CN113683798A

CN113683798A - Straw-based mulching film with heavy metal adsorption function and preparation method thereof

Info

Publication number: CN113683798A
Application number: CN202110868772.7A
Authority: CN
Inventors: 姜曼; 陆远; 范烨; 胡翔洲; 王峰; 潘宇
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2021-07-30
Filing date: 2021-07-30
Publication date: 2021-11-23
Anticipated expiration: 2041-07-30
Also published as: CN113683798B

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-based mulching film with heavy metal adsorption function and preparation method thereof

Technical Field

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

Background

With the rapid development of the Chinese industrialization process, in the development process of industrial production and agricultural production, and in the processes of mechanical manufacture, chemical industry, electronic production and pesticide use, a large amount of heavy metals are lost into the natural soil. Common heavy metals such as lead, copper, chromium and the like in heavy metal pollution can enter human bodies through water, food chains and other approaches, so that the health of human beings is harmed.

Soil in nature is an important foundation for human survival and development, and is a vital environmental resource. Heavy metal pollution is always the main pollutant of soil, and has the characteristics of concealment, long-term influence, biological accumulation, irreversibility and the like, so that the health problems of people and the waste of land caused by heavy metal pollution frequently occur. The polluted soil is very difficult to repair, so that the economic investment is huge and the technical difficulty is also certain. Heavy metal pollution is not degraded along with microorganisms in soil, and is enriched in a human body after entering the human body through a food chain, so that the health of human beings is seriously threatened. Therefore, heavy metal pollution of the land is a problem which needs long-term attention and needs to be solved urgently. At present, the main approaches of soil remediation are heat treatment, stabilization, electric remediation, soil dressing and the like. The heat treatment method has a limited action range, soil is easy to lose the original ecological function, the stabilization method has a large disturbance degree on the soil and influences plant distribution, the electric restoration method has a complex technology and high energy consumption, the soil dressing method has no long-term sustainability, and the implementation range is limited. Therefore, it is very important to research the treatment method for the heavy metal pollution of the soil.

As a traditional big agricultural country, China has rich straw resources, the total resource amount of crop straws in China currently reaches 10.4 hundred million tons, and the resource amount of straws which can be collected reaches 9 hundred million tons, which is equivalent to the calorific value released by about 5 hundred million tons of standard coal or the nutritional value of 2.5 hundred million tons of grains. The main type of crop straws in China is grain crop straws, wherein wheat straws, rice straws and corn straws are the three crop straws with the highest yield and the widest distribution, and account for 2/3 of the total straw resource amount in total. At present, a large amount of straws are burnt or abandoned, so that the problems of resource waste and environmental pollution are caused.

The straw is fully degradable, the production period is short, and the cost is low, so that the idea of treating heavy metal pollution by waste straw is taken as a basis, the important research and application significance of treating the existing heavy metal pollution by using the biomass-based heavy metal ion adsorption composite mulching film is developed, the natural resource utilization can be maximized, and the resource utilization efficiency and value are improved.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the straw-based mulching film with the heavy metal adsorption function and the preparation method thereof, and the mulching film can effectively solve the problems of waste of straw resources and limited use of the existing heavy metal removal method.

In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problems is as follows:

a preparation method of a straw-based mulching film with a heavy metal adsorption function comprises 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.

In the scheme, the straw raw material is treated by adopting steam explosion, so that the use of chemicals can be avoided, the pollution to the environment is reduced, and loose wood fiber materials can be obtained; in the preparation process, dimethyl sulfoxide solution is adopted to swell the wood fiber material, tetrabutyl ammonium hydroxide solution is added into the wood fiber material, and the rich hydrogen bond structures in the cellulose are destroyed through the tetrabutyl ammonium hydroxide solution, so that the crystallinity of the cellulose is reduced, and the dissolving amount of the cellulose is further improved; and then mixing the cellulose solution and chitosan to prepare a base membrane, wherein the base membrane contains a large amount of amino groups, and can be used as an adsorption site to effectively trap heavy metal ions in soil, so that the heavy metal ions are removed.

The mulching film is prepared by using straws as a main raw material and a small amount of chitosan as a modifier, the straws and the mulching film both have good biodegradability, are safe and nontoxic, can improve the environmental safety, and can realize the secondary utilization of wastes and reduce the pollution of the straws to the environment by using the straw raw material.

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

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

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

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

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

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

Further, chitosan was present in a molecular weight of 25 ten thousand.

Further, standing for 2-4h in the step (4), and vacuum drying at 65-80 ℃ for 3-4h after standing.

Further, the basement membrane in the step (5) is soaked in deionized water at the temperature of 20-40 ℃ for 36-72 hours.

In the scheme, the base film is soaked in water, so that the solvent component in the base film can be replaced, the solvent in the base film is removed, and meanwhile, the cellulose and lignin in the solution complete the regeneration and assembly processes, so that the base film is thoroughly formed. During the soaking process, the water is changed for 3-5 times.

