Preparation method of nutrient-loaded biochar slow-release natural polysaccharide mulch material

Abstract

The present invention discloses a method for preparing a nutrient-loaded biochar slow-release natural polysaccharide mulch film material. Urea is loaded onto biochar by a vacuum adsorption method, and enteromorpha polysaccharide is extracted from enteromorpha by an alkali extraction and alcohol precipitation method. Then, the urea-loaded biochar is blended with enteromorpha polysaccharide / konjac glucomannan solution to obtain a film-forming liquid. The film-forming liquid is subjected to film casting and drying to obtain a nutrient-loaded biochar slow-release natural polysaccharide mulch film material. The natural polysaccharide mulch film prepared by the present invention using biochar as a fertilizer carrier has the advantages of slowing down the nutrient release rate and improving the nutrient utilization efficiency. The prepared mulch film material has low cost, simple preparation process, easy biodegradability, good environmental benefits, and can realize the high-value utilization of biomass materials such as plant polysaccharides and marine polysaccharides and the sustainable development of green agriculture.

Description

Technical Field

[0001] The present invention relates to an agricultural mulch film, in particular to a method for preparing a nutrient-loaded biochar slow-release natural polysaccharide mulch film material, which is suitable for soil surface covering films in green sustainable agricultural development and belongs to the field of agricultural and forestry chemical materials. Background Art

[0002] To meet the high demand for food from the growing world population, fertilizers play a vital role in improving soil fertility and increasing crop yields. However, conventional fertilizers have high solubility and low thermal stability and cannot be fully absorbed by crops, resulting in low fertilizer efficiency, posing risks to the environment and causing economic losses. Slow-release fertilizers improve fertilizer efficiency by reducing the solubility of nutrients, slowing down the release rate of nutrients, and meeting the nutrient needs of plant growth at the same time. Fertilizer slow-release fertilizer mulch is a promising strategy that provides nutrients for plant growth while serving as a covering film. However, most traditional mulch films are plastic films made of polyethylene (PE) and polypropylene (PP). The use of plastic films will produce non-degradable plastic residues, which may accumulate in the soil over time, causing serious ecological and environmental problems. Therefore, it is necessary to develop biodegradable films made from natural polysaccharides as alternatives to traditional plastic films.

[0003] Biochar is a porous carbon-rich material, which is formed by high-temperature pyrolysis of biomass materials under hypoxic or anaerobic conditions. Biochar has the advantages of small size, porous structure, large specific surface area, strong adsorption capacity, and rich surface groups, and is a potential fertilizer slow-release carrier. The application of biochar can improve the cation exchange capacity and water holding capacity of the soil and improve the soil; Enteromorpha polysaccharide is a water-soluble polysaccharide extracted from Enteromorpha, which has good gelling and rheological properties. However, the mechanical strength of pure Enteromorpha polysaccharide film is low, and it needs to be applied with other polymers to improve its strength; Konjac glucomannan is a non-ionic natural polysaccharide extracted from konjac tubers, which has good biocompatibility, film-forming ability, thickening, and stability, and has been widely used in the preparation of biodegradable films. Therefore, it is a possible strategy to combine Enteromorpha polysaccharide, Konjac glucomannan with biochar loaded with fertilizer to prepare nutrient-loaded biochar slow-release natural polysaccharide mulch materials. Summary of the invention

[0004] The present invention provides a method for preparing a nutrient-loaded biochar slow-release natural polysaccharide mulch film material, which uses enteromorpha polysaccharide and konjac glucomannan as a matrix and combines them with urea-loaded biochar to prepare a low-cost, environmentally friendly natural polysaccharide mulch film material with nutrient slow-release effect.

[0005] In order to achieve the above-mentioned purpose, the nutrient-loaded biochar slow-release natural polysaccharide mulch material prepared by the present invention has a urea loading rate of 15-20% for the biochar particles, a mulch material thickness of 90-110 μm, a tensile load strength of 4.2-6.6 MPa in a dry state, an elongation at break of 50-70%, and a water vapor permeability of 800-1000 g / (m 2 ·24h), the blocking rate of ultraviolet and visible light is 95~98%, and the cumulative release rate of urea after 12 weeks is 75~80%.

