The Effect of Polymer Additives in Powder Based 3D Printing

Leja PleÅ¡ko¹ and Lidija Korat<sup>2

1</sup>University of Ljubljana, Faculty of Chemistry and Chemical Technology, Večna pot 113, SI‑1000 Ljubljana, Slovenia, plesko.leja@gmail.com

²Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI‑1000 Ljubljana, Slovenia, lidija.korat@zag.si

In general, synthetic gypsum material (SGM) is an industrial by‑product produced in excess quantities from several processes, such as power utilities or acid neutralisation. SGM is widely used as a construction and modelling material in civil engineering, it is used in plasterboards or as an insulating material. However, such use of SGM requires certain mineralogical, chemical and physical properties to achieve the final strength of solid objects. Since SGM is commercially available, it can be re‑used as raw powder material for 3D printing, however the use of additives is therefore required.

The aim of this research was to formulate structurally resistant SGM powder with the addition of synthetic and semi‑synthetic polymer powder for 3D printing. The SGM powder used in this research was obtained from local industrial by‑processes and it is based on calcium sulphate (CaSO₄∙xH₂O), where the x represents the temperature dependence of the powder treatment. For this purpose, a 3D printing technique called binder jetting (BJ3DP) with the application of a liquid binder onto particles of pre‑treated SGM was used, where geometric square prisms of 2 × 2 × 8 cm were printed using CAD models.

Different analytical techniques (XRD, XRF, SEM, BET, TG/DTA, granulometry) were used for the mineralogical, chemical and physical characterization of the SGM powder. Pre‑defined weight percentages (wt%) of various polymer additives (polyvinyl alcohol – PVA and methyl cellulose – MC) were selected according to their chemical properties and added to the powder mixture before printing. During our research, we focused on chemical compatibility and printing parameters, where the successful printing of geometrical shapes and the mechanical properties (density and compressive strength) of solid prisms were our main goal. The results of our research have shown that additives are necessarily in mixtures of SGM in order to achieve the required properties of 3D‑printed solid prisms.

Acknowledgement: This research work was performed under the Slovenian Research Agency (Programme No. Z2‑1861).

Keywords: gypsum, polymer, binder jetting, 3D printing