Cellulose nanocrystals by acid vapour: towards more effortless isolation of cellulose nanocrystals

Abstract

Cellulose nanocrystals (CNCs) are topical in materials science but their full potential is yet to be fulfilled because of bottlenecks in the production: the process consumes huge amounts of water, recycling the strong acid catalyst is difficult, and purification steps are cumbersome, particularly with lengthy dialysis. Production of CNCs with HCl vapour overcomes many of these difficulties but the dispersion of CNCs from the already hydrolysed fibre matrix is a formidable challenge. This study is a fundamental effort to explore very basic means to facilitate CNC dispersion from cotton linter fibres (filter paper), hydrolysed to levelling off degree of polymerization by HCl vapour. The introduction of carboxylic groups on the cellulose crystal surface proved the most efficient method to alleviate dispersion with good yields (ca. 50%) and a provisional possibility to tune the CNC length. By contrast, attempts to directly disperse untreated hydrolysed fibres in various organic solvents and aqueous surfactant solutions were unsuccessful. The results showed that hydrolysis of native cellulose fibres by HCl vapour is indeed a viable method for producing CNCs but it has more potential as a pre-treatment step rather than a full-fledged process on its own.

Recrystallization and size distribution of dislocated segments in cellulose microfibrils—a molecular dynamics perspective

“…Yields in aqueous hydrolysis to produce CNCs are typically low which has been justified by the fringed-fibrillar model which implies losses due to removal and subsequent hydrolysis of 'amorphous' domains from the CMFs. However, these low yields are a direct consequence of the harsh reaction conditions and work-up conditions (centrifugation, dialysis) in aqueous medium, whilst the use of vaporous HCl in hydrolysis revealed nearly quantitative yields (Lorenz et al 2017). Washing the resulting CNC solid with water (Pääkkönen et al 2018) did not give significant amounts of glucose (\1%), which is in clear contrast to the fringed fibrillar model (Kontturi et al 2016).…”

Non-woody Biomass as Sources of Nanocellulose Particles: A Review of Extraction Procedures

“…These processes include alkalization or mercerization, bleaching and acid hydrolysis. Proper combination of these processes helps to remove all other components from the fiber, leaving behind highly crystalline nanocellulose particles (Lorenz et al, 2017;Salama et al, 2018;Agwuncha et al, 2020). The properties of the extracted CNPs are affected by the conditions utilized during each process, making it extremely important to select treatment conditions that will give the desired properties.…”

Characterization of Cellulase-Treated Fibers and Resulting Cellulose Nanocrystals Generated through Acid Hydrolysis

“…Acid hydrolysis with sulfuric (H 2 SO 4 ) [14,15,16] or hydrochloric (HCl) acid [17,18] is the most common method for isolating CNCs [19]. The strong acid degrades the readily accessible glycosidic bonds in the less ordered cellulose chains, whereas the tightly packed highly crystalline region remains recalcitrant as it limits the penetration of acid and water [20].…”