Influence of molecular weight distribution on mechanical and interlayer properties of FFF printed PA12

Abstract Understanding how molecular weight distribution (MWD) influences the mechanical and fracture behaviour of additively manufactured PA12 is essential for establishing reliable process–structure–property relationships. An approach to minimize anisotropy has been to specifically target the feedstock materials with the goal of enhancing interlayer adhesion. In this study, polyamide 12 (PA12) grades of MWD were investigated to determine the effect of MWD on the interlayer bond formation and anisotropy of the printed samples. Three different grades of PA12 were printed into tensile coupons and double cantilever beam (DCB) specimens and the mechanical properties were assessed to study interlayer bond strength using standard fracture toughness technique. A significant improvement in mechanical properties and fracture toughness were observed with higher print temperatures attributed to strong interlayer adhesion owing to longer interlayer bonding times (verified through the Lumped Capacity model and thermocouple data). Fracture toughness assessment also demonstrated that amongst samples printed at the same temperature, PA12 with a lower average MWD provided the highest fracture toughness (G 1C ) values, attributed to the faster diffusion of short polymer chains across the interlayer interface. Tailoring the MWD of feedstock polymers utilized in 3D printing as a strategy to optimize performance and lower anisotropy was demonstrated to be a feasible pathway. These findings were utilized by developing a PA12 blend of broad MWD which provided the highest overall mechanical properties and G 1c , demonstrating the usefulness of incorporating a high proportion of fast diffusing short polymer chains in the development of polymeric feedstock materials. Additionally, for large scale 3D printing applications, where maintaining high chamber temperatures is impractical, these results suggest that optimizing MWD can be an alternative strategy to improve interlayer adhesion and mechanical properties without relying solely on elevated print temperatures.