Low-swelling high-flame-retardant polyvinyl alcohol composite film and preparation method thereof

Abstract

The invention discloses a low-swelling high-flame-retardant polyvinyl alcohol composite film and a preparation method thereof.The low-swelling high-flame-retardant polyvinyl alcohol composite film is prepared through a reaction of a polyvinyl alcohol polymer serving as a matrix, functionalized carbon dots serving as additives and a first solvent, the functionalized carbon dots are prepared through a reaction of a phenylboronic acid derivative R1-C6H4-B (OH) 2, a hydroxyphosphoryl derivative and a second solvent, and the functionalized carbon dots are prepared through a reaction of the phenylboronic acid derivative R1-C6H4-B (OH) 2, the hydroxyphosphoryl derivative and the second solvent. R1 is amino, hydroxyl or aldehyde group. The invention has the advantages of low swelling degree, high flame retardancy, good mechanical strength, hot-pressing remolding, simple and convenient preparation process, greenness and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer composite materials, and particularly relates to a polyvinyl alcohol composite film with low swelling and high flame retardancy and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a biodegradable and renewable polymer that has attracted much attention for its green and environmentally friendly properties. PVA is prepared by the hydrolysis of vinyl acetate and has good water solubility and excellent film forming properties, which makes it show a wide range of application potential in the fields of outer packaging, architectural decoration, electronic appliances, sensors and medical treatment. However, despite these advantages of PVA, its films still have significant technical defects in practical applications, which seriously limit its performance and the expansion of its application range. Specifically, PVA films face the following major problems: high swelling degree, poor water resistance, insufficient mechanical strength and high flammability. These problems make it difficult for unmodified PVA films to meet the requirements of high performance and use in special environments.

[0003] First, the high swelling degree and poor water resistance of PVA film are one of its most prominent defects. Because the PVA molecular chain contains a large number of hydroxyl groups, it has strong hydrophilicity. Untreated PVA film is very easy to swell or even completely dissolve when it comes into contact with water. This characteristic leads to its poor stability in humid environments, limiting its use in application scenarios that require waterproof properties, such as packaging materials or protective layers for electronic components. Secondly, the mechanical strength of PVA film is low and it cannot withstand large external forces, which makes it difficult to use in fields that require high toughness and tensile strength, such as architectural decoration or industrial films. In addition, PVA film exhibits high flammability, and its limiting oxygen index (LOI) is only 19.5%, which is far below the requirements of flame retardant materials. Under the action of flame, PVA film is easily ignited and the flame spreads rapidly, which limits its application in fields such as electronic appliances, architectural decoration, etc. that have high requirements for flame retardant properties.

[0004] To overcome these issues, cross-linking is a common method used in the prior art to modify PVA films. Cross-linking introduces chemical or physical connection points between PVA molecular chains, forming a three-dimensional network structure, thereby improving the film's water resistance and mechanical strength. Commonly used cross-linking agents include borax, formaldehyde, glyoxal, glutaraldehyde, dimethylolurea, and trimethylolmelamine. Taking borax cross-linking as an example, the borate ions in borax react with the hydroxyl groups on the PVA molecular chains to form cross-linking points. However, this method has significant limitations: the cross-link density is significantly affected by the solution pH, temperature, reaction time, and borax concentration, making process control difficult. While the modified PVA films exhibit improved water resistance, they still exhibit high water absorption and swelling rates, resulting in limited improvement in mechanical strength. Furthermore, borax-cross-linked PVA films are prone to de-crosslinking in acidic or alkaline environments, resulting in unstable performance. While other cross-linking agents, such as formaldehyde and glyoxal, can also enhance PVA's water resistance, they are highly toxic and their production process can cause environmental pollution, contradicting PVA's environmentally friendly nature.

