Natural biodegradable polymer water retention material, preparation method and application

Abstract

The invention relates to the field of landscaping water retention, in particular to a preparation method of a natural biodegradable polymer water-retaining material, which comprises the following steps: S1, uniformly mixing an aqueous solution of a vinyl unsaturated carboxylic acid monomer and an unsaturated amide monomer with a water-soluble free radical polymerization initiator and a cross-linking agent; before the initiator cross-linking agent is added, neutralizing the monomer by using an alkaline solution to obtain a mixed solution of an aqueous solution of a monomer unit containing a vinyl unsaturated carboxylic acid monomer and a metal salt of the vinyl unsaturated carboxylic acid monomer; s2, adding a degradable plant matrix material, and uniformly stirring the mixture; s3, in an inert gas environment, stirring the reaction mixture at 30-70 DEG C for 2-6 hours, and standing; and S4, repeatedly washing the obtained gel polymer with absolute ethyl alcohol to remove unreacted monomers, and cutting the gel polymer into pieces after washing. The process method provided by the invention is high in polymerization efficiency, and the water-retaining agent product is good in gel performance, strong in water-retaining effect, high in biodegradability and wide in garden application.

Description

Technical Field

[0001] The present invention relates to the field of water conservation in landscaping, and specifically relates to a natural biodegradable polymer water retention material, a preparation method and an application thereof. Background Art

[0002] With the rapid development of landscaping construction and the influence of factors such as arid climate and less precipitation, the water consumption of urban landscaping has increased year by year. The phenomenon of poor growth of lawns, flowers and seedlings due to water shortage is widespread. Especially in some remote areas where water sources are not easily accessible, such as the greening projects of the central isolation belts of expressways and national highways, how to save water and improve the utilization rate of garden water has become a prominent problem in urban landscaping.

[0003] A water retention material is a new type of polymer chemical material. It can quickly absorb and retain deionized water hundreds or even thousands of times its own weight and saline water dozens to nearly a hundred times in the soil, forming a gel-like substance that is difficult to dehydrate under external forces. In order to scientifically solve some landscaping water problems and save precious fresh water resources to the greatest extent, the use of water retention agents has become an important topic in the current water conservation research in the landscaping industry.

[0004] Currently, there are many kinds of soil water retention agents on the market. For example, the patent document CN108383945A discloses a method using an environmentally friendly monomer chitosan and guar gum to provide an agricultural water retention agent and a preparation method thereof. The prepared water retention agent has a strong water retention effect and salt tolerance. This document mainly involves agricultural water retention agents, and contains chitosan and guar gum, and the raw material prices are relatively expensive. The patent document CN108456528A discloses a composite water retention agent, using straw as a raw material and adding silver nitrate and amino acids at the same time, making the water retention agent not only have a high water absorption ratio, but also have a certain antibacterial effect. However, there are many kinds of raw materials, and it is impossible to clarify the specific action mechanism of the water retention agent and the universality of the application field.

[0005] In the prior art, most water retention agents are prepared from a chemical material. Especially, many water retention agents are not easily degraded in the soil and will remain. If selected improperly, it is easy to cause irreparable effects on the physical and chemical properties of the soil. There is a need to develop a natural biodegradable polymer water retention material to improve the water retention efficiency.

[0006] Since, when the concentration of the water retention agent exceeds a certain value in the use of the water retention agent, negative effects will also appear. It is not that the more water retention agent is applied in the soil, the better. When the dosage of the water retention agent is too large, it will damage the soil structure to a certain extent and cause soil compaction. During the research process, it was also found that if the water retention agent is selected improperly, there will also be a situation where the plant roots rot due to high water absorption.

[0007] At present, there are also some methods for preparing water retaining agents using starch, cellulose, etc. as raw materials on the market. However, such processes usually have low polymerization efficiency, and the prepared water retaining agents have defects such as poor gel performance, poor water retention effect, poor biodegradability, low versatility, and poor quality.

[0008] For the above reasons, when selecting a suitable water retaining agent for landscaping soil, it is necessary to focus on being inexpensive, environmentally friendly, and having a good water retention effect. Summary of the Invention

[0009] In view of the problems existing in the above-mentioned prior art, the present invention provides a natural biodegradable polymer water retaining material, a preparation method and an application thereof. The process method involved in the present invention has high polymerization efficiency, the water retaining agent product has good gel performance, strong water retention effect, high biodegradability, and wide garden applications.

