Lignin is the third most abundant biopolymer and the only one with a large aromatic network. 50 million tons of it are produced annually.1 Lignin is synthesized inside the plant by the radical polymerization of phenol groups and makes up to forty percent of the dry weight of plants.2 Lignin is produced as a waste by-product from the paper making industry. Most of the lignin produced by these processes are burned as fuel. Recently, rising environmental concerns have led to growing need for bio renewable resources. To this end, research has shifted into the study of biopolymers, such as lignin and increasing the value of waste products1. The radical polymerization nature of lignin leads to a random structure of the monolignol subunits. This inconsistent structure makes lignin very difficult to characterize and can vary from plant to plant2. However, the potential usefulness of lignin as a renewable cheap material for polymer blends, outweighs its drawbacks. Lignin has been shown to increases thermal stability3, is a natural fire retardant4, and has excellent UV-blocking capabilities5. These properties can be used to reinforce polymer properties with the creation of polymer lignin composites.
1Vijay Kumar Thakur, et al. ACS Sustainable Chemistry & Engineering 2014 2 (5), 1072-1092
2 Amina Naseem, et al. I. J. of Biological Macromolecules 2016, 93, 296-313
3Gordobil, Oihana, et al. J. Polymer Degradation and Stability 2014, 108, 330–338.
4Lina Liu, et al. ACS Sustainable Chemistry & Engineering 2016 4 (4), 2422-2431
5Qianqiu Xing,et al. ACS Sustainable Chemistry & Engineering 2017 5 (11), 10342-10351