Flame-retardant and UV-resistant polyvinyl alcohol composite film and preparation method thereof

Abstract

The present invention discloses a flame-retardant, UV-resistant polyvinyl alcohol (PVA) composite film and a preparation method thereof. Based on the coordination interaction between ions and metal-ligands, the flame-retardant, UV-resistant agent DAD@Ni is prepared using 4,4-diaminodiphenyl sulfone, p-aminobenzenesulfonic acid, diethylenetriaminepenta(methylenephosphonic acid), and nickel nitrate. The flame-retardant, UV-resistant agent is added to a PVA system to produce a PVA composite film that is flame-retardant, UV-resistant, transparent, and has excellent mechanical properties. DAD@Ni exhibits a good flame-retardant effect in PVA. Furthermore, because 4,4-diaminodiphenyl sulfone and p-aminobenzenesulfonic acid contain a large number of aromatic rings, the conjugated system undergoes a π-to-π* conversion upon energy absorption, significantly enhancing the UV absorption capacity of the PVA composite film.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and particularly relates to a flame retardant and UV-resistant polyvinyl alcohol composite film and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble polymer formed by the hydrolysis of polyvinyl acetate. It has a carbon backbone and a large number of hydroxyl groups on its side chains. PVA has excellent film-forming properties, and thin films made from it are non-toxic, odorless, highly transparent, biocompatible, have good gas barrier properties, and possess excellent mechanical properties. They are widely used in drug delivery, separation membrane materials, green packaging materials, tissue engineering, and other fields. However, polyvinyl alcohol is a flammable substance with a limiting oxygen index of only approximately 19%. Combustion can rapidly spread fire, accompanied by thick smoke and a pungent odor, posing a serious threat to personal and property safety. Therefore, to meet the diverse applications of PVA and mitigate its potential safety risks, the development of highly flame-retardant PVA is of great significance.

[0003] Incorporating flame retardants into a PVA matrix is ​​the most effective method for improving the flame retardancy of PVA films. However, this often comes at the expense of optical clarity and mechanical properties. Patent CN 113845678B discloses a method for preparing a transparent, flame-retardant polyvinyl alcohol film, produced from a mixed solution of acid-dissolved L-aspartic acid and polyvinyl alcohol. However, the tensile strength of the flame-retardant polyvinyl alcohol film produced by this method is significantly reduced. Patent CN 101235180A discloses a polyvinyl alcohol material containing phosphorus and nitrogen flame retardants. However, the PVA produced by this method is opaque. Moreover, the additives are inert and physically mix with the PVA, not chemically reacting with it. During use, they easily migrate out of the film upon contact with water, reducing its flame retardancy and causing the film's properties to become unstable. Therefore, developing a simple, mild, and efficient preparation method that imparts excellent flame retardancy and UV resistance to polyvinyl alcohol films without compromising the transparency and mechanical properties of the PVA film remains a pressing technical challenge. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a flame retardant and UV resistant polyvinyl alcohol composite film and a preparation method thereof, aiming to simultaneously give the polyvinyl alcohol film excellent flame retardant and UV resistant properties without reducing its transparency.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention first discloses a flame retardant and anti-ultraviolet agent, which is based on the coordination interaction between ions and metal-ligands and is prepared by using 4,4-diaminodiphenyl sulfone, p-aminobenzenesulfonic acid, diethylenetriamine penta (methylene phosphonic acid) and nickel nitrate. The specific preparation method is as follows: 4,4-diaminodiphenyl sulfone (DDS) and p-aminobenzenesulfonic acid (ASC) are dissolved in deionized water and stirred at room temperature for 2 to 4 hours, then an aqueous solution of diethylenetriamine penta (methylene phosphonic acid) (DTPMP) is added, and the mixture is stirred at 50 to 70°C for 2 to 4 hours to obtain a 4,4-diaminodiphenyl sulfone-p-aminobenzenesulfonic acid-diethylenetriamine penta (methylene phosphonic acid) solution, which is recorded as DAD solution; nickel nitrate hexahydrate is completely dissolved in deionized water to obtain a Ni(NO3)2 solution; the Ni(NO3)2 solution is added to the DAD solution, and the mixture is stirred at room temperature for 2 to 4 hours. h; After the reaction is completed, the flame retardant and anti-ultraviolet agent 4,4-diaminodiphenyl sulfone-p-aminobenzenesulfonic acid-diethylenetriamine penta (methylene phosphonate) chelated nickel is obtained by rotary evaporation and vacuum drying, which is denoted as DAD@Ni. Figure 1 shown.

[0007] Furthermore, the molar ratio of 4,4-diaminodiphenyl sulfone, p-aminobenzenesulfonic acid, diethylenetriaminepenta(methylenephosphonic acid), and nickel nitrate hexahydrate is 1:2:0.4:2.

[0008] The present invention also discloses a flame-retardant and UV-resistant polyvinyl alcohol composite film, which is prepared by adding the flame-retardant and UV-resistant agent DAD@Ni to polyvinyl alcohol, wherein the mass percentage of the polyvinyl alcohol and the DAD@Ni is: polyvinyl alcohol 85-100%, DAD@Ni 5-15%.

