High-light-transmittance agricultural greenhouse film and preparation method thereof

Abstract

The invention discloses a high-light-transmittance agricultural greenhouse film and a preparation method thereof in the technical field of greenhouse films. The high-light-transmittance agricultural greenhouse film comprises the following components in parts by weight: 50-70 parts of siloxane modified PBAT, 30-50 parts of PLA, 2-5 parts of a chain extender and 0.5-1 part of an antioxidant. According to the invention, PBAT is modified, a siloxane structure is inserted into PBAT polymer molecular chains, the high flexibility of a siloxane chain segment (Si-O-Si) enables the accumulation among the PBAT molecular chains to be looser, and the proportion of crystalline regions in a polymer matrix is reduced; a crystalline region can form a scattering effect on light, light transmission is reduced, the content of the crystalline region in PBAT is reduced due to introduction of siloxane, the light can penetrate through the material more easily, and the light transmission of the agricultural greenhouse film is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of greenhouse films, and specifically refers to a high-light-transmittance agricultural greenhouse film and a preparation method thereof. Background Art

[0002] With the rapid development of modern agriculture, greenhouse technology is increasingly used in agricultural production. As the core construction material of greenhouses, greenhouse film plays an important role in protecting crop growth, improving the growth environment, and increasing crop yield and quality. However, traditional greenhouse films often have problems such as insufficient light transmittance, poor mechanical properties, low anti-aging performance, and susceptibility to pollution, which makes it difficult to meet the demand for high-quality agricultural greenhouse films in modern agricultural production.

[0003] Light transmittance is one of the important performance indicators of agricultural greenhouse films, which directly affects the photosynthesis efficiency and growth quality of crops. Generally speaking, the higher the light transmittance of the greenhouse film, the better the lighting conditions in the greenhouse, the faster the crops grow, and the yield and quality will also increase accordingly. However, although traditional polyethylene (PE) and ethylene-vinyl acetate copolymer (EVA) greenhouse films are cheap and flexible, their optical properties are not ideal, especially under conditions of light scattering or light attenuation, which can easily lead to uneven lighting in the greenhouse. In addition, traditional greenhouse films are prone to aging under long-term exposure to ultraviolet rays, resulting in a shortened service life and increased agricultural production costs.

[0004] In response to the lack of light transmittance, some greenhouse films with higher light transmittance have appeared on the market in recent years. These greenhouse films are usually made by adding light transmittance additives, modified materials or multi-layer co-extrusion technology to the basic resin material. However, although this type of greenhouse film has improved the light transmittance to a certain extent, it is easy to be attached with dust, water or pollutants during long-term use, thereby reducing the light transmittance. In addition, these modification technologies may also lead to a decrease in the mechanical properties of the greenhouse film, such as tear resistance and impact resistance, which cannot adapt to the complex agricultural environment and long-term use requirements.

[0005] In order to further improve the performance of greenhouse films, some studies have begun to focus on the introduction of functional materials, such as modification through nanotechnology or adding special optical functional materials (such as anti-ultraviolet agents, near-infrared shielding agents, etc.) to the film materials. Nanomaterials have a large specific surface area and unique optical properties, which can significantly improve the light transmittance, anti-ultraviolet ability and anti-fog performance of greenhouse films. However, the production cost of greenhouse films modified by nanotechnology is currently high, the preparation process is complex, and it has not yet been fully industrialized and promoted.

[0006] In addition, the surface treatment technology of greenhouse film is also an important direction to improve light transmittance. For example, by introducing anti-fog and anti-drip coatings on the surface of greenhouse film, light scattering or blocking caused by water droplets on the surface of greenhouse film can be effectively reduced. However, the adhesion and durability of such coatings are still technical difficulties, and they are prone to falling off or failure after long-term use.

[0007] In summary, the development of an agricultural greenhouse film with high light transmittance, aging resistance, excellent mechanical properties and strong anti-pollution ability has become an important demand for the development of modern agriculture. The research on new high-transmittance agricultural greenhouse films not only requires breakthroughs in material selection and modification, but also requires the combination of economy and operability in the preparation process to meet the requirements of large-scale production and application. The development of this new type of greenhouse film can not only effectively improve crop yield and quality, but also reduce agricultural production costs, which has important economic and social significance. Summary of the invention

[0008] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a high-transmittance agricultural greenhouse film and a preparation method thereof. The present invention modifies PBAT (polybutylene adipate / terephthalate) and inserts a siloxane structure into the PBAT polymer molecular chain. The high flexibility of the siloxane segment (Si-O-Si) makes the stacking between the PBAT molecular chains looser, reducing the proportion of crystalline regions in the polymer matrix; the crystalline region will scatter light and reduce light transmittance. The introduction of siloxane reduces the content of crystalline domains in PBAT, making it easier for light to penetrate the material, thereby improving the light transmittance of the agricultural greenhouse film.

