EVOH / organically modified mica powder high-barrier composite blown film and preparation method thereof

Abstract

This invention discloses a high-barrier composite blown film of EVOH / organically modified mica powder and its preparation method, belonging to the field of polymer composite materials and food packaging technology. The composite blown film consists of 90-99 parts by weight of blow-molding grade ethylene-vinyl alcohol copolymer and 1-10 parts by weight of organically modified mica powder. The organically modified mica powder is obtained by surface modification of muscovite powder with silane coupling agent KH-570, with the amount of KH-570 being 1.5-3.0 wt% of the mass of the muscovite powder. In the preparation process, muscovite powder is first added to an alcoholic aqueous solution of KH-570, stirred, filtered, washed, and dried to obtain organically modified mica powder; then, dried EVOH and organically modified mica powder are premixed and melt-blended and granulated using a twin-screw extruder; finally, the composite granules are blown into a film. This invention utilizes the high aspect ratio and hydrophobic surface of organically modified mica powder to form a tortuous path effect in the EVOH matrix, significantly reducing oxygen and water vapor permeability. It exhibits good thermal stability, simple process, and is suitable for barrier packaging of lipid-based foods.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials and food packaging technology, and particularly relates to a high-barrier composite blown film of EVOH / organic modified mica powder and its preparation method. Background Technology

[0002] The gas barrier properties of food packaging films play a crucial role in delaying food oxidation and spoilage and extending shelf life. Lipid-rich foods (such as meat products, nuts, and oils) are rich in unsaturated fatty acids, which are highly susceptible to oxidative rancidity upon contact with oxygen, leading to deterioration in food quality, loss of flavor, and potential formation of harmful oxidation products. Therefore, developing packaging films with excellent gas barrier properties has always been a research hotspot in the food packaging field.

[0003] Ethylene-vinyl alcohol copolymer (EVOH) is one of the best thermoplastic polymers in commercial applications for gas barrier properties. The numerous hydroxyl (-OH) groups on the EVOH molecular chain establish a highly ordered crystalline structure through intermolecular hydrogen bonds, making it difficult for gas molecules to diffuse and permeate within the polymer matrix, thus endowing it with excellent oxygen and carbon dioxide barrier properties. Among these, blow-molding grade EVOH products with an ethylene content of 32–44 mol% are widely used in food flexible packaging, thermoformed containers, and multilayer composite films due to their wide processing window and balanced barrier and mechanical properties.

[0004] However, the gas barrier properties of EVOH are extremely sensitive to relative humidity, which is a major technical bottleneck for its application as a high-performance packaging material. When ambient humidity increases, water molecules competitively bind to the hydroxyl groups on the EVOH molecular chains, disrupting the original hydrogen bond network and ordered arrangement between the chains. This leads to an increase in the free volume of the polymer, a simultaneous increase in the gas molecule diffusion coefficient and solubility coefficient, and a significant increase in gas permeability. Under high humidity conditions (e.g., relative humidity ≥ 85%), the oxygen permeability of EVOH can increase to tens or even hundreds of times that under dry conditions. This defect severely restricts its practical application in high-humidity environments, especially for lipid-based foods that need to be stored and sold under high humidity conditions; pure EVOH films cannot independently meet the barrier requirements for long shelf life.

[0005] To further improve the gas barrier properties of polymer films, researchers have proposed a technique of introducing layered inorganic fillers into the polymer matrix. Layered inorganic fillers possess a high aspect ratio and a sheet-like structure. When uniformly dispersed in the polymer matrix and oriented along the film plane, gas molecules must bypass the impermeable filler layers during permeation, significantly extending the permeation path and effectively reducing gas permeability—a phenomenon known as the tortuous path effect. Among various layered fillers, montmorillonite (MMT) is currently the most widely studied layered silicate filler. After intercalation treatment with quaternary ammonium salt organic modifiers, it can achieve partial exfoliation and dispersion in the polymer matrix, forming a polymer / layered silicate nanocomposite material, which significantly improves the barrier properties of the composite film.

[0006] However, there are several drawbacks to applying montmorillonite to the EVOH system: montmorillonite has a limited cation exchange capacity (CEC). Quaternary ammonium salt organic modifiers are usually intercalated into the montmorillonite interlayer via ion exchange, but their thermal decomposition temperature is usually below 250°C, which is close to or even overlaps with the processing temperature range of EVOH (approximately 190–220°C). This poses a risk of thermal degradation of the modifier during melt blending, and the degradation products may adversely affect the film's color, odor, and overall performance. The relatively small interlayer spacing of montmorillonite requires high-quality processing equipment and conditions to achieve sufficient intercalation and exfoliation dispersion, increasing the complexity of the process. Furthermore, as a natural mineral, montmorillonite's mineral composition and physicochemical properties vary greatly depending on the origin and ore layer, and batch stability needs improvement, which poses a challenge to quality control in industrial production.

[0007] Mica is a typical natural layered silicate mineral, among which muscovite (chemical formula KAl2(AlSi3)O) is an example. 10 (OH)2) belongs to the muscovite subgroup within the mica group, possessing a complete TO-OT type trioctahedral layered crystal structure, with potassium ions (K) forming the interlayers. + Mica powder exhibits tight bonding, stable chemical properties, excellent heat resistance (thermal decomposition temperature > 700℃), low coefficient of thermal expansion, and superior dielectric and mechanical strength. Compared to montmorillonite, mica powder possesses superior thermal stability, a higher aspect ratio, and abundant natural mineral resources. It is widely available, relatively inexpensive, and has a stable and reliable industrial supply. Theoretically, the flaky morphology and structural characteristics of mica powder provide a structural basis for it to replace montmorillonite as a high-performance barrier filler.

