A phosphorus-nitrogen flame retardant and a flame-retardant polyvinyl alcohol composite material based thereon

Abstract

The present invention discloses a phosphorus-nitrogen flame retardant and a flame-retardant polyvinyl alcohol composite material based thereon. The phosphorus-nitrogen flame retardant is produced by reacting phenylphosphoryl dichloride and 1,3-diamino-2-propanol. Adding the phosphorus-nitrogen flame retardant to polyvinyl alcohol via a melt processing method significantly improves the flame retardancy of the polyvinyl alcohol composite material. The phosphorus-nitrogen flame retardant synthesized in the present invention combines the advantages of phosphorus-based and nitrogen-based flame retardants. Furthermore, due to the presence of a large number of hydroxyl groups, the flame retardant has good compatibility with polyvinyl alcohol. Furthermore, the flame retardant is stable at around 200°C and is neither acidic nor alkaline, making it suitable for the melt processing of polyvinyl alcohol films.

Description

Technical Field

[0001] The present invention belongs to the field of flame retardant materials, and in particular relates to a phosphorus-nitrogen flame retardant and a flame retardant polyvinyl alcohol composite material based thereon. Background Art

[0002] Polyvinyl alcohol (PVA) is used in a wide range of applications, including films, fibers, and coatings, due to its excellent water solubility, biocompatibility, and biodegradability. Pure PVA has a limiting oxygen index (LOI) of only around 20%, making it highly flammable. To make PVA materials resistant to emergencies like fires and reduce the resulting casualties and property damage, improving its flame retardancy is crucial, and adding flame retardants is a particularly effective approach. Imparting flame retardancy to PVA films not only significantly improves their safety in high-temperature environments and reduces fire risks, but also expands their application in demanding applications such as packaging, electronics, and building materials.

[0003] Most phosphorus-based and nitrogen-based flame retardants currently on the market are unsuitable for melt processing of PVA films. First, film processing temperatures are high, reaching 180-200°C. Most phosphorus-nitrogen flame retardants readily decompose at these temperatures, losing their flame retardant effectiveness. Second, PVA processing is sensitive to acidic environments. Most phosphorus-based flame retardants are acidic, and their mechanism of action is to decompose at high temperatures to produce phosphoric acid, which promotes the dehydration and carbonization of PVA. Upon addition, within the PVA processing temperature range (180-200°C), they decompose and create an acidic environment, leading to hydrolysis of the PVA. Furthermore, the addition of nitrogen-based flame retardants containing a large number of amino groups, such as melamine, creates an alkaline environment, causing crosslinking between PVA molecules. This leads to hardening during processing and prevents film formation. Against this backdrop, developing a flame retardant suitable for PVA melt processing is crucial. First, the flame retardant must remain stable and non-degradable at high temperatures. Second, it must not be acidic or alkaline. Finally, it must exhibit good flame retardancy and transparency. Summary of the Invention

[0004] Based on the above-mentioned shortcomings of the prior art, the first object of the present invention is to synthesize a polymeric phosphorus-nitrogen flame retardant (PDSPD) from phenylphosphoryl dichloride and 1,3-diamino-2-propanol, combining the advantages of phosphorus-based and nitrogen-based flame retardants while making it suitable for melt processing of PVA films. The second object of the present invention is to produce a polyvinyl alcohol composite material with excellent flame retardancy by adding PDSPD to polyvinyl alcohol.

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

[0006] The present invention first provides a phosphorus-nitrogen flame retardant, which is poly N-(3-amino-2-hydroxypropyl)-P-phenylphosphonamide chloride prepared by reacting phenylphosphoryl dichloride and 1,3-diamino-2-propanol, named PDSPD. The preparation method thereof comprises the following steps:

[0007] First, 1,3-diamino-2-propanol is added to tetrahydrofuran and heated to 40-50°C to completely melt it. Then, triethylamine is added and mixed evenly. Then, trimethylsilyl chloride is added dropwise and stirred for 8-10 hours to allow the trimethylsilyl chloride to protect the hydroxyl group in the 1,3-diamino-2-propanol. Then, triethylamine is added and mixed evenly. Then, the reaction system is placed in a 0°C ice-water bath, phenylphosphoryl dichloride is added dropwise, and the reaction is stirred for 10-12 hours to obtain a mixed solution. Then, glacial acetic acid is added to the obtained mixed solution and stirred for 8-10 hours to remove the protecting group on the hydroxyl group of the 1,3-diamino-2-propanol. The obtained reaction solution is filtered to remove the precipitate (including triethylamine hydrochloride precipitate and triethylamine acetate precipitate) in the solution. Then, the solution is distilled at 140-160°C to remove the solvent tetrahydrofuran and small molecular substances by distillation. During the distillation process, the product repolymerizes to obtain the final product.