[0009] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: the present invention proposes a high-transmittance agricultural greenhouse film, the agricultural greenhouse film comprises the following components in parts by weight: 50-70 parts of siloxane-modified PBAT, 30-50 parts of PLA (polylactic acid), 2-5 parts of chain extender, and 0.5-1 part of antioxidant;

[0010] Preferably, the raw materials for preparing the siloxane-modified PBAT specifically include the following components in parts by weight: 20-23 parts of dichlorosiloxane, 17.5-26.5 parts of ethylene carbonate, 33-41.5 parts of p-dibenzoic acid, 16.5-25.5 parts of 1,4-butanediol, and 30-36.5 parts of adipic acid;

[0011] Preferably, the dichlorosiloxane includes at least one of 1,3-dichlorotetramethyldisiloxane, 1,3-bis(3-chloropropyl)tetramethyldisiloxane and 1,3-bis(chloromethyl)tetramethyldisiloxane;

[0012] Preferably, the chain extender includes at least one of PDI (1,5-pentane diisocyanate), LDI (L-lysine diisocyanate), and HDI (hexamethylene diisocyanate);

[0013] Preferably, the antioxidant includes at least one of antioxidant 1010, antioxidant 1076, antioxidant 1035 and antioxidant 1330;

[0014] Preferably, the preparation method of the siloxane-modified PBAT specifically comprises the following steps:

[0015] S1. Dissolve dichlorosiloxane in tetrahydrofuran (THE), add ethylene carbonate, mix well, add alkaline catalyst, stir at 50-80 rpm, introduce flowing argon after the reaction system is uniform, raise the temperature to 60-70°C, continue the reaction for 4-8 hours, cool, remove excess solvent by vacuum distillation, and obtain hydroxylated siloxane after vacuum drying;

[0016] Preferably, in step S1, the mass concentration of dichlorosiloxane in THE is 0.1-0.2 g / mL;

[0017] Preferably, in step S1, the alkaline catalyst includes at least one of pyridine, triethylamine, potassium hydroxide, potassium carbonate, and calcium carbonate;

[0018] Preferably, in step S1, the added mass of the alkaline catalyst is 5-10% of the mass of dichlorosiloxane;

[0019] Under the action of alkaline catalyst, ethylene carbonate undergoes a ring-opening reaction to form an intermediate, which then undergoes a nucleophilic substitution reaction with dichlorosiloxane to introduce hydroxyl groups at both ends of the siloxane structure to form a diol-like structure.

[0020] S2, placing the hydroxylated siloxane prepared in step S1 in a flask, adding p-dibenzoic acid, adipic acid and 1,4-butanediol, introducing flowing argon, adding tetrabutyl titanate, raising the temperature to 180-200° C., reacting for 8-12 hours, and cooling the reaction to room temperature to obtain a PBAT polymer monomer;

[0021] Preferably, in step S2, the added mass of tetrabutyl titanate is 0.75%-0.9% of the mass of terephthalic acid;

[0022] Tetrabutyl titanate is a Lewis acid catalyst that promotes nucleophilic attack by activating the carboxyl group (-COOH). The hydroxyl group (-OH) of hydroxylated siloxane attacks the carboxyl group of terephthalic acid to generate an intermediate of siloxane-ester bond and removes water at the same time. Hydroxylated siloxane plays the role of a flexible segment in the reaction and forms an alternating microphase structure with the rigid terephthalic acid-1,4-butanediol segment of PBAT. This flexible-rigid coexistence structure improves the toughness and flexibility of PBAT.

