Green preparation of size-controllable cellulose nanofibers from buckwheat husks

Abstract

As a processing waste, buckwheat hulls (BH) have lignocellulose composition and structure similar to eucalyptus wood, which could be served as a potential alternative of wood to produce cellulose-related products. In this study, enzymatic hydrolysis combined with high-pressure homogenizations were used to successfully prepare cellulose nanofibers (CNF) with controllable average diameter from BH. The changes in the physicochemical properties of the fibers, including morphology, functional groups, transmittance, dispersion stability, crystallinity, and thermal stability, were systematically evaluated. Microscopic results showed that the microfiber structure was sufficiently exposed after the purification treatment, and the subsequently enzymatic hydrolysis with an optimal reaction time of 24 h generated a suitable microfiber filament stripping effect. More importantly, when the cycles of homogenization were 1, 5, 10, and 20 times, the average diameters of CNF were 49.98, 40.09, 28.04 and 17.92 nm, respectively. Co-processing was beneficial in increasing CNF yields and reducing costs and energy consumption. Additionally, the thermal stability of samples remained stable after the multi-step treatments, with the initial degradation temperature higher than 300 °C, which are superior to traditional acidic treatments. These findings demonstrate the feasibility of BH as a low-cost source of CNF, and the prospects of the green preparation procedures.