A biodegradable high water vapor barrier film and a method for preparing the same

Abstract

This invention discloses a biodegradable high water vapor barrier film and its preparation method. The film comprises 100 wt% biodegradable matrix resin and 1-20 wt% saturated fatty acid or its monoglyceride by mass ratio. The saturated fatty acid or its monoglyceride has a melting point above 50°C and a hydrophobic parameter calculated to be 5-15. The high water vapor barrier film includes micro-nano-sized plate-like crystals formed by saturated fatty acid or its monoglyceride on its interior and surface. This invention uses high-melting-point saturated fatty acid or its monoglyceride to directly act on the biodegradable matrix resin, which can rapidly crystallize on the surface and inside the resin film to form micro-nano-sized plate-like crystals. This unique structure and morphology, combined with the hydrophobicity of the saturated fatty acid or its monoglyceride itself matching that of the matrix resin, reduces the adsorption, dissolution, and diffusion of water vapor on the surface and inside. Under the combined effect of these two factors, the water vapor barrier properties of the film can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a biodegradable high water vapor barrier film 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 to replace 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, the water vapor barrier properties of commercially available and applied biodegradable polymers such as poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate-co-terephthalate) (PBST), and polylactic acid (PLA) are all poor, 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] For these bulk biodegradable resins (taking PBAT as an example) and their film products, researchers have proposed a variety of methods to improve water vapor barrier properties, including multilayer composites, nanocomposites, surface coatings, blending modifications, etc., and multiple methods can also be used in combination.

[0004] Multilayer films prepared by co-extruding with biodegradable polymers, which have better water vapor barrier properties, can improve their water vapor barrier properties. However, practical barrier layer materials with significantly higher water vapor barrier properties than PBAT and excellent processing stability and toughness are still lacking. When using polypropylene carbonate (PPC) and PBAT for multilayer composites, the advantage is not significant because the water vapor barrier properties of PPC and PHA are only 2-5 times that of PBAT, resulting in limited modification effects. Nanocompositing is the most common method for gas barrier modification, but the common melt intercalation method is difficult to achieve sufficient exfoliation of layered nanofillers, and the modification effect is often limited, generally only improving by 1-5 times. Nanocompositing in a hydrophilic state can improve oxygen barrier properties by two orders of magnitude, but the improvement in water vapor barrier properties is still very limited. Layer-by-layer self-assembly shows better oxygen barrier modification effects, but the water vapor barrier modification effect is still unsatisfactory.

[0005] Melt blending is the simplest and lowest-cost method for polymer modification and can also be used for water vapor barrier modification of biodegradable polymers. For example, (1) Chinese invention patent CN104830035A discloses a "barrier-resistant biodegradable composition" comprising 90-99.9 wt% biodegradable polyester and 0.1-10 wt% waterproofing agent, with a water vapor permeability ≤800 g.m. -2 .d-1 The waterproofing agent is a high-boiling-point hydrocarbon with a boiling point ≥160℃ and an HLB value ≤10, petrolatum, fatty acid esters, aromatic esters, silicone oil, higher alcohols and their esters, and polyisobutylene, preferably a waterproofing agent with a boiling point ≥200℃ and an HLB value of 0.5-8. Most of the waterproofing agents used are non-biodegradable. When 4 wt% of biodegradable trioleate and 8 wt% petrolatum are blended with PBAT, the resulting blend membrane has a water vapor permeability of 1140 g / m. -2 .d -1 Its moisture barrier properties are 1.3 times that of PBAT substrate.

[0006] (2) Chinese invention patent CN104861210A discloses "a hydrophobically stable starch-based fully biodegradable resin", which is prepared by melt blending 20-50 parts of modified starch modified with stearic acid, titanate coupling agent, aluminate coupling agent, low melting point paraffin, mineral oil, and alkenyl succinic acid with 50-80 parts of fully biodegradable polyester. Compared with films made with unmodified starch and fully biodegradable polyester, the weight loss rate after immersion in water is reduced and the water resistance is enhanced. Some embodiments show that the water vapor permeability is increased from 3230 g·m -2 ·d -1 Decreased to 1120 g·m -2 ·d -1 .

[0007] (3) CN114573965A discloses "a high-barrier biodegradable material and its preparation method," which is prepared by melt blending poly(butylene furanyl dicarboxylate-co-diethylene glycol) (PBDF) and polyglycolic acid (PGA) in the presence of compatibilizers, plasticizers, opening agents, antioxidants, and other additives. Compared with PBDF / PGA blends prepared without compatibilizers, it has better compatibility, higher mechanical properties, and improved oxygen and water vapor barrier properties (up to 1 time). It can be seen that the improvement in water vapor barrier properties of these biodegradable modified materials prepared by melt blending is relatively limited and does not reach an order-of-magnitude improvement.

