Tropical crop cellulose-based super absorbent polymer as well as preparation method and application thereof

Abstract

The invention provides a tropical crop cellulose-based super absorbent polymer as well as a preparation method and application thereof, and belongs to the technical field of high polymer materials. The preparation method comprises the following steps: forming cellulose-peach gum composite aerogel with a covalent cross-linked structure from tropical crop cellulose and peach gum under the action of a cross-linking agent, and carrying out allyl functional grafting modification on the composite aerogel to obtain allylated composite aerogel. The allylated composite aerogel is subjected to a synergistic copolymerization reaction with a cross-linking agent and a monomer to prepare the tropical crop cellulose-based super absorbent polymer with high water absorption and a stable three-dimensional network structure, so that the defect that the structure is easy to collapse after a traditional super absorbent material absorbs water is overcome; the tropical crop fiber with abundant resources is adopted as the raw material, the preparation process is simple, the operability is high, and the method can be applied to preparation of agriculture and forestry water retention materials or preparation of food fresh-keeping materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a tropical crop cellulose-based highly water-absorbent polymer and a preparation method and application thereof. Background Art

[0002] Traditional high-molecular-weight, highly absorbent materials (such as polyacrylic acid polymers and polyvinyl alcohol) have broad application prospects in healthcare, agriculture, forestry, food preservation, and other fields due to their strong and repetitive water absorption properties. While the production technology for single-molecule absorbent materials is relatively mature, the raw material selection is limited, and the rising prices of chemical raw materials such as acrylic acid have resulted in high production costs, high product prices, and slow promotion and application. Long-term use also poses challenges such as non-degradability and environmental pollution.

[0003] Cellulose-based superabsorbent polymers have developed rapidly in recent years. On the one hand, cellulose is a hydrophilic polyhydroxy compound, and on the other hand, cellulose is a fibrous substance with many capillaries and a large specific surface area. Therefore, cellulose-based superabsorbent polymers have good water absorption and biocompatibility. Cellulose is a renewable resource that is abundant in nature and is a natural polysaccharide. The use of cellulose grafting to prepare superabsorbent materials is in line with the concepts of environmental protection and sustainable development. Cellulose-based superabsorbent materials can be naturally degraded after long-term use and will not cause pollution to the environment. Existing cellulose-based superabsorbent materials mostly use wood or crop straw as cellulose raw materials. The efficient utilization of tropical crop fibers (such as pineapple leaf fibers and sisal fibers) is still insufficient, and there are still problems such as low water absorption and low mechanical strength. It is difficult to meet some application scenarios with high requirements for material strength. For example, patent application publication number CN 112592431 A produces a cellulose-grafted acrylic acid-based superabsorbent hydrogel. However, the preparation process requires a specific atmosphere reaction apparatus, resulting in relatively stringent preparation conditions. Furthermore, the resulting superabsorbent hydrogel exhibits a water absorption rate of 229.5%, indicating poor water absorption. Therefore, despite the abundance of tropical crop fiber resources, existing technologies for cellulose extraction and functional modification are insufficient, particularly in applications in agriculture and forestry water conservation. Developing superabsorbent cellulose materials based on tropical plant fibers could not only address the environmental shortcomings of traditional synthetic polymer-based absorbent materials but also maximize the value of tropical agricultural resources.

[0004] Therefore, developing a tropical crop cellulose-based super absorbent material with high water absorption rate and good mechanical properties has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] To address the above-mentioned technical problems, the present invention proposes a tropical crop cellulose-based superabsorbent polymer, its preparation method, and application. The present invention utilizes covalent crosslinking technology to first form a crosslinked aerogel structure from tropical crop cellulose and peach gum. The aerogel is then modified by allyl functionalization through grafting. Through the synergistic copolymerization of the crosslinker and monomer, a tropical crop cellulose-based superabsorbent polymer with a network structure that combines high water absorption and mechanical strength is constructed. This overcomes the defect of traditional superabsorbent materials that their structure easily collapses after absorbing water. The superabsorbent polymer prepared by the present invention contains a crosslinked aerogel structure, which not only gives it a high water absorption rate and a structure that is not prone to collapse, but also imparts the material with superior water retention properties, making it widely applicable. Furthermore, the preparation method of the tropical crop cellulose-based superabsorbent polymer of the present invention is simple.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a tropical crop cellulose-based super absorbent polymer comprises the following steps: reacting tropical crop cellulose with peach gum under the action of a glycerol ether crosslinking agent to form a cellulose-peach gum composite aerogel having a covalent crosslinking structure; performing allyl functional grafting modification on the cellulose-peach gum composite aerogel to obtain an allylated composite aerogel; and then subjecting the allylated composite aerogel to a synergistic copolymerization reaction with an acrylate crosslinking agent and a monomer to prepare the tropical crop cellulose-based super absorbent polymer.

[0009] Furthermore, the preparation method of the tropical crop cellulose-based super absorbent polymer comprises the following steps:

[0010] (1) Dispersing tropical crop cellulose and peach gum in water, heating in a water bath and adjusting the pH to alkaline, adding the glycerol ether cross-linking agent and stirring for reaction, and then freeze-drying the reaction product to obtain the cellulose-peach gum composite aerogel;

[0011] (2) crushing the cellulose-peach gum composite aerogel, dispersing it with a NaOH solution, adding an epoxy group-containing allyl compound, and stirring to react to obtain an allylated composite aerogel;

[0012] (3) After dispersing the allylated composite aerogel with water, heating it in a water bath and sequentially adding an initiator, a monomer solution, and an acrylate crosslinking agent to react to obtain a gel product. After washing and drying the gel product, the tropical crop cellulose-based superabsorbent polymer is obtained.

[0013] Preferably, in step (1), the tropical crop cellulose is extracted from pineapple leaf fiber and / or sisal fiber, and the specific preparation method is:

[0014] The raw fibers (pineapple leaf fibers and / or sisal fibers) are cut short and then crushed into small segments with an average size of 1 mm. The crushed powder is added to a 4% by mass NaOH solution for alkali treatment, stirred at 80°C for 3 hours, then filtered and washed three times with distilled water, bleached with sodium hypochlorite, stirred at 70°C for 2 hours, filtered and washed three times, and dried at 50°C to obtain powdered tropical crop cellulose.