[0009] The preparation method of the flame-retardant and UV-resistant polyvinyl alcohol composite film of the present invention is as follows: polyvinyl alcohol and deionized water are added to a three-necked flask, and then placed in a constant temperature oil bath at 95-100°C and stirred until the polyvinyl alcohol is completely dissolved, thereby obtaining a polyvinyl alcohol solution with a mass concentration of 8-12%; a flame-retardant and UV-resistant agent DAD@Ni is added to the polyvinyl alcohol solution, and the solution is magnetically stirred in a constant temperature oil bath at 95-100°C, and then transferred to a polytetrafluoroethylene mold, allowed to stand at room temperature for 24-26 hours, and then dried in an oven at 60-80°C for 8-12 hours, thereby obtaining a flame-retardant and UV-resistant polyvinyl alcohol composite film, which is recorded as PVA / DAD@Ni composite film.

[0010] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0011] 1. The flame retardant and anti-ultraviolet agent DAD@Ni provided by the present invention has good water solubility and can be evenly mixed with polyvinyl alcohol to form a film. The process is simple, the reaction conditions are mild, and the energy consumption is low, making it suitable for industrial promotion and application.

[0012] 2. The flame retardant and anti-ultraviolet agent DAD@Ni provided by the present invention contains nitrogen, phosphorus, and sulfur flame retardant elements, which exhibit high flame retardancy through free radical quenching, condensed phase barrier, and catalytic carbonization effects. In addition, a hydrogen bond cross-linking network is formed between DAD@Ni and PVA, thereby chemically bonding the nitrogen, phosphorus, and sulfur flame retardant elements to the side chains of polyvinyl alcohol. This not only gives the film excellent flame retardant properties (its limiting oxygen index is greater than 28% when containing 10-15 wt% of the flame retardant and anti-ultraviolet agent, and the UL-94 vertical combustion meets the V-0 grade), but also effectively solves the problem of poor compatibility and weak bonding between traditional additive flame retardants and polyvinyl alcohol. At the same time, it improves the tensile strength and elongation at break of polyvinyl alcohol, broadens the application field of polyvinyl alcohol film, and has extremely high industrial production value and prospects.

[0013] 3. The present invention adds the flame retardant and anti-UV agent DAD@Ni to polyvinyl alcohol to produce a polyvinyl alcohol composite film with excellent UV resistance and flame retardancy. Because 4,4-diaminodiphenyl sulfone and p-aminobenzenesulfonic acid contain numerous aromatic rings, the conjugated system undergoes a π→π* conversion upon energy absorption, significantly enhancing the UV absorption capacity of the polyvinyl alcohol composite. Furthermore, the unsaturated double bonds in diethylenetriaminepenta(methylenephosphonic acid) absorb UV light. The synergistic effect of these materials results in the resulting polyvinyl alcohol composite film possessing excellent UV resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the synthetic route of the flame retardant and anti-UV agent DAD@Ni.

[0015] Figure 2 Fourier transform infrared (FTIR) spectra of DAD@Ni, DDS, ASC, and DTPMP.

[0016] Figure 3 XPS spectra of DAD@Ni, including: (a) full spectrum, (b) N 1s, (c) O 1s, (d) P 2p, (e) S2p, and (f) Ni 2p.

[0017] Figure 4 TGA (thermogravimetric analysis) and DTG (differential thermogravimetric) curves of DAD@Ni under N2 atmosphere.

[0018] Figure 5 Thermal stability curves of pure PVA film and PVA / DAD@Ni composite film, where: (a) is the TGA curve and (b) is the DTG curve.

[0019] Figure 6 Heat release rate (HRR) curves of pure PVA film and PVA / DAD@Ni composite film.

[0020] Figure 7Characterization of pure PVA film and PVA / DAD@Ni composite film, where: (a) is a digital photo of the film (a1-a4 correspond to PVA, PVA / 5%-DAD@Ni, PVA / 10%-DAD@Ni, and PVA / 15%-DAD@Ni, respectively), (b) is the FTIR spectrum, (c) is the XRD pattern, (d) is the UV-visible absorption spectrum (UVC, UVB, and UVA are short-wave ultraviolet, medium-wave ultraviolet, and long-wave ultraviolet, corresponding to wavelengths of 200-280 nm, 280-320 nm, and 320-400 nm, respectively), (e) is the visible light transmittance, and (f) is the haze.

[0021] Figure 8 Stress-strain curves of pure PVA film and PVA / DAD@Ni composite film.

[0022] Figure 9 Pure PVA film ( Figure 9 (a)) and PVA / 10%-DAD@Ni composite film ( Figure 9 (b) FTIR spectra of pyrolysis products at different temperatures.

[0023] Figure 10 Digital photos of carbon residues of pure PVA film and PVA / DAD@Ni composite film after cone calorimeter test ( Figure 10 (a)-(d) in), scanning electron microscopy ( Figure 10 (a')-(d') correspond to Figure 10 (a)-(d) in the figure).

[0024] Figure 11 Raman spectra of carbon residues of pure PVA film and PVA / DAD@Ni composite film after cone calorimeter test, where: (a) corresponds to PVA film, (b) corresponds to PVA / 5%-DAD@Ni composite film, (c) corresponds to PVA / 10%-DAD@Ni composite film, and (d) corresponds to PVA / 15%-DAD@Ni composite film.

[0025] Figure 12 FTIR spectra of carbon residues of pure PVA film and PVA / DAD@Ni composite film after cone calorimeter test. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] The polyvinyl alcohol used in the following examples is model 1799.

