Separation of cellulose nanowhiskers from microcrystalline cellulose with an aqueous protic ionic liquid based on ammonium and hydrogensulphate

Abstract

Cellulose nanowhiskers (NWC) have several applications, but its achievement, when held by hydrolysis with strong acids, presents some undesirable aspects as their corrosivity, toxicity and low recovery rate. Recently, [BMIM][HSO4] was proposed as an alternative, but its use has yet disadvantages, mainly due its toxicity and cost. In this sense, this work reports the separation of NWC from MCC by a synthetized protic ionic liquid 2-hydroxyethylamonium hydrogensulphate ([2-HEA][HSO4]) potentially lower toxic than [BMIM][HSO4], which can be easily produced by a low-cost procedure. A stable and polydisperse NWC aqueous suspension was formed exhibiting the birefringence flow typical of nanoparticle dispersions. TEM micrographies confirm needle-shape particles with high average aspect ratio of 50.23 ± 20.93 nm. A good thermal stability was achieved, with Tmax of cellulose decomposition around 234 °C. No ionic liquid residues were observed in the NWC by FTIR analysis. The calculated crystallinity index and crystallite size were 54% and 17.2 nm, respectively. The ionic liquid used in the hydrolysis experiments was successfully recovered in 76.91 ± 0.13% yield, with a similar structure to that of the original ionic liquid. Therefore, [2-HEA][HSO4] was successfully tested as a new, alternative and promising medium to separate cellulose nanowhiskers from cellulosic sources.