RU2763736C1 - Method for producing a composite superabsorbent chitosan-based polymer with improved moisture-absorbing ability - Google Patents

Abstract

FIELD: polymer materials.

SUBSTANCE: invention relates to a method for producing high-molecular compounds, namely, superabsorbent polymers (SAP). Superabsorbent polymers, mesh materials with a spatial structure, capable of absorbing water in amounts several hundred times greater than their own mass, are widely applicable in various fields of human activity, e.g., in agriculture, production of hygienic products, packaging materials, for biomedical purposes, etc. The method for producing a superabsorbent chitosan-based polymer with improved moisture-absorbing ability is characterised by the fact that 1 g of chitosan is placed into a three-necked round-bottomed flask in 100 ml of a 5% aqueous solution of acetic acid, 50 ml of a 20% aqueous solution containing acrylic acid and acrylamide in a molar ratio in the range of 0.1 to 0.9:0.9 to 0.1, N,N-methylene-bis-acrylamide and a persulphate initiator in amounts of 0.5 to 3.5% wt. is added, the mixture is held at room temperature while stirring for 30 min, and then for 2 h at 80°C, the gel-like mass is removed from the reactor, ground, and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used in the synthesis of SAP : alkali 1.0 to 0.8:1.1, after complete absorption of the alkaline solution, the synthesised product is dried in an air flow at 40°C to a constant mass and ground.

EFFECT: provided method for producing a superabsorbent chitosan-based polymer, wherein the superabsorbent polymer is characterised by a degree of swelling in distilled water in the range of 603 to 1,147 g/g.

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Description

The invention relates to a method for producing macromolecular compounds, namely, superabsorbent polymers (SAP). Superabsorbent polymers - mesh materials with a spatial structure capable of absorbing water in quantities several hundred times greater than their own weight, are widely used in various fields of human activity, for example, in agriculture, the production of hygiene products, packaging materials, biomedical purposes, etc. .d.

All currently developed SAP can be divided into three groups:

- fully synthetic - such materials are products of (co)polymerization of acrylic monomers. For example, methods for their preparation are described in RU 2074200 (reticulated copolymer of cobalt salt of acrylic acid), RU 2649144 (triple network copolymer of acrylic acid, maleic anhydride and styrene), RU 96113186 (triple network copolymer of acrylic acid, ammonium acrylate and styrene). Synthetic SAPs are usually characterized by high values of the degree of equilibrium swelling (about 1000 g/g), however, their use is associated with an increased environmental burden on the environment due to their inability to decompose in natural conditions;

- fully biodegradable SAP are most often covalently or ionotropically cross-linked polysaccharides [G.J. Graulus, A. Mignon, S. VanVlierberghe, et al. Cross-linkable alginate-graft-gelatin copolymers for tissue engineering applications. Eur. Polym. J., 72 (2015), pp. 494-506; EN 2227753; S.P. Miguel, M.P. Ribeiro, H. Brancal, P. Coutinho, I.J. Correia. Thermoresponsive chitosan-agarose hydrogel for skin regeneration. Carbohydr. Polym., 111 (2014), pp. 366-373; K. Ravishankar, R. Dhamodharan. Advances in chitosan-based hydrogels: Evolution from covalently crosslinked systems to ionotropically crosslinked superabsorbents. React. Funct. Polym., 149 (2020), p. 104517] or products based on amino acid polymers [W. Shi, M.J. Dumont, E.V. Ly. Synthesis and properties of canola protein-based superabsorbent hydrogels. Eur. Polym. J., 54 (2014), p.172-180; D.C. Hwang, S. Damodaran. Chemical modification strategies for synthesis of protein-based hydrogel. J. Agr. FoodChem., 44 (3) (1996), p. 751-758]. Such products are characterized by low mechanical strength and low degrees of equilibrium swelling, which makes them unattractive for industrial production;

- composite SAP containing polysaccharide units in the acrylate matrix.

The technical result of this approach is a material with a lower environmental impact compared to synthetic polymers. Thus, RU 2634428, RU 2643040 and RU 2574722 present methods for producing composite SAP based on starch, chitosan or carboxymethylcellulose using (meth)acrylic acid acrylamide as comonomers. The disadvantage of the presented approach is the insufficiently high degree of equilibrium swelling, about 300-400 g/g. In RU 2539379, to increase the swelling ability, it is proposed to use an additional comonomer containing a tetrazole ring in the side substituent. However, such monomers are not a large-tonnage product, which makes this approach unprofitable for commercial production.

The closest way to obtain the product is the method of RU 2574722, which consists in the fact that to 5 wt.% solution of polysaccharide in 2% aqueous solution of acetic acid containing 0.01-0.20 wt.% formaldehyde or ascorbic acid, at 18-30 ° With 0.01-0.30 wt.% hydrogen peroxide is added and the reaction mixture is kept with vigorous stirring for 15-40 minutes, then a solution of acrylamide in (meth)acrylic acid or N,N-di(methyl)ethyloxyethyl methacrylate in ratio of 0.1-0.9:0.9-0.1 mole fractions and 0.1-10.0 wt.% N,N-methylene-bis-acrylamide or diethylene glycol dimethacrylate, propylene glycol dimethacrylate, and the reaction mass is kept under stirring in for 3 hours at 18-30°C, freeze-dried.

The disadvantage of this method is the limitation of the degree of equilibrium swelling of the composite SAP, as well as the freeze-drying stage, which involves freezing the resulting product, which can lead to the destruction of polysaccharides.

