A degradable lignin-based grass-pressing paper mulch film and its preparation method

Abstract

The invention discloses a degradable lignin-based pressed straw paper mulch film and a preparation method thereof. The invention comprises the following steps: dissolving a terminal dihydroxy polyol, a terminal dihydroxy or amino organosiloxane and an organic solvent in a mixed solution; adding a diisocyanate and a catalyst to generate a condensation reaction to obtain an isocyanate-terminated polyurethane prepolymer; adding a chain extender to obtain a long molecular chain polyurethane prepolymer through a chain extension reaction; adding triethylamine to neutralize the carboxylate ions in 2,2-dimethylolbutyric acid to obtain a polyurethane coating; the polyurethane coating is added to water and emulsified to obtain an aqueous polyurethane emulsion; lignin is dissolved in water and slowly added to the aqueous polyurethane emulsion to obtain a lignin-based polyurethane paper-based coating; the lignin-based polyurethane paper-based coating is applied to the surface of a paper-based material to obtain a lignin-based pressed straw paper mulch film. The present invention introduces organosiloxane and lignin into the polyurethane coating to improve its waterproofness and oxidation resistance, reduce light transmittance, and also improve the corresponding performance of the paper-based material after being applied to the paper-based material.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural mulch films, and particularly relates to a degradable lignin-based compressed straw paper mulch film and a preparation method thereof. Background Art

[0002] Agricultural mulch films are important agricultural production materials. Their main function is to effectively control soil temperature and humidity, reduce water and nutrient loss, prevent weed growth, and create a favorable microecological environment for crop growth. Therefore, agricultural mulch films play an important role in the process of increasing agricultural production. However, existing agricultural mulch films are mainly composed of difficult-to-degrade polyethylene and polyvinyl chloride films. These components cannot decompose and disappear on their own in the soil. Long-term use will result in a large amount of mulch film fragments remaining in the soil, destroying the soil structure, bringing great difficulties to tillage and sowing, and greatly restricting the further promotion, application and development of mulch films. Therefore, in recent years, the research on degradable agricultural mulch films has attracted great attention at home and abroad. At present, the research on degradable agricultural mulch films mainly focuses on the following aspects: (1) photodegradable agricultural mulch films, which are made by adding photosensitizers and accelerators to resins; (2) biodegradable agricultural mulch films, including structural degradable mulch films, inorganic salt-containing degradable mulch films and starch-added degradable mulch films; (3) plant fiber mulch films. Among them, plant fiber mulch film is made of plant fiber as the basic raw material, with wet strength agents, preservatives, transparent agents and other additives added to the pulp, and the base paper is made using conventional papermaking technology. It is then processed to make the paper have the mechanical strength, light transmittance, water permeability, heat preservation, warming, moisture retention or other functions required by the mulch film. In the subsequent processing process, it can be decomposed by microorganisms in the soil, and its decomposition products can be used as organic fertilizers to increase soil fertility. Therefore, it has significant advantages among degradable agricultural mulch films.

[0003] In recent years, with the increasing use of pesticides during crop growth, the amount of pesticide residues in crop products has also increased, which has seriously affected my country's food safety. Therefore, among the many paper mulch films, the use of grass film to reduce weed growth can undoubtedly reduce the use of pesticides to a certain extent.

[0004] However, due to the strong water absorption and permeability of paper-based materials, the commonly used compressed straw film still does not reach the performance of traditional polyethylene and polyethylene mulch films in terms of dry and wet strength, air permeability, antioxidant and light transmittance. Therefore, the development of a compressed straw paper mulch film with strong hydrophobicity, good air permeability and low light transmittance is of great significance in reducing weed growth, reducing pesticide use and improving soil quality.

[0005] Lignin is the main component of plant cell walls and the only renewable resource in nature that can provide aromatic compounds. Its content in nature is second only to cellulose. As a filling and bonding material, it adheres to cellulose and hemicellulose to form the main component of the plant skeleton. It has structural rigidity, is not easy to rot, has the ability to resist microbial erosion and has high hydrophobicity. It has the following significant advantages: (1) It is thermoplastic and can soften and flow at high temperatures. This property allows lignin to be used to make various plastics, resins, fibers and other materials; (2) It is hydrophobic and can prevent water from entering the cell wall, increasing the plant's resistance to decay; (3) It has antioxidant properties and can resist free radical damage and delay plant aging. This property allows lignin to be used to make various antioxidants or anti-aging agents. At the same time, this property also allows lignin to undergo oxidation or redox reactions under oxidative conditions to produce various phenolic or aldehyde compounds; (4) It is biodegradable and can be decomposed by some microorganisms and insects, providing an organic carbon source for the ecosystem.

