RU2682625C1 - Method for production of nanocrystalline particles of cellulose by catalytic solvolysis in an organic medium - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to chemical treatment of cellulose, in particular to methods of producing ultrafine particles and hydrosols of nanocrystalline cellulose, and can be used in pharmaceutical, food, perfume and other industries for production of organic nanoparticles with ordered structure, biocompatible materials based thereon, rheological modifiers and thickeners, plastics fillers, biodegradable polymer materials and composites, paint stabilizers, fibers and emulsions. Method of producing nanocrystalline cellulose particles by catalytic solvolysis in an organic medium in the form of an aqueous dispersion includes controlled destruction of powdered cellulose obtained from softwood or hardwood, or linen, or cotton, extraction, purification of the end product, wherein decomposition is carried out by catalytic solvolysis of cellulose material in a mixture of acetic acid, octanol-1 and phosphotungstic acid, wherein phosphotungstic acid is taken in amount of 0.2–0.3 % of molar relative to anhydroglucose cellulose unit, the ratio of acetic acid/octanol-1 is 10:1 volume parts, cellulose destruction process is carried out at the boiling point of the obtained mixture for 40 minutes, while adding a hydrogen peroxide solution in amount of 0.05 % of the volume of liquid in system every 5 minutes.EFFECT: improved method of producing NCC from different types of celluloses with lower consumption of reagents and reduced duration of de-structuring process.3 cl, 1 dwg, 1 tbl

Description

The invention relates to the chemical processing of cellulose, in particular to methods for producing ultrafine particles and hydrosols of nanocrystalline cellulose, and can be used in the production of organic nanoparticles with an ordered structure, biocompatible materials based on them, rheological modifiers and thickeners, plastic fillers, biodegradable polymeric materials and composites , stabilizers of paints, fibers, emulsions, in the pharmaceutical, food, perfumery and other industries.

The production of micro- and nanoscale materials based on cellulose with a highly ordered structure of individual particles is based on the peculiarities of its supramolecular organization. Such dispersed particles and systems based on them are in demand and with wide potential for application of the form of the initial polysaccharide - microcrystalline and nanocrystalline cellulose (MCC and NCC, respectively).

It is known that nanocrystalline cellulose, the geometric particle sizes of which, in at least one dimension, do not exceed 100 nm, exhibits fundamentally new properties that are absent in cellulosic materials with a morphology of micrometer scale and higher. NCCs form stable hydrosols that exhibit the property of thixotropy even at low concentrations; capable of film formation. Materials based on such particles have a high specific surface area and strength; form porous foams and hydrogels with a high modulus of elasticity. These properties determine the application of cellulosic nanosized materials - the preparation of biodegradable fillers for gels, films, plastics, drug delivery vehicles, coatings [Kim J., Shim BS, Kim HS, Lee Y., Min S., Jang D., Abas Z. , Kim J. Review of nanocellulose for sustainable future materials // International journal of precision engineering and manufacturing - green technology, 2015, Vol. 2, N. 2, P. 197–213; Moon R. J., Martini A., Nairn J., Simonsenf J., Youngblood J. Cellulose nanomaterials review: structure, properties and nanocomposites // Chem. Soc. Rev., 2011, Vol. 40, N. 7, P. 3941-3994; Voskoboinikov I.V., Konstantinova S.A., Korotkov A.N., Galbraich L.S., Ivanov V.F. The use of nanocrystalline cellulose for the modification of wood-laminated plastics // Chemistry of plant raw materials. 2011. No3. S. 43-46].

An expanded raw material base - the prevalence and botanical diversity of plants and other cellulose producers, many of which are cultivated makes it possible to use standard methods for producing NCC particles with crystallinity, morphology, aggregate and thermal stability, and optical and mechanical properties that differ depending on the origin of the polysaccharide [Jonoobi M ., Oladi R., Davoudpour Y., Oksman K., Dufresne A., Hamzeh Y., Davoodi R. Different preparation methods and properties of nanostructured cellulose from various natural resources and residues: a review // Cellulose (2015) 22: 935–969. + Elazzouzi-Hafraoui S., Nishiyama Y., Putaux J., Heux L., Dubreuil F., Rochas C. The Shape and Size Distribution of Crystalline Nanoparticles Prepared by Acid Hydrolysis of Native Cellulose // Biomacromolecules. 2008, 9, 57–65].

