CN114957896A - Preparation method of degradable mulching film - Google Patents
Preparation method of degradable mulching film Download PDFInfo
- Publication number
- CN114957896A CN114957896A CN202210685691.8A CN202210685691A CN114957896A CN 114957896 A CN114957896 A CN 114957896A CN 202210685691 A CN202210685691 A CN 202210685691A CN 114957896 A CN114957896 A CN 114957896A
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- CN
- China
- Prior art keywords
- mulching film
- degradable
- degradable mulching
- liquid
- humic acid
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- 238000002360 preparation method Methods 0.000 title claims abstract description 31
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- QJZYHAIUNVAGQP-UHFFFAOYSA-N 3-nitrobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid Chemical compound C1C2C=CC1C(C(=O)O)C2(C(O)=O)[N+]([O-])=O QJZYHAIUNVAGQP-UHFFFAOYSA-N 0.000 claims abstract description 94
- 239000004021 humic acid Substances 0.000 claims abstract description 94
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- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical group [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 claims description 26
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- FQENQNTWSFEDLI-UHFFFAOYSA-J sodium diphosphate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-]P([O-])(=O)OP([O-])([O-])=O FQENQNTWSFEDLI-UHFFFAOYSA-J 0.000 claims description 4
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- GZCGUPFRVQAUEE-SLPGGIOYSA-N aldehydo-D-glucose Chemical compound OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C=O GZCGUPFRVQAUEE-SLPGGIOYSA-N 0.000 claims description 2
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
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- 102000004190 Enzymes Human genes 0.000 description 2
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- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
-
- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
- A01G13/00—Protecting plants
- A01G13/02—Protective coverings for plants; Coverings for the ground; Devices for laying-out or removing coverings
- A01G13/0256—Ground coverings
- A01G13/0268—Mats or sheets, e.g. nets or fabrics
- A01G13/0275—Films
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2401/00—Characterised by the use of cellulose, modified cellulose or cellulose derivatives
- C08J2401/08—Cellulose derivatives
- C08J2401/26—Cellulose ethers
- C08J2401/28—Alkyl ethers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2403/00—Characterised by the use of starch, amylose or amylopectin or of their derivatives or degradation products
- C08J2403/02—Starch; Degradation products thereof, e.g. dextrin
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2489/00—Characterised by the use of proteins; Derivatives thereof
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2491/00—Characterised by the use of oils, fats or waxes; Derivatives thereof
- C08J2491/06—Waxes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/32—Phosphorus-containing compounds
- C08K2003/321—Phosphates
- C08K2003/324—Alkali metal phosphate
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/04—Oxygen-containing compounds
- C08K5/05—Alcohols; Metal alcoholates
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
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- C08K5/04—Oxygen-containing compounds
- C08K5/05—Alcohols; Metal alcoholates
- C08K5/053—Polyhydroxylic alcohols
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/16—Nitrogen-containing compounds
- C08K5/17—Amines; Quaternary ammonium compounds
- C08K5/19—Quaternary ammonium compounds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
- C08K5/41—Compounds containing sulfur bound to oxygen
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
- Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
- Y02A40/28—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture specially adapted for farming
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Engineering & Computer Science (AREA)
- Medicinal Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- General Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental Sciences (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Protection Of Plants (AREA)
Abstract
The invention discloses a preparation method of a degradable mulching film, which comprises the following steps: respectively preparing a polyvinyl alcohol solution, a starch pasty liquid and a humic acid solution; uniformly mixing the polyvinyl alcohol solution, the starch pasty liquid and the humic acid solution to obtain a mixed raw material solution; adding the following auxiliary agents into the mixed raw material liquid in sequence: plasticizers, emulsifiers, mineral binders, reinforcing agents, defoamers and wet strength agents; adding the next auxiliary agent after the former auxiliary agent is completely dispersed; after all the auxiliary agents are added, continuously stirring and uniformly mixing, adding phosphoric acid to adjust the pH value, and filtering with gauze to obtain the degradable mulching solution; and slowly stirring the degradable mulching film liquid before use, and uniformly spraying the degradable mulching film liquid on the ground when the degradable mulching film liquid is stirred to be granular, so as to obtain the degradable mulching film. The degradable biological mulching film is prepared by taking polyvinyl alcohol, starch and humic acid as raw materials, and is easy to degrade, good in waterproofness and high in mechanical property.
Description
Technical Field
The invention relates to the technical field of degradable mulching films. In particular to a preparation method of a degradable mulching film.
Background
In agricultural production, the main component of the agricultural covering film is polyethylene or polyvinyl chloride, and the general molecular weight of the agricultural covering film is 25000-30000. Because the molecular structure is relatively fixed and is not easy to degrade, after the agricultural mulching film is applied in a large range for a long time, a large amount of residual film fragments of the agricultural mulching film can be accumulated on a soil plough layer and gradually damage the functional structure of the soil, so that the soil hardening, the air permeability deterioration, the propagation difficulty of plant root systems and the like are caused, and inestimable bad influence is formed on the ecological environment of the cultivated land, so the environmental pollution of the soil mulching film becomes the most serious ecological problem in the Xinjiang area at present. The use of degradable soil mulching film is one of the main means for removing the environmental pollution of the mulching film.
The polyethylene is a main component of the traditional mulching film, is generally black or transparent, is mainly used for covering soil, improving the temperature of the soil, keeping a good soil structure, preventing the loss of soil moisture, preventing and treating plant diseases and insect pests, soil diseases and the like, and can improve the growth and development of crops. The traditional mulching film is difficult to degrade under natural conditions, the degradation period is as high as more than 200 years, and a series of hazards are brought to the agricultural production environment, so that the traditional mulching film is called as farmland 'white pollution'. The residual film remained in the soil can cut off or change the continuity of soil pore modification, so that the infiltration of water is reduced along with the increase of the residual film, the water content and the ventilation performance of the soil are reduced, the activity of soil microorganisms and the formation of a normal soil structure are influenced, and finally, the root system of crops is difficult to grow and develop, thereby causing the yield reduction of the crops.
The degradable mulching film is a mulching film which is degraded under natural conditions through the activity of soil microorganisms. The mulching film can be divided into an incomplete biodegradation mulching film and a complete biodegradation mulching film according to a degradation mechanism, and microorganisms decompose the mulching film into lower molecular compounds after the mulching film is used, and finally the lower molecular compounds are converted into inorganic substances such as water, carbon dioxide and the like. An effective way to solve the 'white pollution' is to widely popularize the biodegradable mulching film. Different formulas have great influence on various performances of the biodegradable mulching film, and the mulching film is also limited by environmental factors.
At present, the research on the biodegradable mulching film mainly focuses on field experiments, the influence of the mulching film on soil temperature, water and crop yield is mainly considered, and the research on the influence of the material type and the use amount of a film forming auxiliary agent of the biodegradable mulching film on the performance of the humic acid degradable mulching film and the optimization research on the hydrolysis performance of the mulching film are less. In order to ensure the degradability of the biological mulching film, the existing biological degradation mulching film generally has the defects of poor waterproofness, non-ideal mechanical properties and the like, so that the application effect of the existing biological degradation mulching film is limited compared with the traditional mulching film due to no advantages, and the popularization is limited, so that the preparation of the degradable mulching film with good waterproofness and excellent mechanical properties is the key for popularizing the biological degradation mulching film.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to provide a preparation method of a degradable mulching film, so as to solve the problem that the existing biodegradable mulching film cannot have degradability, waterproofness and mechanical properties at the same time.
