CN112778060B - Graft copolymerization straw and attapulgite composite water retention material for matrix and preparation method thereof - Google Patents

Graft copolymerization straw and attapulgite composite water retention material for matrix and preparation method thereof Download PDF

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CN112778060B
CN112778060B CN202011566320.5A CN202011566320A CN112778060B CN 112778060 B CN112778060 B CN 112778060B CN 202011566320 A CN202011566320 A CN 202011566320A CN 112778060 B CN112778060 B CN 112778060B
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acrylic acid
acrylamide
water
total mass
attapulgite
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CN112778060A (en
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束胜
王越
郭世荣
周亚广
周鑫鹏
卞越
孙锦
王玉
王健
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Nanjing Agricultural University
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Nanjing Agricultural University
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    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
    • C05G3/80—Soil conditioners
    • 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
    • A01G24/00—Growth substrates; Culture media; Apparatus or methods therefor
    • A01G24/10—Growth substrates; Culture media; Apparatus or methods therefor based on or containing inorganic material
    • 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
    • A01G24/00—Growth substrates; Culture media; Apparatus or methods therefor
    • A01G24/20—Growth substrates; Culture media; Apparatus or methods therefor based on or containing natural organic material
    • A01G24/22—Growth substrates; Culture media; Apparatus or methods therefor based on or containing natural organic material containing plant material
    • 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
    • A01G24/00—Growth substrates; Culture media; Apparatus or methods therefor
    • A01G24/30—Growth substrates; Culture media; Apparatus or methods therefor based on or containing synthetic organic compounds
    • A01G24/35—Growth substrates; Culture media; Apparatus or methods therefor based on or containing synthetic organic compounds containing water-absorbing polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F289/00—Macromolecular compounds obtained by polymerising monomers on to macromolecular compounds not provided for in groups C08F251/00 - C08F287/00
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K17/00—Soil-conditioning materials or soil-stabilising materials
    • C09K17/40—Soil-conditioning materials or soil-stabilising materials containing mixtures of inorganic and organic compounds

Abstract

The invention discloses a graft copolymerization straw and attapulgite composite water retention material for a matrix and a preparation method thereof. The invention uses the straws, the attapulgite and the acrylic acid-acrylamide to carry out polymerization reaction by a microwave radiation polymerization method to generate the super absorbent resin (water retention material), thereby reducing the production cost, having excellent comprehensive performance and wide application range. The straw is creatively and directly used for synthesizing the super absorbent resin, so that the environmental pollution caused by alkali treatment on the super absorbent resin is avoided. The synthesized composite super absorbent resin has excellent comprehensive performance of good water absorption, salt tolerance, high water retention and biodegradability, and is particularly suitable for the fields of soilless culture, agriculture and forestry, environmental protection, gardens and the like.

Description

Graft copolymerization straw and attapulgite composite water retention material for matrix and preparation method thereof
Technical Field
The invention relates to a graft copolymerization straw and attapulgite composite water retention material for a substrate and a preparation method thereof, belongs to the field of preparation of water retention agents of high water absorption materials, and is mainly applied to water retention of seedling raising substrates and soilless culture substrates.
Background
The water-retaining material (water-retaining agent), also called a polymeric water-absorbing agent or a Super Absorbent Polymer (SAP) is a water-swelling polymeric polymer containing strong hydrophilic groups such as carboxyl groups and hydroxyl groups and having a certain degree of crosslinking. The water-absorbing material is insoluble in water and organic solvent, can absorb water which is hundreds to thousands times of the mass of the material compared with the traditional water-absorbing material, has stable gel grid structure formed after water absorption and expansion, is not easy to lose absorbed water under certain pressure, and has good water retention performance. Therefore, the method is widely applied to agriculture and forestry, medical treatment and health, environmental protection, industry and the like.
