Core-shell structure water retention type binder and preparation method thereof

Abstract

The invention relates to the technical field of water-retaining binders, in particular to a water-retaining binder with a core-shell structure and a preparation method of the water-retaining binder. An inner-layer core structure and an outer-layer shell structure are combined through chemical bonding and physical effects, the core structure is composed of marine polysaccharide, the shell structure is composed of anionic polyacrylamide, and the marine polysaccharide is derived from undaria pinnatifida or kelp. Due to the unique core-shell structure, the water absorption and retention performance is excellent; good ecological adaptability and environmental friendliness are achieved; the fertilizer can be used for agriculture and forestry water retention, soil water content improvement, vegetation survival rate increase and plant root growth promotion.

Description

Technical Field

[0001] This invention relates to the field of water-retaining adhesives, specifically to a core-shell structure water-retaining adhesive and its preparation method. Background Technology

[0002] Traditional water-retaining agents, such as synthetic superabsorbent polymers (SAPs), while possessing water absorption and retention capabilities, generally suffer from drawbacks such as high production costs, poor environmental compatibility, non-biodegradability, insufficient salt tolerance, and limited functionality. They also easily cause environmental pollution and are ineffective in saline-alkali areas. Water-retaining agents based on natural materials offer improvements in environmental friendliness and cost, but their preparation processes are complex, and they lack sufficient salt tolerance and repeated water absorption capacity. Furthermore, large-scale production processes, such as electron beam irradiation, can damage equipment. Therefore, there is an urgent need to develop novel, highly efficient, environmentally friendly, biodegradable, salt-tolerant, and process-simplified agricultural and forestry water-retaining binders to provide innovative solutions for sustainable agriculture.

[0003] Chinese invention patent application CN117024660A discloses a water-retaining agent, its preparation method, and its application. The raw materials for preparation include ethylenediamine, guar gum, acrylic acid, ammonium persulfate, and N. N'-methylenebisacrylamide and sodium hydroxide. This invention's water-retaining agent can solve the problem of material degradation. However, the technology still has limitations: First, it has not optimized salt tolerance for saline-alkali environments and lacks water absorption data in saline systems such as sodium chloride solution, making it difficult to meet the water retention needs of complex environments such as deserts and saline-alkali lands; second, it uses graft copolymerization, resulting in limited synergy between the performance of the natural polymer and the synthetic component; third, its function focuses on water retention and degradation, without addressing the direct promotion of plant growth, thus lacking specificity for application scenarios. Summary of the Invention

[0004] The first aspect of this invention provides a core-shell structured water-retaining adhesive, comprising an inner core structure and an outer shell structure bonded together by chemical bonding and physical action. The core structure is composed of marine polysaccharides, and the shell structure is composed of anionic polyacrylamide. The marine polysaccharides are derived from wakame seaweed. (Undaria pinnatifida) or seaweed (Laminaria japonica) .

[0005] The raw materials for preparing the anionic polyacrylamide include acrylamide, acrylate, and initiator.

[0006] The second aspect of the present application provides a preparation method of a core-shell structure water-retention type binder, comprising the following steps: taking Undaria pinnatifida or Laminaria first for pretreatment, then sequentially performing water extraction, concentration purification, and surface activation to obtain an activated marine polysaccharide solution; uniformly mixing the activated marine polysaccharide solution with acrylamide and an acrylate salt to obtain a mixed solution, adding an initiator dropwise in the mixed solution to perform a polymerization reaction, and after the reaction is completed, performing post-treatment to obtain the core-shell structure water-retention type binder.

[0007] The pretreatment comprises the following steps: cleaning the Undaria pinnatifida, removing surface impurities and salt, and shearing the Undaria pinnatifida into small pieces with a length of about 1-2 cm.

[0008] The weight ratio of the Undaria pinnatifida or Laminaria to water used in the water extraction is 1: (10-25).