[0028] Example 1

[0029] In this embodiment, a flame-retardant and UV-resistant polyvinyl alcohol composite film is prepared according to the following steps:

[0030] 1. Preparation of DAD@Ni

[0031] DDS (0.01 mol) and ASC (0.02 mol) were dissolved in 300 mL of deionized water and stirred at room temperature for 3 hours. DTPMP (0.004 mol, as a 50% by mass DTPMP solution) was then added, and the mixture was stirred at 60°C for 3 hours to obtain a DAD solution. Nickel nitrate hexahydrate (0.02 mol) was completely dissolved in 30 mL of deionized water to obtain a Ni(NO₃)₂ solution. Subsequently, the Ni(NO₃)₂ solution was slowly added to the DAD solution, and the mixture was stirred at room temperature for 3 hours. Finally, the deionized water was evaporated using a rotary evaporator to obtain a light green product, which was washed three times with anhydrous ethanol and dried in vacuo at 60°C for 24 hours to obtain the flame retardant and UV-resistant agent DAD@Ni.

[0032] 2. Preparation of flame retardant and UV-resistant polyvinyl alcohol composite film

[0033] 19 g of polyvinyl alcohol and 160 mL of deionized water were weighed and added to a three-necked flask, which was then placed in a constant temperature oil bath at 95°C and stirred until the polyvinyl alcohol was completely dissolved to obtain a polyvinyl alcohol solution. 1 g of DAD@Ni was added to the polyvinyl alcohol solution, and the mixture was magnetically stirred in a constant temperature oil bath at 95°C for 2 h. The resulting film was transferred to a polytetrafluoroethylene mold, allowed to stand at room temperature for 24 h, and then dried in an oven at 70°C for 10 h to obtain a flame-retardant and UV-resistant polyvinyl alcohol composite film, designated as PVA / 5%-DAD@Ni.

[0034] Example 2

[0035] In this example, a flame-retardant and UV-resistant polyvinyl alcohol composite film was prepared by the same method as in Example 1, except that in step 2, the amounts of polyvinyl alcohol and DAD@Ni were 18 g and 2 g, respectively. The obtained film was designated as PVA / 10%-DAD@Ni.

[0036] Example 3

[0037] In this example, a flame-retardant and UV-resistant polyvinyl alcohol composite film was prepared by the same method as in Example 1, except that in step 2, the amounts of polyvinyl alcohol and DAD@Ni were 17 g and 3 g, respectively. The resulting film was designated PVA / 15%-DAD@Ni.

[0038] Comparative Example

[0039] In this comparative example, a pure polyvinyl alcohol film without adding a flame retardant was prepared: 20 g of polyvinyl alcohol and 160 mL of deionized water were weighed and added to a three-necked flask, which was then placed in a constant temperature oil bath at 95°C and stirred until the polyvinyl alcohol was completely dissolved to obtain a polyvinyl alcohol solution; the polyvinyl alcohol solution was transferred to a polytetrafluoroethylene mold, allowed to stand at room temperature for 24 h, and then dried in a 70°C oven for 10 h to obtain a pure PVA film.

[0040] The samples obtained from each embodiment and comparative example were subjected to the following characterization and performance tests:

[0041] Fourier Transform Infrared Spectroscopy (FTIR): Powder samples were tested using the potassium bromide pellet method on a Nicolet 6700 Fourier Transform Infrared Spectrometer (Nicolet Instruments Co., USA). PVA composite films were tested using the attenuated total reflectance (ATR) technique.

[0042] Thermogravimetric testing: TGA / DTG graphs were recorded using a Q50 TGA (TA Instruments, USA) under a nitrogen atmosphere at a heating rate of 10 °C / min.

[0043] Transparency test: The absorption and transmittance of the PVA composite film at 200–800 nm were measured using a UV–visible–near-infrared spectrometer (solid-spec-3700, Japan).

[0044] X-ray diffractometer test (XRD): X-ray diffractometer (D8A, BRUKER, Germany) was used to test the XRD of PVA composite films with a scanning speed of 2 ° / min and a 2θ range of 5-80°.

[0045] Mechanical properties test: A 3010 testing machine (Shenzhen Ruige Instrument Co., Ltd., China) was used to test the mechanical properties of the PVA composite film. The test standard was GB / T 1040.3-2006.

[0046] Limiting Oxygen Index Test (LOI): The LOI of PVA composite film was tested using an HC-2 oxygen index meter (China), and the implementation standard was GB / T 2406.2-2009.

[0047] Vertical Flame Test (UL-94): A ZF-3 vertical flame tester (Jiangning Analytical Instruments, China) was used to test the UL-94 performance of PVA composite films. The implementation standard was ASTM D3801.

[0048] Cone calorimeter test (CCT): The combustion performance of PVA composite film was tested using a 6810 cone calorimeter (Vouch, Suzhou) in accordance with ISO 5660. The heat flux was 50 kW / m2 .

[0049] Thermogravimetric infrared (TG-IR) testing: TGA Q50 thermogravimetric analyzer and Nicolet IS50 Fourier transform infrared spectrometer were used to detect the gas products during the thermal degradation process.

[0050] Scanning electron microscopy (SEM): The microstructure of the carbon residue was observed using a JEOL JSM-7500F cold field emission scanning electron microscope (JEOL Ltd.). The accelerating voltage was 15 kV.

[0051] Laser Raman spectroscopy (Raman): SPEX-1403 laser spectrometer was used to analyze the microstructure of carbon slag, with a test range of 500 ~ 2000 cm -1 .

