Sheet having modified polyvinyl alcohol, method of preparation and use

Abstract

This invention discloses a sheet material with modified polyvinyl alcohol, its preparation method, and its application, relating to the field of packaging materials technology. The modified polyvinyl alcohol comprises a polyvinyl alcohol matrix with a degree of hydrolysis of 70%–99% and a degree of polymerization of 500–3000, an epoxy-based polyol with a number-average molecular weight (Mn) of 300–5000 g / mol and an epoxy value of 0.2–2.0 eq / 100 g, and an epoxy group polyol with a particle size of 20–100 nm and a specific surface area (S) of 50–400 m². 2 / g of silanized nanofiller; wherein the epoxy groups undergo a ring-opening reaction with the hydroxyl groups of polyvinyl alcohol in the range of 60℃~130℃ to form a cross-linked network connected by ether bonds, and the silanized nanofiller is uniformly dispersed in this network. The preparation method includes steps such as dissolving polyvinyl alcohol, adding epoxy polyol for mixing, adding filler in batches for dispersion, and adding additives. The modified polyvinyl alcohol shown in this invention has good barrier properties and is suitable for the preparation of composite sheets.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to a sheet containing modified polyvinyl alcohol, its preparation method, and its application. Background Technology

[0002] In the packaging materials industry, composite sheets are widely used in soft tube packaging for cosmetics, pharmaceuticals, and food. Traditional composite structures are mostly made of plastic and aluminum foil laminations. While these materials possess certain barrier properties and mechanical strength, their multi-layered heterogeneous material composites make effective separation and recycling difficult. Therefore, recyclable soft tubes often refer to single-material plastic extrusion tubes, but their barrier properties are often insufficient. Although aluminum-plastic sheets are theoretically recyclable, in practice, recycling systems are imperfect, sorting costs are high, and the regeneration process causes serious pollution.

[0003] To replace traditional aluminum-plastic composites, researchers have begun to focus on high-barrier, recyclable, or biodegradable polymer materials. Among these, polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH) are two promising barrier materials. PVA is a water-soluble polymer obtained from the alcoholysis of polyvinyl acetate. Its molecular chain contains a large number of hydroxyl groups, exhibiting good film-forming properties, gas barrier properties, and biodegradability. EVOH, on the other hand, is a copolymer of ethylene and vinyl alcohol, prepared by copolymerizing ethylene with vinyl acetate followed by hydrolysis. Its molecules contain both hydrophobic ethylene segments and hydrophilic vinyl alcohol segments. While not as robust as aluminum foil, both still possess good processability and barrier properties.

[0004] Despite their outstanding barrier properties, PVA and EVOH still have some limitations in their applications. PVA has poor water resistance, and its barrier performance drops sharply in high humidity environments; although EVOH has low humidity sensitivity, its oxygen barrier properties also decrease under high humidity conditions, and its cost is relatively high, requiring stringent processing conditions; these limitations restrict their application in flexible tube packaging.

[0005] Therefore, it is necessary to optimize the barrier properties of polyvinyl alcohol materials and expand their water-blocking performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and solve the technical problem of insufficient water-blocking performance of existing polyvinyl alcohol materials.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows.

[0008] In a first aspect, the present invention provides a sheet having modified polyvinyl alcohol, said modified polyvinyl alcohol comprising: Polyvinyl alcohol matrix, with a degree of alcoholysis of 70% to 99% and a degree of polymerization of 500 to 3000; Epoxy polyols with a number-average molecular weight (Mn) of 300-5000 g / mol and an epoxy value of 0.2-2.0 eq / 100g; Silanized nanofillers have a particle size of 20-100 nm and a specific surface area S of 50-400 m². 2 / g; Among them, the epoxy groups in the epoxy polyol are reactive in ring-opening reaction with the hydroxyl groups of the polyvinyl alcohol matrix in the range of 60℃~130℃, forming a cross-linked network connected by ether bonds; the silanized nanofiller is uniformly dispersed in the cross-linked network.

[0009] As a preferred technical solution, the modified polyvinyl alcohol comprises, by weight: 50-75 parts of polyvinyl alcohol matrix; 3-15 parts of epoxy polyol; 0.5-5 parts of silanized nanofiller; 0.1-1 parts of leveling agent; and 0.1-1 parts of surfactant.

[0010] As a preferred technical solution, the epoxy value of the epoxy polyol is 0.5-1.2 eq / 100g, and its number-average molecular weight Mn and the specific surface area of ​​the silanized nanofiller satisfy the following condition: 10≤(Mn / S)≤50.