[0006] The technical solution adopted by the present invention is: a nutrient-loaded biochar slow-release natural polysaccharide mulch film material, wherein urea is loaded on the biochar by a vacuum adsorption method, and enteromorpha polysaccharide is extracted from enteromorpha by an alkali extraction and alcohol precipitation method, and then the urea-loaded biochar is blended with enteromorpha polysaccharide / konjac glucomannan solution to obtain a film-forming liquid, and the film-forming liquid is subjected to cast film formation and drying to obtain the nutrient-loaded biochar slow-release natural polysaccharide mulch film material.

[0007] The biomass charcoal is a porous carbon-rich material obtained by pyrolyzing woody biomass materials such as tree branches at 500-600°C.

[0008] The enteromorpha polysaccharide is a water-soluble polysaccharide extracted from the enteromorpha by using an alkali extraction and alcohol precipitation method.

[0009] The konjac glucomannan is a non-ionic natural polysaccharide with a relative molecular weight of 200,000 to 2,000,000 and a purity of ≥95%.

[0010] The urea is a neutral fertilizer with a nitrogen content of ≥46.4%.

[0011] The method for preparing the above-mentioned nutrient-loaded biochar slow-release natural polysaccharide mulch material comprises the following steps:

[0012] (1) Preparation of urea-loaded biochar: first prepare a urea aqueous solution, then add biochar and keep it under a vacuum state of 0.1 MPa for a period of time, then switch to a normal pressure state, repeat this process 2 to 4 times, filter and dry the treated biochar to obtain urea-loaded biochar powder particles; the mass percentage of the urea aqueous solution is 2 to 6%, the mass ratio of urea to biochar is 1:2 to 1:6, the vacuum treatment temperature is 20 to 40 °C, the vacuum treatment time is 20 to 40 min, and the drying temperature is 40 to 60 °C;

[0013] (2) Extraction of Enteromorpha polysaccharide: First, fresh Enteromorpha is washed, dried, and ground to obtain Enteromorpha powder. Enteromorpha powder is heat-treated with anhydrous ethanol at 50-90°C for a period of time. After the Enteromorpha powder is washed and filtered, it is extracted with sodium hydroxide aqueous solution at 60-90°C for 2-4 times. The filtrate is collected and concentrated to 10% of the original volume. The pH value of the concentrate is adjusted to 7 with acetic acid aqueous solution. Then, anhydrous ethanol is added to precipitate Enteromorpha polysaccharide in the filtrate. Finally, it is freeze-dried at -40°C for 12 hours to obtain white Enteromorpha polysaccharide powder; the mass percentage of sodium hydroxide aqueous solution is 1-1.5%, and the mass percentage of acetic acid aqueous solution is 1.5-2%;

[0014] (3) Preparation of natural polysaccharide mulch: prepare an aqueous solution of Enteromorpha polysaccharide using the Enteromorpha polysaccharide obtained in step (2) at 70-90°C, prepare an aqueous solution of Konjac glucomannan at 50-70°C, then mix the above solutions in equal proportions, add glycerol and the urea-loaded biochar obtained in step (1), and continue stirring to obtain a film-forming solution, and after casting the film-forming solution and drying, obtain a urea-loaded nutrient-loaded biochar slow-release natural polysaccharide mulch; the mass percentages of the components in the film-forming solution are 0.5-1% Enteromorpha polysaccharide, 0.4-0.8% Konjac glucomannan, 0.6-1% urea-loaded biochar, and 0.4-0.6% glycerol, and the blending temperature is 40-80°C.

[0015] In the step (2), the Enteromorpha is a marine algae plant of the Ulvaceae family and the Enteromorpha genus.

[0016] The beneficial effects of the present invention are: using biochar as a fertilizer carrier to adsorb urea, and combining it with natural polysaccharide materials such as Enteromorpha polysaccharide and konjac glucomannan, a nutrient-loaded biochar slow-release natural polysaccharide mulch material is prepared, which has the advantages of slowing down the nutrient release rate and improving the nutrient utilization efficiency; the prepared mulch material has low cost, simple preparation process, easy biodegradability, and good environmental benefits, and can achieve high-value utilization of biomass materials such as plant polysaccharides and marine polysaccharides and green and sustainable development of agriculture. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and beneficial technical effects of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments.

