A biodegradable film with high water vapor barrier property and a preparation method thereof

Abstract

The application relates to the technical field of high polymer materials, and discloses a biodegradable film with high water vapor barrier property and a preparation method thereof. The biodegradable film comprises a biodegradable base resin and alkyl enone dimer; the amount of the alkyl enone dimer is 1-15 wt% of the biodegradable base resin; and the preparation process comprises the following steps: after raw materials containing the biodegradable base resin and the alkyl enone dimer are dried, the raw materials are mixed, melt-extruded, granulated and then formed into a film. In the application, a small amount of biodegradable additive AKD is added to react with the biodegradable base resin to generate a beta-keto ester bond, which has the water vapor barrier effect on one hand and the toughening effect on the other hand when appropriately added. Meanwhile, the existence of the chemical bond can better inhibit the migration of the AKD, the water vapor permeation coefficient of the base resin is reduced by more than 50%, and the film product has excellent thermal stability and mechanical properties, and is excellent in comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a biodegradable thin film with high water vapor barrier properties and its preparation method. Background Technology

[0002] In the field of difficult-to-recycle plastic products, such as agricultural mulch films, garbage bags, compost bags, and food packaging films, using biodegradable films instead of traditional non-degradable films can effectively solve the environmental pollution problems caused by the widespread use of the latter. However, on the other hand, these film products, such as agricultural mulch films and food packaging films, have high requirements for water vapor barrier properties, especially agricultural mulch films, which need to effectively block water vapor penetration to meet the requirements of water retention and moisture conservation. Currently, commercially available biodegradable polymers used in mulch films, such as poly(butylene adipate-co-terephthalate) (PBAT) and polylactic acid (PLA), have poor water vapor barrier properties, only a fraction of those of polyethylene. Therefore, their water retention and moisture conservation properties in agricultural mulch films are far inferior to those of traditional polyethylene mulch films.

[0003] Researchers have proposed various methods to improve the water vapor barrier properties of biodegradable resins and their thin film products, including nanocompositing, blending modification, multilayer composites, and surface coating, and combinations of these methods are also possible. Among these, melt blending a low-water-vapor barrier biodegradable resin with a high-water-vapor barrier biodegradable resin or other organic hydrophobic modifiers is the simplest and lowest-cost method for water vapor barrier modification. However, it often fails to achieve excellent barrier modification results, especially when the modifier content is low.

[0004] For example, CN104861210A discloses a hydrophobically stable starch-based fully biodegradable resin. The film prepared by blending 30 parts of titanate coupling agent (1%) modified starch with 70 parts of PBAT and small amounts of lubricants, antioxidants, and other additives has a water vapor permeability of 1120 g / (m²). 2 ·d), the water vapor barrier is 3 times that of PBAT; CN114573965A discloses a high-barrier biodegradable material made by blending poly(furan dicarboxylic acid-co-diethylene glycol glycol ester) (abbreviated as PBDF) with high-barrier biodegradable PGA resin and compatibilizers, plasticizers, opening agents, antioxidants and other additives. The WVP of PBDF / PGA blend containing 40% PGA is 56% lower than that of PBAT / PLA blend containing 30% PLA, and the water vapor barrier is 2.3 times that of the latter; however, the above blending method uses a large amount of waterproofing additives or blending materials, which has a significant impact on the mechanical properties of the substrate.

[0005] Some studies have shown that combining melt blending with nanocomposites can further improve water vapor barrier properties. CN107418163A discloses a fully biodegradable PBAT water vapor barrier film and its preparation method. The film is prepared by blending PBAT, a biodegradable water-blocking agent (a mixture of animal fats or waxes and plant fats or waxes), organically modified montmorillonite, organic additives, and inorganic additives, followed by extrusion blown film preparation. Under the combined effect of the water-blocking agent and nanocomposites, its water vapor permeability is improved from 1600 g / (m²) of PBAT. 2 ·d) decreased to 280-680g / (m 2 ·d), decreased by 57.5-82.5%, which is equivalent to an increase in water vapor barrier properties of 2.4-5.7 times that of PBAT.