[0008] Combining melt blending with nanocomposite materials can further improve water vapor barrier properties. (1) CN107418163A discloses "a water vapor barrier PBAT fully biodegradable film and its preparation method", which is prepared by blending PBAT, a biodegradable water barrier agent (a mixture of animal fats or waxes and plant fats or waxes), organic modified montmorillonite, organic additives, and inorganic additives, and extruding blown film. Under the combined action of water barrier agent, additives and nanocomposite materials, its water vapor permeability is improved from 1600 g / (m) of PBAT. 2 ·d) decreased to 280-680g.m -2 ·d -1(2) 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 polyester A and B. The composite material prepared by 25-30 wt% PBAT, 70-75 wt% PLA or PGA and 4-6 wt% RBC has a water vapor permeability coefficient of 61.3-83.2 g·mm·m. -2 ·d -1 ·atm -1 Its water vapor barrier properties are approximately 5-7 times that of PBAT.

[0009] Chinese invention patent CN104387605A discloses "a biodegradable plastic agricultural film with a surface covering film," characterized by comprising a biodegradable plastic base film and an oil film layer covering its outer surface. The total thickness of the agricultural film is 2-15 μm, and the thickness of the oil film layer is 0.01-2.5 μm. The material forming the oil film layer is selected from high-boiling-point hydrocarbons, petrolatum, fatty acid esters, aromatic esters, silicone oil, stearates or their methyl esters and glycerides. The methods for forming the oil film layer include surface coating and blending-blown film-diffusion, the latter relying on the slow diffusion (1 month) of the oil film layer material to the surface, precipitating to form a film. Compared with agricultural films without an oil film layer, agricultural films with an oil film layer have a moisture retention rate increased from 40.1% to 69.1-73.5%, but the water vapor permeation results are not disclosed.

[0010] It is evident that existing water vapor barrier modification technologies for biodegradable polymers still suffer from bottlenecks such as cumbersome processes, high costs, and limited modification effects. Developing biodegradable high-barrier films that can significantly improve water vapor barrier properties (such as by an order of magnitude or more) and simple, low-cost preparation techniques with excellent modification effects remain urgent technical problems to be solved. Summary of the Invention

[0011] This invention addresses the problems of cumbersome and complex water vapor barrier modification techniques for biodegradable compounds by providing a high water vapor barrier film for biodegradable compounds. By forming micro-nano-sized sheet-like crystals inside and on the surface of the film with saturated fatty acids or their glycerol monoesters, the film achieves high hydrophobicity on the surface and high water resistance inside, thus significantly improving the water vapor barrier properties of the film.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A biodegradable high water vapor barrier film comprises, by mass percentage, 100wt% biodegradable matrix resin and 1-20wt% saturated fatty acid or its monoglyceride; wherein the saturated fatty acid or its monoglyceride has a melting point above 50°C and a calculated reference value for the hydrophobic parameter (XlogP, or hydrophobic parameter for short) of 5-15.

[0014] The high water vapor barrier film includes micro- and nano-sized sheet-like crystals formed from saturated fatty acids or their glycerol monoesters inside and on the surface. The sheet-like crystals have a thickness of 100-600 nm, a lateral dimension of 1-10 μm, and an average aspect ratio of 5-15.

[0015] The inventors unexpectedly discovered that by directly applying saturated fatty acids or their monoglycerides with high melting points to a biodegradable matrix resin, micro- and nano-sized plate-like crystals can be rapidly crystallized on and inside the resin film. This unique structure and morphology, combined with the hydrophobicity of the saturated fatty acids or their monoglycerides matching that of the matrix resin, can simultaneously reduce the adsorption, dissolution, and diffusion of water vapor on the surface and inside. Under the combined effect of both, the water vapor barrier properties of the film can be significantly improved.

[0016] In this invention, saturated fatty acids or their glycerol monoesters are distributed simultaneously in the form of micro- and nano-scale plate-like crystals inside and on the surface of the film. Inside the film, water vapor has difficulty passing through the plate-like crystals and has to bypass the plate-like crystals to diffuse in the matrix resin, making the diffusion path more tortuous and longer, which indirectly reduces the diffusion coefficient. This can be called the "internal water-blocking effect", which is similar to the effect of layered nanocomposites.

[0017] In this invention, saturated fatty acids or their monoglycerides, due to their strong hydrophobicity, rapidly diffuse to the film surface to form micro- and nano-scale plate-like crystals. The accumulation of these plate-like crystals forms a rough hydrophobic layer, changing the surface from weakly hydrophilic to strongly hydrophobic. This inhibits the adsorption and dissolution of water vapor, reduces the solubility of water vapor, and consequently lowers the water vapor permeability coefficient, thus improving water vapor barrier properties. This effect can be termed the "surface hydrophobic effect."