[0023] S3, adding stannous octoate to the PBAT polymer monomer prepared in step S2, introducing flowing argon, raising the temperature to 230-250° C., and conducting a pre-polycondensation reaction for 2-3 hours, then raising the temperature to 250-270° C., conducting a polycondensation reaction for 6-8 hours, cooling the reaction to room temperature, washing with anhydrous methanol, and drying to obtain siloxane-modified PBAT;

[0024] Preferably, in step S3, the added mass of stannous octoate is 0.6%-0.8% of the mass of terephthalic acid;

[0025] The molecular weight of the polymer is increased through further polycondensation reaction while retaining the flexibility of the siloxane segment, so that the final PBAT material has higher mechanical strength, flexibility and thermal stability.

[0026] The present invention also provides a method for preparing a high-light-transmittance agricultural greenhouse film, which specifically comprises the following steps:

[0027] S4, vacuum drying the siloxane-modified PBAT and PLA, raising the temperature to 160-180° C. under vacuum conditions, stirring at a speed of 60-80 rpm, adding a chain extender, and continuing to raise the temperature to 180-190° C., blending for 20-30 minutes, to obtain a copolymer;

[0028] Siloxane-modified PBAT has a cross-linked structure of flexible Si-O-Si segments. As a dispersed phase, it absorbs stress and guides crack propagation in the PBAT-PLA matrix, preventing rapid crack propagation and causing brittle fracture of the material. The partial compatibility of siloxane segments with PLA (through intermolecular forces) further alleviates interfacial stress concentration, thereby improving the overall toughness of the material.

[0029] S5. Place the copolymer prepared in step S4 in an internal mixer, add an antioxidant, increase the temperature to 130-150° C., perform melt blending at a speed of 60-80 rpm, mix for 40-60 minutes, cool to 40-50° C., place in a mold, and perform hot pressing at 180-200° C. After cooling, obtain an agricultural greenhouse film.

[0030] The beneficial effects achieved by the present invention are as follows:

[0031] The present invention provides a high-light-transmittance agricultural greenhouse film and a preparation method thereof. The present invention modifies PBAT and inserts a siloxane structure into the PBAT polymer molecular chain. The high flexibility of the siloxane segment (Si-O-Si) makes the stacking between the PBAT molecular chains looser, reducing the proportion of the crystalline region in the polymer matrix; the crystalline region scatters light and reduces light transmittance. The introduction of siloxane reduces the content of the crystalline domain in PBAT, making it easier for light to penetrate the material, thereby improving the light transmittance of the agricultural greenhouse film. The present invention adopts a siloxane structure with a halogen structure, introduces hydroxyl groups to both ends of the siloxane structure through a nucleophilic substitution reaction of ethylene carbonate on the halogen, forms a diol structure, and undergoes a condensation reaction with terephthalic acid and 1,4-butanediol to form a PBAT polymer with a siloxane segment; in the P In the amorphous phase of BAT, the presence of siloxane makes the molecular chain segments move more freely, improves the uniformity of the amorphous region, reduces the scattering points of light, and improves the light transmittance of the greenhouse film. During the modification process, siloxane and PBAT are chemically bonded to achieve uniform distribution of the two components on a molecular scale. The compatibility of siloxane improves the optical uniformity of the material and further reduces light scattering. In step S1 of the present invention, siloxane is reacted with ethylene carbonate to generate hydroxylated siloxane, which can react with terephthalic acid or 1,4-butanediol in a subsequent polymerization reaction to form a covalently bonded structure. The introduction of covalent bonds forms a certain degree of chemical cross-linking network between the PBAT molecular chains. This cross-linking structure enhances the tensile strength and impact resistance of the material. The Si-O bond of siloxane has a relatively low bond energy (about 445 kJ / mol) and a larger bond angle (Si-O-Si bond angle can reach more than 130°), which gives siloxane molecules high flexibility. The introduction of siloxane makes the PBAT molecular chain more flexible, reduces stress concentration, and improves the elongation at break and toughness of the material. The siloxane-modified PBAT exhibits better tensile properties. Due to the presence of active groups such as hydroxyl groups on the surface of siloxane-modified PBAT, the compatibility between PLA and PBAT can be improved through hydrogen bonds or van der Waals forces with the polar groups of PLA (such as carbonyl and hydroxyl groups). In the PLA matrix, the modified PBAT usually exists in the form of microphase distribution, forming a composite structure of a flexible PBAT dispersed phase and a rigid PLA matrix phase: the flexible PBAT phase can act as a barrier to crack propagation when subjected to stress, delaying crack propagation and improving elongation at break. The stress buffer formed by microphase dispersion can absorb external forces and improve mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a hydrogen nuclear magnetic resonance spectrum image of the siloxane-modified PBAT prepared in step S3 of Example 1-3 of the present invention;

[0033] Figure 2 The light transmission performance result diagram of the agricultural greenhouse films prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0034] Figure 3 The mechanical properties of agricultural greenhouse films prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention are shown in the figure;

[0035] Figure 4 This is a graph showing the thermal stability results of the agricultural greenhouse films prepared in Example 1 of the present invention and Comparative Examples 1-3.

