Method for producing mulch film based on ultrafine straw / calcium carbonate powder and the product

Abstract

The present invention discloses a method for manufacturing a multilayer film based on ultrafine straw / calcium carbonate powder, including: (1) mixing coarse straw powder and ultrafine calcium carbonate, pulverizing, and sieving to obtain ultrafine straw / calcium carbonate powder with a mesh size of 500-2000; (2) mixing PBAT, PLA, compatibilizer, epoxidized soybean oil, silane coupling agent, and the ultrafine straw / calcium carbonate powder, and manufacturing them into composite particles through a twin-screw extrusion granulator; (3) inflating the composite particles through an inflation molding machine to manufacture a multilayer film. In the method described in the present invention, the 1000-mesh yield of the straw powder is 30% or more. The addition of calcium carbonate powder can significantly improve the straw pulverization effect, effectively avoid electrostatic adsorption or aggregation between calcium carbonate powders and between straw powders, and the calcium carbonate powder does not need to be separated from the straw powder and can function as a multilayer film opening agent. The present invention further discloses a multilayer film manufactured by the above method, which has relatively good tensile strength and elongation at break.

Description

[Technical Field]

[0001] The present invention relates to a method for producing mulch film, in particular to a method for producing mulch film based on ultrafine straw / calcium carbonate powder and the product thereof, which belongs to the agricultural application field. [Background technology]

[0002] As China actively promotes its "dual carbon" strategy, the applications of degradable materials are becoming increasingly widespread, including degradable mulch films and garbage bags. However, degradable materials currently face challenges, primarily due to their high raw material costs and lower performance than traditional materials such as polyethylene, making them difficult to use on a large scale. Degradable mulch films also face similar challenges, necessitating an urgent need for improved methods that can not only reduce the cost of degradable materials but also consistently improve their performance. Prior art Chinese invention patent CN104403174A discloses a method for filling PBAT mulch films with calcium carbonate. While adding calcium carbonate reduces material costs, the addition of too much calcium carbonate to the mulch film results in calcium carbonate leaching into the soil during the decomposition process, hardening the soil and adversely affecting subsequent cultivation, making this method impractical.

[0003] Crop straw is one of the most abundant biomass materials in nature. Its application in mulch films not only improves agricultural waste utilization but also disperses the mulch film into the soil as it decomposes, thereby enabling the straw to be reused in agricultural fields. Prior art Chinese invention patent CN113461983A discloses a method for filling PBAT films with modified straw powder. The straw is first crushed to 500-800 mesh, then the powder is modified, and finally added to the PBAT film. The resulting PBAT film has a breaking elongation of 430-460% and a tensile strength of 32.24-36.43 MPa. While adding straw powder can reduce costs, the costs of straw crushing and modification are significant. Furthermore, the low crushing efficiency of the straw crushing process increases energy consumption, while the large straw particles make it impossible to produce a thin agricultural mulch film, increasing costs and significantly reducing the performance of the mulch film. Therefore, the practical application of this technology is limited.

[0004] Therefore, it is desirable to develop a simple and efficient method for producing straw / PBAT composite mulch film. Therefore, the production and modification of large-mesh straw powder is particularly important. Simple wheat straw is difficult to achieve a good milling effect during the milling process due to its soft nature. The yield of pure straw powder that passed through a 1000-mesh sieve (10 μm) after milling for 3 hours was only 3-9%. Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a mulch film based on ultrafine straw / calcium carbonate powder that effectively increases tensile strength, and a method for producing the same. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides the following technical solutions.

[0007] The present invention provides a method for producing a mulch film based on ultrafine straw / calcium carbonate powder, (1) mixing coarse straw powder and ultrafine calcium carbonate, grinding, and sieving to obtain 500-2000 mesh ultrafine straw / calcium carbonate powder; (2) mixing PBAT, PLA, a compatibilizer, an epoxidized soybean oil, a silane coupling agent and the ultrafine straw / calcium carbonate powder, and then processing the mixture into composite particles through a twin-screw extruder; (3) Inflating the composite particles through an inflation molding machine to produce a mulch film.

[0008] In step 1), the mesh number of the coarse powder is 50 mesh to 100 mesh, which is advantageous for continuing polishing after mixing with calcium carbonate powder.

[0009] In step 1), the mass ratio of the coarse powder to the ultrafine calcium carbonate is 1-4:1, and the mesh number of the ultrafine calcium carbonate powder is 1000-2000 mesh, which can greatly improve the grinding effect and avoid electrostatic adsorption or aggregation between calcium powder and straw powder.

