Enzymatic preparation of nanocrystalline and microcrystalline cellulose

Abstract

Traditional cellulose nanocrystal (CNC) production methods use harsh chemicals, are energetically expensive, and result in a hydrophilic sulfate surface chemistry with limited utility. Enzymatic production of CNCs is a less expensive alternative production method that eliminates the need for harsh chemicals and requires much less energy for mechanical fibrillation and heating. Furthermore, enzymes that selectively degrade the amorphous regions of cellulose fibers, and do not significantly digest the crystalline areas, result in CNCs that retain a hydroxyl group surface chemistry. Retention of hydroxyl groups allows for easier chemical manipulation, and thus an expanded commercial potential. Here we show that cellulase from Aspergillus niger is capable of producing CNC and microfibrillated cellulose (MFC) from well-solubilized kraft pulp feedstock with minimal processing, and that a chimeric cellulase partially digests kraft pulp and live wood feedstock. Additionally, we show that as a feedstock source, milled pulp from bug-killed dead and downed trees has significantly reduced energy requirements to process the feedstock into elementary fibers and MFCs when compared to live wood feedstock sources.