Method for improving thermal stability and whiteness of brominated polystyrene

Abstract

The present application relates to the field of high molecular bromine flame retardant preparation, in particular to a method for improving thermal stability and whiteness of brominated polystyrene. The method for improving thermal stability and whiteness of brominated polystyrene is characterized by: adding a catalyst and a chain protective agent I to a polystyrene solution to form a new polystyrene solution; adding a brominating agent solvent and a chain protective agent II to form a new brominating agent solution; adding the brominating agent solution into the polystyrene solution at a uniform speed to obtain a reaction mixture; adding a small molecule alcohol into the reaction mixture to obtain a mixed solution of an aqueous phase and an organic phase; adding an olefin or an alkyne into the mixed solution to separate the aqueous phase and the organic phase after decolorization; washing the organic phase with water, phase separation to obtain an organic layer solution, and then precipitation and filtration to obtain a powder-like brominated polystyrene. The present application can reduce the amount of bromine source (bromine or bromine chloride) and resource waste under the premise of ensuring high bromine content of the brominated polystyrene, and is easy to realize in industrial production and can achieve immediate results.

Description

Technical Field

[0001] This invention relates to the field of preparation of high molecular weight brominated flame retardants, and particularly to a method for improving the thermal stability and whiteness of brominated polystyrene. Background Technology

[0002] Brominated flame retardants are a widely used type of organic flame retardant, with polybrominated biphenyls (PBPs) and polybrominated diphenyl ethers (PBDEs) once dominating the flame retardant market. However, because PBPs and PBDEs produce carcinogenic substances such as dioxins when burned, posing a health hazard, alternatives have emerged.

[0003] Brominated polystyrene (BPS) is a bromination product of polystyrene (PS). It possesses advantages such as high bromine content, low toxicity, good thermal stability, good dispersibility in polymers, and non-frosting, anti-static, and non-migrating properties. It is widely used in engineering plastics such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyphenylene oxide (PPO), and nylon-66. When applied to flame-retardant polyesters, an addition of approximately 15 wt% is sufficient to achieve UL94 V-0 flame retardancy (0.8 mm); when applied to flame-retardant polyamides, an addition of approximately 20 wt% is sufficient to achieve UL94 V-0 flame retardancy (0.8 mm). Furthermore, brominated polystyrene has minimal impact on the mechanical properties of the materials, retaining 90% or more of their original mechanical properties. Brominated polystyrene is named as brominated polystyrene and polybrominated polystyrene based on its synthetic route. The names indicate that brominated polystyrene is synthesized by brominating polystyrene; polybrominated polystyrene is synthesized by first protecting the olefin bonds in styrene, then brominating it, restoring the olefin bonds, and finally polymerizing it. Based on whether a solvent is used in the synthesis process, it can be divided into solvent-based and non-solvent-based methods. Because solvent-based methods consume less bromine, they are commonly used for synthesis.

[0004] Depending on the solvent source, the process can be divided into the bromine method and the bromine chloride method. The bromine method uses bromine as the brominating reagent to bromine polystyrene. This method consumes a large amount of bromine, resulting in a darker product color, poor chroma, unstable thermal stability, and high production costs, leading to low economic efficiency. The bromine chloride method uses bromine chloride as the brominating reagent to bromine polystyrene. This method produces a darker polystyrene with poor chroma, and its bromine content, thermal stability, and other performance indicators fluctuate significantly. The molecular weight distribution is also wider, and the relevant indicators of different production batches of brominated polystyrene may vary considerably, resulting in unstable product quality and difficulty in meeting the requirements of the high-end product market.

[0005] Therefore, this invention proposes a method to improve the thermal stability and whiteness of the final brominated polystyrene and reduce the molecular weight distribution width during the preparation of brominated polystyrene, thereby improving the quality of brominated polystyrene products. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for improving the thermal stability and whiteness of brominated polystyrene. This method is simple, low-cost, and easy to control, and is mainly applicable to the brominated polystyrene production process route where styrene monomer is first polymerized and then the benzene ring is brominated. The resulting product has the characteristics of high thermal stability, high bromine content, high whiteness, and narrow molecular weight distribution.

