Bamboo fiber degradable mulching film and preparation method thereof

Abstract

The invention discloses a bamboo fiber degradable mulching film and a preparation method thereof, and belongs to the technical field of agricultural environment-friendly materials. The mulching film is prepared from bamboo fibers loaded with a nano silicon dioxide-chitosan composite coating on the surface, acetate-sodium alginate composite modified starch, a lignin-maleic anhydride grafted copolymer cross-linking agent, a bacillus subtilis degradation accelerant and the like. The preparation method comprises the steps of bamboo fiber pretreatment, composite modified starch preparation, graft copolymer synthesis, melt extrusion granulation, film casting, ultraviolet crosslinking and the like. According to the invention, the bamboo fibers are modified by innovatively adopting the nano silicon dioxide-chitosan composite coating, so that the interfacial compatibility and the antibacterial performance are improved; the film-forming property and the air permeability of the matrix are optimized through the acetate-sodium alginate composite modified starch; a lignin-maleic anhydride grafted copolymer is used for replacing a traditional cross-linking agent, and synergy of mechanical enhancement and controllable degradation is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of agricultural environmental protection materials, and particularly relates to a bamboo fiber degradable mulching film and a preparation method thereof. BACKGROUND

[0002] Agricultural mulching film plays a significant role in heat preservation, soil moisture preservation, yield increase and income increase, but traditional polyethylene mulching film is difficult to degrade, leading to soil residual film accumulation and structure damage, thereby restricting the sustainable development of agriculture. The existing degradable mulching film technology has obvious defects: the mechanical properties of starch-based film are poor (the tensile strength is generally < 15 MPa), the water resistance is insufficient (the water absorption rate is > 30%), and the degradation rate is uncontrollable; the natural fiber reinforced mulching film has poor fiber and substrate interface compatibility, high brittleness and low elongation at break (usually < 60%), and the degradation efficiency is less than 80%.

[0003] Part of the technology adopts polyethylene and biodegradable components for blending, which can improve the performance but cannot completely eliminate pollution due to the residual plastic components; or relies on synthetic additives, which has environmental risks. At the same time, the existing process is simple for fiber pretreatment and does not solve the problem of uneven dispersion, and the film body structure stability is poor. Therefore, the development of a full-natural-based, high-strength and controllable-degradation composite mulching film has become the key to solving the agricultural white pollution. SUMMARY

[0004] The application solves the multiple contradictions of "environmental protection-performance-degradation efficiency-function" in the prior art through material system innovation (composite modified bamboo fiber, starch and additives) and process optimization, and provides a bamboo fiber-based composite mulching film with high strength, controllable degradation, multi-functional synergy and low cost, which effectively replaces the traditional plastic mulching film and promotes the green and sustainable development of agriculture.

[0005] To achieve the above-mentioned purposes, the technical scheme adopted by the application is as follows: A bamboo fiber degradable mulching film is composed of the following components in parts by weight: 15-25 parts of bamboo fiber, 30-40 parts of acetate-sodium alginate composite modified starch, 5-10 parts of chitosan, 8-15 parts of citric acid plasticizer, 3-8 parts of organic modified montmorillonite filler, 5-10 parts of lignin-maleic anhydride graft copolymer crosslinking agent, 2-5 parts of bacillus subtilis degradation promoter and 1-3 parts of vitamin E antioxidant. The bamboo fiber is loaded with a nano-silicon dioxide-chitosan composite coating on the surface, the degree of substitution of the acetate-sodium alginate composite modified starch is 0.10-0.15, the grafting rate of the lignin-maleic anhydride graft copolymer is 15%-20%, and the mass ratio of nano-silicon dioxide to chitosan in the nano-silicon dioxide-chitosan composite coating is 1:2-1:3.

[0006] Further, the length-diameter ratio of the bamboo fiber is 20-30:1, and the thickness of the nano-silica-chitosan composite coating is 50-100 nm.

[0007] Further, the mass ratio of starch to sodium alginate in the acetate-sodium alginate composite modified starch is 10:1-10:2.

[0008] Further, the interlayer spacing of the organic modified montmorillonite is 2.5-3.5 nm, and the viable bacterial count of the bacillus subtilis degradation promoter is ≥1×10^9 CFU / g.

[0009] The application discloses a preparation method of a degradable mulching film of bamboo fiber, and comprises the following steps: S1, pretreatment of the bamboo fiber and preparation of a composite coating; S2, preparation of acetate-sodium alginate composite modified starch; S3, preparation of a lignin-maleic anhydride graft copolymer; S4, mixing of the materials; S5, melt extrusion and granulation; S6, casting and film forming; and S7, ultraviolet crosslinking treatment.

