Production of Bio-Composite Filament using Lignin, Polylactic Acid and High Impact Polystyrene for Additive Manufacturing (3D Printing)
Type of DegreeMaster's Thesis
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Petroleum-based plastics, which are excessively used, are non-biodegradable, and lead to environmental pollution. Plant-based bio-products, on the other hand, are abundantly present, sustainable but are less exploited and valued. Lignin is the most promising plant-based polymer which is obtained relatively in a large amount as by-product from pulp-paper industry but have low market value. Additive manufacturing, also known as 3D printing, is rapidly growing manufacturing technology where a three-dimensional object is created by the application of material layer by layer. The main objective of this study was to incorporate lignin in two different polymers namely polylactic acid (PLA) and high impact polystyrene (HIPS) to develop composite filaments that can be used for 3D printing and to study the effect of lignin on the properties of filaments. In the first part of this study, lignin and PLA were added at different ratios to develop filaments. Characterization of those PLA-lignin filaments were performed using thermogravimetric analysis, differential scanning calorimetry, tensile test of filaments, scanning electron microscopy and dynamic mechanical analysis. Till 20 wt.% lignin was incorporated in PLA matrix; however, there was significant decrease in tensile strength and elongation at maximum load compared to that of pure PLA filaments. To further improve the mechanical properties of those filaments, two plasticizers namely PEG 2000 and struktol® TR451 were added separately in varying ratio in PLA and 20 wt.% lignin mixture (PLA_L20 hereafter) and similar characterizations were done. A 2 wt% of PEG in PLA_L20 showed significant improvement in mechanical properties. On the other hand, struktol did not show significant enhancement in tensile stress at maximum load of PLA_L20 composite. In the second part of the study with HIPS and lignin, 5, 10, 15 and 20 wt.% of lignin were extruded with HIPS to develop the filaments. Similar to the first part of the study, thermal, mechanical, and morphological properties were studied in addition to the flame-retardant. Filaments till 10 wt.% addition of lignin had similar mechanical properties as that of lignin; however, on further increasing lignin to 20wt.%, tensile strength and elongation at break were degraded. Additionally, adding unmodified lignin did not contribute to flame resistance of HIPS. Overall, this research provides the prospect of utilizing lignin as a filler material for 3D printing when mixed with polymers such as PLA and HIPS. This could contribute to the lignin valorization. However, lignin cannot be blended at higher amount without compromising mechanical properties of biocomposites.