[0006] Therefore, based on the above properties of lignin, developing a lignin-based coating and applying it to the surface of paper-based materials to prepare a pressed grass film with high hydrophobicity, air permeability, antioxidant and low light transmittance is undoubtedly a feasible solution to the above problems. Summary of the Invention

[0007] In response to the problems of poor hydrophobicity and air permeability, high light transmittance, and difficulty in degradation in the long-term use of medium-pressure straw paper mulch in the existing technology, the present invention provides a degradable lignin-based compressed straw paper mulch and a preparation method thereof. The water resistance of the mulch is improved by using organic silicones and lignin, and the oxidation resistance and degradability of the mulch are improved by using lignin, while the light transmittance is reduced. While preventing the growth of weeds, it does not affect the normal growth of crops.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for preparing a degradable lignin-based compressed straw paper mulch film comprises the following steps:

[0010] (1) Dissolving a dihydroxy-terminated polyol, a dihydroxy-terminated or amino-terminated organosiloxane and an organic solvent, and then adding a diisocyanate and a catalyst to cause a condensation reaction under the catalytic action to obtain an isocyanate-terminated polyurethane prepolymer;

[0011] (2) adding a chain extender to the reaction system of step (1) to obtain a long molecular chain polyurethane prepolymer through a chain extension reaction;

[0012] (3) adding triethylamine to the reaction system of step (2) to neutralize the carboxylate ions in 2,2-dihydroxymethylbutyric acid to obtain a polyurethane coating;

[0013] (4) adding the polyurethane coating in step (3) into water, stirring and emulsifying to obtain a waterborne polyurethane emulsion;

[0014] (5) dissolving lignin in water and slowly adding the solution to the aqueous polyurethane emulsion of step (4) to prepare a lignin-based polyurethane paper-based coating;

[0015] (6) The lignin-based polyurethane paper-based coating in step (5) is applied to the surface of the paper-based material to prepare a lignin-based pressed straw paper mulch film.

[0016] Furthermore, the dihydroxy-terminated polyol in step (1) is one or more of polyethylene glycol, polycaprolactone and polytetrahydrofuran; the molecular weight of the dihydroxy-terminated or amino-terminated organosiloxane is 800-5000 g / mol; the diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate and 4,4'-methylenebis(phenyl isocyanate); the catalyst is dibutyltin dilaurate; and the organic solvent is DMF.

[0017] Furthermore, the chain extender in step (2) is 2,2-dihydroxymethylbutyric acid; the lignin in step (3) is sulfate lignin;

[0018] Furthermore, the molar ratio of the terminal dihydroxy polyol to the terminal dihydroxy or amino organosiloxane in step (1) is 1:2 to 2:1; the molar ratio of the total molar amount of the terminal dihydroxy polyol and the terminal dihydroxy or amino organosiloxane to 2,2-dimethylolbutyric acid is 2:1; and the molar ratio of the total hydroxyl and amine groups in the terminal dihydroxy polyol, the terminal dihydroxy or amino organosiloxane and 2,2-dimethylolbutyric acid to the isocyanate in the diisocyanate is 1:2 to 1:4.

[0019] Furthermore, the amount of the catalyst added in step (1) is 0.04-0.1% of the mass of the terminal dihydroxy polyol; the molar ratio of the amount of triethylamine added in step (3) to 2,2-dihydroxymethylbutyric acid is 1:1; and the mass ratio of water to the terminal dihydroxy polyol in step (4) is 100:1-12.

[0020] Furthermore, the lignin accounts for 5 to 50% of the mass of the dihydroxy-terminated polyol, the dihydroxy-terminated or amino-terminated organosiloxane, the diisocyanate and the 2,2-dihydroxymethylbutyric acid.

[0021] Furthermore, the reaction temperature in step (1) is 40-80°C, and the reaction time is 3-10 hours; the reaction temperature in step (2) is 30-80°C, and the reaction time is 3-6 hours; and the reaction temperature in step (3) is 25-40°C, and the reaction time is 1-2 hours.