Various methods have been proposed for the preparation of NCC, the most numerous group of which is based on the use of various types of acid hydrolysis [RU 2556144, CN 101759807A, US 20100272819A1]. Less common are the methods of radiolysis [RU 2494109], mechanical and chemical-mechanical effects [Liu C., Li B., Haishun D., Lv D., Zhang Y., Yu G., Mu X., Peng H. Properties of nanocellulose isolated from corncob residue using sulfuric acid, formic acid, oxidative and mechanical methods // Carbohydrate Polymers 151 (2016) 716–724], supercritical fluid use [Novo LP, Bras J., García A., Belgacem N., Curvelo AAS Subcritical water: a method for green production of cellulose nanocrystals // ACS Sustainable Chem. Eng. 2015. No. 3 Vol. 11. P. 2839–2846].

The disadvantages of using mineral acids, such as sulfuric and hydrochloric, are the formation of large amounts of waste, the complexity of their regeneration or disposal. In addition, the most common methods using sulfuric acid lead to the often undesirable functionalization of the surface of NCC particles with sulfur-containing groups.

Recently, there has been growing interest in the use of heteropolyacids (HPA) as catalysts for the destruction of cellulose. This is due to the distinctive physicochemical properties of HPA, a variety of compounds of this class. The possibility of obtaining NCC by elemental composition closer to natural cellulose. The value of Hammett's acidity function (H ₀ ) for HPA solutions exceeds the values characteristic of mineral acids, for example, H ₂ SO ₄ . HPA are very strong, thermally stable compounds with high solubility in oxygen-containing solvents.

A known method of producing NCC by hydrolysis of cellulose in a solution of phosphoric tungsten acid (H ₃ PW ₁₂ O ₄₀ , FVC) [Liu Y., Wang H., Yu G., Yu Q., Li B., Mua X. A novel approach for the preparation of nanocrystalline cellulose by using phosphotungstic acid // Carbohydrate polymers. - 2014 .-- Vol. 110. - No. - P. 415-422]. As a result, particles with a length of 100-200 nm and stable hydrosols were obtained. Authors [Lu Q., Cai Z., Lin F., Tang L., Wang S., Huang B. Extraction of Cellulose Nanocrystals with a High Yield of 88% by Simultaneous Mechanochemical Activation and Phosphotungstic Acid Hydrolysis // ACS Sustainable Chem . Eng. - 2016. - Vol. 4. - No. 4. - P. 2165–2172] proposed a method for producing nanosized cellulose particles by mechanochemical treatment, the key stage of which is to process a mixture of cellulose with tungsten phosphoric acid (FVK) in a ball mill. By this method, particles with a length (for three main fractions) of 200-280 nm and a thickness of 30-45 nm were selected. The use of PVA in combination with ultrasound to obtain NCC in an aqueous medium is described in [Bee SAH, Zain SK, Das R., Centi G. Synergic effect of tungstophosphoric acid and sonication for rapid synthesis of crystalline nanocellulose // Carbohydrate Polymers 138 (2016) 349–355.]. Powder cellulose (PC) was used as the starting material in all examples. The disadvantages of these methods are the use of large molar excesses of FFA (ten-hundredth excess relative to the anhydroglucose unit of cellulose), as well as the long course of the hydrolysis process (up to 30 hours), obtaining particles with a thickness of at least 20 nm.

Closest to the invention in technical essence is a method for producing nanocrystalline cellulose RU 2620429, which is carried out by controlled destruction of cellulose raw materials in a mixture of FVC (5-8 mol% relative to the anhydroglucose unit of cellulose) acetic acid and hydrogen peroxide, with an initial concentration of hydrogen peroxide 1-2 % The product is isolated in the form of an aqueous NCC dispersion with particle sizes of 100-300 nm, a thickness of 20-35 nm, and with a crystallinity index of about 0.9. As the source of cellulosic raw materials use pulp powder, obtained on the basis of plant material of various botanical origin.

The objective of the invention is to develop an improved method for producing NCC from various types of celluloses, with a lower consumption of reagents and a shorter duration of the destruction process. This is the technical result.

