Barrier PVC material, PVC hard sheet and preparation method and application thereof

Abstract

This invention belongs to the technical field of barrier packaging materials, and discloses a barrier PVC material, PVC rigid sheets, their preparation method, and applications. The barrier PVC material comprises, by weight, 100 parts PVC resin, 6-8 parts redispersible composite barrier agent, 3-5 parts impact modifier, 1-2 parts epoxidized soybean oil, and 1-1.5 parts heat stabilizer. Cellulose nanofibers and magnesium aluminum hydrotalcite are dispersed in a slurry formed by oxidized polyethylene wax and a silane coupling agent, exhibiting hot-melt redispersibility. The steric hindrance effect of oxidized polyethylene wax modifying the cellulose nanofibers prevents their aggregation, and the ethylene-acrylic acid copolymer modifying the cellulose nanofibers overcomes the problem of water absorption and swelling. The redispersible composite barrier agent added to the PVC resin exhibits excellent hot-melt redispersibility, forming a synergistic barrier in the prepared PVC rigid sheets, suitable for use in pharmaceutical blister packaging.

Description

Technical Field

[0001] This invention relates to the field of barrier packaging materials technology, specifically to a barrier PVC material, PVC rigid sheet, its preparation method, and its application. Background Technology

[0002] PVC (polyvinyl chloride) material possesses excellent thermoforming, plasticity, rigidity, and thermal adhesion, making rigid PVC sheets suitable for blister packaging. Blister packaging formed from rigid PVC sheets is widely used in the individual packaging of solid pharmaceuticals such as tablets and capsules. However, due to the strong polarity of PVC, the molecular chain regularity is poor, making it difficult to form regular and ordered crystalline regions. This results in numerous microscopic voids within the material, limiting its barrier properties against water vapor and oxygen. Pharmaceutical packaging made solely from rigid PVC sheets does not meet the national standards for the packaging industry (water vapor transmission ≤ 2.5 g / (m²)). 2 • 24h), oxygen permeability ≤30cm 3 / (m 2 (24h, 0.1MPa). Especially for the packaging of drugs that are sensitive to high humidity and oxygen, the barrier properties of PVC rigid sheets are required to be even higher.

[0003] Existing technologies for improving the barrier properties of rigid PVC sheets mainly include: multilayer lamination, coating with barrier layers, blending with barrier resins, and adding two-dimensional layered inorganic powders. Examples include multilayer co-extrusion lamination of PVC and EVOH, and coating rigid PVC sheets with a PVDC (polyvinylidene chloride) barrier coating. Multilayer lamination and coating with barrier layers are the most effective technologies, significantly improving the water vapor and oxygen barrier properties of rigid PVC sheets. However, these methods also make the production process more complex, requiring sophisticated equipment and demanding processes.

[0004] Adding barrier-resistant resins such as PVDC, EVOH, PVA, or two-dimensional inorganic powders directly to PVC through blending and extrusion significantly improves the barrier properties against oxygen and water vapor. Compared to multilayer co-extrusion or coating processes, this reduces the requirements for production equipment and simplifies the production process. Domestically published technologies include: Invention patent CN111117110B, which discloses a method and product for preparing a PVC film with both wear resistance and barrier properties, using high aspect ratio and high hardness nano-sheet alumina as a functional filler. The nano-sheet alumina increases the gas permeation path, improving the gas barrier performance of the PVC film; Invention patent CN109810428A, which discloses a pharmaceutical-grade PVC rigid sheet and its production process, using a blend system of PVC, EVOH, and PE-g-MAH to increase the barrier properties of the PVC rigid sheet; and Invention patent CN110746723A, which discloses a high-barrier PVC sheet and its preparation method, improving the barrier properties of the PVC blend material against oxygen and water through co-extrusion of PVC, PVA, EVOH, PA, and mica.

