CN100389870C - Modified soybean protein isolate-based super water-absorbing agent and preparation method thereof - Google Patents

Abstract

The invention provides a modified soybean protein isolate-based super water-absorbing agent and its preparation method, which is characterized in that: firstly, the soybean protein isolate is hydrolyzed into a water-soluble protein with a molecular weight of 10,000-20,000 in a sodium hydroxide solution, and then hydrolyzed with peracetic acid. After hydrophilic modification, it is mixed with an aqueous solution of vinyl monomers, and in the presence of a composite crosslinking agent and a redox initiator, crosslinking and graft copolymerization are performed to obtain a water-absorbing gel, which is pelletized , drying, crushing, and sieving to obtain super absorbent products. The product obtained by the invention has good water absorption and water retention performance, fast permeation speed, good salt resistance and biodegradability, and is suitable for the production of water-absorbing materials for personal hygiene products such as sanitary napkins and paper diapers.

Description

Modified soybean protein isolate-based super water-absorbing agent and preparation method thereof

technical field

The invention relates to a biodegradable modified soybean protein isolate-based super water-absorbing agent and a preparation method thereof, which belong to the field of functional macromolecule material chemistry and also belong to the field of natural macromolecule.

Background technique

Super absorbent (also known as super absorbent resin, referred to as SAP) is a new type of functional polymer material developed in recent years, which can absorb water hundreds to thousands of times its own weight, and has a strong water retention capacity use. Superabsorbent was first successfully developed by the United States Department of Agriculture in 1974, and then it was first industrialized in Japan in 1978 and began to be widely used in hygienic materials. It is now widely used in industry, agriculture, daily life, medical care and other fields. Previous patents proposed the method of using different raw materials to prepare superabsorbents, such as the hydrolyzate of starch-acrylonitrile graft polymer, saponified vinyl acetate-acrylic acid copolymer, and sodium polyacrylate superabsorbent obtained by reverse suspension polymerization. Strong water-absorbing agents, etc., the above-mentioned method also includes issues such as the improvement of the liquid absorption rate of the resin (absorbing water, saline, urine, etc.) and liquid absorption speed. However, as a superabsorbent widely used in industry, agriculture, forestry and horticulture and daily chemical industry, the performance required by its use is different, for example: Chinese patent CN1359974A discloses the title "Preparation method of agricultural superabsorbent composite resin As mentioned in ", there are different requirements for water-absorbing materials used in agriculture. For example, the gel after SAP product particles absorb water must have a certain strength, so that it can maintain a certain shape in the soil and can absorb water well. Water retention for slow release. At the same time, because of the high strength of the hydrogel, the gel is not easy to disintegrate, and the reversibility of water absorption and release is good, so that its effective life in the soil is prolonged. As described in Chinese patent CN1229808A titled "water absorbing agent and its manufacturing method and application", the SAP used as sanitary materials such as women's sanitary napkins is required to have excellent urine resistance, and has the ability to resist any urine composition. Adsorption properties that are stable and change little over time.

According to reports, the production and sales of super absorbents in the world have exceeded 1.5 million tons. At present, SAP is mainly made of acrylic acid as a monomer cross-linked and polymerized, 80% of which are used to make personal care such as disposable baby diapers and women's sanitary napkins. supplies. Like all polymers with C-C bonds as the main chain, high molecular weight cross-linked polyacrylic acid (salt) SAP is difficult to be decomposed by microorganisms and bacteria in the soil, and is a non-biodegradable polymer. my country is a potential big consumer of personal care products such as disposable diapers and sanitary napkins. With the increasing scale of SAP production and the application market of personal care products, traditional cross-linked polyacrylic acid (salt) SAP will inevitably bring Huge environmental pollution problem.

Contents of the invention

The purpose of the present invention is to provide a kind of super absorbent material with biodegradability prepared by using soybean protein isolate through chemical modification, and then grafted and copolymerized with vinyl monomer, which is suitable for the production of sanitary napkins, paper diapers and other personal care products. The water-absorbing agent and the preparation method thereof can save raw material cost, and the preparation process is simple.

