Fused filament fabrication of void-free parts using low viscosity hot melt adhesives

In this work, a polyamide hot melt adhesive was evaluated as a feedstock for material extrusion additive manufacturing (AM). This adhesive, Technomelt PA 6910, is a semicrystalline polymer with a sub-ambient glass transition temperature, intermediate melting temperatures, and low recrystallization temperature. Due to this combination of properties, Technomelt PA 6910 is a room temperature flexible material that exhibits high toughness and strength, and good adhesion. Technomelt PA 6910 was extruded into filament form and printed using fused filament fabrication (FFF), a desktop form of material extrusion AM. The effect of extruder temperature on print quality and mechanical properties and the effect of raster angle and layer height on mechanical properties of prints were studied. Optimized print parameters, as well as the material's low viscosity, resulted in void-free prints that exhibited isotropic tensile properties comparable to or better than compression molded values. This work broadens the material window for FFF and demonstrates that hot melt adhesives can be used to additively manufacture optically transparent, flexible structures capable of >1,200% strain to failure. The mechanical properties of Technomelt PA 6910, combined with FFF as a versatile processing technique, make this material a candidate for a variety of applications in which transparency, design complexity, and flexibility at a wide range of temperatures are desired.