[0018] Preferably, the saturated fatty acid or its monoglyceride has a melting point of 65°C or higher, more preferably 75°C or higher;

[0019] A sufficiently high melting point ensures that the saturated fatty acids or their monoglycerides in the film do not melt at the operating temperature, maintaining their crystalline structure and thus achieving and maintaining high water vapor barrier properties. If a liquid or melting point <50°C is used... ℃Saturated fatty acids or their monoglycerides or other hydrophobic substances make it difficult to form micro- or nano-scale sheet-like crystals inside and on the surface of the film. Even if micro- or nano-scale sheet-like crystals are formed, they will melt and be destroyed at the operating temperature (such as when the temperature of agricultural film in summer reaches above 50°C), thus failing to significantly improve the water vapor barrier properties.

[0020] In this invention, the hydrophobicity of saturated fatty acids or their monoglycerides should be significantly higher than that of the matrix resin, but not excessively higher. A suitable hydrophobic parameter is 5-15. If the hydrophobic parameter is too high, the hydrophobicity is too strong, such as with glyceryl tristearate, which can lead to significant phase separation between the fatty acid and the matrix resin, resulting in defects such as cracks between the dispersed and continuous phases. Gases can easily pass through these defects, leading to a decrease in barrier properties and a poor water vapor barrier modification effect.

[0021] Preferably, the hydrophobicity parameter of the saturated fatty acid or its monoglyceride is 7-13.

[0022] The surface of the high water vapor barrier film is formed by the accumulation of plate-like crystals to create a rough hydrophobic layer, which changes the surface from weakly hydrophilic to hydrophobic. The water contact angle is above 110°. The larger the water contact angle, the stronger the hydrophobicity and the better the water vapor barrier performance of the film. Preferably, the micro-nano scale plate-like crystals are arranged perpendicular to the film surface in an alternating pattern to form a stronger hydrophobic layer with a rougher texture. The water contact angle of the film surface is ≥135°. More preferably, the water contact angle is above 150°.

[0023] The saturated fatty acids or their monoglycerides are selected from saturated fatty acids or their monoglycerides containing 14-32 carbon atoms. Long-chain saturated fatty acids or their monoglycerides have more suitable hydrophobicity, melting point, and the ability to form plate-like crystals inside and on the surface of the matrix resin. They are also biodegradable, and the high water vapor barrier films made from them are fully biodegradable.

[0024] The inventors unexpectedly discovered that several saturated fatty acids or their monoglycerides can satisfy both a melting point above 50°C and appropriate hydrophobicity, forming stable micro-nano-sized sheet-like crystals inside and on the surface of a film. Preferably, the saturated fatty acids or their monoglycerides include one or more of myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, or their monoglycerides.

[0025] More preferably, the saturated fatty acid or its monoglyceride comprises one or more of stearic acid, arachidic acid, behenic acid, glyceryl monostearate, glyceryl monoarachidate, and glyceryl monobehenic acid.

[0026] The biodegradable matrix resin includes polylactic acid (PLA), polybutylene succinate (PBS), polyethylene succinate (PES), polybutylene adipate-co-butylene succinate (PBSA), polybutylene adipate-co-terephthalate (PBAT), polybutylene adipate-co-terephthalate (PBST), polybutylene adipate-co-furandicarboxylate (PBAF), and polybutylene adipate-co-furandicarboxylate (PBAF). A blend of one or more of the following resins: poly(butylene dimethyl terephthalate) (PBSF), poly(butylene carbonate-co-terephthalate) (PBCT), poly(butylene carbonate-co-furandicarboxylate) (PBCF), poly(butylene glycolate-co-terephthalate) (PBGT), poly(butylene glycolate-co-furandicarboxylate) (PBGF), poly(butylene oxalate-co-terephthalate), and poly(butylene oxalate-co-furandicarboxylate).

[0027] Preferably, the mass percentage of saturated fat or its monoglyceride in the high water vapor barrier film is 2-15 wt%, more preferably 4-12 wt%.

[0028] Preferably, the biodegradable matrix resin comprises one or more blends of PBAT, PLA, and PBS. More preferably, the biodegradable matrix resin is a blend of PBAT and PLA, wherein the mass percentage of PLA is 15-25 wt%.

[0029] The high water vapor barrier film further includes at least one additive selected from antioxidants, heat stabilizers, and light stabilizers, with the additive amount being 0.05-5 wt% of the biodegradable matrix resin. Additives with antioxidant, anti-thermal decomposition, and light-stabilizing effects can also be added to the film of the present invention to improve other comprehensive properties of the film.

[0030] The water vapor barrier properties of the high water vapor barrier film are more than twice those of the biodegradable matrix resin film. It uses only a single saturated fatty acid or its monoglyceride as a water barrier agent, and the amount used is not large, but the improvement effect on water vapor barrier properties is amazing. Preferably, the water vapor barrier properties of the high water vapor barrier film are more than 3, 4, 8, or even more than 10, 20, or 40 times that of the biodegradable matrix resin film.

