Morphology and supramolecular structure characterization of cellulose isolated from heat-treated moso bamboo

The change of physical and mechanical properties of bamboo after heat treatment has become a research hotspot recently. However, bamboo was usually used as a whole to investigate the reason why its properties changed. This study focused on cellulose, the skeleton substance of bamboo cell wall. Changes in morphology and supramolecular structure of cellulose isolated from heat-treated moso bamboo were investigated. The results showed bamboo cellulose after heat treatment was more prone to structure changes when treated with alkali solution. Taking the cellulose sample isolated from 200 °C heat-treated bamboo as an example, its X-ray crystallinity index of cellulose increased from 70.5% for the untreated sample to 75.6% for the sample heated to 200 °C including both cellulose I and II peaks. Based on CP/MAS 13C NMR measurements, the cellulose I_α/cellulose I_β ratio decreased from 28 to 22% and the cellulose I/cellulose II ratio decreased from 162 to 49%. These changes in supramolecular structure caused the morphology to suffer tremendous changes, where the cellulose in fibers became shorter, thinner and twisted and the cellulose in parenchyma cells shrunk.