[0005] While improving the barrier properties of rigid PVC sheets through direct blending is a simple process, it has faced significant challenges and has not yet been mass-produced. The main reasons are twofold: First, phase separation easily occurs during the melt processing of PVC and barrier resins, leading to interfacial porosity. PVDC has good barrier properties, but its softening and decomposition temperatures are close during heat processing, making it difficult to process and prone to decomposition. PVA and EVOH have excellent barrier properties, but poor thermoplasticity and water resistance, and their strength decreases significantly after moisture absorption. Second, when adding two-dimensional inorganic powders to PVC to improve barrier properties, the gas diffusion path is extended by completely peeling and dispersing the layered materials, thus requiring high precision in the peeling and directional arrangement of the layered inorganic materials. Rigid PVC, due to its low plasticizer content, high melt viscosity, and poor wettability, faces difficulties in dispersing layered inorganic materials and is prone to re-agglomeration. Once agglomeration occurs, it leads to defective porosity, affecting barrier properties, strength, transparency, and thermal tack. Summary of the Invention

[0006] To address the problems of poor dispersion, interfacial porosity, reduced strength, and decreased transparency in current blending methods for improving the barrier properties of rigid PVC sheets, this invention aims to improve the barrier function by modifying and dispersing cellulose nanofibers and hydrotalcite to form a redispersible composite barrier agent. This enhances the compatibility and dispersibility of the agent in PVC, significantly improving its barrier properties against water vapor and oxygen. Furthermore, this invention proposes a barrier-resistant PVC material, rigid PVC sheets, their preparation method, and applications.

[0007] To achieve the above objectives, in a first aspect, this application provides a barrier PVC material, the composition of which by weight includes: 100 parts of PVC resin, 6-8 parts of redispersible composite barrier agent, 3-5 parts of impact modifier, 1-2 parts of epoxidized soybean oil, and 1-1.5 parts of heat stabilizer. The redispersible composite barrier agent is composed of cellulose nanofibers, magnesium aluminum hydrotalcite, oxidized polyethylene wax, silane coupling agent, and ethylene-acrylic acid copolymer in a mass ratio of (0.5-1):(1-1.5):(2-3):(0.05-0.08):(3-4); The redispersible composite barrier agent is prepared by the following method: First, the oxidized polyethylene wax is completely melted, and then silane coupling agent, cellulose nanofibers, and magnesium aluminum hydrotalcite are added and dispersed into a slurry by high-speed stirring. It is then cold-mixed with ethylene-acrylic acid copolymer, and added to a parallel twin-screw extruder for melt extrusion granulation to obtain a redispersible composite barrier agent.

[0008] This invention disperses cellulose nanofibers and magnesium-aluminum hydrotalcite in hot-melt oxidized polyethylene wax in a slurry form; it is then blended and modified with ethylene-acrylic acid copolymer and granulated to obtain a redispersible composite barrier agent. This not only improves the dispersibility of cellulose nanofibers and magnesium-aluminum hydrotalcite, but also allows for easy melting at relatively low heating temperatures, resulting in low melt flow resistance and facilitating melt redispersibility. When added to PVC resin for hot-melt extrusion to prepare rigid PVC sheets, it provides rapid melt redispersibility.

[0009] Cellulose nanofibers possess a high aspect ratio, good transparency, and reinforcing properties. When uniformly dispersed, they easily form an impermeable barrier, preventing water and gas from directly passing through and forcing them to bypass the fiber surface. This significantly increases the effective diffusion distance of water vapor and oxygen, thereby reducing permeability. However, cellulose nanofibers are difficult to disperse and typically require preparation as a suspension for use, as they cannot be directly heat-melted. This invention disperses cellulose nanofibers in hot-melt oxidized polyethylene wax. A significant amount of oxidized polyethylene wax causes the cellulose nanofibers and magnesium aluminum hydrotalcite to disperse in a slurry-like form. Oxidized polyethylene wax exhibits excellent compatibility with PVC. After modification, the hydrophobic groups of the oxidized polyethylene wax create a steric hindrance effect that prevents the cellulose nanofibers from agglomerating, improving dispersion stability in PVC and effectively extending the diffusion path of gases and water vapor. The acrylic acid in the ethylene-acrylic acid copolymer provides polar groups, modifying the hydroxyl groups of the cellulose nanofibers, while the ethylene segments retain hydrophobicity. This effectively avoids the problem of the hydrophilic hydroxyl groups of cellulose nanofibers easily absorbing water and swelling in high-humidity environments, leading to a decrease in barrier properties. Furthermore, it improves thermal adhesion in rigid PVC sheets.

[0010] Magnesium aluminum hydrotalcite is a layered double hydroxide. It forms a hot melt slurry dispersion with oxidized polyethylene wax and silane coupling agent, which greatly improves its compatibility and dispersibility in PVC. It forms a layer to block the diffusion of small molecules such as oxygen and water vapor, significantly prolonging the permeation path and reducing the permeability.