[0010] In order to achieve the above object, on the one hand, the present invention provides a preparation method of a natural biodegradable polymer water retaining material, comprising the following steps: S1: Uniformly mix an aqueous solution of vinyl unsaturated carboxylic acid monomers and unsaturated amide monomers as monomers with a water-soluble free radical polymerization initiator and a crosslinking agent; before adding the initiator and crosslinking agent, neutralize the mixture of an aqueous solution of monomers containing vinyl unsaturated carboxylic acid monomers and their metal salt monomer units with an alkaline solution; S2: Add a degradable plant matrix material and uniformly stir the mixture; S3: Under an inert gas environment, stir the reaction mixture at 30 - 70 °C for 2 - 6 hours; let it stand; S4: Wash the obtained gel-like polymer repeatedly with absolute ethanol to remove unreacted monomers, and cut it into pieces after washing; S5: Dry it under reduced pressure at 60 - 85 °C for 3 - 6 hours, and dry it in an oven at a constant temperature until it reaches a constant weight; S6: Crush it with a pulverizer and pass through a 50 - 90 mesh sieve to obtain a powdery biodegradable polymer water retaining material.

[0011] A further improvement of the present invention lies in: after the S3 step and before the S4 step, a step of cooling, standing, and then heating is set; Preferably, the cooling range is 40 - 50 °C, stand for 1 - 2 hours, then heat up to 60 - 70 °C, and react for another 1 - 2 hours to obtain a polymer.

[0012] The unsaturated carboxylic acid monomers are one or a combination of methacrylic acid, acrylic acid, and maleic acid.

[0013] The unsaturated amide monomer is one or a combination of N-vinylcaprolactam, acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and isopropylacrylamide.

[0014] The crosslinking agent is at least one of N,N-methylenebisacrylamide, phosphorus oxychloride, adipic acid, N-hydroxymethylacrylamide, and polyethylene glycol.

[0015] The initiator is at least one of ammonium persulfate, potassium persulfate, azodiisobutyramidine hydrochloride, and sodium bisulfite; The mass ratio of the vinyl unsaturated carboxylic acid monomer to the unsaturated amide monomer is 2-5:1-5. Preferably 2:1, more preferably 3:1.

[0016] The total mass ratio of the plant-based matrix material to the monomer is 1:10-20, the addition amount of the crosslinking agent is 0.01 wt%-0.06 wt% of the total weight of the polymerization monomers, and the addition amount of the initiator is 0.1 wt%-0.5 wt% of the total weight of the polymerization monomers The alkaline solution in step S1 is a 5-10 mol / L potassium hydroxide solution or sodium hydroxide solution.

[0017] The degradable plant-based matrix material in step S2 is a starch-based substance and a cellulose-based substance, preferably a starch-based substance.

[0018] The starch-based substances include one or a combination of sweet potato starch, potato starch, wheat starch, corn starch, rice starch, and cassava starch.

[0019] A further modification of the present invention is that: the material is subjected to de-esterification treatment; The de-esterification step includes: mixing starch with a soluble ester solvent, controlling the water content of the mixture, generally in the range of 3%-10%. Heating the mixture to a temperature of 100-200 °C, with a heating time of 30 minutes - 2 hours, and controlling the lipid content in the starch to be below 0.05%. Finally, the treated starch is obtained from the liquid phase of the system. The solvent is selected from methanol, ethanol, and propanol.

[0020] On the one hand, the present invention includes a water-retaining agent prepared by a preparation method of a biodegradable polymer water-retaining material specifically for landscaping soil.

[0021] On the other hand, the present invention provides the use of a water-retaining agent prepared by a preparation method of a biodegradable polymer water-retaining material specifically for landscaping soil in landscaping soil.