[0031] The present invention also provides a method for preparing the biodegradable high water vapor barrier film, characterized by comprising the steps of: mixing a biodegradable matrix resin and the saturated fatty acid or its glycerol monoester at room temperature and then melt-blending them, and then heat-processing the resulting blend to form the high water vapor barrier film.

[0032] In this invention, the melt blending method includes open milling, internal milling and melt extrusion, preferably melt extrusion granulation, more preferably twin-screw extrusion granulation; the thermal processing film forming method includes extrusion blow molding, extrusion casting or hot pressing film forming, preferably extrusion blow molding.

[0033] In this invention, antioxidants, heat stabilizers, and light stabilizers may also be added during the melt blending process to improve processing stability and enhance weather resistance. The total amount of these additives is 0.05-5 wt% of the biodegradable matrix resin.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention uses saturated fatty acids or their glycerol monoesters with high melting point and suitable hydrophobicity as water-blocking agents to form micro-nano-sized sheet crystals inside and on the surface of biodegradable substrate films. This unexpectedly achieves an order-of-magnitude improvement in the water vapor barrier properties of the film by a single component, with a very significant improvement effect.

[0036] (2) The saturated fatty acids or their glycerol monoesters used in this invention do not require modification or pretreatment. The formulation is simple, all components of the film are fully biodegradable, and the physical, mechanical properties and bio-environmental properties of the matrix resin can be well maintained.

[0037] (3) The modified raw materials used in this invention—saturated fatty acids or their glycerol monoesters—are inexpensive and readily available. The film preparation method is simple, efficient, environmentally friendly, and low-cost. Existing plastic processing equipment can be used, making it easy to industrialize. Attached Figure Description

[0038] Figure 1 Cross-sectional SEM images of PBAT membranes and various modified PBAT membranes.

[0039] Figure 2 SEM images of the surface of PBAT membranes and various modified PBAT membranes. Detailed Implementation

[0040] 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.

[0041] The raw materials used in the following specific embodiments are shown in Table 1. Poly(butylene adipate-co-terephthalate), abbreviated as PBAT, is a product of BASF, brand name Ecoflex F Blend C1200; polylactic acid, abbreviated as PLA, is a product of Natureworks, brand name 3251D.

[0042] Table 1. Raw materials used in the examples and comparative examples and their basic properties.

[0043]

[0044] The strength of hydrophobicity of the matrix resin and hydrophobic modifier is represented by the reference value (XlogP) calculated using the hydrophobic parameter. The larger the XlogP value, the stronger the hydrophobicity. The XlogP value is calculated using the method described in the reference (Wang Renxiao, Fu Ying, Lai Luhua. A new method for calculating the lipid-water partition coefficient of organic compounds [J]. Acta Physico-Chimica Sinica, 1997, 13(1), 1-4).

[0045] In the following specific embodiments, water vapor transmission rate and water vapor permeability coefficient were determined using the permeation cup method under test conditions of 38°C and 90% RH. The water vapor permeability coefficient (WVP, unit: g.mm.m) was used. -2 .d -1 .atm -1 The water vapor permeability coefficient (WVTR) is used to represent the water vapor barrier properties of a material. The lower the WVTR, the better the water vapor barrier properties. The WVTR is a material property, while the water vapor transmission rate (WVTR, unit: g·m³) is a different property. -2 ·day -1 Water vapor transmission rate (WVTR) is not a material property but is related to the thickness of the product and the test pressure differential or relative humidity. Since the thickness of 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, agricultural films are typically 10 micrometers thick) and standard test conditions (38℃, 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.

[0046] Furthermore, in the following specific embodiments, WVP (unit: g.mm.m) is used. -2 .d -1 .atm -1The water vapor barrier properties of a material are represented by WVP0, which represents the water vapor permeability coefficient of the matrix resin membrane under the same processing conditions. The water vapor barrier modification factor BIF is defined as WVP0 / WVP, where BIF represents the ratio of the modified film's water vapor barrier properties to those of the matrix resin membrane. A larger BIF indicates a better water vapor barrier modification effect. Comparative Example 1: Pure PBAT matrix resin membrane

[0047] Step 1: Place 60g of PBAT in a vacuum drying oven at 40℃ and dry for 24h. Then add it to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min.

[0048] Step 2: The sample obtained in Step 1 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 on a steel plate with cold water to form a film, which is denoted as PBAT.

[0049] Comparative Example 2: PBAT + 8% Lauric Acid

[0050] Step 1: Place 60g PBAT and 4.8g lauric acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0051] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-LA8.