The present invention is realized by free radical oxidation-reduction initiation and aqueous solution graft copolymerization in the following manner: firstly, the soybean protein isolate powder is hydrolyzed into water-soluble protein with a molecular weight of 10,000-20,000 in sodium hydroxide solution, and then subjected to prophylaxis with peracetic acid. After water-based modification, it is mixed with an aqueous solution of vinyl monomer, and in the presence of a composite cross-linking agent and a free radical redox initiator, cross-linking, grafting, and copolymerization are performed to obtain a water-absorbing gel. Cutting, drying, crushing, and sieving to obtain super absorbent products.

The super absorbent is a cross-linked modified soybean protein isolate-vinyl monomer graft copolymer, and the components and weight percentages are:

Modified soybean protein isolate 8.5～42.0

Vinyl monomer 57.5～90.5

Composite crosslinking agent 0.22～0.55

Ammonium persulfate 0.14～0.29

Sodium bisulfite 0.07～0.22

The water-soluble vinyl monomer used in the present invention is one or more mixtures of sodium acrylate, hydroxyethyl acrylate, acrylamide and sodium allyl sulfonate.

The specific preparation method is:

1) Add 85 to 255 grams of modified soybean protein isolate aqueous solution with a weight percentage of 8% to 15%, 40 to 85 grams of vinyl monomers, and 0.2 to 0.5 grams of composite crosslinking agent in a container with stirring, and stir fully until completely dissolved;

2) Add 6.2 to 19.5 grams of 1.0% sodium bisulfite and 12.3 to 26.0 grams of 1.0% ammonium persulfate, stir evenly and transfer to a stainless steel reaction tray, keep the initial temperature at 35 to 45°C for 30 minutes, and then heat up Continue to react at 60-80°C for 1-2 hours;

3) Cut the polymer gel into pellets, dry at 105° C., pulverize, and sieve to obtain a super water-absorbing agent.

The above-mentioned composite crosslinking agent is composed of N, N'-methylenebisacrylamide and glutaraldehyde, the amount of composite crosslinking agent is 0.22% to 0.55% of the total mass of the polymerization raw The mass ratio of bisacrylamide and glutaraldehyde is 0.8-2.5:1.0. The role of the cross-linking agent is to keep the water-absorbing agent to maintain a certain strength after absorbing water. N, N'-methylenebisacrylamide mainly copolymerizes with vinyl monomers to form a network structure, and glutaraldehyde mainly interacts with free Amino and hydroxyl crosslinks. If the amount is too low, the soluble part in the water-absorbing agent will increase, resulting in a decrease in water absorption, and directly affect the gel strength after water absorption. Good, but there are many cross-linking points during polymerization, the network space formed by cross-linking points becomes smaller, the amount of liquid that can be accommodated is also correspondingly reduced, and the water absorption capacity is significantly smaller.

The above-mentioned initiator is ammonium persulfate-sodium bisulfite redox initiator. The amount of initiator directly affects the chain molecular weight and self-crosslinking degree of the resin. If the amount of initiator is too small, the reaction speed is relatively slow and the polymerization time is long; if the amount of initiator is too large, the polymerization reaction will occur rapidly, which may cause danger, increase the degree of crosslinking and decrease the molecular weight, so the water absorption rate of the obtained water retaining agent At the same time, the amount of initiator also directly affects the grafting rate, and the grafting rate increases with the increase of the initiator amount, but after a certain amount, the grafting rate decreases with the increase of the initiator amount. When the dosage of the initiator increases, the grafting active sites increase, and the grafting rate gradually increases. However, when the initiator is excessive, more monomer free radicals may be generated, and the homopolymerization rate is greater than the grafting copolymerization rate, which is unfavorable for the grafting copolymerization reaction.

