A method for producing a high-strength water-resistant polyvinyl alcohol film

Abstract

The application discloses a production method of high-strength water-resistant polyvinyl alcohol film and relates to the technical field of high polymer materials. When the high-strength water-resistant polyvinyl alcohol film is prepared, first, quaternary phosphonium salt is prepared by reacting 4-bromobutyric acid and tris(4-fluorophenyl) phosphine, then the quaternary phosphonium salt is subjected to esterification with polyvinyl alcohol to prepare modified polyvinyl alcohol; then, functionalized carbon dots are prepared by taking clove extract, branched polyethyleneimine and cysteine as raw materials, and then the functionalized carbon dots are reacted with 4-formaldehyde benzene boronic acid to prepare boronic acid functionalized carbon dots; the modified polyvinyl alcohol, the boronic acid functionalized carbon dots and sodium carboxymethyl cellulose are mixed and reacted, and after being cast into a film, the high-strength water-resistant polyvinyl alcohol film is prepared by a two-way stretching process. The high-strength water-resistant polyvinyl alcohol film prepared by the application has excellent comprehensive performance, and has good mechanical strength, water resistance and functionality.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a method for producing a high-strength, water-resistant polyvinyl alcohol film. Background Technology

[0002] Polyvinyl alcohol (PVA) is a high-performance, water-soluble polymer material widely used in packaging films, medical materials, and textile sizing due to its excellent film-forming properties, adhesion, and mechanical properties. However, traditional PVA films contain a large number of hydrophilic hydroxyl groups in their molecular chains, resulting in poor water resistance. They easily swell or even dissolve in high-humidity environments or water, significantly reducing their mechanical strength. This severely limits their widespread application in humid environments or aqueous media. Furthermore, ordinary PVA films have relatively limited functionality and cannot meet the comprehensive performance requirements for antibacterial, flame-retardant, and other properties in specific scenarios.

[0003] In recent years, with the rapid development of packaging materials, biomedicine, and other fields, the demand for high-performance film materials has been increasing, and the application scenarios of polyvinyl alcohol (PVA) films have been continuously expanding. In applications such as food packaging and medical device packaging, the film not only needs to possess good mechanical strength but also needs to withstand humid environments and have certain antibacterial functions to prevent microbial growth. Meanwhile, in specialized fields such as electronic device packaging, higher requirements are placed on the flame-retardant properties of materials. Therefore, improving the water resistance and mechanical strength of PVA films through physical or chemical modification methods, and endowing them with more functionality, has become a current research hotspot in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing high-strength, water-resistant polyvinyl alcohol film to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for producing a high-strength, water-resistant polyvinyl alcohol film includes the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed and reacted to prepare tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt; polyvinyl alcohol and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt were reacted in anhydrous N,N-dimethylformamide in the presence of EDC·HCl and 4-dimethylaminopyridine to prepare modified polyvinyl alcohol; (2) The clove extract was mixed with branched polyethyleneimine and cysteine ​​and then subjected to hydrothermal reaction to obtain functionalized carbon dots; the functionalized carbon dots were then reacted with 4-formaldehyde phenylboronic acid to obtain boric acid functionalized carbon dots. (3) Modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose are mixed and reacted, cast into a film, dried, and a water-resistant polyvinyl alcohol film is obtained. (4) The water-resistant polyvinyl alcohol film obtained in step (3) is subjected to biaxial stretching to obtain a high-strength water-resistant polyvinyl alcohol film.

[0006] As an optimization, the mass ratio of 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile in step (1) is 1:(1.55~1.6):(400~450), the reaction temperature is 80~90℃, and the reaction time is 6~8h; the mass ratio of polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphonium salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide is 1:(9~9.5):(3.8~4.1):(0.08~0.12):(50~55).

[0007] As an optimization, the polyvinyl alcohol type in step (1) is polyvinyl alcohol 1797.

[0008] As an optimization, the specific process for preparing boric acid functionalized carbon dots in step (2) is as follows: clove and deionized water are mixed at a mass ratio of 1:(8~9) and stirred at 85~95℃ for 10~15 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water are mixed at a mass ratio of 1:(0.4~0.5):(22~26):(40~50) and stirred at 25~30℃ for 10~20 min, then hydrothermally reacted at 180℃ for 8~9 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol are mixed at a mass ratio of 1:(0.8~1):(20~25) and stirred under light-shielding conditions at 25~30℃ for 20~24 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots.

[0009] As an optimization, the cloves are sourced from local farms in Guangdong Province; the branched polyethyleneimine has an average molecular weight of 25,000.

[0010] As an optimization, the mixing reaction in step (3) involves dissolving the modified polyvinyl alcohol obtained in step (1) in a mixed solvent of dimethyl sulfoxide and deionized water to obtain a modified polyvinyl alcohol solution; dissolving the boric acid functionalized carbon dots obtained in step (2) in a mixed solvent of dimethyl sulfoxide and deionized water to obtain a boric acid functionalized carbon dot solution; dissolving sodium carboxymethyl cellulose in deionized water to obtain a sodium carboxymethyl cellulose solution; adding the boric acid functionalized carbon dot solution dropwise into the modified polyvinyl alcohol solution for reaction, and then adding the sodium carboxymethyl cellulose solution for mixing reaction.

