Biodegradable mulching film as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of degradable mulching films, and relates to a biodegradable mulching film as well as a preparation method and application thereof, and the biodegradable mulching film is prepared from oxidized starch, hydroxymethyl cellulose, trehalose, polyvinyl alcohol and a plasticizer. According to the invention, natural and synthetic biological materials are compounded, so that the water resistance, thermal stability, tensile property and the like of the mulching film are improved; starch and cellulose are used as main materials, so that resource utilization of agricultural wastes is realized, and the preparation cost is reduced; after degradation, nutrient substances necessary for life activity are provided for soil microorganisms to promote reproduction, and the soil structure is improved; environmental pollution caused by the plastic mulching film is reduced, and agricultural sustainable development is facilitated; the preparation operation is simple, the whole process is normal temperature and normal pressure, liquid is converted into a solid film at normal temperature, and the safety is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of degradable mulching film, and relates to a biodegradable mulching film and a preparation method and application thereof. BACKGROUND

[0002] With the development of modern agriculture, mulching film has been widely used in China due to its effects of improving the growth environment of crops, such as warming and soil conservation. China has become the largest country in the world for mulching planting. Mulching film can inhibit weed growth, reduce evaporation and soil latent heat loss, and increase light uniformity, thus creating good conditions for plant root development and improving crop yield.

[0003] However, the huge amount of film used behind the problem of residual film recycling and recycling, causing resource waste and environmental pollution. Residual film pollutes the soil and affects crop growth, seriously threatening the sustainable development of agriculture in China. Traditional mulching film is mainly made of polyethylene, which is difficult to degrade naturally. Residual film can hinder soil aeration and water permeability, affect crop root extension and nutrient absorption, and reduce soil fertility, resulting in weak seedlings and even dead seedlings. Moreover, after the residual film is broken into plastic particles, it can adsorb heavy metal ions and organic pollutants, increasing the difficulty of soil pollution control. At the same time, the degradation of mulching film produces microplastics and nanoplastics, which may enter the food chain and cause ecological chain reactions. Burning mulching film in the field can release harmful chemicals, polluting the atmosphere and seriously affecting plant growth, causing secondary pollution. In response to plastic mulch pollution and harm, China has introduced a series of policies to promote the research and development and popularization of degradable mulching film to achieve green and sustainable agricultural development.

[0004] At present, many degradable mulching films have been used to reduce the negative effects of traditional mulching film. The main research and development of degradable mulching film can be divided into three categories: photodegradable mulching film, light-biological double-degradable mulching film and biodegradable mulching film. Among them, photodegradable mulching film and light-biological double-degradable mulching film are strongly dependent on the environment for their degradation degree, and their degradation speed and degree are greatly affected by light conditions. The degradation is not complete, unstable, and there are still microplastic particles after degradation, which still cause harm to the environment and human body, and damage the pore structure of the soil, affecting the balance of soil biological community and high cost, etc. have been abandoned by the market. The new type of polymer degradable mulching film has the problems of poor mechanical properties, poor water resistance, short service life, low production capacity and high production cost. Therefore, research and development of new and high-performance biodegradable mulching film has become the development trend of the world mulching film research. SUMMARY

[0005] The main purpose of the present application is to overcome the defects in the prior art, and to provide a biodegradable mulching film and a preparation method and application thereof.

[0006] To achieve the above object, the specific technical scheme is as follows: The application provides a biodegradable mulching film which is prepared from oxidized starch, hydroxymethyl cellulose, trehalose, polyvinyl alcohol and a plasticizer. The oxidized starch is 1.5-2.5 parts by weight, the hydroxymethyl cellulose is 1.5-2.5 parts by weight, the trehalose is 1.5-2.5 parts by weight, the polyvinyl alcohol is 1-1.5 parts by weight and the plasticizer is 2.5-3.5 parts by weight.

