Preparation method and application of degradable seedling pot coating material

Abstract

The application provides a preparation method and application of a degradable seedling pot coating, the coating material is prepared by using lignin, soybean protein isolate hydrolysate, degradable epoxy crosslinking agent and rheological modifier to react in water phase and then being treated by ultrasonic treatment; the material uses lignin as waterproof, reinforcing and mold-proof active substance, uses soybean protein isolate as film forming agent, and uses degradable epoxy compound as crosslinking agent to form a polymerization system, raw materials of the material are widely sourced, the material is biodegradable, harmless to the environment and crops when being applied to plant fiber seedling pots, and can effectively improve structural strength and water retention of the seedling pots under dry / wet conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and particularly relates to a preparation method and application of a degradable seedling pot coating material. BACKGROUND

[0002] Seedling pot seedling is an effective measure to ensure early maturity and high yield of crops. The currently widely used seedling pots are mainly plastic pots made of polyethylene, polyvinyl chloride, etc., and are mostly disposable products. After being discarded, they are difficult to degrade, increasing agricultural carbon emissions and environmental risks. In addition, the plastic pots have poor air permeability and are prone to root lodging. During the transplanting process, the seedling clumps need to be taken out of the pots, which can easily cause root damage and affect the survival rate.

[0003] Natural plant fibers are typical sustainable materials, which have the characteristics of light weight, biodegradability, and biosafety, and are considered as an ideal substitute for disposable agricultural plastics. Using natural plant fiber materials to replace plastics to prepare degradable seedling pots can not only effectively alleviate the environmental pollution of agricultural plastics, but also can be used as fertilizer after natural degradation of the discarded products, thereby increasing soil organic matter and improving soil fertility level. However, the inherent hydrophilic properties and porous structure of plant fiber materials result in poor water resistance and insufficient wet strength of the seedling pots. During the seedling process, the strength of the pot body is significantly reduced due to water absorption / hydration, which is difficult to meet the structural strength requirements during use. At the same time, the plant fiber seedling pots are prone to water loss and have poor water retention, and the water use efficiency during the seedling process is not high, which also restricts the practical application of the seedling pots.

[0004] Using coating technology to decorate the surface of the plant fiber seedling pots is an effective way to solve the problems of low wet strength and poor water retention of the seedling pots. However, the water-resistant coatings currently used for plant fiber products are mainly polyolefins and their derivatives (PP, PE, PS, etc.), fluorocarbon compounds, and wax emulsions. These materials have stable C-C bonds in their structure and are difficult to biodegrade in the natural environment. US Patent US 11051460 B2 discloses a degradable coating technology for improving the water resistance and mechanical properties of plant fiber seedling pots. Polyvinyl alcohol (PVA) and polyvinyl acetate (PVAc) are used as degradable polymer emulsions for impregnating treatment of the seedling pots. However, these emulsions have high cost and poor interfacial compatibility with plant fiber substrates, which limits the application of the coating material. European Patent EP 4039375 A1 discloses a bio-based polymer coating for degradable seedling pots. Polylactic acid (PLA) and ethyl acetate (EtOAc) are dissolved in dichloromethane and other organic solvents to form a 0.2-10% solution for surface coating of the degradable seedling pots. However, the organic solvents used in this coating have high toxicity and cause serious pollution of organic volatile compounds (VOCs). SUMMARY

[0005] To address the aforementioned problems, this invention provides a lignin-based biodegradable coating material to improve the wet strength and water retention of plant fiber products. This material is prepared using a copolymer crosslinking method, exhibits high interfacial compatibility with plant fiber substrates, has abundant raw material sources, is completely degradable, has low cost, and is easier to apply in industrial production.