[0009] Optionally, the weight ratio of the Undaria pinnatifida or Laminaria to water used in the water extraction is 1: (15-25).

[0010] The water extraction is performed at a temperature of 60-90°C for 1-3 h.

[0011] The water extraction is performed at a temperature of 85-90°C for 1-3 h.

[0012] The concentration purification comprises the following steps: first performing filtration, and then performing concentration under reduced pressure to obtain a marine polysaccharide solution, wherein the content of marine polysaccharide in the marine polysaccharide solution is 0.1-2 wt%.

[0013] Optionally, the content of marine polysaccharide in the marine polysaccharide solution is 0.5-2 wt%.

[0014] The surface activation comprises the following steps: heating the marine polysaccharide solution to 50-90°C, and dropwise adding an activator based on 0.02-0.1 wt% of the dry weight of marine polysaccharide in the marine polysaccharide solution.

[0015] Optionally, the surface activation comprises the following steps: heating the marine polysaccharide solution to 50-70°C, and dropwise adding an activator based on 0.05-0.1 wt% of the dry weight of marine polysaccharide in the marine polysaccharide solution.

[0016] The activator comprises at least one of ammonium persulfate, dilute sulfuric acid, dilute hydrochloric acid, sodium hydroxide, sodium persulfate, and hydrogen peroxide.

[0017] The weight ratio of marine polysaccharide to acrylamide in the mixed solution is 1: (20-60).

[0018] Optionally, the weight ratio of marine polysaccharide to acrylamide in the mixed solution is 1: (30-50).

[0019] The weight ratio of the acrylic acid salt and the acrylamide in the mixed solution is 1: (80-120).

[0020] Optionally, the weight ratio of the acrylic acid salt and the acrylamide in the mixed solution is 1: (90-110).

[0021] The dropping time is 0.1-0.3h.

[0022] Optionally, the dropping time is 0.1-0.2h.

[0023] The polymerization time is 6-8h, and the temperature is 60-90℃.

[0024] Optionally, the polymerization time is 7-8h, and the temperature is 60-80℃.

[0025] The post-treatment comprises cooling and filtering, pH value adjustment and freeze-drying in sequence.

[0026] The prepared binder has the activated marine polysaccharide as a core in the polymerization process, and a large number of active sites are provided on the surface of the core, so that the in-situ polymerization and cross-linking reaction of the acrylamide and potassium acrylate monomers occur around the core. By slow dropping of the initiator, the monomers are ensured to be gradually and uniformly polymerized on the surface of the core, so that the core-shell structure polymer with a clear layered interface is accurately constructed under the synergistic action of chemical bonding and physical entanglement, and the molecular weight, water absorption ratio, salt resistance and repeated water absorption ratio are effectively improved.

[0027] Advantages 1. The natural marine polysaccharide (wakame or kelp) is creatively used as a core, and the anionic polyacrylamide formed by copolymerization of acrylamide and potassium acrylate is used as a shell layer, so that a new core-shell structure water-retention binder is constructed, and the molecular weight, water absorption ratio, salt resistance and repeated water absorption ratio are effectively improved.

[0028] 2. The water absorption ratio of the binder in a 0.9wt% sodium chloride solution can reach ≥30 times, and the repeated water absorption ratio is as high as 70% or more, so that the binder can be used for water retention in harsh environments such as saline-alkali soil.

[0029] 3. The specific water extraction and activation parameter limitation can further improve the molecular weight (>40,000), the water absorption ratio (>300 times), the salt resistance (>30 times) and the repeated water absorption ratio (>70%).

[0030] 4. The binder has a hydrolysis degree of >20%, which is helpful to improve the soil water retention and binding capacity; the pH value is about 6.5, which is close to neutral, and is beneficial to the growth of plant roots; the water content is as low as 1.5-2.5%, which is convenient for storage, transportation and application, and effectively delays the evaporation of soil water.