[0005] In addition to chemical cross-linking, existing technologies have also attempted to enhance the performance of PVA films by introducing inorganic nanoparticles (such as silica, alumina, etc.). The addition of inorganic nanoparticles can improve the mechanical properties and water resistance of the film to a certain extent, but due to the poor compatibility between PVA and inorganic particles, the nanoparticles are prone to agglomeration in the matrix, resulting in uneven dispersion and limited effect on improving film performance. More importantly, this method cannot effectively solve the high flammability problem of PVA films. In addition, existing cross-linked PVA films can usually only be recycled through solvent reprocessing and cannot be recycled through thermoplastic methods, which greatly limits its application potential in the field of sustainable materials.

[0006] In summary, PVA films face key technical challenges in practical applications, including high swelling, poor water resistance, insufficient mechanical strength, and high flammability. While existing cross-linking methods can improve some of the properties of PVA films to a certain extent, they still suffer from shortcomings such as difficulty controlling cross-link density, high water absorption, limited improvement in mechanical strength, and inability to be thermoplastically reshaped. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and provide a low-swelling and highly flame-retardant polyvinyl alcohol composite film.

[0008] Another object of the present invention is to provide a method for preparing the low-swelling and highly flame-retardant polyvinyl alcohol composite film.

[0009] The technical solutions of the present invention are as follows:

[0010] A low-swelling, highly flame-retardant polyethylene composite film is prepared by reacting a polyvinyl alcohol-based polymer as a matrix, functionalized carbon dots as an additive, and a first solvent, wherein the functionalized carbon dots are prepared by reacting a phenylboronic acid derivative R1-C6H4-B(OH)2, a hydroxyphosphoryl derivative, and a second solvent, and R1 is an amino group, a hydroxyl group, or an aldehyde group.

[0011] In a preferred embodiment of the present invention, the polyvinyl alcohol-based polymer is selected from PVA 1788, PVA 1799, PVA 2099 and PVA 2488.

[0012] In a preferred embodiment of the present invention, the phenylboronic acid derivative R1-C6H4-B(OH)2 is selected from 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-hydroxyphenylboronic acid and 4-formylphenylboronic acid.

[0013] In a preferred embodiment of the present invention, the hydroxyphosphoryl derivative is selected from phytic acid, 2-hydroxyphosphonoacetic acid, trishydroxymethylphosphine oxide and 3-hydroxyphenylphosphine oxide propionic acid.

[0014] In a preferred embodiment of the present invention, the mass ratio of the polyvinyl alcohol-based polymer to the functionalized carbon dots is 5:0.25-2.

[0015] In a preferred embodiment of the present invention, the first solvent is selected from water, methanol, ethanol+water and methanol+water.

[0016] In a preferred embodiment of the present invention, the second solvent is selected from water, methanol+water and ethanol+water.

[0017] The preparation method of the low-swelling, highly flame-retardant polyethylene composite film is characterized by dispersing the polyvinyl alcohol polymer and functionalized carbon dots in a second solvent, reacting at 95°C for 3 hours, then pouring it into a mold, and then sequentially subjecting it to standing, drying, and heat curing treatment to obtain the film.

[0018] In a preferred embodiment of the present invention, the preparation method of the functionalized carbon dots comprises: dissolving the phenylboronic acid derivative R1-C6H4-B(OH)2 and the hydroxyphosphoryl derivative in a first solvent, mixing them, performing a hydrothermal reaction at 190°C for 12 hours, cooling to room temperature, centrifuging, filtering with a filter membrane, dialysis, rotary evaporation and vacuum drying, and obtaining

[0019] In a preferred embodiment of the present invention, the temperature of the heat curing treatment is 135° C. and the time is 4 hours.

[0020] The beneficial effects of the present invention are:

[0021] 1. In the present invention, PVA is compounded with functionalized carbon dots to achieve the multifunctional integrated effect of the PVA film, simplify the complex process of traditional multi-component addition, and significantly improve the uniformity and processing efficiency of the PVA film material.

