Gradient variations of cellulose supramolecular structures in moso bamboo culm: from nano to micro horizons

Abstract The radially gradient variation in the cellulose supramolecular structures of bamboo culm were systematically studied by XRD and the confocal Raman microspectroscopy. XRD analysis indicated that bamboo yellow (By) has the isotropic crystallite arrangements, while outer bamboo timber (Bt) and bamboo green (Bg) display preferred orientation of crystals. Moreover, both the crystallinity and crystallite sizes notably grow from the inner By to the outer Bg. Raman band ratio (I1095/I2939) was used to predict microfibrils angle (MFA) in different cell wall types, semi-qualitatively. The results showed that the ratio was the highest in parenchyma, followed by narrow layer of fiber wall, and the lowest in the broad layer, which indicated the higher MFA in the parenchyma. Interestingly, the ratio decreased along the successive and alternating broad and narrow lamellae of fiber wall, in accordance with cell wall micromechanical trend. The findings will favor the large-scale utilization for the bamboo-based flexible composites.