[0052] The test results are as follows:

[0053] 1. Structural characterization of DAD@Ni

[0054] The structure of DAD@Ni was preliminarily characterized by Fourier transform infrared spectroscopy (FTIR). Figure 2 For DDS, at 3445 cm -1 and 3392 cm -1 The absorption peaks at 2876 cm-1 belong to the symmetric and asymmetric stretching vibrations of -NH2. -1 The absorption peak at 1245 cm belongs to the stretching vibration of -OH, and the asymmetric vibration of S=O of -SO3H is at 1245 cm -1 , symmetrical vibration at 1038 cm -1 For DTPMP, 3332 cm -1 and 1632 cm -1 The strong and broad absorption peaks at 1186 cm -1 and 935 cm -1 The absorption peaks at 3445 cm -1 and 3392 cm -1 The absorption band of NH at 1655 cm -1 A new peak appears at -NH3 + NH bending vibrations at 3001, 2783, and 2240 cm -1 A new peak appears at -NH3 + NH stretching vibration. This shows that ASC is bound to DDS and DTPMP through ionic bonds. In addition, Ni 2+After modification, DAD@Ni at 1019 cm -1 A weak absorption band appears near the surface of the substrate, which can be attributed to the formation of PO bonds. This may be due to the Ni 2+ The changes in the above characteristic peaks together confirm the successful preparation of DAD@Ni.

[0055] In order to further verify the successful synthesis of DAD@Ni, its elemental composition and chemical state were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 3 (a)-(f) are shown. The test results show that DAD@Ni contains C, N, O, P, S and transition metal Ni, which is consistent with the theoretical design. In the N 1s spectrum of DAD@Ni, the signal peak at 402.12 eV is attributed to the protonated amino group (-NH3 + ). In the O 1s spectrum, 531.28 eV corresponds to PO-Ni 2+ key, indicating Ni 2+ Chelates with the phosphonic acid group (-PO3H2) of DTPMP. 532.46 eV corresponds to PO-NH3 + bonds, indicating that ASC and DTPMP self-assembled successfully. In the P 2p spectrum, 132.98 eV and 133.70 eV correspond to the PC / PO and P=O bonds in DTPMP, respectively. In the S 2p spectrum, 167.96 eV and 169.14 eV are attributed to the S 2p 1 / 2 and S 2p 3 / 2 , the splitting distance is 1.18 eV, which is consistent with the typical characteristics of sulfone group (-SO2-). 1 / 2 and Ni 2p 3 / 2 The peaks of Ni 2p 1 / 2 With Ni 2p 3 / 2 The binding energy difference is 17.65 eV, indicating that Ni exists in the chemical state of +2. The above results confirm the successful preparation of DAD@Ni from the perspectives of elemental composition, chemical bonding, and oxidation state.

[0056] The thermal stability of DAD@Ni was studied by thermogravimetric analysis. Figure 4 As shown. The initial decomposition temperature of DAD@Ni (T 5% ) is 210℃. The thermal decomposition process presents three obvious weight loss stages, corresponding to the maximum weight loss rate temperature (T max ) were 216℃ (T max1 )、368℃(T max2 ) and 709℃ (T max3The weight loss in the first stage is likely attributed to the volatilization of adsorbed water and residual solvent. As the temperature increases, ionic bond breakage, dehydroxylation of phosphonic acid groups, decomposition of CN heterocycles, and further degradation of phosphorus-containing derivatives are observed. At 800°C, the carbon residue of DAD@Ni is 29 wt%, demonstrating its excellent high-temperature carbonization ability.

[0057] 2. Thermal stability of PVA / DAD@Ni composite film

[0058] The thermal decomposition behavior and carbon formation ability of pure PVA film and PVA / DAD@Ni composite film under N2 atmosphere were analyzed by thermogravimetric analyzer. TGA and DTG curves are shown in Figure 2. Figure 5 (a) Figure 5 (b). Table 1 contains relevant information, initial decomposition temperature (T 5% ), maximum weight loss rate temperature (T max1 and T max2 ), and the residual carbon rate at 800℃ obtained from TGA. The pure PVA film has two weight loss stages, namely the elimination of the side groups of the PVA molecules and the degradation of the main chain cleavage. Although the PVA / DAD@Ni composite film also shows a two-stage decomposition, its T 5% 、T max1 and T max2 Both were higher than those of pure PVA films. The weight loss rate of the PVA / DAD@Ni composite film decreased significantly at high temperatures (>450°C), and the residual carbon yield increased with increasing DAD@Ni addition (from 4.7 wt% to 26.4 wt% at 800°C). Because the sulfonic acid compounds produced by the decomposition of DAD@Ni at high temperatures promote the cross-linking and rearrangement of PVA, a denser carbon layer is formed during combustion of PVA, effectively preventing heat and gas exchange within and outside the PVA matrix. This improves the thermal stability of the PVA / DAD@Ni composite film.

[0059] Table 1 Thermal decomposition data of pure PVA film and PVA / DAD@Ni composite film under N2 atmosphere

[0060]

[0061] 3. Flame retardant properties of PVA / DAD@Ni composite film

[0062] In order to intuitively evaluate the fire safety of PVA composite films, the limiting oxygen index (LOI), vertical UL-94 test, and cone calorimeter (CCT) test were carried out.

[0063] The flame retardancy of pure PVA film and PVA / DAD@Ni composite film was measured using the Limiting Oxygen Index (LOI) and vertical flame tests. The corresponding data are shown in Table 2. The LOI value of pure PVA film was 19.0%, making it a flammable material. When 5%, 10%, and 15% DAD@Ni were added to PVA, the LOI values ​​of the PVA / DAD@Ni composite film were 24.5%, 32.3%, and 34.9%, respectively. With increasing DAD@Ni addition, the LOI value of the PVA / DAD@Ni composite film gradually increased, and its flame retardancy improved.

