Straw-based degradable plug seedling mulching film, preparation method and application thereof

Abstract

The application is suitable for the technical field of agricultural mulching film, and provides straw-based degradable seedling transplanting mulching film and a preparation method and application thereof, which comprise the following raw materials in parts by weight: 65-75 parts of straw pulp, 15-20 parts of sulfuric acid modified rice straw biochar, 8-12 parts of enzymatic hydrolysis lignin-PBAT compound, 0.5-0.8 parts of thickening agent, 1.5-1.6 parts of sodium alginate, and 0.3-0.6 parts of low eutectic solvent. Through the synergistic effect of straw fiber, sulfuric acid modified rice straw biochar and low eutectic solvent, the application realizes the synergistic optimization of water retention, salt resistance, weed inhibition and degradation in cold and saline-alkali land, simultaneously improves the mechanical property to adapt to the operation of a seedling transplanting machine, and has ecological and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of agricultural mulch film technology, and particularly relates to a straw-based biodegradable rice transplanting mulch film, its preparation method, and its application. Background Technology

[0002] Mulching technology is widely used in agricultural production, but the plastic pollution it causes is becoming increasingly prominent. Among existing technologies, biodegradable mulch films made from straw have become a research hotspot. For example, CN115918423A discloses a soil-fertilizing straw mulch film, which achieves degradation and fertilization through the composite of straw fiber and low-eutectic solvents; CN116178749A uses modified straw and polylactic acid to improve the aging resistance of the mulch film; CN116762616A utilizes carbon-based materials to enhance water and fertilizer retention capacity; CN116948343A develops a liquid mulch film focusing on water retention and growth promotion; CN119144126A optimizes mechanical properties through enzymatic hydrolysis of lignin and PBAT composite. However, none of the above technical solutions address the salt-blocking problem in saline-alkali soils, and they do not involve matching the degradation cycle with the growth and autumn plowing techniques of cold-climate rice, resulting in residual film affecting the following year's cultivation.

[0003] Specifically, existing straw-based biodegradable mulch films have the following shortcomings in application: First, they are functionally limited, lacking a synergistic design for water retention, salt inhibition, and fertilization in cold, saline-alkali soils; second, their mechanical performance is poorly adaptable, failing to meet the high-speed operation requirements of mulch-based rice transplanters; third, their degradation cycle is poorly matched with the growth cycle of cold-climate rice and does not take into account the agronomical characteristics of autumn plowing after harvest; and fourth, they do not fully utilize the shading and weed-suppressing properties of black carbon-based materials, relying instead on chemical herbicides. Therefore, developing a straw-based biodegradable mulch film suitable for rice cultivation in cold, saline-alkali soils is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a straw-based biodegradable rice transplanting mulch film, which aims to solve the problems mentioned in the background art.

[0005] The present invention is implemented as follows: a straw-based biodegradable rice transplanting mulch film comprises the following raw materials in parts by weight: 65-75 parts straw pulp, 15-20 parts sulfuric acid modified rice straw biochar, 8-12 parts enzymatically hydrolyzed lignin-PBAT complex, 0.5-0.8 parts thickener, 1.5-1.6 parts sodium alginate, and 0.3-0.6 parts eutectic solvent.

[0006] Another objective of this invention is to provide a method for preparing a straw-based biodegradable rice transplanting mulch film, comprising the following steps:

[0007] Material mixing: Add deionized water to straw pulp to adjust the concentration to 10-12%, add sulfuric acid modified rice straw biochar and enzymatic hydrolysis lignin-PBAT complex, stir at high speed, then add thickener, sodium alginate and eutectic solvent, continue stirring, and adjust the solid content to 14%;

[0008] Paper forming: Papermaking is carried out using a paper forming machine.

[0009] Another objective of this invention is to provide an application of straw-based biodegradable rice transplanting mulch in saline-alkali soil environments.

