The effect of cellulose crystal structure and solid-state morphology on the activity of cellulases

Cellulose is the most abundant polymer synthesized by nature. However, the solid-state properties and extensive network of hydrogen bonds complicate cellulose conversion to other bioproducts. Compared to acid and alkaline hydrolysis, cellulase hydrolysis is a more specific, efficient and environmental friendly method. The hydrolyzed cellulose can be converted to ethanol and other chemicals by fermentation. The aim of this research is to determine the effect of cellulose solid-state morphology including crystal structure, allomorphic form, crystallinity, crystallite size and cellulose topology on the activity of different types of cellulases in an effort to increase the degree and rate of cellulose conversion. X-ray diffraction and 13C CP/MAS NMR were employed to confirm the crystal structure and measure the crystallinity, crystallite size of control and hydrolyzed cellulose. Size Exclusion Chromatography (SEC) was used to characterize the molecular weight and molecular weight distribution of cellulose. A cellulose solvent system (TBAF/DMSO) was used to dissolve cellulose and was used as mobile phase for SEC. Scanning Electron Microscopy (SEM) was successfully used to visually compare the surface morphology differences of cellulose substrates and hydrolyzed celluloses. The major firding of this study was that conversion of mercerized cellulose II had higher accessibility to cellulases than native cellulose I and this increased the rate of enzyme hydrolysis. Bacterial microcrystalline cellulose (BMCC) was more accessible than microcrystalline cellulose (MCC).