Phosphorus-nitrogen flame retardant and flame-retardant polyvinyl alcohol composite material based on same

Abstract

The invention discloses a phosphorus-nitrogen flame retardant and a flame-retardant polyvinyl alcohol composite material based on the phosphorus-nitrogen flame retardant, the phosphorus-nitrogen flame retardant is prepared by reacting phenyl phosphorus dichloride with 1, 3-diamino-2-propanol, and the flame retardance of the polyvinyl alcohol composite material can be remarkably improved by adding the phosphorus-nitrogen flame retardant into polyvinyl alcohol through a melt processing method. The phosphorus-nitrogen flame retardant synthesized by the invention combines the advantages of a phosphorus-based flame retardant and a nitrogen-based flame retardant, contains a large amount of hydroxyl groups, has good compatibility with polyvinyl alcohol, has stable properties at about 200 DEG C, is not acidic or alkaline, and can be suitable for the melting processing process of a polyvinyl alcohol film.

Description

Technical Field

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

[0002] Due to its good water solubility, biocompatibility and degradability, polyvinyl alcohol (PVA) is applied in many fields such as films, fibers, coatings, etc. The limiting oxygen index (LOI) of pure PVA is only about 20%, which is highly flammable. In order to enable PVA materials to cope with emergencies such as fires and reduce casualties and property losses caused by fires, it is necessary to improve the flame retardant performance of PVA, and adding a flame retardant is a very effective method. By endowing the PVA film with flame retardant performance, not only can its safety in a high-temperature environment be significantly improved, the fire risk can be reduced, but also its applications in high-demand fields such as packaging, electronic products, and building materials can be expanded.

[0003] At present, most phosphorus-based flame retardants or nitrogen-based flame retardants on the market are not applicable to the melt processing process of PVA films. First of all, the film processing temperature is relatively high, reaching 180 - 200 °C, and most phosphorus-nitrogen flame retardants are prone to decomposition at this temperature, thus losing their flame retardant effect. Secondly, PVA is relatively sensitive to an acidic environment during the processing process, and most phosphorus-based flame retardants are acidic. The mechanism of action is that phosphoric acid is generated by decomposition at high temperature to promote the dehydration and carbonization of PVA. After addition, an acidic environment will be generated within the PVA processing temperature range (180 - 200 °C), resulting in the hydrolysis of PVA. In addition, if a nitrogen-based flame retardant containing a large amount of amino groups, such as melamine, is added, an alkaline environment will be generated, resulting in intermolecular cross-linking of PVA and becoming hard during the processing process and thus unable to form a film. Under this background, it is of great significance to develop a flame retardant applicable to the melt processing of PVA. First of all, the flame retardant should remain stable and not decompose at high temperatures. Secondly, the flame retardant should not be acidic or alkaline. Finally, the flame retardant should have good flame retardant effect and transparency. Summary of the Invention

[0004] Based on the deficiencies existing in the above-mentioned prior art, the first object of the present invention is to synthesize a high-molecular phosphorus-nitrogen flame retardant PDSPD through phenylphosphoryl dichloride and 1,3-diamino-2-propanol, so that it combines the advantages of phosphorus-based flame retardants and nitrogen-based flame retardants, and at the same time it is applicable to the melt processing process of PVA films. The second object of the present invention is to prepare a polyvinyl alcohol composite material with excellent flame retardant performance by adding PDSPD to polyvinyl alcohol.

