Isolation of Thermally Stable Cellulose Nanocrystals by Phosphoric Acid Hydrolysis

Abstract

On account of their intriguing mechanical properties, low cost, and renewable nature, high-aspect-ratio cellulose nanocrystals (CNCs) are an attractive component for many nanomaterials. Due to hydrogen bonding between their surface hydroxyl groups, unmodified CNCs (H-CNCs) aggregate easily and are often difficult to disperse. It is shown here that on account of ionic repulsion between charged surface groups, slightly phosphorylated CNCs (P-CNCs, average dimensions 31 ± 14 × 316 ± 127 nm, surface charge density = 10.8 ± 2.7 mmol/kg cellulose), prepared by controlled hydrolysis of cotton with phosphoric acid, are readily dispersible and form stable dispersions in polar solvents such as water, dimethyl sulfoxide, and dimethylformamide. Thermogravimetric analyses reveal that these P-CNCs exhibit a much higher thermal stability than partially sulfated CNCs (S-CNCs), which are frequently employed, but suffer from limited thermal stability. Nanocomposites of an ethylene oxide-epichlorohydrin copolymer and H-CNCs, S-CNCs, and P-CNCs were prepared, and their mechanical properties were studied by dynamic mechanical thermal analysis. The results show that P-CNCs offer a reinforcing capability that is comparable to that of H-CNCs or S-CNCs.

Preparation and Properties of Holocellulose Nanofibrils with Different Hemicellulose Content

“…In the wood cell wall, cellulose molecules form microfibrils via intra-or intermolecular hydrogen bonds (Aulin et al 2011). The cellulose microfibril has a diameter of 10 nm to 30 nm and can be isolated after chemical or biological pretreatments through mechanical defibrillation processes, such as wet disk-milling (WDM), high-pressure homogenizing, and ball milling (Habibi et al 2010;Siró and Plackett 2010;Wang et al 2012;Espinosa et al 2013;Jang et al 2013;Peng et al 2013;Yu et al 2013;Zhang et al 2015). However, it is difficult to degrade the wood cell wall into its constituents because of its structural heterogeneity and complexity, endowing it with very strong recalcitrant characteristics against chemical or biological treatments (Himmel et al 2007).…”

Properties of Nanocrystalline Cellulose Obtained From Celluloses of Annual Plants

“…Обработка кислотой вызывает селективный гидролиз аморфных областей целлюлозы, тем самым высвобождая нанокристаллические стержне-образные частицы [5,6]. В зависимости от условий кислотной обработки и сырьевого источника целлюлозы размер частиц НКЦ варьируется от 50 до 1160 нм в длину и примерно от 3 до 50 нм в диаметре [7]. При использовании серной кислоты в результате гидролиза поверхностные гидроксиль-ные группы замещаются сульфогруппами, при этом отрицательный заряд поверхности стаби-лизирует водные дисперсии частиц НКЦ за счет электростатического отталкивания [8].…”

Elucidating the Potential Biological Impact of Cellulose Nanocrystals

“…The most commonly studied and used forms are bacterial cellulose (BC), microcrystalline cellulose (MC), microfibrillated cellulose (MFC) and cellulose nanocrystals (CNCs) [2,3]. CNCs, which are also referred to as cellulose nanowhiskers (CNWs) or nanocrystalline cellulose (NCC), are produced by hydrolysis of cellulose pulp with a mineral acid, such as hydrochloric acid [4], sulphuric acid [5] or phosphoric acid [6]. During the acid treatment, the amorphous portions of the hierarchically structured material, which are more prone to hydrolysis than the crystalline domains,…”