Lignin-Rich Nanocellulose Fibrils Isolated from Parenchyma Cells and Fiber Cells of Western Red Cedar Bark

A mild alkaline treatment followed by micro grinding is employed to isolate lignin (23 wt %) containing nanocellulose fibrils (LNFs) from the bark of western red cedar. Microscopic images of the cross section of the bark revealed the high abundance of thin-walled parenchyma cells followed by fiber cells. The mild alkaline treatment resulted in separated cell corners, reduced cell wall thickness, and loose and layered cell wall structure for all of the cells. Confocal and atomic force microscopy-infrared images confirmed that the lignin mainly moved out from the cell corners, parenchyma cells, and Si layers of fiber cells. Within a few passes through a grinder, most of the bark was disintegrated to smaller fibrils. The extracted bark was homogenized to LNFs with a diameter less than 15 nm. The dynamic mechanical analysis and thermogravimetric analysis results showed the high thermal stability of LNF films, compared to those made from bleached nanocellulose fibrils. In addition, the LNF films retained the bulk of mechanical and water vapor barrier properties at high humidities. The films made from LNFs exceeded the tensile performance of most of the other biopolymers reported in the literature.