[0064] The cone calorimetry test (CCT) was used to simulate actual combustion scenarios and demonstrate the flame retardancy of the composite materials. The corresponding data are shown in Table 3. The time to ignition (TTI) of pure PVA film was 44 s. The TTI of PVA / 5%-DAD@Ni, PVA / 10%-DAD@Ni, and PVA / 15%-DAD@Ni composite films increased to 69 s, 78 s, and 85 s, respectively, indicating that DAD@Ni significantly delayed the ignition time of PVA. The maximum heat release rate (pHRR) and total heat release (THR) of pure PVA film were 804.17 kW / m 2 and 67.337 MJ / m 2 , burning violently and releasing a large amount of heat. After the introduction of DAD@Ni, the pHRR and THR values ​​of the composite film were significantly reduced, and the carbon residue rate increased from 4.7% of the pure PVA film to 22.9% of the PVA / 10%-DAD@Ni composite film. The time to reach the maximum heat release rate t-pHRR increased significantly. Compared with the pure PVA film, the pHRR of the PVA / 10%-DAD@Ni composite film was reduced by 63.3% (295.53 kW / m 2 ), THR decreased by 46.8% (35.843 MJ / m 2 ), indicating that the material's fire hazard is significantly reduced. In addition, DAD@Ni changes the heat release rate (HRR) curve characteristics of the composite film (e.g. Figure 6 The HRR curve of pure PVA film exhibits a single sharp peak, while the composite film exhibits a double peak phenomenon: the HRR decreases after the first peak because the dense carbon layer formed in the early stage of combustion hinders heat transfer and gas diffusion; as the internal pyrolysis gas accumulates and breaks through the carbon layer, the HRR rises again to form a second peak, and then gradually decreases as the material burns out.

[0065] In the cone calorimetry test, the smoke generation rate (SPR) and total smoke generation (TSP) of the PVA / DAD@Ni composite film were higher than those of the pure PVA film. It is speculated that the introduction of DAD@Ni caused incomplete combustion of the PVA composite film, releasing more smoke particles. During the combustion process, nitrogen and sulfur groups decomposed to produce a large amount of gas, which diffused outward and carried small carbon residue particles, producing a large amount of smoke. During the combustion process, the CO production rate (COP) and CO2 production rate (CO2P) of the PVA / DAD@Ni composite film were significantly lower than those of the pure PVA film. Specifically, compared with the pure PVA film, the COP values ​​of the PVA / 5%-DAD@Ni, PVA / 10%-DAD@Ni and PVA / 15%-DAD@Ni composite films decreased by 18.3%, 45.0% and 61.5%, respectively, and the CO2P values ​​decreased by 63.0%, 73.3% and 81.5%, respectively. This phenomenon is attributed to the physical barrier effect of the carbon layer and the Ni 2+ Synergistic mechanism of catalysis: the dense carbon layer delays the release of pyrolysis gas, while Ni 2+ The COP value is further reduced by promoting the oxidation of CO to CO2. However, since the carbon layer also inhibits the overall combustion efficiency, the CO2P value also decreases with the increase of DAD@Ni addition, indicating that the combustion process is controlled by the condensed phase barrier effect.

[0066] In order to study the flame retardant effect of DAD@Ni on PVA composite films, the fire performance index (FPI) and fire growth index (FGI), two key parameters for evaluating fire safety, were calculated using the equations "FPI = TTI / pHRR" and "FGI = pHRR / t-pHRR". The higher the FPI value, the lower the fire hazard. The lower the FGI, the longer it takes to reach pHRR, indicating that the material has a lower fire hazard. With the addition of flame retardants, the FPI value gradually increased from 0.055 (m 2 •s) / kW increased to 0.264 (m 2 •s) / kW. Furthermore, the FGI values ​​of the PVA / DAD@Ni composite films were lower than those of pure PVA films. The PVA / 10%-DAD@Ni composite films reduced the fire hazard due to their relatively low FGI and relatively high FPI values.

[0067] PVA / DAD@Ni composite films were subjected to UL-94 testing. The relevant data are summarized in Table 2, where t1 represents the flame duration after the first ignition, and t2 represents the flame duration after the second ignition. Upon contact with the flame, the pure PVA film rapidly shrank and burned violently. Even after the flame was removed, the film continued to burn for over 60 seconds, with droplets igniting the underlying standard cotton pad, resulting in a failure to pass any rating (NR). When the DAD@Ni addition level was 5%, the composite film's combustion behavior was similar to that of the pure PVA film and was still classified as NR. When 10% DAD@Ni was added, the flame persisted for 3 seconds after the first ignition and extinguished within 1 second after the second ignition, without igniting the cotton pad, achieving a V-0 rating. When the DAD@Ni addition level was increased to 15%, the flame extinguished within 1 second after both ignitions, with no droplets generated, achieving a V-0 rating. These results demonstrate that the addition of DAD@Ni significantly improves the flame retardancy of the PVA composite film.