[0010] In step 1), the grinding time is 2-3 h to ensure sufficient grinding of the ultrafine straw / calcium carbonate powder.

[0011] In step 2), the mass ratio of PBAT, PLA, compatibilizer, epoxidized soybean oil, silane coupling agent and ultrafine straw / calcium carbonate powder is 200-800:10-180:2-20:1-15:1-20:20-300.

[0012] The compatibilizer includes an acid anhydride type compatibilizer, an epoxy type compatibilizer, or an ethylene terpolymer.

[0013] In step 2), the extrusion temperatures of the twin-screw extruder are 180 to 200°C in the first zone, 170 to 190°C in the second zone, 170 to 190°C in the third zone, 160 to 180°C in the fourth zone, and 150 to 170°C in the fifth zone, and the rotation speed of the main body is 40 to 80 rpm.

[0014] In step 3), the inflation temperatures of the inflation molding machine are 180 to 200°C in the first zone, 170 to 190°C in the second zone, 170 to 190°C in the third zone, 165 to 185°C in the fourth zone, 160 to 180°C in the fifth zone, and 150 to 170°C in the sixth zone.

[0015] In step (3), the rotation speed of the main body of the inflation molding machine is 10 to 30 rpm, and the pulling speed is 5 to 25 rpm.

[0016] The present invention further provides a mulch film produced by the above method.

[0017] Reaction mechanism: The ultrafine calcium carbonate powder itself has a small particle size and a hard material, so it can function as a grinding friction agent similar to the small balls in a ball mill, and the ultrafine calcium carbonate powder can be well dispersed in the straw powder, preventing electrostatic adsorption or aggregation between the calcium powder and the straw powder. [Effects of the Invention]

[0018] Compared with the prior art, the present invention has the following three significant advantages:

[0019] 1. After mixing ultrafine calcium carbonate powder with straw powder, a good grinding effect can be achieved, with the yield of 1000 mesh straw powder being more than 30%. 2. The ultrafine calcium carbonate powder does not need to be separated from the straw powder and can be added to the mulch film at the same time as the straw powder to act as an opening agent. 3. The ultrafine straw / calcium carbonate powder produced can strengthen the tensile strength of the mulch film. [Brief explanation of the drawings]

[0020] [Figure 1] 10 shows the grinding efficiency of various ratios of ultrafine straw / calcium carbonate powder. [Figure 2] FIG. 1 shows the infrared spectra of straw / calcium carbonate powder before and after sieving. [Figure 3] FIG. 1 shows scanning electron micrographs of pure straw powder and straw / calcium carbonate powder. [Figure 4] Mechanical properties of mulch films made with various straw / calcium carbonate powders. DETAILED DESCRIPTION OF THE INVENTION

[0021] The technical solution of the present invention will be further described below with reference to the drawings.

[0022] Materials: Wheat straw originates from Jiangsu Academy of Agricultural Sciences; ultrafine calcium carbonate powder (1000-2000 mesh): Suzhou Shengyao Plastic New Materials Co., Ltd., lot number SY-2700; thermoplastic biodegradable plastic (PBAT): Jinhui Zhaolong High-Technology Co., Ltd., lot number 1908; silane coupling agent (PLA): Cargill, lot number 2003D; compatibilizer: ethylene terpolymer, DuPont USA, HP441; silane coupling agent: Sinopharm Group Chemical Reagents Co., Ltd., KH570; epoxidized soybean oil: Mycrong.

[0023] Equipment: Twin-screw extrusion granulator: Zhangjiagang Lianjiang Machinery Co., Ltd., LJPS20-PLC; Inflation molding machine: Zhangjiagang Lianjiang Machinery Co., Ltd., SCM25-PLC.

[0024] Example 1 When ultrafine calcium carbonate powders with particle sizes of 1000 mesh, 1500 mesh, and 2000 mesh were selected and sieved, respectively, it was found that the amount of ultrafine calcium carbonate powders of 1000 mesh, 1500 mesh, and 2000 mesh after sieving was small, and a certain amount of aggregation occurred among the calcium powders, resulting in larger particle sizes.

[0025] Preparation of ultrafine straw / calcium carbonate powder: Wheat straw was polished and sieved to obtain coarse wheat straw powder of about 50 mesh, and then the coarse wheat straw powder was mixed with sieved ultrafine calcium carbonate powder of 1000 mesh in a mass ratio of 4:1, and then placed in a grinder and ground for 3 hours to obtain a mixture, which was then sieved through a 1000 mesh sieve to obtain ultrafine straw / calcium carbonate powder.