[0006] CN114656766A discloses a high-barrier green packaging material and its preparation method, which is prepared by melt blending silane-coupled modified reactive bentonite (RBC) with biodegradable polyesters A and B. The composite material, prepared from 25-30 wt% PBAT, 70-75 wt% PLA or PGA, and 4-6 wt% RBC, has a water vapor permeability coefficient of 0.7-0.95 × 10⁻⁶. -11 g·m·m -2 ·s -1 ·Pa -1 If the type and amount of coupling agent are not appropriate during RBC preparation, its water vapor permeability coefficient will increase to 5.3-7.2×10⁻⁶. -11 g·m·m -2 ·s -1 ·Pa -1 The water vapor permeability coefficient of materials prepared by using other compatibilizers instead of RBC is 5.9-11.6×10⁻⁶. -11 g·m·m -2 ·s -1 ·Pa -1 )quite.

[0007] It is evident that the existing melt blending method has a limited effect on improving water vapor barrier properties, or the amount of water-resistant agent used is very large, making it difficult to improve water vapor barrier properties while ensuring the mechanical properties and biodegradability of the matrix material itself. It is difficult to achieve all these properties simultaneously. Summary of the Invention

[0008] This invention addresses the problem that existing biodegradable materials have insufficient water vapor barrier properties, making it difficult to balance mechanical properties and biodegradability. It provides a biodegradable film with high water vapor barrier properties, which can achieve a significant improvement in water vapor barrier properties with only a small amount of alkyl ketene dimer, while maintaining good physical properties and excellent degradability of the matrix.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A biodegradable film with high water vapor barrier properties, the biodegradable film comprising a biodegradable matrix resin and an alkyl ketene dimer; the amount of the alkyl ketene dimer is 1-15 wt% of the biodegradable matrix resin;

[0011] The biodegradable film preparation process includes: drying raw materials containing biodegradable matrix resin and alkyl ketene dimer, mixing and melting them, extruding them, granulating them, and forming a film.

[0012] The alkyl ketene dimer (AKD) has the following structure:

[0013]

[0014] R and R' are long-chain saturated alkyl chains, mainly C14-C18 fatty acid chains. AKD is a commercially available fatty acid derivative, equivalent to a fatty acid dimer, in the form of waxy solid particles. It is hydrophobic, biodegradable, and reactive with hydroxyl groups, and is inexpensive.

[0015] In this invention, by adding a small amount of AKD and blending it with a biodegradable matrix resin, the water vapor barrier properties of the matrix are significantly improved. During high-temperature melt blending, the cyclic ester alkenyl groups in AKD react with the terminal hydroxyl groups in the matrix resin (i.e., reactive blending) to form β-keto ester bonds, thereby bonding AKD to the chain ends of the matrix resin. This improves the compatibility between the matrix resin and the unbonded AKD, resulting in highly efficient water vapor barrier properties. Furthermore, with appropriate addition, it also provides a toughening effect. Simultaneously, the presence of chemical bonding effectively inhibits AKD migration, thus stably maintaining a high level of water vapor barrier modification. Without melt blending, such as conventional solvent mixing, this reaction is difficult to occur effectively, making it difficult to achieve the aforementioned effects.

[0016] The amount of the alkyl ketene dimer is 2-10 wt% of the biodegradable matrix resin. Excessive addition of the additive can lead to uneven dispersion within the matrix, causing agglomeration, which is detrimental to subsequent film preparation, resulting in micropores or microcracks, and potentially reducing barrier properties as well as mechanical properties. More preferably, the amount of the alkyl ketene dimer is 2-5 wt% of the biodegradable matrix resin.

[0017] The biodegradable film further includes organically modified layered nanofillers, the amount of which is 1-13 wt% of the biodegradable matrix resin. Nanomaterials are sheet-like materials with a high aspect ratio, are impermeable to air, and when blended with polymers and dispersed in the matrix, they can extend the diffusion path for gas permeation, thereby improving the gas barrier properties of the polymer.

[0018] The organically modified layered nanofiller is one of organically modified montmorillonite, graphene oxide, and mica;

[0019] The biodegradable film also includes at least one of antioxidants, heat stabilizers, and light stabilizers, the total amount of which is 1-5 wt% of the biodegradable matrix resin.

[0020] The antioxidant is composed of one or more of 168, 425, 1010, BTH, and DLTP mixed in any proportion; the heat stabilizer is composed of one or more of Sanduvor VSU, UV-328, UV-329, and Hostavin B-CAP mixed in any proportion; the light stabilizer is composed of one or more of Chimassorb 944, Tinuvin 783, Sanduvor PR 31, Hostavin N30, and GW-540 mixed in any proportion.