[0068] Table 2 LOI, CCT and UL-94 data of pure PVA film and PVA / DAD@Ni composite film

[0069]

[0070] 4. Transparency and UV resistance of PVA / DAD@Ni composite film

[0071] The transparency of PVA film is crucial to its application in fields such as optical films and packaging materials. Figure 7 (a) is a digital photo of pure PVA film and PVA / DAD@Ni composite film. Pure PVA film has excellent transparency, while the composite film with DAD@Ni is light green but still maintains high light transmittance. The text below the film is clearly visible, indicating that the introduction of DAD@Ni does not significantly affect the transparency. The effect of DAD@Ni on the chemical structure of PVA composite film was analyzed by FTIR (see Figure 7 (b)). The characteristic peaks of pure PVA film include: 3288 cm -1 (-OH stretching vibration), 2925 cm -1 (-CH2 asymmetric stretching vibration), 1442cm -1 (bending vibration of -CH2), 1326 cm -1 (-OH in-plane bending vibration), 920 cm -1 (Asymmetric vibration of CC bond. After adding DAD@Ni, the composite film has a -1 and 1187 cm -1 There is an intensity peak at -NH3 + NH bending vibration and P=O stretching vibration. In addition, the -OH peak of PVA (3288 cm -1) shifts to a lower wavenumber of 3268 cm -1 , confirming that DAD@Ni interacts with PVA molecular chains through hydrogen bonds. The crystal structures of the components in the PVA / DAD@Ni composite film were further evaluated by powder XRD, such as Figure 7 (c) As shown. The pure PVA film shows a broad diffraction peak at 19.6°, which is attributed to the (101) crystal plane, indicating its semi-crystalline nature. After the introduction of DAD@Ni, no peak movement was observed, but the peak intensity decreased with the increase of DAD@Ni, indicating that the addition of DAD@Ni does not change the hydrate crystal structure of the PVA polymer, and the resulting PVA composite film maintains an amorphous structure. However, it interferes with crystallization and reduces the crystallinity. The low crystallinity gives the PVA / DAD@Ni composite film excellent flexibility and light transmittance, which meets the performance requirements of packaging materials.

[0072] UV protection can not only improve the reliability and durability of composite materials in engineering applications, but also reduce the potential harm of UV radiation. Therefore, it is crucial to give the PVA matrix excellent UV resistance. The UV-visible absorption spectra, visible light transmittance and haze of pure PVA film and PVA / DAD@Ni composite film at the same thickness (0.1 mm) were tested. The results are as follows: Figure 7 (d), 7(e), and 7(f). The results show that pure PVA film has weak UV resistance, with high transmittance in the UVB (280-320 nm) and UVA (320-400 nm) regions. The UV transmittance of pure PVA film at 280, 320, and 400 nm is 85.9%, 88.4%, and 92.2%, respectively. PVA / DAD@Ni composite film has excellent UV resistance. With increasing PVA / DAD@Ni dosage, the UV transmittance of PVA / 10%-DAD@Ni composite film at 280, 320, and 400 nm decreases by 63.7%, 44.1%, and 31.3%, respectively. Within the visible wavelength spectrum, pure PVA film has a transmittance of 92.3% and a haze of only 2.7%. With increasing DAD@Ni content, the visible light transmittance of the PVA / DAD@Ni composite decreased slightly but remained above 90.8%, demonstrating that DAD@Ni is well dispersed in the PVA film and maintains excellent visible light transparency. Due to the large number of aromatic rings in DDS and ASC, the conjugated system undergoes a π→π* conversion upon energy absorption, significantly enhancing the UV absorption capacity of the PVA. Furthermore, the unsaturated double bonds in DTPMP can absorb UV light. All of these factors contribute to the excellent UV resistance of the PVA composite film. In summary, DAD@Ni imparts excellent UV resistance to the PVA composite film, making it promising for applications in UV protection.

[0073] 5. Mechanical properties of PVA / DAD@Ni composite films

[0074] The mechanical properties of PVA film are the key to whether it can be used as a packaging material. Through tensile tests, the effect of DAD@Ni on the mechanical properties of PVA film was studied. Figure 8 As shown in Table 3, the tensile strength of pure PVA film was 41.9 MPa, and the elongation at break was 281.2%. Adding 5% DAD@Ni increased the tensile strength of the composite film to 54.6 MPa (a 30.3% increase), and the elongation at break reached 367.4% (a 30.7% increase). This is likely due to the hydrogen-bonded cross-linked network formed between DAD@Ni and PVA, which significantly enhanced the intermolecular interaction strength and thus increased the cohesive energy density of the material. However, when the DAD@Ni content increased to 10%–15%, the tensile strength and elongation at break decreased. The tensile strength of the PVA / 10%-DAD@Ni composite film was 51.1 MPa, and the elongation at break was 340.0%, which decreased compared to the 5% DAD@Ni content but remained higher than that of the pure PVA film. This phenomenon may be due to saturation of hydrogen bonding sites, which prevented additional DAD@Ni from forming bonds with PVA. Excessive DAD@Ni agglomerates due to reduced dispersion, thus limiting performance improvements. Nevertheless, the tensile strength and elongation at break of all PVA / DAD@Ni composite films are significantly better than those of pure PVA films.

[0075] Table 3 Mechanical properties of pure PVA film and PVA / DAD@Ni composite film

[0076]

[0077] 6. Flame retardant mechanism

[0078] Thermogravimetric-infrared (TG-IR) analysis was used to analyze the gas phase products of pure PVA film and PVA / 10%-DAD@Ni composite film during thermal decomposition. The Fourier transform infrared (FTIR) spectra at different temperature stages were as follows: Figure 9 As shown in Figure 3, the gas phase products of pure PVA film and PVA / 10%-DAD@Ni composite film are different in many aspects. It is worth noting that the absorption peak intensity of volatile products of samples containing DAD@Ni is generally reduced, indicating that DAD@Ni inhibits the release of gaseous volatile products.