[0022] Furthermore, in step (6), the coating amount of the lignin-based polyurethane coating is 5-30% of the mass of the paper-based material.

[0023] In the present invention, the degradable lignin-based compressed straw paper mulch film is prepared by the preparation method.

[0024] The preparation method of the lignin-based polyurethane coating in the process of preparing a degradable lignin-based pressed straw paper film according to the present invention is as follows Figure 1 shown, but not limited to.

[0025] Figure 1 This is a method for synthesizing polyurethane coatings. First, a certain amount of polytetrahydrofuran and a diamino-terminated organosiloxane are mixed and placed in a three-necked flask. Under mechanical stirring, the mixture is dissolved in N,N-dimethylformamide. Nitrogen is then applied to the solution. A certain amount of isophorone diisocyanate is added dropwise to the solution using a constant-pressure dropping funnel. After uniform mixing, a certain amount of dibutyltin dilaurate is added. The reaction temperature and time are controlled appropriately to produce two polyurethane prepolymers as shown in the figure. A certain amount of 2,2-dihydroxymethylbutyric acid is dissolved in a certain amount of DMF and slowly added to the above solution for a chain extension reaction. The reaction temperature and time are controlled appropriately to produce polyurethane prepolymers with longer molecular chains and different structures (as shown in ①, ②, and ③ in the figure).

[0026] Beneficial effects

[0027] The present invention introduces organosiloxane and lignin into the polyurethane coating, thereby improving the water resistance and oxidation resistance of the polyurethane coating and reducing the light transmittance of the polyurethane coating. Therefore, after the polyurethane coating is applied to a paper-based material, the corresponding properties of the paper-based material can also be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram of the preparation process of lignin-based polyurethane paper-based coating;

[0029] Figure 2 The figure shows the test results of the oxidation resistance of different compressed straw paper mulches;

[0030] Figure 3 This is the test result of water absorption rate of pressed straw paper mulch;

[0031] Figure 4 This is the light transmittance test result of the straw paper mulch film;

[0032] Figure 5 This is the result diagram of the degradability of compressed straw paper mulch;

[0033] Figure 6 This is a picture of the grass suppression effect of different paper-pressed mulch films. DETAILED DESCRIPTION

[0034] The following describes a method for preparing a degradable lignin-based compressed straw paper mulch film according to the present invention, using specific examples. These examples are provided to further illustrate the present invention and do not limit its scope. Unless otherwise specified, the reagents, equipment, and methods used in the present invention are commercially available and commonly used in the art.

[0035] Example 1

[0036] (1) 4.44 g of polytetrahydrofuran (Mn = 2000 g / mol) was dried under vacuum at 120 °C for 2 h and then mixed with 3.57 g of diamino-terminated organosiloxane (Mn = 800 g / mol). The mixture was then placed in a three-necked flask and dissolved in 20 mL of N,N-dimethylformamide (DMF) under mechanical stirring at 200 r / min. Nitrogen was passed through the flask and 4.44 g of isophorone diisocyanate was added dropwise to the solution using a constant pressure dropping funnel. After mixing evenly, 0.005 g of dibutyltin dilaurate was added and the mixture was reacted at 40 °C for 10 h to obtain a polyurethane prepolymer.

[0037] (2) 0.49 g of 2,2-dihydroxymethylbutyric acid was dissolved in 10 mL of DMF and then slowly added to the above solution to carry out a chain extension reaction. The reaction was carried out at 30 °C for 6 h to obtain a polyurethane prepolymer with a longer molecular chain.

[0038] (3) 0.33 g of triethylamine was added to the reaction system to neutralize the carboxylate ions in 2,2-dihydroxymethylbutyric acid to obtain a polyurethane coating;

[0039] (4) Pour the polyurethane coating into 100 mL of distilled water and emulsify it under stirring to obtain a water-based polyurethane emulsion;

[0040] (5) Add 1.5 g of sodium lignin sulfonate to the aqueous polyurethane emulsion and stir to mix evenly to obtain a lignin-based polyurethane coating;

[0041] (6) The coating is applied to the surface of the paper-based material using a coating rod, and after drying, a degradable lignin-based pressed straw paper film is obtained, wherein the lignin-based polyurethane coating accounts for 5% of the mass of the paper-based material.