[0007] The biodegradable mulching film is prepared by compounding synthetic biodegradable materials and natural biopolymer materials, so that the advantages of the two kinds of materials can be taken and the disadvantages can be made up for, the film has good water resistance, thermal stability and tensile strength, the multifunction of the biodegradable mulching film is integrated, the film can be effectively decomposed by microorganisms in a natural environment and is degraded into carbon dioxide and water, the film does not remain in the soil like traditional plastic mulching films, has good biocompatibility, has little influence on the growth of soil microorganisms and crop roots, can coexist with the soil ecosystem, and part of the material can provide nutrients for soil microorganisms in the degradation process, promote the reproduction of soil microorganisms and improve the soil structure.

[0008] The synthetic biodegradable material polyvinyl alcohol (PVA) has good water solubility, viscosity and stability, can be used as an adhesive, an emulsifier and a dispersant, has excellent film forming property and can significantly improve the tensile strength of the mulching film, has good biodegradability and can be finally decomposed into carbon dioxide and water, and belongs to a typical synthetic degradable polymer material. The natural biopolymer material oxidized starch has good thermal stability, film forming property and freeze-thaw resistance and is a thickening agent with low viscosity and high concentration; the natural biopolymer material carboxymethyl cellulose (CMC) cooperates with starch and PVA to improve the mechanical property of the mulching film; and the natural biopolymer trehalose has good moisturizing property and compatibility, can further optimize the light transmittance of the mulching film, has good stability to heat and acid and alkali, adjusts the degradation rate of the mulching film, is added into the preparation of the mulching film, and can avoid the early failure caused by too fast degradation. The trehalose is mainly fermented by microorganisms such as yeast and bacillus subtilis, the trehalose synthase in the microorganisms converts substrates such as glucose into trehalose, and the cost is low and the yield is high.

[0009] Preferably, the biodegradable mulching film contains 2 parts by weight of the oxidized starch, 2 parts by weight of the hydroxymethyl cellulose, 2 parts by weight of the trehalose, 1.2 parts by weight of the polyvinyl alcohol and 3 parts by weight of the plasticizer.

[0010] Further, the oxidized starch is processed from corn by a sodium hypochlorite oxidation method.

[0011] Specifically, the preparation method of the oxidized starch comprises the following steps: a1: mixing corn starch with water to prepare starch milk with a concentration of 30%-40%; a2: adjusting the pH of the starch milk to 8-10 to create an alkaline reaction environment; a3: slowly adding a sodium hypochlorite solution with a concentration of 5%-10%, controlling the temperature at 20-35°C, and reacting for 1-4 hours while maintaining the pH stable; a4: after the reaction is completed, neutralizing to neutral with an acid, and then washing, dehydrating, and drying to obtain oxidized starch.

[0012] Further, in step a2, an alkali is used to adjust the pH of the starch milk, and preferably, the alkali is sodium hydroxide.

[0013] Further, the mass ratio of the corn starch to the sodium hypochlorite is 10:1-3.

[0014] Further, in step a4, the acid is hydrochloric acid.

[0015] The oxidized starch prepared from corn has good thermal stability, good film-forming property, and good freeze-thaw resistance, and is a thickening agent with low viscosity and high concentration.

[0016] Further, the carboxymethyl cellulose is prepared from wheat straw using a solution method.

[0017] Specifically, the process flow of the preparation of the carboxymethyl cellulose is as follows: wheat straw→pretreatment→wheat straw powder with a mesh size of 40→NaOH treatment→H2O2 treatment→wheat straw cellulose→freeze-thaw cycle method and orthogonal test→homogeneous solution of wheat straw cellulose→etherification reaction of sodium chloroacetate under the condition of 55°C→carboxymethyl cellulose.