[0011] As a preferred technical solution, the epoxy polyol includes at least one or any combination of polyethylene glycol diglycidyl ether, epoxidized castor oil, epoxidized soybean oil, sorbitol polyglycidyl ether, glycerol triglycidyl ether, 1,4-butanediol diglycidyl ether, and neopentyl glycol diglycidyl ether.

[0012] As a preferred technical solution, the silanized nanofiller includes at least one of silicon dioxide, cellulose whiskers, calcium carbonate, aluminum oxide, zinc oxide, and titanium oxide, and is treated with a silane coupling agent.

[0013] As a preferred technical solution, the preparation method of the silanized nanofiller includes adding the nanofiller to a solvent to prepare a suspension with a solid content of 5%-20%, dispersing it evenly by ultrasonication, adding a silane coupling agent dropwise, the amount of silane coupling agent added being 1%-8% of the mass of the nanofiller, adjusting the pH of the reaction system to 4-6, stirring at 40℃-80℃ for 4-8 hours, and after the reaction is completed, centrifuging the product, washing and drying it.

[0014] Secondly, the present invention provides a method for preparing modified polyvinyl alcohol having any of the above-mentioned technical features, comprising the following steps performed sequentially: S01. The polyvinyl alcohol matrix is ​​added to water and stirred at 80℃-95℃ to dissolve it, thereby preparing a polyvinyl alcohol aqueous solution. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, the epoxy polyol is added, and the mixture is mechanically stirred to obtain a mixed solution. S03. The silanized nanofiller is added to the mixed solution in batches during the stirring process. After the addition is completed, the stirring is continued until the silanized nanofiller is evenly dispersed to obtain an intermediate solution. S04. Add the leveling agent and surfactant to the intermediate solution and mix well.

[0015] As a preferred technical solution, after obtaining the intermediate solution in step S03, the intermediate solution is heated to 40℃-60℃ and aged for 2-4 hours.

[0016] Thirdly, the present invention provides a composite sheet comprising a barrier layer formed by coating and curing modified polyvinyl alcohol prepared with any of the above-mentioned technical features.

[0017] As a preferred technical solution, the barrier layer has an oxygen permeability ≤1.0 cm⁻¹ when the dry film thickness is 25 μm. 3 / (m 2 ×24h×0.1MPa); and / or water vapor transmission rate ≤0.2g / (m 2 ×24h).

[0018] The advantages and beneficial effects of this invention are as follows: the epoxy groups in the epoxy polyol undergo ring-opening etherification with the hydroxyl groups on the PVA molecular chain under mild processing conditions of 60℃-130℃, which improves its dimensional stability and barrier performance retention rate in humid environments; at the same time, this invention introduces silanized nanofillers, where the silanol groups formed after the silane coupling agent is hydrolyzed on the filler surface combine with the nanofillers, while the organic functional groups at the other end can chemically react with the hydroxyl groups of PVA or the added epoxy polyol in the system, thereby fixing the nanofillers in the organic polymer crosslinking network, improving the dispersibility of the nanofillers in the matrix and avoiding agglomeration.

[0019] In this invention, nanofillers with high specific surface area, combined with a progressive crosslinking system, can effectively extend the diffusion path of gaseous substances in the barrier layer. By controlling the filler addition steps and introducing a low-temperature curing step in the preparation process, a uniform pre-crosslinked state can be induced in the solution, resulting in a more ordered barrier layer structure with fewer defects after final curing. The barrier layer achieves excellent barrier performance even with a dry film thickness of only 25 μm. Attached Figure Description

[0020] Figure 1 This is a flow chart of the modified polyvinyl alcohol preparation process shown in this invention. Detailed Implementation

[0021] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] This invention provides a sheet material with modified polyvinyl alcohol, its preparation method, and its application. The modified polyvinyl alcohol comprises: a polyvinyl alcohol matrix with a degree of hydrolysis of 70%–99% and a degree of polymerization of 500–3000; an epoxy-based polyol with a number-average molecular weight (Mn) of 300–5000 g / mol and an epoxy value of 0.2–2.0 eq / 100 g; and a particle size of 20–100 nm and a specific surface area (S) of 50–400 m² / g. 2 / g of silanized nanofiller. In this process, the epoxy groups of the epoxy polyol undergo a ring-opening reaction with the hydroxyl groups of the polyvinyl alcohol matrix in the range of 60℃~130℃ to form a cross-linked network connected by ether bonds; the silanized nanofiller is uniformly dispersed in this cross-linked network.