[0007] This invention is achieved through the following technical solution: A method for improving the thermal stability and whiteness of brominated polystyrene includes the following steps: (1) Dissolve polystyrene and brominator in the same solvent to form polystyrene solution and brominator solution respectively; (2) Cool the polystyrene solution to -10℃ to -10℃, add catalyst and chain protectant I, mix well to form a new polystyrene solution; (3) Cool the brominating solvent to -10℃ to -10℃, add chain protectant II, and mix well to form a new brominating solution; (4) Within 5-8 hours, add the brominating agent solution obtained in step (3) to the polystyrene solution obtained in step (2) at a uniform rate to obtain a reaction mixture; (5) Within 7-9 hours, heat the reaction mixture to 15℃-25℃ and maintain this temperature for 1-2 hours to obtain a new reaction solution; (6) Add the small molecule alcohol to the reaction solution, stir for 0.1-1.0 h, then add deionized water and stir for 0.1-1.0 h to obtain a mixture of aqueous and organic phases; (7) Add small molecule olefins or alkynes to the mixture obtained in step (6) to decolorize until the mixture turns slightly yellow or nearly colorless. After 0.1-0.5 h, separate the aqueous phase and the organic phase. (8) The organic phase is washed with water, separated into phases, and the pH value of the aqueous phase is tested. The organic phase is then separated and washed again until the pH value of the aqueous phase reaches 6.0-7.0. The aqueous phase and organic phase are then separated after the last water wash and phase separation to obtain an organic layer solution. (9) Ethanol is added at multiple points at a uniform rate over 0.5-1.0 h to a rapidly stirred organic layer solution, and brominated polystyrene powder is precipitated. The powdered crude brominated polystyrene is obtained by filtration. (10) After washing and soaking the crude brominated polystyrene in ethanol for 2-5 hours, filter and dry to obtain brominated polystyrene in powder form with high thermal stability, high whiteness and high bromine content.

[0008] The above method is applicable to the preparation of brominated polystyrene with two different bromine sources, bromine and bromine chloride, and is suitable for bromination of polystyrene with a molecular weight of 500-200,000, with a wide range of applications.

[0009] In addition to adding chain protectant I to the polystyrene solution, this invention also adds chain protectant II to the brominating agent. This effectively reduces the electron cloud density of bromine in the brominating agent. The chain protectant II works synergistically with chain protectant I to make it easier for bromine to react with the conjugated electrons of the benzene ring in polystyrene, resulting in H substitution of the benzene ring. This greatly reduces H substitution with alkyl chains and improves product yield.

[0010] The preferred technical solution of the present invention is as follows: In step (1), the molar ratio of the benzene ring of polystyrene to the brominating agent is 1:3.03-3.3, the solvent is dichloroethane, the concentration of polystyrene in the polystyrene solution is 6-11wt%, and the amount of brominating agent in the brominating agent solution is 1.5-3.0mol / kg solvent.

[0011] In step (2), the polystyrene solution is cooled to -10℃ to 0℃, and a catalyst and chain protector I are added; when the brominating agent is bromine, the catalyst is aluminum trichloride or aluminum tribromide; when the brominating agent is bromine chloride, the catalyst is antimony trichloride; and chain protector I is titanium tetrachloride or tin tetrachloride.

[0012] In step (3), the brominating solvent is cooled to 0℃-5℃, and then chain protectant II is added. Chain protectant II is silicon tetrachloride, and the dosage is 3-10g / kg polystyrene.

[0013] In step (5), the reaction mixture is heated to 15℃-20℃ and the reaction is maintained at this temperature.

