(689g) Fused Filament Fabrication of Hot Melt Adhesives

Fused filament fabrication (FFF), a desktop form of material extrusion additive manufacturing (AM), is the most common AM technique for thermoplastics. In FFF, thermoplastic filaments are heated until molten, then extruded onto a print surface layer-by-layer. Broader adoption of FFF is limited by challenges such as narrow material range, anisotropic mechanical properties, and inferior mechanical properties as compared to traditional manufacturing techniques such as injection molding or compression molding. The crystalline regimes in semicrystalline polymers enhance their strength and chemical resistance; however, increased crystallinity can also lead to more brittle materials. As a result, in conventional plastics manufacturing, processing conditions and material selection are optimized to lead to the desired crystallinity and resulting properties for a given application. The rapid heating and cooling inherent to FFF leads to complex crystallization behavior, warpage,and poor weld strength.

In this work, we demonstrate FFF of a polyamide hot melt adhesive. This adhesive is a semicrystalline polymers with a sub-ambient glass transition temperature, intermediate melting temperatures, and low recrystallization termperature. Due to this combination, this is a room temperature flexible materials that exhibits high toughness and strength, and good adhesion. The effect of extruder temperature on print quality and the effect of raster angle on mechanical properties of prints was studied. The optimized print parameters, as well as low viscosity and high melt strength of the material, resulted in elimination of voids within the prints. Additionally, tensile properties comparable to or better than compression molded hot melt adhesives are observed. 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 >1200% strain to failure.