Preparation method of lignin-based composite mulching film

Abstract

The invention relates to the technical field of comprehensive utilization of biomass resources, in particular to a preparation method of a lignin-based composite mulching film. According to the method, ammonium lignosulfonate is adopted as a raw material and mixed with a sodium alginate solution, ammonium lignosulfonate-sodium alginate gel is obtained, glutaraldehyde is added into the gel, a catalytic condensation reaction is carried out under the alkaline condition, and the liquid mulching film can be obtained. According to the method, the ammonium lignosulfonate not only contains hydroxyl, but also contains ammonium, the hydroxyl and keto are subjected to aldol condensation reaction, so that a condensation product with a cross-linked spatial network is formed, in the process, the ammonium also reacts with glutaraldehyde, the spatial structure performance of the product is further enhanced, and the molecular weight of the product is increased. Finally, the obtained lignin-based composite mulching film not only has a degradation function, but also is good in tensile property and moisture retention property, can release nitrogen elements in the degradation process, and is beneficial to keeping of soil fertility.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of biomass resources, and in particular to a method for preparing a lignin-based composite mulch film. Background Art

[0002] Lignin is a natural organic compound, one of the main components of plant cell walls, and the second most abundant organic matter in the world. In recent years, with the improvement of environmental awareness and the popularization of the concept of sustainable development, lignin, as a green and sustainable resource, has received more and more attention in the international market.

[0003] Due to the presence of active groups such as aromatic groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, and carbon-based conjugated double bonds in the molecular structure of lignin, it can undergo many chemical reactions such as oxidation, reduction, hydrolysis, alcoholysis, photolysis, sulfonation, halogenation, nitration, polycondensation, or graft copolymerization. Among them, the reaction properties such as oxidation, sulfonation, polycondensation, and graft copolymerization play a particularly important role in the study of the application of lignin, and are also an important way to expand its application. In this process, the sulfonation reaction is the basis and prerequisite for the application of lignin. So far, most of the applications of lignin are used in the form of lignin sulfonates.

[0004] As human society's understanding of environmental issues continues to deepen, in order to solve the "white pollution" caused by abandoned mulch films, develop sustainable agriculture, achieve a benign interaction between humans and the environment, and establish an environmentally friendly society; therefore, the present invention proposes a method for preparing a lignin-based composite mulch film. The prepared degradable mulch film is non-toxic and pollution-free, has good tensile strength and moisture retention properties, and can release nitrogen during the natural degradation process, which also plays a positive and beneficial role in maintaining soil fertility. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a lignin-based composite mulch film, so as to solve the problem that traditional mulch films are non-degradable, cause "white pollution" and are not conducive to environmental protection.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a method for preparing a lignin-based composite mulch film, comprising the following steps:

[0007] S1, using ammonium lignin sulfonate as a raw material, adding ammonium lignin sulfonate to a sodium alginate aqueous solution, stirring and mixing thoroughly to obtain ammonium lignin sulfonate-sodium alginate gel;

[0008] S2, adding glutaraldehyde solution, catalyst, pH regulator and plasticizer to the gel obtained in S1, and obtaining a liquid mulch film after sufficient reaction;

[0009] S3, forming the liquid mulch film obtained in S2 and drying it to obtain the lignin-based composite mulch film of the present invention.

[0010] Furthermore, in S1, the ammonium lignin sulfonate is made from modified lignin, and the source of lignin includes but is not limited to hardwood lignin, softwood lignin and gramineous plant lignin.

[0011] Furthermore, in the S1, the mass ratio of ammonium lignin sulfonate, sodium alginate and solvent water is 1-3:1:50-100.

[0012] Furthermore, in the above-mentioned S1, the temperature for stirring and mixing the ammonium lignin sulfonate and the sodium alginate is 60-80° C., the time for stirring and mixing is 10-30 min, and the stirring intensity is 100-400 rpm.

[0013] Furthermore, in the S2, the catalyst is a solid base catalyst, the pH adjuster is a sodium bicarbonate solution, and the plasticizer is glycerol.

[0014] Furthermore, the mass fraction of the glutaraldehyde solution is 25%, and the added amount is 5-10% of the mass of the ammonium lignin sulfonate-sodium alginate gel; the solid base catalyst is BaO / Al 2 O 3 The particle size is 100-200 meshes, and the added amount is 10-20% of the mass of the ammonium lignin sulfonate-sodium alginate gel; the pH value during the reaction is controlled to be 7-9; the added amount of glycerol is 1-5% of the mass of the ammonium lignin sulfonate-sodium alginate gel.