The super absorbent resin (water retention agent) is mainly divided into three categories according to the source difference of raw materials: starches, celluloses, and synthetic polymers. Currently, most of the superabsorbent polymers on the market are synthetic polymer superabsorbent polymers using petroleum products such as acrylic acid and acrylamide as main raw materials. Although the resin has the advantages of high water absorption rate, high water retention and the like, the resin has the defects of high dependence on non-renewable resources, high production cost, high residual toxicity, difficult degradation, great environmental pollution, incapability of recycling and the like. For the present day that the world is increasingly short of energy and the environmental problem is serious, the application range is gradually limited and the competitiveness in the market is also deteriorated. In order to solve the problem, in recent years, inorganic-organic composite super absorbent resin prepared by using inorganic minerals such as cellulose, plant straws, kaolin, montmorillonite, attapulgite and the like has been developed greatly and shows good comprehensive performance.
As a renewable resource, the straw has abundant yield and low cost in China every year, but the straw is not fully utilized for many years, most of the straw is directly burned after being harvested, so that huge waste of natural resources is caused, and environmental pollution is also caused. The super absorbent resin prepared by using natural plant straws as main raw materials has better biodegradability and salt tolerance, the pH is easy to regulate and control, and a new method is provided for effectively utilizing agricultural waste straws. However, the existing method for preparing super absorbent resin by using plant straws carries out alkali pretreatment on the straws, and a large amount of alkali liquor is generated in the industrial process, thereby causing serious pollution to the environment.
The attapulgite is hydrated magnesium aluminum silicate with a needle-shaped three-dimensional structure, has a large amount of hydrophilic hydroxyl on the surface, can react with organic monomers, is rich in reserves in China, is low in price, and has good salt resistance, adsorption, colloid resistance and other properties. The introduction of the attapulgite clay can not only greatly improve the water absorption and salt tolerance of the resin, but also reduce the production cost, and is beneficial to the industrial production and the widening of the actual application field of the super absorbent resin.
The microwave radiation-promoted chemical reaction technology is a novel high-molecular synthesis technology, and compared with the traditional aqueous solution polymerization method, the microwave radiation polymerization method can greatly shorten the reaction time and improve the production efficiency; the reaction process is uniform, the generation of byproducts can be inhibited, and the environment can not be polluted, so that the method is applied to the field of resin preparation.
Soilless culture refers to a culture method in which water, grass carbon or forest leaf mold, vermiculite and other media are used as substrates for fixing plants, and the plant roots can directly contact with nutrient solution. The components of the nutrient solution in the soilless culture are easy to control and can be adjusted at any time. In places with proper illumination and temperature and no soil, such as deserts, beaches and barren islands, the method can be carried out as long as a certain amount of fresh water is supplied. The soilless culture can effectively save water and fertilizer and achieve high yield, field operations such as intertillage, land turning and the like are not needed, labor and force are saved, the management is convenient, and the requirement of modern development of agriculture in the future is met. Soilless culture is divided into hydroponic culture, aeroponic culture and matrix culture according to the difference of culture media, wherein the matrix culture has great development potential as the main form of soilless culture in China.
The substrate cultivation is a cultivation mode that the root system of the crop is fixed in an organic or inorganic substrate and the crop is supplied with water and nutrient through nutrient solution. The cultivation substrate may be filled in plastic buckets or laid in cultivation trenches or grooves, and is therefore usually carried out in a facility. Compared with the external environment, the temperature of the environment in the facility is higher, and simultaneously, due to the characteristic of strong ventilation of the matrix, the evapotranspiration amount and the leaching loss amount of the matrix moisture are higher, so that the defect that the moisture is not easy to store exists in the matrix cultivation, the water and fertilizer absorption of crops is not uniform, the nutrient deficiency phenomenon frequently occurs, and the sustainable development of the soilless cultivation is restricted. Therefore, the development of the super absorbent resin material suitable for the water retention of the soilless culture substrate is particularly critical, and the water retention capacity is improved and the physical properties are improved by adding the super absorbent resin material into the substrate.
How to make full use of wheat straw resources with rich yield in China and combine with the same rich clay resources, namely attapulgite, to prepare the super absorbent resin suitable for the matrix, and reduce the production cost while exerting the water absorption and retention functions. This is a technical problem to be solved urgently in the technical field.