[0015] Preferably, in step (1), the mass ratio of the tropical crop cellulose, peach gum and glycerol ether cross-linking agent is (1-1.8): (0.2-1): (0.02-0.2); and / or,

[0016] The glycerol ether cross-linking agent is one or more of ethylene glycol diglycidyl ether, glycerol diglycidyl ether, 1,4-butanediol diglycidyl ether and 1,6-hexanediol diglycidyl ether.

[0017] Preferably, in step (1), the pH is adjusted to 11 with NaOH; and / or,

[0018] The stirring reaction temperature is 50° C. and the time is 1-4 hours; and / or,

[0019] The freeze drying step is to freeze the reaction product at -80°C for 24 hours and then freeze-dry it in a vacuum for 48 hours.

[0020] Preferably, in step (2), the cellulose-peach gum composite aerogel is crushed to an average particle size of 2-5 mm; and / or,

[0021] The usage ratio of the cellulose-peach gum composite aerogel, the NaOH solution and the epoxy-containing allyl compound is 2g:100mL:0.5g.

[0022] Preferably, in step (2), the epoxy-containing allyl compound is allyl glycidyl ether, glycidyl acrylate or glycidyl methacrylate; and / or,

[0023] The concentration of the NaOH solution is 40 wt.%.

[0024] Preferably, in step (3), the initiator is one or more of ammonium persulfate, potassium persulfate and sodium persulfate; and / or,

[0025] The acrylate crosslinking agent is one or more of ethylene glycol dimethacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate and 1,6-hexanediol dimethacrylate; and / or,

[0026] The monomer in the monomer solution is acrylic acid, and during the preparation process, the acrylic acid exists in the form of an acrylic acid solution, the concentration of the acrylic acid solution is 0.125 g / mL, and the temperature is 0° C.; and / or,

[0027] The usage ratio of the allylated composite aerogel, the initiator, the monomer solution and the acrylate crosslinking agent is 1 g: (0.025-0.05) g: 40 mL: (0.015-0.025) g.

[0028] Preferably, in step (3), the allylated composite aerogel obtained in step (2) is dispersed with water, an initiator is added, nitrogen is passed through, and the mixture is stirred at room temperature for 10 minutes. Then, the monomer solution is added, the mixture is heated to 60° C. and stirred for 15 minutes. Then, an acrylate crosslinker is added and the mixture is stirred and reacted for 2-4 hours to obtain a gel product.

[0029] The second technical solution of the present invention:

[0030] A tropical crop cellulose-based superabsorbent polymer is prepared according to the preparation method.

[0031] The third technical solution of the present invention:

[0032] The tropical crop cellulose-based superabsorbent polymer is used in preparing agricultural and forestry water-retaining materials or food preservation materials.

[0033] Preferably, in the field of agriculture and forestry water conservation, the tropical crop cellulose-based superabsorbent polymer can be used as an agriculture and forestry soil water conservation agent.

[0034] Preferably, in the field of food preservation, the tropical crop cellulose-based super absorbent polymer can be used as a coating preservation material, such as a litchi coating preservation material. When used as a coating preservation material, the powdered tropical crop cellulose-based super absorbent polymer needs to be prepared into a uniform coating liquid for use. The concentration of the coating liquid can be 2g / L, 5g / L, 8g / L or 10g / L.

[0035] Compared with the prior art, the present invention has the following advantages and technical effects:

[0036] (1) The present invention uses covalent cross-linking technology to form a cross-linked aerogel with tropical crop cellulose and peach gum. In an alkaline environment, the epoxy groups of diglycidyl ether open the ring and react with the abundant hydroxyl groups in cellulose and peach gum respectively to form a stable covalent ether bond. This cross-linked structure can increase the mechanical strength and structural stability of the aerogel. The composite aerogel is then subjected to allyl functionalization grafting modification. By utilizing the characteristics of allyl compounds containing epoxy groups containing two active groups, the ring-opening reaction of the epoxy groups is grafted onto the composite aerogel structure, and the composite aerogel is endowed with allyl cross-linking reaction activity. Then, by the synergistic copolymerization of the allyl composite aerogel, the cross-linking agent and the monomer, a tropical crop cellulose-based superabsorbent polymer with both high water absorption and a stable three-dimensional network structure is prepared, which overcomes the defect that the structure of traditional superabsorbent materials is easily collapsed after absorbing water.

[0037] (2) The present invention uses resource-rich tropical crop fibers as raw materials, and has a simple preparation process and strong operability. The obtained tropical crop cellulose-based superabsorbent polymer superabsorbent material has excellent water absorption performance and high mechanical strength, and can be applied to the fields of agricultural and forestry soil water conservation or food preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0039] Figure 1 FT-IR images of tropical crop cellulose, tropical crop cellulose-based super absorbent polymer, and the water-absorbing polymer prepared in Comparative Example 1, wherein a is tropical crop cellulose; b is the water-absorbing polymer of Comparative Example 1; and c is the tropical crop cellulose-based super absorbent polymer of Example 1.

[0040] Figure 2 This is a SEM image of the tropical crop cellulose-based superabsorbent polymer prepared in Example 1;

[0041] Figure 3 Thermogravimetric (TG) curves of the water-absorbing polymer samples prepared in Example 1 and Comparative Example 1;

[0042] Figure 4 The water absorption performance test results of the water-absorbing polymer samples of the examples and comparative examples are as follows;

[0043] Figure 5 The water retention performance test results of the water-absorbing polymer samples of Examples and Comparative Examples;

[0044] Figure 6 The following are the compressive strength test results of the water-absorbing polymer samples of Examples and Comparative Examples. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] The embodiment of the present invention provides a method for preparing a tropical crop cellulose-based superabsorbent polymer. The method comprises: reacting tropical crop cellulose with peach gum under the action of a glycerol ether crosslinking agent to form a cellulose-peach gum composite aerogel having a covalent crosslinked structure; then, the aerogel is subjected to allyl functionalized grafting modification to obtain an allylated composite aerogel; and then, the allylated composite aerogel is subjected to a synergistic copolymerization reaction with an acrylate crosslinking agent and a monomer to prepare a tropical crop cellulose-based superabsorbent polymer.