[0079] For pure PVA film, its main decomposition products are released at 350℃. Figure 9 (a), 3736 cm -1 The nearby absorption peak belongs to H2O, 2780-2960 cm -1 The absorption peaks between them are mainly the vibration absorption peaks of CH, 2358 cm-1 The characteristic peak at 1720 cm belongs to CO2. -1 The absorption peak near 1050 cm belongs to the vibration absorption peak of C=O. -1 The characteristic peak at belongs to COC compounds, among which hydrocarbons and carbonyl compounds are combustible substances. Figure 9 In (b), it is worth noting that three new peaks are captured, namely 950 cm -1 NH3 at 1339 cm -1 SO2 at 1086 cm -1 These volatile nitrogen, phosphorus, and sulfur products not only dilute the concentration of combustible gases and oxygen but also terminate the chain reaction by capturing H· and OH·, inhibiting the continued combustion reaction. In summary, DAD@Ni achieves efficient flame retardancy through a gas-phase mechanism.

[0080] By analyzing the residual carbon morphology of pure PVA film and PVA / DAD@Ni composite film after CCT, the regulatory mechanism of DAD@Ni on the flame retardant properties of the condensed phase was revealed. Figure 10 (a)-(d) are digital images of carbon residues of pure PVA film and PVA / DAD@Ni composite film. Figure 10 (a')-(d') are scanning electron microscope images of the corresponding samples. After the pure PVA film is burned, the residual carbon is dispersed and broken, and the surface is rough, which cannot effectively block the diffusion of heat and gas. After adding DAD@Ni to PVA, the outer layer of the residual carbon of the PVA / DAD@Ni composite film forms a continuous dense layer. The outer carbon layer becomes denser, and the inner carbon layer is distributed with many bubbles with a continuous closed sac-like structure. This structure extends the diffusion path of combustible gas and oxygen, and at the same time blocks the transfer of heat to the matrix. The phosphorus and sulfur elements in DAD@Ni may catalyze the cross-linking of PVA into carbon, while Ni 2+ Stabilize the carbon layer structure and ultimately significantly improve flame retardancy through the barrier effect of the condensed phase carbon layer.

[0081] In order to determine the degree of graphitization of carbon and further evaluate the thermal stability of carbon residue, Raman spectroscopy was performed (see Figure 11 (a)-(d)). The spectrum can be divided into two peaks, located at about 155 cm -1 (D peak) and 1580 cm -1 (G peak), corresponding to the vibration of disordered carbon and hybrid graphitic carbon, respectively. The area ratio of D peak to G peak (I D / I G The value is usually used to indicate the degree of graphitization of the material. D / I G The lower the value, the higher the degree of graphitization of the residual carbon, corresponding to better thermal stability. D / IG The value is 2.71. Compared with pure PVA film, the I D / I G The I values ​​of carbon residues of PVA / 5%-DAD@Ni, PVA / 10%-DAD@Ni and PVA / 15%-DAD@Ni composite films were D / I G The values ​​of I decreased by 11.44%, 14.40% and 15.87% respectively (relative to pure PVA film). This change is attributed to the fact that DAD@Ni induces the formation of a highly cross-linked carbon network in the PVA matrix during thermal decomposition, thereby improving the degree of graphitization. With the increase of DAD@Ni addition, I D / I G The continuous decrease in the value indicates that the transformation of amorphous carbon into graphitized structure is enhanced, and finally a denser and continuous carbon layer is formed. It is worth noting that when the addition amount exceeds 10%, I D / I G The slowdown in the reduction suggests that the cross-linking promotion effect may be approaching saturation. This structural evolution significantly improves the physical barrier properties of the carbon layer, providing the material with better thermal protection.

[0082] like Figure 12 As shown, the chemical structure of the carbon residue after vertical combustion was analyzed by FTIR spectroscopy. Compared with the spectrum before combustion ( Figure 7 Compared with (b), the carbon residue of PVA / DAD@Ni composite film after combustion is at 3288 cm -1 、1655 cm -1 、1442 cm -1 and 1326 cm -1 The absorption peak intensity at 1187 cm is significantly reduced, indicating that the -NH2 group is almost completely converted into non-combustible gases (N2 and NH3, etc.) through dehydration carbonization reaction. In addition, compared with the carbon residue of pure PVA film, the absorption peak at 1187 cm is significantly reduced, indicating that the -NH2 group is almost completely converted into non-combustible gases (N2 and NH3, etc.) through dehydration carbonization reaction. -1 The characteristic peaks near 1086 cm are due to the stretching vibration of P=O. -1 and 992 cm -1 The characteristic peaks at 1682 cm are the vibrations of POC and POP, which means that there are phosphate and polyphosphate compounds in the carbon residue of PVA / DAD@Ni composite film, confirming that DAD@Ni induces the formation of a phosphorylated cross-linked network. -1The absorption peak at can be attributed to the stretching vibration of aromatic C=C groups, indicating the formation of conjugated structures within the carbon layer, further explaining the increased carbon residue. These results demonstrate that DAD@Ni exerts its flame retardant effect through a dual mechanism: in the gas phase, the decomposition of nitrogen components releases non-combustible gases, diluting oxygen and combustible gases. In the condensed phase, phosphorus components promote the formation of a cross-linked carbon layer and capture free radicals. Sulfur compounds promote early coking, favoring the formation of carbon residue.

