Preparation method of a high-performance hydrophobic polyvinyl alcohol composite film

Abstract

The present invention belongs to the field of polyvinyl alcohol composite films, and specifically relates to a method for preparing a high-performance hydrophobic polyvinyl alcohol composite film. The present invention uses a ternary composite plasticizer to destroy the hydrogen bonding in PVA molecules, reduce the crystallinity and melting point of PVA, and has a significant plasticizing effect on PVA. Compared with single plasticizers and binary plasticizers, the PVA film modified with the ternary composite plasticizer of the present invention has good hydrophobicity and excellent mechanical properties. The present invention also uses a chemical crosslinking method to modify the PVA film, and through the esterification reaction between pyromellitic acid and the hydroxyl groups of PVA, the hydroxyl groups in the PVA molecules are masked, and crosslinking can be achieved, which can not only improve the hydrophobic properties of PVA, but also enhance the mechanical properties of the PVA film.

Description

Technical Field

[0001] The invention belongs to the field of polyvinyl alcohol composite films, and particularly relates to a method for preparing a high-performance hydrophobic polyvinyl alcohol composite film. Background Art

[0002] Polyvinyl alcohol (PVA) has significant potential for use as a pharmaceutical excipient due to its hydrophilicity, barrier properties, film-forming properties, low cost, cross-linking, and biodegradability. In industrial settings, PVA is crucial in the processing of polarizers, packaging, paper, fibers, and adhesives. It is used as an adhesive in the wood and paper industries, and can also be used to manufacture separation membranes.

[0003] Due to the soft mechanical properties and poor water resistance of PVA film, its application is greatly limited and cannot meet the use requirements of PVA film in practical applications. Therefore, PVA film needs to be modified to improve its application properties such as mechanical and water resistance, and to broaden its functions. According to the reaction mechanism or mode of action, the modification methods of PVA film can be divided into chemical cross-linking or grafting modification and physical modification, such as blending modification and nanocomposite. Blending modification and nanocomposite have simple steps and can easily expand the functionality of PVA film; chemical cross-linking modification can form a chemical bond cross-linked network between the polymer chains of PVA film, thereby significantly improving the mechanical properties, thermal stability and water resistance of PVA film.

[0004] Chemical crosslinking refers to the process of linking macromolecular chains through chemical bonds to form a network or spherical polymer structure. Chemical crosslinking can improve polymer properties. Polyvinyl alcohol (PVA), due to the large number of hydrophilic hydroxyl groups in its molecules, exhibits a strong affinity for water during dry-wet cycles. To improve its water resistance, the hydroxyl groups in the PVA molecules must be masked. This can be achieved by chemically reacting the hydroxyl groups on the PVA chains to convert them into water-resistant groups. Alternatively, a crosslinking agent can be added to initiate a crosslinking reaction, re-forming a new polymer.

[0005] Xu Zixuan et al. (Journal of Zhongkai University of Agriculture and Engineering, 2019, 32 (1): 17-22) prepared a series of citric acid-modified starch / polyvinyl alcohol composite films by solution casting. The results showed that citric acid and starch underwent an esterification and cross-linking reaction. The citric acid-modified starch could improve the mechanical properties of the composite film, reduce the haze, hydrophilicity and water vapor permeability of the film, and improve the preservation effect of the film on mangoes. Zhong Le et al. (Packaging Engineering, 2019, 40 (15), 67-73) used stearic acid as a modifier, supplemented with stearic acid-96 as an emulsifier and polyethylene glycol-400 as a plasticizer to modify the polyvinyl alcohol film and studied the preservation of prunes. The results showed that an ester bond was formed between stearic acid and polyvinyl alcohol, and the water resistance of the film was significantly improved. Furthermore, preservation experiments revealed that, compared with the blank and PVA film groups, the stearic acid / PVA group delayed the peak respiratory burst of prunes by 2 days, significantly reduced the mass loss rate of prunes, and slowed the rate of change in soluble solids content. The stearic acid / PVA group extended the shelf life of prunes by 3.3 days. This suggests that modifying polyvinyl alcohol with stearic acid enhances the film's water resistance, improves its packaging strength, and strengthens its preservation effectiveness.

