Wheat straw-based agricultural and forestry water-retaining agent and preparation method thereof

Abstract

The application relates to the technical field of agricultural water-retaining agents, and discloses a wheat straw-based agricultural and forestry water-retaining agent and a preparation method thereof, which is prepared through the following steps: S1, wheat straw cellulose extraction: after being crushed, wheat straw is sequentially subjected to alkali extraction, acid extraction, neutralization reaction liquid pH and ultrasonic treatment, and then filtered to obtain neutral wheat straw cellulose; S2, wheat straw cellulose carboxymethylation modification: wheat straw cellulose is mixed with NaOH and chloroacetic acid, and then washed with ethanol to obtain wheat straw-based carboxymethyl cellulose; and S3, crosslinking reaction: the wheat straw-based carboxymethyl cellulose is dissolved in a NaOH solution, crosslinked by using epichlorohydrin, and washed and dried to obtain the wheat straw-based agricultural and forestry water-retaining agent. The wheat straw is used as a synthetic raw material, which is different from the traditional method, the wheat straw-based agricultural and forestry water-retaining agent also achieves good water absorption effect, and effectively avoids the environmental toxicity risk caused by the monomer residue of the existing market polyacrylate or polyacrylamide water-retaining agent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of agroforestry water-retaining agents, and particularly relates to a wheat straw-based agroforestry water-retaining agent and a preparation method thereof. BACKGROUND

[0002] The commonly used agroforestry water-retaining agents in actual agricultural production are mainly acrylamide-acrylic acid salt copolymer and starch / cellulose grafted acrylic acid salt copolymer 2, and the current market leader is polyacrylic acid-sodium acrylate polymer. Research has found that water-soluble components such as acrylic acid and acrylamide are inevitably left in the agroforestry water-retaining agent. Acrylic acid is biologically toxic to animals, and if the agroforestry water-retaining agent absorbs water to form a hydrogel in the soil, the degradation rate of acrylic acid will be reduced, which may cause harm to crops; acrylamide is listed as a 2A carcinogen by the International Agency for Research on Cancer (IARC), and some studies have shown that acrylamide monomers can be transferred from agroforestry water-retaining agent hydrogels to crops, and then amplified through the food chain, so the acrylamide left in the agroforestry water-retaining agent will pose a potential threat to human health.

[0003] Chen et al. found that when corn seedlings were cultured with polyacrylic acid sodium and polyacrylic acid potassium type water-retaining agents, the leaf tips of the corn seedlings curled and turned yellow after 3 days of culture, and the root system was significantly atrophied and deformed; after 6 days of culture, the leaf blades of the seedlings treated with polyacrylic acid sodium and polyacrylic acid potassium were withered, and the root system was rotten (Chen X, Huang L, Mao X, et al. A comparative study of the cellular microscopic characteristics and mechanisms of maize seedling damage from superabsorbent polymers[J]. Pedosphere, 2017, 27(2): 274-282.). The hydroponic test of corn seedlings showed that when the concentration of acrylic acid in the hydroponic nutrient solution was 2.5 mg / L, the growth of the main roots of corn was significantly inhibited, and the biomass of the aboveground part of the corn seedlings was significantly reduced; when the concentration of acrylic acid was more than 5 mg / L, the roots of the corn seedlings would rot, the root cap ratio would decrease, and the root surface area and volume would also significantly decrease (Chen X, Mao X Y, Lu Q, et al. Characteristics and mechanisms of acrylate polymer damage to maize seedlings[J]. Ecotoxicology and Environmental Safety, 2016, 129: 228-234.).

[0004] The direct synthesis of agro-forestry water retaining agent from wheat straw can avoid the problem of monomer (acrylic acid, acrylamide) residue of high molecular polymer. At present, there are few studies on the preparation of agro-forestry water retaining agent using straw as the only raw material. The related background technology is mainly to use straw as a raw material to graft copolymerize with acrylic acid and acrylamide to synthesize agro-forestry water retaining agent. In fact, the main water absorption performance is still the role of polyacrylate and polyacrylamide. In fact, it is rare to directly use straw to synthesize agro-forestry water retaining agent, but there are some reports on the synthesis of agro-forestry water retaining agent using cellulose and its derivatives (such as carboxymethyl cellulose and hydroxypropyl cellulose).

[0005] In recent years, cellulose derivatives have been widely used in the synthesis of agro-forestry water retaining agents. Common cellulose derivatives include methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose. The prior art discloses a method for preparing hydroxyethyl cellulose (HEC) / carboxymethyl cellulose (CMC) hydrogel using citric acid as a crosslinking agent. Compared with previous crosslinking agents, this method can effectively overcome the toxicity and cost problems. At a citric acid concentration of 3.75%, the prepared hydrogel can achieve an expansion ratio of 900 (Demitri C, Sole R D, Scalera F, et al. Novel superabsorbent cellulose-based hydrogels crosslinked with citric acid [J]. Journal of Applied Polymer Science, 2008, 110(4): 2453-2460.).