[0025] The polyvinyl alcohol (PVA) matrix of this invention is the main component of the modified system. Its degree of hydrolysis and degree of polymerization significantly affect the performance of the final barrier layer. A degree of hydrolysis of 70%–99% ensures that the PVA molecular chains contain a sufficient number of hydroxyl groups, providing binding sites for subsequent crosslinking reactions with epoxy polyols. If the degree of hydrolysis is too low, the hydroxyl group density is insufficient, which will significantly weaken the crosslinking ability. It is worth noting that while reducing the degree of hydrolysis is beneficial for reducing hydrophobicity, it also sacrifices its water-soluble processing advantages. If the degree of hydrolysis is too high, it will lead to difficulties in dissolution, high solution viscosity, and a narrowed processing window. A degree of polymerization of 500–3000 indicates a moderate molecular chain length. If the polymerization is too low, the molecular chains are short, resulting in insufficient mechanical strength of the formed barrier layer; if the polymerization is too high, the molecular chains are too long, leading to poor solubility, and the solution viscosity is unfavorable for liquid leveling and uniform film formation during the coating process.

[0026] In this invention, epoxy-based polyols serve as reactive crosslinking agents and structural toughening agents. Their number-average molecular weight (Mn) and epoxy value are interrelated. Mn affects the migration ability of epoxy-based polyols in the PVA matrix, their entanglement with PVA chains, and the segment mobility of the final crosslinked network. If the molecular weight is too low, migration is easy, and the resulting crosslinking points are too dense, potentially leading to network embrittlement; if the molecular weight is too high, the compatibility and diffusivity of long chains in the PVA aqueous phase may deteriorate, affecting the uniformity of crosslinking. The epoxy value reflects the number of reactive epoxy groups per unit mass of polyol and determines the crosslinking density of the epoxy-based polyol. If the epoxy value is too low, there are insufficient crosslinking points, making it difficult to effectively improve the water resistance of PVA; if the epoxy value is too high, the reaction is too active, potentially leading to excessive pre-crosslinking during storage or early processing, resulting in decreased solution stability or poor processing performance.

[0027] The ring-opening etherification reaction between epoxy-based polyols with the aforementioned technical characteristics and PVA hydroxyl groups can be effectively carried out under mild conditions of 60℃ to 130℃, which matches the conditions of conventional coating and drying processes. This reaction can be initiated during the coating process using heated rollers, infrared heating units, etc. The ether bonds formed after the reaction have high chemical stability, which can reduce the hydrophilicity of the crosslinked network, improve its moisture resistance, and retain the advantages of water-soluble processing.

[0028] Flexible segments of epoxy polyols (such as polyethylene glycol chains and long-chain alkyl groups) are chemically bonded to the PVA network, which plays the role of internal plasticization and forced elasticity. While improving water resistance, it can avoid the embrittlement of the barrier layer caused by cross-linking, and maintain the flexibility of the barrier layer and its adhesion to the polyolefin substrate.

[0029] Silanized nanofillers can be uniformly dispersed in a polymer matrix without significantly affecting the transparency and surface finish of the barrier layer. If the particle size of the silanized nanofillers is too small, they are prone to agglomeration due to excessive surface energy; if the particle size is too large, they may become stress concentration points and adversely affect the density of the barrier layer. High specific surface area means that the filler has abundant surface active sites, corresponding to morphologies such as sheet-like, fibrous, or high-porosity (e.g., some nano-silica), which are advantageous in constructing gas barrier pathways. Silanization treatment refers to modifying the surface of the nanofiller using a silane coupling agent. Silane coupling agent molecules typically have a "YR-Si(OR')3" structure, where Y is an organic functional group (such as amino, epoxy, vinyl, etc.) that can react with PVA or epoxy polyols, -R- is an alkyl chain, and Si(OR')3 is a hydrolyzable siloxane group. During the modification process, Si(OR')3 hydrolyzes into silanol groups, which then undergo a condensation reaction with hydroxyl groups on the filler surface, thereby chemically grafting organic segments with Y functional groups onto the filler surface. This endows the originally hydrophilic, nonpolar filler surface with organic reactivity.

[0030] In the subsequent composite and cross-linking process, the Y functional groups on the filler surface can participate in the cross-linking reaction between PVA and epoxy polyol, or form hydrogen bonds with the hydroxyl groups of PVA, thereby dispersing the inorganic nanofiller in the organic cross-linking network through chemical bonds or physical interactions. This makes the filler a multifunctional reinforcing node of the cross-linking network, which not only extends the diffusion path of gas molecules through physical barriers, but also effectively shares stress and improves the water resistance of the barrier layer.