[0010] Further, in the step S1, the pH value of the chitosan acetic acid solution is 4.0-5.0, and the particle size of the nano-silicon dioxide is 20-50 nm.

[0011] Further, in the step S2, the dropping speed of the acetic anhydride is 1-2 mL / min, and the pH value of the reaction system is adjusted to 8.0-9.0 by a sodium hydroxide solution.

[0012] Further, the lignin in step S3 has a molecular weight of 5000-8000 Da, and the reaction is carried out under nitrogen protection.

[0013] Further, the length-diameter ratio of the double-screw extruder in step S5 is 40:1, and the barrel temperature is 130℃, 140℃, 150℃, and 145℃ from the feeding section to the head section.

[0014] Further, the distance of ultraviolet irradiation in step S7 is 15-20 cm, and the conveying speed of the film is 0.5-1.0 m / min.

[0015] Beneficial effects: The mulch film is made of all-natural base materials such as bamboo fiber, composite modified starch, and chitosan, without any synthetic plastic components. It can be completely degraded into carbon dioxide and water in the natural environment through microbial action, with a biodegradation rate reaching the industry-leading level. After degradation, there is no harmful residue, and it can be converted into organic nutrients to improve soil structure, fundamentally solving the problem of soil residue pollution and microplastics caused by traditional plastic mulch, and helping the sustainable development of the agricultural ecosystem.

[0016] Through the modification of the bamboo fiber surface nano-silicon dioxide-chitosan composite coating, the interfacial adhesion between the fiber and the matrix is significantly enhanced. The lignin-maleic anhydride graft copolymer forms a stable three-dimensional network structure, which, together with the microphase separation design of the composite modified starch, makes the mulch film have high strength and flexibility, and the tear resistance meets the requirements of mechanized laying. At the same time, vitamin E antioxidant delays material aging, and the ultraviolet cross-linking process regulates the structural stability, ensuring that the mulch film maintains its integrity during the crop growth period and avoids premature damage and failure.

[0017] Organic modified montmorillonite effectively blocks soil water evaporation and improves water use efficiency; moderate light transmittance (72%-78%) balances the needs of soil temperature rise and crop photosynthesis; chitosan coating slowly releases antibacterial ingredients, reducing the incidence of soil-borne diseases; the air permeability of the composite modified starch matrix is optimized to avoid oxygen deficiency of crop roots. The residual ingredients after degradation can improve the soil aggregate structure and soil fertility, realizing the virtuous cycle of "mulch use-degradation-soil improvement".

[0018] In the preparation process, alkali treatment and ultrasonic pretreatment of bamboo fiber are used instead of high-energy nanogrinding process, and industrial by-products lignin is used to synthesize cross-linking agents, reducing the dependence on petrochemical resources. The whole process has no harmful emissions, meeting the clean production standard; the raw material cost is reduced by 15%-20% compared with polylactic acid mulch, and it is compatible with existing mulch production lines, without the need for large-scale equipment modification to realize industrialization, providing an economically feasible technical solution for the green transformation of agriculture. DETAILED DESCRIPTION The technical solutions in the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0019] Embodiment 1 Treated with alkali (5% sodium hydroxide solution, stirring at 65 ℃ for 2.5 hours), ultrasonic treatment (350 W, ultrasonic at 45 ℃ for 40 minutes) and loaded with nano-silica-chitosan composite coating (nano-silica 1.5%, chitosan 2.5%) 20 parts of bamboo fiber, mixed with acetate-sodium alginate composite modified starch (starch: sodium alginate = 10:1.5, degree of substitution 0.12) 35 parts, chitosan 8 parts, lignin-maleic anhydride graft copolymer (grafting rate 18%) 8 parts, bacillus subtilis degradation promoter 3 parts, organic montmorillonite 5 parts, vitamin E antioxidant 2 parts. High-speed mixing (900 r / min, 18 minutes), twin-screw extrusion granulation (screw speed 220 r / min, barrel temperature 140 ℃), casting film forming (die temperature 150 ℃, cooling roller temperature 35 ℃, pulling speed 1.8 m / min), ultraviolet crosslinking (254 nm, 120 W irradiation for 8 minutes) to prepare the mulch film.

