CN113683798B - Straw-based mulching film with heavy metal adsorption function and preparation method thereof - Google Patents

Abstract

The invention provides a straw-based mulching film with a heavy metal adsorption function and a preparation method thereof, wherein the preparation process comprises the following steps: carrying out ultrasonic-assisted steam explosion pretreatment on the straw raw material, and washing to obtain a wood fiber material with a loose tissue structure; adding dimethyl sulfoxide solution into the wood fiber material, stirring and reacting for 0.4-0.8h, then continuously adding tetrabutyl ammonium hydroxide solution, and stirring and reacting for 0.8-1.5 h; centrifuging, collecting supernatant, adding chitosan into the supernatant, and stirring for reaction for 0.2-1 h; flatly paving the reacted solution on a substrate, standing and then carrying out vacuum drying to obtain a base film; and (3) soaking the base film in deionized water, taking out the base film, and drying to obtain the straw-based mulching film. The mulching film can effectively solve the problems of waste of straw resources and limited use of the existing heavy metal removal method.

Description

Straw base film with heavy metal adsorption function and preparation method thereof

technical field

The invention relates to the technical field of mulch films, in particular to a straw base film with heavy metal adsorption function and a preparation method thereof.

Background technique

With the rapid development of China's industrialization process, in the process of industrial production and agricultural production, in the process of machinery manufacturing, chemical industry, electronic production and pesticide use, a large amount of heavy metals are lost to the natural soil. Heavy metals such as lead, copper, and chromium commonly found in heavy metal pollution can enter the human body through water bodies, food chains, etc., thus endangering human health.

Soil in nature is an important foundation for human survival and development, and a vital environmental resource. Heavy metal pollution has always been the main pollutant of soil, and has the characteristics of concealment, long-term impact, bioaccumulation and irreversibility, which makes public health problems and land desolation caused by heavy metal pollution occur frequently. The remediation of contaminated soil is very difficult, not only with huge economic investment, but also with certain technical difficulties. Heavy metal pollution is not degraded by microorganisms in the soil. After entering the human body through the food chain, it accumulates in the body, which seriously threatens human health. Therefore, heavy metal pollution of land is a problem that needs long-term attention and needs to be solved urgently. At present, the main methods of soil remediation include heat treatment, stabilization, electric remediation, and soil remediation. The heat treatment method has a limited scope of action, and it is easy to cause the soil to lose its original ecological function. The stabilization method has a greater degree of disturbance to the soil and has an impact on the distribution of plants. Long-term sustainability and limited scope for implementation. Therefore, it is very important to study the treatment methods for soil heavy metal pollution.

As a traditional agricultural country, my country is rich in straw resources. At present, the total amount of crop straw resources in China has reached 1.04 billion tons, and the amount of straw can be collected is 900 million tons. The nutritional value of a ton of grain is equivalent. The main types of crop straws in my country are grain crop straws, among which wheat straw, rice straw and corn straw are the three crop straws with the highest yield and the widest distribution, accounting for about 2/3 of the total straw resources. At present, a large number of straws are burned or abandoned, resulting in waste of resources and environmental pollution.

Straw can be fully degraded, the production cycle is short, and the cost is low. Therefore, a biomass-based heavy metal ion adsorption composite mulch film was developed to treat the existing heavy metal pollution with the idea of "treating waste with waste" in the treatment of heavy metal pollution with waste straw. It has great research and application significance, which can maximize the utilization of natural resources and improve the efficiency and value of resource utilization.

SUMMARY OF THE INVENTION

In view of the above deficiencies in the prior art, the present invention provides a straw base film with heavy metal adsorption function and a preparation method thereof, which can effectively solve the waste of the existing straw resources and the limited use of the existing heavy metal removal methods. question.

For realizing the above-mentioned purpose, the technical scheme that the present invention solves its technical problem adopts is:

A method for preparing a straw base film with heavy metal adsorption function, comprising the following steps:

(1) carrying out ultrasonic-assisted steam explosion pretreatment on the straw raw material, and washing with water to obtain a lignocellulosic material with loose tissue structure;

(2) Add dimethyl sulfoxide solution to the lignocellulosic material, stir and swell for 0.4-0.8h, then continue to add tetrabutylammonium hydroxide solution, stir and dissolve for 0.8-1.5h;

(3) centrifuging the solution in step (2), collecting the supernatant, then adding chitosan to the supernatant, stirring and reacting for 0.2-1 h;

(4) spreading the reacted solution in step (3) on the substrate, and vacuum drying after standing to obtain a base film;

(5) soaking the base film in step (4) in deionized water, then taking out the base film and drying to obtain a straw base film.