[0008] However, unmodified mica powder faces significant interfacial compatibility issues in practical applications. The surface of mica powder contains a large number of hydroxyl groups (-OH), exhibiting strong hydrophilicity. This results in weak interfacial bonding with the highly polar EVOH matrix, making it prone to agglomeration during melt blending and hindering uniform dispersion. Consequently, the tortuous path effect expected from its high aspect ratio flake morphology cannot be effectively utilized, leading to limited improvement in barrier properties. Furthermore, the introduction of interfacial defects and stress concentration points may even reduce the mechanical properties and appearance quality of the film.

[0009] Therefore, developing a technical solution that effectively combines organically modified mica powder with EVOH and prepares high-performance barrier films through a mature and stable blown film forming process is of great theoretical significance and industrial application value for meeting the actual demand for high barrier performance in lipid-based food packaging. This solution aims to overcome the problems of barrier performance degradation of pure EVOH films under high humidity conditions, difficulty in uniform dispersion of unmodified mica powder, and insufficient thermal stability of existing montmorillonite system modifiers. Summary of the Invention

[0010] The technical problem to be solved by this invention is to address the aforementioned shortcomings in the existing technology by providing a high-barrier composite blown film of EVOH / organically modified mica powder and its preparation method. Specifically, this invention aims to solve the following technical problems: First, the gas barrier performance of pure EVOH blown film decreases significantly under high humidity environments; second, unmodified mica powder has poor compatibility with the EVOH matrix and is prone to agglomeration during melt blending, failing to effectively utilize the barrier advantages of its sheet-like morphology; third, the existing modified montmorillonite system has insufficient thermal stability of the modifier within the EVOH processing temperature window, posing a risk of thermal degradation; fourth, the existing high-barrier film preparation process is complex, costly, and requires demanding processing equipment.

[0011] To address the aforementioned technical problems, the present invention provides the following technical solutions.

[0012] A high-barrier composite blown film made of EVOH / organically modified mica powder is prepared from the following components in parts by weight: 90-99 parts of ethylene-vinyl alcohol copolymer (EVOH) and 1-10 parts of organically modified mica powder. The EVOH is blown molding grade, with an ethylene molar content of 32-44 mol%; the organically modified mica powder is obtained by surface modification of muscovite powder with a silane coupling agent.

[0013] Furthermore, the D of the mica powder 50The particle size is 10–30 μm, and the aspect ratio is not less than 50. The silane coupling agent is γ-methacryloxypropyltrimethoxysilane (KH-570), and its dosage is 1.5–3.0 wt% of the mica powder mass. Surface modification of mica powder with KH-570 introduces organic segments containing methacryloxy groups onto the mica powder surface. This imparts hydrophobic properties to the mica powder surface and improves the interfacial compatibility between the mica powder and the EVOH matrix, enabling the mica powder sheets to be uniformly dispersed and highly oriented along the film plane during melt blending and biaxial stretching of blown film. Furthermore, KH-570 has a thermal decomposition temperature much higher than 250℃ and exhibits excellent thermal stability within the blown film processing temperature range of EVOH (approximately 190–220℃), fundamentally avoiding the thermal degradation problems that may occur with quaternary ammonium salt modifiers in existing technologies during processing.

[0014] As a preferred embodiment, the amount of organically modified mica powder added is 3 to 7 parts by weight. Within this range, the organically modified mica powder can achieve uniform dispersion and effective orientation in the EVOH matrix, fully utilizing the tortuous path effect to significantly reduce the oxygen permeability and water vapor permeability of the composite film, while maintaining the mechanical properties of the film, especially the elongation at break, at a level that meets the requirements of actual packaging applications. More preferably, the amount of organically modified mica powder added is 5 parts by weight, at which the barrier properties and mechanical properties of the composite film achieve the best balance.

[0015] Furthermore, the melt index of the EVOH is 3–8 g / 10 min at 190°C and 2160 g load. EVOH in this melt index range has both good melt processing fluidity and sufficient melt strength, making it particularly suitable for blown film forming processes. It can produce thin film products with uniform thickness and good appearance under appropriate blow-up ratio and traction speed.

[0016] This invention also provides a method for preparing the above-mentioned EVOH / organically modified mica powder high-barrier composite blown film, comprising the following steps: Step (1) Preparation of organically modified mica powder: After drying the mica powder, it is added to an alcohol-water solution containing the silane coupling agent KH-570. The mixture is stirred at 80-90℃ for 2-3 h, filtered, washed, dried, ground, and sieved to obtain the organically modified mica powder. The alcohol-water solution is preferably a mixture of ethanol and water, with a volume ratio of ethanol to water of 95:5; the concentration of KH-570 in the alcohol-water solution is 1-3 wt%; the drying is carried out at 100-110℃ to constant weight. This step achieves surface modification of the mica powder from hydrophilic to hydrophobic by the silane coupling agent undergoing a hydrolysis-condensation reaction on the mica powder surface, chemically grafting organic functional groups onto the mica powder surface.

[0017] Step (2) Melt blending and granulation: The dried EVOH and the organic modified mica powder obtained in step (1) are premixed evenly according to the formula, and then melt-blended and extruded by a twin-screw extruder to obtain composite granules. Preferably, the temperature of each zone of the twin-screw extruder is set as follows: feeding section 180℃, melting section 190~200℃, mixing section 195~210℃, discharge section 200~215℃, and die head temperature 210~220℃; the screw speed is 120~150 rpm; and the feeding speed is 8~12 kg / h. EVOH needs to be vacuum dried before processing to reduce its moisture content to below 0.1 wt% to avoid polymer degradation caused by trace moisture during processing.