[0022] Specifically, it includes the application in the nursery of garden plants. When using a water-retaining agent for seed dressing, according to the ratio of water-retaining agent: seeds: water = 1:30 - 50:150 - 200, stir evenly into a hydrogel state, pour in the seeds, fully stir evenly, then spread it flat in a cool place and slightly dry it before sowing; Or, the application in the transplanting of garden plants. For bare-root seedlings transported long distances, according to the ratio of water-retaining agent: water: soil of 1:200 - 400:50 - 80, dip the roots with a water-retaining agent slurry, and wrap the roots with a plastic film to keep the roots from losing water for a long time, thereby improving the survival rate of transplanted trees.

[0023] Or directly apply it. In the garden green spaces on highways and remote roads where fine application is not suitable, it can be directly and evenly spread, and the application rate of the water-retaining agent is 5 - 15 g / ㎡.

[0024] The beneficial effects of the present invention: In the preparation process of the present invention, an innovative attempt is made to add de-fatted starch in the traditional polymerization process of the water-retaining agent. Compared with adding ordinary starch, the polymerization process with de-fatted starch added can shorten the gel time. Moreover, after the product is applied to the soil, the product swells when encountering water, has a higher gel strength, a larger water absorption ratio, and the biodegradation rate is also improved. The starch after de-fatted treatment participates in the polymerization reaction, reducing the generation of cross-linked aliphatic polymers, and improving the performance and quality of the water-retaining agent product. Through experiments, it is found that the product of the present invention also has the effect of controlling soil evaporation and improving soil water-holding performance, thereby enabling the product to have more excellent water-retaining performance and water-retaining quality.

[0025] In addition, the raw materials of the present invention are simple, the process is streamlined, and it can ensure the stable progress of the cross-linking polymerization reaction. The present invention creatively adopts one-time cooling and two-time heating in the polymerization reaction. Such operations have a positive promoting effect on the entire reaction system, making the raw materials of the entire reaction system react evenly, reducing the phenomenon that the raw materials quickly settle when the gel degree is not high in the process of the process, and improving the polymerization efficiency in the entire process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present disclosure, and are used together with the specification to explain the principles of the present disclosure, and do not constitute an improper limitation of the present disclosure.

[0027] Figure 1 It is a curve graph showing the influence of water-retaining agent treatment on the daily variation of soil surface evaporation (the abscissa is in hours as the unit of time, and the ordinate is the soil surface evaporation amount, with the unit of the soil water evaporation amount per pot expressed in g) DETAILED DESCRIPTION OF THE INVENTION

[0028] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. The endpoints and any values disclosed herein for ranges are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values.

[0029] For the water absorption performance test method of the water retaining agent of the present invention, take 0.50 g of the product, put it into a nylon cloth bag, place it in a 2000 ml beaker, add about 1500 ml of deionized water, soak it at room temperature for 12 hours to obtain the gel after water absorption, take it out and weigh it as m. The water absorption rate (times) A = ((m - 0.5) / 0.5)×100% is calculated.

[0030] For the biodegradation performance test method of the water retaining agent of the present invention, weigh about 1 g of the dried and pulverized sample, soak it in 500 mL of CH3COOH-NaOH buffer solution containing 0.3 mg / mL of cellulase and pH 5, and use the one soaked in 500 mL of buffer solution without enzyme as a control. Place the above samples in a constant temperature incubator at 30°C, cultivate for 15 days, filter, dry and weigh. The biodegradation rate R = ((m1 - m2) / m0)×100% is calculated. In the formula, m1 is the mass of the residue in the control experiment, and m0 and m2 are the masses of the sample before and after enzyme treatment, respectively.

[0031] The time of the first appearance of the gel-like polymer, the emergence time of the seedlings, the mild wilting of the transplanted plant leaves, the time of the appearance of mild drought on the soil surface, and the soil water retention performance test of the product of the present application in the experiments of this example and the control example are all obtained through conventional experimental method recording means. Example 1

[0032] Put 10 g of defatted wheat starch and 1000 ml of distilled water into a 2000 ml three-necked flask, stir evenly and pass nitrogen to remove oxygen, add the polymerization monomers methacrylic acid and N,N-dimethylacrylamide in sequence according to a mass ratio of 2:1, with a total monomer weight of 100 g, and adjust the reaction solution to neutral with 6 mol / L dilute potassium hydroxide solution. Add 0.01 g of N,N-methylenebisacrylamide and 0.1 g of potassium persulfate, stir and react at 70°C for 3 hours; let it stand, wash it repeatedly with 60% anhydrous ethanol to remove the unreacted monomers, cut it into pieces after washing, dry it under reduced pressure at 60 - 85°C for 3 - 6 hours, and dry it to constant weight in an oven at a constant temperature; pulverize it with a pulverizer and pass through a 50 - 90 mesh sieve to obtain a powdery biodegradable polymer water retaining material, and store it in a dry environment.