The preparation method of the modified soybean protein isolate used in the present invention is:

(1) Add deionized water to the soybean protein isolate powder to a concentration of 8% to 15%, add 0.2 to 0.5 grams of 5% β-mercaptoethanol per kilogram of protein dry weight, stir, add NaOH solution to adjust the pH to 13.0 to 14.0, and use The mincer grinds the protein gel, puts it into the reaction kettle, stirs, and heats to 100°C, so that the soybean globinin undergoes a dissociation reaction under alkaline conditions and degrades into components with a molecular weight of 10,000 to 20,000. And the disulfide bond is cracked, the structure of glycinin is unfolded, and a linear polymer protein aqueous solution is formed;

(2) Cool down the protein solution to 70-80° C., add peracetic acid of 0.2%-0.5% of protein dry weight, and stir for 15-30 minutes. Peracetic acid can oxidize the sulfhydryl group on the protein side chain into a strongly hydrophilic sulfonic acid group, and at the same time bleach the protein solution to increase its whiteness after polymerization.

The deionized water absorption rate Q _(water) of the protein-based superabsorbent prepared by the present invention is 145-538g.g ^-1 ; the absorption rate Q _(salt) of 0.9% saline solution is 42-66.7gg ^-1 .

Compared with the prior art, the present invention has characteristics:

1) Using modified soybean protein isolate and water-soluble vinyl monomer as the main raw material for graft copolymerization, the prepared water-absorbing agent has excellent water absorption and water retention performance, and its salt resistance and urine resistance are better than pure acrylic homopolymer. The cost is reduced, and the utility model has better economic benefits.

2) The solution polymerization method is adopted, and the polymerization reaction is initiated at room temperature, the process is simple, and the operation is easy.

3) Introducing natural protein chain links into the polymer network can make the water-absorbing agent biodegradable after use and waste, which has good environmental benefits.

Detailed ways

Below directly adopt the mode of embodiment to describe the present invention in detail:

Example 1:

1. Preparation of modified soybean protein isolate

(1) Add deionized water to soybean protein isolate powder to a concentration of 12.0%, add 0.3 grams of 5% β-mercaptoethanol per kilogram of protein (dry weight), stir, add NaOH solution to adjust pH=14, and grind the protein After the gel is crushed, it is sent into the reaction kettle, stirred and heated to 100°C, so that the glycinin dissociation reaction occurs under alkaline conditions, and it is degraded into a protein aqueous solution of linear polymer with a molecular weight of 10,000-20,000.

(2) Cool down the protein solution to 75°C, add 0.4% peracetic acid of protein dry weight, stir and react for 20 minutes, the sulfhydryl group on the protein side chain can be oxidized into a strongly hydrophilic sulfonic acid group, and at the same time make the protein The solution was bleached to obtain a modified protein solution with a solid content of 12%.

2. Preparation of modified soybean protein-based superabsorbent: 150 grams of modified soybean protein isolate aqueous solution of 12% by weight, 100 grams of deionized water, and 65 grams of vinyl monomer sodium acrylate were added to a container with stirring. gram, N, N'-methylenebisacrylamide 0.15 grams and 25.0% glutaraldehyde 0.56 grams, fully stirred until completely dissolved; then add 1.0% sodium bisulfite 10.0 grams, 1.0% ammonium persulfate 15.0 After stirring evenly, move it into a stainless steel reaction tray, keep the initial temperature at 35-45°C for 30 minutes, then raise the temperature to 70°C and continue the reaction for 2 hours, then cut the polymer gel into pellets, dry at 105°C, pulverize, and sieve The superabsorbent product was obtained, its deionized water absorption Q (water) = 324g.g ^-1 ; absorption rate of 0.9% saline solution Q (salt) = 51.2gg ^-1 .