[0031] The preparation method of this invention includes the following steps: First, the PVA matrix is ​​fully dissolved in hot water at 80℃-95℃. Heating is used to break the hydrogen bonds between PVA molecules, promoting complete dissolution. After cooling to room temperature, an epoxy polyol is added to ensure uniform dispersion of the epoxy polyol in the PVA solution. Adding it at high temperatures may cause premature partial ring-opening of the epoxy groups, leading to a sharp increase in solution viscosity or even gelation, thus compromising processability. Simultaneously, the reactivity of the epoxy groups is kept to a low level. Subsequently, the pre-prepared silanized nanofiller is added to the mixed solution in batches. Each batch of filler should be fully dispersed under shear force before adding the next batch. After dispersion, leveling agents and surfactants are added to improve the spreadability and wetting properties of the coating solution.

[0032] In some preferred embodiments, after obtaining a homogeneous intermediate solution, it is heated to 40°C-60°C and aged for 2-4 hours. This temperature is lower than the initiation temperature of the vigorous crosslinking reaction between the epoxy groups and PVA hydroxyl groups, but higher than room temperature, providing sufficient molecular kinetic energy. Under these conditions, the pre-crosslinking and structural assembly of the system proceed in a controlled and slow manner; sufficient physical adsorption and molecular rearrangement can occur between the functional groups on the surface of the silanized filler and the PVA molecular chains, and between the PVA chains and the flexible segments of the epoxy polyol; the highly active functional groups on the filler surface may undergo a relatively slow chemical reaction with the nearest PVA hydroxyl groups, initially establishing chemical connection points; the mild thermal effect also facilitates the escape of microbubbles in the solution and the homogenization of local concentration gradients.

[0033] This process ensures that the entire system possesses a highly uniform and partially ordered microstructure precursor before entering the high-temperature coating-curing stage. Subsequently, in the curing stage after coating, for example, by infrared heating the barrier layer to 100°C-130°C, the cross-linking reaction of epoxy groups and hydroxyl groups proceeds rapidly and orderly based on the pre-assembled structure. These embodiments, by reducing network structure defects caused by excessively rapid reactions and insufficient molecular chain movement, can form a denser, more uniform barrier layer structure with fewer defects, exhibiting better barrier performance.

[0034] In some embodiments, to balance the crosslinking density, flexibility, and processing performance of the barrier layer, the modified polyvinyl alcohol, by weight, comprises: 50-75 parts of polyvinyl alcohol matrix, 3-15 parts of epoxy polyol, 0.5-5 parts of silanized nanofiller, 0.1-1 parts of leveling agent, and 0.1-1 parts of surfactant. When the epoxy polyol content is less than 3 parts, the crosslinking points are insufficient, resulting in limited improvement in water resistance and network strength; when it is more than 15 parts, there is excessive crosslinking.

[0035] In some embodiments, the epoxy value of the epoxy polyol is preferably 0.5-1.2 eq / 100g, and its number-average molecular weight Mn and the specific surface area S of the silanized nanofiller must satisfy: 10 ≤ (Mn / S) ≤ 50. The Mn / S ratio can be understood as "the polymer chain length (or volume) allocated per unit filler surface area". If the ratio is too small, it means that the filler specific surface area is too large or the polyol molecular weight is too small. This may cause a large number of small polyol molecules to be strongly adsorbed on the filler surface and consumed in interface modification, and unable to effectively enter the PVA matrix network to participate in the construction of a continuous cross-linked structure. At the same time, the system viscosity may increase abnormally. If the ratio is too large, it means that the polyol molecular chain is too long or the filler specific surface area is too small. Excessively long chain segments may not be able to form effective encapsulation and bonding on the filler surface, resulting in weak interfacial bonding between the filler and the polymer matrix, and the filler is prone to becoming a weak point.

[0036] It is worth noting that excessively long flexible chains may also overly soften the barrier layer. Controlling the Mn / S ratio between 10 and 50 ensures that the chain length of the epoxy polyol matches the surface characteristics of the filler: the polyol segments can both wet and bond to the filler surface to form a strong interfacial layer, and also have enough to extend into the PVA matrix to play an effective role in connection and toughening.

[0037] In some embodiments, the epoxy polyol includes at least one selected from polyethylene glycol diglycidyl ether, epoxidized castor oil, epoxidized soybean oil, sorbitol polyglycidyl ether, glycerol triglycidyl ether, 1,4-butanediol diglycidyl ether, and neopentyl glycol diglycidyl ether. Epoxidized vegetable oils are naturally derived and have long-chain alkyl structures, providing excellent hydrophobicity and flexibility while crosslinking; multifunctional derivatives of sorbitol or glycerol can form a network of nodes with high crosslinking density, improving the moisture resistance of the barrier layer; diglycidyl ethers of aliphatic diols have simple structures, low viscosity, high reactivity, and are readily available.

