Theoretical and experimental study of dissolution mechanism of cellulose

Abstract

Cellulose is one of the most abundant, sustainable and renewable materials on Earth. Accordingly, its utilization in different forms on different scales is in focus. Cellulose-based nanomaterials are considered to be one of the most exciting nanomaterials. Preparation of cellulose-based materials necessitates formation of cellulose-based solutions using environmentally hazardous solvents, which stems from the chemical nature of cellulose. In this work, an experimental and theoretical study of cellulose dissolution is described. As a model system, dissolution of cellulose in Schweizer's reagent is studied experimentally and theoretically as a model non-derivatizing method, elucidating and describing the physico-chemical aspects of the process. Dissolution of individual fibers pulled off banana woolery and cotton linters is studied experimentally. It is observed that a fiber can begin to swell before dissolution, even though it does not happen always. Then, the cross-sectional fiber size diminishes linearly in time, allowing direct measurement of the rate of cellulose dissolution. The theoretical model developed here links the rate of dissolution with the number of hydrogen bonds associated with hydroxyls on the surface of cellulose molecule required to be broken by chelating copper ions. This number is shown to be within the range of 1.28 × 1010–4.05 × 1010 cm−2, indicating that nanocellulose fibrils of length of 100–1000 nm are chipped off from cellulose during dissolution process. In concert with the dissolution rate, osmotically- driven flow of solvent towards the dissolving cellulose surface was also found.