Disclosure of Invention
Aiming at the problems of rapid water evaporation, difficult preservation, unbalanced nutrients and the like of a soilless culture substrate, the invention provides the graft copolymerization straw and attapulgite composite water retention material for the substrate and the preparation method thereof.
The purpose of the invention can be realized by the following technical scheme:
a preparation method of a graft copolymerization wheat straw and attapulgite composite water-retaining material comprises the following steps:
(1) taking straws as raw materials, drying and crushing the straws at 70 ℃ after cleaning, sieving the straws with a 100-mesh sieve for later use, and crushing attapulgite and sieving the crushed attapulgite with a 200-mesh sieve for later use;
(2) putting an acrylic acid solution into an ice-water bath, neutralizing part of acrylic acid with a sodium hydroxide solution to obtain an acrylic acid-sodium acrylate mixed solution, wherein the neutralization degree of the acrylic acid is 50% -80%, then weighing a certain amount of acrylamide, dissolving the acrylamide in the acrylic acid-sodium acrylate mixed solution, adding distilled water to control the water content of a reaction system to be 65% -70%, sequentially adding potassium persulfate and sodium thiosulfate pentahydrate serving as redox composite initiators, adding N, N' -methylene bisacrylamide serving as a cross-linking agent after dissolving, stirring and dissolving, and storing the mixed solution in the ice-water bath for later use;
(3) putting the straw powder obtained in the step (1) into a beaker, adding distilled water for wetting, putting into a microwave oven, gelatinizing at a medium-low fire gear, taking out, adding the attapulgite powder in the step (1), uniformly mixing, and cooling in an ice-water bath;
(4) adding the mixed solution obtained in the step (2) into the beaker obtained in the step (3), mechanically stirring for 10min, sealing the opening of the beaker by using a preservative film, putting the beaker into an ultrasonic device for ultrasonic dispersion for a period of time, taking out the beaker for cooling in an ice water bath, then putting the beaker into a microwave oven, carrying out microwave radiation polymerization reaction for 9-10min at a low fire level to obtain a honeycomb product, washing unreacted substances on the product by using absolute ethyl alcohol, soaking the product for 12h, finally drying the product in a 70 ℃ oven to constant weight, and shearing to obtain a composite water-retaining agent; wherein the straw powder accounts for 7.5-20.0% of the total mass of the acrylic acid and the acrylamide, and the attapulgite powder accounts for 5.0-25.0% of the total mass of the acrylic acid and the acrylamide.
As a preferable selection of the invention, the straws are selected from wheat straws, rice straws, corn straws and sorghum straws, and wheat straws are preferable.
In a further preferred embodiment of the present invention, the acrylic acid solution in the step (2) has a mass fraction of 50%, the sodium hydroxide solution has a mass fraction of 30%, and the molar ratio of acrylic acid to sodium hydroxide is 10: 5-10: 8, preferably 10: 6; the mass ratio of acrylic acid to acrylamide is 1: 2-5: 1, preferably 2:1,; the molar ratio of the potassium persulfate to the sodium thiosulfate pentahydrate is 3: 1, the total mass of the potassium persulfate and the sodium thiosulfate pentahydrate accounts for 0.6-1.6 percent of the total mass of the acrylic acid and the acrylamide, and the total mass is preferably 1.0 percent; the N, N' -methylene-bisacrylamide accounts for 0.05-0.30%, preferably 0.15% of the total mass of the acrylic acid and the acrylamide.
As a further preferred aspect of the present invention, the mass ratio of the wheat straw powder to the distilled water in step (3) is 1: 10, the power of the microwave oven is 280W, and the radiation time is 2 min.
As a further preferred aspect of the present invention, the ultrasonic dispersion in step (4) has a power of 300W, a frequency of 40kHz, an ultrasonic dispersion time of 1h, and a microwave power of 119W.
As a further optimization of the invention, the wheat straw powder accounts for 15.0 percent of the total mass of the acrylic acid and the acrylamide.