[0021] Preferably, the biodegradable film comprises a biodegradable matrix resin, an alkyl ketene dimer, an organically modified layered nanofiller, and other additives; the amounts of the alkyl ketene dimer, the organically modified layered nanofiller, and the other additives are 1-15 wt%, 1-13 wt%, and 1-5 wt% of the biodegradable matrix resin, respectively; the other additives are one or more of antioxidants, heat stabilizers, and light stabilizers.

[0022] In the prior art, the water vapor permeability coefficient of the matrix can usually be reduced by 40-60% by mixing additives. However, the water vapor permeability coefficient of the biodegradable film described in this invention is reduced by more than 50% compared to the corresponding biodegradable matrix resin, preferably more than 65%, and more preferably more than 80%.

[0023] The biodegradable matrix resin includes one or more of polylactic acid (PLA), polycaprolactone (PCL), polyglycolic acid (PGA), poly(butylene succinate) (PBS), poly(butylene adipate) (PBA), poly(ethylene succinate) (PES), polyhydroxyalkanoates (PHAs), poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene adipate-co-terephthalate) (PBST), poly(butylene adipate-co-furandicarboxylate) (PBAF), poly(butylene adipate-co-furandicarboxylate) (PBSF), poly(butylene carbonate-co-terephthalate) (PBCT), poly(butylene carbonate-co-furandicarboxylate) (PBCF), poly(butylene glycolate-co-terephthalate) (PBGT), and poly(butylene glycolate-co-furandicarboxylate) (PBGF), or copolymers thereof.

[0024] Preferably, the biodegradable matrix resin is one or a mixture of PBAT, PBST, and PLA.

[0025] The present invention also provides a method for preparing the biodegradable polymer film with high water vapor barrier properties, comprising the steps of: drying raw materials containing biodegradable matrix resin and alkyl ketene dimer, mixing and melt-extruding, granulating and forming a film to obtain the biodegradable film.

[0026] The melt extrusion temperature is 120-220℃, and the time is 1-10 minutes. Preferably, the melt extrusion temperature is 150-220℃, and the processing time is 2-5 minutes. Excessive processing time will lead to degradation of the matrix resin and affect the overall performance.

[0027] The film-forming method includes blow molding, extrusion casting, or hot pressing. The film-forming temperature is 120-220℃, preferably 150-200℃.

[0028] Preferably, the film-forming method is blow molding, which is superior to hot pressing for producing products with less gas barrier.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) In this invention, the introduction of a small amount of AKD into the biodegradable matrix resin can significantly reduce the water vapor permeability coefficient of the matrix resin and significantly improve the water vapor barrier properties of the prepared film. At the same time, since AKD is a biodegradable material, it is inexpensive and readily available, and has no effect on the biodegradability of the matrix resin.

[0031] (2) In this invention, AKD is chemically bonded to the matrix resin through melt blending. Under certain conditions, it can ensure the mechanical properties and good thermal properties of the matrix, and has a certain toughening effect. AKD is not easy to migrate, and the water vapor barrier properties of the material are long-lasting and stable.

[0032] (3) The present invention uses existing plastic processing equipment and methods to prepare the composition and its film products. The preparation method is simple, efficient, environmentally friendly, low in cost, and easy to industrialize. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0034] All raw materials used in the following specific embodiments were purchased commercially: poly(butylene adipate-co-terephthalate), abbreviated as PBAT, is a product of BASF, brand name Ecoflex F Blend C1200; poly(butylene succinate-co-terephthalate), abbreviated as PBST, is a product of Yizheng Chemical Fiber Co., Ltd., brand name TS159; poly(1,2-propylene carbonate), abbreviated as PPC, is a product of Zhongke Jinlong Co., Ltd., brand name 8001; polylactic acid, abbreviated as PLA, is a product of Natureworks, brand name 3251D. AKD was purchased from Shanghai Yuanye Biotechnology Co., Ltd., and the AKD emulsion used was purchased from Qingyang Plastics. The organically modified montmorillonite was 1.34TCN from NANOCOR Corporation, USA.