[0018] Example 1 Preparation of nutrient-loaded biochar slow-release natural polysaccharide mulch material

[0019] Step 1: Preparation of urea-loaded biochar. Prepare a urea aqueous solution first, then add biochar and keep it under 0.1MPa vacuum for 20 minutes, then switch to normal pressure. Repeat this process 4 times, filter and dry the treated biochar to obtain urea-loaded biochar powder particles; the mass percentage of urea aqueous solution is 2%, the mass ratio of urea to biochar is 1:2, the vacuum treatment temperature is 20°C, and the drying temperature is 40°C;

[0020] Step 2: Extraction of Enteromorpha polysaccharide. First, fresh Enteromorpha is washed, dried, and ground to obtain Enteromorpha powder. Enteromorpha powder is heat-treated with anhydrous ethanol at 50°C for a period of time. After the Enteromorpha powder is washed and filtered, it is extracted 4 times with an aqueous sodium hydroxide solution at 60°C. The filtrate is collected and concentrated to 10% of the original volume. The pH value of the concentrate is adjusted to 7 with an acetic acid aqueous solution. Then, anhydrous ethanol is added to precipitate the Enteromorpha polysaccharide in the filtrate. Finally, it is freeze-dried at -40°C for 12 hours to obtain white Enteromorpha polysaccharide powder; the mass percentage of the sodium hydroxide aqueous solution is 1%, and the mass percentage of the acetic acid aqueous solution is 1.5%;

[0021] Step 3: Preparation of natural polysaccharide mulch. Prepare an aqueous solution of Enteromorpha polysaccharide using the Enteromorpha polysaccharide obtained in the second step at 70°C, prepare an aqueous solution of Konjac glucomannan at 50°C, then mix the above solutions in equal proportions, add glycerol and the urea-loaded biochar obtained in the first step, and continue stirring to obtain a film-forming liquid. The film-forming liquid is subjected to film casting and drying to obtain a urea-loaded nutrient-loaded biochar slow-release natural polysaccharide mulch; the mass percentages of each component in the film-forming liquid are 0.5% Enteromorpha polysaccharide, 0.4% Konjac glucomannan, 0.6% urea-loaded biochar, and 0.4% glycerol, and the blending temperature is 80°C.

[0022] Example 2 Preparation of nutrient-loaded biochar slow-release natural polysaccharide mulch material

[0023] Step 1: Preparation of urea-loaded biochar. Prepare a urea aqueous solution first, then add biochar and keep it under 0.1MPa vacuum for 30 minutes, then switch to normal pressure. Repeat this process 3 times, filter and dry the treated biochar to obtain urea-loaded biochar powder particles; the mass percentage of urea aqueous solution is 4%, the mass ratio of urea to biochar is 1:4, the vacuum treatment temperature is 30°C, and the drying temperature is 50°C;

[0024] Step 2: Extraction of Enteromorpha polysaccharide. First, fresh Enteromorpha is washed, dried, and ground to obtain Enteromorpha powder. Enteromorpha powder is heat-treated with anhydrous ethanol at 70°C for a period of time. After the Enteromorpha powder is washed and filtered, it is extracted three times with an aqueous sodium hydroxide solution at 80°C. The filtrate is collected and concentrated to 10% of the original volume. The pH value of the concentrate is adjusted to 7 with an acetic acid aqueous solution. Then, anhydrous ethanol is added to precipitate the Enteromorpha polysaccharide in the filtrate. Finally, it is freeze-dried at -40°C for 12 hours to obtain white Enteromorpha polysaccharide powder; the mass percentage of the sodium hydroxide aqueous solution is 1.25%, and the mass percentage of the acetic acid aqueous solution is 1.75%;