In order to solve the technical problems, the invention provides the following technical scheme:
a preparation method of the degradable mulching film comprises the following steps:
step A: respectively preparing a polyvinyl alcohol solution, a starch pasty liquid and a humic acid solution;
and B: uniformly mixing the polyvinyl alcohol solution, the starch pasty liquid and the humic acid solution to obtain a mixed raw material solution; because polyvinyl alcohol is insoluble in water at normal temperature, the polyvinyl alcohol is usually dissolved in boiling water and then cooled to prepare a polyvinyl alcohol solution; the starch is also insoluble in water, and when the addition amount of the starch is slightly more, wrapping particles are easily formed, and the dispersibility is poor, so that the polyvinyl alcohol, the starch and the humic acid are prepared into dispersion liquid respectively and then mixed, and the condition of uneven mixing caused by one-step mixing can be effectively avoided;
step C: adding the following auxiliary agents into the mixed raw material liquid in sequence: plasticizers, emulsifiers, mineral binders, reinforcing agents, defoamers and wet strength agents; adding the next auxiliary agent after the former auxiliary agent is completely dispersed; after all the auxiliary agents are added, continuously stirring and uniformly mixing, adding phosphoric acid to adjust the pH value, and filtering with gauze to obtain the degradable mulching solution; the plasticizer is added firstly, so that the fluidity of the mixed solution is improved, and the emulsifier is added secondly, so that the later rapid dissolution and dispersion of various auxiliary agents are facilitated; the purpose of filtering by using gauze is to filter non-dispersed particulate matters so as to avoid the occurrence of particulate foreign matters on the mulching film formed by the degradable mulching film liquid during film forming;
step D: and slowly stirring the degradable mulching film liquid before use, and uniformly spraying the degradable mulching film liquid on the ground when the degradable mulching film liquid just generates granules to obtain the degradable mulching film. When the degradable mulching liquid generates granular substances, chemical reaction is generated inside the degradable mulching liquid, the film is formed in the solution, and spraying is needed as soon as possible at the moment to avoid the influence of the precipitation of the auxiliary agent on the spraying effect.
In the step A, the relative molecular mass of the polyvinyl alcohol is 10-30 ten thousand, and the alcoholysis degree is greater than or equal to 85 mol%; if the molecular weight of the polyvinyl alcohol is smaller, the formed film has lower strength and is easy to damage; however, if the molecular weight is too high, the solubility is poor, the solution fluidity is low, and the film to be formed is thick. The polyvinyl alcohol has higher alcoholysis degree, is favorable for forming hydrogen bonds or carrying out chemical reaction with other two raw materials, and has more stable structure and higher strength.
The preparation method of the polyvinyl alcohol solution comprises the following steps: adding polyvinyl alcohol into water, heating and stirring for 2.5-3.5 hours at 90-100 ℃ to completely dissolve the polyvinyl alcohol, and obtaining a polyvinyl alcohol solution;
the preparation method of the starch paste liquid comprises the following steps: adding water into starch, heating and stirring for 1-2 hours at 50-80 ℃ to enable the starch and the water to form viscous pasty liquid, and obtaining starch pasty liquid; heating and stirring the starch for 1-2 hours is beneficial to hydrolyzing the starch into cyclodextrin and the like with lower molecular weight, and is beneficial to more uniform distribution of the starch;
the preparation method of the humic acid solution comprises the following steps: dissolving humic acid in water, mixing, stirring and filtering to prepare a humic acid solution; humic acid contains ash content of 10 wt% or less, water content of 8 wt% or less, and iron content of 0.3 wt% or less, and is produced by Tianjin Bailungsi Biotechnology Co.
According to the preparation method of the degradable mulching film, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 2-5 wt%; the mass fraction of starch in the starch paste liquid is 8-11 wt%, and the starch is corn starch; the mass fraction of humic acid in the humic acid solution is 1-5 wt%.
In the step B, the mass ratio of the polyvinyl alcohol solution to the starch paste solution to the humic acid solution is 24-40: 10-16: 23-40.
According to the preparation method of the degradable mulching film, the mass ratio of the polyvinyl alcohol solution to the starch paste solution to the humic acid solution is 2.4:1: 2.3. The amount of polyvinyl alcohol has an influence on whether the mulching film can be finally used by a spraying method, and if too much prepared solution cannot be used by the spraying method, film formation cannot be realized if too little prepared solution is used. The starch used is degradable, and the degradation time of the mulching film is adjusted to a certain extent. Humic acid is used as an important raw material, the color of the mulching film is effectively changed, and organic matters in soil can be increased after the mulching film is degraded.
In the preparation method of the degradable mulching film, in the step C, the plasticizer is glycerol and/or ethylene glycol; the emulsifier is one or a mixture of two or more of sodium dodecyl sulfate, sodium pyrophosphate and liquid paraffin; the mineral binder is sodium silicate, and the reinforcing agent is sodium carboxymethylcellulose and/or gelatin; the defoaming agent is n-octanol and/or soybean oil; the wet strength agent is one or the mixture of two or more of polyamide epichlorohydrin resin PAE, acrylic resin PAA, urea-formaldehyde resin UF, melamine formaldehyde resin MF or glyoxal modified acrylamide.
In the step C, the plasticizer is glycerol, the emulsifier is sodium dodecyl sulfate, the mineral binder is sodium silicate, the reinforcing agent is sodium carboxymethyl cellulose, the defoaming agent is n-octanol, and the wet strength agent is polyamide epichlorohydrin resin PAE.
The preparation method of the degradable mulching film comprises the following steps: the weight of glycerol is 40-70 wt% of the weight of the starch paste liquid, the weight of sodium dodecyl sulfate is 3-9 wt% of the weight of the starch paste liquid, the weight of sodium water glass is 3-12 wt% of the weight of the starch paste liquid, the weight of sodium carboxymethyl cellulose is 0.8-2.6 wt% of the weight of the starch paste liquid, the weight of n-octanol is 0.2-1.2 wt% of the weight of the starch paste liquid, and the weight of polyamide epichlorohydrin resin PAE is 0.5-3 wt% of the weight of the starch paste liquid.
According to the preparation method of the degradable mulching film, in the step C, phosphoric acid is added to adjust the pH value of the degradable mulching film to 7.5, phosphorus in the phosphoric acid is an essential nutrient element for crops, the adverse effect of the pH value adjusted by the phosphoric acid on soil is small, the pH value of the degradable mulching film is adjusted to 7.5 to be close to neutral and slightly alkaline, and the influence of too low or too high pH value on the acidity and alkalinity of the soil can be avoided.
In the step D, the stirring speed of the degradable mulching film liquid is 100-500 rpm, and the stirring time is 1-2 hours; standing for 16-24 hours after spraying to obtain the degradable mulching film; the stirring is used for accelerating the film forming of the film forming agent, the film forming is too fast due to the too fast stirring, the dispersing of the auxiliary agent is not uniform, and the insufficient dispersing of the auxiliary agent is caused due to the too slow stirring.
The technical scheme of the invention achieves the following beneficial technical effects:
1. the degradable biological mulching film which is easy to degrade, good in waterproofness and high in mechanical property is prepared by taking polyvinyl alcohol, starch and humic acid as raw materials and adding a plasticizer, an emulsifier, an ore binder, a reinforcing agent, a defoaming agent and a wet strength agent.
2. The starch and the polyvinyl alcohol both have high-strength hydrophilicity, and PAE resin is added as a wet strength agent in the film forming process, so that the mulching film still has the mechanical strength meeting the requirements after being wetted by water; the wet strength agent PAE resin is combined with the hydroxyl in the degradable mulching film to form a covalent bond, so that the degradable mulching film has a better waterproof effect. A part of high molecular polymers in the wet strength agent resin are doped among fibers of the mulching film, and a staggered chain structure is formed near the fibers, so that the performances of preventing starch and polyvinyl alcohol from absorbing water and wetting, reducing deformation of the mulching film and the like are realized, and the wet strength of the mulching film is improved.
3. At the in-process of preparation degradable plastic film, can produce a large amount of bubbles in the degradable plastic film liquid owing to the stirring, the existence of these bubbles can lead to fashioned plastic film mechanical properties relatively poor, adds the defoaming agent, not only can eliminate the bubble when the stirring, and the existence of defoaming agent can cooperate other assistants effectively to reduce the surface tension of degradable plastic film liquid in film forming process moreover to show the mechanical properties that promotes degradable plastic film.