[0008] Preferably, the molar ratio of triethylamine to 1,3-diamino-2-propanol added for the first time is 1.2-1.4:1, the molar ratio of trimethylsilyl chloride to 1,3-diamino-2-propanol is 1:1, the molar ratio of triethylamine to 1,3-diamino-2-propanol added for the second time is 2.4-2.8:1, and the molar ratio of phenylphosphoryl dichloride to 1,3-diamino-2-propanol is 1:1.

[0009] The reaction process of preparing PDSPD of the present invention is as follows Figure 1 As shown:

[0010] Phenyl dichloro sphosphineoxide (PDS), a phosphorus-containing intermediate, is often used as a key raw material for constructing phosphorus-based skeletons in the synthesis of flame retardants. It plays a central role in the preparation of environmentally friendly, highly efficient, phosphorus-nitrogen synergistic flame retardant systems. Its active structure enables it to react with a variety of compounds, thereby designing new flame-retardant materials with diverse structures and excellent performance.

[0011] 1,3-Diamino-2-propanol (DAP) is a trifunctional compound containing two amino groups (–NH2) and one hydroxyl group (–OH) in its structure. It exhibits strong chemical reactivity and is widely used in organic synthesis and biopharmaceuticals, but has not been used in flame retardant synthesis. The present invention discovered that 1,3-diamino-2-propanol can be used as a building block in flame retardant synthesis, making it particularly suitable for the preparation of phosphorus-nitrogen synergistic reactive flame retardants. It enhances the chemical activity and carbonization capacity of flame retardants, and, due to its high hydroxyl content, exhibits good compatibility with PVA.

[0012] In the preparation of PDSPD, the hydroxyl groups in 1,3-diamino-2-propanol are first protected with trimethylsilyl chloride to prevent reaction with phenylphosphoryl dichloride. The hydroxyl protecting groups are then removed under the acidic conditions provided by acetic acid to obtain a hydroxyl-rich phosphorus-nitrogen flame retardant. During the reaction, triethylamine is used as an acid-binding agent to prevent the removal of the protecting groups on 1,3-diamino-2-propanol in the acidic environment.

[0013] The present invention further provides a flame-retardant polyvinyl alcohol composite material, which is prepared by adding the PDSPD to polyvinyl alcohol. In the polyvinyl alcohol composite material, the mass percentage of PDSPD is 10-20%.

[0014] The flame-retardant polyvinyl alcohol composite material is prepared by mixing PDSPD and polyvinyl alcohol powder, placing the mixture in an internal mixer at 170-190° C. for melt processing and internal mixing for 2.5-3 minutes, removing the mixture, placing the mixture in a mold, placing the mixture in a flat plate vulcanizer at 150-160° C. for flattening for 2-3 minutes, and cooling the mixture to obtain the flame-retardant polyvinyl alcohol composite material.

[0015] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0016] 1. The present invention synthesizes a phosphorus-nitrogen flame retardant PDSPD by using phenylphosphoryl dichloride and 1,3-diamino-2-propanol, which combines the advantages of phosphorus-based flame retardants and nitrogen-based flame retardants. At the same time, due to the presence of a large number of hydroxyl groups, PDSPD has good compatibility with PVA. In addition, PDSPD is stable at around 200°C and is neither acidic nor alkaline, making it suitable for the melt processing of PVA films.