[0031] 5. The present application not only realizes non-toxic residues and conforms to the green environmental protection concept by introducing natural marine polysaccharides, but also has good biodegradability and effectively reduces the long-term burden on the environment.

[0032] 6. The present application realizes effective construction of the core-shell structure by optimizing the extraction conditions of marine polysaccharides and the copolymerization process of acrylamide and potassium acrylate, and ensures the stability and high performance of the product. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The infrared spectrum of the adhesive prepared in Example 1.

[0034] Figure 2 The infrared spectrum of the adhesive prepared in Example 1. 1 H-NMR spectrum. DETAILED DESCRIPTION

[0035] Example 1 A core-shell structure water-retaining adhesive is combined by chemical bonding and physical action of an inner core structure and an outer shell structure, the core structure is composed of marine polysaccharides, and the shell structure is composed of anionic polyacrylamide, and the marine polysaccharides are derived from Undaria pinnatifida (Undaria pinnatifida) .

[0036] The raw materials for preparing the anionic polyacrylamide are acrylamide, potassium acrylate and an initiator (ammonium persulfate).

[0037] A preparation method of a core-shell structure water-retaining adhesive is as follows: S1: Extraction and surface activation of marine polysaccharides 1. Raw material treatment: select fresh Undaria pinnatifida, clean, remove surface impurities and salt, and cut into small pieces of about 1-2 cm.

[0038] 2. Water extraction: put 500 g of cut Undaria pinnatifida into 10 kg of deionized water (solid-liquid ratio 1:20), and extract at 85°C for 2h.

[0039] 3. Concentration and purification: the extract is filtered through a 200 mesh stainless steel screen to remove undissolved solid residues. The filtered extract is concentrated to 0.5% (w / v) marine polysaccharide solution by rotary evaporator under reduced pressure for standby.

[0040] 4. Surface activation: The 0.5% (w / v) marine polysaccharide solution prepared above was heated to 60°C, and 0.05% (w / w, based on the dry weight of the polysaccharide) aqueous ammonium persulfate solution was slowly added dropwise, with continuous stirring for 30 min. Subsequently, the system was cooled to room temperature, and the pH value was adjusted to neutral, obtaining the activated marine polysaccharide solution.

[0041] S2: Preparation of core-shell structure water-retention type binder 1. Preparation of reaction system: 200 g of acrylamide and 2 g of potassium acrylate were added to 1 L of the 0.5% (w / v) activated marine polysaccharide solution prepared above. The system was uniformly mixed under magnetic stirring for 30 min to ensure that the acrylamide and potassium acrylate were fully dissolved.

[0042] 2. Addition of initiator: Nitrogen was continuously introduced for 20 min through a nitrogen protection system to completely remove oxygen from the system; 2 g of ammonium persulfate was weighed and dissolved in 50 mL of deionized water. The initiator solution was added dropwise to the above mixed system at a slow and constant rate through a constant-pressure dropping funnel, and the dropping time was 10 min.

[0043] 3. Formation of core-shell structure and control of reaction conditions: The reaction system was heated to 70°C by water bath heating and stirring to maintain a constant temperature, and the reaction time was set to 6 h.

[0044] S3: Post-treatment 1. Cooling and filtration: After the reaction was completed, the system was naturally cooled to room temperature. The un-polymerized condensed particles and other impurities were removed by filtration through a 100-mesh stainless steel screen.

[0045] 2. pH adjustment: The pH value of the reaction solution was accurately adjusted to 6.5 using 0.1 M dilute acetic acid.

[0046] 3. Freeze-drying: The pH-adjusted solution was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for about 24 h; after freeze-drying was completed, the white crystalline powder obtained was collected.

[0047] Example 2 The specific implementation is the same as in Example 1; the difference is that the amount of acrylamide used in Example 2 is 350 g.

[0048] Example 3 The specific implementation is the same as in Example 1; the difference is that the amount of acrylamide used in Example 3 is 150 g, and the reaction system is heated to 90°C.