In the above scheme, the use of steam explosion to treat the straw raw material can avoid the use of chemicals, reduce the pollution to the environment, and obtain loose lignocellulosic materials; Swelling treatment is carried out, and then tetrabutylammonium hydroxide solution is added to it, which destroys the abundant hydrogen bond structure in cellulose, reduces the crystallinity of cellulose, and then increases the dissolving amount of cellulose; then mix the cellulose solution with chitosan The base film is mixed to make a base film, which contains a large number of amino groups, which can be used as adsorption sites to effectively capture heavy metal ions in the soil and realize the removal of heavy metal ions.

The mulch film in the present invention is made of straw as the main raw material and a small amount of chitosan as the modifier, both of which have good biodegradability, are safe and non-toxic, can improve the safety to the environment, and use the straw raw material , which can realize the secondary utilization of waste and reduce the pollution caused by straw to the environment.

The process parameters of ultrasonic steam explosion pretreatment are: steam explosion pressure of 0.5-2.5MPa, ultrasonic power of 100-500W, frequency of 24-80KHz, duty ratio of 0.2-0.8, and ultrasonic time of 3-30min.

Further, in step (2), the cellulose raw material accounts for 4-7% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution.

Further, in step (2), the volume ratio of the dimethyl sulfoxide solution to the tetrabutylammonium hydroxide solution is 2-5:1.

Further, the mass concentration of tetrabutylammonium hydroxide in step (2) is 40-50%.

Further, in step (3), the centrifugal speed is 8000-12000r/min, and the time is 1-4min.

Further, the mass percentage of chitosan in the solution in step (3) is 1-5%.

Further, chitosan has a molecular weight of 250,000.

Further, in step (4), the standing time is 2-4 h, and after standing, the product is dried under vacuum at 65-80° C. for 3-4 h.

Further, in step (5), the soaking time of the base film in deionized water at 20-40° C. is 36-72 h.

In the above scheme, soaking the base film in water can replace the solvent component in the base film and remove the solvent in the base film. At the same time, the cellulose and lignin in the solution complete the process of regeneration and assembly, so that the base film is completely forming. During the soaking process, change the water 3-5 times.

Further, in step (5), the base film is dried at 35-50° C. for 20-30 hours.

The beneficial effects produced by the present invention are:

In the present invention, straw is used as the main raw material, and in the process of soaking in deionized water, the cellulose chains are reassembled to form an interlaced network structure in the base film, so that the base film is formed; Modifier, the degradable mulch film can be prepared, and the fiber components in the straw have degradable properties; chitosan also has good degradability; chitosan has a large number of active amino groups, which can be used as adsorption sites for heavy metals, and It is used to adsorb heavy metals in the soil, realize the enrichment of heavy metals, and then realize the treatment of heavy metal-contaminated soil; after chemical precipitation of the heavy metal-enriched straw mulch, the concentrated products of heavy metals can be obtained, and the heavy metals can be recovered by chemical means. secondary use.

Description of drawings

Fig. 1 is the SEM image of the mulch film in Example 3, wherein A is before degradation, B is degradation for 15 days, C is degradation for 30 days, and D is degradation for 45 days;

Fig. 2 is the change diagram of mulching film mass loss in Example 3;

Fig. 3 is the thermogravimetric test change diagram after mulching film is degraded in Example 3;

4 is the SEM of the straws used in Example 3 and Comparative Example 2; a is the straw in Comparative Example 2, and b is the straw after steam explosion in Example 3.

Detailed ways

The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Example 1

A straw base film with heavy metal adsorption function, the preparation method thereof comprises the following steps:

(1) carrying out ultrasonic-assisted steam explosion pretreatment on the corn stalk raw material, and washing with water to obtain a lignocellulosic material with loose tissue structure;

(2) Add dimethyl sulfoxide solution to the lignocellulosic material, stir and swell the planet for 0.4h, and then continue to add tetrabutylammonium hydroxide solution with a mass concentration of 40%, dimethyl sulfoxide solution and tetrabutylammonium hydroxide solution The volume ratio is 2:1, and the planetary stirring is dissolved for 0.8h, wherein the lignocellulosic material accounts for 4% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution;

(3) Centrifuge the solution in step (2) at a speed of 8000 r/min for 2 min, collect the supernatant, and then add chitosan to the supernatant, so that the mass percentage of chitosan in the solution is 2%. Stir the reaction for 0.2h;

(4) The solution after the reaction in step (3) is spread on a glass substrate, and after standing for 2 hours, vacuum-dried at 65° C. for 3 hours to obtain a base film;

(5) Soak the base film in step (4) in deionized water at 20° C. for 36 hours, then take out the base film and dry it at 35° C. for 20 hours to obtain a straw base film.