Drawings
FIG. 1 is a schematic flow chart of a preparation process of the degradable mulching film in the embodiment of the invention;
FIG. 2 is a graph showing the effect of polyvinyl alcohol content on the tensile strength and elongation at break of a mulching film in an example of the present invention;
FIG. 3 is a graph showing the influence of humic acid content on the tensile strength and elongation at break of the mulching film in the example of the present invention;
FIG. 4 is a graph showing the effect of glycerol usage on tensile strength and elongation at break of a mulching film in an example of the present invention;
FIG. 5 is a graph showing the effect of sodium dodecyl sulfate on the tensile strength and elongation at break of a mulching film according to an embodiment of the present invention;
FIG. 6 is a graph showing the effect of sodium carboxymethylcellulose on the tensile strength and elongation at break of a mulching film according to an embodiment of the present invention;
FIG. 7 is a graph showing the effect of sodium silicate usage on the tensile strength and elongation at break of a mulching film in an example of the present invention;
FIG. 8 is a graph showing the effect of heating temperature on gelation time of a degradable mulching film according to an embodiment of the present invention;
FIG. 9 is a graph of the 1/T-Int curve of the degradable mulching film in the embodiment of the invention;
FIG. 10 is a graph showing the influence of temperature on the weight loss rate of the degradable mulching film in the embodiment of the present invention;
FIG. 11 is a graph showing the effect of pH on weight loss rate of degradable mulching film in the embodiment of the present invention;
FIG. 12 is a graph illustrating the effect of hydrophobic modifier species on water absorption of a degradable mulch film in an embodiment of the invention;
FIG. 13 is a graph illustrating the effect of the type of hydrophobizing modifier on the wet strength of a degradable mulch film in an embodiment of the present invention;
FIG. 14 is a graph showing the effect of the amount of polyamide epichlorohydrin resin (PAE) used in the examples of the present invention on the degradable plastic film tensile strength and wet strength;
FIG. 15 is a graph showing the effect of n-octanol dosage on degradable film tensile strength and elongation at break in examples of the present invention;
FIG. 16 is a graph showing a relationship between a weight loss ratio of a degradable mulching film and soil burying time in an embodiment of the present invention;
FIG. 17 is a graph showing the relationship between the molecular weight of the degradable mulching film and the burying time;
FIG. 18 is a scanning electron microscope image (x 1000) of the common mulching film degraded for 30d in the embodiment of the present invention;
FIG. 19 is an electron microscope scanning image (x 1000) of the degradable mulching film a after being degraded for 30d in the embodiment of the invention;
FIG. 20 is an electron microscope scanning image (x 1000) of the degradable mulching film b after being degraded for 30d in the embodiment of the invention;
FIG. 21 is an electron microscope scanning image (x 1000) of the degradable mulching film c after being degraded for 30d in the embodiment of the invention;
FIG. 22 is a diagram of a substance of degradable mulching solution prepared when preparing the degradable mulching film c in the embodiment of the present invention;
FIG. 23 is a diagram of a film forming object after spraying of the degradable mulching solution in the embodiment of the present invention;
FIG. 24 is a pictorial view of a piece of paper after the degradable mulching film is formed and removed in an embodiment of the invention.
Detailed Description
First part of the materials and methods
1.1 Experimental materials, reagents and instruments
(1) The experimental materials used in this example are shown in table 1.
TABLE 1
(2) The experimental reagents used in this example are shown in table 2.
TABLE 2
(3) The experimental apparatus used in this example is shown in table 3.
TABLE 3
1.2 preparation of degradable mulching film
(1) Preparation method of humic acid degradable mulching film
Preparing degradable mulching liquid: putting 10g of polyvinyl alcohol into 250mL of water, heating at 100 ℃ for about 3h, and cooling to room temperature after the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution for later use; dissolving 10g of corn starch in 100mL of water, heating and stirring for 1h at 60 ℃ to obtain a viscous paste, and obtaining a starch paste for later use; dissolving 10g of humic acid (the ash content of the humic acid is less than or equal to 10wt percent), the water content is less than or equal to 8wt percent, and the iron content is less than or equal to 0.3wt percent) in 250mL of water, and filtering to obtain a humic acid solution for later use; mixing the prepared polyvinyl alcohol solution, the starch pasty liquid and the humic acid solution together to obtain a mixed raw material liquid; adding the following auxiliary agents into the mixed raw material liquid in sequence: glycerol or glycol serving as a plasticizer, sodium dodecyl sulfate, sodium pyrophosphate or liquid paraffin serving as an emulsifier, sodium silicate serving as an ore binder (sodium silicate is dissolved in water to form sodium silicate), sodium carboxymethyl cellulose or gelatin serving as a reinforcing agent, n-octyl alcohol serving as a defoaming agent, soybean oil or liquid paraffin, polyamide epichlorohydrin resin PAE serving as a wet strength agent, acrylic resin PAA, urea resin UF, melamine formaldehyde resin MF or glyoxal modified polyacrylamide; all the auxiliary agents used in the preparation process are calculated according to the percentage of the addition amount of the starch paste liquid, and the next auxiliary agent is added after the former auxiliary agent is completely dispersed; and after all the auxiliary agents are added, continuously stirring and uniformly mixing, adjusting the pH to about 7.5 by using phosphoric acid, and filtering by using gauze to obtain the degradable mulching solution. Different degradable mulching films are prepared by changing the types of the plasticizer, the emulsifier, the mineral binder, the reinforcing agent, the defoaming agent and the wet strength agent.
Preparing the degradable mulching film: slowly stirring the degradable mulching film liquid until granular matters just appear, and uniformly spraying the degradable mulching film liquid on the smooth ground to obtain the humic acid degradable mulching film, wherein the preparation technical path is shown in figure 1.
(2) Mechanical property test of humic acid degradable mulching film
The tensile strength and the elongation at break of the degradable mulching film sample are measured according to the standard GB/T I040.2-2006/ISO 527-2:1993 tensile property measurement standard, and the steps are as follows: cutting the degradable mulching film into long strips according to standard regulations, and 5 samples in each group. The thickness is less than 1mm, and the width of the sample is accurate to 0.1 mm. The thickness and width measurements of each specimen were averaged over a standard distance. Fixing the sample in two clamps of a testing machine, coinciding the central lines of the upper clamp and the lower clamp with the longitudinal axis of the sample, wherein the tightness is enough to prevent the sample from breaking or sliding in the clamps, starting the testing machine to test at the speed of 50mm/s, and reading the required mechanical property parameters after the sample breaks.
(3) Rheological property test of humic acid degradable mulching film
Determining the rheological property of the humic acid degradable mulching film by adopting an iron plate method according to GB 5259-85: 2g of newly prepared humic acid mulching film is placed on a heating plate preheated to the experimental temperature, the initial temperature is measured by a thermometer, then timing is started, the flow condition of the mulching film is tested by a glass rod, the time from the start of heating to the start of wire drawing of the mulching film is recorded, and the time period is recorded as the gelation time. And repeating the operations, raising the temperature by 5 ℃ every time, recording the gelation time, and drawing a heating temperature and gelation time curve of the mulching film to obtain the temperature between which the gelation of the mulching film mainly occurs and the storage temperature range of the mulching film. Since gelation time is a rate process, the dependence of gelation time on temperature can be expressed by the Arrhenius equation containing activation energy:
t＝A×e E/RT
in the formula: t-gelation time, s; a-pre-finger factor; e-reaction activation energy, KJ/mol; r-gas constant; T-Absolute temperature, K. Two-sided logarithm of the above formula was taken, and ln T ═ ln a + E/RT was obtained, and lnt was plotted versus 1/T. And (4) performing unary linear regression on the curve, and obtaining the gelation activation energy according to the slope.
(4) Hydrolysis experiment of humic acid degradable mulching film
Under the condition that the temperature of the low-temperature thermostatic bath is 15 ℃, the prepared humic acid degradable mulching film is used as a raw material, and the thickness of the mulching film is 6 multiplied by 6cm 2 Taking seven blocks of 6X 6cm as standard 2 The mulching films are used for standby, seven test tubes are taken, the weighed mulching films are respectively placed into seven 50mL test tubes, the serial numbers of the test tubes are marked with 1-7, 35mL of prepared buffer solution with the pH value of 8.5 is added, the test tubes are sealed by preservative films, and the test tubes are uniformly placed into a low-temperature constant-temperature tank. Taking out the mulching film in one test tube every day, and drying in the shadeAnd weighing, and calculating the weight loss rate to analyze the hydrolysis rate. The hydrolysis rate is analyzed by testing the weight loss rate of the humic acid degradable mulching film by setting the temperature to be 25 ℃, 35 ℃ and 45 ℃ respectively in the same method.
Under the condition that the temperature of the low-temperature thermostatic bath is 15 ℃, the prepared humic acid biodegradable mulching film is used as a raw material, and the thickness of the mulching film is 6 multiplied by 6cm 2 Taking seven blocks of 6X 6cm as standard 2 And (3) taking seven test tubes, respectively placing the weighed biodegradable mulching films into seven 50mL test tubes, marking the test tubes with the serial numbers of 1-7, adding 35mL of buffer solution with the pH value of 7.4, sealing the test tubes with preservative films, and uniformly placing the test tubes into a low-temperature constant-temperature tank. The mulching film in one test tube is taken out every day, dried in the shade, weighed, and the hydrolysis rate is analyzed by calculating the weight loss rate. The hydrolysis rate is analyzed by testing the weight loss rate of the humic acid degradable mulching film with the same pH value (7.8, 8.2 and 8.7).