[0005] The present invention adopts the following technical solutions to achieve the purpose: The present invention firstly provides a phosphorus-nitrogen flame retardant, which is poly-N-(3-amino-2-hydroxypropyl)-P-phenylphosphonamide chloride prepared by reacting phenylphosphoryl dichloride with 1,3-diamino-2-propanol, named PDSPD. The preparation method comprises the following steps: Firstly, add 1,3-diamino-2-propanol into tetrahydrofuran, heat it to 40-50 °C to completely melt it, then add triethylamine and mix evenly, and then dropwise add trimethylchlorosilane, and stir for 8-10 h to form a protection for the hydroxyl group in 1,3-diamino-2-propanol; add triethylamine again and mix evenly, then place the reaction system in an ice-water bath at 0 °C, dropwise add phenylphosphoryl dichloride, and stir and react for 10-12 h to obtain a mixed solution; add glacial acetic acid to the obtained mixed solution and stir for 8-10 h to remove the protecting group on the hydroxyl group of 1,3-diamino-2-propanol; filter the obtained reaction solution to remove the precipitates in the solution (including triethylamine hydrochloride precipitate and triethylamine acetate precipitate), and then distill the solution at 140-160 °C to remove the solvent tetrahydrofuran and small molecule substances through distillation, and the product undergoes repolymerization during the distillation process to obtain the final product.

[0006] Preferably, 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 trimethylchlorosilane 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.

[0007] The reaction process for preparing PDSPD in the present invention is as Figure 1 shown: Phenylphosphoryl dichloride (PDS), as a phosphorus-containing intermediate, is often used as a key raw material for constructing a phosphorus-based skeleton in the synthesis of flame retardants, and plays a core role especially in the preparation of an environmentally friendly, efficient, phosphorus-nitrogen synergistic flame retardant system. Its active structure enables it to react with a variety of compounds, thereby designing new flame retardant materials with diverse structures and excellent properties.

[0008] 1,3-Diamino-2-propanol (DAP for short) is a trifunctional compound containing two amino groups (–NH2) and one hydroxyl group (–OH) in its structure. It has strong chemical reactivity and is widely used in the fields of organic synthesis and biopharmaceuticals, but it has not been applied in the field of flame retardant synthesis. The present invention discovers that 1,3-diamino-2-propanol can be used as a building monomer in the synthesis of flame retardants, especially suitable for the preparation of phosphorus-nitrogen synergistic reactive flame retardants. It can not only enhance the chemical activity of the flame retardant and improve the carbonization ability, but also has good compatibility with PVA due to the large amount of hydroxyl groups it contains.

[0009] When preparing PDSPD, the hydroxyl group in 1,3-diamino-2-propanol is first protected by trimethylchlorosilane to avoid its reaction with phenylphosphoryl dichloride, and then the hydroxyl protecting group is removed under the acidic condition provided by acetic acid to obtain a phosphorus-nitrogen flame retardant rich in hydroxyl groups. In the reaction, triethylamine is used as an acid-binding agent to prevent the removal of the protecting group on 1,3-diamino-2-propanol in an acidic environment.

[0010] The present invention further provides a flame-retardant polyvinyl alcohol composite material, which is prepared by adding the above-mentioned PDSPD to polyvinyl alcohol. In the polyvinyl alcohol composite material, the mass percentage of PDSPD is 10-20%.

[0011] The preparation method of the flame-retardant polyvinyl alcohol composite material is as follows: Mix PDSPD and polyvinyl alcohol powder, put them into a mixer and melt and mix them at 170-190°C for 2.5-3 minutes, take them out, put them into a mold, and put them into a flat vulcanizer to flatten them at 150-160°C for 2-3 minutes, and then cool them to obtain the flame-retardant polyvinyl alcohol composite material.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention synthesizes a phosphorus-nitrogen flame retardant PDSPD from phenylphosphoryl dichloride and 1,3-diamino-2-propanol, combining the advantages of phosphorus-based flame retardants and nitrogen-based flame retardants. At the same time, due to the large amount of hydroxyl groups it contains, it has good compatibility with PVA, and PDSPD is stable at about 200°C, neither acidic nor basic, and can be applied to the melting process of PVA films.