[0018] Step (3) Blown Film Forming: The composite granules obtained in step (2) are blown into film using a blown film forming unit. The blow-up ratio is controlled to be 2.5 to 3.5. After cooling, shaping, and winding, the composite blown film is obtained. Preferably, the temperatures of each zone of the blown film forming unit are set as follows: extruder feeding section 185℃, melting section 195 to 205℃, homogenization section 200 to 210℃, die head temperature 205 to 215℃; screw speed 60 to 90 rpm; traction speed 8 to 15 m / min; die gap 0.8 to 1.2 mm. Within the above blow-up ratio range, the melt film bubble is subjected to tensile action in both the longitudinal and transverse directions. The sheet-like organic modified mica powder is highly oriented along the film plane under the action of the biaxial tensile force field, which greatly extends the permeation path of gas molecules in the film thickness direction, and the tortuous path effect is fully utilized.

[0019] The EVOH / organic modified mica powder high-barrier composite blown film of the present invention can be applied to barrier packaging of lipid-based foods, including but not limited to meat products, nuts, oils and fat-containing cooked foods.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects.

[0021] First, the gas barrier properties are significantly improved. Organically modified mica powder can achieve uniform dispersion in the EVOH matrix. Its high aspect ratio plate-like crystals are highly oriented along the film plane during biaxial stretching of the blown film, forming a significant tortuous path effect. This forces gas molecules to bypass the impermeable filler layers when permeating along the film thickness direction, greatly extending the permeation path and thus significantly reducing the gas permeability of the composite film. Experiments have verified that, at the optimal addition amount, the oxygen permeability of the composite film can be reduced by 30%–55% compared to the pure EVOH film.

[0022] Second, the water vapor barrier performance is significantly improved. After surface modification with silane coupling agent KH-570, the surface of mica powder changes from hydrophilic to hydrophobic, and the layers are uniformly dispersed in the EVOH matrix, effectively blocking the permeation channels of water molecules. At the same time, the presence of hydrophobic organic segments in the matrix inhibits the adsorption of water molecules by EVOH to a certain extent, reducing the water vapor permeability of the composite film by 30% to 40% compared with the pure EVOH film.

[0023] Third, it exhibits excellent thermal stability and processing adaptability. The thermal decomposition temperature of the silane coupling agent KH-570 is far above 250℃, demonstrating excellent thermal stability within the blown film processing temperature range of EVOH. It avoids the problem of product discoloration or performance degradation caused by the thermal degradation of the modifier. Furthermore, the introduction of organically modified mica powder requires no modification to existing twin-screw extrusion and blown film equipment, resulting in a simple process, controllable costs, and promising prospects for industrial application.

[0024] Fourth, mechanical properties are improved in a balanced way. The good dispersion and orientation of the high aspect ratio flake mica powder in the EVOH matrix can effectively transfer and disperse the applied stress, thereby improving the tensile strength and modulus of the composite film. This achieves a comprehensive optimization of mechanical properties while realizing high barrier performance. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a comparison of the Fourier transform infrared spectra of unmodified mica (mica) and organically modified mica (K-mica) in an embodiment of the present invention.

[0027] Figure 2 This is a comparison diagram of the surface water contact angles of unmodified mica (mica) and organically modified mica (K-mica) in the embodiments of the present invention.

[0028] Figure 3 This is a comparison of X-ray diffraction patterns of unmodified mica (mica) and organically modified mica (K-mica) in an embodiment of the present invention. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0031] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0032] The main raw material sources and parameters used in the following embodiments and comparative examples are as follows: Mica powder was purchased from Chuzhou Gree Mining Co., Ltd. 50 The particle size was 15–20 μm, with an aspect ratio of approximately 80, and no further treatment was performed before use; the blow-molding grade ethylene-vinyl alcohol copolymer (EVOH) was purchased from Kuraray Co., Ltd., Japan, under the brand name EVAL. TM F171B, with an ethylene molar content of 38 mol% and a melt index (190℃, 2160 g) of 5.5 g / 10 min; γ-methacryloyloxypropyltrimethoxysilane (KH-570) was purchased from Nanjing Shuguang Chemical Group Co., Ltd., with a purity ≥98%; anhydrous ethanol and glacial acetic acid were both analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.

[0033] The test methods and conditions for film performance are as follows: Oxygen permeability (OTR) is determined according to GB / T 1038-2000 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method". The test temperature is 23℃, and the relative humidity is 0% RH. The unit is cc / (m). 2 The water vapor transmission rate (WVTR) is expressed as g / (m²·atm). It is determined according to GB / T 1037-2021 "Test Method for Water Vapor Permeability of Plastic Films and Sheets - Cup Method", with a test temperature of 38℃ and a relative humidity of 90% RH. 2 The thickness of the films obtained in each embodiment and comparative example was controlled within the range of 50±2 μm. At least five parallel samples were tested for each group of samples, and the results were taken as the arithmetic mean. Tensile strength and elongation at break were determined according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", with a tensile speed of 50 mm / min. Contact angle was measured using a German KRÜSS DSA100 contact angle meter, with deionized water as the test liquid and a droplet volume of 3 μL. Five measurements were taken for each group of samples, and the average value was taken. Fourier transform infrared spectroscopy (FTIR) was performed using a US Thermo Fisher Nicolet iS50 infrared spectrometer, using the KBr pellet method, with a scanning range of 4000–400 cm⁻¹. -1 The resolution is 4 cm. -1The number of scans was 32. X-ray diffraction (XRD) analysis was performed using a Rigaku SmartLab X-ray diffractometer from Japan, with Cu Kα radiation (λ=0.15406nm), tube voltage of 40 kV, tube current of 40 mA, scanning range of 2θ=5°~40°, and scanning speed of 2° / min.