The weight loss rate of the mulching film is measured by adopting a weighing method, the weight of an original mulching film sample is measured before the film is hydrolyzed, the residual film is washed in clear water after each sampling, the temperature in a dryer is set to be 25 ℃, and the weight is measured after the drying.
In the formula: m 1 -initial mulch mass g; m 2 And g, residual film mass after hydrolysis.
(5) Humic acid degradable mulching film hydrolysis performance optimization
In order to enable the mulching film to have excellent waterproof performance, a wet strength agent is added in the film forming process to enhance the waterproof performance of the mulching film. The corn starch and the polyvinyl alcohol both have high-strength hydrophilicity, and some wet strength agents are added in the film forming process, so that the mulching film still has the mechanical strength meeting the requirements after being wetted by water; and the wet strength agent is combined with hydroxyl in the mulching film and has covalent bonds, so that the mulching film has a better waterproof effect. The action mechanism of the wet strength agent is that a part of high molecular polymers in the wet strength agent resin are doped among fibers of the mulching film, a staggered chain structure is formed near the fibers, the corn starch and the polyvinyl alcohol are prevented from absorbing water and wetting, the deformation and other performances of the mulching film are reduced, and therefore the wet strength of the mulching film is improved.
The water absorption rate is measured according to the national standard GB 1034-70: drying degradable mulching film of 6cm multiplied by 6cm at 100 ℃ to constant weight (W) 0 ) Soaking in distilled water at room temperature (about 25 deg.C), taking once a day, drying with filter paper, and weighing (W) 1 ) And calculating the water absorption rate, calculating seven groups in total, and taking an average value.
In the formula: w 0 -oven dry total weight, g; w 1 -total weight absorbed, g.
Firstly measuring the tensile strength T of the degradable mulching film before water absorption according to the national standard GB1040-79 1 (ii) a Then placing the degradable mulching film sample in distilled water at room temperature (about 25 ℃), taking out once a day, sucking the surface water by using filter paper, and testing the tensile strength T after water absorption according to the national standard GB1040-79 2 And calculating the wet strength, calculating seven groups in total, and taking an average value.
In the formula: t is 1 Tensile Strength before Water absorption, N/mm 2 ；T 2 Tensile Strength after Water absorption, N/mm 2 。
Stirring mixed liquid can produce a large amount of bubbles at the in-process of preparation degradable plastic film, can lead to fashioned plastic film mechanical properties relatively poor, for avoiding stirring mixed liquid to produce the bubble, the bubble is eliminated when adding the defoaming agent stirring. Thereby reducing the surface tension of the mixed liquid of the mulching film to improve the mechanical property of the mulching film. In this example, three types of defoaming agents were selected: soybean oil, n-octanol and liquid paraffin are added in the process of film formation, and the tensile strength and the elongation at break of the mulching film are tested after the film formation to analyze the performances of the mulching film.
(6) Degradability of humic acid degradable mulching film
Respectively preparing the degradable mulching films a, b and c according to the' (1) preparation method of the humic acid degradable mulching film, wherein the used plasticizer is glycerol, the emulsifier is lauryl sodium sulfate, the mineral binder is sodium silicate, the reinforcing agent is sodium carboxymethylcellulose, the antifoaming agent is n-octanol, and the wet strength agent is polyamide epichlorohydrin resin PAE; and respectively spraying the degradable mulching films a, b and c onto a flat glass surface with a certain area, uniformly smearing, standing for 20h, and forming a film to obtain the degradable mulching films a, b and c, wherein the thicknesses of the degradable mulching films a, b and c are less than 0.04 mm.
A commercially available ordinary mulching film (PE, the same applies hereinafter) was used as a control, and polyethylene was used as a main component, and the width and thickness thereof were 70cm and 0.007mm, respectively. The soil tested for degradability test was: in an orchard between a Yifu experimental building of Tarim university and a basketball court in western regions, the soil texture is loam, the soil water content is 19.1 percent, the soil pH is 8.8, and the number of bacteria in the soil is 1.5 multiplied by 10 7 Per gram of dry soil, the number of fungi is 3.22 multiplied by 10 4 The number of actinomycetes per gram of dry soil is 4.78 multiplied by 10 5 One per gram of dry soil.
Microbial degradation experiments: and (3) observing the growth rate of the microorganisms by taking the tested samples (degradable mulching films a, b and c) as the only carbon source and energy source. Cutting the degradable mulching film a, the degradable mulching film b and the degradable mulching film c into squares of 60mm multiplied by 60mm respectively, disinfecting the squares with 75% alcohol, washing the squares with sterile water, drying the squares in a dryer, weighing the squares in sequence, and preparing carbon-source-free culture medium plates of fungi, bacteria and actinomycetes respectively. Taking 10g of soil to be tested, adding 90mL of sterile water, and shaking for 20min to prepare a soil suspension; then 1mL of soil suspension is respectively added into a carbon source-free culture medium of fungi, bacteria and actinomycetes at 45 ℃, half of the culture medium is poured out to prepare a flat plate, a test membrane is paved on the flat plate, the other half of the culture medium is paved on the membrane, and the culture dish is inverted; incubate at 28 ℃ for 28 d. After the culture is finished, disinfecting the culture medium by using alcohol with the volume fraction of 75%, cleaning the culture medium by using sterile water, drying the culture medium in a dryer, weighing the culture medium, and observing the growth condition of microorganisms on a membrane by taking no soil suspension as a control.
Indoor soil burying experiment: and (3) treating 4 degradable mulching films a, b, c and common mulching films, and respectively measuring the molecular weights of the 3 degradable mulching films. The mulching film is respectively cut into squares of 60mm multiplied by 60mm, the squares are weighed one by one, the squares are buried in a disposable plastic flowerpot containing 200g of soil samples, the buried depth is 5cm, and watering is carried out at intervals to ensure that the soil keeps certain humidity. Samples were taken every 10 days, mulch film morphology was observed, mulch film weight and molecular weight were measured, and 3 replicates were measured.
In the degradation test, a weight loss rate of the mulching film is measured by adopting a weighing method, the weight of an original mulching film sample is measured before film burying, the residual mulching film is washed in clear water after each sampling, and the residual mulching film is weighed after being dried in a dryer.
In the formula: m 1 -initial mulch mass g; m 2 And g, the mass of the degraded residual film.
The viscosity of the dilute polymer solution was determined using a capillary viscometer as per GB/T1632.1-2008/ISO 1628-1:1998 plastics part 1: general rules measures the viscosity average molecular weight of the mulching film sample. And (3) acquiring a film surface microstructure by adopting a Quanta 250FEG field emission scanning electron microscope, and observing the shapes of the four kinds of film soil buried for 30 days.
Second part of the results and analysis
2.1 analysis of mechanical Properties
(1) Influence of polyvinyl alcohol content on mechanical property of degradable mulching film
In this embodiment, the content of the polyvinyl alcohol refers to the mass fraction of the polyvinyl alcohol solution in the degradable mulching solution; when the degradable mulching films are prepared according to experiment numbers 1-5 in table 4, the mass fractions of humic acid solutions in the degradable mulching film liquids of the groups are 21.05 wt%, the plasticizers are glycerol and 59 wt% of the added mass of the starch paste liquid, the emulsifiers are sodium dodecyl sulfate and 4.48 wt% of the added mass of the starch paste liquid, the reinforcing agents are sodium carboxymethyl cellulose and the added amount is 1.74 wt% of the added mass of the starch paste liquid; the mineral binder is sodium silicate, and the adding amount of the mineral binder is 8.84 wt% of the adding mass of the starch paste; no reinforcing agent and no defoamer were added.
TABLE 4 Effect of polyvinyl alcohol content on mulch tensile Strength and elongation at Break
As can be seen from FIG. 2, the tensile strength of the humic acid degradable mulching film increases with the increase of the polyvinyl alcohol content, and is 0.55MPa when the polyvinyl alcohol content is 23.68 wt%, and is 1.1MPa when the polyvinyl alcohol content is 42 wt%. The elongation at break is increased along with the increase of the content of the polyvinyl alcohol and is gradually reduced after reaching a maximum value; when the content of the polyvinyl alcohol is 34 wt%, the elongation at break is about 154.85%, the tensile strength is 1.1Mpa, the elongation at break is the maximum value, and the tensile strength meets the national standard. In conclusion, when the content of the polyvinyl alcohol is about 34 wt%, the tensile strength and the elongation at break of the degradable mulching film are higher, the mechanical property is improved, and the degradable mulching film meets the application requirements of GB13735-1992 polyethylene blow molding agricultural ground covering film.