[0006] In addition, concentrated aqueous solutions of cellulose derivatives, such as carboxymethyl cellulose, hydroxypropyl cellulose (HPC), and methyl cellulose (MC), can undergo crosslinking reactions under ionizing radiation, thereby preparing cellulose-based hydrogels. Carboxymethyl cellulose with high substitution degree and high concentration can be effectively crosslinked to form CMC hydrogel by irradiation. Zhang Zhicheng et al. used carboxymethyl cellulose as a raw material and epichlorohydrin (ECH) as a crosslinking agent to successfully synthesize an agro-forestry water retaining agent with a water absorption capacity of up to 969 g / g (Zhang Zhicheng. Synthesis and slow-release fertilizer application of salt-tolerant water retaining agent [D]. Shanghai: East China University of Technology, 2019.).

[0007] In summary, there is no technology or method in the prior art for extracting wheat straw cellulose, preparing wheat straw-based carboxymethyl cellulose from wheat straw cellulose, and crosslinking wheat straw-based carboxymethyl cellulose with low-dose epichlorohydrin to prepare a high-water-absorption-performance straw-based agro-forestry water retaining agent. The present invention creates a technology for directly preparing agro-forestry water retaining agent from straw, providing an important technical reference for the preparation of green agro-forestry water retaining agent. SUMMARY

[0008] The present application aims to develop a new straw-based agricultural and forestry water retaining agent based on the need for resource utilization of agricultural waste and the ecological and environmental toxicity risk of existing agricultural and forestry water retaining agents, so as to reduce or avoid the environmental toxicity risk problem caused by the monomer residue (acrylic acid, acrylamide) of traditional commercial agricultural and forestry water retaining agents (such as polyacrylate). The agricultural and forestry water retaining agent is synthesized by agricultural waste wheat straw, which provides a new path and technical support for straw resource utilization and green agricultural and forestry water retaining agent research and development.

[0009] In order to achieve the above-mentioned purpose, the present application provides a preparation method of a wheat straw-based agricultural and forestry water retaining agent, characterized by the following steps:

[0010] S1, wheat straw cellulose extraction: after the wheat straw is crushed, it is sequentially subjected to alkali extraction (NaOH solution, 105 DEG C reaction for 2h), acid extraction (H2SO4 solution, 115 DEG C reaction for 2h), neutralization of the reaction solution pH, ultrasonic treatment, and finally filtration to obtain neutral wheat straw cellulose;

[0011] S2, carboxymethylation modification of wheat straw cellulose: wheat straw cellulose is reacted with NaOH and chloroacetic acid at a mass ratio of 1:0.8:1, using 100 ml of 90% ethanol solution as the reaction medium, at 70 DEG C for 2h, and then washed with ethanol to obtain wheat straw-based carboxymethyl cellulose;

[0012] S3, crosslinking reaction: wheat straw-based carboxymethyl cellulose is mixed with NaOH solution at a mass / volume ratio of 1.0-1.3 g:10 mL, stirred uniformly, then epoxy chloropropane is added, stirred uniformly, and the reaction solution is placed in an oven for 12h, washed and dried to obtain a wheat straw-based agricultural and forestry water retaining agent.

[0013] Preferably, the mass concentration of sodium hydroxide solution for alkali extraction and acid extraction in S1 is 1%-10%, preferably 5%; the concentration of sulfuric acid solution is 1%-10%, preferably 5%; the reaction solution for cellulose extraction by acid and alkali combination needs to be treated by ultrasonic treatment for 5-30 min, preferably 20 min, and washed with deionized water until the pH of the reaction solution is neutral (pH 7-8).

[0014] Preferably, the concentration of the ethanol solution used to wash the wheat straw-based carboxymethyl cellulose in S2 is 65%-90%, preferably 70%.

[0015] Preferably, the mass concentration of NaOH solution used in S3 is 1%-10%, preferably 9%.

[0016] Preferably, the amount (mass) of epoxy chloropropane used in S3 is 20%-110% of the mass of wheat straw-based carboxymethyl cellulose, preferably 30%.

[0017] Preferably, the oven setting temperature range in S3 is 30-100℃, preferably 60℃.

[0018] Preferably, the drying method in S3 is fumehood drying for 12-24 h or 60℃ oven drying for 12 h, preferably fumehood drying for 24 h.

[0019] The application provides a wheat straw-based agricultural and forestry water-retaining agent, and the water absorption multiple is 0-300 g / g (deionized water).

[0020] The application provides an application of the wheat straw-based agricultural and forestry water-retaining agent, and the wheat straw-based agricultural and forestry water-retaining agent is used for soil moisture retention, crop root moisture retention or desertification treatment in a drought area.