[0006] Specifically, this application is implemented through the following technical solution:

[0007] First, this application provides a method for preparing a biodegradable seedling pot coating material, which is prepared by the following method:

[0008] Step (1): Disperse soy protein isolate and biodegradable epoxy crosslinking agent evenly in water at a mass ratio of 1:(0.25~0.58), adjust the pH of the dispersion to 9.0 with an alkaline regulator, and then stir the reaction at 85~95℃ for 30~60min to obtain the reaction product;

[0009] Step (2): Add enzymatically hydrolyzed lignin to the reaction product obtained in step (1), adjust the pH of the reaction system to 9.3~9.6 with an alkaline regulator, stir thoroughly to completely dissolve the lignin, and then conduct an open reaction at a temperature of 45~60℃ for 1~4 h. After cooling to room temperature, add an appropriate amount of rheology modifier, stir evenly, and then sonicate for a period of time to obtain a brown biodegradable coating material with a pH of 8.6~9.3, a viscosity ≤2000 mPa·s, and a solid content of 6.59~10.50%.

[0010] The biodegradable epoxy crosslinking agent in step (1) above is one of polyethylene glycol diglycidyl ether (PEGDGE) and epoxidized soybean oil (ESO), preferably PEGDGE.

[0011] In step (1) above, the mass ratio of soy protein isolate to water is 1:19~25, and the mass ratio of soy protein isolate to lignin is 100:40~60. "Soy protein isolate" is a conventional raw material, and its preparation method is disclosed in the literature "Influence of heat treatment and drying method on the thermal aggregation behavior and gel properties of soy protein isolate during preparation" (Tan Wenhao et al., Modern Food Science and Technology, 2024).

[0012] The alkaline regulator in steps (1) and (2) above is preferably an easily volatile ammonia solution (preferably with a mass concentration of 25-28%) to ensure that there is no residue after the coating dries.

[0013] The lignin mentioned above is enzymatically hydrolyzed lignin with high reactivity, wide availability, and close resemblance to natural lignin. "Enzymatically hydrolyzed lignin" is a conventional raw material, as its preparation method is disclosed in the literature "Isolation and Structural Study of Enzymatically Hydrolyzed Lignin" (Liu Xiaoling et al., Cellulose Science and Technology, 2007).

[0014] In step (2) above, the rheology modifier is preferably montmorillonite or attapulgite, and the mass ratio of the added rheology modifier to soy protein isolate is (0.5~5):100.

[0015] The preferred ultrasonic treatment conditions for step (2) above are ultrasonic power of 600~1000w and ultrasonic time of 5~10min.

[0016] Secondly, this application provides the application of the above-mentioned biodegradable coating material in the preparation of plant fiber seedling pots, that is, the plant fiber seedling pots are coated on the surface by spraying, dipping or other methods, and the material is cured into a biodegradable coating.

[0017] In this application, the plant fiber seedling pot is a conventional seedling pot in the field, which is a product obtained by pulping, sucking (or injecting, scooping), molding, shaping and drying of raw materials such as pulp and straw fiber.

[0018] This application uses lignin as a waterproof, reinforcing, and mildew-resistant active substance, soy protein isolate as a film-forming agent, and a biodegradable epoxy compound as a crosslinking agent to form a polymer system, constructing a biodegradable coating material for surface treatment of plant fiber seedling pots to improve the wet strength and water retention of the pots. In this invention, the rigid structure, natural hydrophobic properties, and antibacterial properties of lignin endow the coating material with functionality; the film-forming properties of soy protein and its strong covalent / non-covalent (hydrogen bond) interaction with plant fibers ensure the interfacial bonding between the coating material and the substrate; and the "bridging" effect of the biodegradable epoxy compound ensures effective crosslinking between the lignin functional phase and the film-forming agent. The biodegradable coating formed by the copolymerization and crosslinking of these three components exhibits excellent adhesion to plant fiber seedling pots and can significantly improve the wet strength and water retention of the substrate. Compared with existing coatings, this invention has the following beneficial effects:

[0019] (1) The coating material of the present invention is biodegradable in all components and has good biosafety. When used for surface coating of plant fiber agricultural products, it does not affect the biodegradable green properties of the products.

