阅读说明：本技术 一种壳聚糖接枝聚丙烯酸的复合吸水树脂和制备方法 (Composite water-absorbent resin of chitosan grafted polyacrylic acid and preparation method ) 是由 徐颖 于 2021-01-25 设计创作，主要内容包括：本发明涉及吸水树脂技术领域,且公开了一种壳聚糖接枝聚丙烯酸的复合吸水树脂,以溴代异丁酯基壳聚糖作为大分子引发剂,在溴化亚铜和六甲基三乙基四胺的配位引发体系中,通过原子转移自由基聚合过程,引发丙烯酸在壳聚糖基体中发生原位交联聚合,得到壳聚糖接枝聚丙烯酸的复合吸水树脂,通过化学键接枝的方法,将聚丙烯酸分子链引入到壳聚糖基体中,形成层次更加丰富,结构更加稳定的三维网络结构,具有良好的结构稳定性,避免在长时间吸水过程中,树脂基体分解和破坏而影响其保水性,同时壳聚糖接枝聚丙烯酸含有丰富的羟基、氨基和羧基亲水基团,具有优异的吸水和吸盐水性能。(The invention relates to the technical field of water-absorbent resin, and discloses a composite water-absorbent resin of chitosan grafted polyacrylic acid, which takes isobutyl bromide chitosan as a macromolecular initiator, in a coordination initiation system of cuprous bromide and hexamethyl triethyltetramine, initiating acrylic acid to generate in-situ cross-linking polymerization in a chitosan matrix through an atom transfer radical polymerization process to obtain the composite water-absorbent resin of chitosan grafted polyacrylic acid, by a chemical bond grafting method, polyacrylic acid molecular chains are introduced into a chitosan matrix to form a three-dimensional network structure with more abundant layers and more stable structure, the structural stability is good, the influence on the water retention property of the resin matrix due to decomposition and damage of the resin matrix in the long-time water absorption process is avoided, meanwhile, the chitosan grafted polyacrylic acid contains abundant hydroxyl, amino and carboxyl hydrophilic groups, and has excellent water absorption and saline water absorption performances.)

1. The chitosan grafted polyacrylic acid composite water-absorbent resin is characterized in that: the preparation method of the chitosan grafted polyacrylic acid composite water-absorbent resin is as follows:

(1) adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, and stirring for reacting for 2-6h to obtain ammonium sulfate chitosan;

(2) adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 4-8h at 25-45 ℃, adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, and reacting for 36-72h to obtain bromo-isobutyl sulfate ammonium chitosan;

(3) adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, and stirring for 30-60min to obtain bromo-isobutyl chitosan;

(4) adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N' -methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, and carrying out in-situ crosslinking polymerization reaction to obtain the composite water absorbent resin of chitosan grafted polyacrylic acid.

2. The chitosan-polyacrylic acid grafted composite water absorbent resin as claimed in claim 1, wherein: the mass ratio of the chitosan to the sodium dodecyl sulfate in the step (1) is 10: 35-50.

3. The chitosan-polyacrylic acid grafted composite water absorbent resin as claimed in claim 1, wherein: the mass ratio of the 2-bromoisobutyric acid, the dicyclohexylcarbodiimide, the N-hydroxysuccinimide and the ammonium sulfate chitosan in the step (2) is 250-300:200-240:350-420: 100.

4. The chitosan-polyacrylic acid grafted composite water absorbent resin as claimed in claim 1, wherein: in the step (4), the mass ratio of isobutyl bromide chitosan, acrylic acid, N' -methylenebisacrylamide, cuprous bromide and hexamethyltriethylenetetramine is 3-8:100:2.5-6: 1.5-5.

5. The chitosan-polyacrylic acid grafted composite water absorbent resin as claimed in claim 1, wherein: the reaction temperature of the in-situ crosslinking polymerization reaction in the step (4) is 25-45 ℃, and the reaction time is 20-30 h.

Technical Field

The invention relates to the technical field of water-absorbent resins, in particular to a chitosan grafted polyacrylic acid composite water-absorbent resin and a preparation method thereof.