[0035] In the following specific embodiments, the water vapor permeability coefficient is determined using the permeation cup method, with test conditions of 38°C and 90% RH. The water vapor permeability coefficient (P, unit: 10⁻⁶) is used. -11 g·m·m -2 ·s -1 ·Pa -1 Compare the water vapor barrier properties of different materials. The lower the water vapor permeability coefficient, the better the water vapor barrier properties. The water vapor permeability coefficient is a material property, while the water vapor transmission rate (WVTR, unit: g·m³) is a different property. -2 ·day -1 The water vapor transmission rate (WVTR) is not a property of the material itself, but rather a property of the finished product, and is related to the product's thickness and the test pressure differential. Since the thickness of thin film products often varies, the water vapor transmission rate cannot be directly used to represent the material's water vapor barrier properties. However, the water vapor transmission rate can be converted to the water vapor transmission rate under standard thickness (10 micrometers) and standard test conditions (90% relative humidity), denoted as WVTR.10 Because the thickness and pressure differential are specified (depending on the relative humidity), WVTR 10 It can also be used to indicate the degree of water vapor barrier properties of a material.

[0036] Furthermore, in the following specific embodiments, P represents the water vapor permeability coefficient of the composition sample, P0 represents the water vapor permeability coefficient of the matrix resin under the same processing conditions, (P0-P) / P0 represents the degree of decrease in the water vapor permeability coefficient of the composition relative to the matrix resin, and P0 / P represents the multiple of the water vapor barrier property of the composition relative to the matrix resin. The larger (P0-P) / P0 and P0 / P are, the better the water vapor barrier modification effect is.

[0037] Example 1: PBAT + 1% AKD

[0038] Step 1: Place 0.6g AKD and 60g PBAT in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0039] Step 2: The mixture is added to a preheated internal mixer and melt-blended at 50 rpm and 150°C for 5 min. The resulting composition sample is named PBAT-AKD1.

[0040] Step 3: The sample was melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes. Afterwards, it was cooled to form a film on a steel plate circulated with cold water. Its water vapor permeability coefficient is shown in Table 1.

[0041] Example 2: PBAT + 2% AKD

[0042] Step 1: Place 1.2g AKD and 60g PBAT in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0043] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 150°C for 5 min to obtain a composition sample, named PBAT-AKD2.

[0044] Step 3: The sample is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0045] Its water vapor permeability coefficient is shown in Table 1.

[0046] Example 3: PBAT + 5% AKD

[0047] Step 1: Place 3g AKD and 60g PBAT in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0048] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 150°C for 5 min to obtain a composition sample, named PBAT-AKD5;

[0049] Step 3: The sample is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0050] Its water vapor permeability coefficient is shown in Table 1.

[0051] Example 4: PBAT + 10% AKD

[0052] Step 1: Place 6g AKD and 60g PBAT in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0053] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 150°C for 5 min to obtain a composition sample, named PBAT-AKD10.

[0054] Step 3: The sample is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0055] Its water vapor permeability coefficient is shown in Table 1.

[0056] Example 5: PBAT + 15% AKD

[0057] Step 1: Place 9g AKD and 60g PBAT in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0058] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 150°C for 5 min to obtain a composition sample, named PBAT-AKD15.

[0059] Step 3: The sample is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0060] Its water vapor permeability coefficient is shown in Table 1.

[0061] Example 6: PBST + 2% AKD

[0062] Step 1: Place 1.2g AKD and 60g PBST in a vacuum drying oven at 40℃ and dry for 24h, then mix them evenly at room temperature;

[0063] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 150°C for 5 min to obtain a composition sample, named PBST-AKD2;

[0064] Step 3: The sample is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0065] Its water vapor permeability coefficient is shown in Table 1.

[0066] Example 7: PPC + 2% AKD

[0067] Step 1: Vacuum dry 1.2g AKD and 60g PPC at 40℃ and 20℃ respectively for 24h, then mix them evenly at room temperature;

[0068] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 140°C for 5 min to obtain a composition sample, named PPC-AKD2.

[0069] Step 3: The sample is melted at 140°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0070] Its water vapor permeability coefficient is shown in Table 1.

[0071] Example 8: PBAT / PLA + 2% AKD

[0072] Step 1: Place 1.2g AKD, 48g PBAT and 12g PLA in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0073] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 180°C for 5 min to obtain a composition sample, named PBAT / PLA-AKD2.

[0074] Step 3: The sample is melted at 180°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0075] Its water vapor permeability coefficient is shown in Table 1.

[0076] Example 9: PBAT + 2% AKD + ​​5% OMMT

[0077] Step 1: Place 1.2g AKD, 3.0g organic modified montmorillonite (OMMT) and 60g PBAT in a vacuum drying oven at 40℃ and dry for 24h, then mix them evenly at room temperature;

[0078] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 160°C for 5 min to obtain a composition sample, named PBAT-AKD2-OMMT5.

