Biodegradable superabsorbent polymer and preparation method thereof

Abstract

The invention relates to a biodegradable superabsorbent polymer and a preparation method thereof, and belongs to the technical field of high polymer materials, the preparation method comprises the following steps: firstly, carrying out ring-opening polymerization reaction on polyol I and tepenoic acid to generate a carboxyl-containing side chain oligomer, and then carrying out polycondensation crosslinking reaction on the carboxyl-containing side chain oligomer and polyol II to obtain a degradable crosslinked polymer, and finally, reacting the degradable cross-linked polymer with sodium salt to obtain the biodegradable super-absorbent polymer. The polyol I is ethylene glycol, propylene glycol, butanediol, hexanediol, octylene glycol, isosorbide, isomannitol, isoidurol, IIDML, IMDML, ISDML, 1, 4-cyclohexanedimethanol or furandimethanol, and the polyol II is glycerol, triethanolamine, 1, 2, 4-butantriol, pentaerythritol or erythritol; the chemical structural formula of the product is # imgabs 0 # or # imgabs 1 #, and the number-average molecular weight of the product is 10000-80000 g / mol. The method is simple in process; the product has super water absorption capacity and excellent biodegradability.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and relates to a biodegradable super absorbent polymer and a preparation method thereof. Background Art

[0002] Super absorbent polymers (SAPs) are functional polymer materials that contain a large number of hydrophilic groups and have very high water absorption capacity. They are widely used in hygiene and biological related fields. Among them, baby diapers, female hygiene products and adult incontinence products account for more than 95% of the super absorbent polymer market.

[0003] Water absorption capacity is a standard parameter that describes the water retention capacity of SAPs, which is defined as the weight of absorbed liquid (g) divided by the dry weight of SAPs (g). At present, the common super absorbent resins on the market are mainly polyacrylic acid and its sodium salt series products, which have super strong water absorption capacity. Although polyacrylic acid and its sodium salt series products have brought great convenience to people's lives, as the number of uses increases, the environmental problems caused by the use of this series of products have gradually attracted people's attention. Since most of these products are disposable and cannot be degraded in the natural environment, white pollution in nature is increasing, causing great damage to the ecological environment. Therefore, the research and development of degradable super absorbent polymers is very urgent and necessary.

[0004] Degradable super absorbent resins can be prepared from a variety of materials, which can be divided into natural and synthetic polymers according to the source of the materials. Natural polymers mainly include materials such as cellulose, starch and alginate. There are a large number of hydroxyl groups in the chemical structure of cellulose, which is highly hydrophilic, but its water absorption capacity is still insufficient for SAPs applications. Starch is the most abundant polysaccharide in plants, with the advantages of low cost, easy modification and good processing performance. Starch is also a natural macromolecule rich in hydroxyl groups and has high SAP development potential. However, starch has a low specific surface area and needs to be further chemically modified to enhance its water absorption capacity. Alginate is a naturally occurring anionic polymer with large output and low price, but the water absorption and mechanical properties of natural alginate resin are poor and cannot meet the requirements of actual use.

[0005] To solve the above problems, the prior art often further improves the water absorption performance by grafting acrylic molecules. For example, patent CN 103122049 B adds (NH 4 ) 2 S 2 O 8The cellulose was modified by using an aqueous solution of sodium acrylate to propose a method for preparing a cellulose super absorbent resin, which absorbs 975 g of water per gram of resin. Patent CN 103073684 B developed a super absorbent resin based on a starch / sodium alginate / acrylic acid composite system by adding starch to a polymerization system of sodium alginate and acrylic acid, which absorbs 960 g of water per gram of resin. However, although the above method can achieve high water absorption of the resin, it cannot be completely degraded due to the introduction of non-degradable acrylic acid, and there is even a risk of deriving microplastics.