[0020] (2) In this invention, the lignin functional phase is an inherent component of plant fibers. It and cellulose are both natural polar polymer materials and can be bonded through hydrogen bonds and covalent bonds, thus exhibiting good interfacial compatibility. This belongs to the category of "self-reinforced composite". In the embodiments of this application, the mechanical properties of the substrate under both dry and wet conditions are significantly improved after coating, indicating that there is a good bond between the coating and the substrate, which indirectly proves the good interfacial compatibility between the coating and the substrate.

[0021] (3) The raw materials of the coating material of the present invention are widely available, the preparation process is simple, and water is used as the reaction medium. It is non-toxic and environmentally friendly, has a friendly operating environment, low viscosity, is suitable for a variety of coating methods, and has good adaptability to substrates. Attached Figure Description

[0022] Figure 1 A photograph of the biodegradable seedling pot coating material prepared in Example 1.

[0023] Figure 2 Photos of the seedling pots before and after coating application.

[0024] Figure 3 The dynamic water absorption rate of the straw fiber seedling pots before and after coating application is shown in Examples 1-4.

[0025] Figure 4 The results of the maximum water absorption rate test of straw fiber seedling pots before and after coating in Examples 1-4 are shown.

[0026] Figure 5 The results of water retention tests on seedling pots before and after coating application in Examples 1-4 are shown.

[0027] Figure 6 The results show the changes in dry / wet tensile strength of the seedling pots before and after coating application in Examples 1-4.

[0028] Figure 7 The results show the biodegradability test results of the seedling pots before and after coating application. Detailed Implementation

[0029] Sources of raw materials and reagents for the example:

[0030] The soy protein isolate was purchased from Linyi Shansong Biological Products Co., Ltd., with a protein content of ≥90% and product CAS number 9010-10-0. This protein is obtained by refining the supernatant from defatted soybean meal, a byproduct of the soybean oil industry, through water extraction and low-temperature centrifugation. In practice, commercially available soy protein isolate prepared using other conventional methods in the field can also be used.

[0031] The manufacturer of polyethylene glycol diglycidyl ether is Shanghai Aladdin Biochemical Technology Co., Ltd., and the product CAS number is 72207-80-8.

[0032] The enzymatically hydrolyzed lignin was purchased from Shandong Longli Biotechnology Co., Ltd.

[0033] The epoxidized soybean oil was purchased from Jinan Luying Chemical Co., Ltd., with an epoxy value of 6.2. Example 1

[0034] (1) Mix soy protein isolate, polyethylene glycol diglycidyl ether and water in a mass ratio of 1:0.58:19 to obtain a dispersion; then adjust the pH of the dispersion to 9.0 with 25% ammonia water (the same below), and stir the reaction at 85℃ for 30 min under sealed conditions to obtain the reaction product.

[0035] (2) Add enzymatically hydrolyzed lignin equivalent to 40% of the soybean protein isolate to the reaction product obtained in step (1). Adjust the pH of the reaction system to 9.42 with ammonia. After thoroughly stirring at room temperature until the lignin is completely dissolved, transfer the mixture to an open container at 45°C for 1 hour (ensuring good ventilation, the same below). After cooling to room temperature, add montmorillonite equivalent to 3% of the soybean protein isolate, stir evenly, and then sonicate (600 W) for 10 minutes to obtain the coating material. Its form is a brown liquid, such as... Figure 1 As shown.

[0036] According to the method of national standard GB / T 14074-2017, the pH of the coating material is 9.06, the viscosity is 1822 mPa·s, and the solid content is 9.25%. Example 2

[0037] (1) Mix soy protein isolate, epoxidized soybean oil and water in a mass ratio of 1:0.58:19, then adjust the pH of the dispersion to 9.0 with 25% ammonia water, and stir the reaction under sealed conditions at 85℃ for 30 min to obtain the reaction product.

[0038] (2) Add enzymatically hydrolyzed lignin equivalent to 40% of the amount of soybean protein isolate to the reaction product obtained in step (1), adjust the pH of the system to 9.30 with ammonia, stir thoroughly at room temperature to completely dissolve the lignin, and then transfer to an open reaction at 60°C for 1 hour. After cooling to room temperature, add montmorillonite equivalent to 3% of the amount of soybean protein isolate, stir evenly, and then sonicate at 600 W for 10 minutes to obtain the coating material.