[0020] Embodiment 2 Treated with alkali (8% sodium hydroxide solution, stirring at 70 ℃ for 3 hours), ultrasonic treatment (400 W, ultrasonic at 50 ℃ for 45 minutes) and loaded with nano-silica-chitosan composite coating (nano-silica 2%, chitosan 3%) 25 parts of bamboo fiber, mixed with acetate-sodium alginate composite modified starch (starch: sodium alginate = 10:2, degree of substitution 0.15) 40 parts, chitosan 10 parts, lignin-maleic anhydride graft copolymer (grafting rate 20%) 10 parts, bacillus subtilis degradation promoter 5 parts, organic montmorillonite 8 parts, vitamin E antioxidant 3 parts. High-speed mixing (1000 r / min, 20 minutes), twin-screw extrusion granulation (screw speed 250 r / min, barrel temperature 150 ℃), casting film forming (die temperature 160 ℃, cooling roller temperature 40 ℃, pulling speed 2.0 m / min), ultraviolet crosslinking (254 nm, 150 W irradiation for 10 minutes) to prepare the mulch film.

[0021] Embodiment 3 The bamboo fiber 15 parts, which is treated by alkali (5% sodium hydroxide solution, stirring at 60°C for 2 hours), ultrasonic (300W, ultrasonic at 40°C for 30 minutes) and loaded with nano-silica-chitosan composite coating (1% nano-silica, 2% chitosan), is mixed with acetic acid ester-sodium alginate composite modified starch (starch: sodium alginate = 10:1, degree of substitution 0.10) 30 parts, chitosan 5 parts, lignin-maleic anhydride graft copolymer (grafting rate 15%) 5 parts, bacillus subtilis degradation promoter 2 parts, organic montmorillonite 3 parts, vitamin E antioxidant 1 part. The mulch is prepared by high-speed mixing (800 r / min, 15 minutes), twin-screw extrusion granulation (screw speed 200 r / min, barrel temperature 130°C), casting film formation (die temperature 140°C, cooling roller temperature 30°C, pulling speed 1.5 m / min), and ultraviolet crosslinking (254 nm, 100W irradiation for 5 minutes).

[0022] Comparative Example 1 The difference from Example 1 (lack of nano-silica-chitosan composite coating): the bamboo fiber is only treated by alkali and ultrasonic pretreatment, and is not loaded with nano-silica-chitosan composite coating. The other components and process parameters are consistent with Example 1.

[0023] Comparative Example 2 The difference from Example 1 (lack of lignin-maleic anhydride graft copolymer): equal mass of maleic anhydride (without grafting lignin) is used to replace the lignin-maleic anhydride graft copolymer. The other components and process parameters are consistent with Example 1.

[0024] Comparative Example 3 The difference from Example 1 (use of unmodified starch): ordinary corn starch is used to replace the acetic acid ester-sodium alginate composite modified starch. The other components and process parameters are consistent with Example 1.

[0025] The following table is the explanation and test results table of the bamboo fiber-based composite mulch examples and comparative examples: Result analysis Advantages of the examples: the tensile strength (22.1-25.2 MPa), elongation at break (82%-95%), and biodegradation rate (97%-99%) of Examples 1-3 are significantly better than those of the comparative examples, and the water absorption rate is low (12%-16%), which meets the "full biodegradable material" standard (biodegradation rate ≥ 90%) in GB / T 20197-2006 "Definition, Classification, Marking and Biodegradation Performance Requirements of Biodegradable Plastics".

[0026] Comparative Example Defects: Comparative Example 1 has weak interface bonding between bamboo fibers and the matrix due to the absence of a composite coating, and the tensile strength decreases by 28.5% (from 23.5 MPa to 16.8 MPa); Comparative Example 2 has insufficient crosslinking network rigidity due to the absence of a graft copolymer, and the water absorption rate increases by 78.6% (from 14% to 25%); Comparative Example 3 has poor matrix film-forming properties due to the use of unmodified starch, and the biodegradation rate decreases by 20.6% (from 98% to 78%).

[0027] The above results show that the biodegradable mulch film of the present application realizes the synergistic improvement of mechanical properties, degradation efficiency and agricultural functions through material modification and process optimization.

[0028] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A biodegradable mulch film of bamboo fiber, characterized by, The application discloses a kind of composite granules for improving the degradation of bamboo fiber, which is composed of the following components by weight: 15-25 parts of bamboo fiber, 30-40 parts of acetate-sodium alginate composite modified starch, 5-10 parts of chitosan, 8-15 parts of citric acid plasticizer, 3-8 parts of organic modified montmorillonite filler, 5-10 parts of lignin-maleic anhydride graft copolymer crosslinking agent, 2-5 parts of bacillus subtilis degradation promoter, and 1-3 parts of vitamin E antioxidant.The bamboo fiber is loaded with a nano-silicon dioxide-chitosan composite coating on its surface, the degree of substitution of the acetate-sodium alginate composite modified starch is 0.10-0.15, the grafting rate of the lignin-maleic anhydride graft copolymer is 15%-20%, and the mass ratio of nano-silicon dioxide to chitosan in the nano-silicon dioxide-chitosan composite coating is 1:2-1:

3.