[0079] Step 3: The sample is melted at 160°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes, and then cooled to form a film on a steel plate with cold water.

[0080] Its water vapor permeability coefficient is shown in Table 1.

[0081] Example 10: PBAT + 2% AKD + ​​5% OMMT extrusion blown film

[0082] Step 1: Place 24g AKD, 60g organic modified montmorillonite (OMMT) and 1200g PBAT in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. During the mixing process, add 3.6g antioxidant 1010.

[0083] Step 2: Add the mixture to a torque rheometer with a twin-screw, set the temperature to 150-170-160℃ and the rotation speed to 50 rpm, and extrude and pelletize to obtain a composition sample, named PBAT-AKD2-OMMT5*.

[0084] Step 3: The granules are plasticized and extruded through a single screw into a small blown film extrusion unit for blow molding to obtain film products.

[0085] Its water vapor permeability coefficient is shown in Table 1.

[0086] Comparative Example 1: PBAT

[0087] Step 1: Place 60g of PBAT in a vacuum drying oven at 40℃ and dry for 24 hours;

[0088] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 150°C for 5 minutes.

[0089] Step 3: The sample obtained in Step 2 is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes. Afterwards, it is cooled to form a film on a steel plate circulated with cold water. Its water vapor permeability coefficient is shown in Table 1.

[0090] Comparative Example 2: PBAT + 3wt% antioxidant

[0091] Step 1: Place 1200g of PBAT in a vacuum drying oven at 40℃ and dry for 24 hours. Add 3.6g of antioxidant 1010 and mix well at room temperature.

[0092] Step 2: Add the mixture to a torque rheometer with a twin-screw extruder, set the temperature to 150-170-160℃ and the speed to 50 rpm, and extrude and pelletize it, denoted as PBAT*.

[0093] Step 3: PBAT* granules are plasticized and extruded into a small blown film unit via a single screw extruder for blow molding to obtain film products.

[0094] Its water vapor permeability coefficient is shown in Table 1.

[0095] Comparative Example 3: PBST

[0096] Step 1: Place 60g of PBST in a vacuum drying oven at 40℃ and dry for 24 hours;

[0097] Step 2: Add the dried PBST to a preheated internal mixer and mix at 50 rpm and 150°C for 5 minutes.

[0098] Step 2: The PBST obtained in Step 2 is melted at 150°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes. After that, it is cooled to form a film on a steel plate with cold water flowing through it. Its water vapor permeability coefficient is shown in Table 1.

[0099] Comparative Example 4: PPC

[0100] Step 1: Place 60g of PPC in a vacuum drying oven at 20℃ and dry for 24 hours;

[0101] Step 2: Add the dried PPC to a preheated internal mixer and mix at 50 rpm and 140°C for 5 minutes.

[0102] Step 2: The PPC obtained in Step 2 is melted at 140℃ without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10MPa for 5 minutes. After that, it is cooled to form a film on a steel plate with cold water flowing through it. Its water vapor permeability coefficient is shown in Table 1.

[0103] Comparative Example 5: PBAT / PLA

[0104] Step 1: Place 48g PBAT and 12g PLA in a vacuum drying oven at 40℃ and dry for 24 hours, then mix them evenly at room temperature;

[0105] Step 2: Add the mixture to a preheated internal mixer and melt-blend at 50 rpm and 180°C for 5 min to obtain a composition sample, named PBAT / PLA;

[0106] Step 3: The sample was melted at 180°C without pressure for 5 minutes, then placed between the plates of a hot press and melted under a pressure of 10 MPa for 5 minutes. Afterwards, it was cooled to form a film on a steel plate circulated with cold water. Its water vapor permeability coefficient is shown in Table 1.

[0107] Comparative Example 6: PBAT coated with AKD emulsion

[0108] The PBAT film prepared in the comparative example was coated with AKD emulsion using a coating machine. After natural drying at room temperature, it was further vacuum dried at 65°C until constant weight. The mass of the AKD coating was 2 wt% of the PBAT mass.