The technical result is achieved by the fact that the method of producing nanocrystalline cellulose particles by catalytic solvolysis in an organic medium in the form of an aqueous dispersion, including controlled degradation of powdered cellulose obtained from coniferous or deciduous wood, or flax or cotton, isolation, purification of the target product, according to the invention, destruction carry out catalytic solvolysis of cellulosic raw materials in a mixture of acetic acid, octanol-1 and phosphoric tungsten acid, while phosphoric tungsten acid they take 0.2-0.3% mole relative to the anhydroglucose unit of cellulose, the ratio of acetic acid / octanol-1 is 10: 1 volume parts, the process of cellulose destruction is carried out at the boiling temperature of the mixture for 40 minutes, while adding each 5 min. A solution of hydrogen peroxide in an amount of 0.05% of the volume of liquid in the system. In addition, the destruction of cellulose is carried out at a temperature of 115 ⁰ C; the target product is obtained with a rod-like particle length of 150-400 nm and a thickness of 6.2 to 9.6 nm with a crystallinity index above 0.7.

The method is as follows.

1. Regulated destruction (solvolysis of cellulose in an organic medium).

The source cellulosic material, acetic acid, octanol-1 and the catalyst (FVC) are placed in a reactor equipped with a stirrer, thermometer and heater, carrying out the solvolysis process at a temperature of 115 ° C for 40 min, with regular addition of hydrogen peroxide.

The fluid module for acetic acid is 8-12 (preferably 10). The ratio of acetic acid / octanol-1 is 10: 1 (by volume). FVK take in an amount of 0.2-0.3% molar relative to the anhydroglucose unit of cellulose.

2. Cleaning and obtaining an aqueous dispersion of NCC.

The precipitate is separated from the reaction mixture obtained at the end of the solvolysis process, dispersed in ethanol or isopropyl alcohol and centrifuged, repeating this process twice. The resulting suspension is treated with an aqueous solution of NaOH and purified by dialysis or by multiple centrifugation, or (preferably) a combination of these methods. A stable aqueous dispersion is obtained containing, depending on the type of source cellulose, NCC rod-shaped particles with a length of 150 to 400 nm and a thickness of 6.2 to 9.6 nm.

The main materials and reagents used in the proposed method: glacial acetic acid, phosphoric tungsten acid (H ₃ PW ₁₂ O ₄₀ ), octyl alcohol, hydrogen peroxide (preferably a concentration of 20-30%); powdered cellulose based on cotton and flax fiber or cellulose isolated from various coniferous and deciduous woods. The average degree of polymerization of the PC 150-300.

The proposed method is characterized by a combination of features that improve the technical result, compared with known methods:

1. Reduced costs by reducing the duration of the main processes.

2. The duration of the process of controlled destruction of cellulose is reduced to 40 minutes, which is 4-5 times less than in the known method.

3. The method includes simple, scalable manufacturing operations.

4. Available reagents are used.

5. The use of phosphoric tungsten acid is minimized - compared with the closest analogues of the proposed method: the consumption of PVA decreases by 20 or more times, to 0.2-0.3 mol% relative to the anhydroglucose unit of cellulose.

6. The consumption of water and hydrogen peroxide is reduced.

7. The resulting NCC particles have a thickness of not more than 12 nm, which ensures a qualitative change in the properties of the material.

When implementing the method excludes the use of large volumes of mineral acids per unit of the resulting product. FVK used as a catalyst for destruction and acetic acid used as a solvent are regenerated and returned to the technological cycle.

The method is efficient and simple to implement, includes two main stages, does not require highly specialized equipment, high energy and raw materials costs, expensive reagents, sources of ionizing radiation, work under pressure or in vacuum. Suitable for producing nanoparticles based on various types of celluloses.

Analysis of the known technical level did not reveal technical solutions with a set of features for the implementation of the above result, which indicates the compliance of the claimed technical solution with the criteria of "novelty", "inventive step".

The essence of the proposed solutions and the possibility of their implementation is confirmed by examples. The examples given are further illustrated in Figure 1, which shows the images of NCC particles obtained on the basis of various types of celluloses and a table with the characteristics of the products obtained as a result of the implementation of the present invention.

Figure 1: AFM micrographs of NCC particles obtained by the proposed method in the system of acetic acid / octanol-1 / FVK.