[0025] Step 3: Preparation of natural polysaccharide mulch. Prepare an aqueous solution of Enteromorpha polysaccharide using the Enteromorpha polysaccharide obtained in the second step at 80°C, prepare an aqueous solution of Konjac glucomannan at 60°C, then mix the above solutions in equal proportions, add glycerol and the urea-loaded biochar obtained in the first step, and continue stirring to obtain a film-forming liquid. The film-forming liquid is subjected to film casting and drying to obtain a urea-loaded nutrient-loaded biochar slow-release natural polysaccharide mulch; the mass percentages of each component in the film-forming liquid are 0.75% Enteromorpha polysaccharide, 0.6% Konjac glucomannan, 0.8% urea-loaded biochar, and 0.5% glycerol, and the blending temperature is 60°C.

[0026] Example 3 Preparation of nutrient-loaded biochar slow-release natural polysaccharide mulch material

[0027] Step 1: Preparation of urea-loaded biochar. Prepare a urea aqueous solution first, then add biochar and keep it under 0.1MPa vacuum for 40 minutes, then switch to normal pressure. Repeat this process twice, filter and dry the treated biochar to obtain urea-loaded biochar powder particles; the mass percentage of urea aqueous solution is 6%, the mass ratio of urea to biochar is 1:6, the vacuum treatment temperature is 40°C, and the drying temperature is 60°C;

[0028] Step 2: Extraction of Enteromorpha polysaccharide. First, fresh Enteromorpha is washed, dried, and ground to obtain Enteromorpha powder. Enteromorpha powder is heat-treated with anhydrous ethanol at 90°C for a period of time. After the Enteromorpha powder is washed and filtered, it is extracted twice with an aqueous sodium hydroxide solution at 90°C. The filtrate is collected and concentrated to 10% of the original volume. The pH value of the concentrate is adjusted to 7 with an acetic acid aqueous solution. Then, anhydrous ethanol is added to precipitate the Enteromorpha polysaccharide in the filtrate. Finally, it is freeze-dried at -40°C for 12 hours to obtain white Enteromorpha polysaccharide powder; the mass percentage of the sodium hydroxide aqueous solution is 1.5%, and the mass percentage of the acetic acid aqueous solution is 2%;

[0029] Step 3: Preparation of natural polysaccharide mulch. Prepare an aqueous solution of Enteromorpha polysaccharide using the Enteromorpha polysaccharide obtained in the second step at 90°C, prepare an aqueous solution of Konjac glucomannan at 70°C, then mix the above solutions in equal proportions, add glycerol and the urea-loaded biochar obtained in the first step, and continue stirring to obtain a film-forming liquid. The film-forming liquid is subjected to film casting and drying to obtain a urea-loaded nutrient-loaded biochar slow-release natural polysaccharide mulch; the mass percentage of each component in the film-forming liquid is 1% Enteromorpha polysaccharide, 0.8% Konjac glucomannan, 1% urea-loaded biochar, and 0.6% glycerol, and the blending temperature is 40°C.

[0030] The natural polysaccharide mulch materials produced in Examples 1-3 were tested: the urea loading rate of the biochar particles reached 17-20%, the thickness of the mulch material was 90-100 μm, the tensile load strength in the dry state was 4.5-6 MPa, the elongation at break was 60-70%, and the water vapor permeability was 900-1000 g / (m 2 · 24h), the blocking rate of ultraviolet light and visible light is 95-97%, and the cumulative release rate of urea after 12 weeks is 75-78%. It can be seen that the ground film material of the present invention can not only slowly release urea, but also has good mechanical properties, water vapor barrier properties and light barrier capabilities.

[0031] The above description points out and describes several preferred embodiments of the present invention, but it should be understood that the present invention is not limited to the form disclosed herein and should not be regarded as excluding other embodiments. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nutrient-loaded biochar slow-release natural polysaccharide mulch material, characterized in that: Urea is loaded on biochar by vacuum adsorption method, and the mass ratio of urea to biochar is 1:2-1:

6. Enteromorpha polysaccharide is extracted from Enteromorpha by alkali extraction and alcohol precipitation method. Then, the urea-loaded biochar is blended with Enteromorpha polysaccharide / konjac glucomannan solution to obtain a film-forming liquid. The mass percentages of the components in the film-forming liquid are 0.5-1% of Enteromorpha polysaccharide, 0.4-0.8% of konjac glucomannan, 0.6-1% of biochar loaded with urea, and 0.4-0.6% of glycerol. The blending temperature is 40-80°C. The film-forming liquid is subjected to film casting and drying to obtain a nutrient-loaded biochar slow-release natural polysaccharide mulch film material.