[0109] Table 1. Composition and water vapor permeation test results of the examples and comparative examples

[0110]

[0111]

[0112] P: Water vapor permeability coefficient measured from the composite film sample, unit: 10. -11 g·m·m -2 ·s -1 ·Pa -1 ;

[0113] P0: Water vapor permeability coefficient of the matrix resin film sample, measured in units of 10. -11 g·m·m -2 ·s -1 ·Pa -1 ;

[0114] (P0-P) / P0*100%: The percentage decrease in water vapor permeability coefficient of the composition compared to the matrix resin;

[0115] WVTR 10 Water vapor permeability of a 10 μm thick film at 38℃ and 90% relative humidity, calculated based on the water vapor permeability coefficient. Unit: g·m -2 ·day -1 .

[0116] *: Example 10: Compared to Comparative Example 1 (P0 = 6 * 10) -11 g·m·m -2 ·s -1 ·Pa -1 P0 / P = 10; compared to Comparative Example 2 (P0 = 3.7 * 10), -11g·m·m -2 ·s -1 ·Pa -1 ), P0 / P = 6.2.

[0117] The oxygen permeability, thermal stability, and mechanical properties of Examples 2-4 and Comparative Example 1 were tested. The oxygen test standard was GB / T 1038-2000, and the test conditions were 0.1 MPa and 23℃. Thermogravimetric analysis was performed using a thermogravimetric analyzer. The tensile properties of the samples at room temperature were determined using a universal testing machine according to GB / T 16421-1996. The results are shown in Table 2.

[0118] Table 2. Test results of physical and mechanical properties of Examples 2-4 and Comparative Example 1

[0119] Serial Number <![CDATA[P O2 (sweep)]]> <![CDATA[T d,5 (℃)]]> <![CDATA[σ b (MPa)]]> <![CDATA[ε b (%)]]> Example 2 0.72 336 18.8 431 Example 3 0.69 332 18.1 421 Example 4 0.75 327 17.8 416 Comparative Example 1 0.73 343 20.4 423

[0120] P O2 : Oxygen permeability coefficient of the membrane; T d,5 : Temperature of 5% weight loss of the sample; σ b : Tensile strength of the sample; ε b : Elongation at break of the sample.

[0121] Results Analysis

[0122] Table 1 shows that the introduction of AKD has a significant impact on the water vapor permeability coefficient of the PBAT film. In Example 2, when the AKD content was 1 and 2 wt%, the water vapor permeability coefficient increased from 6.0 × 10⁻⁶ for PBAT. -11 g·m·m -2 ·s -1 ·Pa -1 Significantly decreased to 2.8 and 1.8 × 10⁻⁶ -11 g·m·m -2 ·s -1 ·Pa -1 Compared to PBAT, these figures represent a decrease of 53% and 70% respectively;

[0123] When the AKD content is 2-10 wt%, the water vapor permeability coefficient of the PBAT-AKD blend membrane remains basically unchanged. Moreover, while significantly improving the water vapor barrier properties, it can ensure that the thermal and mechanical properties of the biodegradable matrix resin remain basically unchanged (as shown in Table 1). The applicant has made some attempts, and when the AKD content is less than 1 wt%, the water vapor barrier modification effect weakens. If the content is too high, it will cause AKD to be difficult to disperse evenly in the matrix resin, resulting in agglomeration, causing microcracks or pores in the film, which will worsen the material barrier properties and lead to a decrease in the initial decomposition temperature of the composition and a decrease in mechanical properties. For example, in Example 5, the AKD content is 15 wt%, but the water vapor permeability coefficient only decreases by 25%. Although there is some improvement, the effect is not very ideal.

[0124] The water vapor permeability coefficient was converted to the water vapor transmission rate (WVTR) of a 10-micron-thick film. 10 The results are also listed in Table 1. It can be seen that introducing 1-10 wt% AKD into PBAT makes the PBAT-AKD1 composite film meet the requirements of Class B products (800-1600 g·m³) of the national standard GB / T35795-2017 "Fully Biodegradable Agricultural Ground Cover Film". -2 ·d -1 ).

[0125] Examples 6 and 7 demonstrate that the water vapor barrier function of AKD is applicable to other biodegradable matrix resins, and the resulting PBST-AKD2 and PPC-AKD2 can meet the requirements of Class A products.

[0126] Example 8 illustrates that the water vapor barrier function of AKD is also applicable to blends of biodegradable polymers, and the resulting PBAT / PLA-AKD2 meets the requirements of Class B products.

[0127] Example 9 illustrates that combining PBAT / AKD blends with PBAT / OMMT nanocomposites can further improve water vapor barrier properties, meeting the requirements of Class A products (<800 g·m³). -2 ·d -1 ).