[0011] As an optimization, the mass ratio of modified polyvinyl alcohol, dimethyl sulfoxide, and deionized water in the modified polyvinyl alcohol solution in step (3) is 1:(6.5~7):(13~15); the mass ratio of boric acid functionalized carbon dots, dimethyl sulfoxide, and deionized water in the boric acid functionalized carbon dot solution is 1:(28~32):(65~75); the concentration of the sodium carboxymethyl cellulose solution is 0.3wt%~0.5wt%; and the mass ratio of modified polyvinyl alcohol, boric acid functionalized carbon dots, and sodium carboxymethyl cellulose is 1:(0.15~0.35):(0.08~0.12).

[0012] As an optimization, the reaction conditions after adding the boric acid functionalized carbon dot solution to the modified polyvinyl alcohol solution in step (3) are: reflux and stirring at 120~130℃ for 2~2.5h; the reaction conditions after adding the sodium carboxymethyl cellulose solution are: cooling to 50~60℃ and reflux and stirring for 6~8h; the drying conditions are: drying at 120℃ for 10~12h; and the solid content needs to be reduced to 10wt% before casting.

[0013] As an optimization, the sodium carboxymethyl cellulose in step (3) has an average degree of substitution of 0.7 and a molecular weight of approximately 90,000 g / mol.

[0014] As an optimization, the bidirectional stretching in step (4) is synchronous bidirectional stretching, with a transverse stretching ratio of 2 to 3 times, a longitudinal stretching ratio of 2 to 3 times, and a stretching rate of 15% / s.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention provides a method for producing a high-strength, water-resistant polyvinyl alcohol (PVA) film. First, a quaternary phosphonium salt is generated by reacting 4-bromobutyric acid with tris(4-fluorophenyl)phosphine, and then grafted onto the PVA molecular chain. The introduced quaternary phosphonium salt structure exhibits excellent antibacterial properties, effectively inhibiting bacterial growth. Simultaneously, the presence of phosphorus promotes char formation during combustion, thus acting as a flame retardant. Carbon dots are prepared using clove extract, polyethyleneimine, and cysteine ​​as raw materials, and then functionalized with 4-formaldehyde phenylboronic acid. The resulting boric acid-functionalized carbon dots not only retain the optical stability and biocompatibility of the carbon dots themselves but also introduce a large number of phenylboronic acid groups. These groups can act as crosslinking points to form dynamic borate ester bonds with the hydroxyl groups on the modified PVA, significantly enhancing the mechanical strength and water resistance of the film. Furthermore, the active ingredients in the clove extract endow the carbon dots with good antioxidant and antibacterial capabilities, thereby improving the film's anti-aging properties and long-lasting antibacterial activity.

[0016] Secondly, sodium carboxymethyl cellulose (CMC) is introduced into the crosslinking system of modified polyvinyl alcohol (PVA) and boric acid-functionalized carbon dots. In aqueous solution, CMC dissociates into negatively charged carboxylate ions, which can undergo ionic crosslinking with positively charged quaternary phosphonium salts grafted onto the PVA molecular chains, forming a double-crosslinked network structure that significantly improves the film's density and structural stability. Simultaneously, the hydroxyl groups of CMC itself can form hydrogen bonds with the system, further optimizing the film's overall performance. After casting, simultaneous biaxial stretching is performed to ensure the molecular chains are orderly arranged along the stretching direction, further improving the film's tensile strength and dimensional stability. This invention, through the chemical grafting of functionalized quaternary phosphonium salts, the construction of dynamic covalent crosslinks using boric acid-functionalized carbon dots, the formation of an ionic crosslinking network between CMC and quaternary phosphonium salts, and the combination of biaxial stretching, results in a PVA film that simultaneously possesses excellent mechanical strength, water resistance, antibacterial properties, flame retardancy, and anti-aging properties, showing broad application prospects in food packaging, medical materials, and special packaging. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] To more clearly illustrate the method provided by the present invention, the following embodiments will be described in detail.

