Biodegradable dark color mulching film and preparation method thereof

Abstract

The present application relates to a kind of biodegradable dark color mulch and its preparation method, and dark color mulch is made of cellulose, hemicellulose and degradable coating.The manufacturing method includes the preparation of dark color mulch substrate, coating layer coating.It specifically includes slurry compounding, beating, additive addition, is formed by papermaking, dehydration, pre-drying, coating, sizing, drying, calendering, product after drying.The local film has good wet strength, light resistance, weather resistance, heat preservation and entropy increasing effect.The results of farmland degradation experiment show that the mulch can be biodegraded after 50~60 days, and the biodegradation rate is more than 90%.

Description

Technical Field

[0001] This invention relates to the fields of paper coatings and greenhouse mulch film technology, specifically to a biodegradable dark-colored mulch film and its preparation method, which is mainly used in greenhouse vegetable cultivation. Background Technology

[0002] Mulching technology offers numerous benefits, including heat and moisture retention, weed control, pest prevention, growth promotion, and yield increase, making it a crucial method for increasing production in modern agriculture. Currently, the most widely used mulch films are primarily organic polymer films based on polyethylene. However, in recent years, the widespread use of non-degradable plastic agricultural mulch films has led to increasingly prominent environmental pollution and soil degradation problems, causing severe "white pollution" globally. Addressing the pollution issues caused by plastic mulch films in agricultural mulching technology has become paramount; therefore, biodegradable agricultural mulch films have become a key research focus.

[0003] Paper-based mulch film is a biodegradable mulch film made primarily from plant cellulose, with the addition of other auxiliary materials and chemical additives. This type of mulch film has advantages such as abundant raw materials, simple process, low cost, and complete biodegradability, and has become one of the main research directions for biodegradable mulch films.

[0004] However, the current paper-based mulch has shortcomings such as insufficient strength and poor water resistance (He Wenqing, Liu Qi, Li Yuanqiao, et al. Development and industrialization prospects of biodegradable mulch film [J]. Biotechnology Industry, 2017(2).DOI:10.3969 / j.issn.1674-0319.2017.02.001; Zhao Yan, Li Shufen, Wu Xinghong, et al. Application status and development trend of biodegradable mulch film in my country [J]. Modern Agricultural Science and Technology, 2010(23):3.DOI:10.3969 / j.issn.1007-5739.2010.23.060; [1] Liu Min, Huang Zhanbin, Yang Yujiao. Research progress and development trend of biodegradable mulch film [J]. Chinese Agricultural Science Bulletin, 2008, 24(9):5.DOI:CNKI:SUN:ZNTB.0.2008-09-099).

[0005] Therefore, the preparation of a biodegradable dark-colored mulch film that can effectively utilize resources, has high strength, and degrades quickly has become the primary choice for greenhouse paper base film. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to prepare a biodegradable dark-colored mulch film, which is composed of cellulose, hemicellulose, and a biodegradable coating. The manufacturing method includes the preparation of the dark-colored mulch film substrate and the application of a coating. The process flow consists of the following steps: raw material selection, cooking, washing, pulping, pulp preparation, wet end, pressing, drying, sizing, drying, calendering, obtaining base paper, coating, and further drying.

[0007] This invention provides a method for preparing a biodegradable dark-colored mulch film, which includes the following steps:

[0008] 1) Pulping stage: The trough beater further beats the pulp, adjusting the freeness to 25-35°SR, and beats the pulp into a free suspension; the pulp is waste paper pulp and bleached softwood pulp;

[0009] 2) Pulp preparation stage: 80-95% waste paper pulp base mixed with 5-20% bleached softwood pulp is used for pulp blending;

[0010] 4) Papermaking and drying: The pulp is sprayed onto the wire section through the headbox, and wet paper sheets are formed by water absorption and extrusion; then the wet paper sheets are placed in the drying section of the papermaking machine at 80-90℃ to dry, and then transferred to an oven at 130-180℃ to continue drying to complete the curing and cross-linking.