[0013] 2. The PDSPD prepared by reacting phenylphosphoryl dichloride with 1,3-diamino-2-propanol will decompose at high temperature to release phosphate groups and their derivatives, promoting the dehydration of hydroxyl groups (-OH) in the composite material, reducing the generation of flammable volatiles, and at the same time inducing the formation of a carbon layer with a high carbon content in the composite material, 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 down the flame propagation. 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 retardancy of the PVA composite material without affecting its transparency, which helps to expand the application of PVA in flame retardancy. Description of the Drawings

[0014] Figure 1 It is a process route diagram for synthesizing PDSPD from phenylphosphoryl dichloride and 1,3-diamino-2-propanol.

[0015] Figure 2 It is the FTIR spectra of phenylphosphoryl dichloride, 1,3-diamino-2-propanol, and PDSPD in Example 1.

[0016] Figure 3 It is the 1H NMR spectrum of PDSPD in Example 1.

[0017] Figure 4 It is a bar chart of the transparency and haze degree of the polyvinyl alcohol composite materials obtained in the comparative example and Examples 1-3.

[0018] Figure 5 It is a digital photo of the polyvinyl alcohol composite materials obtained in the comparative example and Examples 1-3. Detailed Embodiments

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0020] The polyvinyl alcohol used in the following embodiments has the model number 1799.

[0021] Example 1 The flame-retardant polyvinyl alcohol composite material is prepared in the following steps: 1. Preparation of PDSPD First, place 200 mL of tetrahydrofuran in a 1 L flat-bottom flask, add 9.01 g of 1,3-diamino-2-propanol, heat it to 45 °C to completely melt it, then add 12.1 g of triethylamine and mix evenly. Next, slowly drop in 10.86 g of trimethylchlorosilane, stir at 500 rpm for 8 h, and then add 24.2 g of triethylamine and mix evenly. Place the flat-bottom flask in an ice-water bath, maintain at 0 °C, slowly drop in 19.5 g of phenylphosphoryl dichloride, and stir at 500 rpm for 12 h. Then add 10 g of glacial acetic acid to the resulting mixture and stir at 500 rpm for 8 h. Finally, filter the obtained reaction solution to remove the precipitate in the solution, and then distill the solution at 140 °C. During the distillation process, the product undergoes repolymerization to obtain the final product.

[0022] The FTIR spectra of phenylphosphoryl dichloride, 1,3-diamino-2-propanol, and PDSPD are as Figure 2 shown: (1) For the FTIR spectrum of phenylphosphoryl dichloride, the peaks around 1500 cm -1 , 1580 cm -1 , and 1600 cm -1 are for the benzene ring skeleton vibration. The weak peak around 3125 cm -1 is for the C-H stretching vibration. The strong peak around 1100 m -1 is the characteristic stretching vibration peak of the P=O bond. And the peak around 700 cm -1 is assigned as the absorption peak of the C-P bond in the skeleton structure. The peaks near 500 - 650 cm -1 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 in the region of 3200 cm -1 to 3550 cm -1 , and due to the presence of hydrogen bonds, the peak is broad. The -NH2 stretching vibration appears between 3300 cm -1 and 3500 cm -1 . This absorption peak is usually strong, and since the amino group participates in hydrogen bonding, the absorption peak becomes broad. The stretching vibration of the amino group usually has two relatively strong absorption peaks because -NH2 is a dihydrogen atom group, so two stretching vibration peaks (one strong and one weak) can be seen, and the positions of these two peaks are around 3400 cm -1 and 3300 cm -1 respectively. The -NH2 bending vibration appears between 1580 cm -1 and 1650 cm -1 . This absorption peak mainly reflects the bending motion of the amino group and is the characteristic absorption peak of this group. The characteristic absorption peak of the -CH2- group is relatively prominent. Its stretching vibration appears at 2800 cm-1 to 3000 cm -1 region. This absorption peak is usually strong and is mainly related to the symmetric and asymmetric stretching vibrations of methylene groups. (3) The characteristic peak at 1100 cm -1 in the FTIR spectrum of phenylphosphoryl dichloride is clearly visible in the FTIR spectrum of PDSPD. At the same time, the strong characteristic peak of the P-Cl bond at 500 cm -1 -650 cm -1 disappears. The characteristic peaks at 2800 cm -1 ~3000 cm -1 and 3200 cm -1 ~3550 cm -1 in the FTIR spectrum of 1,3-diamino-2-propanol are clearly visible in the FTIR spectrum of PDSPD. The characteristic peaks of the -NH2 group at 3300 cm -1 and 3400 cm -1 disappear, indicating the successful synthesis of PDSPD from phenylphosphoryl dichloride and 1,3-diamino-2-propanol.

