Date of Award

8-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Natural Resources

Major Professor

Siqun Wang, Timothy M. Young

Committee Members

Frank M. Guess, Seung-Hwan Lee

Abstract

In this dissertation, cellulose nanocrystals three-dimensional morphology, size distribution, and the crystal structure were statistically and quantitatively investigated. Lognormal distribution was identified as the most likely for cellulose nanocrystals’ size distribution. Height and width dimensions were shown to decrease toward the ends from the midpoint of individual CNCs, implying a spindle-like shape. XRD analysis of crystallite size accompanied with TEM and AFM measurements revealed that the cross-sectional dimensions of individual switchgrass CNC were either rectangular or elliptical shape, with an approximately 3~5 nm [nanometer] lateral element length range. A sponge-like carbon aerogel from microfibril cellulose with high porosity, ultra-low density, hydrophobic properties, and reusability was synthesized. Carbon aerogels heat-treated at 700 and 900 oC [Celsius] were examined and compared. Sample C-700 (521 m2 /g [square meter/gram]) exhibits significantly higher BET surface area than Sample C-950 (149 m2 /g [square meter/gram]). It also achieved highest normalized sorption capacity (86 g/g [gram/gram]) for paraffin oil. The removal of hydrophilic function groups of carbon aerogel proved by FTIR results to its highly hydrophobic properties. The Oil absorption ability is favored by its highly porous 3D network structure with interconnected cellulose nanofibrils. Simultaneous effects of processing parameters (peak temperature, heating rate) for carbon aerogel processing were investigated using response surface methodology (RSM). Results indicated that the optimum conditions were: 300 °C [Celsius] of the peak temperature and 8.0 °C/min [Celsius/minute] of the heating rate with approximately 90.1 g/g [gram/gram] of the normalized oil absorption capacity. An electron microscopy investigation was performed to link the micro-structure and properties of carbonized cellulose and lignin with the structure of original biomass components. Structure details at micro and molecular levels have been investigated by scanning transmission electron microscopy (STEM). Atomic resolution images revealed the presence of random, fractured graphene fragments in carbonized cellulose (C-CNC) and of large domains of parallel stacked graphene in carbonized lignin (C-Lignin). The randomly arranged small graphene fragments in C-CNC create a network of interconnected micropores and mesopores and contribute to the increased BET surface area. Formation of parallel stacks of graphene structures is favored by the pre-existence of aromatic components in lignin.

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