Visualization of Structural Changes in Thermochemically Pretreated Plant Cell Wall Polymers

Second-generation biofuels made from lignocellulosic biomass hold immense potential in serving as an alternative source of energy. Due to the rigid cell wall structure, the biomass has to be pretreated with chemicals, often at high temperature and pressure, to breakdown the cell wall structure and increase cellulose accessibility to hydrolytic enzymes. Through years of research, a great amount has been learned about the structural rearrangements that occur after pretreatment and have resulted in proposed reasons for recalcitrance to enzyme hydrolysis that occurs even after pretreatment. But why the structural re-arrangement took place the way it did during pretreatment is largely unknown. This is because our current understanding of how polymers are interacting and influencing each other’s structures during pretreatment is lacking. The overall aim of the work is to understand how plant cell wall polymers interact in lignocellulose and the changes that occur in these interactions during hot water or dilute acid pretreatment. Our approach involves studying polymer-polymer interactions using model systems and conducting comparative studies in natural variants of poplar and switchgrass. Using x-rays and neutrons based scattering techniques, we studied the impact different kinds of hemicelluloses have on the hierarchical structure of cellulose before and after pretreatment. We also studied intact biomass and used a comparative approach to study the sugar release differences before and after pretreatment for two poplar woods with different lignin content. Lastly, we also explored the interactions of pectin with lignin to determine if pectin can influence the lignin aggregate formation. Overall, information on this fundamental knowledge of polymer interactions can help design milder pretreatments or plants that are more susceptible to deconstruction which would decrease the cost of thermochemical pretreatment.