Preferably, as a further preference of the present invention, the attapulgite powder accounts for 5.0% of the total mass of acrylic acid and acrylamide.
The graft copolymerization straw and attapulgite composite water-retaining agent prepared by the preparation method is provided.
The invention relates to application of a graft copolymerization straw and attapulgite composite water-retaining material in preparing a seedling culture or cultivation substrate.
The graft copolymerization straw and attapulgite composite water retention material can be used as a soil water retention agent in agricultural production, is applied to soil to improve the water retention capacity of the soil and relieve drought stress on crops, and has biodegradability and no pollution to the soil due to the fact that the straw and attapulgite are used as main components.
The graft copolymerization straw and attapulgite composite water retention material can be blended with a seedling culture substrate or a culture substrate, is used for facility soilless substrate culture, improves the water retention capacity of the substrate, reduces the water evaporation loss caused by high temperature in the facility, and reduces the loss of nutrients.
Has the advantages that:
1. the composite water-retaining material is synthesized by using cheap materials such as wheat straws, attapulgite and the like, so that the production cost is reduced, the comprehensive performance is excellent, and the application range is wide. The wheat straw is creatively and directly used for synthesizing the water-retaining agent, so that the environmental pollution caused by alkali treatment on the wheat straw is avoided. The synthesized composite water-retaining agent has excellent comprehensive performance of good water absorption, salt tolerance, high water retention and biodegradability, and is particularly suitable for the fields of soilless culture, agriculture and forestry, environmental protection, gardens and the like.
2. The invention adopts the microwave radiation polymerization method for polymerization reaction, greatly shortens the reaction time, improves the synthesis efficiency, reduces the energy consumption, can also reduce the generation of byproducts, does not pollute the environment, does not need nitrogen protection in the synthesis process and has safe synthesis compared with the traditional aqueous solution polymerization method.
3. The invention has the advantages of simple preparation process, wide raw material source, low cost, no toxicity, environmental protection and no pollution.
Drawings
FIG. 1 is a flow chart of a synthetic process of a graft copolymerization wheat straw and attapulgite composite water-retaining material;
FIG. 2 is a diagram showing the appearance of the graft copolymer wheat straw and attapulgite composite water-retaining material before and after water absorption;
FIG. 3 is a schematic view showing the effect of the mass ratio of Acrylic Acid (AA) and Acrylamide (AM) on the liquid-absorbing capacity of the composite water-retaining material;
FIG. 4 is a schematic view showing the effect of Acrylic Acid (AA) neutralization degree on the liquid-absorbing capacity of the composite water-retaining material;
FIG. 5 is a schematic illustration of the effect of initiator dosage on the absorbency of a composite water retention material;
FIG. 6 is a schematic illustration of the effect of the amount of cross-linking agent on the absorbency of the composite water retention material;
FIG. 7 is a schematic view showing the effect of the amount of wheat straw powder on the liquid absorbency of the composite water-retaining material;
FIG. 8 is a schematic view showing the effect of the amount of attapulgite powder on the liquid absorption rate of the composite water-retaining material.
Detailed Description
The present invention is further described with reference to specific examples, but the examples described are only a part of the examples of the present invention, and not all of the examples.
Example 1:
a preparation method and a liquid absorption rate test of a composite water-retaining material comprise the following steps:
(1) preparing wheat straw powder: washing with water to remove soil and dust on the surface of wheat straw, oven drying the straw in a 70 deg.C oven, pulverizing with a pulverizer, sieving with 100 mesh sieve, and storing in a sealed bag for use, wherein the wheat straw is purchased from Huaian Chaihe agricultural science and technology GmbH.