(2) Influence of humic acid content on mechanical property of degradable mulching film
In the embodiment, the content of humic acid refers to the mass fraction of humic acid solution in the degradable mulching solution; when the degradable mulching films are prepared according to experiment numbers 1-5 in table 5, the mass fractions of the polyvinyl alcohol solutions in the degradable mulching film solutions of the groups are 23.68 wt%, the plasticizers are glycerol, the addition amount of the plasticizers is 59 wt% of the addition amount of the starch paste solution, the emulsifiers are sodium dodecyl sulfate, the addition amount of the emulsifiers is 4.48 wt% of the addition amount of the starch paste solution, the reinforcing agents are sodium carboxymethyl cellulose, and the addition amount of the reinforcing agents is 1.74 wt% of the addition amount of the starch paste solution; the mineral binder is sodium silicate, and the adding amount of the mineral binder is 8.84 wt% of the adding mass of the starch paste; no reinforcing agent and no defoamer were added. .
TABLE 5 influence of humic acid content on tensile Strength and elongation at Break of mulching film
As can be seen from fig. 3, the tensile strength of the degradable mulching film increases with the humic acid content, and when the humic acid content reaches about 32 wt%, the rate of elongation at break begins to decrease. The elongation at break is gradually increased along with the increase of the content of humic acid, so that the elongation at break is a turning point of the elongation at break of the mulching film when the mass of the humic acid is 32 wt%, and then the elongation at break is reduced along with the increase of the content of the humic acid. When the content of humic acid is 32 wt%, the mulching film has good tensile strength and elongation at break, the mechanical property is improved, and the application requirement of GB13735-1992 polyethylene blow molding agricultural ground covering film is met.
(3) Selection of type and dosage of plasticizer for degradable mulching film
The content of the plasticizer is the percentage of the added mass of the plasticizer in the degradable mulching liquid to the added mass of the starch paste liquid. When the degradable mulching films are prepared by all experimental groups in the part, except the plasticizer, the contents of other components in all groups of degradable mulching films are as follows: the mass fractions of the polyvinyl alcohol solution and the humic acid solution are 23.68 wt%, 21.05 wt%, the emulsifier is sodium dodecyl sulfate, the addition amount of the emulsifier is 4.48 wt% of the addition amount of the starch paste, the reinforcing agent is sodium carboxymethyl cellulose, and the addition amount of the reinforcing agent is 1.74 wt% of the addition amount of the starch paste; the mineral binder is sodium silicate, and the addition amount of the mineral binder is 8.84 wt% of the addition amount of the starch paste liquid; no reinforcing agent and no defoamer were added.
TABLE 6 Effect of different plasticizers on tensile Strength and elongation at Break of mulching films
From table 6, it is seen that the tensile strength and elongation at break of the mulching film prepared with ethylene glycol in the reinforcing agent are stronger than those of the mulching film prepared with glycerin. From the physical properties, the mulching film prepared by the ethylene glycol is dry, dull and easy to crack, is easy to peel in a short time, is short in film forming time, and the mulching film prepared by the glycerol is glossy, soft, easy to uncover, long in film forming time and easy to spread, so that the glycerol is selected as the plasticizer under the same condition.
As can be seen from fig. 4, the tensile strength of the mulching film gradually decreases with the increase of the content of glycerin, while the elongation at break gradually increases, and starts to gradually decrease when the content of glycerin reaches 68.26 wt%. The tensile strength of the mulching film is gradually reduced along with the increase of the using amount of the glycerol, the using amount of the glycerol is 68.26 wt% and is a turning point of the breaking elongation of the degradable mulching film, and when the using amount of the glycerol is 58.91 wt% -68.26 wt%, the tensile strength and the breaking elongation of the degradable mulching film are high and meet the application requirements of GB13735-1992 polyethylene blow-molded agricultural ground covering film.
(4) Selection of type and dosage of emulsifier by humic acid degradable mulching film
The content of the emulsifier is the percentage of the added mass of the emulsifier in the degradable mulching liquid to the added mass of the starch paste liquid. When the degradable mulching films are prepared by all experimental groups in the part, except the emulsifier, the contents of other components in all groups of degradable mulching films are as follows: the mass fractions of the polyvinyl alcohol solution and the humic acid solution are 23.68 wt%, 21.05 wt%, the plasticizer is glycerol, the addition amount of the plasticizer is 59 wt% of the addition amount of the starch paste, the reinforcing agent is sodium carboxymethyl cellulose, and the addition amount of the reinforcing agent is 1.74 wt% of the addition amount of the starch paste; the mineral binder is sodium silicate, and the addition amount of the mineral binder is 8.84 wt% of the addition amount of the starch paste liquid; no reinforcing agent and no defoamer were added.
TABLE 7 Effect of different emulsifiers on tensile Strength and elongation at Break of mulching films
From table 7, it can be seen that the elongation at break of the degradable mulching films prepared by adding different emulsifiers is substantially the same under the same conditions. From the physical properties, the degradable mulching film prepared by adding the sodium pyrophosphate and the liquid paraffin is not easy to demould, is easy to tear and has poor film forming effect, and the mulching film prepared by the sodium dodecyl sulfate is softer, is easy to tear, has longer film forming time and is easy to spread, so the sodium dodecyl sulfate is selected as the emulsifier under the same condition.
As can be seen from fig. 5, the tensile strength of the degradable mulching film increases with the amount of sodium dodecyl sulfate, and starts to gradually decrease when the amount of sodium dodecyl sulfate reaches 4.48 wt%. The breaking elongation rate is gradually increased along with the increase of the dosage of the sodium dodecyl sulfate, which shows that the tensile strength is greatly turned when the dosage of the sodium dodecyl sulfate is 4.48 wt%, and the breaking elongation rate is gradually increased. When the amount of the degradable mulching film is 4.48 wt%, the mechanical properties of the degradable mulching film such as tensile strength and elongation at break are preferably improved, and the degradable mulching film meets the application requirements of GB13735-1992 polyethylene blow-molded agricultural ground covering films.
(5) Selection of type and dosage of reinforcing agent by humic acid degradable mulching film
The content of the reinforcing agent is the percentage of the adding mass of the reinforcing agent in the degradable mulching liquid to the adding mass of the added starch paste liquid. When the degradable mulching film is prepared by each experimental group in the part, except the reinforcing agent, the contents of other components in each group of degradable mulching film are as follows: the mass fractions of the polyvinyl alcohol solution and the humic acid solution are 23.68 wt%, 21.05 wt%, the plasticizer is glycerol, the addition amount of the plasticizer is 59 wt% of the addition amount of the starch paste, the emulsifier is sodium dodecyl sulfate, the addition amount of the emulsifier is 4.48 wt% of the addition amount of the starch paste, and the mineral binder is sodium silicate, the addition amount of the mineral binder is 8.84 wt% of the addition amount of the starch paste; no reinforcing agent and no defoamer were added.
TABLE 8 Effect of different reinforcing agents on mulch tensile Strength and elongation at Break
From table 8, it is understood that under the same conditions, the tensile strength of the mulching film prepared by adding different reinforcing agents and carboxymethyl cellulose sodium is the same as that of the mulching film prepared by gelatin, and the elongation at break of carboxymethyl cellulose sodium is stronger than that of gelatin. From the physical properties, the mulching film formed by the gelatin is not easy to strip and is easy to tear, so the reinforcing agent is selected from sodium carboxymethyl cellulose under the same condition.
As can be seen from fig. 6, the tensile strength of the mulching film remained unchanged as the content of sodium carboxymethylcellulose was gradually increased. Initially, the elongation at break gradually increased with the increase of the content of sodium carboxymethylcellulose, and gradually decreased when the content of sodium carboxymethylcellulose was 1.74 wt%. Namely 1.74 wt% is the turning point, and the elongation at break of the mulching film is gradually reduced along with the increase of the content of the sodium carboxymethyl cellulose. When the content of the sodium carboxymethylcellulose is 1.74-2.16 wt%, the tensile strength is kept unchanged, and the elongation at break better meets the application requirements of GB13735-1992 polyethylene blow-molded agricultural ground covering film.
