Preparation and thermostability of cellulose nanocrystals and nanofibrils from two sources of biomass: rice straw and poplar wood

Abstract

Two types of nanocellulose (cellulose nanocrystals—CNCs and cellulose nanofibrils—CNFs) were isolated from two biomass resources. The morphology, crystallinity and thermal stability of the nanocelluloses were systematically compared in this paper. CNCs derived from rice straw (CNC-Rs) and poplar wood (CNC-Ps) by sulfuric acid hydrolysis had short rod-shaped structures and average diameters of 9.1 nm for CNC-Rs and 11.4 nm for CNC-Ps. CNFs derived from rice straw (CNF-Rs) and poplar wood (CNF-Ps) by grinding had web-network structures and average diameters of 13.3 nm for CNF-Rs and 18.5 nm for CNF-Ps. After freeze-drying, the CNCs and CNFs retained their nano structures. CNFs and CNC-Ps consisted of the typically pure cellulose I, while CNC-Rs consisted of cellulose I and II. The CrI of the nanocellulose followed the order of CNC-Ps (72.9%) > CNC-Rs (68.0%) > CNF-Ps (56.4%) > CNF-Rs (54.4%). The thermal stability of the nanocellulose was correlated with their source biomass materials and preparation method, which led to the differences in their dimensions, crystallinity, and sulfate groups. Nanocellulose isolated from poplar wood showed the slightly higher thermal stability than that of nanocellulose from rice straw. CNFs exhibited the higher thermal stability than that of CNCs. The apparent activation energy (E) was calculated to evaluate the degradation process. The nanocellulose had E of 85.17–101.98 kJ/mol for CNCs and 94.92–108.76 kJ/mol for CNFs.