[0011] Preferably, the cellulose nanofibers have a diameter of 1-100 nm and a length of 1-5 μm.

[0012] Preferably, the particle size of the magnesium aluminum hydrotalcite is <2μm.

[0013] Preferably, the acrylic acid content of the ethylene-acrylic acid copolymer is 8-12%.

[0014] Preferably, the silane coupling agent is one of KH-550 or KH-560. The silane coupling agent modifies cellulose nanofibers and magnesium aluminum hydrotalcite, enhancing their dispersibility and interfacial adhesion with PVC, and can effectively eliminate micropores caused by interfacial defects.

[0015] Preferably, the PVC resin is a medical-grade suspension PVC resin with an average degree of polymerization of 1000-1100, a viscosity of 107-118 mL / g, and a residual vinyl chloride monomer content of ≤1 ppm.

[0016] Preferably, the impact modifier is at least one of methyl methacrylate-butadiene-styrene copolymer (MBS) and acrylate core-shell polymer (ACR). More preferably, the impact modifier is methyl methacrylate-butadiene-styrene copolymer (MBS), which has a smaller impact on the transparency of PVC rigid sheets.

[0017] PVC resin molecules have structural defects that cause them to release hydrogen chloride when heated above 120°C, accelerating PVC decomposition. Epoxidized soybean oil and heat stabilizers can effectively prevent thermal degradation of PVC during processing. Epoxidized soybean oil, used in PVC processing, can promptly capture the released hydrogen chloride, interrupting the degradation chain reaction and increasing thermal stability. Furthermore, epoxidized soybean oil can wedge itself into the PVC molecular chains, giving PVC good processing plasticity and preventing migration and exudation, making it suitable for pharmaceutical packaging.

[0018] Preferably, the heat stabilizer is an organotin heat stabilizer or a calcium-zinc composite stabilizer. The organotin heat stabilizer is at least one of methyltin mercaptan or octyltin mercaptan, which achieves PVC thermal stability by absorbing hydrogen chloride and displacing unstable chlorine atoms to block the degradation chain reaction of PVC. The calcium-zinc composite stabilizer is a commercially available medical-grade calcium-zinc composite stabilizer.

[0019] Secondly, this application provides a PVC rigid sheet, which is prepared from the above-mentioned barrier PVC material.

[0020] Thirdly, this application provides a method for preparing the above-mentioned rigid PVC sheet. The specific preparation process is as follows: after mixing the barrier PVC material, it is added to a conical twin-screw extruder for melt extrusion, then fed into a two-roll mill for compounding and sheeting, and finally calendered by a four-roll calender, cooled and shaped, trimmed, and wound to obtain a rigid PVC sheet.

[0021] Preferably, the conical twin-screw extruder is an anti-rotating conical twin-screw extruder with extrusion temperatures of: Zone 1 150-160℃, Zone 2 170-180℃, Zone 3 170-180℃, Zone 4 180-185℃, and Zone 5 180-185℃. The anti-rotating conical twin-screw extruder provides efficient plasticization, low shear force, and stable feeding, thus avoiding thermal shear degradation of PVC.

[0022] Preferably, the temperatures of each roll of the four-roll calender are: 160-165℃ for the first roll, 170-175℃ for the second roll, 190-195℃ for the third roll, and 180-185℃ for the fourth roll.

[0023] Preferably, the thickness of the PVC rigid sheet is 0.2-0.4 mm.

[0024] Fourthly, this application provides the application of the aforementioned PVC rigid sheet in pharmaceutical blister packaging.

[0025] Compared with existing technologies, the technical advantages of this invention are reflected in: (1) In this invention, cellulose nanofibers and magnesium aluminum hydrotalcite are dispersed in oxidized polyethylene wax and silane coupling agent in a slurry, and then sheared and extruded with ethylene-acrylic acid copolymer to obtain a redispersible composite barrier agent. It is easy to be redispersed by hot melting. When added to PVC resin, it has excellent dispersibility and compatibility. The cellulose nanofibers and magnesium aluminum hydrotalcite in the prepared PVC rigid sheet are uniformly dispersed to form a synergistic barrier to block the diffusion of gas and water vapor, which is suitable for use in pharmaceutical blister packaging.