Background

The super absorbent resin is a resin material with strong hydrophilicity, has a large amount of hydrophilic groups such as hydroxyl, carboxyl, amino and the like, has a special three-dimensional network structure, has strong water absorption, can absorb water with mass much larger than the self mass, and has important application in the aspects of daily chemical industry, medical treatment, agriculture and forestry and the like.

The traditional acrylic acid super absorbent resin has strong water absorption performance, but the water absorption performance of the traditional acrylic acid super absorbent resin in salt solutions such as sodium chloride, potassium chloride and the like is poor, and the stability of a matrix structure is influenced for a long time due to the absorption of a large amount of water, so that the water retention property is reduced, the chitosan has good biodegradability and biocompatibility and contains rich hydroxyl and amino, and a strategy of grafting chitosan to a polyacrylic acid molecular chain can be adopted to obtain the composite acrylic acid water absorbent and saline absorbent resin containing rich hydrophilic hydroxyl, amino and carboxyl.

Technical problem to be solved

Aiming at the defects of the prior art, the invention provides the chitosan grafted polyacrylic acid composite water-absorbent resin and the preparation method thereof, and the chitosan grafted polyacrylic acid composite water-absorbent resin has excellent water absorption, salt water absorption and water retention.

(II) technical scheme

In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of chitosan grafted polyacrylic acid composite water-absorbent resin is as follows:

(1) adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring and reacting for 2-6h, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 4-8h at 25-45 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, reacting for 36-72h, cooling in an ice water bath, adding diethyl ether and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromo-isobutyl ester ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 30-60min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N' -methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, carrying out in-situ crosslinking polymerization reaction, filtering a solvent, washing with distilled water, and carrying out dialysis purification to obtain the chitosan grafted polyacrylic acid composite water absorbent resin.

Preferably, the mass ratio of the chitosan to the sodium dodecyl sulfate in the step (1) is 10: 35-50.

Preferably, the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan in the step (2) is 250-300:200-240:350-420: 100.

Preferably, the mass ratio of the isobutyl bromide chitosan, the acrylic acid, the N, N' -methylenebisacrylamide, the cuprous bromide and the hexamethyltriethyltetramine in the step (4) is 3-8:100:2.5-6: 1.5-5.

Preferably, the reaction temperature of the in-situ crosslinking polymerization reaction in the step (4) is 25-45 ℃, and the reaction time is 20-30 h.

(III) advantageous technical effects

Compared with the prior art, the invention has the following chemical mechanism and beneficial technical effects:

according to the chitosan grafted polyacrylic acid composite water-absorbent resin, amino groups of chitosan are protonated in an acetic acid medium to form NH³⁺Cation, SO with sodium dodecyl sulfate₄ ^-And (3) performing electrostatic attraction on anions to obtain ammonium sulfate chitosan, protecting amino groups, preventing the amino groups from reacting with 2-bromoisobutyric acid, better reacting the 2-bromoisobutyric acid with hydroxyl of the chitosan to obtain bromoisobutyl sulfate ammonium sulfate chitosan, further removing dodecyl sulfate anions in a Tris buffer salt solution, and regenerating the amino groups to obtain the bromoisobutyl chitosan.

According to the chitosan grafted polyacrylic acid composite water absorbent resin, isobutyl bromide chitosan is used as a macroinitiator, acrylic acid is initiated to generate in-situ cross-linking polymerization in a chitosan matrix through an atom transfer radical polymerization process in a coordination initiation system of cuprous bromide and hexamethyltriethyltetramine to obtain the chitosan grafted polyacrylic acid composite water absorbent resin, a polyacrylic acid molecular chain is introduced into the chitosan matrix through a chemical bond grafting method to form a three-dimensional network structure with richer layers and more stable structure, the structure stability is good, the influence on the water retention of the resin matrix due to decomposition and destruction of the resin matrix in a long-time water absorption process is avoided, and meanwhile, the chitosan grafted polyacrylic acid contains abundant hydroxyl, amino and carboxyl hydrophilic groups and has excellent water absorption and salt water absorption properties.