[0023] Figure 3 Figure is the 1H NMR spectrum of PDSPD. The four sets of multiplets with chemical shifts between 7-8 correspond to the four different chemical environments of H on the benzene ring. The quartet at a chemical shift of 3.1 ppm corresponds to the -CH2- group in the polymer. The triplet at a chemical shift of 1.2 ppm corresponds to the -OH group in the polymer. The triplet at a chemical shift of 3.7 ppm corresponds to the -NH- group in the polymer. The miscellaneous peak at 1.8 ppm corresponds to the -CH- group. Thus, it can be seen that the polymer PDSPD is successfully synthesized from phenylphosphoryl dichloride and 1,3-diamino-2-hydroxypropanol.

[0024] 2. Preparation of Flame-Retardant Polyvinyl Alcohol Composite Materials Weigh 3.6 g of PDSPD and 32.4 g of polyvinyl alcohol powder, mix them, put them into a mixer and melt and mix at 180 °C for 3 min, take them out, place them in a mold, put them into a flat vulcanizer and flatten at 160 °C for 2 min, and then cool to obtain the flame-retardant polyvinyl alcohol composite material.

[0025] Example 2 The flame-retardant polyvinyl alcohol composite material is prepared according to the following steps in this example: 1. Preparation of PDSPD The same as in Example 1.

[0026] 2. Preparation of Flame-Retardant Polyvinyl Alcohol Composite Materials Weigh 5.4 g of PDSPD and 30.6 g of polyvinyl alcohol powder, mix them, put them into a mixer and melt and mix at 180 °C for 3 min. Take them out, place them in a mold, put them into a flat vulcanizer and press them flat at 160 °C for 2 min, and then cool to obtain a flame-retardant polyvinyl alcohol composite material.

[0027] Example 3 The flame-retardant polyvinyl alcohol composite material was prepared in the following steps in this example: 1. Preparation of PDSPD The same as in Example 1.

[0028] 2. Preparation of the flame-retardant polyvinyl alcohol composite material Weigh 7.2 g of PDSPD and 28.8 g of polyvinyl alcohol powder, mix them, put them into a mixer and melt and mix at 180 °C for 3 min. Take them out, place them in a mold, put them into a flat vulcanizer and press them flat at 160 °C for 2 min, and then cool to obtain a flame-retardant polyvinyl alcohol composite material.

[0029] Comparative example The blank polyvinyl alcohol material was prepared in the following steps in this comparative example: Weigh 36 g of polyvinyl alcohol powder, put it into a mixer and melt and mix at 180 °C for 3 min. Take it out, place it in a mold, put it into a flat vulcanizer and press it flat at 160 °C for 2 min, and then cool to obtain a polyvinyl alcohol material.

[0030] The following performance tests were carried out on the polyvinyl alcohol composite materials obtained in each example and comparative example: Limiting oxygen index instrument: HC-2C oxygen index instrument of Jiangning Analytical Instrument Co., Ltd., China, and the test conditions were carried out according to ASTM D2863; Transmittance / haze meter: WGT-S type transmittance / haze measurement, and the sample mass was 5.0 ± 0.5 mg; Cone calorimeter: Nanjing Jiangning Instrument Analysis Factory, China, and the test conditions were carried out according to ISO 5660-1:2002.