[0034] Comparative Example 1 (Pure EVOH film) The blown EVOH granules were vacuum dried in an 80℃ oven for 10 h. A moisture analyzer determined the moisture content to be 0.08 wt% (i.e., less than 0.1 wt%), meeting the requirements for blown film processing. The dried EVOH granules were directly fed into the hopper of a single-screw blown film mill, and blown film processing was performed according to the following parameters: extruder feeding section temperature 190℃, melting section temperature 200℃, homogenization section temperature 205℃, connector temperature 210℃, die head temperature 210℃; screw speed 75 rpm; blow-up ratio (BUR) 3.0; traction speed 10 m / min; die gap 1.0 mm. After the film bubble was fully cooled and shaped by the air ring, it was guided into the traction roller through a herringbone clamp and wound up to obtain pure EVOH blown film (Comparative Example 1), with a film thickness controlled at 50±2 μm.

[0035] The oxygen permeability (OTR) of the pure EVOH film (50 μm) obtained in Comparative Example 1 was tested to be 0.80 cc / (m). 2 Water vapor transmission rate (WVTR) = 8.0 g / (m·day·atm) (23℃, 0% RH) 2 (day) (38℃, 90% RH). This set of data serves as a benchmark for comparing the performance improvement of subsequent embodiments. The oxygen barrier performance of pure EVOH films deteriorates sharply under high humidity conditions (e.g., relative humidity ≥85%). Actual testing showed that at 23℃ and 90% RH, its OTR spiked to approximately 28.5 cc / (m²). 2 The humidity (day·atm) is more than 35 times that under dry conditions. This data fully illustrates the severity of the performance degradation of pure EVOH films under high humidity conditions and also reflects the necessity of developing moisture-resistant barrier films.

[0036] Preparation Example 1: Preparation of Organically Modified Mica Powder (K-mica) Take 100 g of mica powder, spread it evenly on a stainless steel tray, and dry it in an 85℃ forced-air oven for 5 h to fully remove the surface physically adsorbed water. Simultaneously, prepare the coupling agent solution: accurately weigh 2.5 g of γ-methacryloyloxypropyltrimethoxysilane (KH-570) (KH-570 is 2.5 wt% of the mica powder mass) and slowly add it to 200 mL of anhydrous ethanol / deionized water mixed solution (volume ratio 95:5) under stirring. To promote the hydrolysis and condensation of the silane coupling agent, add glacial acetic acid dropwise to adjust the pH to 4.5–5.0, and pre-hydrolyze at room temperature for 30 min to fully hydrolyze the methoxy group of KH-570 into a silanol group, forming a reactive silanol group. The dried mica powder was added to the coupling agent solution and heated to 85°C in a constant temperature water bath. The mixture was then stirred continuously for 2.5 h under mechanical stirring (300 rpm). After the reaction was complete, the mixture was filtered while hot. The filter cake was washed three times with anhydrous ethanol, approximately 150 mL each time, to thoroughly remove unreacted free coupling agent and soluble byproducts. The washed filter cake was transferred to a clean porcelain dish and dried in a 105°C oven to constant weight (approximately 4 h). After drying, the powder was lightly ground in a mortar and pestle and passed through a 100-mesh standard sieve to obtain the organically modified mica powder, named K-mica, which was then sealed and stored in a desiccator for later use.

[0037] The organically modified mica powder (K-mica) prepared according to the above method was characterized using the following methods to verify its modification effect. The results are shown in the corresponding figures. Figure 1 , Figure 2 and Figure 3 FTIR analysis (see...) Figure 1 The results showed that K-mica at a wavenumber of 2920 cm⁻¹ -1 and 2850cm -1 A distinct CH stretching vibration absorption peak was observed at the position, which were attributed to the -CH2- and -CH3 groups on the methacryloyloxypropyl segment of the KH-570 molecule, respectively. The unmodified mica powder showed no significant absorption at the same position, indicating that the KH-570 molecule had been successfully grafted onto the mica powder surface via chemical bonding or strong physical adsorption. Surface water contact angle test (see...) Figure 2 The results showed that the water contact angle of unmodified mica powder was approximately 67°, exhibiting obvious hydrophilic properties. After modification with KH-570, the contact angle of K-mica significantly increased to approximately 124°, indicating that its surface had changed from hydrophilic to hydrophobic, which will help improve its interfacial compatibility with the EVOH matrix. XRD analysis (see [link to XRD analysis]). Figure 3 This indicates that the mica powder before and after modification corresponds to d at 2θ≈8.85°. 001The characteristic diffraction peaks (corresponding to a mica interlamellar spacing of approximately 1.0 nm) showed no shift in position, and the peak shape and intensity remained essentially unchanged, confirming that the modification effect of KH-570 is mainly a chemical modification of the mica powder surface, rather than intercalation into the interlamellae. This is consistent with the effect of montmorillonite after quaternary ammonium salt intercalation. 001 This is fundamentally different from the phenomenon of a significant shift in the peak towards a lower angle.

[0038] To facilitate the use of different coupling agent dosages of K-mica in subsequent embodiments, the general method of this preparation example can be adjusted as needed to adjust the dosage of KH-570 (ranging from 1.5 to 3.0 wt% of the mica powder mass), while the remaining steps and process parameters remain unchanged. The specific dosage of KH-570 in K-mica in each embodiment will be described separately in each embodiment.

[0039] Example 1 (K-mica addition amount 1 wt%) (1) Preparation of organic modified mica powder: In this example, K-mica was prepared according to the general method of preparation example 1, wherein the amount of KH-570 used was 1.5 wt% of the mass of the mica powder (i.e., 100 g of mica powder corresponds to 1.5 g of KH-570), and the other operation steps were exactly the same as those in preparation example 1.