[0017] 2. The PDSPD produced by the reaction of phenylphosphoryl dichloride and 1,3-diamino-2-propanol in the present invention decomposes at high temperatures to release phosphoric acid groups and their derivatives, promoting the dehydration of hydroxyl groups (-OH) in the composite material and reducing the production of flammable volatiles. It also induces the composite material to form a char layer with a high carbon content, blocking the transfer of oxygen and heat, inhibiting the combustion process, effectively reducing the heat release rate of the material, reducing the heat released during combustion, and slowing the spread of flames. The nitrogen element in PDSPD releases inert gases such as ammonia (NH3) and nitrogen (N2) during combustion, diluting the oxygen concentration in the combustion zone and inhibiting combustion. The addition of PDSPD can significantly improve the flame retardant properties of PVA composites without affecting their transparency, helping to expand the application of PVA in flame retardancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The process roadmap for the synthesis of PDSPD from phenylphosphoryl dichloride and 1,3-diamino-2-propanol.

[0019] Figure 2 FTIR spectra of phenylphosphoryl dichloride, 1,3-diamino-2-propanol, and PDSPD in Example 1.

[0020] Figure 3 is the hydrogen nuclear magnetic resonance spectrum of PDSPD in Example 1.

[0021] Figure 4 The figure is a bar graph showing the transparency and haze of the polyvinyl alcohol composite materials obtained in the comparative example and examples 1-3.

[0022] Figure 5 These are digital photos of the polyvinyl alcohol composite materials obtained in the comparative example and examples 1-3. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0024] The polyvinyl alcohol used in the following examples is model 1799.

[0025] Example 1

[0026] In this embodiment, the flame retardant polyvinyl alcohol composite material is prepared according to the following steps:

[0027] 1. Preparation of PDSPD

[0028] First, place 200 mL of tetrahydrofuran in a 1 L flat-bottom flask, add 9.01 g of 1,3-diamino-2-propanol, and heat to 45°C to completely dissolve. Then, add 12.1 g of triethylamine and mix thoroughly. Then, slowly add 10.86 g of trimethylsilyl chloride dropwise, stir at 500 rpm for 8 hours, and then add 24.2 g of triethylamine and mix thoroughly. Place the flat-bottom flask in an ice-water bath maintained at 0°C, slowly add 19.5 g of phenylphosphoryl dichloride dropwise, and stir at 500 rpm for 12 hours. Then, add 10 g of glacial acetic acid to the resulting mixture, and stir at 500 rpm for 8 hours. Finally, filter the resulting reaction solution to remove any precipitate, then distill the solution at 140°C. During the distillation process, the product repolymerizes to obtain the final product.

[0029] FTIR spectra of phenylphosphoryl dichloride, 1,3-diamino-2-propanol, and PDSPD are as follows: Figure 2 As shown: (1) FTIR spectrum of phenylphosphoryl dichloride at 1500 cm -1 、1580cm -1 , 1600cm -1 The peaks on the left and right are the vibrations of the benzene ring skeleton, 3125cm -1 The weak peaks on the left and right are CH stretching vibrations, 1100m -1 The strong peaks around are the characteristic stretching vibration peaks of P=O bonds, and at 700cm -1 The peaks around 500-650 cm are assigned to the absorption peaks of the CP bond in the skeleton structure. -1 The peaks near the 1,3-diamino-2-propanol molecule are the characteristic stretching vibration peaks of P-Cl. (2) The 1,3-diamino-2-propanol molecule contains a hydroxyl (-OH) functional group. In the FTIR spectrum, the -OH stretching vibration appears at 3200 cm -1 to 3550cm -1 The -NH2 stretching vibration appears at 3300cm -1 to 3500cm -1 This absorption peak is usually strong, and the amino group participates in hydrogen bonding, which broadens the absorption peak. The stretching vibration of the amino group usually has two relatively strong absorption peaks. Because -NH2 is a dihydrogen atom group, two stretching vibration peaks (one strong and one weak) will be seen. The positions of these two peaks are 3400cm -1 and 3300cm -1 -NH2 bending vibration appears at 1580cm -1 to 1650cm -1 This absorption peak mainly reflects the bending motion of the amino group and is the characteristic absorption peak of the group. The characteristic absorption peak of the -CH2- group is more significant. Its stretching vibration appears at 2800cm-1 to 3000cm -1 This absorption peak is usually strong and is mainly related to the symmetric and asymmetric stretching vibrations of the methylene group. (3) 1100 cm-1 in the FTIR spectrum of phenylphosphoryl dichloride -1 The characteristic peak at 500 cm is clearly visible in the FTIR spectrum of PDSPD. -1 -650cm -1 The strong characteristic peak of the P-Cl bond disappeared, and the peak at 2800 cm in the FTIR spectrum of 1,3-diamino-2-propanol -1 ~3000cm -1 3200cm -1 ~3550cm -1 The characteristic peak at 3300 cm -1 and 3400cm -1 The characteristic peak of -NH2 group disappeared, indicating that PDSPD was successfully synthesized from phenylphosphoryl dichloride and 1,3-diamino-2-propanol.