[0033] Steps for preparing defatted wheat starch: Mix an appropriate amount of starch with methanol, and control the water content of the mixture within the range of 3% - 10%. Heat the mixture to a temperature of 100 - 200 °C for 30 minutes - 2 hours, and control the lipid content in the starch to be below 0.05%. Finally, obtain the treated starch from the liquid phase of the system.

[0034] Perform a water absorption performance test on the water retaining agent product according to the method of this example. Its water absorption rate is 630 times, and the biodegradation rate in 15 days is 20%.

[0035] According to the method of Example 1, for the water retaining agent product prepared, in the application of the water retaining agent in the seedling raising of flowers and herbs, use the water retaining agent for seed dressing. Select the water retaining agent of small particle type for seed dressing. According to water retaining agent: seeds: water = 1:30 - 50:150 - 200, stir evenly into a hydrogel state, pour in the seeds, stir well after fully stirring evenly, spread out and slightly dry in a cool place and then sow; Example 2

[0036] Put 15 g of defatted corn starch and 1000 ml of distilled water into a 2000 ml three-necked flask, stir evenly and introduce nitrogen to remove oxygen. Add polymerization monomers acrylic acid and acrylamide successively according to a mass ratio of 3:1. The total weight of the monomers is 200 g. Adjust the reaction solution to neutral with 6 mol / L dilute sodium hydroxide solution. Add 0.06 g of polyethylene glycol and 0.6 g of sodium bisulfite, and stir and react at 70 °C for 3 hours; wash repeatedly with 60% anhydrous ethanol to remove unreacted monomers, cut into pieces after washing, and stir and react at 70 °C for 3 hours; let stand, wash repeatedly with 60% anhydrous ethanol to remove unreacted monomers, cut into pieces after washing, and perform vacuum drying at 60 - 85 °C for 3 - 6 hours, and dry in an oven at a constant temperature until constant weight; crush with a pulverizer and pass through a 50 - 90 mesh sieve to obtain a powdery biodegradable polymer water retaining material, and store it in a dry environment.

[0037] Steps for preparing defatted corn starch: The same as in Example 1.

[0038] Perform a water absorption performance test on the water retaining agent product according to the method of this example. Its water absorption rate is 650 times, and the biodegradation rate in 15 days is 24%.

[0039] According to the method of Example 2, for the water retaining agent product prepared, in the application of the water retaining agent in the transplanting of shrubs and arbors, for long-distance transported bare-root seedlings, dip the roots with the water retaining agent mud. The general ratio of water retaining agent: water: soil is 1: 200 - 400:50 - 80, and then wrap the roots with a plastic film, which can keep the roots from losing water for a long time and improve the survival rate of transplanted trees. Example 3

[0040] Put 15 g of defatted potato starch and 1000 ml of distilled water into a 2000-ml three-necked flask, stir evenly and introduce nitrogen to remove oxygen. Add polymerization monomers methacrylic acid and isopropylacrylamide successively according to a mass ratio of 4:1, with a total monomer weight of 220 g. Adjust the reaction solution to neutral with 6 mol / L dilute potassium hydroxide solution. Add 0.13 g of adipic acid and 1.1 g of ammonium persulfate, and stir and react at 70 °C for 3 hours to obtain a viscous gel-like polymer. Wash repeatedly with 60% anhydrous ethanol to remove unreacted monomers. After washing, cut it into pieces and stir and react at 70 °C for 3 hours. Let it stand, wash repeatedly with 60% anhydrous ethanol to remove unreacted monomers. After washing, cut it into pieces and dry under reduced pressure at 60 - 85 °C for 3 - 6 hours, and then dry in an oven at a constant temperature until constant weight. Crush it with a pulverizer and sieve it through a 50 - 90 mesh sieve to obtain a powdery biodegradable polymer water-retaining material, and store it in a dry environment.