[0010] The present invention provides a straw-based biodegradable rice transplanting mulch film, which achieves synergistic optimization of water retention, salt inhibition, weed suppression, and degradation in cold saline-alkali land through the synergistic effect of straw fiber, modified biochar, and low eutectic solvent. At the same time, it improves mechanical properties to adapt to rice transplanter operation, thus combining ecological and economic benefits. Attached Figure Description

[0011] Figure 1 In the diagram, a is a schematic diagram of ordinary paper film, b is a schematic diagram of the film prepared in Example 1 of the present invention, c is a schematic diagram of the field application of ordinary paper film, and d is a schematic diagram of the field application of the film prepared in Example 1 of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0014] Example 1: A straw-based biodegradable rice transplanting mulch film, the preparation method of which includes the following steps:

[0015] (1) Extraction of lignin by enzymatic hydrolysis:

[0016] Enzymatic hydrolysis of lignin was prepared using rice straw from Zhongkefa 5 as raw material. Taking advantage of the high lignin content (approximately 15-20%) of rice straw, the product's weight-average molecular weight was ensured to be 4000-6000. Specific steps included:

[0017] Take Zhongkefa 5 rice straw (remove leaves, retain stems, and crush to 0.5-1cm), add deionized water at a solid-liquid ratio of 1:10, and adjust the pH to 4.5-5.0 (suitable for the enzymatic hydrolysis environment of rice straw fibers). Add 2.5% (by weight of straw) of cellulase (filter paper enzyme activity ≥100FPU / g) and 1.2% (enzyme activity ≥5000U / g) (if the hemicellulose content of rice straw is slightly high, the amount of enzyme should be increased appropriately). Enzymatically hydrolyze in a constant temperature water bath at 50-55℃ for 50 hours (the optimal enzymatic hydrolysis time should be determined based on preliminary experiments to ensure that lignin is fully released and the molecular weight meets the target). During the process, the mixture was stirred once every 6 hours (300 r / min). After the enzymatic hydrolysis was completed, the temperature was raised to 90℃ for 10 min to inactivate the enzyme. The residue was filtered and a 5% NaOH solution (solid-liquid ratio 1:8) was added to the residue. The mixture was stirred in an 80℃ water bath for 2.5 h (to enhance the dissolution of lignin from rice straw). The filtrate was collected after filtration. The pH was adjusted to 2.0 with 10% hydrochloric acid, and the mixture was allowed to stand for 4 h to precipitate. The precipitate was collected by centrifugation (3000 r / min, 10 min), washed until neutral, and then vacuum dried at 60℃ to obtain enzymatically hydrolyzed lignin. The weight-average molecular weight was 4800, which met the requirements.

[0018] (2) Preparation of straw pulp:

[0019] To address the characteristics of rice straw fibers being relatively fine (10-20 μm in diameter) and highly resilient, the pretreatment and grinding processes were optimized to prepare uniformly dispersed pulp. Specific steps include:

[0020] Pretreatment: Take the stems of Zhongkefa 5 rice straw, cut them into 2-4cm sections, add 3% by mass of a eutectic solvent (choline chloride and urea molar ratio of 1:2, prepared at 70℃), and soak until the straw is completely hydrated (rice straw has a high water absorption rate, so the moisture content must be 60-65%), and let it stand at room temperature for 12 hours (to weaken the lignin binding between rice straw fibers).

[0021] Cooking: Add the pretreated straw segments to deionized water at a solid-liquid ratio of 1:6 and cook at 120℃ for 0.6 hours (rice straw fibers are relatively easy to soften, so slightly extending the cooking time can improve fiber separation).

[0022] Grinding: Press to a moisture content of 70%, first grind at 600 r / min for 3 rounds (6 min per round), then grind at 900 r / min for 4 rounds (4 min per round) (to meet the dispersion requirements of fine rice straw fibers), to obtain pulp with a fiber length of 0.4-1.8 mm, for later use.

[0023] (3) Preparation of straw biochar:

[0024] Biochar is prepared using rice straw (which has a high silicon content, approximately 5-8%). Silicon enhances the structural stability of biochar, and the carbonization process is optimized to suit its properties. Specific steps include:

[0025] Take the stems of Zhongkefa 5 rice straw (naturally air-dried to a moisture content of ≤10%, cut into 2-3cm pieces), put them into a tube furnace, and heat them to 550-600℃ at 10℃ / min under nitrogen protection (flow rate 50mL / min) (rice straw has a high ash content, and at this temperature, volatile matter can be effectively removed while retaining the silicon skeleton), and carbonize them for 2.5h (slightly extend the carbonization time to ensure that the organic components are fully decomposed); after cooling, grind and sieve to obtain black biochar with a particle size of ≤5μm.