[0018] Specifically, the preparation method of the carboxymethyl cellulose comprises the following steps: b1: pretreatment of wheat straw: after removing impurities, the non-molded wheat straw is washed, dried at 60-70°C to a constant weight, and then crushed to pass through a 40-mesh sieve to obtain straw powder; b2: NaOH treatment: the straw powder is added to a 3-5% mass concentration NaOH solution according to a solid-liquid ratio of 1:10-14, and then stirred and reacted at 40-50°C for 2-4h, washed to neutral, and then dried; b3: H2O2 treatment: the dried product is added to a 3-5% mass concentration H2O2 solution according to a solid-liquid ratio of 1:13-17, the pH is adjusted to 10-11, and then reacted at 45-55°C for 1-2h, washed to remove residual H2O2, and then vacuum dried to obtain cellulose; b4 Homogeneous solution preparation: using NaOH concentration of 6-8% and urea concentration of 11-13% aqueous solution, adding cellulose according to solid-liquid ratio 1:23-27, freezing and thawing cycle at least times of-20--16℃ for 5-7h, 23-27℃ for 1-3h, combining L9(3 4 ) orthogonal test to optimize parameters, obtaining homogeneous solution with transmittance ≥90%; b5 Etherification reaction: under the condition of 50-60℃, adding reactants according to the molar ratio of cellulose to sodium chloroacetate 1:2-3, maintaining pH 8-9 for 2-4h, precipitating, washing and drying with 70-80% ethanol to obtain carboxymethyl cellulose.

[0019] The carboxymethyl cellulose prepared from wheat straw is easily dissolved in water, forming a transparent and viscous solution, and the viscosity is proportional to the concentration and temperature, which remains stable below 60℃, and is mainly used as an adhesive to improve the mechanical properties of the mulch film in cooperation with starch and PVA.

[0020] Further, the plasticizer is glycerol.

[0021] As a plasticizer, glycerol can insert between high molecular chains, reduce intermolecular forces, and improve the flexibility and ductility of the mulch film to prevent the mulch film from breaking during use.

[0022] The application also provides a preparation method of the biodegradable mulch film, comprising the following steps: (1) heating 350-450 parts of distilled water, adding oxidized starch, hydroxymethyl cellulose, polyvinyl alcohol, trehalose, stirring and uniformly mixing the plasticizer to obtain a mixed solution; (2) uniformly pouring the mixed solution into a 304 stainless steel plate coated with solid paraffin in advance, the stainless steel plate is smooth and dry, and is placed in a flat place, and is naturally air-dried under room temperature drying conditions, and the formed biodegradable mulch film is taken out.

[0023] The biodegradable mulch film is prepared by simple operation under normal temperature and pressure, and is converted from liquid to solid film at normal temperature, which is safe; the solid paraffin (high-level alkane) used as a good release agent can successfully take out the formed mulch film.

[0024] Further, the thickness of the biodegradable mulch film is 0.1-0.14mm, and the water content of the biodegradable mulch film is 5-7%, preferably 6%.

[0025] Further, in step (1), the distilled water is preferably 400 parts.

[0026] Further, in step (1), the distilled water is heated to 70-90℃.

[0027] The distilled water is heated to 70-90 DEG C, which is beneficial to the raw materials to be dissolved in the solution and to be fully reacted.

[0028] Further, in step (1), the distilled water is heated by water bath heating.

[0029] Preferably, in step (1), after 350-450 parts of distilled water is heated, the oxidized starch is added and stirred uniformly; then the hydroxymethyl cellulose and polyvinyl alcohol are added and stirred uniformly; then the trehalose is added and stirred uniformly; finally, the plasticizer is added and stirred uniformly, without flocculation, to obtain the mixed solution.

[0030] The above-mentioned sequence of adding raw materials has the advantage that the raw materials can react with each other and better form a film.

[0031] Further, in step (1), the stirring speed is 3000-4000 r / min.

[0032] Further, in step (2), the relative humidity of the natural air drying is 40-60%.

[0033] The application further provides the application of the above-mentioned biodegradable mulch film in the field of agricultural product planting.