[0128] Examples 1-9 all used the commonly used laboratory hot-pressing method to prepare film samples, while Example 10 used the extrusion blown film method. Comparing Examples 9 and 10, it is evident that, under the same conditions, extrusion blown film forming is beneficial for further improving water vapor barrier properties. The water vapor permeability coefficient is one-tenth that of the hot-pressed PBAT film and approximately one-sixth that of the blown PBAT film. The blown film process involves a certain stretching effect, which has a certain stretching and orientation effect on both the matrix resin itself and the nanolayered filler, thus contributing to improved water vapor barrier properties.

[0129] Compared to Example 2, Comparative Example 6 directly coated the PBAT film surface with AKD emulsion (AKD emulsion is commonly used as a neutral sizing agent for paper, coated on the paper surface to improve its hydrophobicity). The resulting composite film had the same AKD content as Example 2 and also exhibited significantly improved water vapor barrier properties. However, due to the low drying temperature, it was difficult for AKD and PBAT to form chemical bonds, resulting in weak bonding between AKD and the PBAT film surface. The AKD layer on the surface was easily detached, and after gentle wiping with toilet paper, its water vapor barrier properties decreased significantly, only slightly higher than those of the PBAT film. In contrast, the water vapor barrier properties of the film in Example 2 only decreased slightly after gentle wiping with toilet paper. This demonstrates that reactive blending in the molten state is beneficial for the chemical bonding of AKD and PBAT, which is beneficial for both improving and maintaining high water vapor barrier properties.

Claims

1. A biodegradable film with high water vapor barrier properties, characterized in that, The biodegradable film comprises a biodegradable matrix resin, an alkyl ketene dimer, and an organically modified layered nanofiller; the amounts of the alkyl ketene dimer and the organically modified layered nanofiller are 2-5 wt% and 1-5 wt% of the biodegradable matrix resin, respectively; the preparation process of the biodegradable film includes: drying the raw materials containing the biodegradable matrix resin, the alkyl ketene dimer, and the organically modified layered nanofiller, mixing and melt-extruding, granulating, and then forming a film to obtain the film; The organically modified layered nanofiller is organically modified montmorillonite of grade 1.34TCN from NANOCOR Corporation, USA.

2. The biodegradable film with high water vapor barrier properties according to claim 1, characterized in that, The biodegradable film also includes at least one of antioxidants, heat stabilizers, and light stabilizers, the total amount of which is 1-5 wt% of the biodegradable matrix resin.

3. The biodegradable film with high water vapor barrier properties according to claim 2, characterized in that, The antioxidant is composed of one or more of 168, 425, 1010, BTH, and DLTP mixed in any proportion; And / or, the heat stabilizer is composed of one or more of Sanduvor VSU, UV-328, UV-329, and Hostavin B-CAP mixed in any proportion; And / or, the light stabilizer is composed of one or more of Chimassorb 944, Tinuvin 783, Sanduvor PR 31, Hostavin N30, and GW-540 mixed in any proportion.

4. The biodegradable film with high water vapor barrier properties according to claim 1, characterized in that, The biodegradable matrix resin includes one or more of polylactic acid, polycaprolactone, polyglycolic acid, poly(butylene succinate), poly(butylene adipate), poly(ethylene succinate), polyhydroxyalkanoate, poly(butylene adipate-co-terephthalate), poly(butylene adipate-co-terephthalate), poly(butylene adipate-co-furandicarboxylate), poly(butylene adipate-co-furandicarboxylate), poly(butylene carbonate-co-terephthalate), poly(butylene carbonate-co-furandicarboxylate), poly(butylene glycolate-co-terephthalate), and poly(butylene glycolate-co-furandicarboxylate), or copolymers thereof.

5. The biodegradable film with high water vapor barrier properties according to claim 1, characterized in that, The water vapor permeability coefficient of the biodegradable film is reduced by more than 50% compared to the corresponding biodegradable matrix resin.

6. The method for preparing a biodegradable polymer film with high water vapor barrier properties according to any one of claims 1-5, characterized in that, The process includes the following steps: after drying, raw materials containing a biodegradable matrix resin and an alkyl ketene dimer are mixed, melt-extruded, granulated, and then formed into a film to obtain the biodegradable film.

7. The method for preparing a biodegradable thin film with high water vapor barrier properties according to claim 6, characterized in that, The melt extrusion temperature is 120-220℃, and the time is 1-10 min; And / or, the film-forming method includes blow molding, extrusion casting, or hot pressing.

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