[0052] Comparative Example 3: PBAT + 8% Methyl Stearate

[0053] Step 1: Place 60g PBAT and 4.8g methyl stearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0054] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-MS8.

[0055] Comparative Example 4: PBAT + 8% n-butyl stearate

[0056] Step 1: Place 60g PBAT and 4.8g n-butyl stearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0057] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-BS8.

[0058] Comparative Example 5: PBAT + 8% Triglyceride

[0059] Step 1: Place 60g PBAT and 4.8g triglyceride in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0060] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-GTO8.

[0061] Comparative Example 6: PBAT + 8% Calcium Stearate

[0062] Step 1: Place 60g PBAT and 4.8g calcium stearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 170℃ for 5min to obtain the blend sample.

[0063] Step 2: The sample was melted at 170°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 was cooled on a steel plate with cold water to form a film, named PBAT-CS8.

[0064] Comparative Example 7: PBAT + 8% N,N'-ethylenebis-stearamide

[0065] Step 1: Place 60g PBAT and 4.8g N,N'-ethylene bis-stearamide in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 170℃ for 5min to obtain the blend sample.

[0066] Step 2: The sample was melted at 170°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 was cooled on a steel plate with cold water to form a film, named PBAT-EBS8.

[0067] Comparative Example 8: PBAT + 8% Glycol Distearate

[0068] Step 1: Place 60g PBAT and 4.8g ethylene glycol distearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0069] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-EDS8.

[0070] Comparative Example 9: PBAT + 8% Glyceryl Tristearate

[0071] Step 1: Place 60g PBAT and 4.8g glyceryl tristearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0072] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-GTS8.

[0073] Comparative Example 10: PBAT + 8% pentaerythritol tetrastearate

[0074] Step 1: Place 60g of PBAT and 4,8-pentaerythritol tetrastearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0075] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-PETS8.

[0076] Example 1: PBAT + 8% myristic acid

[0077] Step 1: Place 60g PBAT and 4.8g myristic acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0078] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-MA8.

[0079] Example 2: PBAT + 8% palmitic acid

[0080] Step 1: Place 60g PBAT and 4.8g palmitic acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0081] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-PA8.

[0082] Example 3: PBAT + 8% stearic acid

[0083] Step 1: Place 60g PBAT and 4.8g stearic acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0084] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-SA8.

[0085] Example 4: PBAT + 8% arachidic acid

[0086] Step 1: Place 60g PBAT and 4.8g arachidic acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0087] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-AA8.

[0088] Example 5: PBAT + 8% behenicol

[0089] Step 1: Place 60g PBAT and 4.8g behenic acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0090] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-DA8.

[0091] Examples 6-8: PBAT + 2%, 4%, or 12% stearic acid

[0092] The preparation process was the same as in Example 3, except that the amount of stearic acid was changed to 2wt%, 4wt%, and 12wt%, respectively. The resulting modified PBAT films were named PBAT-SA2, PBAT-SA4, and PBAT-SA12, respectively.

[0093] Examples 9-12: PBAT + 2%, 4%, 6% or 12% arachidic acid

[0094] The preparation process was the same as in Example 4, except that the amount of arachidic acid was changed to 2wt%, 4wt%, 6wt%, and 12wt%, respectively. The resulting modified PBAT films were named PBAT-AA2, PBAT-AA4, PBAT-AA6, and PBAT-AA12, respectively.

[0095] Example 13: PBAT + 8% glyceryl monostearate

[0096] Step 1: Place 60g PBAT and 4.8g glyceryl monostearate in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 150℃ for 5min to obtain the blend sample.

[0097] Step 2: 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. After that, it was cooled on a steel plate with cold water to form a film, named PBAT-GMS8.

[0098] Example 14: PBAT / PLA + 8% behenicol

[0099] Step 1: Place 48g PBAT, 12g polylactic acid and 4.8g behenic acid in a vacuum drying oven at 40℃ and dry for 24h. Then mix them evenly at room temperature. Add the mixture to a preheated HAAKE Polylab OS torque rheometer and melt-blend at 50rpm and 165℃ for 5min to obtain the blend sample.

[0100] Step 2: The sample was melted at 170°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 was cooled on a steel plate with cold water to form a film, named PBAT / PLA-DA8.

[0101] Example 15: PBAT / PLA + 8% behenicol

[0102] Step 1: Place 1.6 kg PBAT, 0.4 kg polylactic acid, and 0.16 kg behenic acid in a vacuum drying oven at 40°C and dry for 24 hours. Then, mix them with 4 g antioxidant 1010, 4 g antioxidant 626, and 10 g light stabilizer 1164 at room temperature until homogeneous. Add the mixture to a twin-screw extruder and melt-blend at 50 rpm and 185°C. Extrude and granulate to obtain blended granules.