[0051] In an embodiment of the present invention, the method for preparing a tropical crop cellulose-based super absorbent polymer comprises the following steps:

[0052] (1) Dispersing tropical crop cellulose and peach gum in water, heating in a water bath and adjusting the pH to alkaline, adding the glycerol ether cross-linking agent and stirring for reaction, and then freeze-drying the reaction product to obtain the cellulose-peach gum composite aerogel;

[0053] (2) crushing the cellulose-peach gum composite aerogel, dispersing it with a NaOH solution, adding an epoxy group-containing allyl compound, and stirring to react to obtain an allylated composite aerogel;

[0054] (3) After dispersing the allylated composite aerogel with water, heating it in a water bath and sequentially adding an initiator, a monomer, and an acrylate crosslinking agent to react to obtain a gel product. After washing and drying the gel product, the tropical crop cellulose-based superabsorbent polymer is obtained.

[0055] In step (1) of the preferred embodiment of the present invention, the tropical crop cellulose is extracted from pineapple leaf fiber and / or sisal fiber, and the specific preparation method is as follows:

[0056] The raw fibers (pineapple leaf fibers and / or sisal fibers) are cut short and then crushed into small segments with an average size of 1 mm. The crushed powder is added to a 4% by mass NaOH solution for alkali treatment, stirred at 80°C for 3 hours, then filtered and washed three times with distilled water, bleached with sodium hypochlorite, stirred at 70°C for 2 hours, filtered and washed three times, and dried at 50°C to obtain powdered tropical crop cellulose.

[0057] In step (1) of the preferred embodiment of the present invention, the mass ratio of tropical crop cellulose, peach gum and glycerol ether cross-linking agent is (1-1.8): (0.2-1): (0.02-0.2); and / or,

[0058] The glyceryl ether crosslinking agent is one or more of ethylene glycol diglycidyl ether, glycerol diglycidyl ether, 1,4-butanediol diglycidyl ether and 1,6-hexanediol diglycidyl ether.

[0059] Preferably, in step (1), the pH is adjusted to 11 with NaOH; and / or,

[0060] The stirring reaction temperature is 50°C and the time is 1-4 hours; and / or,

[0061] Freeze drying was performed by freezing the reaction product at -80°C for 24 h and then freeze drying it in a vacuum for 48 h.

[0062] In step (2) of the preferred embodiment of the present invention, the cellulose-peach gum composite aerogel is crushed to an average particle size of 2-5 mm; and / or,

[0063] The usage ratio of cellulose-peach gum composite aerogel, NaOH solution and epoxy-containing allyl compound is 2g:100mL:0.5g.

[0064] In step (2) of a preferred embodiment of the present invention, the epoxy-containing allyl compound is allyl glycidyl ether, glycidyl acrylate or glycidyl methacrylate; and / or,

[0065] The concentration of the NaOH solution was 40 wt.%.

[0066] In step (3) of the preferred embodiment of the present invention, the initiator is one or more of ammonium persulfate, potassium persulfate and sodium persulfate; and / or,

[0067] The acrylate crosslinking agent is one or more of ethylene glycol dimethacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate and 1,6-hexanediol dimethacrylate; and / or,

[0068] The monomer is acrylic acid, and during the preparation process, the acrylic acid exists in the form of an acrylic acid solution, the concentration of the acrylic acid solution is 0.125 g / mL, and the temperature is 0° C.; and / or,

[0069] The usage ratio of the allylated composite aerogel, the initiator, the acrylic acid solution and the acrylic ester crosslinking agent is 1 g: (0.025-0.05) g: 40 mL: (0.015-0.025) g.

[0070] In step (3) of the preferred embodiment of the present invention, the allylated composite aerogel obtained in step (2) is dispersed with water, an initiator is added, nitrogen is passed through, and the mixture is stirred at room temperature for 10 minutes. Then, an acrylic acid solution is added, the mixture is heated to 60° C. and stirred for 15 minutes. Then, an acrylic acid ester crosslinker is added and the mixture is stirred and reacted for 2-4 hours to obtain a gel product.

[0071] Exemplarily, the tropical crop cellulose-based super absorbent polymer in an embodiment of the present invention specifically includes the following steps:

[0072] (1) Cutting raw fibers (pineapple leaf fibers and / or sisal fibers, including but not limited to the above fibers) into short pieces with an average size of 1 mm, adding the crushed powder to a 4% by mass NaOH solution for alkali treatment, stirring at 80° C. for 3 hours, then filtering and washing with distilled water three times, then bleaching with sodium hypochlorite, stirring at 70° C. for 2 hours, filtering and washing three times, and drying at 50° C. to obtain powdered tropical crop cellulose;

[0073] (2) 1-1.8 g of the tropical crop cellulose obtained in step (1) and 0.2-1 g of peach gum were dissolved in 50 mL of water respectively. After being completely dispersed and dissolved, the two were mixed and placed in a beaker, heated and stirred in a 50° C. water bath, and the pH was adjusted to 11 with NaOH. After stirring for 30 minutes, 0.02-0.2 g of a glycerol ether crosslinking agent (one or more of ethylene glycol diglycidyl ether, glycerol diglycidyl ether, 1,4-butanediol diglycidyl ether, and 1,6-hexanediol diglycidyl ether) was added, and the reaction was stirred for 1-4 hours. The reaction product was then placed in a -80° C. ultra-low temperature refrigerator and frozen for 24 hours, and then vacuum-freeze-dried for 48 hours to obtain a cellulose-peach gum composite aerogel;

[0074] (3) The cellulose-peach gum composite aerogel obtained in step (2) was crushed into particles with an average particle size of 2-5 mm, 2 g of the crushed cellulose-peach gum composite aerogel was dispersed in 100 mL of a NaOH solution (40 wt%), and stirred in a 50° C. water bath for 30 minutes, followed by the addition of 0.5 g of an epoxy-containing allyl compound (allyl glycidyl ether, glycidyl acrylate, or glycidyl methacrylate), and the mixture was stirred and reacted for 1 hour, filtered, and dried to obtain an allylated composite aerogel;

[0075] (4) 1 g of the allylated composite aerogel obtained in step (3) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse evenly. 0.025-0.05 g of initiator (one or more of ammonium persulfate, potassium persulfate, and sodium persulfate) was added and stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of monomer (acrylic acid solution containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at 0° C. was added and heated to 60° C. and stirred for 15 minutes. 0.015-0.025 g of an acrylate crosslinker (ethylene glycol) was added. The method comprises the following steps: preparing a cellulose-based superabsorbent polymer of tropical crops by mixing with water (the mixture is stirred for 2-4 hours) with one or more of the following: 1,2-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate and 1,6-hexanediol dimethacrylate), continuing to stir and react for 2-4 hours to obtain a gel product, taking out the product and cutting it into blocks, immersing it in anhydrous ethanol for 8 hours to remove unreacted monomers, and drying it in an oven at 50°C to obtain a cellulose-based superabsorbent polymer of tropical crops.