[0021] Compared with the prior art, the application has the beneficial effects that:

[0022] The wheat straw-based agricultural and forestry water-retaining agent uses wheat straw as a synthetic raw material, which is completely different from the traditional method of preparing a water-absorbing resin agricultural and forestry water-retaining agent by monomer polymerization. The wheat straw-based agricultural and forestry water-retaining agent also achieves good water absorption effect, effectively avoids the environmental toxicity risk caused by monomer residue of a polyacrylate or polyacrylamide agricultural and forestry water-retaining agent in the market. The preparation condition is normal temperature and pressure, the reaction raw material is cheap and easy to obtain, and there is no monomer (acrylic acid, acrylamide) residue and heavy metal, so that the wheat straw-based agricultural and forestry water-retaining agent is a new type of agricultural and forestry water-retaining agent. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The XRD characterization graph of the agricultural and forestry water-retaining agent product prepared in the application is shown in the figure;

[0024] Figure 2 The FT-IR characterization graph of the agricultural and forestry water-retaining agent product prepared in the application is shown in the figure;

[0025] Figure 3 The EDS characterization graph of the agricultural and forestry water-retaining agent product prepared in the application is shown in the figure;

[0026] Figure 4 The SEM characterization graph of the agricultural and forestry water-retaining agent product prepared in the application is shown in the figure;

[0027] Figure 5 The TG-DSC characterization graph of the agricultural and forestry water-retaining agent product prepared in the application is shown in the figure;

[0028] Figure 6 The technical route schematic diagram of preparing the agricultural and forestry water-retaining agent from the wheat straw in the application is shown in the figure. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the technical solutions of the present application will be described in detail below with specific examples and comparative examples to ensure that those skilled in the art can fully understand and implement the present application.

[0030] Example 1: 50.0 g of wheat straw was dried, crushed by a crusher, and sieved through a 40-mesh sieve to obtain wheat straw powder. 20.0 g of the wheat straw powder was taken into a 1000 mL three-necked flask, and 400 mL of a 5% (w / w) NaOH solution was added. The three-necked flask was placed in a heat collecting constant temperature magnetic stirrer (silicon oil as heat conducting medium), the temperature was set to 105°C, a condensation reflux device was added, and magnetic stirring was performed for 2 h. After the reaction was completed, the reaction solution was cooled to room temperature, and the wheat straw alkali extract retained on the sieve was washed with deionized water for 4 times, each time for 30 s. Then, the wheat straw alkali extract on the sieve was transferred to a 1000 mL beaker, 800 mL of deionized water was added, 1% (w / w) H2SO4 solution was used to adjust the pH to 7-8, and the solution in the beaker was filtered through a 300-mesh sieve to obtain a neutral wheat straw alkali extract.

[0031] The neutral wheat straw alkali extract was transferred to a 1000 mL three-necked flask, 400 mL of a 5% (w / w) H2SO4 solution was added, the three-necked flask was placed in a heat collecting constant temperature magnetic stirrer, the temperature was set to 115°C, a condensation reflux device was added, and magnetic stirring was performed for 2 h. After the reaction was completed, the reaction solution was filtered through a 300-mesh sieve, the wheat straw acid extract retained on the sieve was washed with deionized water for 4 times, each time for 30 s. Then, the wheat straw acid extract on the sieve was transferred to a 1000 mL beaker, 800 mL of deionized water was added, ultrasonic treatment was performed for 20 min, 1% (w / w) NaOH solution was used to adjust the pH to 7-8, and the solution in the beaker was filtered through a 300-mesh sieve to obtain a neutral wheat straw acid extract. The neutral wheat straw acid extract was subjected to suction filtration, and the filter cake was placed in an oven for 12 h (60°C). The filter cake was the extracted wheat straw cellulose.

[0032] The filter cake was crushed and sieved through a 40-mesh sieve to obtain wheat straw cellulose powder. 5.0 g of the extracted wheat straw cellulose powder was taken into a 1000 mL three-necked flask, and 100 mL of an ethanol solution with a volume fraction of 90% was added.

[0033] Subsequently, experiments were carried out according to the mass ratio of cellulose: sodium hydroxide: chloroacetic acid of 1:0.8:1, 4.0 g of NaOH was added, magnetic stirring was carried out at 30℃ for 40 min, the temperature was set to 70℃, a condensation reflux device was installed on the three-necked flask, 5.0 g of chloroacetic acid was added, and magnetic stirring was continued for 2 h. After the reaction was completed, the reaction liquid was suction filtered, the filter cake was transferred to 100 mL of 75% ethanol solution, magnetic stirring was carried out for 1 min, suction filtration was carried out, the filter cake was washed with 100 mL of 75% ethanol solution again, magnetic stirring was carried out for 1 min, suction filtration was carried out, the filter cake was transferred to 250 mL of 70% ethanol solution for washing, magnetic stirring was carried out for 10 min, suction filtration was carried out, and the washed filter cake was placed in a 60℃ oven for 12 h. The filter cake was crushed and sieved through a 40 mesh sieve to obtain the straw-based carboxymethyl cellulose prepared from wheat straw cellulose.

[0034] The prepared straw-based carboxymethyl cellulose was crushed and sieved through a 40 mesh sieve, 10 mL of a 9% mass concentration NaOH solution was added to a 10 mL beaker, 1.1 g of straw-based carboxymethyl cellulose powder (CMC) was added, and slow stirring was carried out to mix them uniformly until they were completely dissolved. Then, 0.3 mL of epichlorohydrin was added, slow stirring was carried out for 1 min, the 10 mL beaker was sealed with aluminum foil, and the rubber band was tightened. The reaction was carried out in a 60℃ oven for 12 h. The reaction was taken out, and the product was placed in a fume hood for air drying for 24 h.

