SUSTAINABLE 3D PRINTED COMPOSITES WITH TUNABLE PROPERTIES AND FUNCTIONAL MICROSTRUCTURES

Abstract

The environmental impact of petroleum-based plastics has prompted the search for eco-friendly alternatives. Nature-based sustainable materials emerge as compelling substitutes, given their abundance, renewability, biocompatibility, and biodegradability, effectively addressing both environmental and health risks associated with petroleum-based plastics. Recent advances in green biocomposites from plant-derived fiber and crop-derived matrix have stimulated interests in developing engineering-grade and multifunctional materials for additive manufacturing (AM). Direct ink writing (DIW) is an AM technique that enables the customized and precision fabrication of composites with enhanced mechanical properties through microstructural control. This dissertation focuses on developing 3D printable, recyclable, biodegradable, and functional advanced composites to mitigate the environmental and health hazards linked with petroleum-based plastics. The composite material is derived from amylopectin-rich corn starch and cellulose fibers sourced from corn products and waste. We leveraged a thermally activated gelatinization process of amylopectin molecules to achieve optimal rheological properties of the corn-based composite for 3D printability in DIW. The process utilized the thermal treatment effect on hydrogen bonding formation among amylopectin molecules as well as between amylopectin and cellulose fibers interfaces, thereby enhancing mechanical robustness. The process-structure-property relationships revealed tunable mechanical properties up to 3.3-fold in the printed specimens. Furthermore, recyclability tests demonstrated stable mechanical performance of the 3D printed specimens over 10 cycles compared to pristine samples. Additionally, we introduced a process-microstructure guided manufacturing approach for fabricating three-dimensional porous structures with hierarchical porosity for application in emerging fields like tissue engineering, bone scaffold, and drug delivery due to their distinctive porosity-driven functional properties. By harnessing the degree of amylopectin gelatinization coupled with 3D printing, we attained precise control over pore size at multiple length scales (macro, micro, and nano). Macropores are engineered via printing path design, while degree of gelatinization governs micro and nanopores formation. process-microstructure relationships demonstrated up to 2.3-fold control over micropores and over 3-fold for nanopores. The novel approaches reported in this dissertation offer opportunities to achieve tailored porosity at macro, micro, and nano scales within composite microstructure. These composites, derived solely from biomass and waste, represent a novel class of additively manufacturable sustainable materials that underscore the potential for replacing petroleum-based plastic, marking a significant stride towards sustainable manufacturing practices. With the rising demand for eco-friendly solutions, these natural material-based composites offer compelling alternatives with diverse applications across advanced engineering and biomedical fields.