Detailed Description

To achieve the above object, the present invention provides the following embodiments and examples: a chitosan grafted polyacrylic acid composite water-absorbent resin is prepared as follows:

(1) adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring and reacting for 2-6h, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 4-8h at 25-45 ℃, then adding dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid, the dicyclohexylcarbodiimide, the N-hydroxysuccinimide and the ammonium sulfate chitosan is 250-300:200-240:350-420:100, reacting for 36-72h, cooling in an ice water bath, adding diethyl ether and acetone solvent to precipitate, filtering the solvent, and washing by distilled water to obtain the bromo-isobutyl ester sulfate ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 30-60min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 25-45 ℃ for 20-30h, filtering a solvent, washing with distilled water, dialyzing and purifying to obtain the chitosan grafted polyacrylic acid composite water absorbent resin, wherein the mass ratio of isobutyl bromide chitosan to acrylic acid to N, N' -methylenebisacrylamide to cuprous bromide to hexamethyltriethyltetramine is 3-8:100:2.5-6: 1.5-5.

0.5g of the dried chitosan-grafted polyacrylic acid composite water absorbent resin was placed in 1000mL of distilled water, immersed for 6 hours, taken out, and then the surface moisture was dried, and weighed, and the water absorption of the composite water absorbent resin was calculated, and the water absorption was ═ 0.5/0.5 (weight after water absorption).

0.5g of the dried chitosan-grafted polyacrylic acid composite water-absorbent resin was placed in 1000mL of a sodium chloride solution at a concentration of 0.9% and immersed for 12 hours, and after taking out, the surface water was dried and weighed, and the salt water absorption rate of the composite water-absorbent resin, which was (weight after salt water absorption-0.5)/0.5, was calculated.

Example 1

(1) Adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring and reacting for 2 hours, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 4 hours at 25 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan is 250:200:350:100, reacting for 36 hours, cooling in an ice water bath, adding an ether solvent and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromoisobutylethyl ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 30min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, wherein the mass ratio of the isobutyl bromide chitosan to the acrylic acid to the N, N' -methylenebisacrylamide to the cuprous bromide to the hexamethyltriethyltetramine is 3:100:2.5:1.5, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 25 ℃ for 20h, filtering the solvent, washing with distilled water, dialyzing and purifying to obtain the chitosan grafted polyacrylic acid composite water-absorbent resin, wherein the water absorption rate is 719.2g/g, and the saline absorption rate is 72.8 g/g.

Example 2

(1) Adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring and reacting for 4 hours, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 2h at 45 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan is 260:210:370:100, reacting for 72h, cooling in an ice water bath, adding an ether solvent and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromoisobutylethyl ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 40min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, wherein the mass ratio of the isobutyl bromide chitosan to the acrylic acid to the N, N' -methylenebisacrylamide to the cuprous bromide to the hexamethyltriethyltetramine is 4.5:100:3.5:2.2, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 35 ℃ for 30h, filtering the solvent, washing with distilled water, dialyzing and purifying to obtain the chitosan grafted polyacrylic acid composite water-absorbing resin, wherein the water absorption rate is 1169.2g/g, and the water absorption rate is 95.8 g/g.

Example 3

(1) Adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring for reacting for 46h, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 6 hours at 35 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan is 280:230:400:100, reacting for 48 hours, cooling in an ice water bath, adding an ether solvent and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromoisobutylethyl ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 40min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, wherein the mass ratio of the isobutyl bromide chitosan to the acrylic acid to the N, N' -methylenebisacrylamide to the cuprous bromide to the hexamethyltriethyltetramine is 6:100:4.8:4, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 35 ℃ for 24h, filtering the solvent, washing with distilled water, dialyzing and purifying to obtain the chitosan grafted polyacrylic acid composite water absorbent resin, wherein the water absorption rate is 1069.0g/g, and the salt absorption rate is 114.2 g/g.

