Plant biomass is a renewable, sustainable raw material for a wide variety of bio-based based products including ethanol, paper, polylactic acid, wood plastic composites etc. Plant cell walls have a complex internal porous structure that has a significant influence on the efficiency of the biomass conversion process, the properties of the materials and their end-use applications. When subjected to pretreatment, one or more of the cell wall components degrade altering the internal structure and thus affect further conversion processes. With the advent of novel materials characterization techniques it is now possible to non-intrusively visualize the internal three dimensional structure of porous materials and attempt to better understand structure property functional relationships. Techniques such as Raman Spectroscopy, Atomic Force Microscopy, and Scanning Electron Microscopy etc. provide topochemical and structural information. But in order to get a true sense of the internal ultrastructure of the cellwall 3D visualization techniques are required. Previous work on characterization of 3D porous biomaterials was accomplished using X-ray computed tomography which provides excellent visualization at the micron scale. Even though micron scale structural details may be sufficient in many applications of biomaterials, in order to better understand the ultrastructure of plant cell walls and their role in biomass conversion processes, it is necessary to probe the ultra-structural features at the nanoscale. The 3D computed tomography technique mentioned above is now being extended to other imaging techniques such as Transmission Electron Microscopy (TEM). It provides an X-Y resolution of upto 1-2nm. The technique is based on capturing a series of images by successive tilts around a single axis and reconstructing the 3D image by back projection.
Using the information from TEM computed nanotomography (TEM-n-CT), the porosity, pore size distribution, interfacial area, structural tortuosity and diffusion characteristics of the biomass can be determined. The cell wall material can be considered to be made up of two phases- namely void spaces comprising of cell lumen, pits etc. and a solid cell wall comprising of cellulose microfibrils embedded in lignocellulose polymer matrix It is also possible to track the changes in the 3D structure asthe biomass undergoes pre-treatment and bioconversion processes. . The effect of pre-treatment processes using hot water, acid, and alkali etc on the 3D ultrastructure of biomass can be explored.
In addition, using the actual 3D structure of biomass we propose a simultaneous transport and reaction engineering modeling using stochastic dynamic approach and survival probabilities. This will include random walk simulations in cell wall structures to simulate the diffusive transport of reactants in the pores with possible adsorption and reaction at the cell wall surface following thermodynamic and reaction kinetics considerations of individual biomass components. This will help gain fundamental insights on biomass recalcitrance and how they can be addressed in developing effective conversion strategies.