[0038] In some embodiments, the silanized nanofiller includes at least one selected from silica, cellulose whiskers, calcium carbonate, alumina, zinc oxide, and titanium dioxide. For silica, γ-glycidoxypropyltrimethoxysilane is commonly used for modification, grafting epoxy groups onto its surface, allowing it to directly participate in the cross-linking reaction of the system. For cellulose whiskers, aminosilane modification is commonly used, and the introduced amino groups can react with the epoxy groups.

[0039] In some embodiments, the preparation method of silanized nanofillers includes: adding the nanofiller to water to prepare a suspension with a solid content of 5%-20% (mass percentage); ultrasonically dispersing the suspension until uniform, then adding a silane coupling agent dropwise; adjusting the pH of the reaction system to a weakly acidic condition of 4-6 to facilitate the formation and condensation of silanols; stirring the suspension at 40℃-80℃ for 4-8 hours; after the reaction is complete, separating the product by centrifugation, washing, and drying to obtain a powder with a surface grafted with a silane coupling agent.

[0040] This invention also provides a composite sheet comprising a barrier layer formed by coating and subsequent curing of the aforementioned modified polyvinyl alcohol. The coating method can be conventional methods such as gravure coating, slot coating, doctor blade coating, or spraying, with the coating temperature typically ranging from room temperature to 40°C to accommodate the rheological properties of the coating liquid. Curing after coating is usually carried out in a hot air oven, ultimately achieving cross-linking at 100°C-130°C.

[0041] In some preferred embodiments, the oxygen permeability of the barrier layer can be ≤1.0 cm when the dry film thickness is 25 μm. 3 / (m 2 (×24h×0.1MPa), water vapor transmission rate can be ≤0.2 g / (m 2 ×24h).

[0042] The present invention will be further explained and illustrated below with reference to specific embodiments; in each embodiment and comparative example, the oxygen transmission rate was tested in accordance with standard GB / T 19789-2005; the water vapor transmission rate was tested in accordance with standard GB / T 21529-2008; the epoxy value was determined in accordance with standard GB / T 1677-2008 "Determination of Epoxy Value of Epoxy Resin", using the hydrochloric acid-acetone method.

[0043] [Example 1] A method for preparing a sheet containing modified polyvinyl alcohol includes the following steps: S01. Add a polyvinyl alcohol matrix with a degree of alcoholysis of 85% and a degree of polymerization of 1500 to deionized water, stir and dissolve at 90°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 15 wt%. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, polyethylene glycol diglycidyl ether with a number average molecular weight Mn of 2000 g / mol and an epoxy value of 1.0 eq / 100g is added, and the mixture is mechanically stirred for 30 minutes to obtain a mixed solution. S03, with a particle size of 50 nm and a specific surface area S of 200 m² 2 / g of silanized nano-silica was added to the mixed solution in three batches during the stirring process, with an interval of 10 minutes between each batch. After the addition was completed, stirring was continued for 60 minutes to obtain an intermediate solution. S04. Add 0.5 parts of leveling agent and 0.5 parts of surfactant to the intermediate solution, stir for 20 minutes to mix evenly, and the modified polyvinyl alcohol coating liquid is obtained.

[0044] The modified polyvinyl alcohol prepared in this embodiment comprises, by weight, 65 parts of polyvinyl alcohol matrix, 8 parts of polyethylene glycol diglycidyl ether, 2 parts of silanized nano silica, 0.5 parts of leveling agent, and 0.5 parts of surfactant.

[0045] The modified polyvinyl alcohol prepared in this embodiment was coated between two layers of polyethylene (PE) base film using a slot coating method. After curing in a 100°C oven, a barrier layer with a dry film thickness of 25 μm was formed, resulting in a composite sheet. Its oxygen permeability was measured to be 0.8 cm. 3 / (m 2 ·24h·0.1 MPa), water vapor transmission rate is 0.18 g / (m 2 •24h).

