Effects of Polymerization and Microstructure on the Printing and Annealing of Acrylonitrile-Butadiene-Styrene (ABS) for Material Extrusion Additive Manufacturing

Acrylonitrile-butadiene-styrene (ABS) is one of the most common material used for material extrusion additive manufacturing (MatEx AM), owing to its favorable rheological properties for extrusion and printing. Although a wide range of ABS sources have already been available on the market, a truly systematic study which entails the ABS polymerization and its microstructure and their evolution during extrusion, printing, and annealing have not been done. Such lack of systematic study has led to empircally driven studies that yield wildly different properties depending on the printer, its parameter, and the grads of ABS. In this work, the processing-structure-property relationships are evaluated using as-printed and annealed impact strength between four ABS grades with distinct characteristics, i.e., polymerization methods (mass vs emulsion polymerization), and uni- or bimodal distribution of rubber particles. The as-printed trend of the four ABS are remarkably different when they are annealed, which is largely impacted by microstructure and its rheology during printing and annealing. In particular, the ABS produced by mass polymerization yields the lowest as-printed impact strength, however the annealed impact strength is the highest among the grades, very close to its bulk injection-molded strength. Optical and rheological analysis of these results elucidates the processing-structure-property relationships of ABS for MatEx AM.