[0042] Among the above components, the molar ratio of terminal dihydroxy polyol to terminal diamino organosiloxane is 1:2, the molar ratio of the total molar amount of terminal dihydroxy polyol and terminal diamino organosiloxane to 2,2-dimethylolbutyric acid is 2:1, and the molar ratio of the total hydroxyl group (-OH) in the terminal dihydroxy polyol, terminal diamino organosiloxane and 2,2-dimethylolbutyric acid to the isocyanate (-NCO) in isophorone diisocyanate is 1:2; sodium lignin sulfonate accounts for 11.59% of the total mass of the terminal dihydroxy polyol, terminal diamino organosiloxane, diisocyanate and 2,2-dimethylolbutyric acid.

[0043] Example 2

[0044] (1) 1.33 g of polytetrahydrofuran (Mn = 800 g / mol) was dried under vacuum at 120 °C for 2 h and then mixed with 4.17 g of terminal dihydroxy organic siloxane (Mn = 5000 g / mol). The mixture was then placed in a three-necked flask and dissolved in 20 mL of N,N-dimethylformamide (DMF) under mechanical stirring at 200 r / min. Under nitrogen protection, 4.44 g of isophorone diisocyanate was added dropwise to the above solution using a constant pressure dropping funnel. After mixing evenly, 0.005 g of dibutyltin dilaurate was added and the mixture was reacted at 40 °C for 10 h to obtain a polyurethane prepolymer.

[0045] (2) 0.37 g of 2,2-dihydroxymethylbutyric acid was dissolved in 10 mL of DMF and then slowly added to the above solution to carry out a chain extension reaction. The reaction was carried out at 30 °C for 6 h to obtain a polyurethane prepolymer with a longer molecular chain.

[0046] (3) 0.25 g of triethylamine was added to the reaction system to neutralize the carboxylate ions in 2,2-dihydroxymethylbutyric acid to obtain a polyurethane coating;

[0047] (4) Pour the polyurethane coating into 100 mL of distilled water and emulsify it under stirring to obtain a water-based polyurethane emulsion;

[0048] (5) Add 2.4 g of sulfate lignin to the aqueous polyurethane emulsion and stir to mix evenly to obtain a lignin-based polyurethane coating;

[0049] (6) The coating is applied to the surface of the paper-based material using a coating rod, and after drying, a degradable lignin-based pressed straw paper film is obtained; wherein the lignin-based polyurethane coating accounts for 30% of the mass of the paper-based material.

[0050] Among the above components, the molar ratio of the terminal dihydroxy polyol to the terminal dihydroxy organosiloxane is 2:1, the molar ratio of the total molar amount of the terminal dihydroxy polyol and the terminal dihydroxy organosiloxane to 2,2-dihydroxymethylbutyric acid is 2:1, the molar ratio of the total hydroxyl group (-OH) in the terminal dihydroxy polyol, the terminal dihydroxy organosiloxane and 2,2-dihydroxymethylbutyric acid to the isocyanate (-NCO) in the dibutyltin dilaurate is n(-OH):n(-NCO)=1:4; and the percentage of sulfate lignin in the total amount of the terminal dihydroxy polyol, the terminal dihydroxy organosiloxane, the dibutyltin dilaurate and 2,2-dihydroxymethylbutyric acid is 23.28%.

[0051] Example 3

[0052] (1) 11.17 g of polytetrahydrofuran (Mn = 5000 g / mol) was dried in vacuum at 120 °C for 2 h and mixed with 4.47 g of terminal dihydroxy organic siloxane (Mn = 2000 g / mol). The mixture was then placed in a three-necked flask and dissolved in 20 mL of N,N-dimethylformamide (DMF) under mechanical stirring at 200 r / min. Under nitrogen protection, 4.44 g of isophorone diisocyanate was added dropwise to the above solution using a constant pressure dropping funnel. After mixing evenly, 0.005 g of dibutyltin dilaurate was added and the mixture was reacted at 40 °C for 10 h to obtain a polyurethane prepolymer.

[0053] (2) 0.33 g of 2,2-dihydroxymethylbutyric acid was dissolved in 10 mL of DMF and then slowly added to the above solution to carry out a chain extension reaction. The reaction was carried out at 30 °C for 6 h to obtain a polyurethane prepolymer with a longer molecular chain.

