Agricultural waste corn stover has very little value but can be good renewable, biodegradable, and inexpensive source to produce value-added products such as cellulose and nanocellulose. Cellulose was extracted from corn stover by the processes of alkali treatment and delignification, resulting in a >93% purity. The particle size of the extracted cellulose was reduced by mechanical shearing through high pressure homogenization. When passing through a homogenizer thirty times, the cellulose nanofibril (CNF) can be obtained. The diameters of the CNF ranged between 5 – 50 nm, and the lengths were microns. The mechanical properties of the films, made by corn stover cellulose, with and without high pressure homogenization shearing were evaluated using an Instron instrument. The films made by cellulose without shearing exhibited weaker mechanical properties, while the CNF films exhibited stronger mechanical properties. The linear rheological properties of CNF suspensions were investigated using mechanical rheometry and results show solid-like viscoelastic behavior. The microrheology of corn stover CNF suspensions was investigated by the novel technique diffusion wave spectroscopy (DWS) and compared with mechanical rheometry measuremants. DWS microrheology measurements were in excellent agreement with the conventional mechanical rheological studies for corn stover CNF. By comparing the mean-square displacement (MSD) of the microbeads embedded in five concentrations of corn stover CNF, we found that the suspensions exhibited slight heterogeneity behavior at the lower concentration of 0.25%, while the material displayed a definite degree of heterogeneity at higher concentrations. The magnitude of high-frequency viscoelastic moduli (|G*(ω)|) for the corn stover CNF is proportional to the 3/4 power of the frequency (ω), which is the semi- flexible polymer behavior. The identified properties of the corn stover CNF will provide us the useful information for utilizing this kind of nanocellulose.
Jingyuan Xu earned his Ph.D. degree of biophysics and biophysical chemistry from the Johns Hopkins University, School of Medicine. He currently is a research physical scientist at National Center for Agricultural Utilization Research, Agricultural Research Service, US Department of Agriculture. His research is focusing on agricultural biodegradable materials, new food product development, and nano-technology. He has published more than 70 peer- review journal publications and has been invited to present his research at numerous domestic and international conferences.