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Hua, Qi

University of British Columbia

This study presents an innovative two-step chemical modification process for softwood kraft lignin (SKL), adhering to green chemistry principles. The initial hydroxyethylation step produced fractionated SKL samples with varying molecular weights, imparting diverse properties. The second step, which introduced vinyl groups through esterification with acrylic acid (AA) or cinnamic acid (CA) endowed SKL with lower glass transition temperature, improved hydrophobicity, radical polymerization capability, electron-donating ability, and enhanced solubility in select organic chemicals. Introducing vinyl groups within lignin facilitated reactivity towards polymerization, opening avenues for the production of advanced materials. The two-step esterification reaction was found to replace polar hydroxyl groups on lignin with non-polar compounds, significantly enhancing the solubility of lignin in oil-based monomers. Consequently, vinyl-lignin and vinyl-monomers (e.g., styrene, poly (ethylene glycol) diacrylate, or methyl cinnamate) could be reacted into copolymers with desired properties. Additionally, the esterified softwood kraft lignin (SKL) exhibited a reduced glass transition temperature (Tg), enabling thermal processing at relatively moderate temperatures. The CA modified lignin was successfully melt-spun with poly (butylene adipate-co-terephthalate) (PBAT, brand name Ecoflex®) at specific weight ratios into fibers, which were then hot-pressed into films with multiple functions suitable for food packaging. Furthermore, after esterification with cinnamic acid, the modified lignin enhanced the toughness of blends significantly more than the original SKL when blended with PBAT or used by itself. In another application, CA modified lignin could be melt-spun into continuous fibers with a small diameter (<50µm) without the need for additives as carbon fibre precursors. This lignin derivative was well-suited for producing carbon fiber precursors. Compared to polyacrylonitrile (PAN), which requires a thermal stabilization stage to induce cyclization and crosslinking reactions for the formation of aromatic structures, the lignin cinnamate we produced already contains abundant aromatic structures. Consequently, the resulting 100% lignin derivative fiber could be carbonized using a more time-efficient and cost-effective method compared to PAN-based carbon fiber, involving an acid treatment to replace the thermal stabilization stage.

Text

2024-08-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89090

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/