An original deep-dive article by Longrun Capital
Figure 1: Pine trees. Image License: Public Domain Dedication (CC0)
Lignin, a highly abundant and widely available biopolymer, is gaining recognition as a promising alternative to traditional fossil-fuel-derived materials. As society continues to prioritize sustainability and seeks out green solutions, lignin is emerging as a valuable resource with a wide range of potential applications. Its unique properties, such as its rigid three-dimensional structure and resistance to degradation, make it an attractive material for use in a variety of industries, including bioplastics, adhesives, and carbon fiber production. However, until very recently, the potential has been seemingly out of reach, and most lignin has been burned for energy.
Lignin is a significant renewable resource due to its natural abundance. It is a complex polymer that is composed of various monomers, and it is one of the most chemically diverse natural materials. Lignin plays a crucial role in plant cell walls, providing structural support, strength, and rigidity to trees, woody plants, and some grasses. In essence, lignin is the icing that holds together the fluffy cellulose cake layers in the plant (Fig. 2)
Figure 2: Simplified lingnocellulose structure showing the components of lignin (brown), cellulose (green) and hemicellulose (yellow).
Despite its abundance and potential, the utilization of lignin as a high-value material remains relatively low, with only around 5% of the 170 million metric tons of lignocellulose produced annually being used in high-value products as of 2021 (Hélder & Figueiredo, 2021). However, recent technical advancements in lignin extraction, refinement, and modification have generated renewed interest in lignin as a sustainable and versatile material. Researchers, lignin producers, and manufacturers are collaborating to make lignin both high-value and cost-competitive. The low cost of oil has been one aspect that has held back the adoption of lignin in manufacturing, but with environmental concerns increasingly making oil less attractive, lignin may finally have its day.
The past decade has seen a significant increase in scientific publications focused on lignin, highlighting its potential as a novel material. For example, in 2019, Zhang et al. reported on the potential use of lignin-based materials for biomedical applications, including drug delivery, tissue engineering, and wound healing. Other studies have explored the use of lignin in the production of advanced materials, such as lignin-based carbon fibers and nanocomposites.
Figure 3: Number of peer-reviewed articles and reviews published annually, from 1980 to 2023. Search results from Scopus.com retrieved 2023-05-11.
Until recently, the lignin-rich black liquor by-product produced from delignification (the process of separating lignin from its cellulose neighbors) was only used as fuel to generate steam and electricity in pulp and paper mills. However, with advances in technology and research, lignin is now a hot new resource for green solutions, being used in innovative ways in various market segments. Thanks to newly developed processes used to break apart and refine lignin depending on the desired final product, lignin can be used in products such as asphalts, protective coatings and paints, adhesives, resins, batteries, concrete, foam, and even cosmetics. Lignin can also be converted to vanillin, a flavoring agent used in the food industry. Lignin can be added to soil to improve its quality, and it can be used to make carbon fibers, which have various applications in the aerospace and automobile industries.