Hydrolysis, cellulose nanocrystal

There are basically two families of nanosized cellulosic particles (1) Nanofibrillar cellulose, which includes mechanically isolated microfibrils, chemically isolated microfibrils (TEMPO-oxidation), bacterial cellulose and can be considered spaghetti-like, and (2) Cellulose nanocrystals - rods of highly crystalline cellulose which are isolated by acid hydrolysis. Cellulose nanocrystals are represented in literature by synonyms like cellulose whiskers, cellulose nanowhiskers, cellulose microfibrils, micro-crystalline cellulose and nanocrystalline cellulose because they are not yet commercially available. These are needle-shaped (100 run to 200 run X 10 nm), highly crystalline, strong (E - 150 GPa) and form liquid crystal suspensions. 

Cellulose nanocrystals are rods of highly crystalline cellulose which are usually isolated by acid hydrolysis Cellulose nanocrystals are represented in literature by synonyms like cellulose whiskers, cellulose nanowhiskers, cellulose microfibrils. 

Ultrasonic treatments [70] have the potential to change the morphology of the formed whiskers. When hydrolysis is carried out under ultrasonic treatment, a combination of both sulfuric and hydrochloric acids during the hydrolysis appears to generate spherical cellulose nanocrystals instead of rod like nanocrystal which are the typical morphology of whiskers. These spherical cellulose nanocrystals show better thermal stability mainly because they possess fewer sulfate groups on their surfaces [71]. 

Bondeson, D., Mathew, A., Oksman, K. Optimization of the isolation of nanocrystals from microcrystalline cellulose by acid hydrolysis. Cellulose 13, 171-180 (2006)... 

Several terms are used in the scientific literature to denote the rod-like nanoparticles isolated as a result of cellulose hydrolysis nanowhiskers, nanocrystals, or crystalline nanoparticles. Here we use predominantly the last term. 

Stable aqueous suspensions of polysaccharide nanocrystals can be prepared by the acid hydrolysis of vegetable biomass. Different descriptors of the resulting colloidal suspended particles are used, including whiskers, mono-crystals and nanocrystals. The designation whiskers is used to describe elongated rod-like nanoparticles. These crystallites have also often been referred in the literature as microfibrils, microcrystals or microcrystallites, despite their nanoscale dimensions. Most of the studies reported in the literature refer to cellulose nanocrystals. A recent review described the properties and applications of cellulose whiskers in nanocomposites [31]. 

Starch occurs as a flour-like white powder, which is insoluble in cold water after its extraction from plants. Native starches contain between 15 and 45% of crystalline material. Starch crystallite, starch nanocrystal, microcrystalline starch and hydrolysed starch all refer to the crystalline part of starch, which are obtained by different extents of acidic hydrolysis. We will focus on starch nanocrystals. Cellulose nanocrystals are 100% crystalline materials, but starch nanocrystals consist of 45% crystalline portion. 

Enzyme hydrolysis and bleaching of sisal fibres was used for preparation of cellulose nanocrystals. The nanocrystals were dispersed in NR to form nanocomposites that exhibited increased modulus. Enzyme treatment provided nanoparticles that could be specifically prepared for varying thermomechanical properties. 

Menezes et al. [118] also extracted cellulose nanocrystals or whiskers of ramie fibres by acid hydrolysis. Acid hydrolysis of native ramie cellulose fibres leads to aqueous suspensions of elongated nanocrystals with high aspect ratio. The geometric average length and diameter were around 134 59 nm and 10.8 4.5 nm, respectively, giving rise to an aspect ratio around 12. A minimum of 228 and 70 measurements were used to determine the length and the diameter, respectively, of ramie whiskers. They noticed that more than 50% of the... 

Bai W, Holbery J, Li K (2009) A technique for production of nanocrystalline cellulose with a narrow size distribution. Cellulose 16 455-465 Balasubramani M, Kumar TR, Babu M (2001) Skin substitutes a review. Bums 27 534—544 Barud HS, Barrios C, Regiani T et al (2008) Selfsupported silver nanoparticles containing bacterial cellulose membranes. Mater Sci Eng C-Biomim Supramol Syst 28 515-518 Battista OA (1950) Hydrolysis and crystallization of cellulose. Ind Eng Chem 42 502-507 Battista OA, Coppick S, Howsmon JA et al (1956) Level-off degree of polymerization. Relation to polyphase stracture of cellulose fibres. Ind Eng Chem 48 333-335 Beck-Candanedo S, Roman M, Gray DG (2005) Effect of reaction conditions on the properties and behavior of wood cellulose nanocrystal suspensions. Biomacromolecules 6 1048-1054... 

Bondeson D, Oksman K (2007a) Dispersion and characteristics of surfactant modifled cellulose whiskers nanocomposites. Compos Interface 14 617-630 Bondeson D, Oksman K (2007b) Polylactic acid/cellulose whisker nanocomposites modifled by polyvinyl alcohol. Compos Part A 38 2486-2492 Bondeson D, Mathew A, Oksman K (2006a) Optimization of the isolation of nanocrystals from microcrystalline cellulose by acid hydrolysis. Cellulose 13 171-180 Bondeson D, Kvien 1, Oksman K (2006b) ACS symposium series, vol 938. American Chemical Society, Washington, DC... 

Habibi Y, Goffin AL, Schiltz N et al (2008) Bionanocomposites based (m poly(epsilgrafted cellulose nanocrystals by ring-opening polymerization. J Mater Chan 18 5002-5010 Hakansson H, Ahlgren P (2005) Acid hydrolysis of some industrials pulps of hydrolysis conditions... 

At nanoscale thickness, fibrils are named as nanofibrillar cellulose (NFC) or nanocellulose [26-28]. Highly crystalline cellulose nanowhiskers, also called cellulose micelles, cellulose nanorods, cellulose nanocrystals, or nanocrystalline cellulose are produced under strong acid hydrolysis (e.g., mineral acids such as hydrochloric acid or sulphuric acid) combined with mechanical shearing [22, 29]. 

In 2013, cellulose nanocrystals (CNs) were fabricated from sulfuric acid hydrolysis of cottonseed finter. The crystals were then utifized to prepare nitrile rubber (NBR)/CNs nanocomposites by mixing a water suspension of CNs and the NBR latex directly. CNs formed a strong filler-filler network in the NBR matrix which resulted in an obvious Payne effect [110]. 

In 1959, Marchessault et al. [32] reported on the formation of liquid crystals in suspensions of cellulose nanocrystals prepared from cellulose by acid hydrolysis in sulfuric acid (see Fig. 6.17 for a microscopic image of cellulose nanorods). 

Camarero, E. S., Kuhnt, T., Foster, E. J., Weder, C. (2013). Isolation of thermally stable cellulose nanocrystals by phosphoric acid hydrolysis. 14(4), 1223-1230. 

Kargarzadeh H, Ahmad I, Abdullah I, Dufrensne A, Zainudin SY, Sheltami RM. Effects of hydrolysis conditions on the morphology, crystallinity and thermal stability of cellulose nanocrystals extracted from kenaf bast fibers. Cellulose 2012 19 855-866. 

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