[0041] The preparation steps of defatted potato starch: the same as in Example 1.

[0042] Test the water absorption performance of the water-retaining agent product according to the method of this example. Its water absorption rate is 600 times, and the biodegradation rate in 15 days is 19%.

[0043] According to the method of Example 3 of this example, for the water-retaining agent product prepared, when applying the water-retaining agent in the highway, remote roads and green spaces in gardens where fine management is not suitable, directly sprinkle 8 g / m 2 of the water-retaining agent once at the same greening soil location. Example 4

[0044] Put 10 g of defatted wheat starch and 1000 ml of distilled water into a 2000-ml three-necked flask, stir evenly and introduce nitrogen to remove oxygen. Add polymerization monomers methacrylic acid and N,N-dimethylacrylamide successively according to a mass ratio of 2:1, with a total monomer weight of 100 g. Adjust the reaction solution to neutral with 6 mol / L dilute potassium hydroxide solution. Add 0.01 g of N,N-methylenebisacrylamide and 0.1 g of potassium persulfate, and stir and react at 70 °C for 3 hours. Let it stand, continue to cool to 20 °C, and after standing for 1 hour, continue to heat to 70 °C and react for 1 hour to obtain a gel polymer. Wash repeatedly with 60% anhydrous ethanol to remove unreacted monomers. After washing, cut it into pieces and dry under reduced pressure at 60 - 85 °C for 3 - 6 hours, and then dry in an oven at a constant temperature until constant weight. Crush it with a pulverizer and sieve it through a 50 - 90 mesh sieve to obtain a powdery biodegradable polymer water-retaining material, and store it in a dry environment.

[0045] The preparation steps of defatted wheat starch are the same as in Example 1.

[0046] Test the water absorption performance of the water-retaining agent product according to the method of this example. Its water absorption rate is 700 times, and the biodegradation rate in 15 days is 21%.

[0047] The application method of the water retention agent is the same as that in Example 1.

[0048] Comparative Example 1 Replace the defatted starch in Example 1 with ordinary commercially available wheat starch, and the uses of the water retention agent prepared by other process methods are the same as those in Example 1.

[0049] According to this process method, the time when the viscous gel-like polymer first appears is 5 minutes later than the time when the gel-like polymer first appears in the process method described in Example 1, and 7 minutes later than the time when the gel-like polymer first appears in the process method described in Example 4.

[0050] According to this method, the water absorption performance of the water retention agent product is tested, and its water absorption rate is 520 times, and the biodegradation rate in 15 days is 14%.

[0051] According to this method, the water retention agent is used for seedling raising test. Under the same conditions, the seedling emergence time is 2 days later than that in Example 1.

[0052] Comparative Example 2 Replace the defatted starch in Example 2 with ordinary commercially available corn starch, and the uses of the water retention agent prepared by other process methods are the same as those in Example 2.

[0053] According to this process method, the time when the viscous gel-like polymer first appears is 3 minutes later than the time when the gel-like polymer appears in the process method described in Example 2.

[0054] According to this method, the water absorption performance of the water retention agent product is tested, and its water absorption rate is 540 times, and the biodegradation rate in 15 days is 16%.

[0055] According to this method, the water retention agent is used for the test of mild wilting of transplanted plant leaves. Under the same conditions, after transplantation, the mild wilting condition of the transplanted plant leaves appears 2 - 4 days earlier than that of the transplanted plants described in Example 2.

[0056] Comparative Example 3 Replace the defatted starch in Example 3 with ordinary commercially available potato starch, and the uses of the water retention agent prepared by other process methods are the same as those in Example 3.

[0057] According to this process method, the time when the viscous gel-like polymer first appears is 6 minutes later than the time when the gel-like polymer appears in the process method described in Example 3.

[0058] According to this method, the water absorption performance of the water retention agent product is tested. The water absorption rate in the landscape green spaces on highways and remote roads that are not suitable for fine management is 500 times, and the biodegradation rate in 15 days is 12%.

[0059] According to this method, when the water retaining agent is applied to the garden green spaces on highways and remote roads that are not suitable for fine management, under the same conditions, the time when mild drought appears on the soil surface is advanced by 3 - 5 days.