Example 1

Cotton cellulose powder pulp was placed in a reactor equipped with a heating jacket, a stirrer, a reflux condenser and a temperature control device. Acetic acid (liquid module 10), octanol-1 (1.0 volume per 10 volumes of acetic acid), and FVC were added. The content of PVA relative to the anhydroglucose unit of cellulose is 0.20% mole.

The process of cellulose destruction was carried out at the boiling temperature of the resulting mixture (115 ^° C) for 40 minutes, every 5 minutes. adding a solution of hydrogen peroxide in an amount of 0.05% of the volume of liquid in the system.

At the end, the reaction mixture was cooled. The precipitate was separated in a centrifuge, dispersed in ethanol (the operation was repeated twice). The resulting cellulosic material was transferred to a 0.5 mol / L NaOH solution, held for 4 hours, and then centrifuged again (4000 rpm × 30 min). The resulting precipitate was dispersed in distilled water and further purified by dialysis against distilled water in membranes with a pore size of 12-14 kDa. A stable dispersion was obtained containing rod-shaped NCC particles with a length of 150 nm and a thickness of 8.7 nm.

Example 2

Carried out analogously to example 1, but with a total content of phosphoric tungsten acid relative to cellulose 0.30% mole.

Example 3

Carried out analogously to example 1, using as starting material a powder of cellulose obtained on the basis of flax pulp.

Example 4

Carried out analogously to example 2, using as starting material powdered cellulose obtained on the basis of flax pulp

Example 5

Carried out analogously to example 1, using as starting material a powder of cellulose obtained on the basis of soft bleached pulp.

Example 6

Carried out analogously to example 2, using as starting material a powder of cellulose obtained on the basis of soft bleached pulp.

Example 7

Carried out analogously to example 1, using as starting material a powder of cellulose obtained on the basis of hardwood bleached pulp.

Example 8

Carried out analogously to example 2, using as starting material a powder of cellulose obtained on the basis of hardwood bleached pulp.

Thus, the invention allows to obtain rod-shaped cellulose particles with a length of 150 to 400 nm and a thickness of 6.2 to 9.6 nm, depending on the type of source cellulose (cotton, linen, cellulose of hardwood or coniferous wood), with a crystallinity index of particles above 0.7 based on powdered cellulose obtained from various plant materials: coniferous and deciduous wood, flax and cotton. The claimed method is characterized by a low consumption of catalyst and a reduced duration of the process of controlled destruction (solvolysis).

Table

Characteristics of NCC particles obtained by the proposed method in the system of acetic acid / octanol-1 / FVK

Example length
particles, nm The largest
thickness nm Index
Crystallinity
(according to Segal) Exit
regarding
source pulp,% one 150 8.7 ± 1.0 0.82 34 ± 5 2 400 7.3 ± 0.6 0.77 30 ± 4 3 258 6.2 ± 0.2 0.80 33 ± 3 four 249 9.6 ± 1.2 0.72 31 ± 5 5 167 8.3 ± 0.9 0.83 33 ± 6 6 390 7.2 ± 0.7 0.76 29 ± 5 7 244 6.2 ± 0.4 0.79 30 ± 3 8 230 9.3 ± 0.8 0.74 30 ± 4

Claims (3)

1. The method of producing nanocrystalline cellulose particles by catalytic solvolysis in an organic medium in the form of an aqueous dispersion, comprising controlled degradation of powdered cellulose obtained from coniferous or deciduous wood, or flax, or cotton, isolation, purification of the target product, characterized in that the destruction is carried out by catalytic by solvolysis of cellulosic raw materials in a mixture of acetic acid, octanol-1 and phosphoric tungsten acid, while phosphoric tungsten acid is taken in an amount of 0.2-0.3% molar cellulose anhydroglucose unit, the ratio of acetic acid / octanol-1 is 10: 1 volume parts, the process of cellulose degradation is carried out at the boiling temperature of the mixture for 40 minutes, while adding every 5 minutes a solution of hydrogen peroxide in the amount of 0.05% of volume fluid in the system. 2. The method according to p. 1, characterized in that the destruction of cellulose is carried out at a temperature of 115 ° C. 3. The method according to p. 1, characterized in that the target product is obtained with a length of rod-shaped particles from 150 nm to 400 nm and a thickness of from 6.2 nm to 9.6 nm with a crystallinity index above 0.7.

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