(2) Putting a 50mL round bottom glass beaker in an ice-water bath, adding 6.67mL distilled water and 6.36mL Acrylic Acid (AA), fully stirring and mixing to obtain an acrylic acid solution with the mass fraction of 50%, then neutralizing the acrylic acid solution with 5.58mL of 30% sodium hydroxide solution by mass fraction, fully stirring and mixing to obtain an acrylic acid-sodium acrylate mixed solution with the neutralization degree of 60%, then weighing 3.33g of Acrylamide (AM) to be dissolved in the acrylic acid-sodium acrylate mixed solution, adding 8mL of distilled water, fully stirring and mixing to obtain a composite monomer mixed solution, simultaneously respectively weighing 0.077g of potassium persulfate, 0.023g of sodium thiosulfate pentahydrate and 0.015g of N, N' -methylenebisacrylamide (NMBA), and sequentially adding the composite monomer mixed solution, fully mixing to obtain a mixed reaction solution, and placing for later use under the ice-water bath condition.
(3) 1.5g of wheat straw powder is put into a 200mL round bottom glass beaker, added with 15mL of distilled water and stirred uniformly, put into a P70D20TP-C6(W0) type Glanshi microwave oven and gelatinized for 2min at a medium and low fire gear to obtain a straw gelatinized substance, then 0.5g of attapulgite powder (200 meshes) is weighed and added into the beaker, mixed uniformly and put into an ice water bath for cooling, and the attapulgite powder is produced in Xuyi county of Jiangsu province.
(4) Pouring the mixed reaction liquid obtained in the step (2) into the glass beaker obtained in the step (3), uniformly mixing, mechanically stirring for 10min by using a magnetic stirrer, sealing the mouth of the beaker by using two layers of preservative films, putting the beaker into an ultrasonic cleaner with the power of 300W and the frequency of 40kHz, ultrasonically dispersing for 1h, taking out the beaker, putting the beaker into an ice-water bath for cooling for 5min, uniformly shaking the mixed liquid, putting the mixed liquid into a microwave oven, carrying out microwave radiation polymerization reaction for 9min at a low-fire gear, taking out, putting the obtained honeycomb colloid into absolute ethyl alcohol, washing for 2 times, shearing, continuously adding the absolute ethyl alcohol, soaking for 12h, and finally putting the honeycomb colloid into a 70 ℃ oven to dry to constant weight to obtain the finished product composite water-retaining agent.
Tests prove that the maximum distilled water absorption rate of the obtained graft copolymerization wheat straw and attapulgite composite water-retaining material reaches 929.64g/g, and the maximum physiological saline water absorption rate reaches 42.97 g/g.
The method for testing the liquid absorption rate is as follows:
weighing 0.25g of water-retaining agent, putting the water-retaining agent into a 500mL glass beaker, adding 500mL of distilled water or normal saline, swelling at room temperature until the water absorption is saturated, taking out, standing for 30min under a 200-mesh screen until no water is dripped within 30s, weighing the mass of the resin at the moment, and calculating the liquid absorption rate according to the following formula:
Q＝(m1-m2)/m2
wherein Q-liquid absorption Rate, g/g
m1-water retentionMass of the agent after imbibition saturation, g
m2Mass of water-retaining agent before imbibition, g
Example 2:
as described in example 1, except that the amount of attapulgite powder was changed: 1.0g of attapulgite powder is added into a 500mL beaker and mixed with gelatinized wheat straw, and the rest of the operation is the same as that in example 1.
Tests prove that the maximum distilled water absorption rate of the obtained graft copolymerization wheat straw and attapulgite composite water-retaining material reaches 900.56g/g, and the maximum physiological saline water absorption rate reaches 37.46 g/g.
Example 3:
as described in example 1, except that the amount of the cross-linking agent and the amount of the attapulgite powder were changed: adding 0.020g of NMBA into the composite monomer mixed solution, fully and uniformly stirring, and carrying out the same operation as in example 1; 1.0g of attapulgite powder is added into a 500mL beaker and mixed with gelatinized wheat straw, and the rest of the operation is the same as that in example 1.
Tests prove that the maximum distilled water absorption rate of the obtained graft copolymerization wheat straw and attapulgite composite water-retaining material reaches 855.96g/g, and the maximum physiological saline water absorption rate reaches 38.06 g/g.