[0030] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of PDSPD. The four groups of multiple peaks with chemical shifts between 7 and 8 correspond to H in four different chemical environments on the benzene ring. The quartet with a chemical shift at 3.1 ppm corresponds to the -CH2- group in the polymer. The triplet with a chemical shift at 1.2 ppm corresponds to the -OH group in the polymer. The triplet with a chemical shift at 3.7 ppm corresponds to the -NH- group in the polymer. The miscellaneous peak at 1.8 ppm corresponds to the -CH- group. It can be seen that the polymer PDSPD was successfully synthesized from phenylphosphoryl dichloride and 1,3-diamino-2-hydroxypropanol.

[0031] 2. Preparation of flame-retardant polyvinyl alcohol composite materials

[0032] 3.6 g PDSPD and 32.4 g polyvinyl alcohol powder were weighed and mixed, placed in an internal mixer and melt-processed at 180°C for 3 minutes, removed, placed in a mold, placed in a flat plate vulcanizer and flattened at 160°C for 2 minutes, and cooled to obtain a flame retardant polyvinyl alcohol composite material.

[0033] Example 2

[0034] In this embodiment, the flame retardant polyvinyl alcohol composite material is prepared according to the following steps:

[0035] 1. Preparation of PDSPD

[0036] Same as Example 1.

[0037] 2. Preparation of flame-retardant polyvinyl alcohol composite materials

[0038] 5.4 g of PDSPD and 30.6 g of polyvinyl alcohol powder were weighed and mixed, placed in an internal mixer and melt-processed at 180°C for 3 minutes, removed, placed in a mold, placed in a flat plate vulcanizer, and flattened at 160°C for 2 minutes. The mixture was cooled to obtain a flame-retardant polyvinyl alcohol composite material.

[0039] Example 3

[0040] In this embodiment, the flame retardant polyvinyl alcohol composite material is prepared according to the following steps:

[0041] 1. Preparation of PDSPD

[0042] Same as Example 1.

[0043] 2. Preparation of flame-retardant polyvinyl alcohol composite materials

[0044] 7.2 g of PDSPD and 28.8 g of polyvinyl alcohol powder were weighed and mixed, placed in an internal mixer and melt-processed at 180°C for 3 minutes, removed, placed in a mold, placed in a flat plate vulcanizer, and flattened at 160°C for 2 minutes. The mixture was cooled to obtain a flame-retardant polyvinyl alcohol composite material.

[0045] Comparative Example

[0046] This comparative example prepared a blank polyvinyl alcohol material according to the following steps:

[0047] Weigh 36 g of polyvinyl alcohol powder, put it into an internal mixer and melt-process it at 180° C. for 3 minutes, remove it, put it into a mold, put it into a flat plate vulcanizer and flatten it at 160° C. for 2 minutes, and cool it to obtain a polyvinyl alcohol material.

[0048] The following performance tests were performed on the polyvinyl alcohol composite materials obtained in each embodiment and comparative example:

[0049] Limiting oxygen index instrument: HC-2C oxygen index instrument from China Jiangning Analytical Instrument Co., Ltd., the test conditions are in accordance with ASTMD2863;

[0050] Transmittance / haze tester: WGT-S transmittance / haze tester, sample mass 5.0±0.5 mg;

[0051] Cone calorimeter: Nanjing Jiangning Instrument Analysis Factory, China. Test conditions were in accordance with ISO5660-1:2002.

[0052] Table 1 shows the limiting oxygen index (LOI), peak heat release rate (pHRR), total heat release rate (THR), time to ignition (TTI) and carbon residue rate of the samples obtained from the comparative example and examples 1-3. Figure 4 and Figure 5 The figures are the transparency histograms and digital photos of the films of the samples obtained in the comparative example and examples 1-3 respectively.