[0015] Furthermore, during the reaction process, the temperature is 60-80° C., the reaction time is 2-4 hours, and the stirring intensity is 100-400 rpm.

[0016] Furthermore, after the reaction is completed, the solid base catalyst is separated by filtering while hot.

[0017] Furthermore, in the above S3, the obtained liquid mulch is unfolded, and the thickness of the liquid mulch after unfolding is 0.1-0.3 g / cm 2 ; The drying temperature is 50-60°C and the drying time is 6-12h.

[0018] Furthermore, the tensile strength of the lignin-based composite mulch film is 8-10 MPa, and the water vapor permeability is less than 0.5×10 -6 g·m -1 ·Pa -1 ·h -1 .

[0019] Beneficial effects of the present invention:

[0020] 1. The lignin-based degradable mulch film obtained by the method of the present invention solves the problem of "white pollution" caused by traditional non-degradable mulch films, is more environmentally friendly, and contributes to the development of sustainable agriculture and the establishment of an environmentally friendly society;

[0021] 2. The lignin-based degradable mulch film obtained by the method of the present invention has good film-forming properties. The addition of sodium alginate not only makes the mulch film of the present invention have good film-forming properties, but the hydroxyl groups in the sodium alginate can also undergo an aldol condensation reaction with the ketone groups, thereby enhancing the tensile properties and soil moisture retention properties of the mulch film of the present invention, making it more convenient for practical application.

[0022] 3. The lignin obtained by the method of the present invention can degrade the mulch film and release nitrogen during the degradation process, thereby helping to maintain soil fertility and being more convenient for use in agricultural production. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0024] Example 1

[0025] Take a three-necked flask, add 100 mL of deionized water into it, and continue to add 1.5 g of sodium alginate to the three-necked flask with a stirring intensity of 200 rpm. After stirring and dissolving, continue to add 3 g of ammonium lignin sulfonate and increase the temperature at the same time. When the temperature reaches 70°C, stop heating and continue stirring for 20 minutes to ensure that the ammonium lignin sulfonate and sodium alginate are fully mixed.

[0026] To the above reaction system, 8 g of 25% glutaraldehyde solution and 15 g of solid base catalyst BaO / Al were added. 2 O 3 and 3g of propylene glycol, maintaining the aforementioned stirring and temperature conditions unchanged, continuing the reaction, and constantly adjusting the pH of the reaction system during the process. The pH of the reaction system is controlled to be 7-9 by adding sodium bicarbonate solution drop by drop. The reaction is continued for 3h, and then filtered while hot to remove the solid base catalyst in the reaction system to obtain a liquid mulch film.

[0027] The obtained liquid mulch film is spread out to control the thickness of the mulch film to be between 0.1 and 0.3 g / cm 2 , and then drying at 50-60° C. to obtain the lignin-based composite mulch film of the present invention.

[0028] After testing, the tensile strength of the lignin-based composite mulch obtained in this example is 8.6 MPa, and the water vapor permeability is 0.463×10 -6 g·m -1 ·Pa -1 ·h -1, has good tensile strength and soil moisture retention, and is easy to use in actual production.

[0029] Comparative Example 1

[0030] In this comparative example, sodium lignin sulfonate was used to replace the ammonium lignin sulfonate in Example 1, and the rest was the same as in Example 1, and finally a lignin-based composite mulch film was obtained.

[0031] After testing, the tensile strength of the lignin-based composite mulch obtained in this comparative example is 10.3 MPa, and the water vapor permeability is 0.729×10 -6 g·m -1 ·Pa -1 ·h -1 It can be seen that although the tensile strength of the lignin-based composite mulch film obtained in this comparative example is improved, its water vapor permeability is obviously poor, which is not conducive to soil moisture retention; the reason is that in this comparative example, only the alcohol-aldehyde condensation reaction occurs, and there is no reaction between ammonium root and aldehyde, thereby increasing the cross-linking degree between sodium lignin sulfonate and pentanediol, thereby increasing the tensile strength; and the increase in water vapor permeability is due to the insufficient dense cross-linking in the microstructure.

[0032] Comparative Example 2

[0033] In this comparative example, no solid base catalyst was added during the reaction, and the other steps were the same as those in Example 1, and a lignin-based composite ground film was finally obtained.

[0034] After testing, the tensile strength of the lignin-based composite mulch obtained in this comparative example is 2.2 MPa. It can be seen that without the use of a solid base catalyst, the efficiency of the reaction process is significantly reduced, the ammonium lignin sulfonate and glutaraldehyde are not fully cross-linked, and are combined together by van der Waals forces, resulting in low tensile strength, which is not conducive to practical application.