[0006] Based on the above technical status, in recent years, researchers have begun to focus on developing a new generation of SAPs that are more environmentally friendly. For example, using bio-based raw materials to develop low-carbon or degradable products. Itaconic acid (IA) is a bio-based monomer. The double bonds in its chemical structure can undergo free radical polymerization and have a structure very similar to acrylic acid. Researchers have developed some new SAPs around itaconic acid. Although itaconic acid has a structure very similar to acrylic acid, the olefin bond faces greater steric hindrance, and the molecular weight of the polymer prepared by itaconic acid is low. In order to overcome this problem, patent CN113089181 B proposes to prepare a copolyester with high strength and good water absorption by reacting sodium p-styrene sulfonate, diol, initiator, and itaconic acid. However, whether it is homopolymerization or copolymerization, itaconic acid is used as the polymer skeleton for the CC bond structure, which is extremely stable under natural conditions, so the final product prepared does not have biodegradability.

[0007] In order to obtain better biodegradability, some new technical solutions have also been introduced. Some researchers have used a degradable substrate as a base and sprayed a water-absorbing material to achieve the purpose of water absorption. For example, patent CN 111920587 B proposes to use a polylactic acid fiber mesh as a matrix, spray it with polyvinyl alcohol super absorbent resin powder after heat reinforcement, so as to prepare a degradable water-absorbing composite material for use in disposable sanitary products. The polylactic acid fiber mesh used in this method can be biodegraded, however, the added polyvinyl alcohol super absorbent resin powder is still non-degradable SAPs, so it does not fundamentally solve the problem of the degradability of the absorbent resin. Patent CN 112625306 B prepares a fully degradable super absorbent resin by mixing natural degradable polymer materials (carboxymethyl chitosan, chitosan quaternary ammonium salt, carboxymethyl starch, sodium alginate, carboxymethyl cellulose, hydroxypropyl cellulose, gelatin, etc.) with calcium chloride through a simple solution blending process. Although the fully degradable super absorbent resin in this patent has excellent degradation performance and water absorption capacity, it is prepared by solution processing. A large amount of organic solvents are used in the preparation process, causing environmental pollution and endangering the health of operators. In addition, trace amounts of solvent residues may be toxic.

[0008] Therefore, it is of great significance to study a biodegradable super absorbent polymer and a preparation method thereof to solve the problem that the super absorbent polymer in the prior art cannot have super absorbent capacity, excellent biodegradability and processing performance. Summary of the invention

[0009] The purpose of the present invention is to solve the problems existing in the prior art and provide a biodegradable super absorbent polymer and a preparation method thereof.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing a biodegradable super absorbent polymer, comprising: firstly, performing a ring-opening polymerization reaction on polyol I and terpene acid to generate a carboxyl side chain oligomer, then performing a polycondensation crosslinking reaction on the carboxyl side chain oligomer and polyol II to obtain a degradable crosslinked polymer, wherein the degradable crosslinked polymer has poor water absorption performance, and finally reacting the degradable crosslinked polymer with a sodium salt (other high-valent salts such as calcium salts and aluminum salts, Ca²⁺ and Al³⁺ will crosslink with multiple carboxylic acid groups, resulting in a compact network structure and greatly reducing the water absorption capacity) to obtain a biodegradable super absorbent polymer, wherein after the degradable crosslinked polymer reacts with the sodium salt to form sodium carboxylate, an osmotic pressure difference is formed during water absorption, thereby further absorbing water, and the biodegradable super absorbent polymer has excellent water absorption performance;

[0012] Polyol I is ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, octanediol, isosorbide, isomannide, isoidide, IIDML (isoidose-2,5-dimethanol, )、IMDML(isomannose-2,5-dimethanol, )、ISDML(isosorbide-2,5-dimethanol, ), 1,4-cyclohexanedimethanol or furandimethanol, polyol I includes but is not limited to these aliphatic diols and cyclic diols, such as cyclic diols can also be Galx-OH (2,3:4,5-di-O-Methylene-galactitol, ), Manx-OH (2,3:4,5-di-O-Methylene-D-mannitol, ), BCD (4,4'-Bicyclohexanone Glycerol Diketal, ), CHD (1,4-Cyclohexanedione Glycerol Diketal, ), CaG (Camphorquinone Diketal Glycerol, ), CM diol (2,4:3,5-di-O-camphor-D-mannitol, ), etc., polyol II is a triol such as propylene glycol, triethanolamine, 1,2,4-butanetriol, or a tetraol such as pentaerythritol, erythritol, etc. Similarly, polyol II includes but is not limited to these two types of polyols.