[0076] In step (2) of the preparation process of tropical crop cellulose-based superabsorbent polymer of the present invention, taking 1,4-butanediol diglycidyl ether as a cross-linking agent as an example, a covalent cross-linking technology is used to form a cross-linked aerogel with tropical crop cellulose and peach gum. In an alkaline environment, the epoxy groups of diglycidyl ether are ring-opened to react with the abundant hydroxyl groups in cellulose and peach gum respectively to form stable covalent ether bonds. This cross-linking structure can increase the mechanical strength and structural stability of the aerogel. The cross-linking structure of the obtained cellulose-peach gum composite aerogel is schematically shown as follows:

[0077]

[0078] Wherein, R1 is the structural formula of tropical crop cellulose, and n is 100-500; R2 is the structural formula of peach gum, and m is 100-200, n is 30-50, o is 100-200, and p is 10-50; R3 is ring-opened 1,4-butanediol diglycidyl ether. When the cross-linking agent is glycerol diglycidyl ether, ethylene glycol diglycidyl ether, or 1,6-hexanediol diglycidyl ether, R3 is replaced by ring-opened glycerol diglycidyl ether, ethylene glycol diglycidyl ether, or 1,6-hexanediol diglycidyl ether.

[0079] In step (3) of the preparation process of tropical crop cellulose-based superabsorbent polymer of the present invention, the composite aerogel is subjected to allyl functional grafting modification. Taking allyl glycidyl ether as an example of the allyl compound containing epoxy group, the allyl compound containing epoxy group is grafted onto the composite aerogel structure by the ring-opening reaction of the epoxy group, and the composite aerogel is endowed with allyl cross-linking reaction activity. The structure of the obtained allylated composite aerogel is shown as follows:

[0080]

[0081] Wherein, R4 is a ring-opened allyl glycidyl ether. When the epoxy-containing allyl compound is glycidyl acrylate or glycidyl methacrylate, R4 is correspondingly replaced by a ring-opened glycidyl acrylate or glycidyl methacrylate.

[0082] In step (4) of the preparation process of the tropical crop cellulose-based super absorbent polymer of the present invention, by the synergistic copolymerization reaction of the allylated composite aerogel, the crosslinking agent and the monomer, taking 1,4-butanediol dimethacrylate as an example of the crosslinking agent, the structure of the tropical crop cellulose-based super absorbent polymer having both high water absorbency and a stable three-dimensional network structure is prepared as follows:

[0083]

[0084] in, The allylated composite aerogel long chain or polyacrylic acid long chain obtained in step (3) has the structural formula of n=200-2000; R5 is 1,4-butanediol dimethacrylate. When the crosslinking agent is ethylene glycol dimethacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, or 1,6-hexanediol dimethacrylate, R5 is replaced by ethylene glycol dimethacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, or 1,6-hexanediol dimethacrylate.

[0085] The embodiment of the present invention further provides a tropical crop cellulose-based super absorbent polymer, which is prepared according to the above preparation method.

[0086] The tropical crop cellulose-based superabsorbent polymer prepared in the embodiment of the present invention is used in the field of water conservation in agriculture and forestry, for example, as a water-retaining agent for agricultural and forestry soil or a coating preservation material.

[0087] The technical solution of the present invention is further illustrated by the following examples.

[0088] Example 1

[0089] A method for preparing a tropical crop cellulose-based superabsorbent polymer comprises the following steps:

[0090] (1) Pineapple leaf fibers are cut short and crushed into small segments with an average size of 1 mm. The crushed powder is added to a 4% by mass NaOH solution for alkali treatment, stirred at 80° C. for 3 h, then filtered and washed three times with distilled water, bleached with sodium hypochlorite, stirred at 70° C. for 2 h, filtered and washed three times with distilled water, and dried at 50° C. to obtain powdered tropical crop cellulose;

[0091] (2) 1.2 g of the tropical crop cellulose obtained in step (1) and 0.8 g of peach gum were dissolved in 50 mL of water respectively. After being completely dispersed and dissolved, the two were mixed and placed in a beaker, heated and stirred in a 50°C water bath, and the pH was adjusted to 11 with NaOH. After stirring for 30 minutes, 0.02 g of a cross-linking agent, 1,4-butanediol diglycidyl ether, was added and stirred for 2 hours. The reaction product was then placed in a -80°C ultra-low temperature refrigerator and frozen for 24 hours, and then vacuum-freeze-dried for 48 hours to obtain a cellulose-peach gum composite aerogel;

[0092] (3) The cellulose-peach gum composite aerogel obtained in step (2) was crushed into particles with an average particle size of 2-5 mm, 2 g of the crushed cellulose-peach gum composite aerogel was dispersed in 100 mL of NaOH solution (40 wt%), and stirred in a 50° C. water bath for 30 minutes, followed by the addition of 0.5 g of allyl glycidyl ether, and the reaction was continued with stirring for 1 hour. The mixture was filtered and dried to obtain an allylated composite aerogel;

[0093] (4) 1 g of the allylated composite aerogel obtained in step (3) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse uniformly. 0.025 g of initiator ammonium persulfate was added and stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of monomer (acrylic acid solution, containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at a temperature of 0° C. was added and heated to 60° C. and stirred for 15 minutes. 0.015 g of cross-linking agent ethylene glycol dimethacrylate was added and stirred for 4 hours to obtain a gel product. The product was taken out and cut into blocks, immersed in anhydrous ethanol for 8 hours to remove unreacted monomers, and placed in a 50° C. oven to dry to obtain a tropical crop cellulose-based superabsorbent polymer.

