WEB Microstructural and surface properties of mechanically dispersed cellulose nano fiber aqueous sol
Cellulose nanofiber (CNF)-derived functional papers hold promise for application to various fields due to their unique properties such as gas barriers, high strength, transparency, etc. Mechanochemistry offers environmentally benign and sustainable synthesis of the functionalized CNF (e.g., combination with photocatalytic TiO2). The CNF could also work favorably to produce oxygen vacancy of TiO2 that enables visible responsive photocatalysis. Then, what physicochemical effects happen on the CNF during the mechanochemical treatment? In this study, changes in microstructural and surface properties of the CNF aqueous sol before/after planetary milling were investigated based on rheological behavior, crystallinity and water vapor adsorption. Decreased thixotropy hysteresis loop observed in the low rotation speed (100 rpm) -treated CNF indicates weaker interaction among fibers but still having three-dimensional structure. Further increase in rotation speed (300 rpm-) could collapse them. Decreased x-ray diffraction peak intensity of (200) plane observed in the 500 rpm-treated CNF could indicate rather split in fiber’s bundle than shred. Increased amount of water vapor adsorption in the 500 rpm-treated CNF also supports exposure of new surface with hydroxyl groups derived from glucose unit. Such newly born hydroxyl groups can be effective reaction site with, for example, TiO2 precursor and perhaps works favorably to improve photocatalytic performance. The proposed process requires short time (30 minutes in this study) and effective way as sustainable process to produce the functional papers.