[0054] (3) 0.23 g of triethylamine was added to the reaction system to neutralize the carboxylate ions in 2,2-dihydroxymethylbutyric acid to obtain a polyurethane coating;

[0055] (4) Pour the polyurethane coating into 100 mL of distilled water and emulsify it under stirring to obtain a water-based polyurethane emulsion;

[0056] (5) Add 6.2 g of sulfate lignin to the aqueous polyurethane emulsion and stir to mix evenly to obtain a lignin-based polyurethane coating;

[0057] (6) The coating is applied to the surface of the paper-based material using a coating rod, and after drying, a degradable lignin-based pressed straw paper film is obtained; wherein the lignin-based polyurethane coating accounts for 20% of the mass of the paper-based material.

[0058] Among the above components, the molar ratio of the terminal dihydroxy polyol to the terminal dihydroxy organosiloxane is 1:1, the molar ratio of the total molar amount of the terminal dihydroxy polyol and the terminal dihydroxy organosiloxane to 2,2-dimethylolbutyric acid is 2:1, the molar ratio of the total hydroxyl group (-OH) in the terminal dihydroxy polyol, the terminal dihydroxy organosiloxane and 2,2-dimethylolbutyric acid to the isocyanate (-NCO) in isophorone diisocyanate is n(-OH):n(-NCO)=1:3; and the percentage of lignin in the total amount of the terminal dihydroxy polyol, the terminal dihydroxy organosiloxane, the isophorone diisocyanate and the 2,2-dimethylolbutyric acid is 30%.

[0059] Comparative Example 1

[0060] Compared with Example 1, the coating prepared in this comparative example does not contain lignin.

[0061] Comparative Example 2

[0062] Compared with Example 2, the coating prepared in this comparative example does not contain lignin.

[0063] Comparative Example 3

[0064] Compared with Example 3, the coating prepared in this comparative example does not contain lignin.

[0065] Practical effect examples

[0066] 1. Mechanical properties

[0067] The present invention measures the mechanical properties of Examples 1 to 3 and Comparative Examples 1 to 4 to compare the effects of different lignin contents on the mechanical properties of polyurethane coatings.

[0068] Table 1 Maximum stress strain and fracture absorption energy of the samples

[0069]

[0070] By comparing the above data analysis, it is shown that adding lignin to polyurethane coatings can improve the mechanical strength (stress) of the coatings. This property is beneficial to improving the mechanical properties of paper after the coating is applied to the paper, so that the pressed straw paper can maintain good integrity even in a long-term wind and sun environment.

[0071] 2. Antioxidant properties

[0072] When grass-pressing paper mulch is exposed to the natural environment for a long time and is affected by sunlight, it is easy to produce a large number of free radicals inside the paper, which decompose the cellulose molecular chains inside the paper, causing the paper mulch to become brittle and lose its grass-pressing effect before reaching the plant's growth cycle. Therefore, improving the antioxidant properties of paper mulch is an important way to extend its service life.

[0073] The present invention applies a polyurethane coating with different lignin contents to the surface of a paper material to prepare a lignin-based compressed straw paper mulch film, and then weighs 0.1g of the compressed straw paper mulch films with different lignin contents into 50ml centrifuge tubes, and then adds 10ml of 0.2mmol / l DPPH solution to the centrifuge tubes and shakes them evenly. At the same time, the above different compressed straw paper mulches are placed in 50ml centrifuge tubes, 10ml of anhydrous ethanol is added, and the mixture is shaken evenly as a comparison sample. The absorbance of the sample and the control sample is tested at a wavelength of 517nm using an ultraviolet spectrophotometer. The residual DPPH content is calculated using the following formula to characterize the antioxidant properties of the different compressed straw paper mulches;

[0074]

[0075] Where: is the absorbance of pressed straw paper film in DPPH dilution solution.

[0076] is the absorbance of pressed straw paper film in ethanol solution.

[0077] t is the soaking time, h.

[0078] and is the absorbance at t=0.

[0079] The test results of the antioxidant properties of the compressed straw paper mulch films prepared in the examples of the present invention and the comparative examples (the lower the residual DPPH content, the stronger the antioxidant properties of the compressed straw paper mulch films) are as follows: Figure 2 As shown by Figure 2 It can be seen that compared with Comparative Examples 1 to 3 (pressed straw paper films without lignin), the antioxidant properties of Examples 1 to 3 (pressed straw paper films containing lignin) are significantly improved, indicating that lignin plays an outstanding role in improving the antioxidant properties of pressed straw paper films.

