Facile Chemical Modification of Lignin for Synthesis of Lignin-Based Sustainable Polymers

Lignin is abundant and low-cost biomass polymer that has high concentration of aromaticity. Therefore, the lignin may provide high mechanical and thermal properties which are not easily available from other bioplastics. In addition, because lignin is not a human food, the supply and cost are very stable. However, a natural lignin cannot be used as an original form because of its poor processibility and compatibility with other materials. This presentation will discuss 1) chemical modification of lignin for further material applications and 2) synthesis of well-defined degradable lignin-based polymers. Commonly available kraft lignin, byproduct of paper industry, is not readily processible to produce commodity polymers due to its poor compatibility to other polymers. Thus, a new technology is developed to modify the lignin that possess carboxylic acids in the presence of capping agents. Herein the addition of capping agent is croitically important because the capping agent deactivates excessive number of active functional groups on lignin. The remaining a few selected functional groups of lignin works for the next reaction. Without the capping agent, the lignin-based polymer proceeds to unwanted reactions through the excessive functional groups. The unwanted reactions led solubility change and brittleness of the yielding polymers. The modified lignin was then used for a new polyester synthesis. The new lignin-based polyester is a graft copolymer (lignin-graft-poly(ethylene brassylate)) that has strong and stable covalent bonds between lignin and poly(ethylene brassylate) rather than blending of two polymers. The new polymer’s main linkage, ester, is scientifically proven biodegradable functional group in natural conditions. The new lignin modification and polymer synthesis method will enable to produce 100% biomass-based and completely biodegradable commodity polymers.