(235b) Effects of ABS Variants with Distinct Microstructures on Interlayer Bond Formation in Matex AM Based on Their Morphological, and Rheological Aspects.

Acrylonitrile-butadiene-styrene (ABS) is an amorphous polymer, generally consisting of a continuous Styrene-Acrylonitrile (SAN) copolymer phase in which rubber spherical formed particles (mainly polybutadiene-PB) grafted with SAN are dispersed. This microstructure is mainly influenced by various factors such as PB rubber particle size and distribution, and others. The resulting microstructure allows ABS to lead to a complex failure mechanism involving cavitation, crazing, and localized shear yielding, resulting in a combination of stiffness and toughness.

Due to these favorable mechanical properties and its rheological behavior suitable for printing, ABS is one of the most common materials used for material extrusion additive manufacturing (MatEx AM). Despite the availability of a wide range of ABS grades on the market and numerous studies utilizing them, there has been limited research into understanding the relationships between ABS microstructure and interlayer bond formation.

In this study, we evaluate these relationships by comparing the as-printed and annealed impact strengths of various ABS grades with distinct morphological and rheological characteristics. Notably, ABS grade with larger rubber particle size exhibits a remarkable annealing effect. Despite initially having the lowest as-printed impact strength (1,396 J/m2), this grade achieves the highest impact strength (17,479 J/m2) after fixtured annealing, closely approaching the performance of their bulk injection-molded counterparts.

We hypothesize that the unique microstructure of ABS inhibits interlayer bond formation during printing due to its unfavorable rheological properties. However, our results suggest that after annealing, these initially unfavorable rheological properties induce increased interlayer contact pressure and potentially promote a more even distribution of rubber particles within the interlayer. Our hypothesis is supported by morphological analysis using AFM modulus mapping (e.g., rubber size and distribution on weld line) and rheological analysis using parallel plate rheometer (e.g., reptation time or Weissenberg number).