[0040] (2) Preparation of EVOH / K-mica composite granules: Blow-molding grade EVOH granules were dried in a vacuum oven at 80℃ for 10 h until the moisture content was reduced to below 0.1 wt%. 3000 g of dried EVOH granules and 30.3 g of K-mica powder (calculated as equal mass due to extremely low moisture content) were accurately weighed according to a mass ratio of EVOH / K-mica = 99 / 1 (i.e., the mass fraction of K-mica in the composite system was 1 wt%), and added together to a high-speed mixer. The mixture was premixed at 800 rpm for 5 min to ensure that the K-mica powder adhered uniformly to the surface of the EVOH granules. The premixed material was transferred to the hopper of a co-rotating twin-screw extruder (screw diameter 35 mm, length-to-diameter ratio L / D = 44) for melt blending extrusion granulation. The temperature settings for each zone along the screw direction of the twin-screw extruder are as follows: feeding zone 180℃, melting zone 1 190℃, melting zone 2 195℃, mixing zone 1 200℃, mixing zone 2 205℃, mixing zone 3 210℃, discharge zone 210℃, and die head temperature 215℃; the screw speed is set to 130 rpm; and the feeding rate is set to 10 kg / h. The extruded melt is water-cooled, air-dried, and pelletized to obtain EVOH / K-mica composite granules. The obtained composite granules are then placed in an 80℃ vacuum oven for further drying for 8 hours to reduce the moisture content to below 0.1 wt%, and then sealed for storage.

[0041] (3) Blown film forming: The EVOH / K-mica (1 wt%) composite granules obtained in step (2) are transferred to the hopper of a single-screw blown film mill. The temperatures of each zone of the blown film mill are set as follows: extruder feeding section 185℃, melting section 195℃, homogenization section 200℃, connector 205℃, die head temperature 210℃; screw speed 75 rpm; blow-up ratio (BUR) 3.0; traction speed 10 m / min; die gap 1.0 mm. After the film bubble is fully cooled and shaped by the air ring, it is guided into the traction roller through the herringbone clamp and wound up to obtain the EVOH / K-mica (1 wt%) composite blown film (Example 1), with the film thickness controlled at 50±2 μm.

[0042] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Example 1 was tested to be 0.72 cc / (m). 2 (day·atm) (23℃, 0% RH), water vapor transmission rate WVTR = 7.2 g / (m 2 (day) (38℃, 90% RH). Compared with the pure EVOH film in Comparative Example 1, the OTR decreased by about 10%, and the WVTR decreased by about 10%. Under low addition conditions, the barrier performance has been initially improved, indicating that the introduction of a small amount of K-mica has begun to exert a tortuous path effect, but the improvement is relatively limited. The main reason is that when the filler content is low, the distance between the layers is large, and the increase in the bypass path of gas molecules is not yet obvious.

[0043] Example 2 (K-mica addition amount 3 wt%) (1) Preparation of organic modified mica powder: In this example, the amount of KH-570 was adjusted to 2.0 wt% of the mass of mica powder, and the remaining preparation steps were the same as in preparation example 1.

[0044] (2) Preparation of EVOH / K-mica composite particles: Weigh the raw materials according to the mass ratio EVOH / K-mica = 97 / 3 (i.e., the mass fraction of K-mica is 3 wt%), and the rest of the operation is the same as step (2) in Example 1.

[0045] (3) Blown film forming: The process parameters are the same as those in step (3) of Example 1, and EVOH / K-mica (3 wt%) composite blown film (Example 2) is obtained, with the film thickness controlled at 50±2 μm.

[0046] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Example 2 was tested to be 0.60 cc / (m). 2 (day·atm) (23℃, 0% RH), water vapor transmission rate WVTR = 6.1 g / (m 2(day) (38°C, 90% RH). Compared with the pure EVOH film of Comparative Example 1, the OTR decreased by approximately 25%, and the WVTR decreased by approximately 24%. Compared with Example 1, when the K-mica addition amount increased from 1 wt% to 3 wt%, the improvement in barrier performance was significantly greater, indicating that the increase in filler content required gas molecules to bypass more impermeable layers inside the film, further extending the permeation path and significantly enhancing the tortuous path effect. At the same time, the uniform distribution of hydrophobic organic segments on the K-mica surface in the EVOH matrix also inhibited the competitive binding of water molecules to the EVOH hydroxyl groups to a certain extent, thus simultaneously improving the water vapor barrier performance.

[0047] Example 3 (K-mica addition amount 5 wt%, preferred implementation scheme) (1) Preparation of organically modified mica powder: In this example, the amount of KH-570 used was 2.5 wt% of the mass of the mica powder, and the preparation steps were the same as those described in Preparation Example 1. The obtained K-mica is the product of Preparation Example 1, and its FTIR, contact angle and XRD characterization results are detailed in Preparation Example 1.

[0048] (2) Preparation of EVOH / K-mica composite particles: Weigh the raw materials according to the mass ratio EVOH / K-mica = 95 / 5 (i.e., the mass fraction of K-mica is 5 wt%), and the rest of the operation is the same as step (2) in Example 1.

[0049] (3) Blown film forming: The blown film process parameters in this embodiment were appropriately optimized based on those in Example 1: extruder feeding section 185℃, melting section 200℃, homogenization section 205℃, connector 210℃, die head temperature 210℃; screw speed 80 rpm; blow-up ratio adjusted to 3.2; traction speed 10 m / min; die gap 1.0 mm. A slightly higher blow-up ratio is beneficial for applying a stronger orientation force to the lamellar K-mica in the transverse stretching direction, promoting its directional alignment along the film plane. After the film bubble is cooled and shaped, it is wound up to obtain an EVOH / K-mica (5 wt%) composite blown film (Example 3), with the film thickness controlled at 50±2 μm.

[0050] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Example 3 was tested to be 0.44 cc / (m). 2 (day·atm) (23℃, 0% RH), water vapor transmission rate WVTR = 5.1 g / (m 2 (day) (38℃, 90% RH). Compared with the pure EVOH film of Comparative Example 1, the OTR was reduced by about 45% and the WVTR was reduced by about 36%, with a significant improvement in barrier performance.