[0035] The water absorption of Example 1 was tested. After the straw-based agricultural and forestry water retaining agent was dried, an agricultural and forestry water retaining agent sample with a mass of about 0.01-0.05 g was cut with scissors, weighed, and the mass was recorded as m1. Then, it was placed in 100 mL of deionized water, and the water absorption was carried out for 24 h. Then, the free water was filtered out through a 100 mesh sieve, the water gel retained on the sieve was taken out and weighed, recorded as m2, and the water absorption multiple was obtained. At the same time, chlorine star water retaining agent, green alliance water retaining agent, green full water retaining agent, and water water retaining agent were used as controls, and the same method was used to obtain the water absorption multiple.

[0036] WAC = m2 / m1, the water absorption multiple (WAC) of the agricultural and forestry water retaining agent was calculated according to the above formula, and the final water absorption multiple of Example 1 was 176 g / g (deionized water).

[0037] Example 2: 50.0 g of wheat straw was dried, crushed by a crusher, and passed through a 40-mesh sieve to obtain wheat straw powder. 20.0 g of the wheat straw powder was taken into a 1000 mL three-necked flask, and 400 mL of 5% (w / w) NaOH solution was added. The three-necked flask was placed in a heat collecting constant temperature magnetic stirrer (silicon oil as heat conducting medium), and the temperature was set to 105°C. A condensation reflux device was added, and magnetic stirring was performed for 2 h. After the reaction was completed, the reaction solution was cooled to room temperature, and the reaction solution was filtered through a 300-mesh sieve. The wheat straw alkali extract retained on the sieve was washed with deionized water for 4 times, each time for 30 s. Then, the wheat straw alkali extract on the sieve was transferred to a 1000 mL beaker, 800 mL of deionized water was added, 1% (w / w) H2SO4 solution was used to adjust the pH to 7-8, and the solution in the beaker was filtered through a 300-mesh sieve to obtain a neutral wheat straw alkali extract.

[0038] The neutral wheat straw alkali extract was transferred to a 1000 mL three-necked flask, and 400 mL of 5% (w / w) H2SO4 solution was added. The three-necked flask was placed in a heat collecting constant temperature magnetic stirrer, and the temperature was set to 115°C. A condensation reflux device was added, and magnetic stirring was performed for 2 h. After the reaction was completed, the reaction solution was filtered through a 300-mesh sieve. The wheat straw acid extract retained on the sieve was washed with deionized water for 4 times, each time for 30 s. Then, the wheat straw acid extract on the sieve was transferred to a 1000 mL beaker, 800 mL of deionized water was added, and ultrasonic treatment was performed for 20 min. Then, 1% (w / w) NaOH solution was used to adjust the pH to 7-8, and the solution in the beaker was filtered through a 300-mesh sieve to obtain a neutral wheat straw acid extract. The neutral wheat straw acid extract was subjected to suction filtration, and the filter cake was placed in an oven and dried for 12 h (60°C). The filter cake was the extracted wheat straw cellulose, which was crushed and passed through a 40-mesh sieve to obtain wheat straw cellulose powder. 5.0 g of the extracted wheat straw cellulose powder was taken into a 1000 mL three-necked flask, and 100 mL of 90% (v / v) ethanol solution was added.

[0039] Subsequently, experiments were carried out according to the mass ratio of cellulose: sodium hydroxide: chloroacetic acid of 1:0.8:1, 4.0 g of NaOH was added, magnetic stirring was carried out at 30℃ for 40 min, the temperature was set to 70℃, a condensation reflux device was installed on the three-necked flask, 5.0 g of chloroacetic acid was added, and magnetic stirring was continued for 2 h. After the reaction was completed, the reaction solution was suction filtered, the filter cake was transferred to 100 ml of 75% ethanol solution, magnetic stirring was carried out for 1 min, suction filtration was carried out again, the filter cake was washed with 100 mL of 75% ethanol solution, magnetic stirring was carried out for 1 min, suction filtration was carried out again, the filter cake was transferred to 250 mL of 70% ethanol solution for washing, magnetic stirring was carried out for 10 min, suction filtration was carried out again, and the washed filter cake was placed in a 60℃ oven for 12 h. The filter cake was crushed and sieved through a 40 mesh sieve to obtain the straw-based carboxymethyl cellulose prepared from wheat straw cellulose.

[0040] The prepared straw-based carboxymethyl cellulose was crushed and sieved through a 40 mesh sieve, 10 mL of a 9% mass concentration NaOH solution was added to a 10 mL beaker, 1.2 g of straw-based carboxymethyl cellulose powder (CMC) was added, and slow stirring was carried out until it was uniformly mixed and fully dissolved. Then, 0.3 mL of epichlorohydrin was added, slow stirring was carried out for 1 min, the 10 mL beaker was sealed with aluminum foil, and the rubber band was tightened. The reaction was carried out in a 60℃ oven for 12 h. The reaction was taken out, and the product was placed in a fume hood for 24 h of air drying.