[0103] Step 2: The granules are fed into a single-screw extruder for melt extrusion. The temperatures in the feeding zone, plasticizing zone, and homogenizing zone are 165℃, 175℃, and 185℃, respectively. The blend melt is fed into a blown film unit. The temperatures in the die connection zone and the die zone are 185℃ and 180℃, respectively. The film is blown into a bubble through the die, cooled, stretched, and wound up to obtain a film product named PBAT / PLA-DA8*.

[0104] The formulations, melting points, contact angles, and water vapor barrier properties of the pure PBAT matrix resin films and modified PBAT films prepared in the above comparative examples and embodiments are summarized in Table 2.

[0105] Table 2. Formulations, contact angles, and water vapor barrier properties of pure PBAT matrix resin films and modified PBAT films.

[0106]

[0107]

[0108] Note: X = A, B, or C, representing the water vapor transmission rate requirement level in GB / T 35795-2017: A: <800g.m -2 .d -1 B: 800-1600g.m -2 .d -1 C: ≥1600g.m -2 .d -1 .

[0109] Analysis and explanation of the results in Table 2:

[0110] In Comparative Example 1, the water vapor permeability coefficient P of the PBAT matrix resin film is... WV,0 419±43 g·mm·m -2 ·d -1 ·atm -1 Converted to WVTR 10 2500g.m -2 .d -1 This is equivalent to a water vapor permeability of 2500 g·m for a 10 μm thick PBAT membrane at 38°C / 90% RH. -2 .d -1 It only meets the Class C requirements of the national standard GB / T 35795-2017 "Fully Biodegradable Agricultural Ground Cover Film" (hereinafter referred to as the national standard).

[0111] In Examples 1-5, PBAT was modified with 8 wt% of five saturated fatty acids (myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid), each with a melting point >50℃, to prepare five modified films. The fatty acids formed micro-nano-scale plate-like crystals both inside and on the surface of the films, with an average thickness of 200-500 nm, a lateral dimension of 2-8 μm, and an average aspect ratio of 5-12 (see...). Figure 1 Furthermore, the plate-like crystals on the surface of the thin film are basically arranged perpendicularly to the surface in an alternating pattern, forming a very rough hydrophobic layer (see...). Figure 2 The surface water contact angle is as high as 138-153°, and the BIF value of the modified PBAT film is 3.4-10.7, which means that their water vapor barrier properties are 3.4-10.7 times that of the PBAT matrix resin film. The water vapor barrier modification effect is significant. Except for implementation 2, all meet the national standard Class A requirements. Among them, the water vapor barrier properties of the modified PBAT film using 8wt% arachidic acid and behenic acid are 10.7 and 10.2 times that of PBAT, respectively, which means that the modification effect is more than one order of magnitude.

[0112] Compared to Examples 1-5, Comparative Example 2 used 8 wt% lauric acid to modify PBAT. Lauric acid has a melting point of 44°C, which is lower than 50°C. No lamellar crystals formed on the interior or surface of the resulting PBAT-LA8 film. Although the film surface was relatively rough, the contact angle was only 111°, significantly lower than in Examples 1-5. Its water vapor barrier properties were even worse than those of the PBAT-based resin film. Lauric acid and myristic acid have similar structures, differing only by two CH2 atoms, but lauric acid has a lower melting point and lower hydrophobicity. The internal and surface structures of the film prepared by blending lauric acid with PBAT differed greatly from those in Examples 1-5, as did its water vapor barrier properties. This indicates that the formation of lamellar crystals and a rough surface morphology on the interior and surface of the film significantly contributes to the water vapor barrier properties, and also suggests that a lower melting point is unfavorable for forming this structure and morphology.

[0113] Comparative Examples 3-5 used low-melting-point methyl stearate (T m 37-41℃) and butyl stearate (T m 27.5℃) and liquid triglycerides (T m PBAT was modified using agents at -5℃. These modifiers did not form plate-like crystals inside or on the surface of the film, but rather created micropores inside the film. Figure 1 ), forming stripes, spherical particles, or smooth planes on the film surface. Figure 2 These films actually exhibited worse water vapor barrier properties than pure PBAT films, indicating that they did not perform water vapor barrier modification. This suggests that if the modifier has a low melting point or is liquid at room temperature, it cannot form plate-like crystals and a rough surface morphology, thus failing to achieve a good water vapor barrier modification effect.

[0114] Comparative Examples 6-7: PBAT was modified with 8 wt% calcium stearate (CS) and N,N'-ethylene bis-stearamide (EBS). These two modifiers have melting points much higher than 50℃ and also exhibit strong hydrophobicity, but the surface water contact angle is only about 100°. Compared to pure PBAT films, their water vapor barrier properties were not improved, but rather worsened. Figure 1 and Figure 2 As shown, the PBAT-CS8 film has a relatively smooth surface with a small number of plate-like or spherical CS particles; the PBAT-EBS8 film has irregularly shaped EBS crystals on its surface and also has a certain degree of roughness, but its morphology is completely different from that of Examples 1-5. This result indicates that although long-chain saturated aliphatic metal salts or amide derivatives have high melting points and suitable hydrophobicity, they cannot achieve good water vapor barrier modification effects because they cannot form plate-like crystals inside and on the surface of the film, and the film surface lacks a rough hydrophobic structure.