[0094] Example 2

[0095] A method for preparing a tropical crop cellulose-based superabsorbent polymer comprises the following steps:

[0096] (1) Cutting sisal fibers into short pieces and crushing them into small pieces with an average size of 1 mm, adding the crushed powder into a 4% by mass NaOH solution for alkali treatment, stirring at 80°C for 3 hours, then filtering and washing three times with distilled water, bleaching with sodium hypochlorite, stirring at 70°C for 2 hours, filtering and washing three times, and drying at 50°C to obtain powdered tropical crop cellulose;

[0097] (2) 1 g of the tropical crop cellulose obtained in step (1) and 1 g of peach gum were dissolved in 50 mL of water respectively. After being completely dispersed and dissolved, the two were mixed and placed in a beaker, heated and stirred in a 50°C water bath, and the pH was adjusted to 11 with NaOH. After stirring for 30 minutes, 0.1 g of the cross-linking agent ethylene glycol diglycidyl ether was added, and the reaction was stirred for 4 hours. The reaction product was then placed in a -80°C ultra-low temperature refrigerator and frozen for 24 hours, and then vacuum-freeze-dried for 48 hours to obtain a cellulose-peach gum composite aerogel;

[0098] (3) The cellulose-peach gum composite aerogel obtained in step (2) was crushed into particles with an average particle size of 2-5 mm, 2 g of the crushed cellulose-peach gum composite aerogel was dispersed in 100 mL of a NaOH solution (40 wt%), and stirred in a 50° C. water bath for 30 minutes. Then, 0.5 g of glycidyl methacrylate was added, and the reaction was continued with stirring for 1 hour. The mixture was filtered and dried to obtain an allylated composite aerogel;

[0099] (4) 1 g of the allylated composite aerogel obtained in step (3) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse evenly. 0.03 g of initiator potassium persulfate was added and stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of monomer (acrylic acid solution containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at a temperature of 0°C was added. The mixture was heated to 60°C and stirred for 15 minutes. 0.02 g of cross-linking agent 1,4-butanediol diacrylate was added and the mixture was stirred for 3 hours to obtain a gel-like product. The product was taken out and cut into blocks. The unreacted monomers were removed after being immersed in anhydrous ethanol for 8 hours. The product was placed in a 50°C oven to dry to obtain a tropical crop cellulose-based superabsorbent polymer.

[0100] Example 3

[0101] A method for preparing a tropical crop cellulose-based superabsorbent polymer comprises the following steps:

[0102] (1) Pineapple leaf fibers are cut short and crushed into small segments with an average size of 1 mm. The crushed powder is added to a 4% by mass NaOH solution for alkali treatment, stirred at 80° C. for 3 h, then filtered and washed three times with distilled water, bleached with sodium hypochlorite, stirred at 70° C. for 2 h, filtered and washed three times with distilled water, and dried at 50° C. to obtain powdered tropical crop cellulose;

[0103] (2) 1.5 g of the tropical crop cellulose obtained in step (1) and 0.5 g of peach gum were dissolved in 50 mL of water respectively. After being completely dispersed and dissolved, the two were mixed and placed in a beaker, heated and stirred in a 50° C. water bath, and the pH was adjusted to 11 with NaOH. After stirring for 30 minutes, 0.12 g of the cross-linking agent ethylene glycol diglycidyl ether was added, and the reaction was stirred for 2 hours. The reaction product was then placed in a -80° C. ultra-low temperature refrigerator and frozen for 24 hours, and then vacuum-freeze-dried for 48 hours to obtain a cellulose-peach gum composite aerogel;

[0104] (3) The cellulose-peach gum composite aerogel obtained in step (2) was crushed into particles with an average particle size of 2-5 mm, 2 g of the crushed cellulose-peach gum composite aerogel was dispersed in 100 mL of NaOH solution (40 wt%), and stirred in a 50° C. water bath for 30 minutes, followed by the addition of 0.5 g of glycidyl acrylate, and the reaction was continued with stirring for 1 hour. The mixture was filtered and dried to obtain an allylated composite aerogel;

[0105] (4) 1 g of the allylated composite aerogel obtained in step (3) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse evenly. 0.04 g of initiator sodium persulfate was added and stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of monomer (acrylic acid solution containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at a temperature of 0°C was added. The mixture was heated to 60°C and stirred for 15 minutes. 0.018 g of cross-linking agent 1,3-butanediol dimethacrylate was added and the mixture was stirred for 2 hours to obtain a gel product. The product was taken out and cut into blocks. The unreacted monomers were removed after being immersed in anhydrous ethanol for 8 hours. The product was then placed in an oven at 50°C to dry to obtain a tropical crop cellulose-based superabsorbent polymer.

[0106] Example 4

[0107] A method for preparing a tropical crop cellulose-based superabsorbent polymer comprises the following steps:

[0108] (1) Cutting raw sisal fiber into short pieces and crushing them into small pieces with an average size of 1 mm, adding the crushed powder into a 4% by mass NaOH solution for alkali treatment, stirring at 80°C for 3 hours, then filtering and washing three times with distilled water, bleaching with sodium hypochlorite, stirring at 70°C for 2 hours, filtering and washing three times, and drying at 50°C to obtain powdered tropical crop cellulose;

[0109] (2) 1.8 g of the tropical crop cellulose obtained in step (1) and 0.2 g of peach gum were dissolved in 50 mL of water respectively. After being completely dispersed and dissolved, the two were mixed and placed in a beaker, heated and stirred in a 50°C water bath, and the pH was adjusted to 11 with NaOH. After stirring for 30 minutes, 0.2 g of a cross-linking agent, 1,6-hexanediol diglycidyl ether, was added and stirred for 1 hour. The reaction product was then placed in a -80°C ultra-low temperature refrigerator and frozen for 24 hours, and then vacuum-freeze-dried for 48 hours to obtain a cellulose-peach gum composite aerogel;

[0110] (3) The cellulose-peach gum composite aerogel obtained in step (2) was crushed into particles with an average particle size of 2-5 mm, 2 g of the crushed cellulose-peach gum composite aerogel was dispersed in 100 mL of NaOH solution (40 wt%), and stirred in a 50° C. water bath for 30 minutes, followed by the addition of 0.5 g of allyl glycidyl ether, and the reaction was continued with stirring for 1 hour. The mixture was filtered and dried to obtain an allylated composite aerogel;

[0111] (4) 1 g of the allylated composite aerogel obtained in step (3) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse evenly. 0.05 g of initiator ammonium persulfate was added and stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of monomer (acrylic acid solution containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at a temperature of 0° C. was added and heated to 60° C. and stirred for 15 minutes. 0.025 g of cross-linking agent 1,4-butanediol dimethacrylate was added and the stirring reaction was continued for 2 hours to obtain a gel-like product. The product was taken out and cut into blocks, immersed in anhydrous ethanol for 8 hours to remove unreacted monomers, and placed in a 50° C. oven to dry to obtain a tropical crop cellulose-based superabsorbent polymer.