[0041] The water absorption of Example 2 was tested. After the straw-based agricultural and forestry water retaining agent was dried, an agricultural and forestry water retaining agent sample with a mass of about 0.01-0.05 g was cut with scissors, weighed, and the mass was recorded as m1. Then, it was placed in 100 mL of deionized water for 24 h of water absorption, and then the free water was filtered out through a 100 mesh sieve. The water gel retained on the sieve was taken out and weighed, recorded as m2, and then the water absorption capacity (WAC) was obtained. At the same time, chlorine star water retaining agent, green alliance water retaining agent, green full water retaining agent, and water water retaining agent were used as controls, and the same method was used to obtain the water absorption capacity.

[0042] WAC = m2 / m1, the water absorption capacity (WAC) of the agricultural and forestry water retaining agent was calculated according to the above formula, and the final water absorption capacity of Example 2 was 144 g / g (deionized water).

[0043] Example 3: 50.0 g of wheat straw was dried and crushed by a pulverizer and passed through a 40-mesh sieve to obtain wheat straw powder. 20.0 g of the wheat straw powder was taken into a 1000 mL three-necked flask, and 400 mL of 5% (w / w) NaOH solution was added. The three-necked flask was placed in a heat collecting constant temperature magnetic stirrer (silicon oil as heat conducting medium), and the temperature was set to 105°C. A condensation reflux device was added, and magnetic stirring was performed for 2 h. After the reaction was completed, the reaction solution was cooled to room temperature, and the reaction solution was filtered through a 300-mesh sieve. The wheat straw alkali extract retained on the sieve was washed with deionized water for 4 times, each time for 30 s. Then, the wheat straw alkali extract on the sieve was transferred to a 1000 mL beaker, 800 mL of deionized water was added, 1% (w / w) H2SO4 solution was used to adjust the pH to 7-8, and the solution in the beaker was filtered through a 300-mesh sieve to obtain a neutral wheat straw alkali extract.

[0044] The neutral wheat straw alkali extract was transferred to a 1000 mL three-necked flask, and 400 mL of 5% (w / w) H2SO4 solution was added. The three-necked flask was placed in a heat collecting constant temperature magnetic stirrer, and the temperature was set to 115°C. A condensation reflux device was added, and magnetic stirring was performed for 2 h. After the reaction was completed, the reaction solution was filtered through a 300-mesh sieve. The wheat straw acid extract retained on the sieve was washed with deionized water for 4 times, each time for 30 s. Then, the wheat straw acid extract on the sieve was transferred to a 1000 mL beaker, 800 mL of deionized water was added, and ultrasonic was performed for 20 min. 1% (w / w) NaOH solution was used to adjust the pH to 7-8, and the solution in the beaker was filtered through a 300-mesh sieve to obtain a neutral wheat straw acid extract. The neutral wheat straw acid extract was suction filtered, and the filter cake was placed in an oven and dried for 12 h (60°C). The filter cake was the extracted wheat straw cellulose, which was crushed and passed through a 40-mesh sieve to obtain wheat straw cellulose powder. 5.0 g of the extracted wheat straw cellulose powder was taken into a 1000 mL three-necked flask, and 100 mL of 90% (v / v) ethanol solution was added.

[0045] Subsequently, experiments were carried out according to the mass ratio of cellulose:sodium hydroxide:chloroacetic acid of 1:0.8:1, 4.0 g of NaOH was added, magnetic stirring was carried out at 30℃ for 40 min, the temperature was set to 70℃, a condensation reflux device was installed on the three-necked flask, 5.0 g of chloroacetic acid was further added, and magnetic stirring was continued for 2 h. After the reaction was completed, the reaction solution was suction filtered, the filter cake was transferred to 100 mL of 75% ethanol solution, magnetic stirring was carried out for 1 min, suction filtration was carried out again, the filter cake was washed with 100 mL of 75% ethanol solution again, magnetic stirring was carried out for 1 min, suction filtration was carried out again, the filter cake was transferred to 250 mL of 70% ethanol solution for washing, magnetic stirring was carried out for 10 min, suction filtration was carried out again, and the washed filter cake was placed in a 60℃ oven for 12 h. The filter cake was crushed and sieved through a 40-mesh sieve to obtain the straw-based carboxymethyl cellulose prepared from wheat straw cellulose.

[0046] The prepared straw-based carboxymethyl cellulose was crushed and sieved through a 40-mesh sieve. 10 mL of a 9% mass concentration NaOH solution was added to a 10 mL beaker, 1.3 g of the straw-based carboxymethyl cellulose powder (CMC) was added, and slow stirring was carried out until it was uniformly mixed and fully dissolved. Then, 0.3 mL of epichlorohydrin was added, slow stirring was carried out for 1 min, the 10 mL beaker was sealed with aluminum foil, and the rubber band was tightened. The reaction was carried out in a 60℃ oven for 12 h. The reaction was taken out, and the product was placed in a fume hood for air drying for 24 h.

[0047] The water absorption of Example 3 was tested. After the straw-based agricultural and forestry water retaining agent was dried, an agricultural and forestry water retaining agent sample with a mass of about 0.01-0.05 g was cut with scissors, weighed, and the mass was recorded as m1. Then, it was placed in 100 mL of deionized water, and the water absorption was carried out for 24 h. Then, the free water was filtered out through a 100-mesh sieve, the hydrogel retained on the sieve was taken out and weighed, and the mass was recorded as m2. Then, the water absorption capacity (WAC) was obtained. At the same time, chlorine star water retaining agent, green alliance water retaining agent, green full water retaining agent, and water water retaining agent were used as controls, and the same method was used to obtain the water absorption capacity.