[0115] Comparative Examples 8-10: PBAT was modified with 8 wt% ethylene glycol distearate, glyceryl tristearate, and pentaerythritol tetrastearate. These three modifiers have high melting points (61℃, 71℃, 63℃) and higher hydrophobic parameters (17.3, 25.8, 36.2), but they did not form lamellar crystals inside the film. Instead, significant microphase separation occurred between the modifier and the PBAT matrix resin, with obvious cracks at the phase interface. Although some lamellar crystals formed on the film surface, they were few in number and in a "fallen" state, resulting in low surface roughness and relatively low water contact angles (117°, 113°, 114°). Although there was some water vapor barrier modification effect, the BIF values ​​were 1.40, 1.36, and 1.16, respectively, indicating limited modification effect. This result shows that stronger hydrophobicity is not necessarily better for the modifier; it should have appropriate hydrophobicity, that is, its hydrophobicity should be significantly higher than that of the matrix resin but not too high.

[0116] The above results indicate that hydrophobic modifiers should simultaneously possess a high melting point and suitable hydrophobicity, and generate lamellar crystals both inside and on the surface of the film, as well as form a hydrophobic rough structure on the surface. These three conditions are necessary for obtaining excellent water vapor barrier modification effects, and none of them can be omitted.

[0117] Examples 6-7 reduced the amount of stearic acid to 2-4 wt%, achieving a water vapor barrier performance 1.5-2.2 times that of the PBAT film. While the modification effect was slightly reduced compared to Example 3 (8 wt% stearic acid), good water vapor barrier modification was still achieved, meeting the requirements of national standards Class C and Class B, respectively. Example 8 increased the amount of stearic acid to 12 wt%, achieving a water vapor barrier performance 4.49 times that of the PBAT film. This further improved the modification effect compared to Example 3 (8 wt% stearic acid), meeting the requirements of national standard Class A. This demonstrates that the amount of modifier has a significant impact on the modification effect; with increasing dosage, surface hydrophobicity increases (contact angle increases), and water vapor barrier performance improves.

[0118] Examples 9-11 reduced the arachidic acid dosage to 2wt%, 4wt%, and 6wt%, respectively. Compared to Example 4, the modification effect decreased, but good water vapor barrier modification effects were still achieved. The water vapor barrier properties were 1.50 times, 2.50 times, and 4.69 times that of PBAT, respectively, meeting the national standard requirements for Class C, Class B, and Class A. Example 12 increased the arachidic acid dosage to 12wt%, resulting in a PBAT-AA12 film with a contact angle as high as 152° and a superhydrophobic surface. Its water vapor barrier properties were significantly improved compared to Example 4, reaching 46.6 times that of the PBAT film, achieving an excellent water vapor barrier modification effect. This further illustrates that the type and dosage of modifier have a significant impact on the water vapor barrier modification effect. Compared to stearic acid, the surface hydrophobicity and water vapor barrier properties increased more significantly with increasing arachidic acid dosage.

[0119] Example 13 used 8 wt% glyceryl monostearate to modify PBAT. Glyceryl monostearate still formed plate-like crystals inside and on the surface of the film. A small portion of the plate-like crystals on the surface were arranged perpendicularly to the film surface, while most were in a "fallen" state. Therefore, its water contact angle was only 110°, significantly smaller than the 153° and 148° of Examples 4-5. The water vapor barrier modification effect was lower than that of Examples 4-5, but it still achieved a modification effect comparable to Example 3, meeting the national standard Class A requirements. This further illustrates that the extremely rough surface morphology formed by the plate-like crystals arranged perpendicularly to the film surface has a significant impact on water vapor barrier properties.

[0120] Example 14 used PBAT and PLA, two biodegradable polyesters, as matrix resins. 8 wt% DA was used to modify them for water vapor barrier properties. The water vapor barrier properties of the PBAT / PLA-DA8 film were 8.2 times that of the PBAT / PLA blend film, meeting the national standard Class A requirements. This indicates that this water vapor barrier modification is also applicable to blend films of biodegradable polymers.

[0121] The formulation of Example 15 is basically the same as that of Example 10, except that 0.05 wt% of antioxidant 1010 and 0.2 wt% of antioxidant 626 are added. The mixture is blended using a twin-screw extruder and blown into film using a single-screw extruder and blown film machine. The resulting PBAT / PLA-DA8 film has a water contact angle as high as 146°, and the water vapor barrier modification effect is still very good. The BIF is as high as 8.7, which is slightly better than that of Example 10 and meets the national standard Class A requirements.

