(587k) Changes in Cellulose Crystalline Structure in Lignocellulosic Biomass During Delignification Studied By Sum Frequency Generation (SFG) Spectroscopy and X-Ray Diffraction (XRD)

Changes
in cellulose crystalline structure in lignocellulosic biomass during
delignification studied by sum frequency generation (SFG) spectroscopy and x-ray
diffraction (XRD)

Kabindra
Kafle¹, Christopher Lee¹, Heenae Shin^2,3, Justin O. Zoppe², David K. Johnson⁴,
Seong H. Kim^1,*, Sunkyu Park^2,3,*

¹ Department of
Chemical Engineering and Material Research Institute, The Pennsylvania State
University, University Park, PA 16802, USA

² Department of
Forest Biomaterials, North Carolina State University, Raleigh, NC 27695

³ Department of
Forest Sciences, Seoul National University, Seoul, Korea

⁴ National Renewable Energy Laboratory,
Golden, CO 80401

*
Corresponding authors: shkim@engr.psu.edu, sunkyu_park@ncsu.edu

Abstract

Bioethanol production
from renewable sources such as lignocellulosic has been an attractive way to reduce
dependence on traditional petroleum fuels. However, ethanol yields are far from
efficient because of the presence of hemicelluloses and lignins in the
lignocellulosic material. Thus, removal of lignin from intact lignocellulose is
necessary in order for enzymes to access cellulose and hydrolyze them.
Thermo-chemical pretreatment methods are commonly used to delignify the
lignocellulose, during which the native cellulose structure and assembly is
likely altered. In this work, the structural changes in cellulose crystalline
structure during oxygen and sodium chlorite delignification were studied using sum
frequency generation vibration (SFG) spectroscopy and X-ray diffraction (XRD).
SFG can selectively detect the ordering of crystalline cellulose without any
interference from other cell wall polymers. The removal of lignin was higher
during sodium chlorite delignification compared to oxygen. The ordering of crystalline
cellulose microfibrils in hardwood (lignocellulose source), over optical length
scale, increased drastically at an elevated temperature in presence of water.
This also corresponded to an increase in crystal size from XRD analyses. The
crystal size increase was pronounced with the elevation of temperature without
using reagents or removing discernible amount of lignin. Quantification of
crystalline cellulose based on calibration curves from α
-cellulose showed a non-linear relation between glucan amount present and SFG
intensity. Structural changes in cellulose in terms of crystal size and better
aggregation/ordering are suggested to play an important role during the
delignification of lignocellulosic material. The ability of SFG to selectively
detect crystalline cellulose structure and organization in biomass from native
and delignified wood samples could help engineer better methods in biomass
utilization.