[0048] WAC = m2 / m1, the water absorption capacity (WAC) of the agricultural and forestry water retaining agent was calculated according to the above formula, and the final water absorption capacity of Example 3 was 296 g / g (deionized water).

[0049] In order to explore the best reaction ratio of wheat straw-based carboxymethyl cellulose, sodium hydroxide (initiator), and epichlorohydrin (crosslinking agent) in the preparation of straw-based agricultural and forestry water retaining agent, a series of treatment groups were set (using analytical pure carboxymethyl cellulose as a blank control), and the results are shown in Table 1. The reaction ratio was further optimized based on Table 1, and the results are shown in Table 2. The best straw-based agricultural and forestry water retaining agent product in Table 1 of the present application (No. 12 in Table 1) was characterized, and the specific methods were as follows:

[0050] Fourier transform infrared spectroscopy (FTIR) analysis: The straw-based agricultural and forestry water-retaining agent was determined by infrared spectroscopy using a Bruker INVENIO infrared spectrometer. The sample was freeze-dried, crushed through a 100-mesh sieve, and then the powder was used for determination. The scanning range was 400-4000 cm -1 ;

[0051] X-ray diffraction (XRD) analysis: The crystallinity of the straw-based agricultural and forestry water-retaining agent was analyzed using a D8 Advance X-ray polycrystalline diffractometer. The sample was freeze-dried, crushed through a 100-mesh sieve, and then the powder was used for determination. The scanning range was 0-80°.

[0052] Thermogravimetric analysis-differential scanning calorimetry (TG-DSC) analysis: The sample was freeze-dried and then crushed through a 100-mesh sieve. The TG-DSC of the material was analyzed using a NETZSCH STA449 instrument with a test temperature range of 0-800℃.

[0053] Scanning electron microscope (SEM);

[0054] Energy dispersive spectroscopy (EDS) analysis: The sample was freeze-dried and crushed through a 100-mesh sieve. The SEM characterization and energy spectrum EDS characterization of the material were performed using a Zeiss Sigma360 instrument. The specific magnification of the morphology was 20000 times, the scale requirement was 500 nm, and the EDS detection elements were Na and Cl for energy spectrum surface scanning.

[0055] In order to reflect the difference between the prepared straw-based agricultural and forestry water-retaining agent and the actual commercial agricultural and forestry water-retaining agent, four commercial agricultural and forestry water-retaining agents (trade names: water water-retaining agent, green alliance water-retaining agent, green world water-retaining agent, and chloro star water-retaining agent) were selected for water absorption ratio comparison.

[0056] Table 1 Water absorption ratio of wheat straw-based carboxymethyl cellulose and analytical pure carboxymethyl cellulose for preparing agricultural and forestry water-retaining agent

[0057]

[0058] Note: * indicates that the group uses pure carboxymethyl cellulose (analytical pure) for experiment, and no * group uses wheat straw-based carboxymethyl cellulose for experiment; water absorption ratio A refers to the water absorption ratio of wheat straw-based agricultural and forestry water-retaining agent prepared by air drying for 12 h, and water absorption ratio B refers to the water absorption ratio of wheat straw-based agricultural and forestry water-retaining agent prepared by drying for 12 h.

[0059] Table 2 Water absorption ratio of wheat straw-based agricultural and forestry water-retaining agent after optimization of formula

[0060]

[0061] Note: Water absorption multiple A refers to the water absorption multiple of the prepared agro-forestry water retaining agent after air drying for 24 h.

[0062] Table 3 Water retention performance of straw-based agro-forestry water retaining agent and four commercial agro-forestry water retaining agents

[0063]

[0064] Table 3 shows that the water absorption multiple of the straw-based agro-forestry water retaining agent of the present application is better than that of two commercial agro-forestry water retaining agents (chlorine star water retaining agent, green alliance water retaining agent), and the water absorption performance (322.52 g / g) is not much different from that of the water retaining agent, and the water absorption multiple (545.92 g / g) is lower than that of the green full water retaining agent. However, the straw-based agro-forestry water retaining agent can achieve the performance of traditional polymer-based agro-forestry water retaining agent products, indicating that the straw-based agro-forestry water retaining agent has good water absorption performance and application value.

[0065] Figure 1 The XRD pattern of the molecular structure of the straw-based agro-forestry water retaining agent shows that the XRD pattern of the straw-based agro-forestry water retaining agent has multiple diffraction peaks, and there are obvious peak values at about 22°, 34°, 45°, etc. These peak values correspond to the reflection of crystal faces of different crystal structures in the sample, indicating that the straw-based agro-forestry water retaining agent has three different crystalline regions, which may be carboxymethyl cellulose crystal region, sodium hydroxide crystal region and cellulose crystal region. The peak near 22° may be the characteristic peak of cellulose and other materials, indicating that the sample contains a certain amount of cellulose impurities. The strong diffraction peak of the straw-based agro-forestry water retaining agent appears at 31.82°, but the diffraction peak of the sample is wide and the intensity is low, and the peak shape is not sharp enough, indicating that the crystallinity of the sample is poor, further confirming the low crystallinity characteristics of the sample. Overall, the XRD results show that the straw-based agro-forestry water retaining agent has poor crystallinity, loose molecular structure and a large number of amorphous regions, which is beneficial to the rapid adsorption and diffusion of water.