[0036] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein may be applied to the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only and are not intended to limit the content of this application.

[0039] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials and test strains used in the following examples are purchased from commercial channels unless otherwise specified.

[0040] Example 1

[0041] This embodiment provides a high-transmittance agricultural greenhouse film, which includes the following components in parts by weight: 50 parts of siloxane-modified PBAT, 50 parts of PLA, 2 parts of PDI, and 0.5 parts of antioxidant 1010;

[0042] The raw materials for preparing siloxane-modified PBAT specifically include the following components in parts by weight: 20 parts of 1,3-dichlorotetramethyldisiloxane, 17.5 parts of ethylene carbonate, 33.5 parts of p-dibenzoic acid, 20.7 parts of 1,4-butanediol, and 30 parts of adipic acid;

[0043] The preparation method of siloxane-modified PBAT specifically comprises the following steps:

[0044] S1. Add molecular sieves to a drying bottle, add THE, place it on a vacuum pump to evacuate and dry THE, take 2g of 1,3-dichlorotetramethyldisiloxane and place it in a round-bottom flask, add 10mL of THE after dehydration, mix until 1,3-dichlorotetramethyldisiloxane is completely dissolved, add 1.76g of ethylene carbonate, mix well, introduce flowing nitrogen, mix pyridine and tetrahydrofuran, prepare a 1mol / L pyridine solution, take 0.3mL of pyridine solution and add it to the reaction system, stir at 80rpm, after the reaction system is uniform, raise the temperature to 60°C, continue the reaction for 8h, after the reaction is cooled to room temperature, remove the excess solvent by reduced pressure distillation, wash repeatedly with dichloromethane three times, place it at 40°C and vacuum dry for 24h to obtain hydroxylated siloxane;

[0045] S2. The hydroxylated siloxane prepared in step S1 was placed in a three-necked flask, vacuum dried at 40°C for 1 hour, 2.0 g of 1,4-butanediol was added, and after mixing, 3.3 g of terephthalic acid and 3.0 g of adipic acid were added. Under a flowing argon atmosphere, 25 mg of tetrabutyl titanate was added, the temperature was raised to 200°C, and the reaction was continued for 8 hours. After the reaction was cooled to room temperature, it was washed repeatedly with anhydrous ethanol and deionized water three times in sequence, and then vacuum dried at 50°C for 12 hours to obtain a PBAT polymer monomer;

[0046] S3, taking the PBAT polymer monomer prepared in step S3 and placing it in a flask, after flowing nitrogen, the reaction system is fully dried, 20 mg of stannous octoate is added, the temperature is raised to 250° C. for a pre-polycondensation reaction for 2 hours, and then the temperature is continuously raised to 270° C. for a further polycondensation reaction. After the reaction is cooled to room temperature, it is repeatedly washed three times with anhydrous ethanol, and then placed at 60° C. for vacuum drying for 12 hours to obtain siloxane-modified PBAT;

[0047] This embodiment also provides a method for preparing a high-light-transmittance agricultural greenhouse film, which specifically includes the following steps:

[0048] S4. Accurately weigh 10 g of siloxane-modified PBAT and 10 g of PLA, dry them at 60° C. for 2 h, transfer them to a dry flask, raise the temperature to 180° C., stir at 60 rpm, mix well, add 0.4 g of PDI, raise the temperature to 190° C., blend for 20 min, and obtain a copolymer;

[0049] S5. Place the copolymer prepared in step S4 in an internal mixer, add 0.1 g of antioxidant 1010, increase the temperature to 150° C., perform melt blending at 60 rpm, mix for 40 min, cool to 40° C., place on a flat fluidizer for hot pressing, adjust the hot pressing temperature to 200° C., hot press for 10 min, and perform cold pressing to obtain an agricultural greenhouse film.