[0006] Lim et al. (Prog Org Coat, 2015, 85:68-75) prepared five different cross-linked polyvinyl alcohol / boric acid (PVA / BA) hybrid films via a solution blending method. Their results showed that the physical properties of the PVA / BA hybrid films depended on the BA content and cross-linking density. With increasing BA content, the size and number of PVA crystals decreased, while the cross-linking density increased, resulting in more compact molecular packing and lower free volume in the amorphous regions. Increasing the BA content (0-5%) significantly improved the glass transition temperature and thermal stability of the films, and all films exhibited good transparency.

[0007] Acetalization can improve the properties of PVA, resulting in products with good water resistance and mechanical properties. The water resistance of PVA films can be improved by acetalization with aldehydes such as formaldehyde, acetaldehyde, and butyraldehyde, or by cross-linking with glyoxal, N-methylol urea, N-methylol melamine, and N-methylol ethylene urea.

[0008] Zhang Li et al. (Functional Materials, 2020, 51 (4): 4153-4159) used glutaraldehyde and urea to acetal cross-link polyvinyl alcohol, and by adding different types of plasticizers (propylene glycol, PEG-400, MgCl2) to destroy the hydrogen bonding of PVA and reduce its crystallinity, thereby achieving a plasticizing modification effect. Luo Yafang et al. (Guangzhou Chemical Industry, 2018, 46 (24): 53-56) used electrospinning technology and glutaraldehyde as a post-crosslinking agent to explore the effect of glutaraldehyde concentration on the water resistance of PVA fiber film. The results showed that after glutaraldehyde cross-linking treatment, the morphology of PVA fibers was not destroyed, and the water resistance was significantly improved. The change of glutaraldehyde concentration had little effect on the water resistance.

[0009] As a water-soluble polymer, polyvinyl alcohol is not only simple to prepare and low-cost, but also has excellent hydrophilicity, gas barrier properties, acid and alkali resistance, and organic solvent resistance, as well as outstanding biosafety and good film-forming ability. Through modification processes such as esterification cross-linking, aldol condensation, compound plasticization, nano-reinforcement, and blending hybridization, the mechanical and water resistance properties of polyvinyl alcohol films can be significantly improved, greatly promoting the practical application of polyvinyl alcohol films. Despite this, at present, there are still some problems with the modified polyvinyl alcohol films, such as the tensile strength and toughness of the polyvinyl alcohol films. In addition, in terms of preparation, solution blending and cast molding are mainly used. Compared with the melt blending and blow molding methods of traditional packaging materials such as PP, PVC and PE, this method has disadvantages such as low production capacity and difficulty in accurately controlling film thickness. Summary of the Invention

[0010] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a high-performance hydrophobic polyvinyl alcohol composite film. The polyvinyl alcohol composite film prepared by the method of the present invention has good hydrophobicity.

[0011] The present invention is achieved through the following technical solutions:

[0012] A method for preparing a high-performance hydrophobic polyvinyl alcohol composite film comprises the following steps:

[0013] 1) Plasticization of polyvinyl alcohol: Add polyvinyl alcohol and water to a reactor, then add a plasticizer, heat and stir to react, and obtain a plasticized polyvinyl alcohol mixed solution;

[0014] 2) Hydrophobic modification of polyvinyl alcohol: adding a crosslinking agent and an emulsifier to the polyvinyl alcohol mixed solution obtained in step 1), and performing an esterification reaction under constant temperature and stirring conditions to obtain a hydrophobically modified polyvinyl alcohol composite material;

[0015] 3) Preparation of a polyvinyl alcohol hydrophobic film: The polyvinyl alcohol composite material obtained in step 2) is added with a toughening modifier under stirring at 80°C to 90°C, uniformly dispersed, cooled to room temperature, and ultrasonically treated to obtain a uniform and stable film solution. The film is cast and then dried to obtain a high-performance hydrophobic polyvinyl alcohol composite film;

[0016] Wherein: the plasticizer in step 1) is a ternary complex of urea, magnesium chloride and magnesium nitrate;

[0017] The cross-linking agent in step 2 is selected from pyromellitic acid.