[0039] According to the method of national standard GB / T 14074-2017, the pH of the coating material is 9.05, the viscosity is 1912 mPa·s, and the solid content is 9.46%. Example 3

[0040] (1) Mix soy protein isolate, polyethylene glycol diglycidyl ether and water in a mass ratio of 1:0.58:19. Then adjust the pH of the dispersion to 9.0 with 25% ammonia. Stir and react for 30 min under sealed conditions at 85°C to obtain the reaction product.

[0041] (2) Add enzymatically hydrolyzed lignin equivalent to 60% of the amount of soybean protein isolate to the reaction product obtained in step (1), adjust the pH of the system to 9.34 with ammonia, stir thoroughly at room temperature to completely dissolve the lignin, and then transfer to an open reaction at 45°C for 1 hour. After cooling to room temperature, add montmorillonite equivalent to 3% of the amount of soybean protein isolate, stir evenly, and then sonicate at 600 W for 10 minutes to obtain the coating material.

[0042] According to the method of national standard GB / T 14074-2017, the pH of the coating material is 8.85, the viscosity is 1964 mPa·s, and the solid content is 10.5%. Example 4

[0043] (1) Mix soy protein isolate, polyethylene glycol diglycidyl ether and water in a mass ratio of 1:0.25:19, then adjust the pH of the dispersion to 9.0 with 25% ammonia water, and stir the reaction at 85℃ for 30 min under sealed conditions to obtain the reaction product.

[0044] (2) Add enzymatically hydrolyzed lignin equivalent to 40% of the amount of soybean protein isolate to the hydrolysis product obtained in step (1), adjust the pH of the system to 9.36 with ammonia, stir thoroughly at room temperature to completely dissolve the lignin, and then transfer to an open reaction at 45°C for 4 hours. After cooling to room temperature, add montmorillonite equivalent to 3% of the amount of soybean protein isolate, stir evenly, and then sonicate at 600 W for 10 minutes to obtain the coating material.

[0045] According to the method of national standard GB / T 14074-2017, the pH of the coating material is 9.02, the viscosity is 1977 mPa·s, and the solid content is 6.87%.

[0046] The coating materials obtained in Examples 1-4 were sprayed onto the surface of plant fiber seedling pots. Specifically, the coating materials prepared in Examples 1-4 were uniformly sprayed onto the inner and outer surfaces of the straw fiber seedling pots at a coating weight of 0.1 g (coating) / g (substrate), and then cured at 90°C for 2 hours to obtain the coated seedling pots (photos of the seedling pots before and after coating are shown in the image). Figure 2 As shown). The straw fiber seedling pots used in this embodiment were prepared according to the method disclosed in "Development of Biodegradable Seedling Pots (Huang Xiaomei et al., Industrial Textiles, 2001)" (in specific implementation, other conventional methods of preparing plant fiber seedling pots can also be used).

[0047] The effects of coating materials on the water resistance, water retention, mechanical strength, and biodegradability of plant fiber seedling pots were investigated using water absorption, water retention, mechanical property, and biodegradability tests. In this embodiment, the water absorption and water retention testing methods were based on the methods disclosed in the literature "Performance Testing of Completely Degradable Seedling Pots Based on Citrus Peel Residue (Pan Lang et al., 2018)"; mechanical property testing was conducted on a universal testing machine according to the methods in GB / T 12914-2018; and biodegradability testing was performed according to the methods reported in the literature "Degradation Performance Test of Degradable Nursery Pots Based on Paper and Straw". The test results are as follows. Figures 3-7 As shown.