[0050] Example 2

[0051] This embodiment provides a high-transmittance agricultural greenhouse film, which includes the following components in parts by weight: 60 parts of siloxane-modified PBAT, 40 parts of PLA, 3.5 parts of LDI, and 0.8 parts of antioxidant 1076;

[0052] The raw materials for preparing siloxane-modified PBAT specifically include the following components in parts by weight: 23 parts of 1,3-bis(3-chloropropyl)tetramethyldisiloxane, 26.5 parts of ethylene carbonate, 41.5 parts of p-dibenzoic acid, 16.5 parts of 1,4-butanediol, and 36.5 parts of adipic acid;

[0053] The preparation method of siloxane-modified PBAT specifically comprises the following steps:

[0054] S1. Add molecular sieves to a drying bottle, add THE and place it on a vacuum pump to evacuate and dry THE. Take 2.3g of 1,3-di(3-chloropropyl)tetramethyldisiloxane and place it in a round-bottom flask. Add 23mL of THE after dehydration and mix until 1,3-dichlorotetramethyldisiloxane is completely dissolved. Then, add 2.65g of ethylene carbonate. After mixing evenly, introduce flowing nitrogen, add 0.26g of potassium carbonate, and stir at a speed of 50rpm. After the reaction system is uniform, increase the temperature to 70°C, continue the reaction for 4h, and after the reaction is cooled to room temperature, remove the excess solvent by reduced pressure distillation. After washing three times with dichloromethane, place it at 40°C and vacuum dry it for 24h to obtain hydroxylated siloxane.

[0055] S2. The hydroxylated siloxane prepared in step S1 was placed in a three-necked flask, vacuum dried at 40°C for 1 hour, 1.65 g of 1,4-butanediol was added, and after mixing, 4.15 g of terephthalic acid and 3.65 g of adipic acid were added. Under a flowing argon atmosphere, 35 mg of tetrabutyl titanate was added, and the temperature was raised to 180°C. After reacting for 12 hours, the reaction was cooled to room temperature, and then washed repeatedly with anhydrous ethanol and deionized water three times in sequence, and then vacuum dried at 50°C for 12 hours to obtain a PBAT polymer monomer;

[0056] S3. The PBAT polymer monomer prepared in step S3 is placed in a flask, and after flowing nitrogen, the reaction system is fully dried, 33 mg of stannous octoate is added, the temperature is raised to 230° C. for a pre-polycondensation reaction for 3 hours, and then the temperature is continuously raised to 250° C. for a further polycondensation reaction. After the reaction is cooled to room temperature, it is repeatedly washed three times with anhydrous ethanol, and then placed at 60° C. for vacuum drying for 12 hours to obtain siloxane-modified PBAT.

[0057] The present invention also provides a method for preparing a high-light-transmittance agricultural greenhouse film, which specifically comprises the following steps:

[0058] S4. Accurately weigh 12 g of siloxane-modified PBAT and 8 g of PLA, dry them at 60° C. for 2 h, transfer them to a dry flask, raise the temperature to 160° C., stir at 70 rpm, mix well, add 0.7 g of LDI, raise the temperature to 180° C., blend for 30 min, and obtain a copolymer;

[0059] S5. Place the copolymer prepared in step S4 in an internal mixer, add 0.16 g of antioxidant 1076, raise the temperature to 130° C., perform melt blending at 80 rpm, mix for 60 min, cool to 50° C., place on a flat fluidizer for hot pressing, adjust the hot pressing temperature to 190° C., hot press for 10 min, and perform cold pressing for qualitative determination to obtain an agricultural greenhouse film.

[0060] Example 3

[0061] This embodiment provides a high-transmittance agricultural greenhouse film, which includes the following components in parts by weight: 70 parts of siloxane-modified PBAT, 30 parts of PLA, 5 parts of PDI, and 1 part of antioxidant 1035;

[0062] The raw materials for preparing siloxane-modified PBAT specifically include the following components in parts by weight: 23 parts of 1,3-bis(chloromethyl)tetramethyldisiloxane, 22 parts of ethylene carbonate, 37 parts of p-dibenzoic acid, 25.5 parts of 1,4-butanediol, and 32.5 parts of adipic acid;

[0063] The preparation method of siloxane-modified PBAT specifically comprises the following steps:

[0064] S1. Add molecular sieves to a drying bottle, add THE, place it on a vacuum pump to evacuate and dry THE, take 2.3g of 1,3-bis(chloromethyl)tetramethyldisiloxane and place it in a round-bottom flask, add 15mL of THE after dehydration, mix until 1,3-dichlorotetramethyldisiloxane is completely dissolved, add 2.2g of ethylene carbonate, mix well, introduce flowing nitrogen, mix triethylamine and tetrahydrofuran, prepare a 1mol / L triethylamine solution, take 2mL of triethylamine solution and add it to the reaction system, stir at 80rpm, after the reaction system is uniform, raise the temperature to 65°C, continue the reaction for 6h, after the reaction is cooled to room temperature, remove excess solvent by reduced pressure distillation, wash repeatedly with dichloromethane three times, place it at 40°C and vacuum dry for 24h to obtain hydroxylated siloxane;

[0065] S2. The hydroxylated siloxane prepared in step S1 was placed in a three-necked flask, vacuum dried at 40°C for 1 hour, 2.55 g of 1,4-butanediol was added, and after mixing, 3.7 g of terephthalic acid and 3.25 g of adipic acid were added. Under a flowing argon atmosphere, 33 mg of tetrabutyl titanate was added, and the temperature was raised to 190°C. After reacting for 10 hours, the reaction was cooled to room temperature, and then washed repeatedly with anhydrous ethanol and deionized water three times in sequence, and then vacuum dried at 50°C for 12 hours to obtain a PBAT polymer monomer;

[0066] S3. The PBAT polymer monomer prepared in step S3 is placed in a flask, and after flowing nitrogen, the reaction system is fully dried, 26 mg of stannous octoate is added, the temperature is raised to 240° C. for a pre-polycondensation reaction for 2 hours, and the temperature is continuously raised to 260° C. for a further polycondensation reaction. After the reaction is cooled to room temperature, it is repeatedly washed three times with anhydrous ethanol, and then placed at 60° C. for vacuum drying for 12 hours to obtain siloxane-modified PBAT.

[0067] This embodiment also provides a method for preparing a high-light-transmittance agricultural greenhouse film, which specifically includes the following steps:

[0068] S4. Accurately weigh 14 g of siloxane-modified PBAT and 6 g of PLA, dry them at 60° C. for 2 h, transfer them to a dry flask, raise the temperature to 170° C., stir at 80 rpm, mix well, add 1 g of PDI, raise the temperature to 190° C., blend for 30 min, and obtain a copolymer;

[0069] S5. Place the copolymer prepared in step S4 in an internal mixer, add 0.2 g of antioxidant 1035, raise the temperature to 140° C., perform melt blending at 70 rpm, mix for 50 min, cool to 45° C., place on a flat fluidizer for hot pressing, adjust the hot pressing temperature to 180° C., hot press for 10 min, and perform cold pressing for characterization to obtain an agricultural greenhouse film.

[0070] Comparative Example 1

[0071] This comparative example provides an agricultural greenhouse film and a preparation method thereof, which is different from Example 1 only in that PLA is not included in the components and is replaced by PBAT in the same weight portion, and the remaining components and component contents are the same as those in Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides an agricultural greenhouse film and a preparation method thereof, which differs from Example 1 only in that the siloxane-modified PBAT in the components is replaced by the same weight portion of PBAT, and the remaining components and component contents are the same as those in Example 1;

[0074] Comparative Example 3

[0075] This comparative example provides an agricultural greenhouse film and a preparation method thereof, which differs from Example 1 only in that the siloxane-modified PBAT in the components is replaced by the same weight portions of PBAT and terminal hydroxyl polydimethylsiloxane, the mass ratio between the PBAT and the terminal hydroxyl polydimethylsiloxane is 2:1, and the terminal hydroxyl polydimethylsiloxane (CasNo: 156327-07-0) is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with the item number C303003. The remaining components and component contents are the same as those in Example 1.

[0076] Experimental Example 1

[0077] In this experimental example, the structure of the siloxane-modified PBAT prepared in step S3 of Example 1-3 was characterized, and the siloxane-modified PBAT was measured by hydrogen nuclear magnetic resonance spectroscopy. 15 mg of the sample was taken, deuterated chloroform was used as a solvent, tetramethylsilane was used as an internal standard, and dissolved for 4 h at room temperature, and tested by a solid-liquid dual-purpose nuclear magnetic resonance instrument.