[0013] The present invention utilizes polyols and terpene acids to carry out ring-opening polymerization and alkyd polycondensation, increases the polymer molecular weight through ring-opening polymerization, provides cross-linking sites through alkyd polycondensation, and constructs a new polymer system in which the polymer main chain is degradable and has excellent water absorption performance. Compared with traditional non-degradable polyacrylic acid super absorbent materials, due to the presence of ester groups in the polymer main chain, the prepared biodegradable super absorbent polymer can be degraded under conditions such as hydrolysis, soil, composting, and microorganisms. Due to the presence of sodium carboxylate groups in the polymer side chains, the prepared biodegradable super absorbent polymer has excellent water absorption performance, and the biodegradable super absorbent polymer has cross-linking characteristics, which can ensure that it can still maintain a solid shape after absorbing water.

[0014] As the preferred technical solution:

[0015] In the method for preparing a biodegradable super absorbent polymer as described above, the chemical structural formula of terpene acid is , where R 1 and R 2 Each is independently selected from one of a methyl group, an ethyl group and an aldehyde group.

[0016] A method for preparing a biodegradable super absorbent polymer as described above, wherein the ring-opening polymerization reaction is carried out under the action of a catalyst A, and the catalyst A is one or more of stannous octoate, tin tetrachloride, aluminum isopropoxide and stannous chloride;

[0017] The temperature of the ring-opening polymerization reaction is 100~150℃, and the time is 1~5h.

[0018] In the method for preparing a biodegradable super absorbent polymer as described above, the molar ratio of polyol I to terpene acid is 1:2-18, and the added amount of catalyst A is 0.07-0.12 mol% of polyol I.

[0019] In the method for preparing a biodegradable super absorbent polymer as described above, the molecular weight of the oligomer containing a carboxyl side chain is 300-3000 g / mol.

[0020] In the method for preparing a biodegradable super absorbent polymer as described above, the polycondensation cross-linking reaction is carried out under the action of a catalyst B, and the catalyst B is one or more of tetrabutyl titanate, antimony trioxide, antimony acetate and ethylene glycol antimony;

[0021] The temperature of the polycondensation cross-linking reaction is 160~200°C. The reaction is first carried out at normal pressure for 1~3 hours, and then continued under vacuum conditions for 1~2 hours.

[0022] In the method for preparing a biodegradable super absorbent polymer as described above, the molar ratio of polyol II to the oligomer containing a carboxyl side chain is 1:50-100, and the added amount of catalyst B is 0.05-0.1 mol% of polyol II.

[0023] The method for preparing a biodegradable super absorbent polymer as described above, wherein the sodium salt is NaCl, Na 2 CO 3 or NaHCO 3 ;

[0024] The molar ratio of the sodium salt to the degradable cross-linked polymer is 1 to 1.5;

[0025] The temperature for the reaction of the degradable cross-linked polymer with the sodium salt is 50-100°C and the time is 1-2 hours.

[0026] The present invention also provides a biodegradable super absorbent polymer prepared by the preparation method described in any one of the above items, the chemical structure of which is shown in formula (I) or formula (II);

[0027] ;

[0028] (I)

[0029] ;

[0030] (II)

[0031] In the formula, R is , , , , , , , , , , , , , , , , , or , R 1 and R 2 Each is independently selected from a methyl group, an ethyl group and an aldehyde group, R 3 for , or , R 4for or , n is the degree of polymerization;

[0032] The number average molecular weight of the biodegradable super absorbent polymer is 10000~80000 g / mol.