[0046] [Example 2] A method for preparing a sheet containing modified polyvinyl alcohol includes the following steps: S01. Add a polyvinyl alcohol matrix with a degree of alcoholysis of 75% and a degree of polymerization of 800 to deionized water, stir and dissolve at 85°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 12 wt%. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, add epoxidized castor oil with a number-average molecular weight Mn of 800 g / mol and an epoxy value of 0.6 eq / 100g, and mechanically stir for 30 minutes to obtain a mixed solution. S03, with a particle size of 80 nm and a specific surface area S of 120 m² 2 / g of silanized nano-calcium carbonate was added to the mixed solution in two batches during the stirring process, with an interval of 15 minutes between each batch. After the addition was completed, stirring was continued for 60 minutes to obtain an intermediate solution. S04. Heat the intermediate solution to 50°C and let it mature for 3 hours. S05. Add 0.3 parts of leveling agent and 0.3 parts of surfactant, stir for 20 minutes to mix evenly, and the modified polyvinyl alcohol coating liquid is obtained.

[0047] The modified polyvinyl alcohol prepared in this embodiment comprises, by weight, 60 parts of polyvinyl alcohol matrix, 5 parts of epoxidized castor oil, 1.5 parts of silanized nano-calcium carbonate, 0.3 parts of leveling agent, and 0.3 parts of surfactant.

[0048] The oxygen permeability of the barrier layer formed by coating and curing the modified polyvinyl alcohol prepared in this embodiment was measured to be 0.9 cm. 3 / (m 2 • 24h • 0.1 MPa), water vapor transmission rate is 0.19 g / (m 2 •24h).

[0049] [Example 3] A method for preparing a sheet containing modified polyvinyl alcohol includes the following steps: S01. Add a polyvinyl alcohol matrix with a degree of alcoholysis of 95% and a degree of polymerization of 2500 to deionized water, stir and dissolve at 92°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 18 wt%. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, add sorbitol polyglycidyl ether with a number average molecular weight Mn of 3500 g / mol and an epoxy value of 1.5 eq / 100g, and mechanically stir for 30 minutes to obtain a mixed solution. S03, with a particle size of 30 nm and a specific surface area S of 350 m² 2 / g of silanized nano-alumina was added to the mixed solution in four batches during the stirring process, with an interval of 10 minutes between each batch. After the addition was completed, stirring was continued for 90 minutes to obtain an intermediate solution. S04. Heat the intermediate solution to 45°C and mature for 4 hours; S05. Add 0.8 parts of leveling agent and 0.8 parts of surfactant, stir for 20 minutes to mix evenly, and the modified polyvinyl alcohol coating liquid is obtained.

[0050] The modified polyvinyl alcohol prepared in this embodiment comprises, by weight, 70 parts of polyvinyl alcohol matrix, 12 parts of sorbitol polyglycidyl ether, 4 parts of silanized nano-alumina, 0.8 parts of leveling agent, and 0.8 parts of surfactant.

[0051] The oxygen permeability of the barrier layer formed by coating and curing the modified polyvinyl alcohol prepared in this embodiment was measured to be 0.7 cm. 3 / (m 2 ·24h·0.1 MPa), water vapor transmission rate is 0.16 g / (m 2 •24h).

[0052] [Example 4] A method for preparing a sheet containing modified polyvinyl alcohol includes the following steps: S01. Add a polyvinyl alcohol matrix with a degree of alcoholysis of 80% and a degree of polymerization of 1200 to deionized water, stir and dissolve at 88°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 10 wt%. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, add 1,4-butanediol diglycidyl ether with a number average molecular weight Mn of 500 g / mol and an epoxy value of 0.3 eq / 100g, and mechanically stir for 30 minutes to obtain a mixed solution. S03, with a particle size of 100 nm and a specific surface area S of 80 m² 2 / g of silanized nano-silica was added to the mixed solution in two batches during the stirring process, with an interval of 20 minutes between each batch. After the addition was completed, stirring was continued for 60 minutes to obtain an intermediate solution. S04. Add 0.2 parts of leveling agent and 0.2 parts of surfactant, stir for 20 minutes to mix evenly, and the modified polyvinyl alcohol coating liquid is obtained.

[0053] The modified polyvinyl alcohol prepared in this embodiment comprises, by weight, 55 parts of polyvinyl alcohol matrix, 4 parts of 1,4-butanediol diglycidyl ether, 0.8 parts of silanized nano silica, 0.2 parts of leveling agent, and 0.2 parts of surfactant.

[0054] The oxygen permeability of the barrier layer formed by coating and curing the modified polyvinyl alcohol prepared in this embodiment was measured to be 1.0 cm. 3 / (m 2 ·24h·0.1 MPa), water vapor transmission rate is 0.20 g / (m 2 •24h).