[0034] Compared with the prior art, the application has the following remarkable beneficial effects: The biodegradable mulch film is compounded by using natural and synthetic organisms as materials, which takes the advantages of both and increases the water resistance, thermal stability, tensile property, etc. of the mulch film; the starch and cellulose are used as main materials, which realizes the resource utilization of agricultural waste and reduces the preparation cost; the mulch film is fully biodegradable, provides the necessary nutrients for the life activities of soil microorganisms after degradation, promotes the reproduction of soil microorganisms, and improves the soil structure; reduces the environmental pollution problem caused by plastic mulch, and helps to realize the sustainable development of agriculture; and the preparation operation is simple, the whole process is under normal temperature and pressure, the liquid is converted into solid film at normal temperature, and the safety is high. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0036] Figure 1 is the tensile strength diagram of the mulch film of the application; Figure 2 is the degradation diagram of the mulch film of the application; Figure 3 is the tomato emergence rate diagram of the application using different mulch films; Figure 4 Figure is a hydrophobic performance chart of the mulch film of the present application. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0038] In the embodiments of the present application, the specific techniques or conditions not specified are performed according to the techniques or conditions described in the literature in the art or according to the product instructions; the reagents or instruments not specified by the manufacturer are all conventional products that can be purchased through a regular channel.

[0039] Embodiment 1 The present embodiment provides a biodegradable mulch film, and the specific preparation method is as follows: (1) 2 parts of oxidized starch, 2 parts of hydroxymethyl cellulose, 2 parts of trehalose, 1.2 parts of polyvinyl alcohol, 3 parts of glycerol and 400 parts of distilled water are weighed by weight parts; The oxidized starch is processed from corn by sodium hypochlorite oxidation method, and the specific steps are as follows: a1. Slurry preparation: corn starch is mixed with water to prepare a starch milk with a concentration of 35%; a2. pH adjustment: the pH value of the starch milk is adjusted to 9 by sodium hydroxide to create an alkaline reaction environment; a3. Oxidation reaction: slowly add 8% concentration sodium hypochlorite solution, control the temperature at 30℃, and maintain the pH stable during the reaction for 3 hours; the mass ratio of the corn starch to the sodium hypochlorite is 5:1; a4. Termination and post-treatment: after the reaction is completed, neutralize to neutral with hydrochloric acid, and then wash, dehydrate and dry to obtain the oxidized starch.

[0040] The carboxymethyl cellulose is processed from wheat straw by solution method, and the specific steps are as follows: b1. Wheat straw pretreatment: after impurity removal, the non-molded wheat straw is washed, dried at 65℃ to constant weight, and then crushed to pass through a 40-mesh sieve to obtain straw powder; b2. NaOH treatment: the straw powder is added to a 4% mass concentration NaOH solution at a solid-liquid ratio of 1:2, stirred at 45℃ for 3h, washed to neutral, and then dried; b3 H2O2 treatment: the above dried product was added into 4% mass concentration H2O2 solution according to solid-liquid ratio 1:5, pH was adjusted to 10.5, reacted at 50℃ for 1.5h, washed until no H2O2 residue, and then vacuum dried to obtain cellulose; b4 homogeneous solution preparation: using NaOH concentration of 7% and urea concentration of 12% aqueous solution, cellulose was added according to solid-liquid ratio 1:25, and the freezing-thawing cycle was repeated twice, i.e. freezing for 6h at-18℃ and thawing for 2h at 25℃, combined with L9(34 4 ) orthogonal test to optimize parameters, and a homogeneous solution with transmittance ≥90% was obtained; b5 etherification reaction: under the condition of 55℃, the reactant was added dropwise according to the molar ratio of cellulose to sodium chloroacetate 1:2.5, and the pH was maintained at 8.5 for 3h, and then carboxymethyl cellulose was obtained by precipitation, washing and drying with 75% ethanol.

[0041] (2) evenly coat solid paraffin on the stainless steel plate; (3) pour 400 parts of distilled water into the enamel cylinder, and under the condition of water bath at 80℃, add oxidized starch, and stir with a high-speed stirrer at 3000r / min for 1.5min; then add hydroxymethyl cellulose and polyvinyl alcohol in turn, and stir at 3000r / min for 1.5min; then add trehalose, and stir at 3500r / min for 1.5min; finally add glycerol, and stir at 3500r / min until the solute and solvent are fully dissolved, and there is no flocculation, to obtain a mixed solution; (4) evenly pour the mixed solution into the stainless steel plate coated with solid paraffin in advance, and place it in a flat place under the condition of room temperature and relative humidity of 50%, and then naturally air dry to form a biodegradable mulch film (referred to as PC) with a thickness of 0.14mm.