[0033] As the preferred technical solution:

[0034] A biodegradable super absorbent polymer as described above, wherein the biodegradable polymer main chain has a degradable ester group, and can be degraded under conditions such as hydrolysis, soil, composting and microorganisms;

[0035] The hydrolysis conditions are alkaline solution, acidic solution, freshwater environment or marine environment. The alkaline solution is preferably an alkaline solution with a pH of 10 to 14, the acidic solution is preferably an acidic solution with a pH of 1 to 4, the freshwater environment is preferably a river, a lake and a simulated aqueous culture solution, and the marine environment is preferably seawater;

[0036] Soil degradation: Under soil landfill conditions, polymers can eventually be decomposed into simple compounds such as carbon dioxide or methane and water;

[0037] Composting degradation means that under household composting conditions or industrial composting conditions, polymers can eventually be decomposed into simple compounds such as carbon dioxide or methane, water, etc.

[0038] Microbial degradation means that under the action of microorganisms, polymers can eventually be decomposed into simple compounds such as carbon dioxide or methane, water, etc.

[0039] Biodegradable superabsorbent polymers can be degraded within 1 to 10 months in the presence of compost or microorganisms;

[0040] The absorption rate of biodegradable superabsorbent polymers for distilled water at room temperature is 100~200g / g, and the absorption rate for saline is 30~60g / g.

[0041] Beneficial effects:

[0042] (1) The present invention discloses a method for preparing a biodegradable super absorbent polymer, which uses bio-based polyol I and terpene acid as raw materials, and constructs a new polymer system with a degradable polymer main chain and excellent water absorption performance through ring-opening polymerization and condensation polymerization cross-linking process; the system degrades in nature and will not produce persistent microplastics when released into the environment, thereby reducing the risk of microplastic pollution; at the same time, due to the presence of sodium carboxylate groups on the polymer side chains, the system has excellent water absorption performance, and the product system can be used in current super absorbent application fields, such as disposable sanitary products, soil water retention agents, absorbent pads, etc.

[0043] (2) The present invention provides a method for preparing a biodegradable super absorbent polymer, which introduces water-absorbing groups through in-situ modification to prepare the biodegradable super absorbent polymer. The preparation process is simple and environmentally friendly.

[0044] (3) The biodegradable super absorbent polymer of the present invention has both super absorbent capacity and excellent biodegradability, and can be degraded in the natural environment and under limited artificial simulated degradation conditions, thereby effectively protecting the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a reaction flow chart of the preparation method of biodegradable super absorbent polymer. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0047] The test methods involved in the performance indicators in the embodiments and comparative examples of the present invention are as follows:

[0048] Number average molecular weight: GB / T 36214.1-2018 standard is used to test the number average molecular weight of carboxyl side chain oligomers and degradable super absorbent polymers.

[0049] Absorption rate of distilled water and saline: GB / T 39748-2021 standard is used to test the absorption rate of degradable super absorbent polymers for distilled water and saline.

[0050] Degradation experiment: The composting experiment was carried out according to GB / T 19277.1-2011 standard. Household composting is based on soil at a temperature of 25°C; industrial composting is based on farm and garden waste at a temperature of 58°C. The microbial degradation experiment was carried out according to GB / T 41010-2021 standard to test the biodegradation rate of degradable super absorbent polymers.

[0051] Example 1

[0052] A method for preparing a biodegradable super absorbent polymer, the specific steps are as follows:

[0053] (1) Preparation of raw materials:

[0054] Catalyst A: stannous octoate;

[0055] Polyol I: Propylene glycol;

[0056] Terpene acids: ;

[0057] Catalyst B: tetrabutyl titanate;

[0058] Polyol II: triethanolamine;

[0059] Sodium salt: NaCl;

[0060] (2) If Figure 1 As shown, under the action of catalyst A, polyol I and terpene acid undergo a ring-opening polymerization reaction at 100°C for 5 hours to generate a carboxyl side chain oligomer with a molecular weight of 300 g / mol;

[0061] The molar ratio of polyol I to terpene acid is 1:2, and the amount of catalyst A added is 0.07 mol% of polyol I;

[0062] (3) Under the action of catalyst B, the carboxyl side chain oligomer and polyol II are subjected to polycondensation crosslinking reaction at 160°C under normal pressure for 3 hours, and then continue to react under vacuum conditions for 1 hour to obtain a degradable crosslinked polymer;

[0063] The molar ratio of polyol II to carboxyl side chain oligomer is 1:50, and the amount of catalyst B added is 0.1 mol% of polyol II;

[0064] (4) The degradable cross-linked polymer is reacted with the sodium salt at 50°C for 2 hours to obtain a biodegradable super absorbent polymer;

[0065] The molar ratio of the sodium salt to the degradable cross-linked polymer is 1.