2. The degradable mulch film of claim 1, wherein, The length-diameter ratio of the bamboo fiber is 20-30:1, and the thickness of the nano-silicon dioxide-chitosan composite coating is 50-100 nm.

3. The degradable mulch film of claim 1, wherein, The mass ratio of starch to sodium alginate in the acetate-sodium alginate composite modified starch is 10:1-10:

2.

4. The biodegradable mulch film of claim 1, wherein, The interlayer spacing of the organic modified montmorillonite is 2.5-3.5 nm, and the viable bacterial count of the bacillus subtilis degradation promoter is greater than or equal to 1×10^9 CFU / g.

5. A method for preparing a degradable mulch film of bamboo fiber for manufacturing the mulch film according to any one of claims 1 to 4, characterized in that, The application further discloses a preparation method of the composite granules, which comprises the following steps: S1, bamboo fiber pretreatment and composite coating preparation: bamboo fiber is immersed in a sodium hydroxide solution with a mass concentration of 5-8%, stirred and treated at 60-70°C for 2-3 hours, washed with deionized water until neutral, placed in an ultrasonic instrument, ultrasonically treated at a power of 300-400 W and a temperature of 40-50°C for 30-45 minutes, dried, crushed through a 200-300 mesh sieve, immersed in a chitosan acetic acid solution containing 1%-2% nano-silicon dioxide, stirred at 50-60°C for 1-2 hours, and dried to obtain bamboo fiber loaded with a composite coating on its surface; S2, acetate-sodium alginate composite modified starch preparation: starch and sodium alginate are mixed according to a mass ratio of 10:1-10:2, 3-5% sodium hydroxide is added as a catalyst, and acetic anhydride is added, stirred and reacted at 50-60°C for 2-3 hours, and then washed, dried to obtain a composite modified starch; S3, lignin-maleic anhydride graft copolymer preparation: lignin and maleic anhydride are mixed according to a mass ratio of 1:2-1:3, reacted at 80-90°C for 3-4 hours, and a graft copolymer with a grafting rate of 15%-20% is prepared; S4, mixture preparation: the composite coating bamboo fiber of step S1, the composite modified starch of step S2, chitosan, citric acid plasticizer, and organic modified montmorillonite are added into a high-speed mixer according to a proportion, and mixed at a rotating speed of 800-1000 r / min for 15-20 minutes; S5, melt extrusion granulation: the graft copolymer of step S3, bacillus subtilis degradation promoter, and vitamin E antioxidant are added into the mixture of step S4, uniformly mixed, and then added into a twin-screw extruder, the screw rotating speed is controlled to be 200-250 r / min, and the barrel temperature is controlled to be 130-150°C, so as to obtain a composite master batch through extrusion granulation. S6, casting film forming: the composite master batch is added into a casting machine, the temperature of the die head is controlled at 140-160 DEG C, the temperature of the cooling roller is 30-40 DEG C, the pulling speed is 1.5-2.0 m / min, and a film with a thickness of 0.05-0.1 mm is formed; S7, ultraviolet crosslinking treatment: the casting film is placed in an ultraviolet irradiation instrument, and is irradiated at a wavelength of 254 nm and a power of 100-150 W for 5-10 minutes to obtain the bamboo fiber degradable mulch film.

6. The preparation method according to claim 5, characterized in that, The pH value of the chitosan acetic acid solution in step S1 is 4.0-5.0, and the particle size of the nano-silicon dioxide is 20-50 nm.

7. The preparation method according to claim 5, characterized in that, The dropping speed of acetic anhydride in step S2 is 1-2 mL / min, and the pH value of the reaction system is adjusted to 8.0-9.0 by sodium hydroxide solution.

8. The preparation method according to claim 5, characterized in that, The molecular weight of the lignin in step S3 is 5000-8000 Da, and the reaction is carried out under nitrogen protection.

9. The preparation method according to claim 5, characterized in that, The length-diameter ratio of the double-screw extruder in step S5 is 40:1, and the barrel temperature is 130 DEG C, 140 DEG C, 150 DEG C and 145 DEG C from the feeding section to the die head section.

10. The method of claim 5, wherein, The distance of ultraviolet irradiation in step S7 is 15-20 cm, and the conveying speed of the film is 0.5-1.0 m / min.

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