[0014] In step (6), the small molecule alcohol is one or both of methanol and ethanol, and its concentration is ≥99.5%.

[0015] In step (7), the small molecule olefin or alkyne is one of ethylene, acetylene, propylene, propyne, butene and butadiene.

[0016] In step (8), the organic phase is cycled more than or equal to 2 times.

[0017] In step (9), the ethanol is anhydrous ethanol with a concentration of ≥99.5%.

[0018] The beneficial technical effects of the present invention are as follows: (1) By implementing the method of the present invention, the bromine content, color and thermal stability of brominated polystyrene products can be improved, especially the 1% and 5% thermal weight loss temperatures; (2) In the method provided by the present invention, dichloroethane and ethanol can be separated, purified and recycled; (3) The method provided by the present invention reduces the amount of bromine source (bromine or bromine chloride) used while ensuring the high bromine content of brominated polystyrene, thus reducing resource waste; (4) The method provided by the present invention is very easy to implement in industrial production and can achieve immediate results. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Examples 1-10: Brominated polystyrene of different molecular weights was prepared using the method of the present invention in conjunction with Examples 1-10, and compared and analyzed with similar products at home and abroad. Based on the classification of domestic and foreign products, the examples used polystyrene with a weight-average molecular weight of 4000 and 60,000 for bromination.

[0021] The reagents and conditions used in the specific implementation of the method of the present invention for polystyrene (weight average molecular weight 4000) in Examples 1 to 10 are shown in Table 1: Table 1. Reagents and conditions used in each example of the polystyrene (4000) bromination process. The implementation steps are as follows: (1) Dissolve 1.5 kg of polystyrene (weight average molecular weight 4000) in 15 kg of dichloroethane solution in a 50 L glass jacketed reactor and seal it. Prepare a dichloroethane solution of brominating agent in a 20 L glass jacketed reactor and seal it (wherein, for bromine solution, bromine: dichloroethane = 7 kg: 18 kg; for bromine chloride solution, bromine: chlorine: dichloroethane = 3.5 kg: 1.553 kg: 18 kg). (2) Start stirring and cool the polystyrene solution to -2°C by connecting an external refrigeration unit through the glass kettle jacket. Add 30.0g of catalyst (types listed in Table 1 for each embodiment) and 20.0g of chain protectant I (types listed in Table 1 for each embodiment). Seal and mix evenly. (3) Turn on the stirrer and cool the brominating agent solution to 2°C by connecting the external refrigeration unit through the glass kettle jacket. Add 22.0g of chain protectant II silicon tetrachloride, seal and mix evenly. (4) The brominating agent solution is pumped into the polystyrene solution at a rate of 2.5 L / h through a corrosion-resistant diaphragm metering pump. At the same time, the gas outlet of the 50 L glass reactor is opened. The gas outlet is connected to the drying device and then to the gas absorption device. (5) After the pumping is completed, adjust the temperature of the chiller every hour, increasing it by 2.5°C each time, until the temperature reaches 18°C ​​and is maintained for 2 hours; (6) Add 150.0g of small molecule alcohol (types listed in Table 1 for each example) to a 50-liter glass reactor, stir for 30 minutes, then add 2.1kg of deionized water and stir for 30 minutes; (7) Add an appropriate amount of small molecule olefins or alkynes (listed according to the types in Table 1 for each example) slowly through a pipe to the mixture under stirring until the mixture turns slightly yellow or nearly colorless. Continue stirring for 20 minutes, then let it stand to promote the separation of the aqueous phase and the organic phase. (8) Separate the organic layer and wash it with water. After washing three times, the pH value of the aqueous phase is greater than 6. Separate the organic layer solution. (9) Add 30.5 kg of ethanol to the organic layer solution under rapid stirring at a rate of 60 L / h using a small centrifugal pump. Connect a shower outlet after the pump. As the ethanol is pumped in, the brominated polystyrene precipitates out as powder. After the ethanol is completely pumped in, continue stirring for 30 min and then filter. After filtration, put the filter cake into 15.3 kg of ethanol and continue stirring for 3.0 h. After filtration and drying, the brominated polystyrene product is obtained. The product is tested for bromine content, whiteness and thermal stability.