[0066] The chemical structure of the biodegradable super absorbent polymer finally obtained is , the number average molecular weight is 10000 g / mol; the biodegradable super absorbent polymer can be degraded within 1 month under the condition of home composting; the absorption rate of the biodegradable super absorbent polymer for distilled water at room temperature is 100 g / g, and the absorption rate of saline is 30 g / g.

[0067] Example 2

[0068] A method for preparing a biodegradable super absorbent polymer, the specific steps are as follows:

[0069] (1) Preparation of raw materials:

[0070] Catalyst A: tin tetrachloride;

[0071] Polyol I: Butanediol;

[0072] Terpene acids: ;

[0073] Catalyst B: antimony trioxide;

[0074] Polyol II: erythritol;

[0075] Sodium salt: Na 2 CO 3 ;

[0076] (2) If Figure 1 As shown, under the action of catalyst A, polyol I and terpene acid undergo a ring-opening polymerization reaction at 110°C for 4 hours to generate a carboxyl side chain oligomer with a molecular weight of 1000 g / mol;

[0077] The molar ratio of polyol I to terpene acid is 1:6, and the amount of catalyst A added is 0.08 mol% of polyol I;

[0078] (3) Under the action of catalyst B, the carboxyl side chain oligomer and polyol II are subjected to polycondensation crosslinking reaction at 180°C under normal pressure for 2 hours, and then continue to react under vacuum conditions for 1.5 hours to obtain a degradable crosslinked polymer;

[0079] The molar ratio of polyol II to carboxyl side chain oligomer is 1:60, and the amount of catalyst B added is 0.06 mol% of polyol II;

[0080] (4) The degradable cross-linked polymer is reacted with the sodium salt at 60°C for 1.75h to obtain a biodegradable super absorbent polymer;

[0081] The molar ratio of the sodium salt to the degradable cross-linked polymer is 1.1.

[0082] The chemical structure of the biodegradable super absorbent polymer finally obtained is , the number average molecular weight is 30000g / mol; the biodegradable super absorbent polymer can be degraded within 3 months under the condition of home composting; the absorption rate of the biodegradable super absorbent polymer for distilled water at room temperature is 121g / g, and the absorption rate of salt water is 38g / g.

[0083] Example 3

[0084] A method for preparing a biodegradable super absorbent polymer, the specific steps are as follows:

[0085] (1) Preparation of raw materials:

[0086] Catalyst A: aluminum isopropoxide;

[0087] Polyol I: 1,4-cyclohexanedimethanol;

[0088] Terpene acids: ;

[0089] Catalyst B: antimony acetate;

[0090] Polyol II: 1,2,4-butanetriol;

[0091] Sodium salt: NaHCO 3 ;

[0092] (2) Under the action of catalyst A, polyol I and terpene acid undergo a ring-opening polymerization reaction at 120°C for 3 h to generate a carboxyl side chain oligomer with a molecular weight of 1700 g / mol;

[0093] The molar ratio of polyol I to terpene acid is 1:10, and the amount of catalyst A added is 0.1 mol% of polyol I;

[0094] (3) Under the action of catalyst B, the carboxyl side chain oligomer and polyol II are subjected to polycondensation crosslinking reaction at 200°C under normal pressure for 1 hour, and then continue to react under vacuum conditions for 2 hours to obtain a degradable crosslinked polymer;

[0095] The molar ratio of polyol II to carboxyl side chain oligomer is 1:80, and the amount of catalyst B added is 0.05 mol% of polyol II;

[0096] (4) The degradable cross-linked polymer is reacted with the sodium salt at 80°C for 1.5 hours to obtain a biodegradable super absorbent polymer;

[0097] The molar ratio of the sodium salt to the degradable cross-linked polymer is 1.3.