[0018] In some embodiments, the mass ratio of urea, magnesium chloride and magnesium nitrate is 1:(0.5-2):(0.5-2), more preferably 1:1:1.

[0019] In some embodiments, the mass ratio of the plasticizer to the polyvinyl alcohol in step 1) is 1:1-20, more preferably 1:5-10.

[0020] In some embodiments, the emulsifier is selected from one or more of Tween-60, Tx-10, tristyrylphenol polyoxyethylene ether, tristyrylphenol polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, fatty alcohol polyoxyethylene ether and cardanol polyoxyethylene ether.

[0021] In some embodiments, the toughening modifier is one or both of sodium carboxymethyl cellulose and microcrystalline cellulose.

[0022] In some embodiments, the mass ratio of polyvinyl alcohol to water is 1:1-20, preferably 1:3-10.

[0023] In some embodiments, the heating temperature in step 1) is 60-100°C, more preferably 70-90°C.

[0024] In some embodiments, the heating and stirring reaction time in step 1) is 30 min-3 h, more preferably 1-2 h.

[0025] In some embodiments, the mass ratio of the cross-linking agent to the polyvinyl alcohol in step 2) is (0.5-2):1, more preferably (1-1.5):1.

[0026] In some embodiments, the mass ratio of the toughening modifier to polyvinyl alcohol in step 3) is (0.5-2):1, more preferably (0.4-0.6):1.

[0027] On the other hand, the present invention provides a high-performance hydrophobic polyvinyl alcohol composite film, which is prepared by any of the methods described above.

[0028] Pure PVA film suffers from shortcomings such as brittleness, low elongation at break, and poor water resistance. Plasticizers are often added to improve the mechanical properties and water resistance of PVA film. Commonly used plasticizers for PVA film include small-molecule polyols, alcoholamines, and amides. These small-molecule substances plasticize PVA by forming hydrogen bonds with the hydroxyl groups on the PVA molecular chain, reducing intra- and intermolecular hydrogen bonding, thereby reducing PVA crystallinity and improving its thermoplastic processing properties. Because the effects of a single plasticizer are often unsatisfactory, composite plasticizers are often used to modify PVA.

[0029] The present invention has achieved the following beneficial effects:

[0030] The ternary composite plasticizer used in the present invention can disrupt hydrogen bonds in PVA molecules, reduce PVA's crystallinity and melting point, and significantly plasticize PVA. Compared to single plasticizers and binary plasticizers, the modified PVA film exhibits improved hydrophobicity and mechanical properties.

[0031] In order to further improve the mechanical properties of the PVA film, the present invention also uses chemical cross-linking to modify the PVA film. By performing an esterification reaction between pyromellitic acid and the hydroxyl groups of PVA, the hydroxyl groups in the PVA molecules are masked and cross-linking can be achieved, which can not only improve the hydrophobic properties of PVA, but also greatly enhance the mechanical properties of the PVA film.

[0032] The present invention combines physical modification and chemical cross-linking modification, and the prepared PVA composite film has high hydrophobicity and good mechanical properties and has broad application prospects. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] The endpoints and any values of the ranges described herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0035] Example 1

[0036] 1) Plasticization of polyvinyl alcohol: Add 10 parts of polyvinyl alcohol and 50 parts of water, followed by 2 parts of plasticizer, to a reactor, heat to 90°C, and stir for 1 hour to obtain a plasticized polyvinyl alcohol mixed solution;

[0037] 2) Hydrophobic modification of polyvinyl alcohol: 10 parts of pyromellitic acid and 0.5 parts of emulsifier Tween-60 were added to the polyvinyl alcohol mixed solution obtained in step 1), and an esterification reaction was carried out under reflux stirring for 1 hour to obtain a hydrophobically modified polyvinyl alcohol composite material;

[0038] 3) Preparation of a polyvinyl alcohol hydrophobic film: 4 parts carboxymethyl cellulose and 2 parts polydimethylsiloxane were added to the polyvinyl alcohol composite material obtained in step 2) under stirring at 80°C, the mixture was uniformly dispersed, cooled to room temperature, and ultrasonically treated to obtain a uniform and stable film solution. The film was cast and then dried to obtain a high-performance hydrophobic polyvinyl alcohol composite film;

[0039] Wherein: the plasticizer is a mixture of urea, magnesium chloride and magnesium nitrate in a mass ratio of 1:1:1.