[0022] 2. The functionalized carbon dots in this invention act as nano-crosslinkers, forming a strong, three-dimensional structure in PVA through both chemical and physical crosslinking mechanisms. This significantly reduces the swelling rate of the PVA film (after immersion in room temperature water for 12 hours, the swelling is less than 50%, far lower than the swelling rate of conventional PVA films (typically exceeding 400%)), thereby improving the water contact angle, water resistance, and mechanical strength. Furthermore, the carbon dots exert a nano-reinforcement effect, further enhancing the mechanical strength of the PVA film.

[0023] 3. The hydroxyl groups in the PVA molecular chains of the present invention react with the phenylboronic acid groups and hydroxyphosphoryl groups on the surface of the functionalized carbon dots to form dynamic covalent chemical bonds based on borate and phosphate esters, which have reversible exchange properties. This allows the broken PVA film fragments to be reshaped into films by hot pressing. The mechanical properties of the film after multiple cycles of reprocessing remain good, which meets the development needs of green materials.

[0024] 4. The flame retardant performance of the PVA film modified with functional group carbon dots is improved, with an oxygen index greater than 30% and a combustion test level reaching VTM-0. Compared with the flammability of existing PVA films (LOI = 19.5%), the flame retardant performance is greatly improved, greatly expanding the application range of PVA.

[0025] 5. The preparation method of the present invention adopts simple processes such as blending, casting and post-curing to prepare PVA composite film, which is simple to operate and easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (a) Transmission electron microscopy image and (b) infrared spectrum of the functionalized carbon dots in Example 1 of the present invention.

[0027] Figure 2 The water contact angles of the PVA (a) prepared in Comparative Example 1 of the present invention and the low swelling and high flame retardant polyethylene composite film (b) prepared in Example 1 are shown.

[0028] Figure 3 This is a schematic diagram of the reprocessing of the low-swelling and highly flame-retardant polyethylene composite film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further illustrated and described below through specific implementation methods in conjunction with the accompanying drawings.

[0030] Example 1

[0031] (1) Weigh 2.5 g of 3-aminophenylboronic acid and 3.75 g of phytic acid, add them to 75 mL of H2O, and dissolve them fully by stirring and ultrasonic treatment to form a uniform mixed solution; then, transfer the mixed solution to a 100 mL reactor and place it in a forced air oven at 190°C for 12 h. After cooling to room temperature, take it out and centrifuge, filter it with a filter membrane, and dialyze it to obtain a carbon dot solution; finally, the carbon dot solution is rotary evaporated at 60°C to obtain a solid, which is further dried in a vacuum oven at 60°C for 24 h to finally obtain functionalized carbon dots.

[0032] (2) 5 g of PVA1799 and 1 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of H2O and reacted at 95°C for 3 h. The resulting mixture was then cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was then heat-cured in a forced-air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0033] Example 2

[0034] (1) Weigh 2.5 g of 2-aminophenylboronic acid and 3.75 g of 2-hydroxyphosphonoacetic acid, add them to 75 mL of methanol, and dissolve them fully by stirring and ultrasonic treatment to form a uniform mixed solution; then, transfer the mixed solution to a 100 mL reactor and place it in a forced air oven, react at 190 ° C for 12 h, and take it out after cooling to room temperature. Then, centrifuge, filter and dialyze to obtain a carbon dot solution; finally, the carbon dot solution is rotary evaporated at 60 ° C to obtain a solid, which is further dried in a vacuum oven at 60 ° C for 24 h to finally obtain functionalized carbon dots.

[0035] (2) 5 g of PVA1788 and 1 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of a mixed solvent of methanol and H₂O. After reacting at 95°C for 3 h, the mixture was cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was thermally cured in a forced air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0036] Example 3

[0037] (1) 2.5 g of 4-hydroxyphenylboronic acid and 3.75 g of tris(hydroxymethyl)phosphine oxide were weighed and added to a mixed solvent of 75 mL of ethanol and H2O. The mixture was fully dissolved by stirring and ultrasonic treatment to form a uniform mixed solution. Subsequently, the mixed solution was transferred to a 100 mL reactor and placed in a forced air oven. The reaction was carried out at 190°C for 12 h. After the temperature was cooled to room temperature, the mixture was taken out and centrifuged, filtered through a filter membrane, and dialyzed to obtain a carbon dot solution. Finally, the carbon dot solution was rotary evaporated at 60°C to obtain a solid, which was further dried in a vacuum oven at 60°C for 24 h to finally obtain functionalized carbon dots.