Example 2

A straw base film with heavy metal adsorption function, the preparation method thereof comprises the following steps:

(1) carrying out ultrasonic-assisted steam explosion pretreatment on the corn stalk raw material, and washing with water to obtain a lignocellulosic material with loose tissue structure;

(2) Add dimethyl sulfoxide solution to the lignocellulosic material, stir and swell the planet for 0.8h, and then continue to add tetrabutylammonium hydroxide solution with a mass concentration of 50%, dimethyl sulfoxide solution and tetrabutylammonium hydroxide solution The volume ratio is 5:1, and the planetary stirring is dissolved for 1.5h, wherein the lignocellulosic material accounts for 7% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution;

(3) Centrifuge the solution in step (2) at a speed of 12000 r/min for 4 min, collect the supernatant, and then add chitosan to the supernatant, so that the mass percentage of chitosan in the solution is 5%. Stir the reaction for 1h;

(4) The solution after the reaction in step (3) is spread on a glass substrate, and after standing for 3 hours, vacuum-dried at 80° C. for 4 hours to obtain a base film;

(5) Soak the base film in step (4) in deionized water at 30° C. for 48 hours, then take out the base film and dry it at 50° C. for 30 hours to prepare a straw base film.

Example 3

A straw base film with heavy metal adsorption function, the preparation method thereof comprises the following steps:

(1) carrying out ultrasonic-assisted steam explosion pretreatment on the corn stalk raw material, and washing with water to obtain a lignocellulosic material with loose tissue structure;

(2) Add dimethyl sulfoxide solution to the lignocellulosic material, stir and swell the planet for 0.5h, and then continue to add tetrabutylammonium hydroxide solution with a mass concentration of 45%, dimethyl sulfoxide solution and tetrabutylammonium hydroxide solution The volume ratio is 4:1, and the planet is stirred and dissolved for 1h, wherein the lignocellulosic material accounts for 5% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution;

(3) Centrifuge the solution in step (2) at a speed of 10000r/min for 3min, collect the supernatant, then add chitosan to the supernatant, so that the mass percentage of chitosan in the solution is 5% planetary Stir the reaction for 0.5h;

(4) spreading the reacted solution in step (3) on a glass substrate, standing for 4 hours and then vacuum-drying at 70° C. for 4 hours to obtain a base film;

(5) The base film in step (4) was soaked in deionized water at 40°C for 72 hours, then the base film was taken out and dried at 40°C for 24 hours to obtain a straw base film.

Comparative Example 1

A straw base film with heavy metal adsorption function, the preparation method thereof comprises the following steps:

(1) carrying out ultrasonic-assisted steam explosion pretreatment on the corn stalk raw material, and washing with water to obtain a lignocellulosic material with loose tissue structure;

(2) Add dimethyl sulfoxide solution to the lignocellulosic material, stir and swell the planet for 0.8h, and then continue to add tetrabutylammonium hydroxide solution with a mass concentration of 50%, dimethyl sulfoxide solution and tetrabutylammonium hydroxide solution The volume ratio is 4:1, and the planetary stirring is dissolved for 1.5h, wherein the lignocellulosic material accounts for 5% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution;

(3) Centrifuge the solution in step (2) at a speed of 12000 r/min for 4 min, and collect the supernatant.

(4) The solution after the reaction in step (3) is spread on a glass substrate, and after standing for 2 hours, vacuum-dried at 80° C. for 4 hours to obtain a base film;

(5) Soak the base film in step (4) in deionized water at 40° C. for 48 hours, then take out the base film and dry at 40° C. for 36 hours to obtain a straw base film.

Comparative Example 2

A straw base film with heavy metal adsorption function, the preparation method thereof comprises the following steps:

(1) Add dimethyl sulfoxide solution to the pulverized corn stalk raw material, stir and swell with planetary stirring for 0.5h, and then continue to add tetrabutylammonium hydroxide solution with a mass concentration of 45%, dimethyl sulfoxide solution and tetrabutyl hydroxide The volume ratio of the ammonium solution is 4:1, and the planet is stirred and dissolved for 1 hour, wherein the lignocellulosic material accounts for 5% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution;

(2) Centrifuge the solution in step (2) at a speed of 10000r/min for 3min, collect the supernatant, then add chitosan to the supernatant, so that the mass percentage of chitosan in the solution is 5% planetary Stir the reaction for 0.5h;

(3) The solution after the reaction in step (3) is spread on a glass substrate, and after standing for 24 hours, vacuum-dried at 70° C. for 4 hours to obtain a base film;

(4) Soak the base film in step (4) in deionized water at 40° C. for 48 hours, then take out the base film and dry it at 40° C. for 24 hours to prepare a straw base film.