[0055] [Example 5] A method for preparing a sheet containing modified polyvinyl alcohol includes the following steps: S01. Add a polyvinyl alcohol matrix with a degree of alcoholysis of 90% and a degree of polymerization of 2800 to deionized water, stir and dissolve at 95°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 20 wt%. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, add glycerol triglycidyl ether with a number average molecular weight Mn of 4000 g / mol and an epoxy value of 1.8 eq / 100g, and mechanically stir for 30 minutes to obtain a mixed solution. S03, with a particle size of 20 nm and a specific surface area S of 400 m² 2 / g of silanized nano-silica was added to the mixed solution in five batches during the stirring process, with each batch spaced 10 minutes apart. After the addition was completed, stirring was continued for 120 minutes to obtain an intermediate solution. S04. Heat the intermediate solution to 60°C and mature for 2 hours; S05. Add 1.0 part of leveling agent and 1.0 part of surfactant, stir for 20 minutes to mix evenly, and the modified polyvinyl alcohol coating liquid is obtained.

[0056] The modified polyvinyl alcohol prepared in this embodiment comprises, by weight, 75 parts of polyvinyl alcohol matrix, 14 parts of glycerol triglycidyl ether, 4.5 parts of silanized nano silica, 1.0 part of leveling agent, and 1.0 part of surfactant.

[0057] The oxygen permeability of the barrier layer formed by coating and curing the modified polyvinyl alcohol prepared in this embodiment was measured to be 0.6 cm. 3 / (m 2 • 24h • 0.1 MPa), water vapor transmission rate is 0.15 g / (m 2 •24h).

[0058] [Example 6] A method for preparing a sheet containing modified polyvinyl alcohol includes the following steps: S01. Add a polyvinyl alcohol matrix with a degree of alcoholysis of 70% and a degree of polymerization of 500 to deionized water, stir and dissolve at 80°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 8 wt%. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, neopentyl glycol diglycidyl ether with a number average molecular weight Mn of 300 g / mol and an epoxy value of 0.2 eq / 100g is added, and the mixture is mechanically stirred for 30 minutes to obtain a mixed solution. S03, with a particle size of 60 nm and a specific surface area S of 300 m² 2 / g of silanized cellulose nanofiber whiskers were added to the mixed solution in three batches during the stirring process, with an interval of 15 minutes between each batch. After the addition was completed, stirring was continued for 60 minutes to obtain an intermediate solution. S04. Add 0.1 parts of leveling agent and 0.1 parts of surfactant, stir for 20 minutes to mix evenly, and the modified polyvinyl alcohol coating liquid is obtained.

[0059] The modified polyvinyl alcohol prepared in this embodiment comprises, by weight, 50 parts of polyvinyl alcohol matrix, 3 parts of neopentyl glycol diglycidyl ether, 0.5 parts of silanized nanocellulose whiskers, 0.1 parts of leveling agent, and 0.1 parts of surfactant.

[0060] The oxygen permeability of the barrier layer formed by coating and curing the modified polyvinyl alcohol prepared in this embodiment was measured to be 1.0 cm. 3 / (m 2 ·24h·0.1 MPa), water vapor transmission rate is 0.20 g / (m 2 •24h).

[0061] [Comparative Example 1] A commercially available ordinary PVA coating solution (88% alcoholysis, 1700 degree of polymerization) was applied between two layers of PE base film, resulting in a dry film thickness of 25 μm. After curing, the oxygen permeability was measured to be 5.2 cm. 3 / (m 2 • 24h • 0.1 MPa), water vapor transmission rate is 2.5 g / (m 2 •24h).

[0062] [Comparative Example 2] A commercially available EVOH coating solution (32% ethylene content) was used to coat two layers of PE base film, resulting in a dry film thickness of 25 μm. After curing, the oxygen permeability was measured to be 1.5 cm. 3 / (m 2 • 24h • 0.1 MPa), water vapor transmission rate is 0.8 g / (m 2 •24h).

[0063] [Comparative Example 3] The preparation method was the same as in Example 1, but without the addition of silanized nanofillers. The resulting composite sheet had an oxygen permeability of 2.8 cm⁻¹. 3 / (m 2 (24h·0.1 MPa), water vapor transmission rate is 1.2 g / (m 2 •24h).

[0064] [Comparative Example 4] The preparation method was the same as in Example 1, but the epoxy polyol was replaced with an equal mass of ordinary polyethylene glycol. The resulting composite sheet had an oxygen permeability of 4.5 cm⁻¹. 3 / (m 2 ·24h·0.1 MPa), water vapor transmission rate is 1.8 g / (m 2 •24h).

[0065] [Comparative Example 5] The preparation method was the same as in Example 1, but in step S02, the solution was not cooled to room temperature; the epoxy polyol was added directly at 90°C. This resulted in a sharp increase in solution viscosity, uneven coating, and obvious defects in the film after formation, with an oxygen permeability of 3.6 cm⁻¹. 3 / (m 2 • 24h • 0.1 MPa), water vapor transmission rate is 1.5 g / (m 2 •24h).

