Print Quality Optimisation of Upcycled Biomaterials for Ambient 3D printing

Abstract

With growing concern over our reliance on non-renewable resources and the environmental impact of conventional manufacturing, the quest for sustainable materials and production processes has intensified. This pursuit has extended to the field of additive manufacturing, where bio-materials have emerged as promising alternatives, aiming to reduce energy consumption and utilise material waste streams. While biopolymers like PLA are a good step forward, they still pose sustainability challenges, primarily related to energy-intensive melting processes, competition with food sources for production, slow biodegradability, and inadequate waste disposal systems. Consequently, researchers have turned to utilizing biomass waste streams to create 3D printable materials that solidify at ambient temperatures. However, the currently existing bio-based materials for ambient printing exhibit inconsistencies in quality. To allow for commercial adoption of these materials, enhancements in print quality are necessary.

This thesis addresses the core issue of lower print quality in room-temperature printing of biomaterials. Its primary aim is to develop and optimize the print quality of these materials, fostering a deeper understanding of the key factors that influence their printing performance. Within the context of print quality, the study examines parameters such as dimensional accuracy, bridging, overhang performance, warpage, corner sharpness, surface finish, and precision. Furthermore, the research investigated the feasibility of reprinting these materials and its impact on their print quality. Extra attention was dedicated to investigating the influence of the rheology characteristics of the materials on the resulting print quality.

The research led to the creation of two materials, AB1 and CLAB4 and the optimization of print parameters to enhance their print quality. In doing so it elaborates on the influences of material composition, preparation and printing parameters on the print quality of biomaterials printed at room temperatures.
Of the materials developed, AB1 demonstrated exceptional bridging capabilities, achieving distances of up to 15 mm, minimal shrinkage (averaging 6% in the xy-directions and 4% in the z-direction), and good result precision. In contrast, CLAB4 excelled in surface finish, printing overhangs up to 40 degrees, and showcased higher efficiency in material preparation. Most noteworthy of both materials is their reprintability without evident degradation in print quality, a crucial feature for sustainable printing methodologies.

In this Research, rheology characteristics have proven to be pivotal due to their direct influence on material flow and behaviour. Unlike conventional melting-based printing, where materials flow upon heating and solidify once they are extruded, ambient printing requires inks to have specific rheology behaviours caused by changes in shear. Rheology governs how easily the ink flows when extruded and its ability to retain shape once extruded. Optimizing the shear-thinning behaviour and elastic recovery behaviour is crucial. This study elaborates on the specific aspect of rheology to improve enhancements in print quality, including Yield stress, flow stress, storage modulus, loss tangent and thixotropic response and recovery. Additionally, it presents interesting insights into how to optimise them based on material composition and preparation. Mixing the material before extrusion, for example, was shown to significantly increase the thixotropic response time, leading to more precise extrusion.