[0078] Figure 1 The nuclear magnetic resonance hydrogen spectrum image of the siloxane-modified PBAT prepared in step S3 of Examples 1-3 of the present invention, wherein A is Example 1, B is Example 2, and C is Example 3. As shown in the figure, absorption bands appear at δ=7.83 and δ=8.03, corresponding to the resonance absorption of the four H atoms on the benzene ring, and an absorption band appears at δ=0.15, corresponding to the resonance absorption of the hydrogen atoms in the methyl CH3- connected to Si in the Si-O-Si structure, indicating that the siloxane is connected to the polymer molecule of PBAT. In the chain, the difference between A, B and C is that in B, absorption vibration peaks of methylene appear at δ=0.67, δ=1.53 and δ=4.13, corresponding to the resonance absorption of three methylene hydrogen atoms on three chloropropyl groups in the raw material 1,3-bis(3-chloropropyl)tetramethyldisiloxane, and in C, the resonance absorption of methylene hydrogen atoms on chloromethyl in 1,3-bis(chloromethyl)tetramethyldisiloxane appears at δ=3.42, while there is no resonance absorption peak corresponding to hydrogen atoms in A.

[0079] Experimental Example 2

[0080] In this experimental example, the light transmittance of the agricultural greenhouse films prepared in Examples 1-3 and Comparative Examples 1-3 was tested by using an ultraviolet spectrophotometer, with a wavelength of 500 nm, a black opaque baffle as a reference, and a baseline set. Three repetitions were set.

[0081] Figure 2The light transmittance results of the agricultural greenhouse films prepared by Examples 1-3 and Comparative Examples 1-3 of the present invention are shown in the figure. As shown in the figure, the light transmittance of the agricultural greenhouse films prepared by Examples 1-3 is between 72.7% and 75.2%, the light transmittance of the agricultural greenhouse film prepared by Comparative Example 1 is 55.7%, the light transmittance of the agricultural greenhouse film prepared by Comparative Example 2 is 48.6%, and the light transmittance of the agricultural greenhouse film prepared by Comparative Example 3 is 52.6%. The light transmittance of PBAT film is poor, generally between 40%-50%, while the light transmittance of PLA is better, generally above 80%. After blending PLA and PBAT, the optical properties of PBAT can be improved. However, due to the poor compatibility between PBAT and PLA, the improvement in optical properties after blending the two is not obvious. Embedding siloxane molecules into the PBAT polymer molecular chain can improve the interface properties between PLA and PBAT through polar groups. In the process of forming greenhouse film, it can increase the entanglement between molecular chains, hinder crystallization during the film formation process, and thus improve the light transmittance of the film.

[0082] Experimental Example 3

[0083] In this experimental example, the mechanical properties of the agricultural greenhouse films prepared in Examples 1-3 and Comparative Examples 1-3 were tested. According to GB / T 1040.1-2006 and GB / T 1040.3-2006, the tensile strength and elongation at break of the samples were measured according to the dumbbell type, and the stretching speed was set to 100 mm / min until the sample was broken.

[0084] Figure 3 The mechanical properties result diagram of the agricultural greenhouse films prepared by Examples 1-3 of the present invention and Comparative Examples 1-3 is shown in the figure. As shown in the figure, the agricultural greenhouse films prepared by Examples 1-3 are more outstanding in mechanical properties. In the present invention, the polymer molecular chain of PBAT is modified, and a siloxane structure (Si-O-Si) is introduced to provide a flexible chain end, which can significantly improve the toughness of the film. At the same time, it also solves the problem of poor compatibility between PLA and PBAT, thereby achieving a balance in various performances of the agricultural greenhouse film.

[0085] Experimental Example 4

[0086] In this experimental example, the thermal stability of the agricultural greenhouse films prepared in Example 1 and Comparative Examples 1-3 was tested by using a thermal synchronous analyzer to record the thermal weight loss;

[0087] Figure 4The thermal stability result diagram of the agricultural greenhouse film prepared by Example 1 of the present invention and Comparative Examples 1-3 is shown in the figure. As shown in the figure, the agricultural greenhouse film prepared by Example 1 of the present invention is significantly higher than that of Comparative Examples 1-3 in terms of thermal stability. Examples 1-3 of the present invention introduce Si-O-Si segment structures into the PBAT molecular chain. The main chain of PBAT is mainly composed of structures such as ester group (-COO-), alkyl group (CC) and aromatic group (benzene ring). The carbon-carbon bond is an important component of the polymer skeleton. The introduction of Si-O-Si structure may have a certain steric effect and intermolecular action. The bond energy of Si-O bond is higher and has stronger stability.

