Efficient conversion of an underutilized low-lignin lignocellulosic biomass to cellulose nanocrystals and nanofibers via mild chemical-mechanical protocols

Abstract

The production of high-quality nanocellulose (NC) from an underutilized low-lignin lignocellulosic biomass source, Phalaris aquatica L., was investigated via three conversion protocols. Initially, a conventional chemical protocol (Scenario I) was optimized using statistically designed experiments, and cellulose nanocrystals (CNCs) that exhibited an adequate crystallinity index (CI) were produced under mild conditions: short processing times, reduced temperatures and decreased use of chemicals and solvents. Hydrolysis temperature was found to contribute significantly to the variation of CI. Furthermore, two additional scenarios based on a planetary ball mill were comparatively applied, namely a combined chemical-mechanical (Scenario II) and an alternative (Scenario III) protocol, in which the ball milling step followed or replaced the acid hydrolysis step, respectively. In Scenarios II and III the NC structure was modified to cellulose nanofibrils (CNFs) and microfibrillated cellulose (MFC), respectively. Accordingly, the three different NC grades (CNCs, CNFs and MFC) were correlated with the three conversion protocols.