Cellulose nanocrystals, a class of fascinating bio-based nanoscale materials, have received a tremendous amount of interest both in industry and academia owing to its unique structural features and impressive physicochemical properties such as biocompatibility, biodegradability, renewability, low density, adaptable surface chemistry, optical transparency, and improved mechanical properties. This nanomaterial is a promising candidate for applications in fields such as biomedical, pharmaceuticals, electronics, barrier films, nanocomposites, membranes, supercapacitors, etc. New resources, new extraction procedures, and new treatments are currently under development to satisfy the increasing demand of manufacturing new types of cellulose nanocrystals-based materials on an industrial scale. Therefore, this review addresses the recent progress in the production methodologies of cellulose nanocrystals, covering principal cellulose resources and the main processes used for its isolation. A critical and analytical examination of the shortcomings of various approaches employed so far is made. Additionally, structural organization of cellulose and nomenclature of cellulose nanomaterials have also been discussed for beginners in this field.

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Recent progress in cellulose nanocrystals: sources and production

Nanocellulose, a tiny fiber with huge applications

Microcrystalline cellulose: Isolation, characterization and bio-composites application-A review.

Recent developments in nanocellulose-based biodegradable polymers, thermoplastic polymers, and porous nanocomposites

This study investigated the impact of cellulose polymorphs on cellulose nanocrystals (CNCs) preparation. Cellulose samples with different types of polymorphs (cellulose I, cellulose II, and cellulose III) were prepared. Subsequently, CNCs were obtained from the above cellulose samples by sulfuric acid hydrolysis. The initial cellulose and CNCs were characterized by X-ray diffraction (XRD), thermo gravimetric analysis (TGA), scanning electronic microscopy (SEM) and particle size distribution (PSD). A comparative study showed that the properties of CNCs were closely related to the polymorphs of initial cellulose. The original polymorphs of cellulose I and cellulose II were retained, while that of cellulose III was converted back to cellulose I during the sulfuric acid hydrolysis process of CNCs preparation. For cellulose I and cellulose II, the crystallinity of both corresponding CNCs continuously increased with the increase of sulfuric acid concentration, until reaching a maximum at approximately 84.0%, while the crystallinity of CNCs obtained from cellulose III was slightly affected by sulfuric acid concentration. The yields of CNCs obtained from cellulose II and cellulose III with 61 wt% H2SO4 were extremely high, reaching 46.8% and 43.4%, respectively. Smaller CNCs particles with short-length were obtained by sulfuric acid hydrolysis of cellulose II. In addition, the properties (yield, dimension and thermal degradation behavior) of CNCs obtained from cellulose III were more susceptible to the acid concentration compared with those of CNCs obtained from cellulose I.

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Research on cellulose nanocrystals produced from cellulose sources with various polymorphs

Nanocrystalline cellulose (NCC) was extracted from microcrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis process. NCC samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size distribution (PSD) analysis, Fourier-transformed infrared spectra (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and rheological measurement. It was found that NCC yield reached 40.4 % under the optimum process of low-intensity ultrasonic-assisted sulfuric acid hydrolysis, while it was only 33.0 % in the absence of ultrasonic treatment. Furthermore, the results showed that the two NCC samples obtained from ultrasonic-assisted hydrolysis and conventional hydrolysis were very similar in morphology, both exhibiting rod-like structures with widths and lengths of 10–20 and 50–150 nm, respectively. XRD result revealed that the NCC sample from ultrasonic-assisted hydrolysis contained a small amount of cellulose II and possessed a Segal Crystallinity Index of 90.38 % and a crystallite size of 58.99 A, higher than those of the NCC sample from conventional hydrolysis. Moreover, PSD analysis demonstrated that the former exhibited a smaller value in average particle size than the latter. In addition, rheological measurements showed that the NCC suspensions from the ultrasonic-assisted process exhibited a lower viscosity over the range of shear rate from 0.1 to 100 s−1 in comparison with that prepared in the absence of ultrasonic treatment.

Preparation and characterization of nanocrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis

Starch-based composites have become promising materials for eco-friendly packaging applications because of their biodegradability and cost-effectiveness. However, the inherently poor mechanical and barrier properties of starch-based composite films hinder their market potential. Here, nanocrystalline cellulose (NCC) was isolated from cotton cellulose powders using sulfuric acid hydrolysis. Starch-based composite suspensions/films reinforced with 0.1–0.5 wt % of NCC were prepared and characterized. Surface sizing application of the reinforced composite suspensions on cellulosic paper was subsequently studied for improving the mechanical properties and the resistance to air permeability of cellulosic paper. Results revealed that NCC reinforced composite suspensions showed the characteristics of non-Newtonian fluids. The rheological behavior of these suspensions showed strong NCC concentration dependence. NCC addition improved the thermal stability of starch-based composite films. In addition, both the mecha...

Surface Treatment of Cellulosic Paper with Starch-Based Composites Reinforced with Nanocrystalline Cellulose

Preparation method and use of paper surface sizing agent

Enhanced photodegradation of methyl and parent PAH over flower-sphere Ag/rGO/BiOBr composite: Performance, mechanism and pathway.

The invention discloses a preparation method of a high-concentration nano microcrystalline cellulose gel. According to the preparation method, the particle size of a low-concentration nano microcrystalline cellulose dispersion solution prepared by a sulfuric acid hydrolysis method is 10-20nm, the concentration is around 0.5%, and the pH value is equal to 7.0; the low-concentration neutral nano microcrystalline cellulose dispersion solution is put into a rotary evaporator to obtain the high-concentration nano microcrystalline cellulose gel by regulating and adjusting evaporation process conditions; and the water is evaporated out and is collected for reuse, so that the production cost, the loading size and the weight are minimized to obtain the high-concentration nano microcrystalline cellulose gel, the density of the gel is not increased along with the evaporation of water, and a gel with any concentration can be prepared by adding water at the same time. The preparation method adopts a pure physical method, is simple in operation, can not cause environmental pollution, and is obviously reduced in cost.

Shujie Yang

Papers

Preparation and characterization of nanocrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis

Surface Treatment of Cellulosic Paper with Starch-Based Composites Reinforced with Nanocrystalline Cellulose

Preparation method and use of paper surface sizing agent

Enhanced photodegradation of methyl and parent PAH over flower-sphere Ag/rGO/BiOBr composite: Performance, mechanism and pathway.

Preparation method of high-concentration nano microcrystalline cellulose gel