate of 80 % and a pressure of 90 kPa result in the best in-process surface quality for PLA and PDMS, respectively. The tensile strength of the PLAPDMS specimen is 311.8 kPa, and the flexural modulus, strength, and energy absorption are 530.5 MPa, 25.3 MPa, and 2 MPa, respectively. A purely interfacial failure is observed between PLA and PDMS under both tensile and bending loads. This study provides a guideline for investigating the interfacial behavior between thermoplastics and thermosets fabricated using MPAM.