(6) Selection of humic acid degradable mulching film for using amount of sodium water glass as mineral binder
The dosage of the sodium silicate is the percentage of the adding mass of the sodium silicate in the added starch paste liquid in the degradable mulching liquid. When the degradable mulching films are prepared by all experimental groups in the part, except the mineral adhesive, the contents of other components in all groups of degradable mulching films are as follows: the mass fractions of the polyvinyl alcohol solution and the humic acid solution are 23.68 wt%, 21.05 wt%, the plasticizer is glycerol, the addition amount of the plasticizer is 59 wt% of the addition amount of the starch paste, the emulsifier is sodium dodecyl sulfate, the addition amount of the emulsifier is 4.48 wt% of the addition amount of the starch paste, the reinforcing agent is sodium carboxymethyl cellulose, and the addition amount of the reinforcing agent is 1.74 wt% of the addition amount of the starch paste; no reinforcing agent and no defoamer were added.
As can be seen from fig. 7, the tensile strength and the elongation at break of the degradable mulching film increase with the increase of the amount of the sodium silicate, and when the amount of the sodium silicate reaches 8.84 wt%, the tensile strength and the elongation at break gradually decrease. Therefore, the tensile strength and the elongation at break of the mulching film are changed by taking the amount of 8.84 wt% sodium silicate as a turning point when the amount of the sodium silicate is increased, and the tensile strength and the elongation at break of the mulching film optimally meet the application requirements of GB13735-1992 polyethylene blow-molded agricultural ground covering films when the amount of the sodium silicate is 8.84 wt%.
2.2 analysis of rheological Properties of humic acid degradable mulching films
The rheological property of the humic acid degradable mulching film is measured by adopting a GB5259-85 iron plate method, and the gelation time is recorded to obtain the temperature between which the gelation of the mulching film mainly occurs and also obtain the excellent storage temperature range of the mulching film. Meanwhile, the gel activation energy is obtained through a relational expression of the gelation time and the temperature.
As can be seen from fig. 8, the gelation time of the degradable mulching film decreases with the increase of the heating temperature. The temperature is about 80 ℃, the gelation time is about 350s, the gelation time is only about 50s at about 100 ℃ along with the increase of the temperature, the gelation time is 10s at 110 ℃, and the gelation time is only 1-2s at 120 ℃. Therefore, the humic acid degradable mulching film has good stability at 80 ℃ and excellent storage stability at normal temperature. When the temperature is 110-120 ℃, the gelation time is only a few seconds, which shows that the main influence of the temperature on the gelation time of the mulching film is about 110-120 ℃.
Since gelation time is a rate process, the dependence of gelation time on temperature can be expressed by an equation containing activation energy. As can be seen from fig. 9, the gel activation energy was obtained from the slope of the curve in the unary linear regression of the curve, and the gel activation energy was 83.14KJ/mol because the slope k ═ E/R.
2.3 analysis of hydrolysis Properties
(1) Influence of different temperatures on hydrolysis of humic acid degradable mulching film
As can be seen from fig. 10, with the increase of the hydrolysis time, the humic acid degradable mulching film has the smallest weight loss rate at the temperature of 15 ℃ and the largest weight loss rate at the temperature of 45 ℃, so the hydrolysis rate is faster as the temperature is higher. However, the rate of hydrolysis did not change much, more slowly, as the temperature rose to 45 ℃. The weight loss rate of the humic acid degradable mulching film along with the increase of hydrolysis time is larger, the weight loss rate is larger when the temperature is higher, and when the temperature reaches a certain value, the weight loss rate is slowly increased.
(2) Influence of different pH values on hydrolysis of humic acid degradable mulching film
As can be seen from fig. 11, as the hydrolysis time increases, the humic acid degradable mulching film has the smallest weight loss rate at the pH value of 7.4 and the largest weight loss rate at the pH value of 8.7, and therefore the larger the pH value, the slower the weight loss rate. However, the weight loss rate did not change much when the pH increased to 8.7, but was slow. The larger the weight loss rate of the humic acid degradable mulching film along with the increase of degradation time is, the larger the pH value is, the slower the weight loss rate is, and when the pH value reaches a certain value, the weight loss rate is slowly increased.
2.4 Performance optimization analysis of degradable mulching films
(1) Selection of the type of wet strength agent
When the degradable mulching film is prepared by each experimental group in the part, except the moisture-removing strengthening agent, the contents of other components in each group of degradable mulching film liquid are as follows: the mass fractions of the polyvinyl alcohol solution and the humic acid solution are 23.68 wt%, 21.05 wt%, the plasticizer is glycerol, the addition amount of the plasticizer is 59 wt% of the addition amount of the starch paste, the emulsifier is sodium dodecyl sulfate, the addition amount of the emulsifier is 4.48 wt% of the addition amount of the starch paste, the reinforcing agent is sodium carboxymethyl cellulose, and the addition amount of the reinforcing agent is 1.74 wt% of the addition amount of the starch paste; the mineral binder is sodium silicate, and the addition amount of the mineral binder is 8.84 wt% of the addition amount of the starch paste liquid; no defoamer was added.
As can be seen from fig. 12-13, the polyamide epichlorohydrin resin (PAE) has the lowest water absorption rate compared with the other four wet strength agents, and can improve the wet strength of the mulching film to the greatest extent, and can improve the waterproof performance of the mulching film to the greatest extent, and cannot be easily hydrolyzed, so that the mulching film can be better paved. The PAE is water-soluble cationic thermosetting resin, and the degradation performance of the PAE is superior to that of a permanent wet strength agent, namely glyoxal modified acrylamide, acrylic resin (PAA) and the like, so that the PAE is selected as the optimal hydrophobization modified wet strength agent.
(2) Determination of the amount of wet strength agent
The tensile strength of the mulching film is measured according to the standard GB/T I040.2-2006/ISO 527-2:1993 tensile property measurement standard. As can be seen from fig. 14, the performance of the mulching film is best when the amount of PAE (which is the percentage of the added mass of PAE in the degradable mulching film liquid to the added mass of starch paste) is 1.5 wt%, and the performance of the mulching film cannot be improved when the amount of PAE is increased. The reason is that when the amount of PAE is low, many hydrophilic hydroxyl groups in the corn starch and polyvinyl alcohol molecules are not complexed, and the water resistance and mechanical properties are poor. However, when the amount of the PAE is high, polymerization itself occurs in an excessive amount to deteriorate the mechanical properties of the film.
(3) Selection of the type of defoaming agent
When the degradable mulching film is prepared by each experimental group in the part, except the defoaming agent, the contents of other components in each group of degradable mulching film are as follows: the mass fractions of the polyvinyl alcohol solution and the humic acid solution are 23.68 wt%, 21.05 wt%, the plasticizer is glycerol, the addition amount of the plasticizer is 59 wt% of the addition amount of the starch paste, the emulsifier is sodium dodecyl sulfate, the addition amount of the emulsifier is 4.48 wt% of the addition amount of the starch paste, the reinforcing agent is sodium carboxymethyl cellulose, and the addition amount of the reinforcing agent is 1.74 wt% of the addition amount of the starch paste; the mineral binder is sodium silicate, and the adding amount of the mineral binder is 8.84 wt% of the adding mass of the starch paste; no wet strength agent was added.
TABLE 9 Effect of different defoamers on mulch tensile strength and elongation at break
It can be seen from table 9 that the addition of the defoamer greatly improves the film forming effect compared with the initial mulching film without the defoamer, the defoaming performance of the n-octyl alcohol in the added defoamer is the best, the paved mulching film is smooth and has no bubbles, and the tensile strength of the mulching film is also the best.
(4) Determination of the amount of antifoam
As can be seen from fig. 15, when the amount of n-octanol (which is the percentage of the added mass of n-octanol to the added mass of starch paste in the degradable mulching solution) is 0.4 wt%, the mechanical properties of the mulching film are strongest. When the using amount of n-octanol is reduced, bubbles in the mixed solution are not completely eliminated, and the mechanical property of the mulching film is influenced. When the amount of n-octanol is excessive, the mechanical properties of the membrane are reduced by the excessive n-octanol. Therefore, too much or too little n-octanol antifoaming agent is not favorable for defoaming.