[0042] Comparative Example 1 This comparative example provides a preparation method of a biodegradable mulch film, which is different from Example 1 in that the stainless steel plate is not coated with solid paraffin, and the demolding effect of this comparative example is not good.

[0043] Comparative Example 2 This comparative example provides a biodegradable mulch film, and the specific preparation method is as follows: (1) according to weight parts, take 4 parts of oxidized starch, 4 parts of hydroxymethyl cellulose, 3 parts of trehalose, 3 parts of polyvinyl alcohol, 3 parts of glycerol, and 400 parts of distilled water; (2) evenly coat solid paraffin on the stainless steel plate; (3) Pour 400 parts of distilled water into the enamel basin, add oxidized starch under the condition of 80℃ water bath, and stir with a high-speed stirrer at 3000 r / min for 1.5 min; then add hydroxymethyl cellulose in turn, and stir at 3000 r / min for 1.5 min; then add trehalose and polyvinyl alcohol together, and stir at 3500 r / min for 1.5 min; finally add glycerol, and stir at 3500 r / min until the solute and solvent are fully dissolved without flocculation; (4) Pour the mixed solution into a stainless steel plate coated with solid paraffin in advance, and place it in a flat place for natural air drying under room temperature drying conditions; it is found that the solution has moldability, but the prepared film has high viscosity and is not easy to demold.

[0044] Comparative Example 3 This comparative example provides a commercially available polyethylene mulch film, which is a mulch film with a material of polyethylene (PE) produced by Shandong Wanchen Plastic Technology Co., Ltd. (referred to as PE).

[0045] Comparative Example 4 This comparative example provides a commercially available degradable mulch film, which is a degradable mulch film with a material of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) produced by Zhejiang Jiale Honey Company (referred to as PM).

[0046] The biodegradable mulch film prepared in Example 1 (referred to as PC), the commercially available polyethylene mulch film of Shandong Wanchen Plastic Technology Co., Ltd. (referred to as PE), and the commercially available degradable mulch film of Zhejiang Jiale Honey Company (referred to as PM) are tested for performance and agricultural effect.

[0047] Experimental Example 1: Determination of Tensile Resistance of Mulch Film Instrument: tensile tester (Meters E43.104); According to GB / T1040.3-2006 Determination of Tensile Properties of Plastics, the sample is cut into a 1x10 cm strip, and after being baked in a constant temperature oven at 40℃ for 2h, uniaxial tension is performed on a tensile testing machine at a speed of 50 mm / min, and each group has at least 3 times, and the calculation formula is as follows: In the formula, Ts is the tensile strength (MPa), Fm is the maximum tensile stress of the sample (N); W is the width of the sample (mm); T is the thickness of the sample (mm), and the results are shown in Figure 1 .

[0048] Tensile strength reflects the ability of the mulch film to resist external forces, and is determined by Figure 1It can be seen that the tensile strength test shows that the tensile strength of PM mulch is the largest, which is 28.9 Mpa, followed by PE mulch, which is 20.9 Mpa, and PC mulch, which is 1.7 Mpa. According to GB / T35795-2017, PC mulch meets the national standard requirements in terms of tensile strength.

[0049] Experimental example 2: mulch degradability determination Instrument: constant temperature incubator (Zhejiang Topu Yunagri Technology Co., Ltd.); 2x2cm mulch samples were buried in soil (temperature 20℃, soil humidity 77%, pH 7.5), slightly compacted and placed in an incubator (temperature 19~21℃). On the 0th, 9th, 19th day, remove the attached soil as much as possible, observe the surface morphology change of the sample as the mulch degradability, and the results are shown in Figure 2 .

[0050] From Figure 2 It can be seen that after burying the mulch in the soil for 1d, 9d, 19d, the degradation of PE and PM is unchanged, and the edge of PC mulch is damaged on the 19th day.