[0011] 4) Sizing stage: The surface sizing method is adopted, using dry strength agent cellulose nanofibers, wet strength agent polyamide epichlorohydrin resin, and sizing agent AKD for sizing.

[0012] 5) Calendering: The base paper is obtained by hot pressing and cooling using a calender's hot rollers;

[0013] 6) Coating: The coating liquid is applied to the base paper by immersion and adsorption, and excess liquid is removed until the weight of the wet paper sheet is 190-210% of the weight of the base paper.

[0014] 7) Drying again: Place the coated base paper in an oven to dry and obtain the finished dark-colored floor film.

[0015] Specifically, in step 1), the beating degree is adjusted to 30°SR; in step 2), 90% waste paper pulp base is mixed with 10% bleached softwood pulp for pulp blending.

[0016] Preferably, step 3) specifically involves: placing the film in the drying section of the die-making machine at 85°C for 15 minutes, and then transferring it to an oven at 150°C for another 10 minutes to complete the curing and crosslinking.

[0017] Preferably, in step 4), the concentration of the dry strength agent cellulose nanofibers is 0.5–2%, the concentration of the wet strength agent polyamide epichlorohydrin resin is 0.5–2%, and the sizing agent AKD is 0.9–1.1 g / m³. 2 .

[0018] Specifically, in step 6), the weight of the wet paper sheet is 200% of the original paper, with an allowable error of ±5%; in step 7), the coated original paper is placed in a 100°C oven and dried for 15 minutes to obtain the finished dark-colored ground film.

[0019] More specifically, the preparation method of the coating liquid is as follows:

[0020] (1) Dissolve the dispersant by stirring distilled water and sodium hexametaphosphate with a high-speed disperser;

[0021] (2) Add carbon black in sequence and continue stirring to fully disperse the pigment;

[0022] (3) Add EAA emulsion and stir thoroughly;

[0023] (4) Add carboxymethyl cellulose and modified chitosan, and stir to mix and disperse;

[0024] (5) Add styrene-butadiene latex and continue stirring until well mixed;

[0025] (6) Add sodium hypophosphite hydrophobic agent and stir to mix evenly to obtain the target coating liquid.

[0026] Preferably,

[0027] In step (1), 100 parts of distilled water and 0.5-1.5 parts of sodium hexametaphosphate are stirred in a high-speed disperser at a speed of 800-1200 r / min for 5-15 min to dissolve the dispersant.

[0028] (2) Add 20-30 parts of carbon black and continue stirring at a speed of 4000-6000 r / min for 20-30 min to fully disperse the pigment;

[0029] (3) Add 4-6 parts of EAA emulsion and stir at 2500-3500 r / min for 20 min;

[0030] (4) Add 1-3 parts of carboxymethyl cellulose and modified chitosan dry strength agent, and the mass ratio of carboxymethyl cellulose and modified chitosan dry strength agent is 4-6:1. Mix and disperse at a speed of 2000-3000r / min for 15-25min, and add an appropriate amount of polyether defoamer.

[0031] (5) Add 25-35 parts of styrene-butadiene latex and stir at 2500-3500 r / min for 15 min;

[0032] (6) Add 1-3 parts of sodium hypophosphite hydrophobic agent, stir at 1500-2500r / min for 8-12min, and mix evenly to obtain the target coating.

[0033] More preferably,

[0034] In step (1), 100 parts of distilled water and 1 part of sodium hexametaphosphate are stirred at 1000 r / min for 10 min using a high-speed disperser to dissolve the dispersant.

[0035] (2) Add 25 parts of carbon black and continue stirring at 5000 r / min for 25 min to fully disperse the pigment.

[0036] (3) Add 5 parts of EAA emulsion and stir at 3000r / min for 20min.

[0037] (4) Add 2 parts of carboxymethyl cellulose and modified chitosan dry strength agent (the mass ratio of carboxymethyl cellulose and modified chitosan dry strength agent is 5:1), mix and disperse at a speed of 2500r / min for 20min, and add an appropriate amount of polyether defoamer.