[0019] Example 1: A method for producing a high-strength, water-resistant polyvinyl alcohol film, comprising the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed at a mass ratio of 1:1.55:400 and refluxed at 80°C for 6 h. The mixture was then evaporated under reduced pressure to obtain tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt. Polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide were weighed at a mass ratio of 1:9:3.8:0.08:50. Polyvinyl alcohol and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 90°C. The mixture was cooled to 25°C and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl and 4-dimethylaminopyridine were added sequentially. The mixture was stirred and reacted for 18 h. Two volumes of deionized water were added and stirred for 10 min. The mixture was then centrifuged to obtain modified polyvinyl alcohol. (2) Clove and deionized water were mixed at a mass ratio of 1:8 and stirred at 85°C for 10 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water were mixed at a mass ratio of 1:0.4:22:40 and stirred at 25°C for 10 min, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated at 180°C for 8 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol were mixed at a mass ratio of 1:0.8:20 and stirred at 25°C under light-shielding conditions for 20 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots; (3) Weigh modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.08; mix modified polyvinyl alcohol, dimethyl sulfoxide and deionized water in a mass ratio of 1:6.5:13 and stir at 90°C until completely dissolved to obtain a modified polyvinyl alcohol solution; mix boric acid functionalized carbon dots, dimethyl sulfoxide and deionized water in a mass ratio of 1:28:65 and stir at 25~30°C until completely dissolved to obtain a boric acid functionalized carbon dot solution; dissolve sodium carboxymethyl cellulose in deionized water at 0.3wt% to obtain a sodium carboxymethyl cellulose solution; add the boric acid functionalized carbon dot solution dropwise to the modified polyvinyl alcohol solution, reflux and stir at 120°C for 2h, cool to 50°C, add sodium carboxymethyl cellulose solution, reflux and stir for 6h, rotary evaporate to a solid content of 10wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 10h to obtain a water-resistant polyvinyl alcohol film; (4) The water-resistant polyvinyl alcohol film was placed in a biaxial stretching apparatus and simultaneously stretched by 2.5 times in the transverse direction and 2.5 times in the longitudinal direction to obtain a high-strength water-resistant polyvinyl alcohol film.

[0020] Example 2: A method for producing a high-strength, water-resistant polyvinyl alcohol film, comprising the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed at a mass ratio of 1:1.58:430 and refluxed at 85°C for 7 h. The mixture was then evaporated under reduced pressure to obtain tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt. Polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide were weighed at a mass ratio of 1:9.3:4:0.1:53. Polyvinyl alcohol and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 95°C. The mixture was cooled to 27°C and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl and 4-dimethylaminopyridine were added sequentially. The mixture was stirred for 22 h and then added twice the volume of deionized water and stirred for 20 min. The mixture was then centrifuged to obtain modified polyvinyl alcohol. (2) Clove and deionized water were mixed at a mass ratio of 1:8.5 and stirred at 90°C for 13 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water were mixed at a mass ratio of 1:0.45:24:45 and stirred at 27°C for 15 min, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated at 180°C for 8.5 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol were mixed at a mass ratio of 1:0.9:23 and stirred at 27°C under light-shielding conditions for 22 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots; (3) Weigh modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.1; mix modified polyvinyl alcohol, dimethyl sulfoxide and deionized water in a mass ratio of 1:6.8:14 and stir at 95°C until completely dissolved to obtain a modified polyvinyl alcohol solution; mix boric acid functionalized carbon dots, dimethyl sulfoxide and deionized water in a mass ratio of 1:30:70 and stir at 27°C until completely dissolved to obtain a boric acid functionalized carbon dot solution; dissolve sodium carboxymethyl cellulose in deionized water at 0.4 wt% to obtain a sodium carboxymethyl cellulose solution; add the boric acid functionalized carbon dot solution dropwise to the modified polyvinyl alcohol solution, reflux and stir at 125°C for 2.3 h, cool to 55°C, add the sodium carboxymethyl cellulose solution, reflux and stir for 7 h, rotary evaporate to a solid content of 10 wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 11 h to obtain a water-resistant polyvinyl alcohol film; (4) The water-resistant polyvinyl alcohol film was placed in a biaxial stretching apparatus and simultaneously stretched by 2.5 times in the transverse direction and 2.5 times in the longitudinal direction to obtain a high-strength water-resistant polyvinyl alcohol film.

[0021] Example 3: A method for producing a high-strength, water-resistant polyvinyl alcohol film, comprising the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed at a mass ratio of 1:1.6:450 and refluxed at 90°C for 8 h. The mixture was then evaporated under reduced pressure to obtain tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt. Polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide were weighed at a mass ratio of 1:9.5:4.1:0.12:55. Polyvinyl alcohol and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 100°C. The mixture was cooled to 30°C and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl and 4-dimethylaminopyridine were added sequentially. The mixture was stirred for 24 h and then 2 times the volume of deionized water was added and stirred for 30 min. The mixture was then centrifuged to obtain modified polyvinyl alcohol. (2) Clove and deionized water were mixed at a mass ratio of 1:9 and stirred at 95°C for 15 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water were mixed at a mass ratio of 1:0.5:26:50 and stirred at 30°C for 20 min, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated at 180°C for 9 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol were mixed at a mass ratio of 1:1:25 and stirred at 30°C under light-shielding conditions for 24 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots; (3) Weigh the modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.12; mix the modified polyvinyl alcohol, dimethyl sulfoxide and deionized water in a mass ratio of 1:7:15 and stir at 100°C until completely dissolved to obtain a modified polyvinyl alcohol solution; mix the boric acid functionalized carbon dots, dimethyl sulfoxide and deionized water in a mass ratio of 1:32:75 and stir at 30°C until completely dissolved to obtain a boric acid functionalized carbon dot solution; dissolve sodium carboxymethyl cellulose in deionized water at 0.5 wt% to obtain a sodium carboxymethyl cellulose solution; add the boric acid functionalized carbon dot solution dropwise to the modified polyvinyl alcohol solution, reflux and stir at 130°C for 2.5 h, cool to 60°C, add the sodium carboxymethyl cellulose solution, reflux and stir for 8 h, rotary evaporate to a solid content of 10 wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 12 h to obtain a water-resistant polyvinyl alcohol film; (4) The water-resistant polyvinyl alcohol film was placed in a biaxial stretching apparatus and simultaneously stretched by 2.5 times in the transverse direction and 2.5 times in the longitudinal direction to obtain a high-strength water-resistant polyvinyl alcohol film.

