Improving Polyamide Multi Jet Fusion Additive Manufacturing by Controlling Degradation Reactions and Incorporating Postindustrial Waste

Multi jet fusion (MJF) is an interesting manufacturing technique for printing polyamide (PA) parts, with the control of (i) thermal and thermo-oxidative degradation reactions and (ii) degradation reactions induced by its chemical agents as the molecular-scale problem. Sustainability challenges are (i) the maximized use of unavoidable postindustrial waste, due to the need of a structural support during processing, and (ii) the introduction of biobased materials such as PA11 compared to conventional PA12. In the present work, in the first part, the performance of virgin, vacuum-aged, and air-aged PA11 and PA12 powders is compared, analyzing molecular, thermal, rheological, and mechanical properties. While the (overall) thermal (th) decomposition rate coefficient is almost equal for both polymers (k_Mp,th of 2.0 × 10^–6 and 2.4 × 10^–6 s^–1; M_p; peak average molar mass), PA12 is more prone to oxidative (ox) degradation (k_Mp,ox,PA11 of 3.2 × 10^–7 s^–1 vs k_Mp,ox,PA12 of 4.6 × 10^–6 s^–1), although PA11 has more discoloration at the surface. In a second part, it is shown that the incorporation of (PA11) postindustrial waste powder can be considered during printing, with even better mechanical properties possible upon applying vacuum treatment, in case the impact strength is less critical. With air treatment, a strong drop in the performance is obtained due to (imide-driven) microphase separation and scission-driven molecular degradation, the latter enlarged if one isolates the influence of 2-pyrrolidone and triethylene glycol, the main components of the chemical agents. The insights in the present work are valuable for material selection and process optimization strategies for MJF technology, contributing to its broader implementation in the automotive, aerospace, and healthcare industries.