2.5 analysis of test results on degradation Properties of degradable mulching film
(1) Growth of microorganisms on mulch
Respectively taking test films (the degradable mulching film a, the degradable mulching film b, the degradable mulching film c and the common mulching film) as unique carbon sources and energy sources, inoculating by using a soil suspension, observing the growth conditions of microorganisms on different test films after 28 days, and showing the growth results in a table 11; the raw material ratios of the degradable mulching film a, the degradable mulching film b and the degradable mulching film c are shown in table 10 (the addition amounts of other additives are the optimal addition amounts in the embodiment), in table 10, the humic acid content refers to the mass fraction of the humic acid solution in the degradable mulching film, and the polyvinyl alcohol content refers to the mass fraction of the polyvinyl alcohol solution in the degradable mulching film.
TABLE 10 raw material ratio in humic acid degradable mulching film
TABLE 11 growth of microorganisms on test membranes
As can be seen from table 11, bacteria, fungi, and actinomycetes all grow in different degradable mulching films to different degrees, and the coverage degree of the fungi and the actinomycetes is higher; therefore, fungi and actinomycetes play a leading role in the degradation process of the humic acid degradable mulching film, and bacteria, fungi and actinomycetes do not grow on the surface of the common mulching film. The surface integrity of the common mulching film is observed by naked eyes, holes and fine lines appear on the surface of the degradable mulching film, and the quality of the degradable mulching film is reduced to a certain extent after weighing, mainly because the raw materials in the degradable mulching film can be used as carbon sources and energy sources for the growth of microorganisms.
(2) Effect of soil suspension inoculation on mulching film degradation
The biodegradation performance of the test membrane in the bacterial culture medium, the fungal culture medium and the actinomycete culture medium was measured by soil suspension inoculation, and the results are shown in Table 12, with no soil suspension added as a control.
TABLE 12 influence of soil suspension on mulch weight loss ratio (%)
Note: different lower case letters after the same column of values indicate that the difference between different treatments is up to a 5% significance level (n-3).
As can be seen from Table 12, the ordinary mulching film is hardly degraded, and the weight loss rate of the ordinary mulching film is far smaller than that of the degradable mulching film. The weight loss ratio of the degradable mulching film added with the soil suspension is far greater than that of a control without the soil suspension, which indicates that microorganisms beneficial to mulching film degradation exist in the soil. Compared with different degradable mulching films, the weight loss rate of the mulching film c in three culture media is the maximum, the weight loss rate of the mulching film a is the minimum, which is probably related to the content of humic acid, and the enzyme secreted by the microorganisms in the soil can rapidly degrade the humic acid, so that the weight loss is faster. Compared with different culture media, the three degradable mulching films have the highest weight loss rate in a fungus culture medium, which shows that the fungi in the soil have the most obvious influence on the degradation of the mulching films, because the fungi in the soil have high propagation speed and strong enzyme secretion capacity and the growth metabolites of the fungi can also promote the degradation of the mulching films.
(3) Actual degradation of mulch in soil
And (3) observing the influence of the soil burying time on the weight loss rate and the molecular weight of the mulching film by adopting a laboratory simulation indoor soil burying experiment, wherein the experimental results are respectively shown in a figure 16 and a figure 17. As can be seen from fig. 16 and 17, with the increase of the degradation time, all three degradable mulching films are degraded in the soil, the weight loss rate of the mulching film gradually increases, the molecular weight of the mulching film gradually decreases, and all three mulching films have biodegradability. The three mulching films have the phenomena of relatively low early-stage degradation rate and relatively high later-stage degradation rate, and the form and the quality of the common mulching film are basically unchanged. The degradable mulching film c has the fastest degradation rate and the most obvious reduction of the molecular weight, the weight loss rate exceeds 10% after 10 days, the area of the mulching film is reduced, and the edge of the mulching film is in a contracted shape; after 30 days, the weight loss rate is close to 50 percent, the mulching film has obvious cracks, and a small part of small blocky mulching film is tightly bonded with soil; after 40 days, the weight loss rate is close to 70%, the mulching film is cracked into a plurality of fragments, and part of fragments are tightly bonded with soil particles and are difficult to peel; after 60 days, the weight loss rate exceeds 80%, the mulching film is not complete, the mulching film is cracked into small fragments, almost completely degraded, and the molecular weight cannot be measured. The degradation rate and the molecular weight of the degradable mulching film b are both more obvious than those of the degradable mulching film a, and the degradable mulching film a and the degradable mulching film b are degraded into fine fragments after 60 d.
(4) Scanning analysis of surface morphology after mulching film degradation
And observing the surface microscopic morphology of the degradable mulching film a, the degradable mulching film b, the degradable mulching film c and the common mulching film PE after the soil is buried and degraded for 30d through a scanning electron microscope. As can be seen from FIGS. 19 to 21, the surface of the common mulching film PE is flat after being degraded for 30d, no obvious degradation sign appears, and the property is stable. The degradable mulching films a, b and c are all acted by microbes in soil, the microbes attack the mulching films to damage the surfaces of the mulching films, and obvious holes and cracks appear. It can be seen from electron microscope photos of the three degradable mulching films that the degradable mulching film c is damaged to a higher degree than the degradable mulching film a and the degradable mulching film b, the surface of the degradable mulching film c is obviously damaged, large holes are formed, cracking products are more, edges are lost, the internal structure is fluffy, the compactness is low, the degradability of the degradable mulching film c is better than that of the degradable mulching film a and the degradable mulching film b, the degradability is closely related to the content of humic acid, and the three mulching films show good biodegradability.
The best preparation conditions for the degradable mulching film are finally determined in the embodiment as follows: in the degradable mulching solution, when the mass fraction of the polyvinyl alcohol solution is 34 wt%, the mass fraction of the humic acid solution is 32 wt%, when the plasticizer is glycerin, the adding mass of the plasticizer is 61 wt% of the adding mass of the added starch paste liquid, the emulsifier is sodium dodecyl sulfate, the adding mass of the emulsifier is 4.48 wt% of the adding mass of the added starch paste liquid, the mineral binder is sodium silicate (namely sodium silicate), the adding mass of the mineral binder is 8.84 wt% of the adding mass of the added starch paste liquid, the reinforcing agent is sodium carboxymethyl cellulose, when the adding mass of the mineral binder is 1.74 wt% of the adding mass of the added starch paste liquid, the wet strength agent is PAE resin, the using amount of the wet strength agent is 1.5 wt% of the mass of the starch paste liquid, the defoaming agent is n-octanol, and the using amount of the defoaming agent is 0.4 wt% of the mass of the starch paste liquid; tests show that the degradable mulching film prepared by the preparation process has better mechanical property, waterproofness, degradability and best comprehensive performance; the degradable mulching liquid is shown in figure 22, and the prepared degradable mulching film is shown in figures 23 and 24.
3 conclusion
(1) Through the determination to humic acid degradable plastic film tensile strength, elongation at break, in the error allowed range to and refer to physical properties and demoulding effect, the research result shows: when the mass fraction of the polyvinyl alcohol solution in the degradable mulching solution is 34.09 wt% and the mass fraction of the humic acid solution is 31.82 wt%, when the plasticizer is glycerol, the adding mass of the plasticizer accounts for 58.19 wt% -68.26 wt% of the adding mass of the added starch paste solution, the emulsifier is sodium dodecyl sulfate, the adding mass of the emulsifier accounts for 4.48 wt% of the adding mass of the added starch paste solution, the mineral binder is sodium silicate (namely sodium silicate), the adding mass of the mineral binder accounts for 6.07 wt% -8.84 wt% of the adding mass of the added starch paste solution, the reinforcing agent is sodium carboxymethyl cellulose, and when the adding mass of the reinforcing agent accounts for 1.74 wt% -2.16 wt% of the adding mass of the added starch paste solution, the proper types and amounts of wet strength agents and defoaming agents are added, so that the degradable mulching film has the highest mechanical property. By measuring the viscosity-average molecular weight of the degradable mulching film, the viscosity-average molecular weight of the degradable mulching film is obtained when the polyvinyl alcohol solution: when the mass ratio of the humic acid solution is 34:32, the degradable mulching film has good elasticity, is easy to form, and has bright luster. In the embodiment, infrared spectrums of the degradable mulching film and humic acid are also considered, and the reaction of carboxyl of the humic acid and hydroxyl of polyvinyl alcohol is found to generate an ester group.
(2) The degradable mulching film has good storage stability at normal temperature by measuring the rheological property of the degradable mulching film, and the gelation time is 350s at the temperature of 80 ℃, so that the gelation time is longer at 80 ℃; when the temperature is 110-120 ℃, the gelation time is only 1-2 seconds, which shows that the main influence of the temperature on the gelation time of the mulching film is about 110-120 ℃, and the gelation activation energy is 83.14 KJ/mol.