[0066] [Comparative Example 6] The preparation method was the same as in Example 1, but the silanized nanofiller was replaced with ordinary nano-silica (same particle size, same surface area) that had not undergone silanization treatment. The resulting composite sheet had an oxygen permeability of 2.5 cm⁻¹. 3 / (m 2 • 24h • 0.1 MPa), water vapor transmission rate is 1.0 g / (m 2 • 24h), and under the same preparation conditions, slight unevenness was observed in the barrier layer of Comparative Example 6.

[0067] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A sheet containing modified polyvinyl alcohol, characterized in that, A barrier layer having modified polyvinyl alcohol, wherein the modified polyvinyl alcohol comprises: Polyvinyl alcohol matrix, with a degree of alcoholysis of 70% to 99% and a degree of polymerization of 500 to 3000; Epoxy polyols with a number-average molecular weight (Mn) of 300-5000 g / mol and an epoxy value of 0.2-2.0 eq / 100g; Silanized nanofillers have a particle size of 20-100 nm and a specific surface area S of 50-400 m². 2 / g; Among them, the epoxy groups in the epoxy polyol are reactive in ring-opening reaction with the hydroxyl groups of the polyvinyl alcohol matrix in the range of 60℃~130℃, forming a cross-linked network connected by ether bonds; the silanized nanofiller is uniformly dispersed in the cross-linked network.

2. The sheet material according to claim 1, characterized in that, The modified polyvinyl alcohol comprises, by weight: 50-75 parts of polyvinyl alcohol matrix; 3-15 parts of epoxy polyol; 0.5-5 parts of silanized nanofiller; 0.1-1 parts of leveling agent; and 0.1-1 parts of surfactant.

3. The sheet according to claim 2, characterized in that, The epoxy value of the epoxy polyol is 0.5-1.2 eq / 100g, and its number-average molecular weight Mn and the specific surface area of ​​the silanized nanofiller satisfy the following condition: 10≤(Mn / S)≤50.

4. The sheet according to claim 3, characterized in that, The epoxy polyols include at least one or any combination of polyethylene glycol diglycidyl ether, epoxidized castor oil, epoxidized soybean oil, sorbitol polyglycidyl ether, glycerol triglycidyl ether, 1,4-butanediol diglycidyl ether, and neopentyl glycol diglycidyl ether.

5. The sheet according to claim 3, characterized in that, The silanized nanofiller includes at least one of silica, cellulose whiskers, calcium carbonate, alumina, zinc oxide, and titanium oxide, and is treated with a silane coupling agent.

6. The sheet according to claim 3, characterized in that, The preparation method of the silanized nanofiller includes: adding the nanofiller to a solvent to prepare a suspension with a solid content of 5%-20%, dispersing it evenly by ultrasonication, and then adding a silane coupling agent dropwise. The amount of silane coupling agent added is 1%-8% of the mass of the nanofiller. The pH of the reaction system is adjusted to 4-6, and the mixture is stirred at 40℃-80℃ for 4-8 hours. After the reaction is completed, the product is centrifuged, washed, and dried.

7. A method for preparing modified polyvinyl alcohol according to any one of claims 1 to 6, characterized in that, This includes the following steps performed sequentially: S01. The polyvinyl alcohol matrix is ​​added to water and stirred at 80℃-95℃ to dissolve it, thereby preparing a polyvinyl alcohol aqueous solution. S02. After the polyvinyl alcohol aqueous solution is cooled to room temperature, the epoxy polyol is added, and the mixture is mechanically stirred to obtain a mixed solution. S03. The silanized nanofiller is added to the mixed solution in batches during the stirring process. After the addition is completed, the stirring is continued until the silanized nanofiller is evenly dispersed to obtain an intermediate solution. S04. Add the leveling agent and surfactant to the intermediate solution and mix well.

8. The preparation method according to claim 7, characterized in that, After obtaining the intermediate solution in step S03, the intermediate solution is heated to 40℃-60℃ and aged for 2-4 hours.

9. A composite sheet, characterized in that, It includes a barrier layer formed by coating and curing of the modified polyvinyl alcohol according to any one of claims 1 to 6.

10. The composite sheet according to claim 9, characterized in that, The barrier layer has an oxygen permeability of ≤1.0 cm when the dry film thickness is 25 μm. 3 / (m 2 ×24h×0.1MPa); and / or Water vapor transmission rate ≤ 0.2 g / (m 2 ×24h).

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