[0038] (5) Add 30 parts of styrene-butadiene latex and stir at 3000 r / min for 15 min.

[0039] (6) Add 1-2 parts of sodium hypophosphite hydrophobic agent, stir at 2000r / min for 10min, and mix evenly to obtain the target coating.

[0040] The beneficial effects of this invention are:

[0041] (1) The present invention has a small amount of additives, the papermaking process is not complicated, the service life of production equipment is increased, the physical strength of the dark mulch film is effectively improved, resource waste is prevented and environmental pollution is reduced.

[0042] (2) This invention uses cellulose nanofibers (CNF) as a dry strength agent. This is a new type of paper strengthening agent. Due to its large aspect ratio, high specific surface area, and the advantages of natural cellulose such as degradability and easy availability, its use in the papermaking field is gradually increasing (Balea A, Luis Sanchez-Salvador J, Concepcion Monte M, et al. In Situ Production and Application of Cellulose Nanofibers to Improve Recycled Paper Production[J]. Molecules, 2019(9):24; Luo Boya, Cao Haibing, An Xingye, et al. Progress in the preparation and application of non-wood fiber nanocellulose[J]. China Papermaking, 2020, 39(7):10.DOI:10.11980 / j.issn.0254-508X.2020.07.012; Wang Aijiao. Research status of the application of cellulose nanofibers in papermaking[J]. Zhejiang Papermaking, 2020(3):4.). Furthermore, compared to traditional paper additives, CNF is smaller in size, more stable in properties, and has a significant effect on filling the gaps between paper fibers. It can form a dense network structure with the fibers, making the fibers and fillers tightly connected.

[0043] (3) This invention uses a self-made coating, in which PVDC and EAA waterproof and moisture-proof agents are added. Both are ideal materials with high barrier properties, strong toughness, and good chemical stability, exhibiting excellent moisture-proof and waterproof performance. This reduces water vapor permeation, making it unique in the coating, packaging, and anti-corrosion industries. It has been widely used in surface coatings, food and pharmaceutical packaging, mechanical parts, and rust prevention of military strategic materials, making it a highly vital polymer material in the global coating, packaging, and anti-corrosion industries.

[0044] (4) The present invention uses a coating method to prepare biodegradable dark-colored mulch film, which is simple in process and operation.

[0045] (5) The local mulch film has good wet strength, light-blocking properties, weather resistance, and heat preservation and entropy-increasing effects. Farmland degradation experiments show that the mulch film can biodegrade on its own after 50 to 60 days, with a biodegradation rate of over 90%. Detailed Implementation

[0046] The present invention will be further described below through specific embodiments, but these embodiments do not constitute a limitation thereof.

[0047] 1) Raw material selection: waste paper pulp and bleached softwood pulp

[0048] 2) Beating stage: The trough beater further beats the pulp, adjusting the beatness to 30°SR, and beats the pulp into a free suspension.

[0049] 3) Pulp preparation stage: 90% waste paper pulp base mixed with 10% bleached softwood pulp is used for pulp blending.

[0050] 4) Papermaking stage: The pulp is sprayed onto the wire section through the headbox, where it absorbs water and is squeezed to form a wet paper sheet. The wet paper sheet is then placed in the drying section of the papermaking machine and dried at 85°C for 15 minutes, and then transferred to an oven at 150°C for another 10 minutes to complete the curing and cross-linking.

[0051] 5) Sizing stage: Surface sizing is used, with 1% dry strength agent (cellulose nanofibers (CNF), 1% wet strength agent (polyamide epichlorohydrin resin (PAE), and 1g / m² sizing agent (AKD). 2 .

[0052] 6) Calendering: The calender presses the paper with hot rollers and then cools it to obtain the base paper.

[0053] The preparation method of the coating liquid is as follows:

[0054] (1) Dissolve 200g of distilled water and 1g of sodium hexametaphosphate in a high-speed disperser at a speed of 1000r / min for 10min.

[0055] (2) Add 47.5g of carbon black in sequence and continue stirring at 5000r / min for 25min to fully disperse the pigment.

