Mechanism-based design of lignin biomaterials and bioprocessing to enable sustainable biorefining

Abstract: Lignin is the second most abundant biopolymer on the planet, yet is also a major waste in paper and pulp industries and biorefinery. Lignocellulosic biorefinery focuses on carbohydrate utilization, leaving lignin as an abundant waste. This waste lignin is often burned to cause carbon emission. Fungible lignin utilization is crucial to sustainability and decarbonization, yet is hindered by the limited understanding of the structure-property relationship of lignin chemistry and product properties. We have advanced such understanding to guide the process and material designs. First, we have discovered that lignin molecular weight, uniformity, linkage profile, and functional groups could impact the lignin biomaterials' properties. For example, the higher molecular weight, better uniformity, and more linear linkages could improve carbon material properties. The understanding has guided the design of a new type of lignin to achieve the highest reported tensile strength for lignin carbon fiber, empowering lightweight applications for emission reduction. This new type of lignin can also promote the performance of plastic blends. Therefore, based on the fundamental understanding, we have designed processes to transform lignin into a precursor for broad biomaterial applications to promote sustainability and decarbonization. Second, we revealed that lignin processing into smaller molecular weight, monomer-containing, and hydroxyl group-enriched fractions will significantly improve the bioprocessibility. Based on the discovery, we designed a ‘plug-in’ module to transform pretreatment technologies into integrated biorefinery for efficient conversion of both carbohydrates and lignin. In particular, we integrated innovative biorefinery and microbial design to enable cost-effective and efficient lignin conversion into biodegradable plastics. Thirdly, we have developed strategies to integrate the first two approaches to deliver a multi-stream lignocellulosic biorefinery, where different lignin fractions can be used for various high value products to maximize the value proposition and carbon emission reduction. Together, the fundamental understanding of relationship among lignin chemistry, processiblity, and biomaterial properties have enabled us to design the lignin-based biomaterials and lignin processing technologies that can substantially improve the sustainability and economics of modern biorefinery and paper and pulping plants.