[0026] (4) Preparation of sulfuric acid modified rice straw biochar:

[0027] To address the high silicon content of rice straw biochar, its surface activity is enhanced through sulfuric acid modification (the reaction of silanol groups with sulfuric acid introduces more active sites). Specific steps include:

[0028] Take 100g of the prepared straw biochar and add 500mL of 8% sulfuric acid solution (solid-liquid ratio 1:5). Stir in an 80℃ water bath for 1.8h (extend the reaction time to promote the reaction between sulfuric acid and silanol groups) at a speed of 200r / min. After the reaction, wash with deionized water until the pH of the filtrate is 6.5-7.0 (no precipitate is detected by barium chloride test). Dry at 105℃ to constant weight. After grinding, the particle size is still ≤5μm.

[0029] (5) Preparation of pulp and film from mixed materials:

[0030] To address the synergistic needs of water retention, salt inhibition, and shading in cold saline-alkali lands, and considering the fine fibers (10-20 μm in diameter) of rice straw and the silicon-based properties of biochar, the raw material formulation is shown in Table 1:

[0031] Table 1 Raw materials and parts by weight

[0032]

[0033] Preparation steps:

[0034] Material mixing: Adjust the straw pulp to a concentration of 10% with deionized water, add sulfuric acid-modified rice straw biochar and enzymatically hydrolyzed lignin-PBAT complex (PBAT is cryogenically pulverized to ≤10μm using liquid nitrogen, and is prepared by co-extrusion of 1.8 parts by weight of enzymatically hydrolyzed lignin, 10.2 parts by weight of PBAT, and 5 parts by weight of glycerol at 140℃), and stir at high speed (1500r / min) for 35min (extend the stirring time to ensure uniform mixing of rice fiber and biochar); then add thickener, sodium alginate, and eutectic solvent, and continue stirring for 20min to adjust the solid content to 14%;

[0035] (2) Paper forming: The paper forming machine controls the thickness to 0.025mm and the width to 1000mm, hot-pressing at 90℃ and 0.5MPa for 30s, cooling and peeling to obtain a straw-based biodegradable rice transplanting mulch film with a thickness of 0.02-0.03mm, which is black in color. Figure 1 As shown.

[0036] Performance testing:

[0037] 1. A comparative analysis was conducted on the sulfuric acid-modified rice straw biochar prepared in Example 1 and regular straw biochar. The results are shown in Table 2.

[0038] Table 2. Performance Comparison between Sulfuric Acid Modified Rice Straw Biochar and Straw Biochar

[0039]

[0040] 2. The performance data of the straw-based biodegradable rice transplanting mulch prepared in Example 1 are as follows:

[0041] Physical properties: Mass per unit area 74 g / m² 2 The longitudinal tensile strength is 40 MPa (measured according to GB / T1040.3), the elongation at break is 490%, and the breakage rate of the rice transplanter claw is 100%.

[0042] Functional performance: 88% light blocking rate, 83% weed suppression rate, 86% water retention rate (silicon-based porous water retention), 64% salt resistance rate (modified active sites enhance salt adsorption).

[0043] Degradation performance: 92% degradation rate 90 days after transplanting (measured according to GB / T20197), and complete degradation 30 days after autumn plowing after autumn harvest, with no residue.

[0044] Performance and benefit analysis:

[0045] 1. Degradation efficiency analysis: The film prepared in Example 1 and ordinary paper film were applied to soils with different degrees of salinization, and the degradation rates were compared. The results are shown in Table 3.

[0046] Table 3 Comparison of mulch film degradation rates under different salinity levels (n=3, x±SD)

[0047]

[0048] As shown in Table 3, the mulch prepared in this embodiment of the invention can achieve controllable degradation in soils with different degrees of salinity and alkalinity. The higher the salinity and alkalinity, the slower the initial degradation rate (high pH value has a certain inhibitory effect on microbial activity), but the degradation rate after 90 days is ≥89.8%. It can be completely degraded after autumn plowing after autumn harvest, which is suitable for the growth cycle and agronomic needs of cold-climate rice. In contrast, ordinary paper film (purchased from Jiele Agricultural Technology Development Co., Ltd. in Wuchang City, Heilongjiang Province, product name: straw fiber mulch film) has a degradation rate of only 3.6%-9.5% after 30 days under the same conditions, the highest degradation rate after 90 days is only 31.5% (slightly saline-alkali land), and the degradation rate after 120 days (after autumn plowing) is less than 50%, with a residual rate of more than 50%. It is difficult to adapt to the saline-alkali soil environment and is prone to residual film accumulation, which affects the following year's cultivation.