[0066] Figure 2 The Fourier transform infrared spectrum (FTIR) of the straw-based agro-forestry water retaining agent, in which the absorption peaks at 880, 1051 cm -1 are characteristic absorption peaks of glucoside bonds in cellulose. The absorption peaks at 1435 cm -1 and 1660 cm -1 correspond to the symmetric and asymmetric stretching vibration of -COO - , respectively. The absorption peak at 1051 cm -1 is the characteristic absorption peak of the ether bond in cellulose, and the characteristic peak at 880 cm -1 is produced by the asymmetric face stretching vibration of cyclic C-O-C or the non-planar rocking vibration of CH2(CH2OH). The absorption peak appearing near 3465 cm -1 is attributed to the stretching vibration of -OH.

[0067] FTIR analysis results show that the experiment successfully carboxymethylated the straw cellulose, introduced -COO - group, while retaining the skeleton structure of cellulose, including the characteristic peak of glucoside bond. This unique structure not only endows the material with excellent hydrophilicity (expressed as strong -OH peak), but also makes it have good ion exchange capacity (carboxylate characteristic), so that the material has high water absorption and is suitable for application in the field of agriculture and forestry water conservation.

[0068] Figure 3 The EDS spectrum of the straw-based agriculture and forestry water conservation agent targeting Na and Cl. EDS can accurately analyze the element range of chlorine (Cl) and sodium (Na) with its sampling depth of about 1 um, thereby more comprehensively understanding the distribution of the initiator (sodium hydroxide) and crosslinking agent (epoxy chloropropane).

[0069] From Figures 4-5 It can be seen that both the crosslinking agent and the initiator are distributed throughout the material. The red area in figure a shows the distribution of sodium elements in the sample, which is relatively uniform, but some areas have higher concentration. The green area in figure b shows the distribution of chlorine elements, which has some overlap with the distribution of sodium elements, but also has independent distribution areas. Figure c shows the surface morphology of the sample, which has obvious pores and layered distribution. Figure d superimposes the distribution of sodium and chlorine on the electron image, showing the spatial distribution relationship of the two elements in the sample, but still showing obvious heterogeneity.

[0070] EDS analysis shows that epoxy chloropropane and carboxymethyl cellulose successfully constructed a stable three-dimensional crosslinked network. This uniform crosslinked structure endows the material with excellent water absorption and water retention performance and structural stability. This result, together with the FTIR and XRD data, verifies the successful synthesis of the straw-based agriculture and forestry water conservation agent, providing a reliable structural basis for its agricultural and forestry application.

[0071] Figure 4 The scanning electron microscope test diagram of the straw-based agriculture and forestry water conservation agent. As can be seen from the figure, the straw-based agriculture and forestry water conservation agent shows obvious heterogeneity and diverse surface structure.

[0072] From figure (a), it can be found that the material has rough and smooth areas. The rough area has many pores and obvious uneven substances, while the smooth area presents greater integrity with fewer pores. It can be seen from figure (a) that there are particle structure substances on the surface of the material, with particle size of about 50 nm.

[0073] Figure (b) reflects the longitudinal distribution of the material, which shows irregular stacking characteristics, indicating that the structure of the material is not uniform during crosslinking, resulting in a disordered spatial distribution of the material.

[0074] Figure (c) reflects the deep pore structure of the material, which penetrates the material so that the material presents a "sponge" structure, which is a characteristic of the long chains of carboxymethyl cellulose, the surface structure is more flat, but there are still some small textures and particles, which may be different processing states of the same material.

[0075] Figure (d) shows a clear regular crystal structure in the lower right corner, which should be the residual sodium hydroxide involved in the reaction in the sample, and the morphology after drying and crystallization. Compared with image (c), the surface of figure (d) is smoother, and the particle size may be smaller, showing the changes after processing.

[0076] SEM analysis shows that the straw-based agricultural and forestry water-retaining agent has a unique "sponge-like" multi-level pore structure, with rough porous and smooth dense regions on the surface. This special morphology gives the material double advantages: on the one hand, the rich micro-nano scale pores (about 50 nm) and deep pore structure provide a large specific surface area and capillary action, significantly improving the water absorption and storage capacity; on the other hand, the skeleton structure formed by the dense region and cross-linked network ensures the mechanical strength of the material in the swollen state.

[0077] Figure 5 The thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) analysis chart of the straw-based agricultural and forestry water-retaining agent. The TG curve (green) shows the change of mass of the sample during heating, the mass increases slightly at the initial stage, then decreases sharply between about 10 min-30 min, indicating that the sample has undergone significant thermal decomposition or weight loss (corresponding to the temperature range 80-200℃) during this period, after which the mass change tends to be stable. The DSC curve (blue) reflects the change of heat of the sample during heating, the curve has a clear exothermic or endothermic peak at about 20 min (corresponding to the temperature range 150℃), corresponding to the weight loss stage of the TG curve, indicating that a thermal reaction occurs at this time, after which the DSC curve tends to be stable, but there is a small fluctuation at about 60 min. The DSC curve is relatively stable, indicating that the thermal reaction of the material tends to be stable. The temperature slowly rises throughout the process, in order to control the decomposition rate of the material. TG-DSC analysis shows that the straw-based agricultural and forestry water-retaining agent begins to decompose at 80℃, which can adapt to the field environment.