[0031] Table 1 shows the limiting oxygen index (LOI), peak heat release (pHRR), total heat release (THR), ignition time (TTI), and char residue rate of the samples obtained in the comparative example and Examples 1-3. Figure 4 and Figure 5 They are respectively the transparency histogram and the digital photo of the film of the samples obtained in the comparative example and Examples 1-3.

[0032] Table 1. Performance test data of polyvinyl alcohol composite materials

[0033] As can be seen from the data in the above table, with the increase in the content of PDSPD, the limiting oxygen index (LOI) of the polyvinyl alcohol composite material increases significantly. In addition, the pHRR and THR of the comparative example are the highest, and the pHRR and THR of the polyvinyl alcohol composite material continuously decrease with the continuous increase in the content of the flame retardant PDSPD, reaching the lowest when the content reaches 20%. Compared with the comparative example, the pHRR of Example 3 decreases by 76.7% and the THR decreases by 93.3%. The amount of residual carbon generated by the combustion of the comparative example is extremely low, only 0.9%, while the residual carbon content of the composite material added with the flame retardant PDSPD is higher than that of the comparative example, and the residual carbon content of Example 3 is the highest, 8.9%. The flame retardant PDSPD has significantly improved the flame retardant effect of the polyvinyl alcohol composite material, and they significantly increase the amount of residual carbon generated by the material at high temperatures. The transmittance / haze of the pure polyvinyl alcohol film and the composite material film was measured using a transmittance / haze meter. With the increase in the addition amount of PDSPD, the transparency of the polyvinyl alcohol composite material only decreases slightly, and the haze only increases slightly. It can be seen that PDSPD has little effect on the transparency and haze of the polyvinyl alcohol composite material. This also proves that the PDSPD flame retardant prepared by the present invention can prepare a polyvinyl alcohol composite material with excellent flame retardant performance and good transparency.

[0034] The above embodiments are all relatively typical embodiments of the present invention and do not impose any limitations on the present invention. Those skilled in the art of the present technology who make adjustments and modifications to the described technical solutions shall fall within the protection scope 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 of the present invention.

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 prepared by reacting phenylphosphoryl dichloride with 1,3-diamino-2-propanol, named PDSPD.

2. The preparation method of the phosphazene flame retardant according to claim 1, characterized in that, It includes the following steps: First, add 1,3-diamino-2-propanol to tetrahydrofuran, heat it to 40-50 °C to completely melt it, then add triethylamine and mix evenly, then dropwise add trimethylchlorosilane, and stir for 8-10 h to protect the hydroxyl group in 1,3-diamino-2-propanol with trimethylchlorosilane; add triethylamine again and mix evenly, then place the reaction system in an ice-water bath at 0 °C, dropwise add phenylphosphoryl dichloride, and stir and react for 10-12 h to obtain a mixed solution; add glacial acetic acid to the obtained mixed solution and stir for 8-10 h to remove the protecting group on the hydroxyl group of 1,3-diamino-2-propanol; filter the obtained reaction solution to remove the precipitate in the solution, and then distill the solution at 140-160 °C. During the distillation process, the product undergoes repolymerization to obtain the final product.

3. The preparation method according to claim 2, characterized in that: 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 trimethylchlorosilane 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.

4. 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.

5. The flame-retardant polyvinyl alcohol composite material according to claim 4, characterized in that: In the flame-retardant polyvinyl alcohol composite material, the mass percentage of PDSPD is 10-20%.

6. A method for preparing the flame-retardant polyvinyl alcohol composite material according to claim 4 or 5, characterized in that: Mix PDSPD and polyvinyl alcohol powder, put them into a mixer and melt and mix at 170-190 °C for 2.5-3 min, take it out, place it in a mold, put it into a flat vulcanizer and flatten it at 150-160 °C for 2-3 min, and cool to obtain the flame-retardant polyvinyl alcohol composite material.

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