[0080] 3. Water absorption

[0081] One of the key issues that is difficult to resolve when using paper-based materials as pressed grass mulch is that, when exposed to the natural environment for a long time and encountering rainy weather, the pressed grass mulch absorbs a large amount of water, thereby reducing the mechanical properties of the paper-based material and, in turn, its service life. The present invention mixes lignin with water-based polyurethane to prepare a lignin-based water-based polyurethane, which is then coated on the surface of a paper-based material to prepare a lignin-based pressed grass paper mulch film. The water absorption rate of the pressed grass paper mulch film is measured using the following method:

[0082] Cut the pressed straw paper mulch into pieces of appropriate size, weigh them with an analytical balance, and soak them in deionized water. Take out the samples every once in a while, dry the surface moisture with filter paper, and weigh them. Calculate the water absorption rate using the following formula:

[0083]

[0084] Where W is the water absorption rate of the compressed straw paper film, %;

[0085] G is the initial weight of the pressed straw paper mulch, g;

[0086] B is the weight of the compressed straw paper film after it is saturated with water, g.

[0087] The water absorption test results of the straw paper mulch films prepared in the examples of the present invention and the comparative examples are as follows: Figure 3 As shown, through Figure 3 It can be seen that the water absorption rate of the compressed straw paper film without lignin (Comparative Examples 1-3) reaches 20% after 72 hours of water absorption test, while the water absorption rate of the compressed straw paper film containing lignin (Examples 1-3) is only 12% after 72 hours. This shows that lignin has high waterproof performance and can greatly improve the waterproof performance of the compressed straw paper film.

[0088] 4. Light transmittance

[0089] Light is an indispensable element for plant growth. Similarly, the light transmittance of the grass-pressing paper mulch directly determines its grass-pressing performance. The present invention uses ultraviolet-visible spectrometry to measure the light transmittance of the grass-pressing paper mulch prepared in Comparative Examples 1 to 3 and Examples 1 to 3 in the range of 200 to 800 nm. The experimental results are as follows: Figure 4 shown.

[0090] pass Figure 4 The results show that the compressed straw paper film without lignin (Comparative Examples 1-3) has a higher light transmittance, while the transmittance of the compressed straw paper film containing lignin (Examples 1-3) is significantly lower than that of the compressed straw paper film without lignin, and with the increase of lignin content, the transmittance of the compressed straw paper film to light shows a gradually decreasing trend, which indicates that lignin plays an outstanding role in reducing the light transmittance of the compressed straw paper film.

[0091] 5. Degradability

[0092] The compressed straw paper mulch films prepared in Comparative Examples 1 to 3 (excluding lignin) and Examples 1 to 3 were buried in the soil respectively. The mass of the compressed straw paper mulch films was measured at regular intervals, and the mass loss rate was calculated according to the following formula.

[0093]

[0094] Where ω is the water absorption rate of the compressed straw paper film, %;

[0095] m0 is the initial weight of the pressed straw paper mulch, g;

[0096] m is the weight of the compressed straw paper film after it is saturated with water, g.

[0097] The degradability test results of the compressed straw paper mulch films prepared in the examples of the present invention and the comparative examples are as follows: Figure 5 As shown, through Figure 5 It can be clearly seen that after the pressed straw paper mulch prepared by the technical solution of the present invention is buried in the soil, the weight of the pressed straw paper mulch gradually decreases with the extension of time, which shows that the pressed straw paper mulch film has high degradability, and with the increase of lignin content in the pressed straw paper mulch film, its degradation rate shows a gradually increasing trend, which shows that lignin, as a biomass resource, is conducive to the degradation of the pressed straw paper mulch film. At the same time, when the pressed straw paper mulch film is used for 6 months, the degradation rate is not high, which shows that the pressed straw paper mulch film can meet normal needs within the plant growth cycle while degrading.

[0098] 6. Grass pressing performance

[0099] After soaking weed seeds, they were evenly sown in loose and breathable soil and placed in a natural environment. Water (20 mL) was sprayed every other day to maintain soil moisture. The compressed grass paper mulch prepared in Comparative Example 1 and Examples 1 to 3 and commercially available black plastic film were covered on the ungerminated soil surface. After 15 days, photos were taken to observe the growth of weeds. The results are as follows: Figure 6 shown.