Example 2

1. Preparation of modified soybean protein isolate

(1) Add deionized water to soybean protein isolate powder to a concentration of 8%, add 0.4 g of 5% β-mercaptoethanol per kilogram of protein (dry weight), stir, add NaOH solution to adjust pH=13, and grind the protein After the gel is crushed, it is sent into the reaction kettle, stirred and heated to 100°C, so that the glycinin dissociation reaction occurs under alkaline conditions, and it is degraded into a protein aqueous solution of linear polymer with a molecular weight of 10,000-20,000.

(2) protein solution is cooled to 80 DEG C, add the peracetic acid of protein dry weight 0.5%, stir reaction 15 minutes, make the sulfhydryl group on the side chain of protein oxidation become the sulfonic acid group of strong hydrophilicity, obtain solid content as 8% modified protein solution.

2. Preparation of modified soybean protein-based superabsorbent: Add 215 grams of modified soybean protein isolate aqueous solution of 8% by weight in a container with stirring, 100 grams of deionized water, 85 grams of sodium acrylate, N, 0.20 g of N'-methylenebisacrylamide, 0.45 g of 25% glutaraldehyde, fully stirred until completely dissolved; then add 16.0 g of 1.0% sodium bisulfite, 22.0 g of 1.0% ammonium persulfate, and stir well Move it into a stainless steel reaction tray, keep the initial temperature at 35-45°C and react for 30 minutes, then raise the temperature to 80°C and continue the reaction for 1.5 hours, cut the polymer gel into pellets, dry at 105°C, crush, and sieve to obtain super absorbent Product, its deionized water absorption rate Q (water) = 469g.g-1; absorption of 0.9% saline solution Q (salt) = 48.2g.g-1.

Example 3

1. Preparation of modified soybean protein isolate

(1) Add deionized water to soybean protein isolate powder to a concentration of 15%, add 0.5 g of 5% β-mercaptoethanol per kilogram of protein (dry weight), stir, add NaOH solution to adjust pH=14, and grind the protein After the gel is crushed, it is sent into the reaction kettle, stirred and heated to 100°C, so that the glycinin dissociation reaction occurs under alkaline conditions, and it is degraded into a protein aqueous solution of linear polymer with a molecular weight of 10,000-20,000.

(2) protein solution is cooled to 70 ℃, adds the peracetic acid of 0.3% of protein dry weight, stirs and reacts for 15 minutes, makes the sulfhydryl group on the protein side chain oxidation becomes the sulfonic acid group of strong hydrophilicity, obtains solid content as 15% modified protein solution.

2. Preparation of modified soybean protein-based super water-absorbing agent: 180 grams of modified soybean protein isolate aqueous solution, 125 grams of deionized water, 58 grams of sodium acrylate, N, 0.25 grams of N'-methylenebisacrylamide, 0.40 grams of 25% glutaraldehyde, fully stirred until completely dissolved; then add 12.0 grams of 1.0% sodium bisulfite, 18.0 grams of 1.0% ammonium persulfate, and stir well Move it into a stainless steel reaction tray, keep the initial temperature at 35-45°C and react for 30 minutes, then raise the temperature to 80°C and continue the reaction for 2 hours, cut the polymer gel into pellets, dry at 105°C, crush, and sieve to obtain super absorbent Product, its deionized water absorption rate Q (water)=297g.g-1; absorption rate of 0.9% saline solution Q (salt)=55.3g.g-1.

Example 4

Others are the same as in Example 1, except that the vinyl monomer is a mixture of 35.0 grams of sodium acrylate and 30.0 grams of acrylamide, and the superabsorbent product obtained by the reaction has a deionized water absorption Q (water)=306g.g -1; absorbing 0.9% saline magnification Q (salt) = 59.3g.g-1.

Example 5

Others are the same as in Example 1, except that the vinyl monomer is a mixture of 25.0 grams of sodium acrylate and 40.0 grams of sodium allyl sulfonate, and the superabsorbent product obtained by the reaction has a deionized water absorption rate Q (water) =523g.g-1; absorbing 0.9% saline magnification Q (salt)=49.7g.g-1.