Example 4

(1) Adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring and reacting for 4 hours, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 8 hours at 45 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan is 300:240:420:100, reacting for 72 hours, cooling in an ice water bath, adding an ether solvent and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromoisobutylethyl ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 60min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, wherein the mass ratio of the isobutyl bromide chitosan to the acrylic acid to the N, N' -methylenebisacrylamide to the cuprous bromide to the hexamethyltriethyltetramine is 8:100:6:5, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 45 ℃ for 30h, filtering the solvent, washing with distilled chitosan water, dialyzing and purifying to obtain the polyacrylic acid grafted composite water-absorbing resin with the water absorption rate of 789.7g/g and the salt absorption rate of 61.2 g/g.

Comparative example 1

(1) Adding distilled water and chitosan into a three-necked bottle, dropwise adding acetic acid until the chitosan is dissolved after uniform ultrasonic dispersion, then adding sodium dodecyl sulfate, wherein the mass ratio of the chitosan to the sodium dodecyl sulfate is 10:30, stirring for reaction for 6 hours, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing with distilled water to obtain ammonium sulfate chitosan, wherein the water absorption rate is 719.2g/g, and the salt absorption water rate is 72.8 g/g.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 4 hours at 45 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan is 230:180:320:100, reacting for 72 hours, cooling in an ice water bath, adding an ether solvent and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromoisobutylethyl ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 50min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, wherein the mass ratio of the isobutyl bromide chitosan to the acrylic acid to the N, N' -methylenebisacrylamide to the cuprous bromide to the hexamethyltriethyltetramine is 1.5:100:1.5:1, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 45 ℃ for 20h, filtering the solvent, washing with distilled water, dialyzing and purifying to obtain the chitosan grafted polyacrylic acid composite water-absorbent resin, wherein the water absorption rate is 519.2g/g, and the saline absorption rate is 58.8 g/g.

Comparative example 2

(1) Adding distilled water and chitosan into a three-necked bottle, uniformly dispersing by ultrasonic, dropwise adding acetic acid until the chitosan is dissolved, adding sodium dodecyl sulfate, stirring and reacting for 6 hours, adding sodium hydroxide to adjust the pH value of the solution to be neutral, filtering the solvent, and washing by distilled water to obtain the ammonium sulfate chitosan.

(2) Adding an N, N-dimethylformamide solvent, 2-bromoisobutyric acid, dicyclohexylcarbodiimide and N-hydroxysuccinimide into a three-necked bottle, stirring and reacting for 8 hours at 25 ℃, then adding a dimethyl sulfoxide solution containing ammonium sulfate chitosan, wherein the mass ratio of the 2-bromoisobutyric acid to the dicyclohexylcarbodiimide to the N-hydroxysuccinimide to the ammonium sulfate chitosan is 330:350:450:100, reacting for 48 hours, cooling in an ice water bath, adding an ether solvent and an acetone solvent to precipitate, filtering the solvent, and washing with distilled water to obtain the bromoisobutylethyl ammonium sulfate chitosan.

(3) Adding a dimethyl sulfoxide solvent and bromo-isobutyl ammonium sulfate chitosan into a three-necked bottle, stirring for dissolving, adding a Tris buffer salt solution, stirring for 60min, adding distilled water, performing centrifugal separation until the upper layer is clear, and washing the lower-layer product with distilled water to obtain the bromo-isobutyl chitosan.

(4) Adding distilled water solution, isobutyl bromide chitosan, acrylic acid and N, N '-methylenebisacrylamide into a three-necked bottle, adding acetic acid-sodium acetate buffer solution, removing oxygen through freezing-vacuumizing-nitrogen circulating treatment, adding cuprous bromide and hexamethyltriethyltetramine, wherein the mass ratio of the isobutyl bromide chitosan to the acrylic acid to the N, N' -methylenebisacrylamide to the cuprous bromide to the hexamethyltriethyltetramine is 10:100:8:6.5, carrying out in-situ crosslinking polymerization reaction at the reaction temperature of 30 ℃ for 30h, filtering the solvent, washing with distilled water, dialyzing and purifying to obtain the chitosan grafted polyacrylic acid composite water absorbent resin, wherein the water absorption rate is 629.0g/g, and the salt absorption rate is 31.1 g/g.