[0049] 2. Soil Improvement Effect Analysis: The mulch film prepared in Example 1 and ordinary paper film were applied to the soil, and compared with traditional planting methods. The soil index results are shown in Table 4.

[0050] Table 4 Comparison of soil indicators between mulched planting and traditional planting (without mulch) (n=3, x±SD)

[0051]

[0052] As shown in Table 4, the organic matter and nitrogen released after degradation of the mulch prepared in this embodiment significantly improve soil fertility, slightly reduce pH, and improve soil aggregate structure, demonstrating a significant effect on improving saline-alkali soil. In contrast, ordinary paper mulch has a slow degradation rate (90-day degradation rate ≤31.5%), resulting in limited release of organic matter and nitrogen from its degradation products. Its effect on improving soil organic carbon, total nitrogen, and soil aggregate structure is weak (organic carbon only increases to 1.1%, aggregate structure ≤28%), and it cannot reduce soil pH. Therefore, its improvement effect is far inferior to that of the mulch film of this invention. No significant changes were observed in soil indicators under traditional non-mulch planting methods.

[0053] 3. Crop growth and yield analysis: The mulch film prepared in Example 1 and ordinary paper film were applied to the soil respectively, and compared with traditional planting methods. The growth and yield results are shown in Table 5.

[0054] Table 5. Growth and yield indicators of rice grown under plastic film and conventional planting (without plastic film) (n=3, x±SD)

[0055]

[0056] As shown in Table 5, the mulch prepared in this embodiment of the invention significantly promotes rice growth through the synergistic effects of water retention, salt inhibition, light shading and weed suppression, and fertilizer supplementation. The yield is 15.6% higher than that of traditional non-mulch planting, demonstrating good planting effect. Ordinary paper film has a low light shading rate (less than 80%) and lacks salt inhibition performance (no modified biochar design). Its weed suppression effect and water retention capacity are limited, resulting in the increase in rice root length and effective tiller number being only 50%-60% of that in Example 1. The yield per mu is 10% lower than that in Example 5, showing that its crop growth promotion effect in saline-alkali land is significantly insufficient.

[0057] 4. Economic Benefit Analysis: The mulch prepared in Example 1 and ordinary paper film were applied to the soil respectively, and compared with traditional planting methods. The economic benefit results are shown in Table 6.

[0058] Table 6. Comparison of economic benefits between mulched planting and traditional planting (without mulch)

[0059]

[0060] As shown in Table 6, although the use of mulch requires the investment of mulch film, the net income of planting using the mulch film method of this invention is 333 yuan / mu higher than that of traditional planting without mulch film due to the reduction of fertilizer, herbicide usage and manual weeding costs, resulting in a significant increase in overall economic benefits. Although the initial cost of ordinary paper film is lower (40 yuan / mu), its insufficient shading results in the emergence of a small number of weeds in the later stages, generating additional costs for manual weeding and herbicide, and the yield is lower (1500 yuan / mu). Its average net income per mu (1280 yuan) is 14.3% lower than that of the mulch film of this invention, and the residual film rate is high (>50%), which will increase the cost of soil remediation in the long term. Therefore, the overall economic benefits are not as good as those of the embodiment of this invention.

[0061] In summary, the straw-based biodegradable rice transplanting mulch prepared in this embodiment of the invention, tailored to the characteristics of rice cultivation in cold saline-alkali land, achieves multiple functions through the synergistic design of straw fiber, modified biochar, and enzymatically hydrolyzed lignin PBAT complex, including water retention (water retention rate ≥85%), salt inhibition (salt inhibition rate ≥60%), shading and weed suppression (weed suppression rate ≥80%), and fertilization. Its mechanical properties are adapted to the high-speed operation requirements of mulch-covered rice transplanters, with a longitudinal tensile strength of 38-42 MPa and an elongation at break of ≥480%. It can be directly broken through by the transplanter claws without the need for pre-punching of planting holes, greatly simplifying the operation process.

[0062] In terms of degradation performance, by adjusting the proportion of low eutectic solvent, the degradation rate of the mulch film is ≥90% within 90-120 days. After autumn harvest, it can be completely degraded by autumn plowing. Moreover, the degradation products can increase the soil organic matter and nitrogen content, improve the structure of saline-alkali land, and reduce the amount of chemical fertilizers by 30-40% compared with traditional mulch film-free planting. It can basically replace chemical herbicides, and the field weed control mainly relies on shading to suppress weeds (the weed suppression rate is ≥80%). The net income per mu is increased by 28.7%, which has both ecological and economic benefits.

