Additive Manufacturing of Biopolymers Via Modified FDM 3D Printing Enabled By the Dissolution Properties of Hydrophilic Ionic Liquids
Authors: Appel Jared , Ho Davina , Dobyns Breanna M , Reichert W. Matthew Matthew , Duranty Edward R. 
Published: November 2022

Additive manufacturing, also known as 3D printing, has become a hot topic of research over the past decade primarily due to the low cost, east of use, and reliability of 3D printing equipment. As a result, numerous 3D printing methods have been developed using a variety of stock materials, such as thermoplastic fused deposition modeling (FDM), stereolithography resin-based printing (SLA), and laser sintering techniques (SLS) targeting both metal and polymeric materials. A common goal in FDM printing is to find and develop methods for printing new materials outside the most common thermoplastics, such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS), that might yield printed parts with different, and potentially advantageous, structural and material properties. One emerging area of interest involves the 3D printing of biopolymers due to their relative abundance as compared to traditional synthetic polymers synthesized from petroleum byproducts. The production of these polymers can be harmful to the environment and the polymers find themselves as waste products in almost every corner of the globe, while biopolymers have the advantage of being biodegradable and often biocompatible.

Cellulose, one of the most abundant biopolymers in existence, was targeted as a viable polymer for use in additive manufacturing in this work. Due to the fact that cellulose degrades under heat, traditional FDM extrusion methods that utilize heat to render polymer stock processible for layer-by-layer deposition was not applicable. Therefore, an FDM 3D printer was modified for printing a cellulose solution that “extruded” via a syringe pump where the ability of cellulose to be dissolved in certain hydrophilic ionic liquids provided the exfoliation required to render the cellulose processable for layer-by-layer deposition. To make the cellulose solution less viscous such that it could be printed, 1 mL of acetonitrile was added for every 4.0g of cellulose to the gel solution. This addition allowed the solution’s viscosity to be lowered to the point that the solution flowed freely from a needle tip once the syringe pump was started. In this fashion, the traditional extrusion head used in FDM printing was replaced on the suspended gantry by this needle tip, from which the cellulose/IL solution was deposited onto a cool print bed.

Once prints were generated using the modified 3D printer, the solvating ionic liquid was displaced by an IL-compatible liquid such as water or alcohol. This process left behind a pure cellulose printed part once the water or alcohol was evaporated, causing the print’s dimensions to shrink. In this work, it was found that all prints shrank reliably, however, some prints warped during the shrinking process, altering their aspect ratio. It seems that the primary factor driving this warping throughout the evaporation process was the amount of surface area available for evaporation from the printed part. For parts where the surface area of the exposed print was restricted by being placed in a partially sealed plastic bag, homogeneous shrinking was observed in the X/Y plane on average to 41.2 ± 2.6 % of their original size while maintaining their original aspect ratio.

Figure 1