[0026] (2) The pre-dispersed cellulose nanofibers of the present invention have transparency and reinforcement properties, and the prepared PVC rigid sheets maintain high transparency and tensile strength, avoiding the impact of the addition of impact modifiers on tensile strength.

[0027] (3) The composite barrier agent of the present invention uses ethylene-acrylic acid copolymer. Acrylic acid, as a polar group, modifies the hydroxyl groups of cellulose nanofibers. The vinyl groups are hydrophobic, which overcomes the problem of water absorption and swelling of cellulose nanofibers leading to a decrease in barrier properties. The ethylene-acrylic acid copolymer improves the thermal adhesion in PVC rigid sheets, and the aluminum foil and PVC blister are more firmly bonded by hot pressing during use.

[0028] (4) This invention simplifies the complex processes of multi-layer composite and coating, and reduces the production cost of PVC rigid sheets by directly blending them on existing PVC sheet calendering production lines. Detailed Implementation

[0029] To more clearly illustrate the technical solution of the present invention, the following embodiments and comparative examples are provided. Unless otherwise stated, the raw materials used are commercially available. Unless specifically stated otherwise, the equipment and process terms involved are technical means understood and well-known to those skilled in the art.

[0030] The material types used in the embodiments and comparative examples of this invention are as follows: PVC resin: M-1000, vinyl chloride monomer residue ≤0.4ppm, medical grade PVC resin, Shanghai Chlor-Alkali Chemical Co., Ltd.

[0031] Impact modifier MBS: Methyl methacrylate-butadiene-styrene copolymer Kane Ace® PA20, Kaneka Chemical.

[0032] Impact modifier ACR: acrylate core-shell polymer Kane Ace® M-577, Kaneka Chemical.

[0033] Calcium-zinc composite stabilizer: HCZ1083S, Zhejiang Haipton New Material Co., Ltd.

[0034] Ethylene-acrylic acid copolymer: Primacor® 3440, 9.7% acrylic acid content, Dow Chemical.

[0035] Example 1 (a) Weight composition of barrier PVC material: PVC resin: 100 parts; Redispersible composite barrier agent: 6 parts; Impact modifier MBS: 3 parts Epoxidized soybean oil: 1 part; Calcium-zinc compound stabilizer: 1.5 parts; The redispersible composite barrier agent is prepared by the following method: 25 kg of oxidized polyethylene wax was heated to 110 °C and completely melted. Then, 0.5 kg of silane coupling agent KH-550, 8 kg of cellulose nanofibers (diameter 1-100 nm, length 1-5 μm), and 10 kg of magnesium aluminum hydrotalcite (particle size < 2 μm) were added and dispersed for 30 minutes under high-speed stirring at 800 rpm to form a uniform slurry. After cooling and crushing, the slurry was mixed evenly with 30 kg of ethylene-acrylic acid copolymer and then melt-extruded into granules using a parallel twin-screw extruder. The temperature was set at 60 °C for the first stage, 90 °C for the second stage, 100 °C for the third stage, 80 °C for the fourth stage, and 70 °C for the fifth stage to obtain a redispersible composite barrier agent.

[0036] (II) Preparation of rigid PVC sheets: After the barrier PVC material is mixed evenly, it is fed into an anti-rotating conical twin-screw extruder for melt extrusion at temperatures of 150°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 180°C in zone 5. The material is then piled up to a two-roll mill for mixing and feeding into sheets, which are then calendered in a four-roll calender at temperatures of 165°C in zone 1, 170°C in zone 2, 190°C in zone 3, and 180°C in zone 4. After cooling and shaping, the sheets are trimmed and rolled up to obtain a PVC rigid sheet with a thickness of 0.25 mm.

[0037] Example 2 (a) Weight composition of barrier PVC material: PVC resin: 100 parts; Redispersible composite barrier agent: 8 parts; Impact modifier ACR: 3 parts Epoxidized soybean oil: 2 parts; Octylthiol Tin: 1 part; The redispersible composite barrier agent is prepared by the following method: 30 kg of oxidized polyethylene wax was heated to 110 °C and completely melted. Then, 0.8 kg of silane coupling agent KH-560, 10 kg of cellulose nanofibers (diameter 1-100 nm, length 1-5 μm), and 10 kg of magnesium aluminum hydrotalcite (particle size < 2 μm) were added and dispersed for 40 minutes under high-speed stirring at 800 rpm to form a uniform slurry. After cooling and crushing, the slurry was mixed evenly with 40 kg of ethylene-acrylic acid copolymer and then melt-extruded into granules using a parallel twin-screw extruder. The temperature was adjusted as follows: first stage 60 °C, second stage 90 °C, third stage 110 °C, fourth stage 90 °C, and fifth stage 80 °C to obtain a redispersible composite barrier agent.