[0088] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

[0089] The present invention and its implementation methods are described above, which is not restrictive. The drawings are only one of the implementation methods of the present invention, and the actual application is not limited thereto. In short, if ordinary technicians in the field are inspired by it and design methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A high light transmittance agricultural greenhouse film, characterized in that: The agricultural greenhouse film comprises the following components in parts by weight: 50-70 parts of siloxane-modified PBAT, 30-50 parts of PLA, 2-5 parts of chain extender, and 0.5-1 part of antioxidant; The raw materials for preparing the siloxane-modified PBAT specifically include the following components in parts by weight: 20-23 parts of dichlorosiloxane, 17.5-26.5 parts of ethylene carbonate, 33-41.5 parts of p-dibenzoic acid, 16.5-25.5 parts of 1,4-butanediol, and 30-36.5 parts of adipic acid; The preparation method of the siloxane-modified PBAT specifically comprises the following steps: S1. Dissolve dichlorosiloxane in THE, add ethylene carbonate, mix well, add alkaline catalyst, stir at 50-80 rpm, introduce flowing argon after the reaction system is uniform, raise the temperature to 60-70°C, continue the reaction for 4-8 hours, cool, remove excess solvent by vacuum distillation, and obtain hydroxylated siloxane after vacuum drying; S2, placing the hydroxylated siloxane prepared in step S1 in a flask, adding p-dibenzoic acid, adipic acid and 1,4-butanediol, introducing flowing argon, adding tetrabutyl titanate, raising the temperature to 180-200° C., reacting for 8-12 hours, and cooling the reaction to room temperature to obtain a PBAT polymer monomer; S3. Add stannous octoate to the PBAT polymer monomer prepared in step S2, introduce flowing argon, raise the temperature to 230-250° C., conduct a pre-polycondensation reaction for 2-3 hours, then raise the temperature to 250-270° C., conduct a polycondensation reaction for 6-8 hours, cool the reaction to room temperature, wash with anhydrous methanol, and dry to obtain siloxane-modified PBAT.

2. The high light transmittance agricultural greenhouse film according to claim 1, characterized in that: The dichlorosiloxane includes at least one of 1,3-dichlorotetramethyldisiloxane, 1,3-bis(3-chloropropyl)tetramethyldisiloxane and 1,3-bis(chloromethyl)tetramethyldisiloxane.

3. The high light transmittance agricultural greenhouse film according to claim 2, characterized in that: The antioxidant includes at least one of antioxidant 1010 , antioxidant 1076 , antioxidant 1035 , and antioxidant 1330 .

4. The high light transmittance agricultural greenhouse film according to claim 3, characterized in that: The chain extender includes at least one of PDI, LDI and HDI.

5. The high light transmittance agricultural greenhouse film according to claim 4, characterized in that: In step S1, the alkaline catalyst includes at least one of pyridine, triethylamine, potassium hydroxide, potassium carbonate, and calcium carbonate.

6. The high light transmittance agricultural greenhouse film according to claim 5, characterized in that: In step S1, the mass concentration of the dichlorosiloxane in THE is 0.1-0.2 g / mL; the added mass of the alkaline catalyst is 5-10% of the mass of the dichlorosiloxane.

7. The high light transmittance agricultural greenhouse film according to claim 6, characterized in that: In step S2, the added mass of tetrabutyl titanate is 0.75%-0.9% of the mass of terephthalic acid.

8. The high light transmittance agricultural greenhouse film according to claim 7, characterized in that: In step S3, the added mass of stannous octoate is 0.6%-0.8% of the mass of terephthalic acid.

9. A method for preparing a high-transmittance agricultural greenhouse film according to any one of claims 1 to 8, characterized in that: The specific steps include: S4, vacuum drying the siloxane-modified PBAT and PLA, raising the temperature to 160-180° C. under vacuum conditions, stirring at a speed of 60-80 rpm, adding a chain extender, and continuing to raise the temperature to 180-190° C., blending for 20-30 minutes, to obtain a copolymer; S5. Place the copolymer prepared in step S4 in an internal mixer, add an antioxidant, increase the temperature to 130-150° C., perform melt blending at a speed of 60-80 rpm, mix for 40-60 minutes, cool to 40-50° C., place in a mold, and perform hot pressing at 180-200° C. After cooling, obtain an agricultural greenhouse film.

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