[0022] Examples 11-20: The reagents and conditions used in the specific implementation of the method of the present invention for polystyrene (weight average molecular weight 60,000) in Examples 11 to 20 are shown in Table 2: Table 2. Reagents and conditions used in each example of the bromination process of polystyrene (60,000). The implementation steps are as follows: (1) Dissolve 1.5 kg of polystyrene (weight average molecular weight 60,000) in 20 kg of dichloroethane solution in a 50 L glass jacketed reactor and seal it. Prepare a dichloroethane solution of brominating agent in a 20 L glass jacketed reactor and seal it (wherein, for bromine solution, bromine: dichloroethane = 7 kg: 18 kg; for bromine chloride solution, bromine: chlorine: dichloroethane = 3.5 kg: 1.553 kg: 18 kg). (2) Turn on the stirrer and cool the polystyrene solution to 0°C by connecting the external refrigeration unit through the glass kettle jacket. Add 32.0g of catalyst (types listed in Table 2 for each embodiment) and 22.0g of chain protectant I (types listed in Table 2 for each embodiment). Seal and mix evenly. (3) Turn on the stirrer and cool the brominating agent solution to 2°C by connecting the external refrigeration unit through the glass kettle jacket. Add 27.0g of chain protectant II silicon tetrachloride, seal and mix evenly. (4) The brominating agent solution is pumped into the polystyrene solution at a rate of 2.5 L / h through a corrosion-resistant diaphragm metering pump. At the same time, the gas outlet of the 50 L glass reactor is opened. The gas outlet is connected to the drying device and then to the gas absorption device. (5) After the pumping is completed, adjust the temperature of the chiller every hour, increasing it by 2.5°C each time, until the temperature reaches 20°C and is maintained for 2 hours; (6) Add 150.0g of small molecule alcohol (types listed in Table 2 for each example) to a 50-liter glass reactor, stir for 30 minutes, then add 2.5kg of deionized water and stir for 30 minutes; (7) Add an appropriate amount of small molecule olefins or alkynes (the types are listed in Table 2 for each example) slowly through a pipe to the mixture under stirring until the mixture turns slightly yellow or nearly colorless. Continue stirring for 20 minutes, then let it stand to promote the separation of the aqueous phase and the organic phase. (8) Separate the organic layer and wash it with water. After washing three times, the pH value of the aqueous phase is greater than 6. Separate the organic layer solution. (9) Add 35.5 kg of ethanol to the organic layer solution under rapid stirring at a rate of 60 L / h using a small centrifugal pump. Connect a shower outlet after the pump. As the ethanol is pumped in, the brominated polystyrene precipitates out as powder. After the ethanol is completely pumped in, continue stirring for 30 min and then filter. After filtration, put the filter cake into 18.3 kg of ethanol and continue stirring for 3.0 h. After filtration and drying, the brominated polystyrene product is obtained. The product is tested for bromine content, whiteness and thermal stability.

[0023] Example 3: Product Comparison Test Results The final products of Examples 1-20 and similar products from domestic and foreign countries were subjected to unified tests for bromine content, whiteness, and thermal stability. The bromine content was tested using the oxygen flask combustion method, the whiteness was tested according to the CID standard using the Ganz whiteness formula with a D65 light source, and the thermal stability was tested using a TG209F3 Netzsch thermogravimetric analyzer (N2, 10℃ / min). The comparison results are shown in Table 3.