[0038] (2) 5 g of PVA 2099 and 1 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of a mixed solvent of ethanol and H₂O (volume ratio: ethanol:H₂O = 3:7). After reacting at 95°C for 3 h, the mixture was cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was thermally cured in a forced air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0039] Example 4

[0040] (1) Weigh 2.5 g of 4-formylphenylboronic acid and 3.75 g of 3-hydroxyphenylphosphinoylpropionic acid, add them to 75 mL of a mixed solvent of methanol and H2O, and fully dissolve them by stirring and ultrasonic treatment to form a uniform mixed solution; then, transfer the mixed solution to a 100 mL reactor and place it in a forced air oven for reaction at 190°C for 12 h. After cooling to room temperature, take it out and centrifuge, filter it with a filter membrane, and dialyze it to obtain a carbon dot solution; finally, the carbon dot solution is rotary evaporated at 60°C to obtain a solid, which is further dried in a vacuum oven at 60°C for 24 h to finally obtain functionalized carbon dots.

[0041] (2) 5 g of PVA 2488 and 1 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of a mixed solvent of methanol and H₂O (volume ratio: methanol:H₂O=1:1). After reacting at 95°C for 3 h, the mixture was cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was thermally cured in a forced air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0042] Example 5

[0043] (1) The preparation method of functionalized carbon dots is the same as that in Example 1.

[0044] (2) 5 g of PVA1799 and 0.25 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of H2O and reacted at 95°C for 3 h. The resulting mixture was then cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was then heat-cured in a forced-air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0045] Example 6

[0046] (1) The preparation method of functionalized carbon dots is the same as that in Example 1.

[0047] (2) 5 g of PVA1799 and 0.5 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of H2O and reacted at 95°C for 3 h. The resulting mixture was then cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was then heat-cured in a forced-air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0048] Example 7

[0049] (1) The preparation method of functionalized carbon dots is the same as that in Example 1.

[0050] (2) 5 g of PVA1799 and 1.5 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of H2O and reacted at 95°C for 3 h. The resulting mixture was then cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was then heat-cured in a forced-air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0051] Example 8

[0052] (1) The preparation method of functionalized carbon dots is the same as that in Example 1.

[0053] (2) 5 g of PVA1799 and 2 g of the functionalized carbon dots prepared in step (1) were dispersed in 45 mL of H2O and reacted at 95°C for 3 h. The resulting mixture was then cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was then heat-cured in a forced-air oven at 135°C for 4 h to further crosslink and form a stable, low-swelling, highly flame-retardant polyethylene composite film.

[0054] Comparative Example 1

[0055] 5 g of PVA1799 was dissolved in 45 mL of H2O and reacted at 95°C for 3 h. The mixture was then cast into a 6 cm × 6 cm × 2 cm (length × width × thickness) mold and allowed to stand at room temperature for 24 h. The resulting mixture was then dried in a vacuum oven at 60°C for 24 h. The dried product was then heat-cured in a forced-air oven at 135°C for 4 h. This was used as a control sample and designated PVA.

[0056] Figure 1 The transmission electron micrograph and infrared spectrum of the functionalized carbon dots obtained in Example 1 above show that the functionalized carbon dots are uniformly dispersed nano-spherical particles with clear and distinct lattice fringes and a lattice spacing of approximately 0.26 nm. The infrared spectrum characterization shows that the functionalized carbon dots have phenylboronic acid groups and hydroxyl phosphate groups on their surfaces.

[0057] Figure 2 The contact angle of the prepared film was characterized as follows: the contact angle of the comparative sample in Comparative Example 1 was measured to be 36.1°, and the contact angle of the PVA / 3-APP-CDs film in Example 1 was 80.8°.