[0051] Experimental example 3: seed emergence rate Instrument: constant temperature incubator (Zhejiang Topu Yunagri Technology Co., Ltd.); In a 10x4x5cm (lengthxwidthxheight) plastic box, fill in soil, sow 25 tomato seeds, set 3 repeats for each mulch, cover 1cm thick dry fine soil with 20 mesh sieve, evenly spray 100ml distilled water, cover mulch, record as the 0th day, place in the room for 3d (temperature 25℃), spray distilled water appropriately every day to supplement water, record the emergence on the 3rd, 4th, 5th day. The emergence rate calculation formula is as follows: ; In the formula, G R is the seed emergence rate: G is the number of emerged plants: S0 is the number of sown seeds, and the results are shown in Figure 3 .

[0052] The experimental results of the effect of mulching on the emergence rate of tomato seeds show that on the 3rd day, the self-developed PC mulch has a significantly higher emergence rate than the commercial mulch (p<0.05); the emergence rate of PC mulch is still significantly higher than that of other mulches (p<0.05), which is 76%; on the 5th day, the emergence rate of PC mulch is significantly higher than that of other mulches (p<0.05), reaching 89.33%, indicating that PC mulch covering significantly improves the seed emergence rate (p<0.05) Experimental example 4: determination of mulch hydrophobicity Instrument: contact angle measuring instrument (Germany Krussdsa100); The sample of the mulch to be tested is placed flat on the test bench, and distilled water is dropped on the surface of the mulch using a microsyringe. After the water droplet stabilizes, the contact angle is immediately measured by a contact angle measuring instrument. Each sample of mulch is measured 3 times at different locations, and the average value is calculated. The results are shown in Table 1. Figure 4 .

[0053] According to GB / T 30693-2014, the hydrophobicity of mulch is measured by static contact angle. When the static contact angle is less than 90°, the solid surface is hydrophilic, and otherwise it is hydrophobic. The results show that the static contact angle of PE is 95.6°, that of PM is 75.2°, and that of PC is 94.9°. The PM mulch is hydrophilic, and the PE and PC mulches are hydrophobic. The PM is more suitable for mulching under drop irrigation, and the PE and PC can be applied to more application scenarios.

[0054] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A biodegradable mulch film, characterized by, The oxidized starch, the hydroxymethyl cellulose, the trehalose, the polyvinyl alcohol and the plasticizer are prepared. The oxidized starch is 2 parts, the hydroxymethyl cellulose is 2 parts, the trehalose is 2 parts, the polyvinyl alcohol is 1.2 parts and the plasticizer is 3 parts by weight.

2. The biodegradable mulch film according to claim 1, characterized in that, The oxidized starch is 2 parts, the hydroxymethyl cellulose is 2 parts, the trehalose is 2 parts, the polyvinyl alcohol is 1.2 parts and the plasticizer is 3 parts by weight.

3. The biodegradable mulch film according to claim 1 or 2, characterized in that, The oxidized starch is processed by the sodium hypochlorite oxidation method.

4. The biodegradable mulch film according to claim 3, characterized in that, The carboxymethyl cellulose is prepared by the solution method.

5. The biodegradable mulch film according to claim 3, characterized in that, The plasticizer is glycerol.

6. A method of producing the biodegradable mulch film according to any one of claims 1 to 5, characterized by, The method comprises the following steps: (1) 350-450 parts of distilled water is heated, and the oxidized starch, the hydroxymethyl cellulose, the polyvinyl alcohol, the trehalose and the plasticizer are stirred to obtain a mixed solution; (2) The mixed solution is uniformly poured into a 304 stainless steel plate coated with solid paraffin in advance, and is naturally air-dried under room temperature and dry conditions to form a biodegradable mulch.

7. The biodegradable mulch film according to claim 6, characterized in that, In step (1), the distilled water is heated to 70-90℃.

8. The biodegradable mulch film according to claim 6, characterized by In step (1), the distilled water is heated by water bath heating.

9. The biodegradable mulch film according to claim 7 or 8, characterized in that, In step (1), the stirring speed is 3000-4000 r / min.

10. The use of the biodegradable mulch according to any one of claims 1-5 in the field of agricultural product planting.

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