Biorefinery lignin as filler material in polylactic acid composite

Abstract

<p>In natural world, lignin is unique and the most abundant renewable carbon source after cellulose, therefore, more applications of adding commercial value of lignin are needed. Polylactic acid (PLA), which has the second highest consumption of bioplastic in the world, is a biodegradable composite with widely application in industry. A filler adding into PLA can decrease the cost of the composite, and change the mechanical and thermal properties compared with original pure PLA. In this thesis report, the objective is to analysis how a lignin-based filler could influence the mechanical and thermal properties of PLA composite. In Chapter II, hydrochloric acid wash was applied to reduce the ash content of Lignin from 7% to 4% and 2%. TGA, FTIR, ICP, MPT and elemental analysis tests were applied to analysis the basic properties of lignin and pure PLA. Then, lignin with 2%, 4% and 7% ash content were applied as fillers in PLA composite with 5%, 10% and 15% weight percentage, respectively. The extruded mixed composite was produced into films to test thermal and mechanical properties by TGA, FTIR and MPT tests, including decomposition temperature, tensile strength, modulus, and strain of lignin-PLA composite. Same tests were also applied in Chapter III. In Chapter III, lignin with 4% ash content was acetylated to remove hydroxyl group before it was added into PLA as filler to produce films. The results were compared with the ones in Chapter II. Also, films made by pure PLA, 4% ash content and 5wt% lignin filler, and 4% ash content and 10wt% acetylated lignin filler were heated at 40oC for 48 and 72 hours.</p> <p>Results showed that compared to pure PLA, adding lignin-based filler would decrease tensile strength and strain, whereas increase tensile modulus and thermal stability. There is an optimum ash content in lignin as filler, high ash content in lignin could reduce both mechanical properties and thermal stability. There is probably a combined effect of lignin and inorganic ash. Samples with acetylated lignin with 4% ash content and 10% weight percentage as filler showed the highest tensile strength, which is very similar to that of pure PLA, and a more stable strain under heat treatment after 48 and 72 hours. After comparison, acetylated lignin can certain increase modulus without reducing tensile strength (up to 10wt%). Meanwhile, lignin-based fillers are able to increase hydrophobicity of the composites.</p>