[0038] (II) Preparation of rigid PVC sheets: After the barrier PVC material is mixed evenly, it is fed into an anti-rotating conical twin-screw extruder for melt extrusion at 160°C in zone 1, 180°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 185°C in zone 5. The material is then piled up to a two-roll mill for mixing and feeding into sheets, which are then calendered in a four-roll calender at 160°C in zone 1, 170°C in zone 2, 195°C in zone 3, and 185°C in zone 4. After cooling and shaping, the sheets are trimmed and wound up to obtain a PVC rigid sheet with a thickness of 0.25 mm.

[0039] Comparative Example 1 (a) Weight composition of barrier PVC material: PVC resin: 100 parts; Impact modifier MBS: 3 parts Epoxidized soybean oil: 1 part; Calcium-zinc compound stabilizer: 1.5 parts; (II) Preparation of rigid PVC sheets: After the barrier PVC material is mixed evenly, it is fed into an anti-rotating conical twin-screw extruder for melt extrusion at temperatures of 150°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 180°C in zone 5. The material is then piled up to a two-roll mill for mixing and feeding into sheets, which are then calendered in a four-roll calender at temperatures of 165°C in zone 1, 170°C in zone 2, 190°C in zone 3, and 180°C in zone 4. After cooling and shaping, the sheets are trimmed and rolled up to obtain a PVC rigid sheet with a thickness of 0.25 mm.

[0040] Comparative Example 2 (a) Weight composition of barrier PVC material: PVC resin: 100 parts; Composite barrier agent: 1.5 parts; Impact modifier MBS: 3 parts Epoxidized soybean oil: 1 part; Calcium-zinc compound stabilizer: 1.5 parts; The composite barrier agent was prepared by the following method: 0.5 kg of silane coupling agent KH-550, 8 kg of cellulose nanofibers (diameter 1-100 nm, length 1-5 μm), and 10 kg of magnesium aluminum hydrotalcite (particle size < 2 μm) were dispersed at high speed of 800 rpm for 30 minutes to obtain a composite barrier agent.

[0041] (II) Preparation of rigid PVC sheets: After the barrier PVC material is mixed evenly, it is fed into an anti-rotating conical twin-screw extruder for melt extrusion at temperatures of 150°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 180°C in zone 5. The material is then piled up to a two-roll mill for mixing and feeding into sheets, which are then calendered in a four-roll calender at temperatures of 165°C in zone 1, 170°C in zone 2, 190°C in zone 3, and 180°C in zone 4. After cooling and shaping, the sheets are trimmed and rolled up to obtain a PVC rigid sheet with a thickness of 0.25 mm.

[0042] Comparative Example 3 (a) Weight composition of barrier PVC material: PVC resin: 100 parts; Redispersible composite barrier agent: 3.56 parts; Impact modifier MBS: 3 parts Epoxidized soybean oil: 1 part; Calcium-zinc compound stabilizer: 1.5 parts; The redispersible composite barrier agent is prepared by the following method: 25 kg of oxidized polyethylene wax was heated to 110 °C and completely melted. Then, 0.5 kg of silane coupling agent KH-550, 8 kg of cellulose nanofibers (diameter 1-100 nm, length 1-5 μm), and 10 kg of magnesium aluminum hydrotalcite (particle size < 2 μm) were added and dispersed for 30 minutes under high-speed stirring at 800 rpm to form a uniform slurry. The slurry was discharged, cooled, and crushed to obtain a redispersible composite barrier agent.

[0043] (II) Preparation of rigid PVC sheets: After the barrier PVC material is mixed evenly, it is fed into an anti-rotating conical twin-screw extruder for melt extrusion at temperatures of 150°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 180°C in zone 5. The material is then piled up to a two-roll mill for mixing and feeding into sheets, which are then calendered in a four-roll calender at temperatures of 165°C in zone 1, 170°C in zone 2, 190°C in zone 3, and 180°C in zone 4. After cooling and shaping, the sheets are trimmed and rolled up to obtain a PVC rigid sheet with a thickness of 0.25 mm.