[0049] Example 4 The specific implementation is the same as example 1; the difference is that the amount of acrylamide used in example 4 is 250 g; initiator: 1 g of ammonium persulfate; dropwise time is 20 min, and reaction time is set to 8 h.

[0050] Example 5 The specific implementation is the same as example 1; the difference is that in example 5, the Undaria pinnatifida is replaced by Laminaria japonica (Laminaria japonica) .

[0051] Example 6 The specific implementation is the same as example 1; the difference is that in example 6, initiator: 1.5 g of ammonium persulfate; reaction temperature is 60°C, and reaction time is set to 7 h.

[0052] Comparative example 1 The specific implementation is the same as example 1; the difference is that in comparative example 1, the Undaria pinnatifida is replaced by Laminaria japonica (Sargassum spp.) .

[0053] Comparative example 2 The specific implementation is the same as example 1; the difference is that in comparative example 2, the solid-liquid ratio is adjusted to 1:30.

[0054] Comparative example 3 The specific implementation is the same as example 1; the difference is that in comparative example 3, the marine polysaccharide is not subjected to a surface activation step after extraction.

[0055] Performance test method 1. The adhesives prepared in the examples and comparative examples are subjected to the following performance tests, and the test data are shown in Table 1. Moisture content: oven drying method; molecular weight determination: Ubbelohde viscosity method; ash content: high-temperature calcination method (800°C, 4 h); degree of hydrolysis: titration method; water absorption ratio (distilled water): weighing method; water absorption ratio (salt water, 0.9wt% NaCl): weighing method; repeated water absorption ratio (5 times): cyclic weighing method.

[0056] 2. The adhesive prepared in example 1 is subjected to infrared spectrum analysis, 1 H-NMR spectrum analysis, as Figure 1 shown, 3421 cm -1 corresponding to N-H amide; 1668 cm -1 , 1557 cm -1 corresponding to C=O amide, respectively; 1453 cm -1 , 1404 cm -1 corresponding to CH2, CH3, respectively. As Figure 2As shown, 4.70 ppm corresponds to N-H amide; 2.14 ppm corresponds to CH2-C=0 amide; 1.55 ppm corresponds to CH2-R.

[0057] Performance test data Table 1

[0058] As can be seen from Table 1, Comparative Example 1 and Example 1 are compared: the molecular weight is reduced to 38000, the water absorption ratio is reduced to 80 times, the salt resistance is reduced to 20 times, and the repeated water absorption ratio is reduced to 55%. The active site of brown algae polysaccharide is less, resulting in low grafting efficiency and significant performance decline; Comparative Example 2 and Example 1 are compared: the molecular weight is reduced to 40000, the water absorption ratio is reduced to 85 times, the salt resistance is reduced to 22 times, and the repeated water absorption ratio is reduced to 60%. Too high solid-liquid ratio leads to low polysaccharide concentration, insufficient active site, and insufficient polymerization; Comparative Example 3 and Example 1 are compared: the molecular weight is reduced to 30000, the water absorption ratio is reduced to 60 times, the salt resistance is reduced to 15 times, and the repeated water absorption ratio is reduced to 45%. No activation leads to insufficient active site and incomplete shell layer, and the water absorption and water retention capacity are greatly reduced.

Claims

1. A core-shell structured water-retaining adhesive, characterized in that, It consists of an inner core structure and an outer shell structure bonded together by chemical bonding and physical action. The core structure is composed of marine polysaccharides, and the shell structure is composed of anionic polyacrylamide. The marine polysaccharides are derived from wakame or kelp.

2. The core-shell structure water-retaining adhesive according to claim 1, characterized in that, The raw materials for preparing the anionic polyacrylamide include acrylamide, acrylate, and initiator.