[0022] Comparative Example 1: The only difference from Example 2 is the step (3), which changes the phrase “weigh the modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.1” to “weigh the modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.05:0.1”.

[0023] Comparative Example 2: The only difference from Example 2 is the step (3), which changes "weighing modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.1" to "weighing modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.15:0.1".

[0024] Comparative Example 3: The only difference from Example 2 is the step (3), which changes the phrase “weigh the modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.1” to “weigh the modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.35:0.1”.

[0025] Comparative Example 4: The only difference from Example 2 is the step (3), which changes the "weighing modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.1" to "weighing modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.45:0.1".

[0026] Comparative Example 5: The only difference from Example 2 is the difference in step (4), where “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 2.5 times in the transverse direction and 2.5 times in the longitudinal direction” is changed to “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 1 time in the transverse direction and 1 time in the longitudinal direction”.

[0027] Comparative Example 6: The only difference from Example 2 is the difference in step (4), where “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 2.5 times in the transverse direction and 2.5 times in the longitudinal direction” is changed to “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 1.5 times in the transverse direction and 1.5 times in the longitudinal direction”.

[0028] Comparative Example 7: The only difference from Example 2 is the difference in step (4), where “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 2.5 times in the transverse direction and 2.5 times in the longitudinal direction” is changed to “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 2 times in the transverse direction and 2 times in the longitudinal direction”.

[0029] Comparative Example 8: The only difference from Example 2 is the difference in step (4), where “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 2.5 times in the transverse direction and 2.5 times in the longitudinal direction” is changed to “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 3 times in the transverse direction and 3 times in the longitudinal direction”.

[0030] Comparative Example 9: The only difference from Example 2 is the difference in step (4), where “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 2.5 times in the transverse direction and 2.5 times in the longitudinal direction” is changed to “the water-resistant polyvinyl alcohol film is placed in a biaxial stretching apparatus for simultaneous biaxial stretching of 3.5 times in the transverse direction and 3.5 times in the longitudinal direction”.

[0031] Comparative Example 10: A method for producing a high-strength, water-resistant polyvinyl alcohol film includes the following steps: (1) Clove and deionized water were mixed at a mass ratio of 1:8.5 and stirred at 90°C for 13 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water were mixed at a mass ratio of 1:0.45:24:45 and stirred at 27°C for 15 min, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated at 180°C for 8.5 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol were mixed at a mass ratio of 1:0.9:23 and stirred at 27°C under light-shielding conditions for 22 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots; (2) Weigh polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.12; mix polyvinyl alcohol, dimethyl sulfoxide and deionized water in a mass ratio of 1:6.8:14 and stir at 95°C until completely dissolved to obtain a polyvinyl alcohol solution; mix boric acid functionalized carbon dots, dimethyl sulfoxide and deionized water in a mass ratio of 1:30:70 and stir at 27°C until completely dissolved to obtain a boric acid functionalized carbon dot solution; dissolve sodium carboxymethyl cellulose in deionized water at 0.4 wt% to obtain a sodium carboxymethyl cellulose solution; add the boric acid functionalized carbon dot solution dropwise to the polyvinyl alcohol solution, reflux and stir at 125°C for 2.3 h, cool to 55°C, add the sodium carboxymethyl cellulose solution, reflux and stir for 7 h, rotary evaporate to a solid content of 10 wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 11 h to obtain a water-resistant polyvinyl alcohol film; (4) The water-resistant polyvinyl alcohol film was placed in a biaxial stretching apparatus and simultaneously stretched by 2.5 times in the transverse direction and 2.5 times in the longitudinal direction to obtain a high-strength water-resistant polyvinyl alcohol film.

[0032] Comparative Example 11: A method for producing a high-strength, water-resistant polyvinyl alcohol film includes the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed at a mass ratio of 1:1.58:430 and refluxed at 85°C for 7 h. The mixture was then evaporated under reduced pressure to obtain tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt. Polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide were weighed at a mass ratio of 1:9.3:4:0.1:53. Polyvinyl alcohol and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 95°C. The mixture was cooled to 27°C and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl and 4-dimethylaminopyridine were added sequentially. The mixture was stirred for 22 h and then added twice the volume of deionized water and stirred for 20 min. The mixture was then centrifuged to obtain modified polyvinyl alcohol. (2) Weigh modified polyvinyl alcohol and sodium carboxymethyl cellulose at a mass ratio of 1:0.12; mix modified polyvinyl alcohol, dimethyl sulfoxide and deionized water at a mass ratio of 1:6.8:14, and stir at 95°C until completely dissolved to obtain a modified polyvinyl alcohol solution; dissolve sodium carboxymethyl cellulose in deionized water at 0.4 wt% to obtain a sodium carboxymethyl cellulose solution; add sodium carboxymethyl cellulose solution dropwise to modified polyvinyl alcohol solution, reflux and stir at 55°C for 7 h, rotary evaporate to a solid content of 10 wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 11 h to obtain a water-resistant polyvinyl alcohol film; (3) The water-resistant polyvinyl alcohol film was placed in a biaxial stretching apparatus and simultaneously stretched by 2.5 times in the transverse direction and 2.5 times in the longitudinal direction to obtain a high-strength water-resistant polyvinyl alcohol film.

