Efficient Extraction of Cellulose Nanofibrils from Pine Sawdust by Integrated Chemical Pretreatment with Alkali/Acid-Chlorite/Tempo-Oxidant

Abstract

Simplifying the process and reducing the use of chemical reagents are major challenges in the industrialization of chemical pretreatments for the extraction of nanocellulosic fibers (CNFs). In this study, an integrated chemical pretreatment approach using alkali/acid-chlorite/TEMPO-oxidant was used for the nano-fibrillation of cellulose from pine sawdust (WS). The alkaline and acid-chlorite pretreatments effectively eliminated the non-cellulosic components present in WS, resulting in the delamination of individual cell layers and swelling of the internal structures within the cellulose fiber bundles and the cellulose microfibrils that form these layers. The spacing between CNFs within the cellulose microfibrils increased from 3.7 nm to 5.5 nm. These loosely packed hierarchical structures facilitated the penetration of the reagent, which led to an increase in the specific surface area during the TEMPO-oxidant reaction and consequently accelerated the reaction rate. The WS was pretreated in a very dilute solution (1% NaOH and 0.5% NaClO2) under mild conditions (70 oC for 1 hour), which resulted in a significant reduction of the TEMPO reaction time (from 6 hours to half an hour) and a lower consumption of the reaction reagent (one fourth of the amount consumed by in the direct oxidation of WS to achieve the same degree of cellulose nano-fibrillation).

Keywords: cellulose nanofibrils, pine sawdust, alkaline and acid-chlorite pretreatments, TEMPO-oxidant, integrated chemical pretreatment