[0026] Preparation of mulch film: 200 parts PBAT, 10 parts PLA, 2 parts compatibilizer, 1 part epoxidized soybean oil (chemical formula: (RC2H2OR'COO)3C3H5), 1 part silane coupling agent, and 20 parts ultrafine straw / calcium carbonate powder were uniformly mixed and processed into composite particles using a twin-screw extruder. The twin-screw extrusion temperatures were 190°C in the first zone, 180°C in the second zone, 180°C in the third zone, 170°C in the fourth zone, and 160°C in the fifth zone, and the extrusion speed was 60 rpm. The mixture was then blown into a 10 μm-thick mulch film using an inflation molding machine. The inflation temperatures were 190°C in the first zone, 180°C in the second zone, 180°C in the third zone, 175°C in the fourth zone, 170°C in the fifth zone, and 160°C in the sixth zone, the rotation speed of the body was 20 rpm, and the pulling speed was 15 rpm.

[0027] Example 2 Preparation of ultrafine straw / calcium carbonate powder: Wheat straw was polished and sieved to obtain coarse wheat straw powder of about 80 mesh. The coarse wheat straw powder was then mixed with 2000 mesh ultrafine calcium carbonate powder in a mass ratio of 2:1, and then placed in a grinder and ground for 2 hours to obtain a mixture, which was then sieved through a 1000 mesh sieve to obtain ultrafine straw / calcium carbonate powder.

[0028] Preparation of mulch film: 800 parts PBAT, 180 parts PLA, 20 parts compatibilizer, 15 parts epoxidized soybean oil, 20 parts silane coupling agent, and 300 parts ultrafine straw / calcium carbonate powder were uniformly mixed and processed into composite particles using a twin-screw extruder. The twin-screw extrusion temperatures were 200°C in the first zone, 190°C in the second zone, 190°C in the third zone, 180°C in the fourth zone, and 170°C in the fifth zone, with a rotation speed of 80 rpm. The mixture was then blown into a 10 μm-thick mulch film using an inflation molding machine. The blown temperature was 200°C in the first zone, 190°C in the second zone, 190°C in the third zone, 185°C in the fourth zone, 180°C in the fifth zone, and 170°C in the sixth zone. The rotation speed of the extruder was 30 rpm, and the towing speed was 25 rpm.

[0029] Example 3 Preparation of ultrafine straw / calcium carbonate powder: Wheat straw was polished and sieved to obtain coarse wheat straw powder of about 100 mesh. The coarse wheat straw powder was then mixed with 1500 mesh ultrafine calcium carbonate powder in a mass ratio of 1:1, and then placed in a grinder and ground for 2.5 hours to obtain a mixture, which was then sieved through a 1000 mesh sieve to obtain ultrafine straw / calcium carbonate powder.

[0030] Preparation of mulch film: 500 parts PBAT, 100 parts PLA, 10 parts compatibilizer, 10 parts epoxidized soybean oil, 10 parts silane coupling agent, and 200 parts ultrafine straw / calcium carbonate powder were uniformly mixed and processed into composite particles using a twin-screw extruder. The twin-screw extrusion temperatures were 180°C in the first zone, 170°C in the second zone, 170°C in the third zone, 160°C in the fourth zone, and 150°C in the fifth zone, with a rotation speed of 40 rpm. The mixture was then blown into a 10 μm-thick mulch film using an inflation molding machine. The blown temperature was 180°C in the first zone, 170°C in the second zone, 170°C in the third zone, 165°C in the fourth zone, 160°C in the fifth zone, and 150°C in the sixth zone, with a rotation speed of 10 rpm and a traction speed of 5 rpm.

[0031] Example 4 Preparation of ultrafine straw / calcium carbonate powder: Wheat straw was polished and sieved to obtain coarse wheat straw powder of about 50 mesh. The coarse wheat straw powder was then mixed with calcium carbonate powder of about 500 mesh in a mass ratio of 1:1, and then placed in a grinder and ground for 3 hours to obtain a mixture, which was then sieved through a 500 mesh sieve to obtain ultrafine straw / calcium carbonate powder.

[0032] Preparation of mulch film: 600 parts of PBAT, 150 parts of PLA, 18 parts of compatibilizer, 12 parts of epoxidized soybean oil, 18 parts of silane coupling agent, and 250 parts of ultrafine straw / calcium carbonate powder were uniformly mixed and processed into composite particles through a twin-screw extruder. The parameters of the twin-screw extruder and inflation extrusion machine were the same as in Example 1.