Test example

Take the soil polluted by copper, lead and chromium elements, divide it into five parts on average, record the content of heavy metals in the soil, and then lay the mulch films prepared in Examples 1-3 and Comparative Examples 1-2 and bury them 20cm below the soil respectively. After 30 days, take out the plastic film, and detect the heavy metal content in the soil respectively. The specific data are shown in Table 1. After being placed for 15 days, 30 days and 45 days respectively, the mulch film in Example 3 was tested, the surface condition of the mulch film was observed, and the change in the weight of the mulch film over time was recorded. The specific results are shown in Figures 1-2; and The plastic film after being degraded for 30 days was subjected to heat treatment, and the thermal weight loss of the plastic film was observed, as shown in Figure 3 for details.

Table 1: Heavy metal content before and after soil treatment

It can be seen from the data in the above table that the plastic film in Example 1-3 has a good removal effect on copper, lead and chromium in the soil, and its removal effect of heavy metal ions is far better than that of the plastic film in Comparative Example 1-2 .

It can be seen from Figures 1-2 that the mulch film has a small-scale rough surface before the degradation, and after the mulch film is degraded in the soil for 15 days, 30 days, and 45 days, the surface of the mulch film has obvious uneven morphology. , the morphology has changed greatly compared with that before the degradation; in addition, as shown in Figure 2, the weight of the mulch film has decreased significantly after being treated in the soil environment, and the weight loss rate has increased significantly with the extension of time. , reached 61.55% at 45 days, indicating that the plastic film has obvious degradation effect under the influence of the natural environment in the soil.

It can be seen from Figure 3 that after soil degradation, the initial decomposition temperature of the mulch film did not change much, and the maximum decomposition rate temperature decreased with the increase of the degradation time. The remaining mass increased significantly with time. The reason may be that the plastic film adsorbed metal ions in the soil, and the metal ions were relatively stable and were not easily decomposed at 800 °C, so the residual mass of thermal decomposition after 45 days of degradation was high. The remaining sample mass after 45 days of degradation was 39.5%. Therefore, in summary, the thermal stability of the sample should decrease with the prolongation of the degradation time, and the thermodynamic stability should increase. However, due to the adsorption of metal ions, the residual mass of thermal decomposition after 45 days of degradation is high.

It can be seen from Figure 4 that the microstructure of the straw before and after steam explosion is obviously different. Combined with the data in Table 1, it can be seen that the loose and broken fiber morphology formed after steam explosion is beneficial to improve the adsorption effect of heavy metals.

Claims (10)

1. A preparation method of a straw-based mulching film with a heavy metal adsorption function is characterized by comprising the following steps:

(1) carrying out ultrasonic-assisted steam explosion pretreatment on the straw raw material, and washing to obtain a wood fiber material with a loose tissue structure;

(2) adding dimethyl sulfoxide solution into wood fiber material, stirring for swelling for 0.4-0.8h, then continuously adding tetrabutyl ammonium hydroxide solution, stirring for dissolving for 0.8-1.5 h;

(3) centrifuging the solution in the step (2), collecting supernatant, adding chitosan into the supernatant, and stirring for reacting for 0.2-1 h;

(4) flatly paving the solution reacted in the step (3) on a substrate, standing and then carrying out vacuum drying to obtain a base film;

(5) and (4) soaking the base film in the step (4) in deionized water, taking out the base film, and drying to obtain the straw-based mulching film.

2. The method for preparing a straw-based mulching film with a heavy metal adsorption function according to claim 1, wherein the wood fiber material in the step (2) accounts for 4-7% of the total mass of the dimethyl sulfoxide solution and the tetrabutylammonium hydroxide solution.

3. The method for preparing a straw-based mulching film with a heavy metal adsorption function according to claim 1, wherein the volume ratio of the dimethyl sulfoxide solution to the tetrabutylammonium hydroxide solution in the step (2) is 2-5: 1.

4. The method for preparing a straw-based mulching film with a heavy metal adsorption function according to claim 1, wherein the mass concentration of tetrabutylammonium hydroxide in the step (2) is 40-50%.

5. The preparation method of straw-based mulching film with heavy metal adsorption function as claimed in claim 1, wherein the centrifugation speed in step (3) is 8000-12000r/min, and the time is 1-4 min.

6. The preparation method of straw-based mulching film with heavy metal adsorption function according to claim 1, wherein the chitosan accounts for 1-5% of the solution in the step (3) by mass.

7. The preparation method of the straw-based mulching film with the heavy metal adsorption function of claim 1, wherein the standing time in the step (4) is 2-4h, and the standing and vacuum drying is performed at 65-80 ℃ for 3-4 h.

8. The preparation method of straw-based mulching film with heavy metal adsorption function according to claim 1, wherein the basement film in the step (5) is soaked in deionized water for 36-72 hours.

9. The preparation method of straw-based mulching film with heavy metal adsorption function according to claim 1, wherein the basement film in the step (5) is dried at 35-50 ℃ for 20-30 h.

10. The straw-based mulching film with the heavy metal adsorption function prepared by the method of any one of claims 1-9.

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