[0040] Example 2

[0041] 1) Plasticization of polyvinyl alcohol: Add 10 parts of polyvinyl alcohol and 90 parts of water, followed by 3 parts of plasticizer, to a reactor, heat to 90°C, and stir for 1 hour to obtain a plasticized polyvinyl alcohol mixed solution;

[0042] 2) Hydrophobic modification of polyvinyl alcohol: 15 parts of pyromellitic acid and 0.5 parts of emulsifier Tween-60 were added to the polyvinyl alcohol mixed solution obtained in step 1), and an esterification reaction was carried out under reflux stirring for 1 hour to obtain a hydrophobically modified polyvinyl alcohol composite material;

[0043] 3) Preparation of a polyvinyl alcohol hydrophobic film: 5 parts of carboxymethyl cellulose and 1 part of polydimethylsiloxane were added to the polyvinyl alcohol composite material obtained in step 2) under stirring at 90°C. After uniform dispersion, the mixture was cooled to room temperature and ultrasonically treated to obtain a uniform and stable film solution. The film was cast and then dried to obtain a high-performance hydrophobic polyvinyl alcohol composite film.

[0044] Wherein: the plasticizer is a mixture of urea, magnesium chloride and magnesium nitrate in a mass ratio of 1:1:1.

[0045] Example 3

[0046] 1) Plasticization of polyvinyl alcohol: Add 10 parts of polyvinyl alcohol and 80 parts of water, followed by 2 parts of plasticizer, to a reactor, heat to 90°C, and stir for 1 hour to obtain a plasticized polyvinyl alcohol mixed solution;

[0047] 2) Hydrophobic modification of polyvinyl alcohol: 10 parts of pyromellitic acid and 0.5 parts of emulsifier Tween-60 were added to the polyvinyl alcohol mixed solution obtained in step 1), and an esterification reaction was carried out under reflux stirring for 1 hour to obtain a hydrophobically modified polyvinyl alcohol composite material;

[0048] 3) Preparation of a polyvinyl alcohol hydrophobic film: 4 parts carboxymethyl cellulose and 2 parts polydimethylsiloxane were added to the polyvinyl alcohol composite material obtained in step 2) under stirring at 80°C, the mixture was uniformly dispersed, cooled to room temperature, and ultrasonically treated to obtain a uniform and stable film solution. The film was cast and then dried to obtain a high-performance hydrophobic polyvinyl alcohol composite film;

[0049] Wherein: the plasticizer is a mixture of urea, magnesium chloride and magnesium nitrate in a mass ratio of 1:0.5:2.

[0050] Example 4

[0051] 1) Plasticization of polyvinyl alcohol: Add 10 parts of polyvinyl alcohol and 80 parts of water, followed by 1 part of plasticizer, to a reactor, heat to 90°C, and stir for 1 hour to obtain a plasticized polyvinyl alcohol mixed solution;

[0052] 2) Hydrophobic modification of polyvinyl alcohol: 10 parts of pyromellitic acid and 0.5 parts of emulsifier Tween-60 were added to the polyvinyl alcohol mixed solution obtained in step 1), and an esterification reaction was carried out under reflux stirring for 1 hour to obtain a hydrophobically modified polyvinyl alcohol composite material;

[0053] 3) Preparation of a polyvinyl alcohol hydrophobic film: 4 parts carboxymethyl cellulose and 2 parts polydimethylsiloxane were added to the polyvinyl alcohol composite material obtained in step 2) under stirring at 80°C, the mixture was uniformly dispersed, cooled to room temperature, and ultrasonically treated to obtain a uniform and stable film solution. The film was cast and then dried to obtain a high-performance hydrophobic polyvinyl alcohol composite film;

[0054] Wherein: the plasticizer is a mixture of urea, magnesium chloride and magnesium nitrate in a mass ratio of 1:0.5:2.

[0055] Comparative Example 1

[0056] The method of Example 1 is referred to, except that the plasticizer is a mixture of urea and magnesium chloride in a mass ratio of 1:1.