[0112] Comparative Example 1

[0113] The same as Example 1, except that the steps of preparing the cellulose-peach gum composite aerogel and the allylation modification are omitted, specifically:

[0114] 0.025 g of ammonium persulfate (initiator) was added to a three-necked flask containing 40 mL of distilled water, and the mixture was stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of 0°C monomer (acrylic acid solution, containing 5 g of acrylic acid by dry weight and a neutralization degree of 75%) was added. The mixture was heated to 60°C and stirred for 15 minutes. 0.015 g of ethylene glycol dimethacrylate (crosslinker) was then added, and the reaction was continued with stirring for 4 hours to obtain a gel-like product. The product was removed and cut into blocks, immersed in anhydrous ethanol for 8 hours to remove unreacted monomer, and then dried in an oven at 50°C to obtain a water-absorbing polymer.

[0115] Comparative Example 2

[0116] The commercially available agricultural and forestry soil water-retaining agent product is a copolymer of polyacrylic acid salt and polyacrylamide, in the form of transparent powder particles with a particle size of 20-100 mesh.

[0117] Comparative Example 3

[0118] The same as Example 1, except that the allylation modification step is omitted, specifically:

[0119] A method for preparing a tropical crop cellulose-based superabsorbent polymer comprises the following steps:

[0120] (1) Pineapple leaf fibers are cut short and crushed into small segments with an average size of 1 mm. The crushed powder is added to a 4% by mass NaOH solution for alkali treatment, stirred at 80° C. for 3 h, then filtered and washed three times with distilled water, bleached with sodium hypochlorite, stirred at 70° C. for 2 h, filtered and washed three times with distilled water, and dried at 50° C. to obtain powdered tropical crop cellulose;

[0121] (2) 1.2 g of the tropical crop cellulose obtained in step (1) and 0.8 g of peach gum were dissolved in 50 mL of water respectively. After being completely dispersed and dissolved, the two were mixed and placed in a beaker, heated and stirred in a 50°C water bath, and the pH was adjusted to 11 with NaOH. After stirring for 30 minutes, 0.02 g of a cross-linking agent, 1,4-butanediol diglycidyl ether, was added and stirred for 2 hours. The reaction product was then placed in a -80°C ultra-low temperature refrigerator and frozen for 24 hours, and then vacuum-freeze-dried for 48 hours to obtain a cellulose-peach gum composite aerogel;

[0122] (3) The cellulose-peach gum composite aerogel obtained in step (2) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse uniformly. 0.025 g of initiator ammonium persulfate was added, and the mixture was stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of monomer (acrylic acid solution, containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at a temperature of 0° C. was added, and the mixture was heated to 60° C. and stirred for 15 minutes. 0.015 g of cross-linking agent ethylene glycol dimethacrylate was added, and the mixture was stirred and reacted for 4 hours to obtain a gel product. The product was taken out and cut into blocks, immersed in anhydrous ethanol for 8 hours to remove unreacted monomers, and placed in a 50° C. oven to dry to obtain a tropical crop cellulose-based superabsorbent polymer.

[0123] Comparative Example 4

[0124] The same as Example 1, except that the addition of peach gum is omitted, specifically:

[0125] (1) Pineapple leaf fibers are cut short and crushed into small segments with an average size of 1 mm. The crushed powder is added to a 4% by mass NaOH solution for alkali treatment, stirred at 80° C. for 3 h, then filtered and washed three times with distilled water, bleached with sodium hypochlorite, stirred at 70° C. for 2 h, filtered and washed three times with distilled water, and dried at 50° C. to obtain powdered tropical crop cellulose;

[0126] (2) 2 g of the powdered tropical crop cellulose obtained in step (1) was dispersed in a three-necked flask containing 40 mL of distilled water and stirred for 30 minutes to disperse uniformly. 0.025 g of ammonium persulfate as an initiator was added and stirred in a water bath at room temperature under nitrogen. After 10 minutes, 40 mL of a monomer (acrylic acid solution containing 5 g of acrylic acid dry weight and a neutralization degree of 75%) at 0° C. was added. The mixture was heated to 60° C. and stirred for 15 minutes. 0.015 g of a cross-linking agent, ethylene glycol dimethacrylate, was added and stirred for 4 hours to obtain a gel-like product. The product was taken out and cut into blocks. The blocks were immersed in anhydrous ethanol for 8 hours to remove unreacted monomers and dried in an oven at 50° C. to obtain a tropical crop cellulose-based superabsorbent polymer.

[0127] Performance Testing

[0128] (1) Infrared spectroscopy (FT-IR) analysis

[0129] The FT-IR images of the tropical crop cellulose, tropical crop cellulose-based super absorbent polymer obtained in step (1) of Example 1 and the super absorbent polymer prepared in Comparative Example 1 are shown in FIG. Figure 1 , wherein a is tropical crop cellulose; b is the water-absorbing polymer of Comparative Example 1; c is the tropical crop cellulose-based super absorbent polymer of Example 1. Figure 1 It can be seen that the 1114cm -1 、1040cm -1 The characteristic peak at 3351cm is the absorption peak of -CH-O-CH, which is the characteristic absorption peak of cellulose structure. -1 Change to 3341cm -1 , which is related to the stretching vibration of -OH; compared with the polymer spectrum of comparative example 1 without cellulose-peach gum composite aerogel, 1114cm -1 、1040cm -1 The characteristic peak of cellulose at 2927 cm was retained, indicating that the cellulose aerogel-based polymer maintained the structural integrity of cellulose. -1 The peak at 1660 cm is due to -CH2. -1 The absorption peak at 1321cm is related to carboxylic acid. -1 -1040cm -1 The peak at 2507 cm is attributed to -COO-, while the peak at 2507 cm -1 The characteristic peak at 1037 cm is related to the -OH of carboxylic acid, indicating that the grafting reaction of acrylic acid has been successful. In addition, compared with the polymer spectrum of the comparative example 1 without cellulose-peach gum composite aerogel, it was found that -1 and 888cm -1New absorption peaks were observed at 40°, representing the stretching vibrations of the -CH-O-CH structure and the =COC- structure, further indicating that a grafting reaction occurred on the cellulose aerogel during the polymerization process. This indicates that the allylated composite aerogel, acrylic acid, and crosslinking agent in this embodiment of the present invention underwent a graft copolymerization reaction, forming a stable network structure.