2. The nutrient-loaded biochar slow-release natural polysaccharide mulch material according to claim 1, characterized in that: The urea loading rate of the biomass carbon particles in the mulch film material is 15-20%, the thickness of the mulch film material is 90-110 μm, the tensile load strength in the dry state is 4.2-6.6 MPa, the elongation at break is 50-70%, and the water vapor permeability is 800-1000 g / (m 2 ·24h), the blocking rate of ultraviolet and visible light is 95-98%, and the cumulative release rate of urea after 12 weeks is 75-80%.

3. The nutrient-loaded biochar slow-release natural polysaccharide mulch material according to claim 1, characterized in that: The biomass charcoal is a porous carbon-rich material obtained by pyrolyzing woody biomass materials at 500-600°C.

4. The nutrient-loaded biochar slow-release natural polysaccharide mulch material according to claim 1, characterized in that: The enteromorpha polysaccharide is a water-soluble polysaccharide extracted from the enteromorpha by using an alkali extraction and alcohol precipitation method.

5. The nutrient-loaded biochar slow-release natural polysaccharide mulch material according to claim 1, characterized in that: The konjac glucomannan is a non-ionic natural polysaccharide with a relative molecular weight of 200,000 to 2,000,000 and a purity of ≥95%.

6. The nutrient-loaded biochar slow-release natural polysaccharide mulch material according to claim 1, characterized in that: The urea is a neutral fertilizer with a nitrogen content of ≥46.4%.

7. A method for preparing the nutrient-loaded biochar slow-release natural polysaccharide mulch material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Preparation of urea-loaded biochar: first prepare a urea aqueous solution, then add biochar and keep it under a vacuum state of 0.1 MPa for a period of time, then switch to a normal pressure state, repeat this process 2 to 4 times, filter and dry the treated biochar to obtain urea-loaded biochar powder particles; the mass percentage of the urea aqueous solution is 2 to 6%, the vacuum treatment temperature is 20 to 40° C., the vacuum treatment time is 20 to 40 min, and the drying temperature is 40 to 60° C.; (2) Extraction of Enteromorpha polysaccharide: First, fresh Enteromorpha is washed, dried, and ground to obtain Enteromorpha powder, and the Enteromorpha powder is heat-treated with anhydrous ethanol at 50 to 90° C. for a period of time. After the Enteromorpha powder is washed and filtered, it is extracted with an aqueous sodium hydroxide solution at 60 to 90° C. for 2 to 4 times, the filtrate is collected and concentrated to 10% of the original volume, and the pH value of the concentrate is adjusted to 7 with an acetic acid solution, and then anhydrous ethanol is added to precipitate the Enteromorpha polysaccharide in the filtrate, and finally freeze-dried at -40° C. for 12 hours to obtain white Enteromorpha polysaccharide powder; the mass percentage of the sodium hydroxide solution is 1 to 1.5%, and the mass percentage of the acetic acid solution is 1.5 to 2%; (3) Preparation of natural polysaccharide mulch: Prepare an aqueous solution of Enteromorpha polysaccharide at 70-90° C. using the Enteromorpha polysaccharide obtained in step (2), prepare an aqueous solution of Konjac glucomannan at 50-70° C., then mix the above solutions in equal proportions, add glycerol and the urea-loaded biochar obtained in step (1), and continue stirring to obtain a film-forming solution. The film-forming solution is subjected to film casting and drying to obtain a urea-loaded nutrient-loaded biochar slow-release natural polysaccharide mulch.

8. The method for preparing the nutrient-loaded biochar slow-release natural polysaccharide mulch material according to claim 7, characterized in that: The Enteromorpha in step (2) is a marine algae plant of the Ulvaceae family and the Enteromorpha genus.