[0033] Comparative Example 12: A method for producing a high-strength, water-resistant polyvinyl alcohol film includes the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed at a mass ratio of 1:1.58:430 and refluxed at 85°C for 7 h. The mixture was then evaporated under reduced pressure to obtain tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt. Polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide were weighed at a mass ratio of 1:9.3:4:0.1:53. Polyvinyl alcohol and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 95°C. The mixture was cooled to 27°C and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl and 4-dimethylaminopyridine were added sequentially. The mixture was stirred for 22 h and then added twice the volume of deionized water and stirred for 20 min. The mixture was then centrifuged to obtain modified polyvinyl alcohol. (2) Clove and deionized water were mixed at a mass ratio of 1:8.5 and stirred at 90°C for 13 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water were mixed at a mass ratio of 1:0.45:24:45 and stirred at 27°C for 15 min, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated at 180°C for 8.5 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol were mixed at a mass ratio of 1:0.9:23 and stirred at 27°C under light-shielding conditions for 22 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots; (3) Weigh the modified polyvinyl alcohol and boric acid functionalized carbon dots at a mass ratio of 1:0.25; mix the modified polyvinyl alcohol, dimethyl sulfoxide, and deionized water at a mass ratio of 1:6.8:14 and stir at 95°C until completely dissolved to obtain a modified polyvinyl alcohol solution; mix the boric acid functionalized carbon dots, dimethyl sulfoxide, and deionized water at a mass ratio of 1:30:70 and stir at 27°C until completely dissolved to obtain a boric acid functionalized carbon dot solution; add the boric acid functionalized carbon dot solution dropwise to the modified polyvinyl alcohol solution, reflux and stir at 125°C for 2.3 h, rotary evaporate to a solid content of 10 wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 11 h to obtain a water-resistant polyvinyl alcohol film; (4) The water-resistant polyvinyl alcohol film was placed in a biaxial stretching apparatus and simultaneously stretched by 2.5 times in the transverse direction and 2.5 times in the longitudinal direction to obtain a high-strength water-resistant polyvinyl alcohol film.

[0034] Comparative Example 13: A method for producing a high-strength, water-resistant polyvinyl alcohol film includes the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed at a mass ratio of 1:1.58:430 and refluxed at 85°C for 7 h. The mixture was then evaporated under reduced pressure to obtain tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt. Polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl, 4-dimethylaminopyridine and anhydrous N,N-dimethylformamide were weighed at a mass ratio of 1:9.3:4:0.1:53. Polyvinyl alcohol and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 95°C. The mixture was cooled to 27°C and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt, EDC·HCl and 4-dimethylaminopyridine were added sequentially. The mixture was stirred for 22 h and then added twice the volume of deionized water and stirred for 20 min. The mixture was then centrifuged to obtain modified polyvinyl alcohol. (2) Clove and deionized water were mixed at a mass ratio of 1:8.5 and stirred at 90°C for 13 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water were mixed at a mass ratio of 1:0.45:24:45 and stirred at 27°C for 15 min, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated at 180°C for 8.5 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol were mixed at a mass ratio of 1:0.9:23 and stirred at 27°C under light-shielding conditions for 22 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots; (3) Weigh modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose in a mass ratio of 1:0.25:0.12; mix modified polyvinyl alcohol, dimethyl sulfoxide and deionized water in a mass ratio of 1:6.8:14 and stir at 95°C until completely dissolved to obtain a modified polyvinyl alcohol solution; mix boric acid functionalized carbon dots, dimethyl sulfoxide and deionized water in a mass ratio of 1:30:70 and stir at 27°C until completely dissolved to obtain a boric acid functionalized carbon dot solution; dissolve sodium carboxymethyl cellulose in deionized water at 0.4 wt% to obtain a sodium carboxymethyl cellulose solution; add the boric acid functionalized carbon dot solution dropwise to the modified polyvinyl alcohol solution, reflux and stir at 125°C for 2.3 h, cool to 55°C, add the sodium carboxymethyl cellulose solution, reflux and stir for 7 h, evaporate to a solid content of 10 wt%, pour onto an plexiglass plate to cast into a film, and dry at 120°C for 11 h to obtain a high-strength water-resistant polyvinyl alcohol film.

[0035] Experimental Example 1: Determination of the optimal amount of boric acid functionalized carbon dots Test method: Determined by solubility. High-strength water-resistant polyvinyl alcohol film was cut into 1cm × 1cm square pieces, dried at 80℃ for 24 hours, and weighed, recorded as W0. These pieces were then immersed in distilled water and stirred at 25~30℃ for 24 hours. The undissolved film was dried at 80℃ for 24 hours and weighed, recorded as W1. The solubility was calculated.