Example 6

Others are the same as in Example 1, except that the vinyl monomer is a mixture of 45.0 grams of sodium acrylate and 20.0 grams of hydroxyethyl acrylate, and the superabsorbent product obtained by the reaction has a deionized water absorption Q (water)=412g .g-1; absorbing 0.9% saline magnification Q (salt) = 48.7g.g-1.

Example 7

Others are the same as in Example 3, except that 255 grams of 15% modified soybean protein isolate aqueous solution, 100 grams of deionized water, 45 grams of sodium acrylate, 0.35 grams of N, N'-methylenebisacrylamide, 25% pentamethylene 0.6 grams of dialdehyde, 16.0 grams of 1.0% sodium bisulfite, 26.0 grams of 1.0% ammonium persulfate, and the reaction polymer gel was pelletized, dried at 105° C., pulverized, and sieved to obtain a super absorbent product. The water absorption rate Q (water) of deionization = 151.g.g-1; the rate of absorption of 0.9% saline solution Q (salt) = 48.2 g.g-1.

Claims (6)

1. A modified soybean protein isolate-based superabsorbent, characterized in that the superabsorbent is a cross-linked modified soybean protein isolate-vinyl monomer graft copolymer, each component is: modified Soy protein isolate, vinyl monomer, composite cross-linking agent, ammonium persulfate, sodium bisulfite, the percentage by weight is: Modified soybean protein isolate 8.5～42.0 Vinyl monomer 57.5～90.5 Composite crosslinking agent 0.22～0.55 Ammonium persulfate 0.14～0.29 Sodium bisulfite 0.07～0.22. 2. The modified soybean protein isolate-based superabsorbent according to claim 1, wherein the vinyl monomer is one or more of sodium acrylate, hydroxyethyl acrylate, acrylamide and sodium allyl sulfonate Several kinds. 3. The modified soybean protein isolate-based superabsorbent according to claim 2, characterized in that the vinyl monomer is a water-soluble vinyl monomer. 4. a preparation method of modified soybean protein isolate base superabsorbent as claimed in claim 1, is characterized in that comprising the following steps: 1) Add 85 to 255 grams of modified soybean protein isolate aqueous solution with a weight percentage of 8% to 15%, 40 to 85 grams of vinyl monomers, and 0.2 to 0.5 grams of composite crosslinking agent in a container with stirring, and stir fully until completely dissolved; 2) Add 6.2-19.5 grams of 1.0% sodium bisulfite and 12.3-26.0 grams of 1.0% ammonium persulfate, keep the initial temperature at 35-45°C for 30 minutes, then heat up to 60-80°C to continue the reaction for 1- After 2 hours, stir evenly and move into the reaction tray to react to obtain a polymer gel; 3) Cut the polymer gel into pellets, dry at 105° C., pulverize, and sieve to obtain a super water-absorbing agent. 5. the preparation method of a kind of modified soybean protein isolate base superabsorbent according to claim 4, is characterized in that composite cross-linking agent is made up of N, N'-methylenebisacrylamide and glutaraldehyde, Its mass ratio is 0.8-2.5:1.0. 6. the preparation method of modified soybean protein isolate base superabsorbent according to claim 4, is characterized in that the modification method of soybean protein isolate is: (1) Add deionized water to soybean protein isolate powder to a concentration of 8% to 15%, add 0.2 to 0.5 grams of 5% β-mercaptoethanol per kilogram of protein dry weight, stir, add NaOH solution to adjust the pH to 13.0 to 14.0, Form a protein gel, mince it, stir and heat to 100°C, so that the glycinin dissociates under alkaline conditions to form a linear polymer protein aqueous solution; (2) cooling the protein aqueous solution to 70-80° C., adding peracetic acid of 0.2%-0.5% of protein dry weight, stirring and reacting for 15-30 minutes to obtain the modified soybean protein isolate aqueous solution.