3D Printing and Characterization of Hydroxypropyl Methylcellulose and Methylcellulose for Biodegradable Support Structures

Abstract

Abstract Additive manufacturing process based on fused deposition modeling (FDM) and material extrusion (ME) typically use thermoplastic materials like ABS, PLA, or nylon to fabricate parts layer-by-layer. In order to build a part successfully with complex features such as pores or holes or irregular shapes, the build part requires support structures to hold the deposited material and to prevent collapse of the finished parts before solidification. The support material acts as a sacrificial layer that should be easily removed later on by chemicals/enzymes, or broken by mechanical force. The present support materials used with FDM technology have challenges of poor dissolvability in chemical solution and difficulty to be removed from the finished part. In addition, these support materials are usually petroleum based which has a negative impact on the environment. The goal of the project is to identify a suitable biomaterial for support structures that will eliminate the challenges of poor dissolvability and toxic waste generated by the current material. This paper is focused on extrusion-based 3D printing process of thermoset biopolymers to fabricate support structures. In this study, three biodegradable cellulose derivatives, i.e. methylcellulose (MC) A4M, HPMC K4M, and hydroxypropyl methylcellulose (HPMC) E4M, with different degree of substitution of hydroxyl group were used. We investigated the effect of concentrations (8, 10, and 12% w/v) of all three cellulose derivatives on the rheological properties for understanding their printability. The rheological analysis revealed that all hydrogels exhibit shear-thinning properties with relatively low yield stress. At the same concentration, the apparent viscosity of HPMC K4M tended to be higher than HPMC E4M, followed by MC A4M. Effects of printing parameters (extrusion rate, nozzle diameter, and printing speed) were optimized to obtain the desired three-dimensional structures. The sample of 12% MC A4M and 12% w/v HPMC K4M showed higher complex shear modulus than other materials, which indicated higher rigidity and shape retention capacity of the printed parts. The ideal material for extrusion during printing and least deformation after printing was also observed for 12% MC A4M, which indicated a relationship between rheological properties and printability. The water dissolution of the MC and HPMC hydrogels allowed easy removal of the support structures from the build material. Biopolymers like MC and HPMC, when 3D printed as a support material via ME processes, help in moving closer towards sustainable manufacturing.