[0036] Solubility (%) = [(W) 0- W1) / W0]×100 The results are shown in Table 1.

[0037] Table 1 ; A comparison of Examples 2 and Comparative Examples 1-4 reveals that the solubility of the high-strength, water-resistant polyvinyl alcohol (PVA) film significantly decreases and then stabilizes with increasing amounts of boric acid-functionalized carbon dots. This is because when the amount of boric acid-functionalized carbon dots is low, the phenylboronic acid groups on the carbon dot surface form borate ester bonds with the hydroxyl groups on the PVA, gradually building a cross-linked network. This consumes some of the hydrophilic hydroxyl groups, and the cross-linked structure restricts the movement of molecular chains, thus significantly reducing the film's water solubility. As the amount of boric acid-functionalized carbon dots continues to increase to a certain range, the cross-linked network gradually becomes more complete and saturated, the internal structure of the film reaches a relatively dense state, and the water solubility remains stable without further decrease. Further increasing the amount of carbon dots has a diminishing effect on improving water solubility. This is because once the cross-linked network is basically formed, the available hydroxyl groups have fully participated in the cross-linking process, and excess carbon dots mainly aggregate or exist as nanospacers, thus contributing little to further reducing water solubility. Therefore, a boric acid-functionalized carbon dot addition amount of 0.25 times the mass of the modified PVA was selected.

[0038] Experimental Example 2: Determination of the optimal stretch ratio for biaxial stretching Test methods: The tensile strength and puncture resistance were determined according to ISO 527-1:2019. The tensile strength of the high-strength water-resistant polyethylene film was tested at a tensile speed of 50 mm / min. The puncture resistance of the high-strength water-resistant polyethylene film was tested according to GB / T 37841-2019. The puncture needle drop speed was 50 mm / min, the inner diameter of the sample fixing ring was 10.0 mm, the diameter of the stainless steel puncture needle was 1 mm, and the hemispherical radius of the needle tip was 0.5 mm. The results are shown in Table 2.

[0039] Table 2 ; A comparison of Examples 2 and Comparative Examples 5-9 reveals that the tensile strength and puncture strength of the high-strength water-resistant polyvinyl alcohol film significantly increase and then decrease with increasing biaxial stretching ratio. This is because under the action of the biaxial stretching force field, both main components in the system undergo structural rearrangement: on the one hand, the polyvinyl alcohol molecular chains align along the stretching direction, simultaneously inducing the crystalline regions to rearrange into a more ordered structure, increasing the size of the crystalline regions and the density of crystalline regions per unit cross-section; on the other hand, sodium carboxymethyl cellulose, as a rigid-chain polymer, also aligns along the in-plane direction under the stretching force field, and its directional alignment further enhances the interfacial interaction with the polyvinyl alcohol matrix. As the stretching ratio increases, the orientation and crystallinity of the polyvinyl alcohol molecular chains continuously improve, and the orientation degree of sodium carboxymethyl cellulose also increases accordingly, with the two synergistically forming a more dense and ordered composite network structure. This highly oriented microstructure can more effectively transfer and disperse stress, while the rigidity of cellulose molecules further enhances the film's resistance to external damage, thus significantly improving its tensile strength and puncture resistance. However, when the stretching ratio is too high, excessive molecular chain orientation leads to excessively tight chain segments, destroying some physical entanglement points. Overstretching may also induce micro-defects or voids. Furthermore, sodium carboxymethyl cellulose, as a rigid molecule, exhibits excessively rigid chain segments due to over-orientation, reducing interfacial compatibility with the polyvinyl alcohol matrix and easily creating stress concentration points. These factors combined disrupt the uniformity of the film's internal structure, resulting in a decrease in mechanical properties. Therefore, the film's mechanical properties reach their optimal level when both the transverse and longitudinal stretching ratios reach 2.5.

[0040] Experimental Example 3: This example tests the properties of the high-strength, water-resistant polyvinyl alcohol films obtained in Examples 1-3 and Comparative Examples 10-13. The specific test items and methods are as follows: Tensile strength test method: The high-strength water-resistant polyvinyl alcohol films obtained in each embodiment and the materials of comparative examples 10-13 were tested for tensile strength according to ISO527-1:2019, with a tensile speed of 50 mm / min.

[0041] Water resistance test method: The high-strength water-resistant polyvinyl alcohol films obtained in each example and the materials of comparative examples 10-13 were cut into 1cm×1cm square pieces, dried at 80℃ for 24h, and weighed, recorded as W0. Then, they were immersed in distilled water and stirred at 25-30℃ for 24h. The undissolved film was dried at 80℃ for 24h and weighed, recorded as W1. The solubility was calculated.

[0042] Solubility (%) = [(W) 0- W1) / W0]×100 Flame retardant performance test method: The high-strength water-resistant polyvinyl alcohol film obtained in each example and the film of comparative examples 10-13 were cut into 12cm×6cm rectangles, and the limiting oxygen index was measured by a VOUCH oxygen index tester (model 5801A).