[0058] Figure 3 Schematic diagram of film fragment reprocessing: The PVA / 3-APP-CDs film in Example 1 can be repeatedly reprocessed under hot pressing conditions at 90°C for 2 hours. Performance data for films prepared in other Examples and Comparative Example 1 are shown in Table 1. Additionally, performance data for thermoplastic reprocessing of the low-swelling, highly flame-retardant polyethylene composite film prepared in Example 1 are shown in Table 3.

[0059] Table 1 Summary of properties of polyvinyl alcohol flame retardant films of Examples and Comparative Examples

[0060]

[0061] Table 2 Summary of properties of polyvinyl alcohol flame retardant films with different carbon dot addition amounts

[0062]

[0063] Table 3 Mechanical properties of low swelling and high flame retardant polyvinyl alcohol films that meet the requirements of thermoplastic recycling

[0064] As is Reprocessing 1 time Reprocessing 2 times Reprocess 3 times Reprocessing 4 times Reprocessing 5 times Tensile strength (MPa) 151.3 150.5 145.1 139.6 128.2 105.2 Young's modulus (GPa) 3.1 3.0 2.9 2.7 2.5 1.9

[0065] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A low swelling and highly flame retardant polyethylene composite film, characterized by: It is made by reacting a polyvinyl alcohol-based polymer as a matrix, functionalized carbon dots as an additive, and a first solvent, wherein the functionalized carbon dots are made by reacting a phenylboronic acid derivative R1-C6H4-B(OH)2, a hydroxyphosphoryl derivative, and a second solvent, and R1 is an amino group, a hydroxyl group, or an aldehyde group.

2. The low swelling and highly flame retardant polyethylene composite film according to claim 1, characterized in that: The polyvinyl alcohol-based polymer is selected from PVA 1788, PVA 1799, PVA 2099 and PVA 2488.

3. The low swelling and highly flame retardant polyethylene composite film according to claim 1, characterized in that: The phenylboronic acid derivative R1-C6H4-B(OH)2 is selected from 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-hydroxyphenylboronic acid and 4-formylphenylboronic acid.

4. The low swelling and highly flame retardant polyethylene composite film according to claim 1, wherein: The hydroxyphosphoryl derivative is selected from phytic acid, 2-hydroxyphosphonoacetic acid, trishydroxymethylphosphine oxide and 3-hydroxyphenylphosphine oxide propionic acid.

5. The low swelling and highly flame retardant polyethylene composite film according to claim 1, characterized in that: The mass ratio of the polyvinyl alcohol-based polymer to the functionalized carbon dots is 5:0.25-2.

6. The low swelling and highly flame retardant polyethylene composite film according to any one of claims 1 to 5, characterized in that: The first solvent is selected from water, methanol, ethanol+water and methanol+water.

7. The low swelling and highly flame retardant polyethylene composite film according to any one of claims 1 to 5, characterized in that: The second solvent is selected from water, methanol+water and ethanol+water.

8. The method for preparing a low-swelling and highly flame-retardant polyethylene composite film according to any one of claims 1 to 7, characterized in that: The method comprises dispersing the polyvinyl alcohol polymer and the functionalized carbon dots in a second solvent, reacting them at 95° C. for 3 hours, pouring them into a mold, and then sequentially subjecting them to standing, drying, and heat curing treatments to obtain the product.

9. The preparation method according to claim 8, wherein: The preparation method of the functionalized carbon dots includes: dissolving the phenylboronic acid derivative R1-C6H4-B(OH)2 and the hydroxyphosphoryl derivative in a first solvent, mixing them, conducting a hydrothermal reaction at 190°C for 12 hours, cooling to room temperature, and then centrifuging, filtering with a filter membrane, dialysis, rotary evaporation, and vacuum drying to obtain the functionalized carbon dots.

10. The preparation method according to claim 8 or 9, characterized in that: The temperature of the heat curing treatment is 135° C. and the time is 4 hours.

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