[0122] In summary, the WVTR shown in Table 1 10 The results showed that the modified PBAT film prepared with 2 wt% saturated fatty acid or its monoglyceride met the national standard Class C requirements for water vapor barrier properties; the modified PBAT film prepared with 4 wt% saturated fatty acid or its monoglyceride met the national standard Class B requirements for water vapor barrier properties; and the modified PBAT film prepared with 8 wt% saturated fatty acid or its monoglyceride mostly met the national standard Class A requirements for water vapor barrier properties. The tensile properties of the PBAT films and modified PBAT films prepared in Comparative Example 1, Examples 1-12, and 14 are summarized in Table 3. It can be seen that compared with the PBAT film (Comparative Example 1), the tensile modulus (E) of the PBAT film modified with 8 wt% long-chain saturated fatty acid containing 14-22 carbon atoms increased from 106 MPa to 122-137 MPa, and the tensile strength (σ) increased significantly. b The strength decreased from 20.4 MPa to 15.7-16.2 MPa, and the elongation at break (ε) decreased. b The increase from 423% to 442-493% indicates that modifying PBAT with these saturated fatty acids leads to a significant decrease in tensile strength, but an increase in tensile modulus and toughness. The results of Examples 3 and 6-8, and Examples 4 and 9-12, show that with increasing amounts of stearic acid or arachidic acid, the modulus tends to increase, while the strength tends to decrease, and the change in elongation at break is not very significant; therefore, the amount used should not be too high.

[0123] The results of Example 14 show that, compared with the PBAT-DA film (Example 5) and the PBAT film (Comparative Example 1), the PBAT / PLA-DA8 film prepared by replacing PBAT with a blend of 80 wt% PBAT and 20 wt% PLA as the matrix resin has a significantly higher tensile modulus (485 ± 55 MPa) and tensile strength (24.9 ± 0.9 MPa), while the elongation at break is slightly lower. This indicates that using a blend of various biodegradable polyesters as the matrix resin to blend with saturated fatty acids to prepare films helps to maintain or even improve the mechanical properties of biodegradable high moisture barrier films.

[0124] Table 3 Tensile mechanical properties of PBAT film, PBAT-DA8 film and PBAT / PLA-DA8 film

[0125]

[0126]

Claims

1. A biodegradable high water vapor barrier film, characterized in that, It is composed of 100wt% biodegradable matrix resin and 4-12wt% saturated fatty acids by weight ratio; The saturated fatty acid has a melting point above 50°C and a hydrophobic parameter calculated to a reference value of 5-15; the saturated fatty acid is one or more of myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid. The high water vapor barrier film includes micro- and nano-sized sheet-like crystals formed from saturated fatty acids on its interior and surface; the surface water contact angle of the high water vapor barrier film is above 110°C.

2. The biodegradable high water vapor barrier film according to claim 1, characterized in that, The biodegradable matrix resin includes one or more blends of polylactic acid, poly(butylene succinate), poly(ethylene succinate), poly(adipate-co-butylene succinate), poly(adipate-co-butylene terephthalate), poly(adipate-co-butylene terephthalate), poly(adipate-co-butylene furanate), poly(adipate-co-butylene furanate), poly(carbonate-co-butylene terephthalate), poly(carbonate-co-butylene furanate), poly(glycolic acid-co-butylene terephthalate), poly(glycolic acid-co-butylene furanate), poly(oxalate-co-butylene terephthalate), and poly(oxalate-co-butylene furanate).

3. The biodegradable high water vapor barrier film according to claim 1, characterized in that, The saturated fatty acid has a melting point above 65°C, and the calculated hydrophobic parameter is 7-13.

4. The biodegradable high water vapor barrier film according to claim 1, characterized in that, The high water vapor barrier film also includes at least one of antioxidants, heat stabilizers, and light stabilizers, with the amount of the additive being 0.05-5 wt% of the biodegradable matrix resin.

5. The biodegradable high water vapor barrier film according to claim 1, characterized in that, The water vapor barrier properties of the high water vapor barrier film are more than twice those of the biodegradable matrix resin film.

6. The method for preparing a biodegradable high water vapor barrier film according to any one of claims 1-5, characterized in that, The process includes the following steps: mixing a biodegradable matrix resin and the saturated fatty acid at room temperature and then melt-blending them; the resulting blend is then heat-processed to form the high water vapor barrier film.

7. The method for preparing a biodegradable high water vapor barrier film according to claim 6, characterized in that, The melt blending method is twin-screw extrusion, and the thermal processing film forming method is extrusion blow molding, extrusion casting, or hot pressing.

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