[0130] (2) SEM analysis

[0131] The tropical crop cellulose-based super absorbent polymer prepared in Example 1 was tested using a Czech TESCAN MIRALMS field emission scanning electron microscope. The results are shown in FIG. Figure 2 It can be seen that the interior of the polymer is mostly porous structure, indicating that the cross-linked aerogel formed by tropical crop cellulose and peach gum forms a polymer network support structure, which also provides more cavity structure for improving the water absorption performance of the polymer, and the structure is not easy to collapse.

[0132] (3) Thermogravimetric analysis

[0133] In N2 atmosphere, the thermogravimetric (TG) curves of the water-absorbing polymer samples prepared in Example 1 and Comparative Example 1 were measured. The results are shown in FIG. Figure 3 It can be seen that the thermal decomposition of the samples mainly involves the following processes. The first stage is mainly the evaporation of water in the sample, resulting in a small amount of weight loss. The second stage is from 100°C to 200°C. The tropical crop cellulose-based superabsorbent polymer in Example 1 is relatively stable, but the cellulose-free superabsorbent polymer in Comparative Example 1 continues to lose weight. The third stage is from 200°C to 360°C. The cross-linked structure within the polymer undergoes fiber thermal decomposition, producing small molecules, and the weight loss reaches a maximum. The fourth stage is the slow decomposition of macromolecular residues, with relatively slow weight loss. The pyrolysis temperature of the tropical crop cellulose-based superabsorbent polymer in Example 1 has a maximum weight loss rate of 260°C; the pyrolysis temperature of the superabsorbent polymer in Comparative Example 1 has a maximum weight loss rate of 248°C. Furthermore, the mass loss rate of the sample in Comparative Example 1 is greater than that of the sample in Example 1. This shows that the tropical crop cellulose-based superabsorbent polymer in the present invention has good stability, and the internal three-dimensional network structure can improve the thermal stability of the superabsorbent polymer to a certain extent.

[0134] (4) Water absorption performance test

[0135] The test samples were samples prepared in the examples and comparative examples. The samples were crushed, 0.2 g of the sample was placed in a 500 mL beaker, 400 mL of deionized water was added, and the product was soaked until it was saturated with water. The sample after water absorption was taken out, and the sample particles after water absorption and swelling were filtered with a 100 mesh filter cloth. The sample particles were suspended for 20 minutes to remove excess water, and the weight of the product after water absorption was weighed; the ratio of the weight of the product after water absorption to the mass of the sample before water absorption was the water absorption rate of the sample.

[0136] The water absorption performance test results of the samples of the embodiment and comparative example are shown in Figure 4 ,Depend on Figure 4 It can be seen that the water absorption rate of the example sample increases rapidly within 1 hour, reaches a certain value after 4 hours, and then tends to saturation. The maximum water absorption rate is rounded to 828 g / g; the water absorption rate of the comparative example sample basically reaches water absorption saturation after 6-8 hours, and the water absorption rate is less than that of the example; This shows that the example sample has good water absorption performance, and the example sample has a cellulose composite aerogel structure and a three-dimensional network porous structure, which helps to improve its water absorption performance.

[0137] (5) Water retention performance test

[0138] After saturation with water, the samples of the embodiment and comparative example were placed in a weighing bottle and placed at room temperature. The remaining mass was measured at regular intervals. The percentage difference between the remaining amount of water absorbed at different times and the mass of the saturated water amount was used as an indicator of water retention performance. The total test time was 60 hours.

[0139] The water retention performance test results of the samples of the embodiment and comparative example are shown in Figure 5 ,Depend on Figure 5 As can be seen, after absorbing water, the mass of the samples in the examples and comparative examples decreases over time, while the water retention rate decreases. The water loss rate is relatively stable, and the water retention rate versus time curve at room temperature approaches a linear relationship. The water retention rate of the comparative example drops to 50% after 24 hours, while the water retention rate of the examples can still be maintained at 60% for 24 hours. Compared with the comparative example, the samples in the examples all have better water retention performance, which is related to their three-dimensional network porous structure.

[0140] (6) Repeated water absorption performance test

[0141] The samples of the embodiment and the comparative example were placed in deionized water to reach the maximum water absorption saturation value, and the water absorption rate was measured. The saturated water absorption samples were then placed in a blast oven and dried at 80°C until the moisture was completely dried out. The experiment was repeated 6 times. The test results are shown in Table 1.

[0142] Table 1 Repeated water absorption performance test results of Examples and Comparative Examples

[0143]

[0144] As shown in Table 1, the water absorption rate of the example samples decreased with the number of repeated water absorptions. The water absorption rate of the samples during the second water absorption cycle remained above 70% of the initial rate. After three repeated water absorptions, the water absorption rate of the water-retaining agent decreased to 40% of the initial rate, and after five repeated water absorptions, the water absorption rate stabilized. The water absorption rate of the comparative example samples also decreased significantly. Because the example samples have a three-dimensional porous network structure, the molecular chains shrink and curl after the water molecules are partially expelled. Repeated water absorption allows the shrinking molecular chains to unfold more easily, creating more pores and exhibiting better repeated water absorption performance.

[0145] (7) Compression strength test

[0146] Dried samples (5 mm in length, 5 mm in width, and 5 mm in height) from the Examples or Comparative Examples were immersed in deionized water until saturated. Excess water was removed with absorbent paper. The samples were then placed in the compression fixture of a universal testing machine. Uniform pressure was applied to the samples at a rate of 5 mm / min until the sample height was reduced by 80%. The compressive strength was recorded. Three sets of measurements were performed for each sample, and the results were averaged.

[0147] The mechanical analysis of the samples of the embodiment and comparative example can reveal the structural changes of the material after absorbing water, ensuring that it can maintain sufficient strength and stability in practical applications. Figure 6 As shown, it can be seen that the compressive strength of the example samples is 0.058-0.065 MPa, and the compressive strength of the comparative samples is 0.022-0.036 MPa. This is because the example samples have a cellulose-peach gum composite aerogel structure and a three-dimensional network structure, and tropical crop cellulose, as a natural polysaccharide fiber material, has significant mechanical support and reinforcement effects; and the long molecular chains and carboxyl groups of the highly absorbent polymer increase the crosslinking density of the polymer and enhance the stability of the network structure.