[0057] Comparative Example 2

[0058] The method of Example 1 is referred to, except that the plasticizer is a mixture of urea and magnesium nitrate in a mass ratio of 1:1.

[0059] Comparative Example 3

[0060] The method of Example 1 was followed, except that 10 parts of stearic acid were used instead of pyromellitic acid.

[0061] Example 5: Water vapor transmission rate test:

[0062] Select examples and comparative samples with no wrinkles, stains, pinholes, and uniform thickness. Add 10 mL of deionized water to the moisture permeable cup, then gently put in a black sealing ring to prevent the sample from contacting the moisture at the bottom of the cup. Then put in the cut sample film, then put in another black sealing rubber ring, and finally put in the white sealing ring and tighten the cup lid to ensure that the sample does not shake significantly. Place all assembled moisture permeable cups in the corresponding chambers in the water vapor permeability tester, and check the water vapor permeability value after 12 hours. Test three times and calculate the average value. The water vapor permeability coefficient conversion formula is:

[0063] WVP=WVTR×(d / ⊿p),

[0064] Where: WVP - water vapor transmission coefficient, g.cm / cm 2 .s.pa;

[0065] WVTR——Water vapor transmission value measured by the instrument, g / (m 2 day)

[0066] The test results are as follows:

[0067]

[0068] Example 6: Mechanical properties test:

[0069] The tensile strength of the composite film was measured using a servo high and low temperature controlled tensile testing machine. The tensile speed was 50 mm and 1 mm / s. Each sample should be tested five times and the calculated results were averaged.

[0070]

[0071] The above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance hydrophobic polyvinyl alcohol composite film, comprising the following steps: 1) Plasticization of polyvinyl alcohol: Add polyvinyl alcohol and water to a reactor, then add a plasticizer, heat and stir to react, and obtain a plasticized polyvinyl alcohol mixed solution; 2) Hydrophobic modification of polyvinyl alcohol: adding a crosslinking agent and an emulsifier to the polyvinyl alcohol mixed solution obtained in step 1), and performing an esterification reaction under constant temperature and stirring conditions to obtain a hydrophobically modified polyvinyl alcohol composite material; 3) Preparation of a polyvinyl alcohol hydrophobic film: The polyvinyl alcohol composite material obtained in step 2) is added with a toughening modifier under stirring at 80°C to 90°C, uniformly dispersed, cooled to room temperature, and ultrasonically treated to obtain a uniform and stable film solution. The film is cast and then dried to obtain a high-performance hydrophobic polyvinyl alcohol composite film; in: The plasticizer in step 1) is a ternary complex of urea, magnesium chloride and magnesium nitrate; The mass ratio of urea, magnesium chloride and magnesium nitrate is 1: (0.5 -2): (0.5 -2); The mass ratio of the plasticizer to the polyvinyl alcohol in step 1) is 1:1-20; The cross-linking agent in step 2 is selected from pyromellitic acid.

2. The preparation method according to claim 1, wherein the mass ratio of urea, magnesium chloride and magnesium nitrate is 1:1:

1.

3. The preparation method according to claim 1, wherein: The emulsifier is selected from one or more of Tween-60, Tx-10, tristyrylphenol polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, fatty alcohol polyoxyethylene ether and cardanol polyoxyethylene ether.

4. The preparation method according to claim 1, wherein: The toughening modifier is one or both of sodium carboxymethyl cellulose and microcrystalline cellulose.

5. The preparation method according to claim 1, wherein: The mass ratio of polyvinyl alcohol to water is 1:1-20.

6. The preparation method according to claim 1, wherein: The heating temperature of step 1) is 60-100° C.; the heating and stirring reaction time of step 1) is 30 min-3 h.

7. The preparation method according to claim 1, wherein: The mass ratio of the cross-linking agent to the polyvinyl alcohol in step 2) is (0.5-2):1; the mass ratio of the toughening modifier to the polyvinyl alcohol in step 3) is (0.5-2):

1.

8. A high-performance hydrophobic polyvinyl alcohol composite film, characterized in that: It is prepared by the method according to any one of claims 1 to 7.

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