[0060] In addition, the applicant also conducted experiments on the soil water retention effect of the present invention, mainly based on the effect experiment of inhibiting soil water evaporation. The main steps were to fill 20 kg of soil in a planting plastic pot, water it by 15%, and apply the water retaining agents of Example 1 and Comparative Example 1 in the same dosage. The experimental results can be seen in the accompanying drawings of the specification. Figure 1 It is a curve graph showing the influence of the water retaining agent treatment on the daily variation of soil surface evaporation (the abscissa is in hours of time, and the ordinate is the soil surface evaporation amount, with the unit of the soil water evaporation amount per pot expressed in g). It can be seen from the graph that the daily variation curve of soil body evaporation is also a single-peak curve, and the water consumption is the largest between about 12:00 - 14:00. The difference in the soil surface evaporation water consumption among different treatments in a day is relatively obvious, and the order of soil surface evaporation water consumption is basically that of Comparative Example 1 being greater than that of Example 1 treatment, especially at the peak value. From this, it can be known that the water retaining agent product obtained by the present invention has better water retention performance.

[0061] The description of the above embodiments is only used to help understand the method of the present invention and its core idea; it should be noted that for those skilled in the art, without departing from the essence and principle of the present invention, the present invention can also be improved and modified, and the protection scope of the present invention shall be subject to the content recorded in the claims.

Claims

1. A method for preparing a natural biodegradable polymer water-retaining material, characterized in that: The following steps are involved: S1. uniformly mixing an aqueous solution of a vinyl unsaturated carboxylic acid monomer and an unsaturated amide monomer with a water-soluble free radical polymerization initiator and a crosslinking agent; before adding the initiator and crosslinking agent, neutralizing the mixed solution of the aqueous solution of the monomer containing monomer units of the vinyl unsaturated carboxylic acid monomer and its metal salt with an alkaline solution; S2 adding a degradable plant-based matrix material and uniformly stirring the mixture; S3 Under an inert gas environment, the reaction mixture is stirred at 30-70 degrees Celsius for 2-6 hours and allowed to stand; The gel polymer obtained in S4 was repeatedly washed with anhydrous ethanol to remove unreacted monomers, and then cut into pieces: S5 Dry under reduced pressure at 60-85℃ for 3-6 hours, and dry in an oven at a constant temperature to constant weight; S6 is crushed by a grinder and passed through a 50-90 mesh sieve to obtain a powdered biodegradable polymer water-retaining material.

2. The method for preparing a natural polymer biodegradable water-retaining material according to claim 1, characterized in that: The unsaturated carboxylic acid monomer is one or a combination of methacrylic acid, acrylic acid and maleic acid.

3. The method for preparing a natural polymer biodegradable water-retaining material according to claim 1, characterized in that: The unsaturated amide monomer is one or a combination of N-vinyl caprolactam, acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide and isopropylacrylamide.

4. The method for preparing a natural polymer biodegradable water-retaining material according to claim 1, characterized in that: The mass ratio of the vinyl unsaturated carboxylic acid monomer to the unsaturated amide monomer is 2-5:1-5.

5. The method for preparing a natural polymer biodegradable water-retaining material according to claim 1, characterized in that: The alkaline solution in step S1 is a 5-10 mol / L potassium hydroxide solution or a sodium hydroxide solution.

6. The method for preparing a natural polymer biodegradable water-retaining material according to claim 1, characterized in that: The degradable plant matrix material is a starch material that has been subjected to a deesterification treatment.

7. The method for preparing a natural polymer biodegradable water-retaining material according to claim 6, characterized in that: The deesterification treatment includes mixing starch with a soluble ester solvent, controlling the water content of the mixture, heating the mixture, and controlling the lipid content in the starch to be below 0.05%.

8. The method for preparing a natural polymer biodegradable water-retaining material according to claim 6, characterized in that: The starch material includes one or a combination of sweet potato starch, potato starch, wheat starch, corn starch, rice starch and tapioca starch.

9. A water-retaining agent prepared by the method for preparing a natural biodegradable polymer water-retaining material according to any one of claims 1 to 8.

10. Use of the water retaining agent prepared by the method for preparing a natural biodegradable polymer water retaining material according to any one of claims 1 to 8 in gardening soil.

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