Comparative example:
as described in example 1, except that the attapulgite powder was not added: putting 1.5g of wheat straw powder into a 200mL round-bottom glass beaker, adding 15mL of distilled water, uniformly stirring, putting into a P70D20TP-C6(W0) type Glanshi microwave oven, gelatinizing for 2min at a low-medium fire position to obtain straw paste, and putting into an ice-water bath for cooling. The rest of the procedure was as in example 1.
Tests show that the maximum distilled water absorption multiplying power of the obtained water-retaining material reaches 742.87g/g, and the maximum physiological saline absorption multiplying power reaches 35.06 g/g.
Optimization experiment of synthesis process conditions of graft copolymerization straw and attapulgite composite water-retaining material
Experiment 1:
when the neutralization degree of acrylic acid is 70%, the adding amount of an initiator potassium persulfate and anhydrous sodium thiosulfate is 1.0% of the total mass of the monomer, the adding amount of a crosslinking agent N, N' -methylenebisacrylamide is 0.20% of the total mass of the monomer, the adding amount of straw powder is 15% of the total mass of the monomer, and the adding amount of attapulgite powder is 10% of the total mass of the monomer, 50 wt% acrylic acid solution with different volumes and acrylamide with different masses are added to change the mass ratio of the composite monomer, and the composite water-retaining agent under different mass ratios of the monomers is synthesized according to the process of example 1, washed, dried and reserved. 0.25g of the composite water-retaining agent was weighed, and the liquid-absorption rate was measured as described in example 1, and the liquid-absorption rate of the obtained water-retaining agent is shown in FIG. 3.
And (4) conclusion: the product absorbency ratio shows a trend of increasing first and then decreasing with the increase of the mass ratio of acrylic acid to acrylamide, and when the mass ratio of the monomers is 2: the deionized water absorption rate and the normal saline absorption rate of the product reach the highest value at 1 hour.
Experiment 2:
when the mass ratio of acrylic acid to acrylamide is 2:1, adding 1.0 percent of initiator potassium persulfate and anhydrous sodium thiosulfate, 0.20 percent of cross-linking agent N, N' -methylene bisacrylamide, 15 percent of straw powder and 10 percent of attapulgite powder, changing the neutralization degree of acrylic acid by adding 30 percent by weight of sodium hydroxide solution with different volumes, synthesizing according to the process of example 1 to obtain the composite water-retaining agent with different acrylic acid neutralization degrees, washing, drying and reserving. 0.25g of the composite water-retaining agent was weighed, and the liquid-absorption rate was measured as described in example 1, and the liquid-absorption rate of the obtained water-retaining agent is shown in FIG. 4.
And (4) conclusion: the influence of the neutralization degree of acrylic acid absorbed by the product by the deionized water absorption rate is relatively small, and the highest acrylic acid neutralization degree is achieved when the neutralization degree of acrylic acid is 55%, while the highest physiological saline absorption rate is achieved when the neutralization degree of acrylic acid is 60%, and the optimal acrylic acid neutralization degree is 60% by comprehensively considering the water absorption and salt absorption performances.
Experiment 3:
when the mass ratio of acrylic acid to acrylamide is 2:1, the neutralization degree of acrylic acid is 60%, the addition amount of a cross-linking agent N, N' -methylene bisacrylamide is 0.20% of the total mass of the monomers, the addition amount of straw powder is 15% of the total mass of the monomers, and when the addition amount of attapulgite powder is 10% of the total mass of the monomers, composite water-retaining agents with different initiator amounts are obtained by synthesizing according to the process of the embodiment 1 by changing the addition amounts of initiators potassium persulfate and sodium thiosulfate pentahydrate, and the composite water-retaining agents are washed, dried and reserved. 0.25g of the composite water-retaining agent was weighed, and the liquid-absorption rate was measured as described in example 1, and the liquid-absorption rate of the obtained water-retaining agent is shown in FIG. 5.
And (4) conclusion: the difference is that the deionized water absorption rate reaches the maximum value at 1.2 percent, the physiological saline absorption rate reaches the maximum value at 1.0 percent, and the optimal initiator addition amount is 1.0 percent under comprehensive consideration.