[0056] (3) Add 33.34g of EAA emulsion (solid content 30%) and stir at 3000r / min for 20min.

[0057] (4) Add 2g of carboxymethyl cellulose and 0.4g of modified chitosan, mix and disperse at 2500r / min for 20min, and add an appropriate amount of polyether defoamer.

[0058] (5) Add 120.11g of styrene-butadiene latex (solid content 50%) and stir at 3000r / min for 15min.

[0059] (6) Add 1.5g of sodium hypophosphite hydrophobic agent, stir at 2000r / min for 10min, and mix evenly to obtain the target coating.

[0060] 7) Coating: The above mixture is coated onto the base paper by impregnation and adsorption. Excess liquid is removed with filter paper until the weight of the wet paper sheet is twice that of the base paper (allowable error ±5%).

[0061] 8) Drying again: Place the coated base paper in a 100℃ oven and dry for 15 minutes to obtain the finished dark-colored mulch film.

[0062] Test case

[0063] (1) Measurement of longitudinal fracture length

[0064] The tensile strength test was conducted according to GB / T12914-2018 on a Sichuan Changjiang DCP-KZ300 tensile strength tester. The specific test steps are as follows:

[0065] ① Paper Sample Collection, Processing, and Preparation: Samples shall be collected according to GB / T450, and subjected to temperature and humidity treatment according to GB / T10739. From undamaged paper and paperboard samples, cut sample strips with a width of (15±0.1) mm and a length sufficient to hold between the two clamps. Avoid touching the sample portion between the clamps with your hands. The two long sides of the sample should be straight, and its parallelism error should not exceed ±0.1 mm over the entire clamping length. The cut of the sample should be neat and undamaged. Cut a sufficient number of sample strips at once.

[0066] ② Adjust the clamp distance to the specified initial test length and clamp the specimen in the clamp. Note that you should not touch the test area between the two clamping lines of the specimen with your hands. Position and clamp the specimen firmly, leaving no slack and ensuring no significant strain occurs. Ensure the specimen is parallel to the direction of the applied tension.

[0067] ③ Testing: Begin the test and continue until the specimen breaks. Record the maximum applied tensile strength and elongation (in mm), and calculate the tensile strength and longitudinal fracture length.

[0068] (2) Wet strength test

[0069] The tensile strength test was conducted according to GB / T 465.2-2008 using a Sichuan Changjiang DCP-KZ300 tensile strength tester. The specific test steps are as follows:

[0070] ① Sample collection, processing and preparation: Take samples according to GB / T450, immerse the sample in water that conforms to GB / T10739 for 10 minutes, remove the sample from the tray, and gently absorb the water on the surface of the sample with filter paper or blotting paper.

[0071] ② Test: After immersing the sample in water, the surface water is then absorbed, and the sample is quickly placed on a tensile strength tester to determine the tensile strength and calculate the wet strength.

[0072] (3) Thermal insulation

[0073] Select a sunny, high-quality agricultural plot and divide it into three equal sections. Lay biodegradable dark-colored mulch and plastic mulch on one section and compare them with open soil. Use a temperature meter to measure the soil surface temperature and the temperature at a depth of 5 cm below the surface. The test time is from 6:00 to 20:00 every day, and the data is recorded every two hours for a week.

[0074] (4) Determination of service life / relative biodegradation rate

[0075] According to GB / T 19275—2003, the specific test steps are as follows:

[0076] ① Paper sample collection, processing and preparation: Cut square paper pieces with a side length of (40±0.1) mm from undamaged paper and paperboard samples.

[0077] ② Sample preparation and testing: First, soil with a moisture content of (60% ± 5%) and good water retention capacity is filled into the incubator. A control cotton strip is introduced to test soil activity. Under the premise of ensuring oxygen circulation within the incubator, the sample is buried, with the soil layer covering the sample not exceeding 12.5 cm in thickness, without compressing the soil in the incubator. The sample is incubated in a biological incubator at a temperature of 29 ± 1℃ and a relative humidity of 95% ± 2%. Within a certain time period, the sample mass loss and strength are measured, and the service life / relative biodegradation rate is calculated.