[0100] pass Figure 6 It can be clearly seen that the lignin-based compressed grass paper mulch prepared by the technical solution of the present invention can achieve a more obvious grass-suppressing effect compared with the compressed grass paper mulch without lignin (the grass-suppressing effect of Comparative Examples 2 to 3 is similar to that of Comparative Example 1), and the effect is better than the pure plastic mulch available on the market.

Claims

1. A method for preparing a degradable lignin-based compressed straw paper mulch film, characterized in that: The following steps are involved: (1) Dissolving a dihydroxy-terminated polyol, a dihydroxy-terminated or amino-terminated organosiloxane and an organic solvent, and then adding a diisocyanate and a catalyst to cause a condensation reaction under the catalytic action to obtain an isocyanate-terminated polyurethane prepolymer; (2) adding a chain extender to the reaction system of step (1) to obtain a long molecular chain polyurethane prepolymer through a chain extension reaction; (3) adding triethylamine to the reaction system of step (2) to neutralize the carboxylate ions in 2,2-dihydroxymethylbutyric acid to obtain a polyurethane coating; (4) adding the polyurethane coating in step (3) into water, stirring and emulsifying to obtain a waterborne polyurethane emulsion; (5) dissolving lignin in water and slowly adding the solution to the aqueous polyurethane emulsion of step (4) to prepare a lignin-based polyurethane paper-based coating; (6) applying the lignin-based polyurethane paper-based coating in step (5) to the surface of the paper-based material to prepare a lignin-based pressed straw paper mulch film; The molar ratio of the terminal dihydroxy polyol to the terminal dihydroxy or amino organosiloxane is 1:2 to 2:1; the molar ratio of the total molar amount of the terminal dihydroxy polyol and the terminal dihydroxy or amino organosiloxane to 2,2-dimethylolbutyric acid is 2:1; and the molar ratio of the total hydroxyl and amine groups in the terminal dihydroxy polyol, the terminal dihydroxy or amino organosiloxane and 2,2-dimethylolbutyric acid to the isocyanate in the diisocyanate is 1:2 to 1:

4.

2. The method for preparing the degradable lignin-based compressed straw paper mulch film according to claim 1, characterized in that: The dihydroxy-terminated polyol in step (1) is one or more of polyethylene glycol, polycaprolactone and polytetrahydrofuran, the molecular weight of the dihydroxy-terminated or amino-terminated organosiloxane is 800-5000 g / mol, the diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate and 4,4'-methylenebis(phenyl isocyanate), the catalyst is dibutyltin dilaurate, and the organic solvent is DMF.

3. The method for preparing the degradable lignin-based compressed straw paper mulch film according to claim 1, characterized in that: The chain extender in step (2) is 2,2-dihydroxymethylbutyric acid; the lignin in step (3) is sulfate lignin.

4. The method for preparing the degradable lignin-based compressed straw paper mulch film according to claim 1, characterized in that: The amount of the catalyst added in step (1) is 0.04-0.1% of the mass of the terminal dihydroxy polyol; the molar ratio of the amount of triethylamine added in step (3) to 2,2-dihydroxymethylbutyric acid is 1:1; and the mass ratio of water to the terminal dihydroxy polyol in step (4) is 100:1-12.

5. The method for preparing the degradable lignin-based compressed straw paper mulch film according to claim 1, characterized in that: The lignin accounts for 5 to 50% of the mass of the terminal dihydroxy polyol, the terminal dihydroxy or amino organic siloxane, the diisocyanate and the 2,2-dihydroxymethylbutyric acid.

6. The method for preparing the degradable lignin-based compressed straw paper mulch film according to claim 1, characterized in that: The reaction temperature in step (1) is 40-80°C, and the reaction time is 3-10 hours; the reaction temperature in step (2) is 30-80°C, and the reaction time is 3-6 hours; the reaction temperature in step (3) is 25-40°C, and the reaction time is 1-2 hours.

7. The preparation method according to claim 1, characterized in that The coating amount of the lignin-based polyurethane coating in step (6) is 5-30% of the mass of the paper-based material.

8. A degradable lignin-based compressed straw paper mulch film prepared by the preparation method according to any one of claims 1 to 7.

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