[0083] Based on the comprehensive mechanistic analysis described above, DAD@Ni exhibits flame retardancy in both the gas and condensed phases. TG-IR data reveal that NH₃, SO₂, and POC enter the gas phase, a key factor in improving LOI and UL-94 performance. With increasing temperature, PVA / DAD@Ni generates more gaseous POC and SO₂, which capture free radicals such as H· and OH· through radical elimination reactions, interrupting the combustion reaction and thus exerting its gas-phase flame retardant effect. Furthermore, non-combustible gases (such as NH₃, CO₂, and H₂O) produced during combustion not only remove the heat of combustion but also dilute combustible gases and oxygen. In the condensed phase, the phosphoric acid derivatives formed by DAD@Ni catalyze the carbonization and dehydration of the PVA matrix, thereby promoting the formation of a dense, structured carbon layer. Furthermore, due to the redox and catalytic effects of transition metal ions, PVA / DAD@Ni not only promotes the conversion of CO to CO₂ but also participates in the catalytic carbonization process. Because the sulfonic acid compounds produced by the decomposition of DAD@Ni at high temperatures promote the cross-linking and rearrangement of PVA, the PVA produces a denser char layer during combustion. This dense char residue acts as a shield, preventing heat transfer and oxygen penetration between the matrix and the combustion zone, thereby protecting the underlying PVA matrix. Therefore, DAD@Ni effectively inhibits heat exchange and gas release during the initial stages of PVA combustion, slowing the spread of fire and providing longer escape time.

[0084] The present invention is based on the coordination interaction between ions and metal-ligands, and utilizes DDS, ASC, DTPMP and transition metal Ni 2+ A flame-retardant and UV-resistant agent, DAD@Ni, was developed and incorporated into a PVA matrix, resulting in the successful preparation of a PVA / DAD@Ni film with excellent flame retardancy, transparency, and UV resistance. Due to the hydrogen-bonded crosslinked network between PVA and DAD@Ni, the PVA / DAD@Ni film exhibited significantly superior tensile strength and elongation at break compared to pure PVA film.

[0085] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of the present invention. Therefore, based on the innovative concept of the present invention, changes and modifications to the embodiments described herein, or equivalent structural or equivalent process transformations made using the contents of the present invention specification, and direct or indirect application of the above technical solutions to other related technical fields are all included in the scope of patent protection of the present invention.

Claims

1. A flame retardant and anti-ultraviolet agent, characterized in that: The flame retardant and anti-ultraviolet agent is based on the coordination interaction between ions and metal-ligands, and is a 4,4-diaminodiphenyl sulfone-para-aminobenzenesulfonic acid-diethylenetriaminepenta(methylenephosphonic acid) chelated nickel prepared using 4,4-diaminodiphenyl sulfone, para-aminobenzenesulfonic acid, diethylenetriaminepenta(methylenephosphonic acid) and nickel nitrate. The flame retardant and anti-ultraviolet agent is recorded as DAD@Ni.

2. A method for preparing the flame retardant and anti-ultraviolet agent according to claim 1, characterized in that: The steps include: 4,4-Diaminodiphenyl sulfone and p-aminobenzenesulfonic acid were dissolved in deionized water and stirred at room temperature for 2 to 4 h. Then, an aqueous solution of diethylenetriamine penta (methylene phosphonic acid) was added and stirred at 50 to 70°C for 2 to 4 h to obtain a 4,4-diaminodiphenyl sulfone-p-aminobenzenesulfonic acid-diethylenetriamine penta (methylene phosphonic acid) solution, which was recorded as DAD solution. Nickel nitrate hexahydrate was completely dissolved in deionized water to obtain a Ni(NO3)2 solution. The Ni(NO3)2 solution was added to the DAD solution and stirred at room temperature for 2 to 4 h. After the reaction, the mixture was rotary evaporated and vacuum dried to obtain a flame retardant and anti-ultraviolet agent 4,4-diaminodiphenyl sulfone-p-aminobenzenesulfonic acid-diethylenetriamine penta (methylene phosphonic acid) chelated nickel, which was recorded as DAD@Ni.

3. The method for preparing the flame retardant and anti-ultraviolet agent according to claim 2, wherein: The molar ratio of 4,4-diaminodiphenyl sulfone, p-aminobenzenesulfonic acid, diethylenetriaminepenta(methylenephosphonic acid) and nickel nitrate hexahydrate is 1:2:0.4:

2.

4. A flame-retardant and UV-resistant polyvinyl alcohol composite film, characterized in that: The flame retardant and anti-ultraviolet polyvinyl alcohol composite film is prepared by adding the flame retardant and anti-ultraviolet agent DAD@Ni described in claim 1 to polyvinyl alcohol.

5. The flame retardant and UV resistant polyvinyl alcohol composite film according to claim 4, characterized in that: The mass percentage of the polyvinyl alcohol and the DAD@Ni is: 85-100% polyvinyl alcohol, 5-15% DAD@Ni.

6. A method for preparing the flame-retardant and UV-resistant polyvinyl alcohol composite film according to claim 4 or 5, characterized in that: Polyvinyl alcohol and deionized water are added to a three-necked flask, which is then placed in a constant temperature oil bath at 95-100°C and stirred until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution; a flame retardant and anti-ultraviolet agent DAD@Ni is added to the polyvinyl alcohol solution, and the solution is magnetically stirred in a constant temperature oil bath at 95-100°C, then transferred to a polytetrafluoroethylene mold, allowed to stand at room temperature for 24-26 hours, and then dried in an oven at 60-80°C for 8-12 hours to obtain a flame retardant and anti-ultraviolet polyvinyl alcohol composite film.

7. The method for preparing the flame-retardant and UV-resistant polyvinyl alcohol composite film according to claim 6, wherein: The mass concentration of the polyvinyl alcohol solution is 8-12%.

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