[0148] (8) Coating preservation test

[0149] The powdered superabsorbent polymer prepared in Example 1 was formulated into a uniform hydrogel aqueous solution (coating agent) with concentrations of 2g / L, 5g / L, 8g / L, and 10g / L. Freshly purchased lychees were washed with clean water and then air-dried. The lychees were immersed in the above-mentioned hydrogel aqueous solution for 20 seconds. At the same time, the lychees were soaked in distilled water (coating agent concentration was 0g / L) as a blank control. Three groups of experiments were performed in parallel. After the coated lychees were placed in a ventilated place to dry, they were placed in a ventilated and dark place indoors for 4 days. The various physical and chemical indicators of the lychees were measured. At the same time, fresh lychees were taken to measure the physical and chemical indicators as a fresh control group. The weight loss rate was determined by weighing; the Vc content was determined according to the "2,6-dichloroindophenol sodium salt titration method" in GB / T6195-1986; the soluble solids content was determined according to the agricultural standard NY / T2637-2014, the determination method for the soluble solids content of fruits and vegetables. The test results are shown in Table 2.

[0150] Table 2 Results of fresh-keeping experiments on powdered superabsorbent polymer coatings at different concentrations

[0151]

[0152] As shown in Table 2, using the superabsorbent polymer prepared in Example 1 of the present invention as a coating agent can achieve freshness preservation of lychees. The superabsorbent polymer coating agent at different mass concentrations consistently reduced the lychee weight loss rate while substantially preserving its flavor. When the coating agent concentration was 5 g / L, all physical and chemical indicators of the lychees reached their optimal values. The lychee weight loss rate decreased with increasing coating agent concentration. However, when the concentration exceeded 5 g / L, further increasing the coating agent dosage slowed the downward trend in the lychee weight loss rate. This is primarily due to the high carboxyl hydrophilic groups inherent in the superabsorbent polymer. Higher coating agent concentrations resulted in greater water absorption capacity, exacerbating water loss within the fruit, resulting in no significant decrease in the lychee weight loss rate. When the concentration of the coating agent is too low, the film layer covering the surface of the litchi is too thin and cannot play a protective role; when the concentration of the coating agent is too high, the film layer on the surface of the litchi is too thick, which may hinder the entry of oxygen, causing anaerobic respiration inside the litchi, causing internal fermentation, corruption and deterioration, thereby aggravating the rot and deterioration of the fruit.

[0153] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a tropical crop cellulose-based superabsorbent polymer, characterized in that: Tropical crop cellulose and peach gum are treated with a glycerol ether cross-linking agent to form a cellulose-peach gum composite aerogel with a covalent cross-linking structure; the cellulose-peach gum composite aerogel is subjected to allyl functional grafting modification to obtain an allylated composite aerogel; the allylated composite aerogel is then subjected to a synergistic copolymerization reaction with an acrylate cross-linking agent and a monomer to prepare the tropical crop cellulose-based superabsorbent polymer.

2. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 1, characterized in that: The following steps are involved: (1) Dispersing tropical crop cellulose and peach gum in water, heating in a water bath and adjusting the pH to alkaline, adding the glycerol ether cross-linking agent and stirring for reaction, and then freeze-drying the reaction product to obtain the cellulose-peach gum composite aerogel; (2) crushing the cellulose-peach gum composite aerogel, dispersing it with a NaOH solution, adding an epoxy group-containing allyl compound, and stirring to react to obtain an allylated composite aerogel; (3) After dispersing the allylated composite aerogel with water, heating it in a water bath and sequentially adding an initiator, a monomer solution, and an acrylate crosslinking agent to react to obtain a gel product. After washing and drying the gel product, the tropical crop cellulose-based superabsorbent polymer is obtained.

3. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 2, characterized in that: In step (1), the mass ratio of the tropical crop cellulose, peach gum and glycerol ether cross-linking agent is (1-1.8): (0.2-1): (0.02-0.2); and / or, The glyceryl ether cross-linking agent is selected from one or more of ethylene glycol diglycidyl ether, glycerol diglycidyl ether, 1,4-butanediol diglycidyl ether and 1,6-hexanediol diglycidyl ether.

4. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 2, characterized in that: In step (1), adjusting the pH to 11 with NaOH; and / or, The stirring reaction is carried out at a temperature of 50° C. and for a period of 1-4 hours.

5. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 2, characterized in that: In step (2), the usage ratio of the cellulose-peach gum composite aerogel, the NaOH solution and the epoxy-containing allyl compound is 2 g:100 mL:0.5 g.

6. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 2, characterized in that: In step (2), the epoxy-containing allyl compound is selected from allyl glycidyl ether, glycidyl acrylate or glycidyl methacrylate.

7. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 2, characterized in that: In step (3), the initiator is selected from one or more of ammonium persulfate, potassium persulfate and sodium persulfate; and / or, The acrylate crosslinking agent is selected from one or more of ethylene glycol dimethacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate and 1,6-hexanediol dimethacrylate; and / or, The monomer solution is an acrylic acid solution; and / or, The usage ratio of the allylated composite aerogel, the initiator, the monomer solution and the acrylate crosslinking agent is 1 g: (0.025-0.05) g: 40 mL: (0.015-0.025) g.

8. The method for preparing a tropical crop cellulose-based super absorbent polymer according to claim 2, characterized in that: The specific steps of step (3) are as follows: after dispersing the allylated composite aerogel with water, adding an initiator and passing nitrogen, stirring at room temperature for 10 minutes, then adding the monomer solution, heating to 60°C and stirring, reacting for 15 minutes, then adding the acrylic crosslinking agent and continuing to stir, and reacting for 2-4 hours to obtain a gel product.

9. A tropical crop cellulose-based super absorbent polymer, characterized in that: The polymer is prepared according to the method for preparing the tropical crop cellulose-based super absorbent polymer according to any one of claims 1 to 8.

10. Use of the tropical crop cellulose-based super absorbent polymer according to claim 9 in the preparation of agricultural and forestry water-retaining materials or food preservation materials.

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