[0044] Comparative Example 4 (a) Weight composition of barrier PVC material: PVC resin: 100 parts; Redispersible composite barrier agent: 3.96 parts; Impact modifier MBS: 3 parts Epoxidized soybean oil: 1 part; Calcium-zinc compound stabilizer: 1.5 parts; The redispersible composite barrier agent is prepared by the following method: 0.5 kg of silane coupling agent KH-550, 8 kg of cellulose nanofibers (diameter 1-100 nm, length 1-5 μm), and 10 kg of magnesium aluminum hydrotalcite (particle size < 2 μm) were dispersed at high speed of 800 rpm for 30 minutes. The mixture was then cold-mixed with 30 kg of ethylene-acrylic acid copolymer and added to a parallel twin-screw extruder for melt extrusion granulation. The temperature was set at 60℃ in the first stage, 90℃ in the second stage, 100℃ in the third stage, 80℃ in the fourth stage, and 70℃ in the fifth stage to obtain a redispersible composite barrier agent.

[0045] (II) Preparation of rigid PVC sheets: After the barrier PVC material is mixed evenly, it is fed into an anti-rotating conical twin-screw extruder for melt extrusion at temperatures of 150°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 180°C in zone 5. The material is then piled up to a two-roll mill for mixing and feeding into sheets, which are then calendered in a four-roll calender at temperatures of 165°C in zone 1, 170°C in zone 2, 190°C in zone 3, and 180°C in zone 4. After cooling and shaping, the sheets are trimmed and rolled up to obtain a PVC rigid sheet with a thickness of 0.25 mm.

[0046] Test case Referring to YBB 00212005-2015 "Polyvinyl Chloride Solid Pharmaceutical Rigid Sheets", the technical requirements for PVC rigid sheets used in blister packaging of solid pharmaceuticals (tablets, capsules) are: water vapor transmission rate ≤ 2.5 g / (m²). 2 • 24h), oxygen permeability ≤30cm 3 / (m 2 • 24h • 0.1MPa) 、 Tensile strength ≥ 44MPa.

[0047] Comparative tests were conducted on the PVC rigid sheets of Examples 1-2 and Comparative Examples 1-4, focusing on water vapor and oxygen transmission, light transmittance, and tensile strength. Water vapor transmission was measured at 23°C and 90% relative humidity using the cup method (method one) of the Water Vapor Transmission Measurement Method (YBB 00092003-2015). Oxygen transmission at 23°C and 50% relative humidity was measured using the first method (differential pressure method) of the Gas Transmission Measurement Method (YBB 00082003-2015). Light transmittance was tested according to GB / T2410-2008. The prepared PVC rigid sheets were tested for tensile strength using the Tensile Properties Test Method (YBB 00112003-2015), Type I sample, at a tensile rate of 100 mm / min. The test data are shown in Table 1.

[0048] Table 1: Barrier Performance, Light Transmittance, and Tensile Strength Tests for Rigid PVC Sheets From the data in Table 1: The PVC rigid sheet in Comparative Example 1 did not use a redispersible composite barrier agent, had good transparency, average strength, and high water vapor and oxygen permeability, failing to meet the packaging requirements of "Polyvinyl Chloride Solid Pharmaceutical Rigid Sheets".

[0049] In Comparative Example 2, cellulose nanofibers and magnesium-aluminum hydrotalcite were treated without the addition of ethylene-acrylic acid copolymer and oxidized polyethylene wax; instead, a silane coupling agent was used for dispersion. This resulted in poor redispersibility, and the cellulose nanofibers exhibited poor dispersibility, hydrophobicity, and compatibility. Consequently, the cellulose nanofibers failed to provide barrier or reinforcement functions in PVC, instead increasing interfacial gaps and leading to uncontrolled oxygen and water barrier properties.

[0050] In Comparative Example 3, no ethylene-acrylic acid copolymer was added when cellulose nanofibers were treated. The cellulose nanofibers were hygroscopic, and the water vapor permeability increased significantly.

[0051] In Comparative Example 4, no oxidized polyethylene wax was added during the treatment of cellulose nanofibers. This resulted in poor redispersion of the cellulose nanofibers in the PVC rigid sheet, and significant differences in the compatibility interface affected the sheet's transparency. The cellulose nanofibers failed to construct a continuous barrier, leading to higher permeability of water vapor and oxygen.