The technical objective of the invention is to increase the degree of swelling of the composite SAP based on chitosan, acrylic acid and acrylamide and to exclude the stage of freeze drying of the synthesized product.

To solve the stated technical problem, a method is proposed for obtaining a composite superabsorbent polymer based on chitosan with improved moisture absorption capacity, characterized in that a 1% solution of chitosan in a 5% aqueous solution of acetic acid is placed in a three-necked round-bottomed flask, 50 ml of a 20% aqueous solution of acetic acid is added, a solution containing acrylic acid and acrylamide in a molar ratio in the range of 0.1-0.9: 0.9-0.1, N,N-methylene-bis-acrylamide and persulphate initiator in amounts of 0.5-3.5% wt. for each, the mixture is kept at room temperature with stirring for 30 minutes, and then for another 2 hours at 80°C, the gel-like mass is removed from the reactor, crushed and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used in the synthesis of SAP : :alkali 1.0-0.8:1.1, after complete absorption of the alkaline solution, the synthesized product is dried in a stream of air at 40°C to constant weight and crushed.

The technical result of the invention is to increase the degree of swelling of the composite SAP based on chitosan, acrylic acid and acrylamide by treating the synthesized product with an aqueous solution of alkali.

The method is carried out as follows.

A 1% solution of chitosan in a 5% aqueous solution of acetic acid is placed in a three-necked round-bottom flask, 50 ml of a 20% aqueous solution containing acrylic acid and acrylamide in a molar ratio in the range of 0.1-0.9:0.9 is added. -0.1, N,N-methylene-bis-acrylamide and persulfate initiator in the amount of 0.5-3.5 wt.% for each, the mixture is kept at room temperature with stirring for 30 minutes, and then for another 2 hours at 80 °C, the gel-like mass is removed from the reactor, crushed and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used in the synthesis of SAP : alkali 1.0-0.8: 1.1, after complete absorption of the alkaline solution, the synthesized product dried in a stream of air at 40°C to constant weight and crushed.

The method is illustrated by the following examples.

Example 1

In a round bottom flask equipped with a stirrer and reflux condenser, make 1 g of chitosan and 100 ml of a 5% aqueous solution of acetic acid. After complete dissolution of the polysaccharide, 50 ml of a 20% aqueous solution containing acrylic acid, acrylamide in a molar ratio of 0.1:0.9, N,N-methylene-bis-acrylamide and persulphate initiator in an amount of 3.5 wt.% . The mixture is kept under stirring for 30 min and another 2 h at 80°C. Then the gel-like mass is removed from the reactor, crushed and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used for the synthesis of SAP : alkali 0.8:1.1. After complete absorption of the alkaline solution, the synthesized product is dried in a stream of air at 40°C to constant weight and crushed.

The yield of the obtained SAP is 94%, the equilibrium degree of swelling in distilled water is 689-858±56 g/g.

Example 2

In a round bottom flask equipped with a stirrer and reflux condenser, make 1 g of chitosan and 100 ml of a 5% aqueous solution of acetic acid. After complete dissolution of the polysaccharide, 50 ml of a 20% aqueous solution containing acrylic acid, acrylamide in a molar ratio of 0.5:0.5, N,N-methylene-bis-acrylamide and persulphate initiator in an amount of 0.5 wt.% . The mixture is kept under stirring for 30 min and another 2 h at 80°C. Then the gel-like mass is removed from the reactor, crushed and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used for synthesis: alkali 0.9:1.1. After complete absorption of the alkaline solution, the synthesized product is dried in a stream of air at 40°C to constant weight and crushed.

The yield of the obtained SAP is 92%, the equilibrium degree of swelling in distilled water is 953-1147±67 g/g.

Example 3

In a round bottom flask equipped with a stirrer and reflux condenser, make 1 g of chitosan and 100 ml of a 5% aqueous solution of acetic acid. After complete dissolution of the polysaccharide, 50 ml of a 20% aqueous solution containing acrylic acid, acrylamide in a molar ratio of 0.9:0.1, N,N-methylene-bis-acrylamide and persulphate initiator in an amount of 1.5 wt. %. The mixture is kept under stirring for 30 min and another 2 h at 80°C. Then the gel-like mass is removed from the reactor, crushed and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used for the synthesis of SAP : alkali 1.0:1.1. After complete absorption of the alkaline solution, the synthesized product is dried in a stream of air at 40°C to constant weight and crushed.

The yield of the obtained SAP is 92%, the equilibrium degree of swelling in distilled water is 603-759±49 g/g.

Implementation of the proposed method allows to obtain composite hydrophilic SAP with a degree of swelling in distilled water in the range of 603-1147 g/g.

Claims (1)

A method for producing a superabsorbent polymer based on chitosan with improved moisture absorption capacity, characterized in that 1 g of chitosan in 100 ml of a 5% aqueous solution of acetic acid is placed in a three-necked round-bottom flask, 50 ml of a 20% aqueous solution containing acrylic acid and acrylamide in molar ratio in the range of 0.1-0.9:0.9-0.1, N,N-methylene-bis-acrylamide and persulphate initiator in amounts of 0.5-3.5 wt.%, the mixture is kept at room temperature with stirring for 30 minutes, and then for another 2 hours at 80°C, the gel-like mass is removed from the reactor, crushed and placed in a container containing an aqueous solution of alkali in a molar ratio of acrylic acid used in the synthesis of SAP : alkali 1.0-0, 8:1.1, after complete absorption of the alkaline solution, the synthesized product is dried in a stream of air at 40°C to constant weight and crushed.