(6t) Tailoring Polymer Chemistry for Biomass-Derived Materials: From Artificial Plant Cell Wall to Fungible Bioproducts

Authors: 
Li, Q., Texas A&M University
Yuan, J., Texas A&M University
Research Interests: My research interests are in biomass-derived renewable polymer materials, which cover carbonaceous materials manufacturing, lignocellulosic biorefinery, and paper engineering. My current work majorly focused on plant-derived carbon fiber, which aims to convert lignin polymer from biorefining and pulping waste streams into quality and applicable carbon fibers.

Polymer chemistry could define the performance of polymer-derived materials and thus their applications. Elucidation of lignin chemistry thereby represents one of the most fundamental questions in lignin polymer research, for example, how lignin structure is manipulated during lignin biosynthesis. Lignin is a major component of cell wall and is considered as the main recalcitrance to biomass deconstruction, enzymatic digestibility and biopolymer material synthesis. Over the past decades, extensive researches have successfully fractionated lignin from polysaccharides matrix, which enabled the processing of cellulose and hemicellulose into advanced paper products and biofuels. Although all processing is defined by lignin chemistry, formation of lignin linkages and the underlying relationship between lignin and polysaccharides in plant cell are less well understood, with studies relying on in-vivo lignification. Alternatively, synthesis of artificial plant cell walls sheds light on such elucidation. I have synthesized a micro-patterned honeycomb bacterial cellulose film by controlling the movement of a cellulose-produced bacterium G. Xylinus, and used such cell wall template to assemble hemicellulose and synthesize lignin as mimicking plant cell wall formation. The research was concluded that xylan serves as the scaffold for lignin deposition in polysaccharides matrix and plays a vital role in enhancing lignin β-O-4 linkage formation, which represented one of the first direct evidences that hemicellulose regulates lignin structure formation.

I have subsequently implemented my fundamental understanding of carbohydrates and lignin chemistry into the researches of biopolymer materials. My second research area addresses one of the most challenging issues in the use of plant biomass for biofuel production: the conversion of highly recalcitrant lignin polymer into fungible bioproducts. I have developed a multi-stream integrated biorefinery (MIBR), which integrated enzymes, electron mediators, and various chemical fractionations to develop several processing platforms able to manipulate lignin chemistry for making quality carbon fiber, superior asphalt binder modifier, and polyhydroxyalkanoate (PHA). Lignin represents an economical and sustainable substitute for traditional PAN polymer precursor for carbon fiber manufacturing. Fractionation technologies produced more uniform lignin fractions as precursors for quality carbon fiber, which had significantly improved mechanical and electroconductive performance and had potential to reduce the carbon fiber cost by half. Furthermore, the fractionated lignin with modified linkages and functional groups served as superior asphalt binder modifier, and the very low molecular weight lignin fraction had improved efficiency and titer when it was bio-converted into PHA using bacterial fermentation. More importantly, one of the most fundamental scientific questions in biomaterials production is chemistry-properties relationship. Using fractionation technologies, I have defined the relationship between lignin processing, lignin chemistry and bioproduct performances, whih in turn guided the development of lignin processing technologies for preparing lignin with suitable chemical characteristics for different products manufacturing. Overall, fractionation enabled multiple product streams from lignin. The MIBR concept has potential to revolutionize the lignocellulosic biorefinery and the traditional carbon fiber industries to maximize the bioproducts output, improve the efficiency, enhance the economics, and promote forestry and rural economy.

Besides lignin processing, lignin chemical features derives from lignin biosynthesis during plant cell wall formation, as mentioned above. My third research area has applied fundamental understanding of processing-chemistry-properties relationship to biomass feedstock design, which aims to manipulate the structure of cell wall polymer in planta with suitable characteristics for quality biomaterials productions. I have studied different sorghum and switchgrass variants, up-regulation mutants and over-expression lines. Lignin in different plant lines displayed significantly different chemical features and the resultant carbon fibers had distinct mechanical and electroconductive performances. Furthermore, it is possible to design biomass feedstock in a way that lignin can be readily processed and separated for biomaterial productions whilst the remaining carbohydrate can be more efficiently degraded or converted into nanomaterials, such as cellulose nanofibers. The feedstock design needs to be optimized together with the biorefinery processing design to enable such a process.

In my future career, I will expand my current bioproduct researches to nanocellulose and energy storage devices. My long term goal in doing research is to leave my footprints on the field of renewable polymer materials as a result of high quality researches on biomass processing design, lignin waste valorization and renewable energy storage devices. I will dedicate to build an internationally reputable program by establishing a biomass-biopolymers-biomaterials (BBB) manufacturing line for renewable polymer material production and modern biorefinery, which high-quality cellulose and lignin-derived biomaterials, such as nanocellulose, carbon fiber and carbonaceous electrodes, will be enabled by developing biomass design and processing technologies to produce cellulose and lignin polymers with specific chemical features for these biomaterials production.

Teaching Interests: Beyond research, I am with my great enthusiasm for teaching and educating next generation scientists. My teaching interests include biotechnology for biofuels and bioproducts, lignocellulosic biorefinery, chemistry of biopolymer, principles of pulping and paper-making. The classes to be given will aim to strengthen the students’ understanding of the technologies of biorefinery, paper engineering and biomaterial manufacturing and how these technologies could transform the bioeconomy of industries.