3. A method for preparing a core-shell structure water-retaining adhesive according to claim 2, characterized in that, Includes the following steps: Pre-treat wakame or kelp, then sequentially extract with water, concentrate and purify, and surface activate to obtain an activated marine polysaccharide solution; The activated marine polysaccharide solution was mixed evenly with acrylamide and acrylate to obtain a mixture. An initiator was added dropwise to the mixture to carry out a polymerization reaction. After the reaction was completed, a core-shell structure water-retaining adhesive was obtained through post-treatment.

4. The preparation method of the core-shell structure water-retaining adhesive according to claim 3, characterized in that, The weight ratio of wakame or kelp to water used in the water extraction is 1:(10-25).

5. The preparation method of the core-shell structure water-retaining adhesive according to claim 4, characterized in that, The weight ratio of wakame or kelp to water used in the water extraction is 1:(15-25).

6. The method for preparing the core-shell structure water-retaining adhesive according to claim 5, characterized in that, The concentration and purification process includes the following steps: first, filtration, then vacuum concentration to obtain a marine polysaccharide solution, wherein the content of marine polysaccharides in the marine polysaccharide solution is 0.1-2 wt%.

7. The method for preparing the core-shell structure water-retaining adhesive according to claim 6, characterized in that, The marine polysaccharide solution contains 0.5-2 wt% marine polysaccharides.

8. The method for preparing the core-shell structure water-retaining adhesive according to claim 7, characterized in that, The surface activation includes the following steps: heating the marine polysaccharide solution to 50-90°C, and adding an activator based on 0.02-0.1 wt% of the dry weight of the marine polysaccharide in the marine polysaccharide solution.

9. The method for preparing the core-shell structure water-retaining adhesive according to claim 8, characterized in that, The surface activation includes the following steps: heating the marine polysaccharide solution to 50-70°C, and adding an activator based on 0.05-0.1 wt% of the dry weight of the marine polysaccharide in the marine polysaccharide solution.

10. The method for preparing the core-shell structure water-retaining adhesive according to claim 3 or 9, characterized in that, The weight ratio of marine polysaccharide to acrylamide in the mixture is 1:(20-60).

11. The method for preparing the core-shell structure water-retaining adhesive according to claim 10, characterized in that, The weight ratio of marine polysaccharide to acrylamide in the mixture is 1:(30-50).

12. The method for preparing the core-shell structure water-retaining adhesive according to claim 10, characterized in that, The weight ratio of acrylate to acrylamide in the mixture is 1:(80-120).

13. The method for preparing the core-shell structure water-retaining adhesive according to claim 3, characterized in that, The dripping time is 0.1-0.3 hours.

14. The method for preparing the core-shell structure water-retaining adhesive according to claim 3, characterized in that, The polymerization reaction takes 6-8 hours and is carried out at a temperature of 60-90°C.

15. The method for preparing the core-shell structure water-retaining adhesive according to claim 14, characterized in that, The polymerization reaction takes 7-8 hours and is carried out at a temperature of 60-80℃.

16. The method for preparing the core-shell structure water-retaining adhesive according to claim 7, characterized in that, The surface activation includes the following steps: heating the marine polysaccharide solution to 50-90°C, and adding an activator based on 0.02-0.1 wt% of the dry weight of the marine polysaccharide in the marine polysaccharide solution.

17. The method for preparing the core-shell structure water-retaining adhesive according to claim 8, characterized in that, The surface activation includes the following steps: heating the marine polysaccharide solution to 50-70°C, and adding an activator based on 0.05-0.1 wt% of the dry weight of the marine polysaccharide in the marine polysaccharide solution.

18. The method for preparing the core-shell structure water-retaining adhesive according to claim 3, characterized in that, The pretreatment includes: cleaning the wakame or kelp, removing surface impurities and salt, and cutting it into small pieces of about 1-2 cm.

19. The method for preparing the core-shell structure water-retaining adhesive according to claim 3, characterized in that, The post-processing includes cooling and filtration, pH adjustment, and freeze drying.

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