[0063] Regarding salt barrier properties, the eutectic solvent (choline chloride-urea) promotes microbial enzyme penetration and regulates the degradation rate by disrupting inter-fiber hydrogen bonds; sulfuric acid-modified biochar generates sulfonic acid groups (-SO3H) on its surface, which adsorb Na+ through ion exchange. + It improves the salt resistance rate, filling the gap in the application of mulch film products in saline-alkali land;

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of a straw-based biodegradable rice transplanting mulch film in saline-alkali soil environments, characterized in that, The straw-based biodegradable rice transplanting mulch comprises the following raw materials in parts by weight: 65-75 parts straw pulp, 15-20 parts sulfuric acid modified rice straw biochar, 8-12 parts enzymatically hydrolyzed lignin-PBAT complex, 0.5-0.8 parts thickener, 1.5-1.6 parts sodium alginate, and 0.3-0.6 parts eutectic solvent; The enzymatically hydrolyzed lignin-PBAT complex is prepared by co-extrusion of 10-15 parts by weight of enzymatically hydrolyzed lignin with 85-90 parts by weight of PBAT and 4-6 parts by weight of glycerol at 130-150°C. The method for preparing enzymatically hydrolyzed lignin includes the following steps: Rice straw is harvested, leaves are removed, stems are retained, and the straw is crushed. Deionized water is added, and the pH is adjusted to 4.5-5.

0. 2.5% (by weight) of cellulase and 1.2% (by weight) of xylanase are added, and the mixture is enzymatically hydrolyzed in a constant temperature water bath at 50-55℃. After enzymatic hydrolysis, the mixture is inactivated, filtered, and the residue is collected. A 5% (by weight) NaOH solution is added to the residue, and the mixture is stirred in a water bath. The filtrate is collected, and the pH is adjusted to 2.0 with 10% hydrochloric acid. The mixture is allowed to settle, and the precipitate is collected by centrifugation. After washing until neutral, the precipitate is vacuum dried to obtain enzymatically hydrolyzed lignin.

2. The application of the straw-based biodegradable rice transplanting mulch film according to claim 1 in saline-alkali soil environment, characterized in that, The method for preparing straw pulp Includes the following steps: Pretreatment: Take rice straw stems, cut them into 2-4cm sections, soak them in a low eutectic solvent, adjust the moisture content to 60-65%, and let them stand at room temperature; Steaming: Add the pretreated straw segments to deionized water and steam. Grinding: Press the straw to a moisture content of 70%, grind at low speed first and then at high speed to obtain straw pulp with a fiber length of 0.4-1.8mm.

3. The application of the straw-based biodegradable rice transplanting mulch film according to claim 1 in saline-alkali soil environments, characterized in that, The preparation method of the sulfuric acid modified rice straw biochar includes the following steps: Take rice straw stems, air dry them naturally, cut them into short pieces, put them into a tube furnace, heat them to 550-600℃ under nitrogen protection, keep them heated and carbonize them, cool them, grind and sieve them to obtain black biochar with a particle size ≤5μm. Take biochar and add sulfuric acid solution with a mass fraction of 5-10%. The solid-liquid ratio of biochar to sulfuric acid solution is 1:4.5-5. Stir in a water bath, wash after reaction, dry to constant weight, and grind to a particle size ≤5μm.

4. The application of the straw-based biodegradable rice transplanting mulch film according to claim 2 in saline-alkali soil environments, characterized in that, The molar ratio of choline chloride to urea in the eutectic solvent is 1:

2.

5. The application of the straw-based biodegradable rice transplanting mulch film according to claim 1 in saline-alkali soil environments, characterized in that, The thickener is sodium carboxymethyl cellulose.

6. The application of the straw-based biodegradable rice transplanting mulch film according to any one of claims 1-5 in saline-alkali soil environments, characterized in that, The preparation method of the straw-based biodegradable rice transplanting mulch film includes the following steps: Material mixing: Add deionized water to straw pulp to adjust the concentration to 10-12%, add sulfuric acid modified rice straw biochar and enzymatic hydrolysis lignin-PBAT complex, stir at high speed, then add thickener, sodium alginate and eutectic solvent, continue stirring, and adjust the solid content to 14%; Paper forming: Papermaking is carried out using a paper forming machine.

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