Further, the basement membrane in the step (5) is dried for 20-30h at the temperature of 35-50 ℃.

The beneficial effects produced by the invention are as follows:

in the invention, straws are used as main raw materials, and cellulose chains are reassembled in the deionized water soaking process to form a mutually staggered network structure in a base film so as to form the base film; the chitosan is a modifier for improving the adsorption performance of heavy metals, the degradable mulching film is prepared, and fiber components in the straw have degradable characteristics; the chitosan also has better degradability; the chitosan has a large amount of active amino groups, can be used as adsorption sites of heavy metals, and is used for adsorbing the heavy metals in soil, so that the enrichment of the heavy metals is realized, and further the treatment of the heavy metal contaminated soil is realized; after the straw mulching film enriched with the heavy metals is subjected to chemical precipitation, a concentrated product of the heavy metals can be obtained, and the heavy metals are recovered by a chemical means, so that the secondary utilization of the heavy metals is realized.

Drawings

FIG. 1 is an SEM image of the mulch film of example 3, wherein A is before degradation, B is 15 days of degradation, C is 30 days of degradation, and D is 45 days of degradation;

FIG. 2 is a graph showing the change in the loss of the mulching film quality in example 3;

FIG. 3 is a graph showing the change of the thermogravimetric test after the degradation of the mulching film in example 3;

FIG. 4 is an SEM of the straw 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 Description

The following detailed description of embodiments of the invention refers to the accompanying drawings.

Example 1

A straw-based mulching film with a heavy metal adsorption function is prepared by the following steps:

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

(2) adding a dimethyl sulfoxide solution into a wood fiber material, carrying out planetary stirring and swelling for 0.4h, then continuously adding a tetrabutyl ammonium hydroxide solution with the mass concentration of 40%, wherein the volume ratio of the dimethyl sulfoxide solution to the tetrabutyl ammonium hydroxide solution is 2:1, and carrying out planetary stirring and dissolving for 0.8h, wherein the wood fiber material accounts for 4% of the total mass of the dimethyl sulfoxide solution and the tetrabutyl ammonium hydroxide solution;

(3) centrifuging the solution in the step (2) at 8000r/min for 2min, collecting supernatant, and adding chitosan into the supernatant to enable the mass percent of the chitosan in the solution to be 2%, and stirring and reacting for 0.2 h;

(4) spreading the solution reacted in the step (3) on a glass substrate, standing for 2h, and then drying in vacuum at 65 ℃ for 3h to obtain a base film;

(5) and (4) soaking the base film in the step (4) in deionized water at 20 ℃ for 36h, taking out the base film, and drying at 35 ℃ for 20h to obtain the straw-based mulching film.

Example 2

(2) adding a dimethyl sulfoxide solution into a wood fiber material, carrying out planetary stirring and swelling for 0.8h, then continuously adding a tetrabutyl ammonium hydroxide solution with the mass concentration of 50%, wherein the volume ratio of the dimethyl sulfoxide solution to the tetrabutyl ammonium hydroxide solution is 5:1, and carrying out planetary stirring and dissolving for 1.5h, wherein the wood fiber material accounts for 7% of the total mass of the dimethyl sulfoxide solution and the tetrabutyl ammonium hydroxide solution;

(3) centrifuging the solution in the step (2) at 12000r/min for 4min, collecting supernatant, and then adding chitosan into the supernatant to ensure that the mass percent of the chitosan in the solution is 5%, and stirring and reacting for 1 h;

(4) spreading the solution reacted in the step (3) on a glass substrate, standing for 3h, and then drying in vacuum at 80 ℃ for 4h to obtain a base film;

(5) and (4) soaking the base film in the step (4) in deionized water at 30 ℃ for 48h, taking out the base film, and drying at 50 ℃ for 30h to obtain the straw-based mulching film.

Example 3

(2) adding a dimethyl sulfoxide solution into a wood fiber material, carrying out planetary stirring and swelling for 0.5h, then continuously adding a tetrabutyl ammonium hydroxide solution with the mass concentration of 45%, wherein the volume ratio of the dimethyl sulfoxide solution to the tetrabutyl ammonium hydroxide solution is 4:1, and carrying out planetary stirring and dissolving for 1h, wherein the wood fiber material accounts for 5% of the total mass of the dimethyl sulfoxide solution and the tetrabutyl ammonium hydroxide solution;

(3) centrifuging the solution in the step (2) at 10000r/min for 3min, collecting supernatant, and then adding chitosan into the supernatant to ensure that the mass percent of the chitosan in the solution is 5%, and stirring and reacting for 0.5 h;

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

(5) and (4) soaking the base film in the step (4) in deionized water at 40 ℃ for 72h, taking out the base film, and drying at 40 ℃ for 24h to obtain the straw-based mulching film.