(3) Through hydrolysis experimental study on the degradable mulching film, when the weight loss rate of the degradable mulching film rises along with the rise of the temperature at the early stage, but reaches 45 ℃, the weight loss rate is slowly increased. The weight loss rate is maximum 44.8% at the temperature of 45 ℃, the waterproof performance is poor when the hydrolysis rate is high, the weight loss rate is minimum 14.5% at the temperature of 15 ℃, and the waterproof performance is good when the hydrolysis rate is low. When the weight loss rate of the degradable mulching film is increased along with the increase of the pH value in the early stage, and when the pH value reaches 8.7, the hydrolysis is slowly increased. The weight loss rate is 49.8 percent at most when the pH value is 8.7, the waterproof performance is poor when the hydrolysis rate is higher, the weight loss rate is 25.2 percent at least when the pH value is 7.4, and the waterproof performance is good when the hydrolysis rate is low.
(4) The experiment for optimizing the performance of the humic acid degradable mulching film can obtain that the wet strength agent PAE resin is added, the waterproof performance is better improved, and the waterproof effect is optimal when the using amount of the wet strength agent is 1.5 wt% of the mass of the starch paste liquid. The addition of the defoaming agent can pave the degradable mulching film with smooth, bright and bubble-free surface, when the dosage of n-octyl alcohol of the defoaming agent is 0.4 wt% of the mass of the starch paste, the paving effect is optimal, the surface has no bubbles, and the mechanical property of the mulching film is effectively improved.
(5) The microbial degradation test shows that the soil suspension plays a role in promoting the degradation of the humic acid degradable mulching film, and microorganisms which are beneficial to the degradation of the humic acid degradable mulching film exist in the soil; the weight loss rate of the 3 humic acid degradable mulching films (a, b and c) is the maximum in a fungus culture medium, which indicates that the fungi in the soil are more helpful to the decomposition of the humic acid mulching films. The indoor soil burying test proves that the weight loss rate of the humic acid degradable mulching film is larger than that of the common mulching film, and the observation of an electron microscope shows that cracks appear on the surface of the mulching film, which indicates that the mulching film has good biodegradability.
Claims (10)
1. The preparation method of the degradable mulching film is characterized by comprising the following steps:
step A: respectively preparing a polyvinyl alcohol solution, a starch pasty liquid and a humic acid solution;
and B: uniformly mixing the polyvinyl alcohol solution, the starch pasty liquid and the humic acid solution to obtain a mixed raw material solution;
and C: adding the following auxiliary agents into the mixed raw material liquid in sequence: plasticizers, emulsifiers, mineral binders, reinforcing agents, defoamers and wet strength agents; adding the next auxiliary agent after the former auxiliary agent is completely dispersed; after all the auxiliary agents are added, continuously stirring and uniformly mixing, adjusting the pH value of the mixture, and then filtering the mixture by using gauze to obtain degradable mulching liquid;
step D: and slowly stirring the degradable mulching film liquid before use, and uniformly spraying the degradable mulching film liquid on the ground when the degradable mulching film liquid just generates granular substances, so as to obtain the degradable mulching film.
2. The method for preparing the degradable mulching film according to claim 1, wherein in the step A, the relative molecular mass of the polyvinyl alcohol is 10 to 30 ten thousand, and the alcoholysis degree is greater than or equal to 85 mol%;
the preparation method of the polyvinyl alcohol solution comprises the following steps: adding polyvinyl alcohol into water, heating and stirring for 2.5-3.5 hours at 90-100 ℃ to completely dissolve the polyvinyl alcohol, and obtaining a polyvinyl alcohol solution;
the preparation method of the starch paste liquid comprises the following steps: adding water into starch, heating and stirring for 1-2 hours at 50-80 ℃ to form thick pasty liquid by the starch and the water, and obtaining starch pasty liquid;
the preparation method of the humic acid solution comprises the following steps: dissolving humic acid in water, mixing, stirring and filtering to obtain the humic acid solution.
3. The preparation method of the degradable mulching film according to claim 2, wherein the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 2-5 wt%; the mass fraction of starch in the starch paste liquid is 8-11 wt%, and the starch is corn starch; the mass fraction of humic acid in the humic acid solution is 1-5 wt%.
4. The preparation method of the degradable mulching film according to claim 1, wherein in the step B, the mass ratio of the polyvinyl alcohol solution to the starch paste solution to the humic acid solution is 24-40: 10-16: 23-40.
5. The method for preparing the degradable mulching film according to claim 4, wherein the mass ratio of the polyvinyl alcohol solution to the starch paste solution to the humic acid solution is 2.4:1: 2.3.
6. The method for preparing the degradable mulching film according to claim 1, wherein in the step C, the plasticizer is glycerol and/or ethylene glycol; the emulsifier is one or a mixture of two or more of sodium dodecyl sulfate, sodium pyrophosphate and liquid paraffin; the mineral binder is sodium silicate, and the reinforcing agent is sodium carboxymethylcellulose and/or gelatin; the defoaming agent is n-octanol and/or soybean oil; the wet strength agent is one or the mixture of two or more of polyamide epichlorohydrin resin PAE, acrylic resin PAA, urea-formaldehyde resin UF, melamine formaldehyde resin MF or glyoxal modified acrylamide.
7. The method for preparing a degradable mulching film according to claim 6, wherein in the step C, the plasticizer is glycerol, the emulsifier is sodium lauryl sulfate, the reinforcing agent is sodium carboxymethyl cellulose, the defoaming agent is n-octanol, and the wet strength agent is polyamide epichlorohydrin resin PAE.
8. The method for preparing the degradable mulching film according to claim 7, wherein in the step C: the weight of glycerol is 40-70 wt% of the weight of the starch paste liquid, the weight of sodium dodecyl sulfate is 3-9 wt% of the weight of the starch paste liquid, the weight of sodium water glass is 3-12 wt% of the weight of the starch paste liquid, the weight of sodium carboxymethyl cellulose is 0.8-2.6 wt% of the weight of the starch paste liquid, the weight of n-octanol is 0.2-1.2 wt% of the weight of the starch paste liquid, and the weight of polyamide epichlorohydrin resin PAE is 0.5-3 wt% of the weight of the starch paste liquid.
9. The method for preparing degradable mulching film according to claim 1, wherein in step C, phosphoric acid is added to adjust the pH to 7.5.
10. The method for preparing the degradable mulching film according to claim 1, wherein in the step D, the stirring speed of the degradable mulching film liquid is 100-500 rpm, and the stirring time is 1-2 hours; and standing for 16-24 hours after spraying to obtain the degradable mulching film.
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| CN103880565A (en) * | 2013-10-10 | 2014-06-25 | 段开红 | Bioactive humic acid mulching film and preparation method thereof |
| CN109593310A (en) * | 2018-11-30 | 2019-04-09 | 烟台沃斯生物技术有限公司 | Starch a kind ofly and preparation method thereof |
| CN110423380A (en) * | 2019-08-12 | 2019-11-08 | 山东农业大学 | A kind of degradable liquid mulch film and preparation method thereof |
| CN110615958A (en) * | 2019-08-16 | 2019-12-27 | 山东森工新材料科技有限公司 | Humic acid composite gel material and preparation method thereof |
| CN111621063A (en) * | 2020-06-09 | 2020-09-04 | 河南功能高分子膜材料创新中心有限公司 | Easily degradable humic acid mulching film |
| CN113698671A (en) * | 2021-09-02 | 2021-11-26 | 李哲 | Preparation method of fully-degradable liquid film |
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| CN103880565A (en) * | 2013-10-10 | 2014-06-25 | 段开红 | Bioactive humic acid mulching film and preparation method thereof |
| CN109593310A (en) * | 2018-11-30 | 2019-04-09 | 烟台沃斯生物技术有限公司 | Starch a kind ofly and preparation method thereof |
| CN110423380A (en) * | 2019-08-12 | 2019-11-08 | 山东农业大学 | A kind of degradable liquid mulch film and preparation method thereof |
| CN110615958A (en) * | 2019-08-16 | 2019-12-27 | 山东森工新材料科技有限公司 | Humic acid composite gel material and preparation method thereof |
| CN111621063A (en) * | 2020-06-09 | 2020-09-04 | 河南功能高分子膜材料创新中心有限公司 | Easily degradable humic acid mulching film |
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