[0052] This invention disperses cellulose nanofibers and magnesium-aluminum hydrotalcite in a slurry with oxidized polyethylene wax and a silane coupling agent, then shears and extrudes them with an ethylene-acrylic acid copolymer to obtain a redispersible composite barrier agent. The hot-melt redispersibility is significant, forming a synergistic barrier against gas and water vapor diffusion within PVC resin. The resulting PVC rigid sheet exhibits water and oxygen barrier properties far exceeding the technical standards of the "Polyvinyl Chloride Solid Pharmaceutical Rigid Sheet"; it approaches the water and oxygen barrier requirements (water vapor permeability ≤ 0.8 g / (m³)) of the multi-layer composite coating process used in "Polyvinyl Chloride / Polyethylene / Polyvinylidene Chloride Solid Pharmaceutical Composite Rigid Sheet". 2 • 24h), oxygen permeability ≤ 3cm 3 / (m 2 (24h·0.1MPa), tensile strength ≥40MPa). Moreover, while improving barrier properties, the transparency and tensile strength of PVC rigid sheets are not significantly affected.

[0053] It should be noted that the above embodiments have been described in detail with reference to preferred solutions. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this application.

Claims

1. A barrier PVC material, characterized in that, The barrier PVC material comprises, by weight: 100 parts PVC resin, 6-8 parts redispersible composite barrier agent, 3-5 parts impact modifier, 1-2 parts epoxidized soybean oil, and 1-1.5 parts heat stabilizer. The redispersible composite barrier agent is composed of cellulose nanofibers, magnesium aluminum hydrotalcite, oxidized polyethylene wax, silane coupling agent, and ethylene-acrylic acid copolymer in a mass ratio of (0.5-1):(1-1.5):(2-3):(0.05-0.08):(3-4); The redispersible composite barrier agent is prepared by the following method: First, the oxidized polyethylene wax is completely melted, and then silane coupling agent, cellulose nanofibers, and magnesium aluminum hydrotalcite are added and dispersed into a slurry by high-speed stirring. It is then cold-mixed with ethylene-acrylic acid copolymer, and added to a parallel twin-screw extruder for melt extrusion granulation to obtain a redispersible composite barrier agent.

2. The barrier PVC material according to claim 1, characterized in that, The cellulose nanofibers have a diameter of 1-100 nm and a length of 1-5 μm; the magnesium aluminum hydrotalcite has a particle size of <2 μm; the ethylene-acrylic acid copolymer has an acrylic acid content of 8-12%; and the silane coupling agent is either KH-550 or KH-560.

3. The barrier PVC material according to claim 1, characterized in that, The PVC resin selected is a suspension PVC resin with an average degree of polymerization of 1000-1100, a viscosity of 107-118 mL / g, and a residual vinyl chloride monomer content of ≤1 ppm.

4. The barrier PVC material according to claim 1, characterized in that, The impact modifier is at least one of methyl methacrylate-butadiene-styrene copolymer and acrylate core-shell polymer.

5. The barrier PVC material according to claim 1, characterized in that, The heat stabilizer is selected from organotin heat stabilizers or calcium-zinc composite stabilizers.

6. A rigid PVC sheet, characterized in that, The PVC rigid sheet is prepared from the barrier PVC material according to any one of claims 1-5.

7. A method for preparing a PVC rigid sheet as described in claim 6, characterized in that, The specific method is as follows: After the barrier PVC material is mixed evenly, it is fed into a conical twin-screw extruder for melt extrusion. The material is then fed into a sheet by a two-roll mill, calendered by a four-roll calender, cooled and shaped, trimmed, and wound to obtain a rigid PVC sheet.

8. The method for preparing PVC rigid sheets according to claim 7, characterized in that, The conical twin-screw extruder is an anti-rotating conical twin-screw extruder with extrusion temperatures of: Zone 1 150-160℃, Zone 2 170-180℃, Zone 3 170-180℃, Zone 4 180-185℃, and Zone 5 180-185℃.

9. The method for preparing PVC rigid sheets according to claim 7, characterized in that, The temperatures of each roll of the four-roll calender are: 160-165℃ for the first roll, 170-175℃ for the second roll, 190-195℃ for the third roll, and 180-185℃ for the fourth roll.

10. The application of the PVC rigid sheet as described in claim 6 in pharmaceutical blister packaging.

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