[0098] The chemical structure of the biodegradable super absorbent polymer finally obtained is , the number average molecular weight is 50000 g / mol; the biodegradable super absorbent polymer can be degraded within 5 months under the condition of industrial composting; the absorption rate of the biodegradable super absorbent polymer for distilled water at room temperature is 150 g / g, and the absorption rate of saline is 45 g / g.

[0099] Example 4

[0100] A method for preparing a biodegradable super absorbent polymer, the specific steps are as follows:

[0101] (1) Preparation of raw materials:

[0102] Catalyst A: stannous chloride;

[0103] Polyol I: Ethylene glycol;

[0104] Terpene acids: ;

[0105] Catalyst B: antimony glycol;

[0106] Polyol II: pentaerythritol;

[0107] Sodium salt: Na 2 CO 3 ;

[0108] (2) Under the action of catalyst A, polyol I and terpene acid undergo a ring-opening polymerization reaction at 130°C for 2 h to generate a carboxyl side chain oligomer with a molecular weight of 2300 g / mol;

[0109] The molar ratio of polyol I to terpene acid is 1:14, and the amount of catalyst A added is 0.11 mol% of polyol I;

[0110] (3) Under the action of catalyst B, the carboxyl side chain oligomer and polyol II are subjected to polycondensation crosslinking reaction at 170°C under normal pressure for 2.5 hours, and then continue to react under vacuum conditions for 1 hour to obtain a degradable crosslinked polymer;

[0111] The molar ratio of polyol II to carboxyl side chain oligomer is 1:90, and the amount of catalyst B added is 0.07 mol% of polyol II;

[0112] (4) The degradable cross-linked polymer is reacted with the sodium salt at 90°C for 1.25h to obtain a biodegradable super absorbent polymer;

[0113] The molar ratio of the sodium salt to the degradable cross-linked polymer is 1.4.

[0114] The chemical structure of the biodegradable super absorbent polymer finally obtained is , the number average molecular weight is 65000g / mol; the biodegradable super absorbent polymer can be degraded within 8 months under the condition of industrial composting; the absorption rate of the biodegradable super absorbent polymer for distilled water at room temperature is 185g / g, and the absorption rate of salt water is 51g / g.

[0115] Example 5

[0116] A method for preparing a biodegradable super absorbent polymer, the specific steps are as follows:

[0117] (1) Preparation of raw materials:

[0118] Catalyst A: aluminum isopropoxide and stannous chloride in a mass ratio of 1:1;

[0119] Polyol I: Isosorbide;

[0120] Terpene acids: ;

[0121] Catalyst B: antimony acetate and antimony glycol in a mass ratio of 1:1;

[0122] Polyol II: propylene glycol;

[0123] Sodium salt: NaHCO 3 ;

[0124] (2) Under the action of catalyst A, polyol I and terpene acid undergo a ring-opening polymerization reaction at 150°C for 1 h to generate a carboxyl side chain oligomer with a molecular weight of 3000 g / mol;

[0125] The molar ratio of polyol I to terpene acid is 1:18, and the amount of catalyst A added is 0.12 mol% of polyol I;

[0126] (3) Under the action of catalyst B, the carboxyl side chain oligomer and polyol II are subjected to polycondensation crosslinking reaction at 190°C under normal pressure for 1.5 h, and then continue to react under vacuum conditions for 2 h to obtain a degradable crosslinked polymer;

[0127] The molar ratio of polyol II to carboxyl side chain oligomer is 1:100, and the amount of catalyst B added is 0.09 mol% of polyol II;

[0128] (4) The degradable cross-linked polymer is reacted with the sodium salt at 100°C for 1 hour to obtain a biodegradable super absorbent polymer;

[0129] The molar ratio of the sodium salt to the degradable cross-linked polymer is 1.5.