[0051] The mechanical properties of the film in Example 3 were tested. Its tensile strength was 68.5 MPa, an increase of approximately 15% compared to the pure EVOH film in Comparative Example 1 (tensile strength 59.6 MPa). The elongation at break was 265%, slightly lower than the pure EVOH film (elongation at break approximately 301%), a decrease of about 12%, but still at a high level, meeting the basic requirements for film flexibility in food flexible packaging. The increase in tensile strength is mainly attributed to the good dispersion and orientation of the high aspect ratio sheet-like K-mica in the EVOH matrix, which plays a role similar to a reinforcing filler, effectively transferring and dispersing tensile stress. The slight decrease in elongation at break is due to the introduction of rigid inorganic fillers, which to some extent restricts the slippage and movement freedom of the polymer molecular chains. Considering both barrier performance and mechanical properties, Example 3 achieves the best balance among various properties and is a preferred embodiment of the present invention.

[0052] To further verify the barrier performance of Example 3 under high humidity conditions, supplementary tests were conducted on the oxygen permeability of the film of Example 3 at 23°C and 90% RH. The measured OTR was 7.8 cc / (m 2 Although the concentration of ·day·atm was higher than that under dry conditions, it was still much lower than that of the pure EVOH film in Comparative Example 1 under the same high humidity conditions (28.5 cc / (m)). 2 The OTR value (day atm) decreased by approximately 73%. This comparative data fully demonstrates that the introduction of organically modified mica powder K-mica not only reduces the absolute permeability of gas molecules through the physical tortuous path effect, but also that the hydrophobic surface of K-mica and the barrier network formed in the matrix effectively inhibit the penetration and diffusion of water molecules into the EVOH matrix, reducing the degree of damage to the EVOH hydrogen bond network by water molecules. Thus, it can still maintain relatively excellent gas barrier performance in high humidity environments, which has important practical application value in the high humidity storage and cold chain transportation environments of lipid-based foods.

[0053] Example 4 (K-mica addition amount 7 wt%) (1) Preparation of organic modified mica powder: In this example, the amount of KH-570 used is 2.8 wt% of the mass of mica powder, and the other preparation steps are the same as those in Preparation Example 1.

[0054] (2) Preparation of EVOH / K-mica composite granules: Weigh the raw materials according to the mass ratio EVOH / K-mica = 93 / 7 (i.e., K-mica mass fraction is 7 wt%), and the remaining operations are the same as step (2) in Example 1. During the twin-screw extrusion process, due to the further increase in filler content, the feeding speed is appropriately adjusted to 9 kg / h to ensure that the material is fully plasticized and mixed in the extruder barrel.

[0055] (3) Blown film forming: The process parameters are the same as those in step (3) of Example 1, but the die head temperature is appropriately increased to 212℃ to appropriately reduce the viscosity of the composite melt under high filler content and ensure stable forming of the film bubble. The blow-up ratio is maintained at 3.0 and the traction speed is 10 m / min. EVOH / K-mica (7 wt%) composite blown film is obtained (Example 4), and the film thickness is controlled at 50±2 μm.

[0056] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Example 4 was tested to be 0.37 cc / (m). 2 (day atm) (23℃, 0% RH), water vapor transmission rate WVTR = 4.5 g / (m 2 (day) (38°C, 90% RH). Compared to the pure EVOH film in Comparative Example 1, the OTR decreased by approximately 54%, and the WVTR decreased by approximately 44%. The absolute values ​​of barrier performance continued to improve, but the rate of improvement slowed significantly compared to Example 3—as the addition amount increased from 5 wt% to 7 wt%, the OTR only decreased by approximately 16% (relative change), far less than the approximately 27% relative decrease in the transition from Example 2 to Example 3 (addition amount increased from 3 wt% to 5 wt%). This trend indicates that as the filler content further increases, the improvement in barrier performance begins to enter the "marginal diminishing returns" region.

[0057] In terms of mechanical properties, the tensile strength of the film in Example 4 was 71.2 MPa, which was slightly higher than that in Example 3, but the elongation at break decreased to 210%, which was about 21% lower than that in Example 3 and about 30% lower than that in Comparative Example 1 (pure EVOH). The trend of deterioration in the flexibility of the film is quite obvious, which may have adverse effects in practical packaging applications (especially in situations requiring folding, heat sealing, and drop impact).

[0058] Example 5 (K-mica addition amount 10 wt%) (1) Preparation of organic modified mica powder: In this example, the amount of KH-570 used is 3.0 wt% of the mass of mica powder, and the other preparation steps are the same as those in Preparation Example 1.

[0059] (2) Preparation of EVOH / K-mica composite granules: Weigh the raw materials according to the mass ratio EVOH / K-mica = 90 / 10 (i.e., K-mica mass fraction is 10 wt%), and the remaining operations are the same as step (2) in Example 1. During the twin-screw extrusion process, the feeding speed was further adjusted to 8 kg / h, and the die head temperature was increased to 220℃ to address the problem of significantly increased melt viscosity caused by high filler content.

[0060] (3) Blown film forming: To ensure the stability of the film bubble under high filler content, the blown film process in this embodiment was specifically adjusted based on Example 1: the die head temperature was increased to 215℃ (significantly higher than 210℃ in Comparative Example 1, the purpose of which is to reduce melt viscosity to maintain processability); the screw speed was appropriately reduced to 65 rpm; the blow-up ratio was adjusted to 2.5 (because the melt strength is reduced under high filler content, an excessively high blow-up ratio can easily lead to film bubble instability or even rupture); the traction speed was correspondingly reduced to 8 m / min to match the production volume. The stability of the resulting film bubble decreased during the forming process, and small irregular "sharkskin" textures occasionally appeared on the surface. The film transparency and appearance uniformity were reduced compared to Examples 3 and 4. The EVOH / K-mica (10 wt%) composite blown film was wound up (Example 5), and the film thickness was controlled at 50±2 μm.