[0043] Antibacterial performance test method: LB broth agar was poured into disposable petri dishes. After solidification, *Escherichia coli* (ATCC25922) and *Staphylococcus aureus* (ATCC6538) were inoculated into the petri dishes respectively. The high-strength, water-resistant polyvinyl alcohol films obtained in each example and the films of comparative examples 10-13 were cut into circles with a diameter of 5 mm and placed on petri dishes. These plates were incubated in a 37°C incubator for 24 h. The diameter of the inhibition zone was measured using calipers.

[0044] Anti-aging performance testing method: The high-strength water-resistant polyvinyl alcohol films obtained in each example and the films of comparative examples 10-13 were placed in an ultraviolet weathering test chamber for accelerated aging. The films were 50cm away from the ultraviolet light source, and the radiation intensity was 1.5-2W / m. 2 The test temperature was 75℃, the humidity was 60~70%, and the UV exposure time was 10 days. After accelerated aging, the sample was taken out to test the tensile strength and calculate the rate of decline in aging performance.

[0045] Aging performance degradation rate = (1 - tensile strength after aging / tensile strength before aging) × 100% The results are shown in Table 3.

[0046] Table 3 ; A comparison of Examples 1-3 and Comparative Example 10 reveals that the flame retardant, antibacterial, and mechanical properties of the film are significantly improved after quaternary phosphonium salt grafting modification of polyvinyl alcohol. This is because in step (1), tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphonium salt is generated by reacting 4-bromobutyric acid with tris(4-fluorophenyl)phosphine, and then grafted onto the polyvinyl alcohol molecular chain, introducing a phosphorus- and fluorine-containing quaternary phosphonium salt structure. In terms of flame retardancy, phosphorus can promote the cross-linking of the polyvinyl alcohol matrix into carbon during combustion, forming a dense carbon layer covering the film surface, effectively blocking the transfer of oxygen and heat, and improving flame retardant performance; in terms of antibacterial properties, the quaternary phosphonium salt structure carries a positive charge, which can interact electrostatically with the negatively charged bacterial cell membrane, destroying the cell membrane integrity, causing the bacterial contents to leak and die, thereby endowing the film with excellent antibacterial properties; in terms of mechanical properties, the grafted quaternary phosphonium salt undergoes ionic cross-linking, greatly improving the density and structural stability of the film.

[0047] A comparison of Examples 1-3 and Comparative Example 11 reveals that the addition of boric acid functionalized carbon dots during film preparation significantly improves the mechanical properties, water resistance, and anti-aging properties of the film. This is because the phenylboronic acid groups on the surface of the boric acid functionalized carbon dots can form dynamic borate ester bonds with the residual hydroxyl groups on the modified polyvinyl alcohol, constructing a chemical cross-linking network. Furthermore, the boric acid functionalized carbon dots are derived from functionalized carbon dots prepared using clove extract as a raw material. The active ingredients in clove extract possess excellent free radical scavenging capabilities, enabling them to capture free radicals generated during ultraviolet light irradiation or thermo-oxidative aging, inhibiting the oxidative degradation of the polyvinyl alcohol molecular chains. Simultaneously, the carbon dots themselves can absorb ultraviolet light and convert it into heat energy or fluorescence emission, acting as ultraviolet shielding, thereby significantly delaying the aging process of the film and improving its anti-aging properties.

[0048] A comparison of Examples 1-3 and Comparative Example 12 reveals that the addition of sodium carboxymethyl cellulose during film preparation enhances the mechanical and water resistance properties of the film. This is because sodium carboxymethyl cellulose dissociates into negatively charged carboxylate ions in aqueous solution, which can undergo ionic crosslinking reactions with the positively charged quaternary phosphonium salt grafted onto the polyvinyl alcohol molecular chain in step (1), forming a three-dimensional physical crosslinking network that significantly enhances the internal structural density of the film. Simultaneously, the long molecular chain of sodium carboxymethyl cellulose, rich in hydroxyl groups, can form multiple hydrogen bonds with the polyvinyl alcohol matrix, increasing the density of physical entanglement points between molecular chains and further improving the stability of the crosslinking network.

[0049] A comparison of Examples 1-3 and Comparative Example 13 reveals that the tensile strength of the water-resistant polyvinyl alcohol (PVA) film is significantly improved after simultaneous biaxial stretching. This is because under the action of the biaxial stretching force field, the PVA molecular chains align along the stretching direction, simultaneously inducing the crystalline regions to rearrange into a more ordered structure, increasing the size of the crystalline regions and improving crystallinity. Sodium carboxymethyl cellulose (CMC), as a rigid-chain polymer, also aligns under the stretching force field, forming a synergistically reinforcing oriented structure with the PVA molecular chains. This highly oriented microstructure can more effectively transfer and disperse stress, while the enhanced inter-chain interactions after orientation significantly improve the tensile strength of the film.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended technical solutions rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the technical solutions are intended to be included within the present invention.