[0048] like Figure 3 , 4The water absorption test results showed that, at the same time, the water absorption rate and water absorption percentage of the plant fiber seedling pots after coating were significantly lower than those of the uncoated products. Figure 3 The maximum water absorption rate (24h) of the seedling pots after coating was 104-115%, which was more than 40% lower than that of the uncoated seedling pots (197%). The reduced water absorption rate indicates that the coating can prevent water from wetting and penetrating the substrate, suggesting that the coating helps improve the water resistance of the substrate.

[0049] Figure 5 The results show the water retention test results of seedling pots before and after coating. It can be seen that the water loss rate of uncoated seedling pots after 24 hours (indoors, temperature 25℃) was 39.88%, while the water loss rate of seedling pots with different coating configurations ranged from 23.12% to 28.29%, a reduction of 29% to 42% compared to uncoated seedling pots. The significant reduction in water loss rate indicates that the water loss rate through the seedling pots decreased after coating, and the water retention performance of the seedling pots was significantly improved. This is of great significance for improving water resource utilization efficiency and saving water during the seedling process.

[0050] Figure 6 The changes in mechanical properties of the material before and after coating are shown. It can be seen that the coating materials with different configurations can effectively improve the mechanical properties of the plant fiber seedling pots. After coating, the tensile strength of the pot wall in the dry state increased by more than 42%, with the highest strength reaching 7.57 MPa, which is 95% higher than the uncoated substrate (3.88 MPa). Wet strength results show that under immersion conditions (24h), the coated plant fiber seedling pots still maintained more than 56% of their mechanical strength, which is 281-386% higher than the wet strength of the uncoated plant fiber seedling pots under the same conditions, confirming that the coating material of this invention can effectively improve the wet strength of plant fiber seedling pots. On the other hand, the above test results show that the mechanical properties of the substrate are significantly improved under both dry and wet conditions after coating, indicating good bonding performance between the coating and the substrate, indirectly proving the good interfacial compatibility between the coating and the substrate.

[0051] Figure 7 The results show the biodegradability of straw fiber seedling pots before and after coating. The seedling pot material after coating showed a weight loss rate of over 85% within 60 days, indicating good biodegradability.

Claims

1. A method for preparing a biodegradable seedling pot coating material, characterized in that, The specific steps are as follows: 1) Disperse soy protein isolate and biodegradable epoxy crosslinking agent evenly in water at a mass ratio of 1:(0.25~0.58), adjust the pH of the dispersion to 9.0, and stir at 85~95℃ for 30~60 min to obtain the reaction product; 2) Add lignin to the reaction product obtained in step 1), adjust the pH of the reaction system to 9.3~9.6, react at 45~60℃ for 1~4h, add rheology modifier, stir evenly and then sonicate to obtain the coating material. The biodegradable epoxy crosslinking agent is at least one of polyethylene glycol diglycidyl ether or epoxidized soybean oil; The mass ratio of soy protein isolate to lignin is 100:40~60; The rheology modifier is montmorillonite or attapulgite; the mass ratio of the added rheology modifier to soy protein isolate is (0.5~5):

100.

2. The method for preparing the biodegradable seedling pot coating material according to claim 1, characterized in that, In step 1), the mass ratio of soy protein isolate to water is 1:19~25.

3. The method for preparing the biodegradable seedling pot coating material according to claim 1, characterized in that, Step 1) Adjusting the pH of the dispersion to 9.0 means adjusting the pH to 9.0 with an ammonia solution of 25-28% by mass; Step 2) Adjusting the pH of the reaction system to 9.3-9.6 means adjusting the pH to 9.3-9.6 with an ammonia solution of 25-28% by mass.

4. The method for preparing the biodegradable seedling pot coating material according to claim 1, characterized in that, The lignin is enzymatically hydrolyzed lignin.

5. The method for preparing the biodegradable seedling pot coating material according to claim 1, characterized in that, Step 2) The ultrasonic treatment refers to an ultrasonic power of 600~1000w and an ultrasonic time of 5~10min.

6. The biodegradable seedling pot coating material prepared by any one of claims 1-4.

7. The application of the biodegradable seedling pot coating material prepared by any one of claims 1-4 in the preparation of biodegradable coatings.

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