[0078] The experimental results are as follows.

[0079] Table 1 shows the longitudinal breaking length wet strength data of the base paper and the finished dark-colored mulch film in Example 1 of the present invention.

[0080] Table 1 Comparison of longitudinal fracture wet strength data

[0081]

[0082] As shown in Table 1, the coated dark-colored mulch film significantly improves the longitudinal breaking length and wet strength of the base paper. Compared with the base paper, the longitudinal breaking length of the finished dark-colored mulch film is increased, and the wet strength of the film is increased by 3 to 4.4 times.

[0083] Table 2 shows the effects of the finished dark-colored mulch film prepared according to the present invention and the black plastic film covering the market on the ground surface temperature.

[0084] Table 2. Effects of paper-based mulch film and plastic mulch film on surface temperature.

[0085]

[0086] As shown in Table 2, the surface temperature under the finished dark-colored mulch film (a type of paper-based mulch film) of this invention and commercially available black plastic film is relatively higher than the open-air surface temperature, both exhibiting a certain degree of heat preservation. At 6:00 AM, the surface temperature under the paper-based mulch film of this invention was 14.1°C, 9.5°C higher than the temperature without mulch film, and 0.3°C lower than the plastic mulch film. As time progresses, sunlight passing through the paper-based mulch film converts solar energy into heat energy, increasing the surface temperature. Due to the insulating effect of the paper-based mulch film, less heat dissipates from under the film to the outside, thus increasing the surface temperature. The temperature reaches its peak at 12:00 PM, at which point the surface temperature under the paper-based mulch film is 23.5°C, 6.8°C higher than the open-air surface temperature, and 0.1°C higher than the surface temperature under the plastic mulch film. Subsequently, due to the heat preservation effect of the paper-based mulch film, the surface temperature under the paper-based mulch film remains at 23.5°C until 4:00 PM. At 6 PM, the surface temperature under the paper-based mulch film was 22.7℃, 8.5℃ higher than the open-air surface temperature and 0.4℃ lower than the surface temperature under the plastic mulch film. Although the surface temperature decreased under the mulch film, the decrease was slower than that under the open-air surface temperature. At 8 PM, the surface temperature under the paper-based mulch film was 20.0℃, 10.0℃ higher than the open-air surface temperature and 0.4℃ lower than the plastic mulch film. The mulch film showed a significant heat preservation effect at night because, without sunlight, a large amount of heat was lost from the air, and the heat stored under the mulch film was released slowly due to its insulating effect. Therefore, although the paper-based mulch film of this invention has slightly lower heat preservation properties than the plastic mulch film, it still has a good heat preservation effect.

[0087] Table 3 shows the effects of the finished dark-colored mulch film prepared according to the present invention (i.e., the paper-based mulch film in the table) and the black plastic film covering in the market on soil temperature.

[0088] Table 3. Effects of paper-based and plastic film mulching on soil temperature.

[0089]

[0090] The effects of paper-based mulch and plastic mulch on temperature at 5cm depth. The table shows that the temperature at 5cm depth under biodegradable dark-colored mulch and plastic mulch are basically the same, proving that paper-based mulch and plastic mulch have similar heat-insulating properties on the soil interior.

[0091] During the day, the soil temperature under the plastic film increased significantly, with a more pronounced warming effect than the soil in the open air. At 6:00 AM, the soil temperature under the paper-based plastic film was 8.7℃, 4.7℃ higher than the open-air soil temperature. As the air temperature increased, the soil absorbed heat and continued to warm up. However, due to the soil's high specific heat capacity and poor thermal conductivity, the warming process was relatively slow, slowing down at 2:00 PM. The temperature reached its peak of 19.0℃ at 4:00 PM, maintaining its heat-insulating effect until after 6:00 PM. By 8:00 PM, the soil temperature under the plastic film decreased along with the outside temperature, but the decrease was significantly slower than that of the open-air soil temperature. This demonstrates that the heat-insulating performance of the paper-based plastic film on the soil is similar to that of plastic plastic film, exhibiting a significant warming and heat-insulating effect.