[0033] Example 5 Investigation of the grinding efficiency of ultrafine straw / calcium carbonate powders with different ratios Pure wheat straw was used as a comparative example and was placed in a grinder and ground for 3 hours. As shown in Figure 1, the yields of particles sized 1000 mesh or larger for Examples 1 to 4 were 35.9%, 51.8%, 30.2%, and 15.7%, respectively, all of which were higher than the 5.1% yield of pure wheat straw. This indicates that the yield of particles sized 1000 mesh or larger increases with increasing calcium carbonate content, but too much calcium carbonate can cause a decrease in grinding efficiency. That is, the highest yield of particles sized 1000 mesh or larger was achieved when the mass ratio of coarse wheat straw powder to ultrafine calcium carbonate powder was 2:1.

[0034] Example 6 Study on the effect of sieving on the content of ultrafine straw / calcium carbonate powder Using pure wheat straw powder and ultrafine calcium carbonate as comparative examples, the infrared spectra of the straw / calcium carbonate powder of Example 2 before and after sieving were measured. As shown in Figure 2, the hydroxyl group peak of the straw / calcium carbonate powder of Example 2 after sieving through a 1000 mesh sieve was almost the same as that of the powder without sieving. This does not mean that the calcium carbonate content is increased and the straw content is decreased, but rather that the ratio of straw to calcium carbonate remains almost unchanged, indicating that sieving has little adverse effect on the calcium carbonate and straw contents.

[0035] Example 7 Investigation of particle size of ultrafine straw powder Using pure straw powder as a comparison example, electron microscope scanning was performed on the straw / calcium carbonate powder of Example 2. As shown in Figure 3, the average particle size of the straw powder in the straw / calcium carbonate powder was 6 μm, which was significantly smaller than the 30 μm of the simple straw grinding, indicating that the addition of calcium carbonate could significantly improve the grinding efficiency.

[0036] Example 8 Examination of the mechanical properties of various mulch films The mulch film produced by the method of Example 1 using pure straw powder was used as a comparative example. Mechanical property tests were conducted on the mulch films of Examples 1 to 4. As shown in Figure 4, the mulch film containing pure straw powder had a tensile strength of 14.87 MPa and a breaking elongation of 488.01%, while the mulch films produced in Examples 1 to 4 had tensile strengths of 21.83 MPa, 26.23 MPa, 21.00 MPa, and 22.9 MPa and breaking elongations of 450.60%, 528.10%, 397.15%, and 447.6%, respectively. While the mulch film containing pure straw powder exhibited obvious spots, resulting in a decrease in mechanical properties and the occurrence of aggregation, the addition of straw / calcium carbonate powder to PBAT in the present invention not only significantly improved the tensile strength but also consistently improved the breaking elongation, demonstrating a significant effect on improving the mulch film quality.

Claims

1. (1) mixing and pulverizing coarse straw powder and ultrafine calcium carbonate powder to obtain ultrafine straw / calcium carbonate powder of a size passing through a 500-2000 mesh sieve; (2) Mixing PBAT, PLA, compatibilizer, epoxidized soybean oil, silane coupling agent and the ultrafine straw / calcium carbonate powder, and extruding the mixture into composite particles through a twin-screw extruder; (3) Inflating the composite particles through an inflation molding machine to produce a mulch film.

2. 2. The method according to claim 1, wherein in step (1), the coarse straw powder has a size that passes through a 50 to 100 mesh sieve.

3. 2. The method according to claim 1, wherein in step (1), the mass ratio of the coarse straw powder to the ultrafine calcium carbonate is 1 to 4:1, and the ultrafine calcium carbonate powder has a size passing through a 1000 to 2000 mesh sieve.

4. 2. The method according to claim 1, wherein in step (1), the grinding time is 2 to 3 hours.

5. 2. The method of claim 1, wherein in step (2), the mass ratio of the PBAT, PLA, compatibilizer, epoxidized soybean oil, silane coupling agent, and ultrafine straw / calcium carbonate powder is 200-800:10-180:2-20:1-15:1-20:20-300.

6. 6. The method of claim 5, wherein the compatibilizer comprises an anhydride-type compatibilizer, an epoxy-type compatibilizer, or an ethylene terpolymer.

7. 6. The method according to claim 5, wherein in step (3), the rotation speed of the main body of the inflation molding machine is 10 to 30 rpm, and the pulling speed is 5 to 25 rpm.

8. A mulch film produced by the method according to any one of claims 1 to 7.

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