[0061] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Example 5 was tested to be 0.35 cc / (m). 2 (day atm) (23℃, 0% RH), water vapor transmission rate WVTR = 3.8 g / (m 2 (day) (38°C, 90% RH). Compared to Comparative Example 1, OTR decreased by approximately 56% and WVTR decreased by approximately 52%. Although the absolute values ​​of barrier performance were the best among all examples, compared to Example 4, OTR only decreased by approximately 5.4% (relative change) and WVTR decreased by approximately 15.6% (relative change), indicating that the improvement in barrier performance has reached saturation.

[0062] In terms of mechanical properties, the tensile strength of the film in Example 5 was 73.8 MPa, while the elongation at break dropped significantly to 196%, a decrease of approximately 35% compared to Comparative Example 1. This significant reduction in elongation at break is closely related to the localized stress concentration induced by the high filler content in the matrix and the debonding effect at the filler-matrix interface. This leads to a marked decrease in the toughness and tear resistance of the film under external forces. Furthermore, a decrease in film bubble stability was observed during the blown film process in Example 5, requiring more precise control of the cooling airflow and traction tension of the air ring. The processing window was significantly narrowed, which is detrimental to process stability control in large-scale industrial continuous production.

[0063] The data from Examples 1 to 5 clearly show that introducing organically modified mica powder K-mica into the EVOH matrix can effectively improve the oxygen and water vapor barrier properties of the composite film. Within the addition range of 1–5 wt%, the improvement in barrier properties increases approximately linearly with the increase of filler content. When the addition exceeds 5 wt%, the improvement tends to plateau or even saturate, accompanied by a continuous decrease in elongation at break and deterioration in processing performance. Therefore, considering the optimal balance between barrier properties, mechanical properties, and processing performance, the preferred addition range of K-mica is 3–7 wt%, with the optimal addition being 5 wt%.

[0064] Comparative Example 2 (unmodified muscovite powder added directly, amount 5 wt%) To visually compare the necessity and technical effects of organic modification treatment, this comparative example directly uses mica powder without any surface chemical treatment as filler, and prepares composite films according to the exact same addition ratio and processing technology as in Example 3.

[0065] (1) Filler preparation: Take unmodified mica powder, whose specifications are exactly the same as those of the raw material used in Preparation Example 1 (D 50 The particles (15-20 μm in diameter and about 80 in aspect ratio) are dried in an oven at 85°C for 5 h to remove surface adsorbed water, without any coupling agent treatment.

[0066] (2) Preparation of composite granules: Weigh the dried EVOH granules and unmodified mica powder according to the mass ratio of EVOH / unmodified mica powder = 95 / 5. The remaining operation steps and twin-screw extrusion process parameters are exactly the same as step (2) in Example 3.

[0067] (3) Blown film forming: The blown film process parameters are exactly the same as those in step (3) of Example 3, and EVOH / unmodified mica powder (5 wt%) composite blown film (Comparative Example 2) is obtained, with the film thickness controlled at 50±2 μm.

[0068] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Comparative Example 2 was tested to be 0.68 cc / (m). 2 (day·atm) (23℃, 0% RH), water vapor transmission rate WVTR = 7.0 g / (m 2 (day) (38°C, 90% RH). Compared with the pure EVOH film of Comparative Example 1, the OTR was reduced by only about 15% and the WVTR was reduced by only about 12.5%. Compared with Example 3 (with the same addition of 5 wt% K-mica, the OTR was reduced by 45% and the WVTR was reduced by 36%), the barrier performance improvement effect of Comparative Example 2 was significantly inferior.

[0069] The results indicate that while unmodified mica powder possesses an advantageous flake-like morphology, its strong surface hydrophilicity and poor interfacial compatibility with the EVOH matrix make it difficult to achieve uniform nano- or micron-level dispersion during melt blending, and even more difficult to effectively align along the film plane during biaxial stretching. A large amount of unmodified mica powder exists in the matrix as agglomerates, resulting in an actual effective aspect ratio far lower than the original aspect ratio, and the tortuous path effect cannot be fully utilized. Simultaneously, the interfacial bonding between the agglomerates and the matrix is ​​weak, potentially forming tiny voids and defects. These interfacial defects themselves can become preferential permeation channels for gas molecules, offsetting to some extent the effect of the lamellar filler itself on extending the permeation path. Furthermore, the presence of agglomerates also adversely affects the optical transparency and appearance uniformity of the film; tiny white granular spots visible to the naked eye can be observed on the film surface. This comparative data strongly demonstrates that organic modification is a key step and necessary prerequisite for achieving full barrier performance of mica powder in the EVOH matrix.

[0070] Comparative Example 3 (KH-570 dosage exceeds the preferred range, with an addition amount of 5.0 wt% of the muscovite powder mass) More silane coupling agent is not necessarily better. When the amount of coupling agent is too high, excessive coupling agent molecules may form multilayer physical adsorption rather than single-layer chemical bonding on the mica powder surface, thus weakening the modification effect. To clarify the reasonable range of coupling agent dosage, this comparative example uses KH-570 at 5.0 wt% of the mica powder mass to prepare organically modified mica powder, with the remaining preparation steps being the same as in Preparation Example 1. Subsequently, composite films were prepared according to the exact same formulation (EVOH / K-mica = 95 / 5) and process conditions as in Example 3.

[0071] The oxygen permeability (OTR) of the composite film (50 μm) obtained in Comparative Example 3 was tested to be 0.55 cc / (m). 2 Water vapor transmission rate (WVTR) = 6.2 g / (m·day·atm) 2 (day). Compared with Comparative Example 1, OTR was reduced by about 31% and WVTR was reduced by about 23%. Although the barrier performance was still better than pure EVOH, it showed a significant decline compared with Example 3 (OTR reduced by 45% and WVTR reduced by 36%).