[0078] Figure 6The technical process flow chart for preparing the straw-based agricultural and forestry water-retaining agent from wheat straw is actually that the water absorption multiple of the wheat straw itself is low (about 10 g / g), because the three elements (cellulose, hemicellulose and lignin) of the straw are closely intertwined and interwoven, so that the structure of the straw is dense, so as to have good mechanical strength and toughness, but this makes the straw difficult to expand. Therefore, from the composition and structure of the straw, the water absorption performance of the straw itself is not very good, but because cellulose has many hydroxyl groups, it can be modified to have stronger hydrophilicity of carboxyl groups (-COOH), and after the cellulose is derived into carboxymethyl cellulose, the hydrophilicity of the cellulose derivative is greatly improved, but the carboxymethyl cellulose is easily soluble in water, and must be crosslinked to form a large molecule with good structure to prepare the agricultural and forestry water-retaining agent. At present, carboxymethyl cellulose (analytical pure) has been successfully synthesized into an agricultural and forestry water-retaining agent by using epichlorohydrin as a crosslinking agent and sodium hydroxide as an initiator.

[0079] In summary, the preparation method of the agricultural water-retaining agent of the present application is to prepare an agricultural and forestry water-retaining agent from wheat straw, thereby avoiding the environmental risk of monomer residues (acrylic acid, acrylamide) of the existing market polyacrylate and polyacrylamide agricultural and forestry water-retaining agents, and promoting the utilization of straw resources. The optimal water absorption multiple of the wheat straw-based agricultural and forestry water-retaining agent is 296 g / g, which meets the requirement of the water absorption multiple (>100 g / g) of the agricultural and forestry water-retaining agent (NY / T 886-2022).

[0080] The above is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a wheat straw-based agroforestry water-retaining agent, characterized in that, It is made by the following steps: S1, wheat straw cellulose extraction: after the wheat straw is crushed, it is sequentially subjected to alkali extraction, acid extraction, neutralization reaction liquid pH, ultrasonic, and finally filtration to obtain neutral wheat straw cellulose; S2, wheat straw cellulose carboxymethylation modification: the wheat straw cellulose is mixed with NaOH and chloroacetic acid, and an ethanol solution is used as a reaction medium, and then the reaction is carried out, and after ethanol washing, wheat straw-based carboxymethyl cellulose is obtained; S3, crosslinking reaction: the wheat straw-based carboxymethyl cellulose is mixed with a NaOH solution, stirred uniformly, then epoxy chloropropane is added, stirred uniformly, the reaction liquid is placed in an oven for reaction, and after washing and drying, the wheat straw-based agricultural and forestry water-retaining agent is obtained.

2. The method of preparing wheat straw based agro-forestry water retaining agent as claimed in claim 1, wherein, The alkali extraction method in S1 is: after the wheat straw is crushed, it is added into a NaOH solution, and reacted at 105 DEG C for 2 hours; the mass concentration of the sodium hydroxide solution is 1%-10%.

3. The preparation method of the wheat straw-based agroforestry water-retaining agent according to claim 2, characterized in that, The acid extraction method in S1 is: after the alkali extraction of the wheat straw, it is added into a H2SO4 solution, and reacted at 115 DEG C for 2 hours; the concentration of the sulfuric acid solution is 1%-10%.

4. The method of preparing wheat straw based agro-forestry water retaining agent as claimed in claim 1, wherein, The concentration of the ethanol solution used for washing the wheat straw-based carboxymethyl cellulose in S2 is 65%-90%.

5. The method of preparing wheat straw based agro-forestry water retaining agent as claimed in claim 1, wherein, The mass ratio of the wheat straw cellulose to NaOH and chloroacetic acid in S2 is 1:0.8:

1.

6. The method of preparing wheat straw based agro-forestry water retaining agent as claimed in claim 1, wherein, The mass concentration of the NaOH solution used in S3 is 1%-10%.

7. The method of preparing wheat straw based agro-forestry water retaining agent as claimed in claim 1, wherein, The amount of the epoxy chloropropane used in S3 is 20%-110% of the mass of the wheat straw-based carboxymethyl cellulose.

8. The method of preparing wheat straw based agro-forestry water retaining agent as claimed in claim 1, wherein, The mass-volume ratio of the wheat straw-based carboxymethyl cellulose to the NaOH solution in S3 is 0.8-1.5 g:10 mL.

9. A wheat straw based agro-forestry water retaining agent prepared according to any one of the processes of claims 1 to 8, characterized in that, The water absorption multiple is 0-300 g / g.

10. Use of the wheat straw-based agro-forestry water-retaining agent according to claim 9, characterized in that, It is used for soil moisture retention in arid regions, crop root moisture retention, or desertification control.

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