[0035] Comparative Example 3

[0036] In this comparative example, the effects of the degradable lignin-based composite mulch films obtained in Example 1 and Comparative Example 1 on soil fertility were investigated.

[0037] Take two glass jars of the same specifications, A and B, and add 2 kg of cultivated soil from the same batch into them. The nitrogen content in the cultivated soil is tested to be 2.44 g / kg.

[0038] The soil in glass jar A was covered with the lignin-based composite mulch film of Example 1, and the soil in glass jar B was covered with the lignin-based composite mulch film of Comparative Example 1; glass jar A and glass jar B were tested under the same conditions, during which the ambient temperature was controlled at 30°C and the lighting time was 12 h / day. 100 mL of deionized water was added to glass jar A and glass jar B along the wall every 3 days, and the test lasted for 30 days.

[0039] After the experimental investigation, the nitrogen content and moisture content of the soil in glass cylinder A and glass cylinder B were tested. The test showed that the nitrogen content of the soil in glass cylinder A was 2.39 g / kg, and the moisture content was 42.7%; the nitrogen content of the soil in glass cylinder B was 2.21 g / kg, and the moisture content was 33.2%.

[0040] It can be seen that the lignin-based composite mulch film of the present invention plays a positive and effective role in maintaining soil fertility, helps to delay the loss of soil fertility, and helps to maintain moisture in the soil, and has broad application prospects in agricultural production.

[0041] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based composite mulch film, characterized in that: The following steps are involved: S1, using ammonium lignin sulfonate as a raw material, adding ammonium lignin sulfonate to a sodium alginate aqueous solution, stirring and mixing thoroughly to obtain ammonium lignin sulfonate-sodium alginate gel; S2, adding glutaraldehyde solution, catalyst, pH regulator and plasticizer to the gel obtained in S1, and obtaining a liquid mulch film after sufficient reaction; S3, forming the liquid mulch film obtained in S2 and drying it to obtain the lignin-based composite mulch film of the present invention.

2. The method for preparing a lignin-based composite mulch film according to claim 1, characterized in that: In S1, the ammonium lignin sulfonate is prepared by modifying lignin, and the source of lignin includes but is not limited to hardwood lignin, softwood lignin and gramineous plant lignin.

3. The method for preparing a lignin-based composite mulch film according to claim 1, characterized in that: In the S1, the mass ratio of ammonium lignin sulfonate, sodium alginate and solvent water is 1-3:1:50-100.

4. The method for preparing a lignin-based composite mulch film according to claim 1, characterized in that: In the above-mentioned S1, the temperature for stirring and mixing ammonium lignin sulfonate and sodium alginate is 60-80° C., the time for stirring and mixing is 10-30 min, and the stirring intensity is 100-400 rpm.

5. The method for preparing a lignin-based composite mulch film according to claim 1, characterized in that: In the S2, the catalyst is a solid base catalyst, the pH regulator is a sodium bicarbonate solution, and the plasticizer is glycerol.

6. The method for preparing a lignin-based composite mulch film according to claim 5, characterized in that: The mass fraction of the glutaraldehyde solution is 25%, and the added amount is 5-10% of the mass of the ammonium lignin sulfonate-sodium alginate gel; the solid base catalyst is BaO / Al2O3, the particle size is 100-200 meshes, and the added amount is 10-20% of the mass of the ammonium lignin sulfonate-sodium alginate gel; the pH value during the reaction is controlled to be 7-9; and the added amount of glycerol is 1-5% of the mass of the ammonium lignin sulfonate-sodium alginate gel.

7. The method for preparing a lignin-based composite mulch film according to claim 6, characterized in that: The temperature during the reaction is 60-80° C., the reaction time is 2-4 hours, and the stirring intensity is 100-400 rpm.

8. The method for preparing a lignin-based composite mulch film according to claim 7, characterized in that: After the reaction is completed, the solid base catalyst is separated by filtering while hot.

9. The method for preparing a lignin-based composite mulch film according to claim 1, characterized in that: In the above S3, the obtained liquid mulch film is unfolded, and the thickness of the liquid mulch film after unfolding is 0.1-0.3 g / cm 2 ; The drying temperature is 50-60°C and the drying time is 6-12h.

10. A method for preparing a lignin-based composite mulch film according to any one of claims 1 to 9, characterized in that: The tensile strength of the lignin-based composite mulch is 8-10 MPa, and the water vapor permeability is less than 0.5×10 -6 g·m -1 ·Pa -1 ·h -1 .