[0072] FTIR analysis showed that the K-mica prepared in Comparative Example 3 was at 1720 cm⁻¹ -1 A distinct shoulder peak signal appeared nearby, which is attributed to the physical adsorption state characteristic absorption of the C=O group in excess KH-570, and mainly exhibits the chemically bonded state characteristic peak (1715 cm⁻¹) as in Example 3. -1The difference in concentration (single sharp peak nearby) indicates a significant difference. This suggests that excessive coupling agent did not further increase the effective chemical grafting amount; instead, it formed a physically adsorbed layer on the mica powder surface through weak interactions such as hydrogen bonds or van der Waals forces. During subsequent melt blending, these physically adsorbed coupling agent molecules are prone to desorption or migration under high temperatures (above 200°C) and high shear forces, forming a weak boundary layer enriched with low molecular weight substances at the filler-matrix interface, which weakens the interfacial bonding strength. Simultaneously, unreacted small molecules of coupling agent remaining at the interface may gradually migrate to the surface during film use, posing a potential risk to food contact safety. The data from this comparative example show that the amount of KH-570 should not be too high; the preferred range of 1.5–3.0 wt% of the mica powder mass is experimentally supported.

[0073] Table 1 Summary of the main properties of the films in each embodiment and comparative example Note: Example 3 is a preferred embodiment of the present invention. OTR test conditions: 23℃, 0% RH; WVTR test conditions: 38℃, 90% RH; all film thicknesses were 50±2 μm. "—" indicates not applicable or not measured. The percentages in the KH-570 dosage column refer to the percentage of KH-570 mass to muscovite powder mass.

[0074] As can be clearly seen from Table 1, with the increase of the amount of organically modified mica powder K-mica added, the oxygen permeability and water vapor permeability of the composite film both showed a gradual decreasing trend. At an addition amount of 5 wt% (Example 3), the best balance between the improvement of barrier performance and the maintenance of mechanical properties was achieved. After exceeding 7 wt%, the improvement of barrier performance tended to saturate, and the elongation at break decreased significantly. The barrier performance improvement effect of unmodified mica powder (Comparative Example 2) was far inferior to that of organically modified K-mica (Example 3) at the same addition amount. Excessive use of coupling agent (Comparative Example 3) actually led to a decrease in barrier performance.

[0075] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An EVOH / organically modified mica powder high barrier composite blown film, characterized by, It is prepared from the following components in parts by weight: 90-99 parts of ethylene-vinyl alcohol copolymer (EVOH); 1-10 parts of organically modified mica powder; The ethylene-vinyl alcohol copolymer is blow-molding grade, with an ethylene molar content of 32-44 mol%; the organic modified mica powder is prepared by surface modification treatment of muscovite powder with a silane coupling agent.

2. The EVOH / organically modified mica powder high-barrier composite blown film according to claim 1, characterized in that, D 50 particle size of 10-30 μm, and a ratio of diameter to thickness of not less than 50; and the silane coupling agent is γ-methacryloxypropyltrimethoxysilane, and the amount of the silane coupling agent is 1.5-3.0 wt% of the mass of the white mica powder.

3. The EVOH / organically modified mica powder high-barrier composite blown film according to claim 1, characterized in that, The amount of organically modified mica powder added is 3 to 7 parts by weight.

4. The EVOH / organically modified mica powder high-barrier composite blown film according to claim 1, characterized in that, The amount of organically modified mica powder added is 5 parts by weight.

5. The EVOH / organically modified mica powder high-barrier composite blown film according to any one of claims 1 to 4, characterized in that, The melt index of the ethylene-vinyl alcohol copolymer is 3 to 8 g / 10 min at 190°C and 2160 g load.

6. A method for preparing a high-barrier composite blown film of EVOH / organically modified mica powder according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step (1) Preparation of organic modified mica powder: After drying the white mica powder, add it to an alcohol-water solution containing silane coupling agent KH-570, stir at 80-90℃ for 2-3 h, filter, wash, dry, grind and sieve to obtain organic modified mica powder. Step (2) Melt blending and granulation: After the dried EVOH and the organic modified mica powder obtained in step (1) are premixed evenly according to the ratio, they are melt blended by a twin-screw extruder and extruded and granulated to obtain composite granules; Step (3) Blown film forming: The composite material granules obtained in step (2) are blown into film by a blown film machine, and the blow-up ratio is controlled to be 2.5 to 3.

5. After cooling and shaping, and winding, the composite blown film is obtained.

7. The preparation method according to claim 6, characterized in that, The alcohol-water solution mentioned in step (1) is a mixed solution of ethanol and water, with a volume ratio of ethanol to water of 95:5; the concentration of KH-570 is 1 to 3 wt%; and the drying is carried out at 100 to 110°C until constant weight.

8. The preparation method according to claim 6, characterized in that, The temperature settings for each zone of the twin-screw extruder in step (2) are as follows: feeding zone 180℃, melting zone 190~200℃, mixing zone 195~210℃, discharge zone 200~215℃, die head temperature 210~220℃; screw speed 120~150 rpm; feeding speed 8~12 kg / h.

9. The preparation method according to claim 6, characterized in that, The temperature settings for each zone of the blown film unit in step (3) are as follows: 185℃ for the extruder feeding section, 195~205℃ for the melting section, 200~210℃ for the homogenization section, and 205~215℃ for the die head; the screw speed is 60~90 rpm; the traction speed is 8~15 m / min; and the die gap is 0.8~1.2 mm.

10. The application of the EVOH / organically modified mica powder high-barrier composite blown film according to any one of claims 1 to 5 in the packaging of lipid-based foods, wherein the lipid-based foods include meat products, nuts, oils and fats and fatty cooked foods.

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