[0130] The chemical structure of the biodegradable super absorbent polymer finally obtained is , the number average molecular weight is 80000 g / mol; the biodegradable super absorbent polymer can be degraded within 10 months under the condition of industrial composting; the absorption rate of the biodegradable super absorbent polymer for distilled water at room temperature is 200 g / g, and the absorption rate of saline is 60 g / g.

Claims

1. A method for preparing a biodegradable super absorbent polymer, characterized in that: Firstly, polyol I and terpene acid undergo a ring-opening polymerization reaction to generate a carboxyl side chain oligomer, then the carboxyl side chain oligomer and polyol II undergo a condensation cross-linking reaction to obtain a degradable cross-linked polymer, and finally the degradable cross-linked polymer reacts with a sodium salt to obtain a biodegradable super absorbent polymer; Polyol I is ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, octanediol, isosorbide, isomannide, isoidide, isoidose-2,5-dimethanol, isomannose-2,5-dimethanol, isosorbide-2,5-dimethanol, 1,4-cyclohexanedimethanol or furandimethanol, and polyol II is glycerol, triethanolamine, 1,2,4-butanetriol, pentaerythritol or erythritol.

2. The method for preparing a biodegradable super absorbent polymer according to claim 1, characterized in that: The chemical structure of terpene acid is , wherein R1 and R2 are each independently selected from one of a methyl group, an ethyl group and an aldehyde group.

3. The method for preparing a biodegradable super absorbent polymer according to claim 1, characterized in that: The ring-opening polymerization reaction is carried out under the action of catalyst A, which is one or more of stannous octoate, tin tetrachloride, aluminum isopropoxide and stannous chloride; The temperature of the ring-opening polymerization reaction is 100~150℃, and the time is 1~5h.

4. The method for preparing a biodegradable super absorbent polymer according to claim 3, characterized in that: The molar ratio of polyol I to terpene acid is 1:2-18, and the added amount of catalyst A is 0.07-0.12 mol% of polyol I.

5. The method for preparing a biodegradable super absorbent polymer according to claim 4, characterized in that: The molecular weight of the carboxyl side chain oligomer is 300~3000g / mol.

6. The method for preparing a biodegradable super absorbent polymer according to claim 1, characterized in that: The polycondensation crosslinking reaction is carried out under the action of catalyst B, which is one or more of tetrabutyl titanate, antimony trioxide, antimony acetate and ethylene glycol antimony; The temperature of the polycondensation cross-linking reaction is 160~200°C. The reaction is first carried out at normal pressure for 1~3 hours, and then continued under vacuum conditions for 1~2 hours.

7. The method for preparing a biodegradable super absorbent polymer according to claim 6, characterized in that: The molar ratio of polyol II to the carboxyl side chain oligomer is 1:50-100, and the added amount of catalyst B is 0.05-0.1 mol% of polyol II.

8. The method for preparing a biodegradable super absorbent polymer according to claim 1, characterized in that: Sodium salt is NaCl, Na2CO3 or NaHCO3; The molar ratio of the sodium salt to the degradable cross-linked polymer is 1 to 1.5; The temperature for the reaction of the degradable cross-linked polymer with the sodium salt is 50-100°C and the time is 1-2 hours.

9. A biodegradable super absorbent polymer obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The chemical structural formula is shown in formula (I) or formula (II); ； （Ⅰ） ； （Ⅱ） In the formula, R is , , , , , , , , , , or , R1 and R2 are each independently selected from a methyl group, an ethyl group and an aldehyde group, and R3 is , or , R4 is or , n is the degree of polymerization; The number average molecular weight of the biodegradable super absorbent polymer is 10000~80000 g / mol.

10. The biodegradable super absorbent polymer according to claim 9, characterized in that: Biodegradable superabsorbent polymers can be degraded within 1 to 10 months in the presence of compost or microorganisms; The absorption rate of biodegradable superabsorbent polymers for distilled water at room temperature is 100~200g / g, and the absorption rate for saline is 30~60g / g.

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