Euro PM2019 – Additive Manufacturing - Material Deposition Technologies © European Powder Metallurgy Association (EPMA) Influence of stearic acid in feedstocks for FFF and PIM Kukla C. 1 , Cano S. 2 , Holzer C. 2 , Gonzalez-Gutierrez J. 2 1 Montanuniversitaet Leoben, Industrial Liaison Department, Peter Tunner Strasse 27, 8700 Leoben, Austria Corresponding author: christian.kukla@unileoben.ac.at 2 Montanuniversitaet Leoben, Department of Polymer Engineering and Science, Institute of Polymer Processing, Otto Gloeckel-Strasse 2, 8700 Leoben, Austria santiago.cano-cano@unileoben.ac.at, clemens.holzer@unileoben.ac.at, joamin.gonzalez- gutierrez@unileoben.ac.at Abstract Material extrusion additive manufacturing with filaments is also known as Fused Filament Fabrication (FFF). FFF is a versatile and popular technology that, when combined with debinding and sintering, can be used for the fabrication of functional metal and/or ceramic parts similar to Powder Injection Moulding (PIM). In order to produce filaments, that are processable by FFF, a complex binder system is needed. The binder is generally composed of the main binder component, the backbone and additives. One popular additive in feedstocks for FFF or PIM is stearic acid (SA), since the use of SA is an effective way to reduce the viscosity, improve the feedstocks homogeneity and increase the solvent debinding rate.. In this investigation, the incorporation of SA into a binder system comprising of acrylic acid-grafted high density polyethylene, paraffin wax and styrene-ethylene/butylene-styrene copolymer has been studied. The effect of the SA on the viscosity, mechanical properties, debinding rate and processing by FFF for zirconia feedstocks is presented. Introduction Metallic and ceramic components can be produced by the material extrusion process known as Fused Filament Fabrication (FFF). In the FFF of metals and ceramics a polymeric binder is used to carry a high fraction of metallic or ceramic powder, obtaining the so-called feedstock. The feedstock is used to produce filaments which are then processed in a conventional FFF process to shape the parts, which must be debound and sintered similarly to the well-established process of Powder Injection Moulding (PIM). Like in PIM, FFF powders of different sizes and shapes can be employed and a wide range of materials can be processed [1]. Moreover, the same feedstocks can be employed for both processes, making possible their combination or the use of FFF as a prototyping method for PIM. In order to be processed as filaments by FFF, the feedstocks must meet many rheological and mechanical requirements [2–4]. One of the main factors affecting the properties of the feedstocks and their processability by FFF is the wetting and adhesion of the polymeric binder to the powder surface. A poor adhesion in particulate filled polymers leads to the separation of both types of materials and to inhomogeneities in the mixture, resulting in a high viscosity and in poor mechanical properties [5–7]. Since the polymers commonly employed as binders in PIM and FFF are highly non-polar, and the powder surface its characterized by a high polarity, additives are incorporated to improve the interaction of both materials. Stearic acid (SA) is the most common additive for the processing of metals and ceramics by PIM. The polar carbonyl group (C=O) in this fatty acid [7] facilitates the wetting and adhesion to the polar surface of the powders. Therefore, SA has been added as surfactant to improve the feedstock homogeneity and reduce the viscosity in both PIM [7–9] and FFF feedstocks [3,4]. In this study, the effect of SA on the properties of zirconia feedstocks developed in our previous study [2] is evaluated and correlated to the processing by FFF and solvent debinding. Experimental Materials TZ-3YS-E (Tosoh Europe B.V., The Netherlands) with 3 mol% of yttria, a specific surface area of 7 ± 2 m 2 /g and a particle size of d50 = 0.09 µm was the zirconia powder selected. A multicomponent binder developed in our previous study [2] comprised of acrylic acid-grafted high density polyethylene (AA-HDPE), paraffin wax (PW) and styrene-ethylene/butylene-styrene copolymer (SEBS) was used.