Experiment 4:
when the mass ratio of acrylic acid to acrylamide is 2:1, the neutralization degree of acrylic acid is 60%, the addition amounts of an initiator potassium persulfate and anhydrous sodium thiosulfate are 1.0% of the total mass of the monomers, the addition amount of straw powder is 15% of the total mass of the monomers, and when the addition amount of attapulgite powder is 10% of the total mass of the monomers, the composite water-retaining agent synthesized according to the process of example 1 under different addition amounts of N, N '-methylenebisacrylamide is researched, washed and dried for later use by changing the addition amount of a cross-linking agent N, N' -methylenebisacrylamide. 0.25g of the composite water-retaining agent was weighed, and the liquid-absorption rate was measured as described in example 1, and the liquid-absorption rate of the obtained water-retaining agent is shown in FIG. 6.
And (4) conclusion: the influence of the using amount of the cross-linking agent on the liquid absorption rate of the product is large, the deionized water absorption rate and the physiological saline absorption rate of the product also show a tendency that the deionized water absorption rate and the physiological saline absorption rate of the product increase firstly and then decrease along with the increase of the using amount of the cross-linking agent, the deionized water absorption rate reaches the maximum value at 0.15 percent, the physiological saline absorption rate reaches the maximum value at 0.10 percent, but when the using amount of the cross-linking agent is 0.10 percent, the surface viscosity of the product is large, the product is easy to adhere to the wall of a container and is difficult to be completely taken out of a reaction container, and the optimal adding amount of the cross-linking agent is 0.15 percent in consideration of the difficulty degree of the operation process and the liquid absorption rate.
Experiment 5:
when the mass ratio of acrylic acid to acrylamide is 2:1, the neutralization degree of acrylic acid is 60%, the adding amounts of an initiator potassium persulfate and anhydrous sodium thiosulfate are 1.0% of the total mass of the monomer, the adding amount of a cross-linking agent N, N' -methylene bisacrylamide is 0.15% of the total mass of the monomer, and the adding amount of attapulgite powder is 10% of the total mass of the monomer, changing the adding amount of the wheat straw powder, synthesizing according to the process of example 1 to obtain the composite water-retaining agents with different wheat straw powder using amounts, washing, drying and reserving. 0.25g of the composite water-retaining agent was weighed, and the liquid-absorption rate was measured as described in example 1, and the liquid-absorption rate of the obtained water-retaining agent is shown in FIG. 7.
And (4) conclusion: the liquid absorption rate of the product shows a trend of increasing firstly and then decreasing along with the increase of the using amount of the wheat straw powder, the deionized water absorption rate reaches the highest at 15.0%, and the physiological saline absorption rates are the highest at 12.5%, 15.0% and 17.5% without obvious difference, so that the optimal using amount of the wheat straw powder is 15.0%.
Experiment 6:
when the mass ratio of acrylic acid to acrylamide is 2:1, the neutralization degree of acrylic acid is 60%, the addition amounts of an initiator potassium persulfate and anhydrous sodium thiosulfate are 1.0% of the total mass of the monomers, the addition amount of a cross-linking agent N, N' -methylenebisacrylamide is 0.15% of the total mass of the monomers, and when the addition amount of wheat straw powder is 15% of the total mass of the monomers, the composite water-retaining agent synthesized according to the process of example 1 under different addition amounts of attapulgite powder is researched, and the composite water-retaining agent is washed, dried and reserved. 0.25g of the composite water-retaining agent was weighed, and the liquid-absorption rate was measured as described in example 1, and the liquid-absorption rate of the obtained water-retaining agent is shown in FIG. 8.
And (4) conclusion: the liquid absorption rate of the product shows a trend of increasing first and then decreasing along with the increase of the dosage of the attapulgite powder, and the deionized water absorption rate and the physiological saline absorption rate of the product reach the highest when the dosage of the attapulgite powder is 5 percent of the total mass of the monomers.