Claims

1. A method for producing a high-strength, water-resistant polyvinyl alcohol film, characterized in that, Includes the following steps: (1) In a nitrogen atmosphere, 4-bromobutyric acid, tris(4-fluorophenyl)phosphine and acetonitrile were mixed and reacted to prepare tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt; polyvinyl alcohol and tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphine salt were reacted in anhydrous N,N-dimethylformamide in the presence of EDC·HCl and 4-dimethylaminopyridine to prepare modified polyvinyl alcohol; (2) The clove extract was mixed with branched polyethyleneimine and cysteine ​​and then subjected to hydrothermal reaction to obtain functionalized carbon dots; the functionalized carbon dots were then reacted with 4-formaldehyde phenylboronic acid to obtain boric acid functionalized carbon dots. (3) Dissolve the modified polyvinyl alcohol obtained in step (1) in a mixed solvent of dimethyl sulfoxide and deionized water to obtain a modified polyvinyl alcohol solution; the mass ratio of modified polyvinyl alcohol, dimethyl sulfoxide and deionized water in the modified polyvinyl alcohol solution is 1:(6.5~7):(13~15); The boric acid functionalized carbon dots obtained in step (2) are dissolved in a mixed solvent of dimethyl sulfoxide and deionized water to obtain a boric acid functionalized carbon dot solution; the mass ratio of boric acid functionalized carbon dots, dimethyl sulfoxide and deionized water in the boric acid functionalized carbon dot solution is 1:(28~32):(65~75). Sodium carboxymethyl cellulose was dissolved in deionized water to obtain a sodium carboxymethyl cellulose solution; the concentration of the sodium carboxymethyl cellulose solution was 0.3 wt% to 0.5 wt%. The modified polyvinyl alcohol, boric acid functionalized carbon dots and sodium carboxymethyl cellulose were mixed in a mass ratio of 1:(0.15~0.35):(0.08~0.12). The boric acid functionalized carbon dot solution was added dropwise to the modified polyvinyl alcohol solution to react. Then, sodium carboxymethyl cellulose solution was added to mix and react. The mixture was cast into a film and dried to obtain a water-resistant polyvinyl alcohol film. (4) The water-resistant polyvinyl alcohol film obtained in step (3) is subjected to biaxial stretching. The biaxial stretching is synchronous biaxial stretching with a transverse stretching ratio of 2 to 3 times and a longitudinal stretching ratio of 2 to 3 times. The stretching rate is 15% / s to obtain a high-strength water-resistant polyvinyl alcohol film.

2. The method for producing high-strength water-resistant polyvinyl alcohol film according to claim 1, characterized in that, In step (1), the mass ratio of 4-bromobutyric acid, tris(4-fluorophenyl)phosphine to acetonitrile is 1:(1.55~1.6):(400~450), the reaction temperature is 80~90℃, and the reaction time is 6~8h; the mass ratio of polyvinyl alcohol, tris(4-fluorophenyl)phosphine carboxybutyl quaternary phosphonium salt, EDC·HCl, 4-dimethylaminopyridine to anhydrous N,N-dimethylformamide is 1:(9~9.5):(3.8~4.1):(0.08~0.12):(50~55).

3. The method for producing high-strength water-resistant polyvinyl alcohol film according to claim 1, characterized in that, The polyvinyl alcohol in step (1) is polyvinyl alcohol 1797.

4. The method for producing high-strength water-resistant polyvinyl alcohol film according to claim 1, characterized in that, The specific process for preparing boric acid functionalized carbon dots in step (2) is as follows: Clove and deionized water are mixed at a mass ratio of 1:(8~9) and stirred at 85~95℃ for 10~15 min to obtain clove extract; branched polyethyleneimine, cysteine, clove extract and deionized water are mixed at a mass ratio of 1:(0.4~0.5):(22~26):(40~50) and stirred at 25~30℃ for 10~20 min, then hydrothermally reacted at 180℃ for 8~9 h, filtered through a 40-mesh sieve, and rotary evaporated to obtain functionalized carbon dots; functionalized carbon dots, 4-formaldehyde phenylboronic acid and methanol are mixed at a mass ratio of 1:(0.8~1):(20~25) and stirred and reacted at 25~30℃ under light-shielding conditions for 20~24 h, rotary evaporated, washed with acetone, and dried to obtain boric acid functionalized carbon dots.

5. The method for producing high-strength water-resistant polyvinyl alcohol film according to claim 4, characterized in that, The branched polyethyleneimine has an average molecular weight of 25,000.

6. The method for producing high-strength water-resistant polyvinyl alcohol film according to claim 1, characterized in that, The reaction conditions after adding the boric acid functionalized carbon dot solution to the modified polyvinyl alcohol solution in step (3) are: reflux and stirring at 120~130℃ for 2~2.5h; the reaction conditions after adding the sodium carboxymethyl cellulose solution are: cooling to 50~60℃ and reflux and stirring for 6~8h; the drying conditions are: drying at 120℃ for 10~12h; and the solid content needs to be reduced to 10wt% before casting.

7. The method for producing high-strength water-resistant polyvinyl alcohol film according to claim 1, characterized in that, The sodium carboxymethyl cellulose mentioned in step (3) has an average degree of substitution of 0.7 and a molecular weight of approximately 90,000 g / mol.