[0053] Table 1. Performance test data of polyvinyl alcohol composite materials

[0054]

[0055] The data in the table above show that the limiting oxygen index (LOI) of the polyvinyl alcohol composite material increases significantly with increasing PDSPD content. Furthermore, the pHRR and THR of the polyvinyl alcohol composite material are the highest. These values ​​decrease with increasing PDSPD content, reaching their lowest values ​​at 20%. Compared to the comparative example, the pHRR and THR of Example 3 decrease by 76.7% and 93.3%, respectively. The carbon residue produced by combustion in the comparative example is extremely low, at only 0.9%. The carbon residue content of the composite materials with the addition of flame retardant PDSPD is higher than that of the comparative example, with Example 3 having the highest carbon residue content at 8.9%. The flame retardant PDSPD significantly enhances the flame retardancy of the polyvinyl alcohol composite material, significantly increasing the carbon residue produced by the material at high temperatures. The transmittance / haze measurements of pure polyvinyl alcohol films and composite films using a transmittance / haze meter revealed that as the amount of PDSPD added increased, the transparency of the polyvinyl alcohol composite material only slightly decreased, while the haze only slightly increased. This indicates that PDSPD has little effect on the transparency and haze of the polyvinyl alcohol composite material. This also demonstrates that the PDSPD flame retardant prepared by the present invention can be used to prepare polyvinyl alcohol composite materials with excellent flame retardancy and good transparency.

[0056] The above embodiments are typical embodiments of the present invention and are not intended to limit the present invention. Any adjustments and modifications to the described technical solutions made by those skilled in the art shall fall within the scope of protection of the present invention as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims.

Claims

1. A phosphorus-nitrogen flame retardant, characterized in that: The phosphorus-nitrogen flame retardant is poly-N-(3-amino-2-hydroxypropyl)-P-phenylphosphonamide chloride, named PDSPD, prepared by reacting phenylphosphoryl dichloride and 1,3-diamino-2-propanol. The preparation method of the phosphorus-nitrogen flame retardant comprises the following steps: First, 1,3-diamino-2-propanol is added to tetrahydrofuran, heated to 40-50°C to completely melt it, then triethylamine is added and mixed evenly, then trimethylsilyl chloride is added dropwise and stirred for 8-10 hours to allow trimethylsilyl chloride to protect the hydroxyl group in 1,3-diamino-2-propanol; then triethylamine is added and mixed evenly, then the reaction system is placed in a 0°C ice water bath, phenylphosphinoyl dichloride is added dropwise, and the reaction is stirred for 10-12 hours to obtain a mixed solution; glacial acetic acid is added to the obtained mixed solution and stirred for 8-10 hours to remove the protection of the hydroxyl group in 1,3-diamino-2-propanol. The obtained reaction solution is filtered to remove the precipitate in the solution, and the solution is distilled at 140-160° C. During the distillation process, the product is repolymerized to obtain a final product; wherein the molar ratio of triethylamine added for the first time to 1,3-diamino-2-propanol is 1.2-1.4:1, the molar ratio of trimethylsilyl chloride to 1,3-diamino-2-propanol is 1:1, the molar ratio of triethylamine added for the second time to 1,3-diamino-2-propanol is 2.4-2.8:1, and the molar ratio of phenylphosphoryl dichloride to 1,3-diamino-2-propanol is 1:

1.

2. A flame-retardant polyvinyl alcohol composite material, characterized in that: The flame-retardant polyvinyl alcohol composite material is prepared by adding the PDSPD described in claim 1 to polyvinyl alcohol.

3. The flame-retardant polyvinyl alcohol composite material according to claim 2, characterized in that: In the flame-retardant polyvinyl alcohol composite material, the mass percentage of PDSPD is 10-20%.

4. A method for preparing the flame-retardant polyvinyl alcohol composite material according to claim 2 or 3, characterized in that: PDSPD and polyvinyl alcohol powders were mixed, placed in an internal mixer, melt-processed and internally kneaded at 170-190°C for 2.5-3 minutes, removed, placed in a mold, placed in a flat plate vulcanizer, and flattened at 150-160°C for 2-3 minutes, and cooled to obtain a flame retardant polyvinyl alcohol composite material.

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