Claims (7)

1. A preparation method of a graft copolymerization straw and attapulgite composite water-retaining material for a substrate is characterized by comprising the following steps:
(1) taking wheat straws as a raw material, cleaning, drying at 70 ℃, crushing, sieving with a 100-mesh sieve for later use, and crushing attapulgite and sieving with a 200-mesh sieve for later use;
(2) placing an acrylic acid solution in an ice-water bath, neutralizing part of acrylic acid with a sodium hydroxide solution to obtain an acrylic acid-sodium acrylate mixed solution, wherein the neutralization degree of the acrylic acid is 60%, then weighing a certain amount of acrylamide, dissolving the acrylamide in the acrylic acid-sodium acrylate mixed solution, adding distilled water to control the water content of a reaction system to be 65% -70%, sequentially adding potassium persulfate and sodium thiosulfate pentahydrate serving as redox composite initiators, adding N, N' -methylene bisacrylamide serving as a cross-linking agent after dissolving, stirring and dissolving, and storing the mixed solution in the ice-water bath for later use; the mass fraction of the acrylic acid solution is 50%, the mass fraction of the sodium hydroxide solution is 30%, and the molar ratio of acrylic acid to sodium hydroxide is 10: 5-10: 8, the mass ratio of acrylic acid to acrylamide is 1: 2-5: 1, the molar ratio of potassium persulfate to sodium thiosulfate pentahydrate is 3: 1, the total mass of potassium persulfate and sodium thiosulfate pentahydrate accounts for 0.6-1.6 percent of the total mass of acrylic acid and acrylamide, and the total mass of N, N' -methylene bisacrylamide accounts for 0.05-0.30 percent of the total mass of acrylic acid and acrylamide;
(3) putting the wheat straw powder obtained in the step (1) into a beaker, adding distilled water for wetting, putting into a microwave oven, gelatinizing at a medium-low fire gear, taking out, adding the attapulgite powder obtained in the step (1), uniformly mixing, and cooling in an ice-water bath; the mass ratio of the wheat straw powder to the distilled water is 1: 10, the wheat straw powder accounts for 7.5-20.0% of the total mass of the acrylic acid and the acrylamide, the power of a microwave oven is 280W, the radiation time is 2min, and the attapulgite powder accounts for 5.0-25.0% of the total mass of the acrylic acid and the acrylamide;
(4) adding the mixed solution obtained in the step (2) into the beaker obtained in the step (3), mechanically stirring for 10min, sealing the opening of the beaker by using a preservative film, putting the beaker into an ultrasonic device for ultrasonic dispersion for a period of time, taking out the beaker to be cooled in an ice water bath, then putting the beaker into a microwave oven, carrying out microwave radiation polymerization reaction for 9-10min at a low fire level to obtain a honeycomb product, washing unreacted substances on the product by using absolute ethyl alcohol, soaking the product for 12h, finally drying the product in a 70 ℃ oven to constant weight, and shearing the product to obtain a composite water retention material; the power of ultrasonic dispersion is 300W, the frequency is 40kHz, the ultrasonic dispersion time is 1h, and the microwave power is 119W.
2. The production method according to claim 1, wherein the molar ratio of acrylic acid to sodium hydroxide in the step (2) is 10: 6.
3. The production method according to claim 1, characterized in that the mass ratio of acrylic acid and acrylamide in the step (2) is 2: 1.
4. The production process according to claim 1, wherein in the step (2), the total mass of potassium persulfate and sodium thiosulfate pentahydrate accounts for 1% of the total mass of acrylic acid and acrylamide, and N, N' -methylenebisacrylamide accounts for 0.15% of the total mass of acrylic acid and acrylamide.
5. The preparation method according to claim 1, wherein the wheat straw powder in the step (3) accounts for 10% of the total mass of the acrylic acid and the acrylamide; the attapulgite powder accounts for 5 percent of the total mass of the acrylic acid and the acrylamide.
6. The graft copolymerization straw and attapulgite composite water retention material prepared by the preparation method of any one of claims 1 to 5.
7. The application of the graft copolymerization straw and attapulgite composite water retention material in the preparation of a soil water retention agent or a seedling/cultivation substrate.
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