[0092] Table 4 shows the degradation data of the finished dark-colored mulch film of this invention.

[0093] Table 4 Degradation data of finished dark-colored mulch film

[0094] 0 35.03 0 10 34.11 2.7 20 31.49 10.1 30 26.16 25.3 40 20.42 41.7 50 8.65 75.3

[0095] As shown in Table 4, the finished dark-colored mulch film prepared by this invention degrades relatively slowly in the first 20 days, while maintaining good film strength. The degradation rate increases significantly from day 30 onwards. By day 50, the degradation rate reaches 75%, and it is expected to be completely degraded in 60 days. Therefore, the mulch film prepared by this invention is a biodegradable dark-colored mulch film.

Claims

1. A method for preparing a biodegradable dark-colored mulch film, characterized in that, Includes the following steps: 1) Pulping stage: The trough beater further beats the pulp, adjusting the freeness to 25-30°SR, and beats the pulp into a free suspension; the pulp is waste paper pulp and bleached softwood pulp; 2) Pulp preparation stage: 80-95% waste paper pulp base mixed with 5-20% bleached softwood pulp is used for pulp blending; 3) Papermaking and drying: The pulp is sprayed onto the wire section through the headbox, and wet paper sheets are formed by water absorption and extrusion; then the wet paper sheets are placed in the drying section of the papermaking machine at 80-90℃ to dry, and then transferred to an oven at 130-180℃ to continue drying to complete curing and cross-linking. 4) Sizing stage: Surface sizing is adopted, wherein the dry strength agent cellulose nanofiber concentration is 0.5-2%, the wet strength agent polyamide epichlorohydrin resin concentration is 0.5-2%, and the sizing agent AKD is 0.9-1.1 g / m³. 2 ; 5) Calendering: The base paper is obtained by hot pressing and cooling using a calender's hot rollers; 6) Coating: The coating solution is applied to the base paper using an immersion and adsorption method. Excess liquid is then removed until the weight of the wet paper sheet is 190-210% of the weight of the base paper. 7) Drying again: Place the coated base paper in an oven to dry and obtain the finished dark-colored floor film; In step 6), the coating liquid is prepared by the following method: (1) Dissolve 200g of distilled water and 1g of sodium hexametaphosphate in a high-speed disperser at a speed of 1000r / min for 10min. (2) Add 47.5g of carbon black in sequence and continue stirring at 5000r / min for 25min to fully disperse the pigment; (3) Add 33.34g of EAA emulsion with a solid content of 30% and stir at 3000r / min for 20min; (4) Add 2g of carboxymethyl cellulose and 0.4g of modified chitosan, mix and disperse at 2500r / min for 20min, and add an appropriate amount of polyether defoamer; (5) Add 120.11g of styrene-butadiene latex with a solid content of 50% and stir at 3000r / min for 15min; (6) Add 1.5g of sodium hypophosphite hydrophobic agent and stir at 2000r / min for 10min until the mixture is homogeneous.

2. The preparation method according to claim 1, characterized in that, In step 1), the beating degree is adjusted to 30°SR; in step 2), 90% waste paper pulp base is mixed with 10% bleached softwood pulp for pulp blending.

3. The preparation method according to claim 1, characterized in that, Step 3) The specific operation is as follows: put it into the drying section of the die-making machine and dry it at 85°C for 15 minutes, then transfer it to the oven at 150°C and continue drying for 10 minutes to complete the curing and crosslinking.

4. The preparation method according to claim 1, characterized in that, In step 4), the dry strength agent cellulose nanofiber concentration is 1%, the wet strength agent polyamide epichlorohydrin resin concentration is 1%, and the sizing agent AKD is 1 g / m³. 2 .

5. The preparation method according to claim 1, characterized in that, In step 6), the weight of the wet paper sheet is 200% of the original paper, with an allowable error of ±5%; in step 7), the coated original paper is placed in a 100℃ oven and dried for 15 minutes to obtain the finished dark-colored mulch film.

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