Valorization of lignin – the most abundant aromatic biopolymer by fractionation

Abstract:

Plastics are widely used for numerous consumable products in our daily life, which have brought up many societal benefits. Yet, most of the plastic products have an extremely short life time. This has generated tremendous amount of plastic wastes that have accumulated in the landfills, oceans, waterways, and other natural environment and further entered into animal and humans bodies, threatening our health. It was estimated by 2015, human beings have produced 5.7 billion tons plastics and of that 4.9 billion tons were discarded into the natural environment.

Wood is a significant raw material in Finland and is exploited to a range of primary products, e.g. pulp, paper, and timber. Lignin constitutes about a third of the wood biomass and is the most abundant aromatic biopolymer. The International Lignin Institute estimates the global production of lignin at 40-50 million tonnes, most of which is burnt for energy as pulp production waste. Lignin is by nature a branched and cross-linked polymer, which contains both hydrophobic and hydrophilic groups. The impressive properties of lignin, such as high abundance, antioxidant, antimicrobial and biodegradable nature, along with its CO2 neutrality and reinforcing capability, make it an interesting building block for developing novel bio-based materials. However, isolated lignins or so-called technical lignins are too heterogeneous in structure, too impure, and too complex for utilization in advanced polymer applications. Thus, fractionation technology has been utilized to produce relatively homogeneous lignin fractions with well-defined characteristics, such as defined range of molar mass and enriched functional groups that are desired in the respective applications. For instance, specific fractions of lignins are seen promising sustainable alternative to the petroleum-based phenol in phenol-formaldehyde (PF) wood adhesive. As another example, fractions isolated by the same fractionation technology were subjected to polymerization catalyzed by laccase and co-polymerized lignins find potential in fiber-based products, e.g. packaging.

​