Correlating microstructural and rheological variations in acrylonitrile-butadiene-styrene (ABS) with interlayer bond formation in material extrusion additive manufacturing

Abstract

Acrylonitrile-Butadiene-Styrene (ABS) is widely used in material extrusion additive manufacturing due to its well-balanced mechanical and rheological properties, as well as its accessibility. Although a wide range of ABS sources are already available on the market, limited research has been conducted to understand the effects of the microstructural and rheological differences among ABS grades on printability, interlayer bond strength, and post-print annealing. In this study, the correlation between microstructure, rheology, and printability are linked by comparing the dimensional stability, interfacial morphology, and part strength of select commercial ABS grades that are as-printed and annealed. Notably, ABS grade produced by mass polymerization (mABS), which has a broader polybutadiene (PBD) particle size distribution, larger PBD size, and higher viscosity, demonstrated the lowest as-printed impact strength (1400 J/m²), while exhibiting a dramatic increase in strength (17,500 J/m²) after annealing, closely approaching its bulk injection-molded counterpart. Such dramatic change is not observed in emulsion ABS (eABS) grades. It is concluded that the primary factors affecting interlayer bond formation in the as-printed state are viscosity and the inherent toughness of the ABS, whereas relaxation behavior and microstructural differences become key factors during annealing. Morphological and rheological analyses supported this hypothesis, helping to elucidate the complex interplay of various ABS properties in material extrusion additive manufacturing.