Comparative example 1

(2) adding a dimethyl sulfoxide solution into a wood fiber material, carrying out planetary stirring and swelling for 0.8h, then continuously adding a tetrabutyl ammonium hydroxide solution with the mass concentration of 50%, wherein the volume ratio of the dimethyl sulfoxide solution to the tetrabutyl ammonium hydroxide solution is 4:1, and carrying out planetary stirring and dissolving for 1.5h, wherein the wood fiber material accounts for 5% of the total mass of the dimethyl sulfoxide solution and the tetrabutyl ammonium hydroxide solution;

(3) and (3) centrifuging the solution in the step (2) at 12000r/min for 4min, and collecting supernatant.

(4) Spreading the solution reacted in the step (3) on a glass substrate, standing for 2h, and then drying in vacuum at 80 ℃ for 4h to obtain a base film;

(5) and (4) soaking the base film in the step (4) in deionized water at 40 ℃ for 48h, taking out the base film, and drying at 40 ℃ for 36h to obtain the straw-based mulching film.

Comparative example 2

(1) adding a dimethyl sulfoxide solution into the crushed corn straw raw material, stirring and swelling for 0.5h in a planetary way, then continuously adding a tetrabutyl ammonium hydroxide solution with the mass concentration of 45%, wherein the volume ratio of the dimethyl sulfoxide solution to the tetrabutyl ammonium hydroxide solution is 4:1, and stirring and dissolving for 1h in a planetary way, wherein the wood fiber material accounts for 5% of the total mass of the dimethyl sulfoxide solution and the tetrabutyl ammonium hydroxide solution;

(2) centrifuging the solution in the step (2) at 10000r/min for 3min, collecting supernatant, and then adding chitosan into the supernatant to ensure that the mass percent of the chitosan in the solution is 5%, and stirring and reacting for 0.5 h;

(3) spreading the solution reacted in the step (3) on a glass substrate, standing for 24h, and then drying in vacuum at 70 ℃ for 4h to obtain a base film;

(4) and (4) soaking the base film in the step (4) in deionized water at 40 ℃ for 48h, taking out the base film, and drying at 40 ℃ for 24h to obtain the straw-based mulching film.

Test examples

The soil polluted by copper, lead and chromium elements is averagely divided into five parts, the content of heavy metals in the soil is recorded, then the mulching films prepared in the examples 1-3 and the comparative examples 1-2 are respectively paved and buried 20cm below the soil, the mulching films are taken out after being placed for 30 days, and the content of the heavy metals in the soil is respectively detected, and the specific data are shown in the table 1. After being placed for 15 days, 30 days and 45 days respectively, the mulching film in the embodiment 3 is detected, the surface condition of the mulching film is observed, and the change condition of the weight of the mulching film after being increased along with time is recorded, and the specific result is shown in the attached drawing 1-2; and carrying out heat treatment on the mulching film after 30 days of degradation, and observing the condition of thermal weight loss of the mulching film, which is shown in figure 3 specifically.

Table 1: heavy metal content before and after soil treatment

As can be seen from the data in the table above, the mulching films in the examples 1 to 3 have better removal effect on copper, lead and chromium in soil, and the removal effect of heavy metal ions is far better than that of the mulching films in the comparative examples 1 to 2.

As can be seen from the attached drawings 1-2, the mulching film has a small-scale rough surface before degradation, and after the mulching film is degraded in soil for 15 days, 30 days and 45 days respectively, the surface of the mulching film has obvious rugged appearance which is greatly changed relative to the appearance before degradation; in addition, as shown in fig. 2, after the mulching film is treated in the soil environment, the weight of the mulching film is obviously reduced, the weight loss rate is obviously increased along with the prolonging of time, and reaches 61.55% at 45 days, which indicates that the mulching film has obvious degradation effect under the influence of the natural environment in the soil.

As can be seen from the attached figure 3, after the mulching film is degraded by soil, the initial decomposition temperature of the mulching film is not changed greatly, the maximum decomposition rate temperature is reduced along with the increase of the degradation time, the maximum decomposition rate temperature is 297.2 ℃ after 45 days of degradation, and meanwhile, the residual mass of thermal decomposition is obviously increased along with the increase of the time, which may be caused by that the mulching film adsorbs metal ions in the soil, the metal ions are stable and are not easily decomposed at 800 ℃, so that the residual mass of thermal decomposition is higher after 45 days of degradation. The mass of the sample remaining after 45 days of degradation was 39.5%. Therefore, in summary, the thermal stability of the sample should be somewhat reduced and the thermodynamic stability should be increased as the degradation time is prolonged, but the residual quality of the thermal decomposition which is degraded in 45 days is higher due to the adsorption of the metal ions.

As can be seen from the attached figure 4, the microstructure of the straw is obviously different before and after steam explosion, and the data in the table 1 show that the loose and broken fiber morphology formed after steam explosion is favorable for improving the heavy metal adsorption effect.

Claims

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

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.