[0024] Table 3 Product Performance Comparison Table After comparing Examples 1-20 with the best existing products at home and abroad, the method provided by the present invention is indeed effective and can improve the thermal stability and whiteness of the product. In terms of bromine content, it is 1-2% higher than the best domestic and international standards. In terms of dry whiteness, it is 4-10% higher than the best domestic and international standards; The 1% thermogravimetric temperature is 4-13℃ higher than the best domestic and international results. The 5% thermal weight loss temperature is 4-10℃ higher than the best domestic and international standards.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the thermal stability and whiteness of brominated polystyrene, characterized by comprising the following steps: (1) Dissolve polystyrene and brominator in the same solvent to form polystyrene solution and brominator solution respectively; (2) Cool the polystyrene solution to -10℃-0℃, add catalyst and chain protectant I, mix well to form a new polystyrene solution; When the brominating agent is bromine, the catalyst is aluminum trichloride or aluminum tribromide; when the brominating agent is bromine chloride, the catalyst is antimony trichloride; chain protector I is titanium tetrachloride or tin tetrachloride. (3) Cool the brominating solvent to 0℃-5℃ and add chain protectant II. Mix well to form a new brominating solution. Chain protectant II is silicon tetrachloride, and the dosage is 3-10 g / kg polystyrene; (4) Within 5-8 hours, add the brominating agent solution obtained in step (3) to the polystyrene solution obtained in step (2) at a uniform rate to obtain a reaction mixture; (5) Within 7-9 hours, heat the reaction mixture to 15℃-25℃ and maintain this temperature for 1-2 hours to obtain a new reaction solution; (6) Add the small molecule alcohol to the reaction solution, stir for 0.1-1.0 h, then add deionized water and stir for 0.1-1.0 h to obtain a mixture of aqueous and organic phases; (7) Add small molecule olefins or alkynes to the mixture obtained in step (6) to decolorize until the mixture turns slightly yellow or nearly colorless. After 0.1-0.5 h, separate the aqueous phase and the organic phase. (8) The organic phase is washed with water, separated into phases, and the pH value of the aqueous phase is tested. The organic phase is then separated and washed again until the pH value of the aqueous phase reaches 6.0-7.

0. The aqueous phase and organic phase are then separated after the last water wash and phase separation to obtain an organic layer solution. (9) Ethanol is added at multiple points at a uniform rate over 0.5-1.0 h to a rapidly stirred organic layer solution, and brominated polystyrene powder is precipitated. The powdered crude brominated polystyrene is obtained by filtration. (10) After washing and soaking the crude brominated polystyrene in ethanol for 2-5 hours, filter and dry to obtain brominated polystyrene in powder form with high thermal stability, high whiteness and high bromine content.

2. The method for improving the thermal stability and whiteness of brominated polystyrene as described in claim 1, characterized in that: In step (1), the molar ratio of the benzene ring of polystyrene to the brominating agent is 1:3.03-3.3, the solvent is dichloroethane, the concentration of polystyrene in the polystyrene solution is 6-11wt%, and the amount of brominating agent in the brominating agent solution is 1.5-3.0mol / kg solvent.

3. The method for improving the thermal stability and whiteness of brominated polystyrene as described in claim 1, characterized in that: In step (5), the reaction mixture is heated to 15℃-20℃ and the reaction is maintained at this temperature.

4. The method for improving the thermal stability and whiteness of brominated polystyrene as described in claim 1, characterized in that: In step (6), the small molecule alcohol is one or both of methanol and ethanol, and its concentration is ≥99.5%.

5. The method for improving the thermal stability and whiteness of brominated polystyrene as described in claim 1, characterized in that: In step (7), the small molecule olefin or alkyne is one of ethylene, acetylene, propylene, propyne, butene and butadiene.

6. The method for improving the thermal stability and whiteness of brominated polystyrene as described in claim 1, characterized in that: In step (8), the organic phase is cycled more than or equal to 2 times.

7. The method for improving the thermal stability and whiteness of brominated polystyrene as described in claim 1, characterized in that: In step (9), the ethanol is anhydrous ethanol with a concentration of ≥99.5%.

Images