A phosphorus-based flame retardant, a preparation method and application thereof

Abstract

The application relates to a phosphorus-based flame retardant as well as a preparation method and application thereof, and belongs to the technical field of flame retardants. The phosphorus-based flame retardant provided by the application is subjected to modification treatment on DOPO, bonds multiple DOPO reactants, and introduces a long carbon chain structure into the phosphorus-based flame retardant, thereby improving the distribution uniformity of the phosphorus-based flame retardant in an epoxy resin matrix and the bonding strength with the epoxy resin. In addition, due to the introduction of the long carbon chain, the production of coke in the condensed phase is promoted in the flame retardation process, the coking rate is improved, and the flame retardation effect is improved. Nitrogen elements introduced in the flame retardation process form nitrogen-containing free radicals into the gas phase, and have a quenching effect on the combustion process. The phosphorus-based flame retardant provided by the application not only can improve the distribution uniformity of DOPO in the epoxy resin matrix and the bonding strength with the matrix, but also can further improve the flame retardation effect, and is a flame retardant material with great application potential.

Description

Technical Field

[0001] This application relates to a phosphorus-based flame retardant, its preparation method, and its application, belonging to the field of flame retardant technology. Background Technology

[0002] Epoxy resins are widely used in many industrial fields due to their excellent mechanical properties, chemical resistance, and heat resistance, such as as casting materials, adhesives, molding materials, and wire and cable assemblies. However, epoxy resins are highly flammable, which greatly limits their application scenarios. Therefore, it is crucial to improve the flame retardancy of epoxy resins without negatively impacting other properties.

[0003] DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is a common commercially available reactive flame retardant. DOPO improves the fire resistance of epoxy resin systems by releasing active phosphorus substances into the gas phase. However, DOPO reacts with ethylene oxide, which negatively affects the glass transition temperature of epoxy composites. Furthermore, the bonding strength between DOPO and epoxy resin is not high, and the uniformity of its distribution in the epoxy resin matrix needs to be improved.

[0004] Therefore, it is necessary to provide a phosphorus-based flame retardant modified with DOPO to overcome the problems existing in the prior art when applied to epoxy resin flame retardancy. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a phosphorus-based flame retardant, its preparation method, and its application. The phosphorus-based flame retardant provided by this application not only exhibits high bonding strength and good distribution uniformity with the epoxy resin matrix, but also significantly improves flame retardant performance, demonstrating great application potential.

[0006] According to one aspect of this application, a phosphorus-based flame retardant is provided, the molecular structure of which is shown in Formula I:

[0007]

[0008] The phosphorus-based flame retardant provided in this application contains two long carbon chain structures, which can significantly improve the interaction between the phosphorus-based flame retardant and the epoxy resin matrix, increase the uniformity of the distribution of the phosphorus-based flame retardant in the epoxy resin matrix, and promote the formation of coke in the condensed phase during the flame retardant process, thereby increasing the coking rate during combustion. The accumulation of coke can drive the DOPO groups to form a barrier, improving the flame retardant effect. On the other hand, the nitrogen element can form nitrogen-containing free radicals that enter the gas phase during the flame retardant process. The nitrogen-containing free radicals can quench the combustion process, further improving its flame retardant effect.

[0009] In this invention, by modifying DOPO, multiple DOPO molecules bond together to form a phosphorus-based flame retardant with a larger molecular weight, which can improve its distribution effect in epoxy resin, significantly improve the aging resistance and strength properties of epoxy resin, and the phosphorus-based flame retardant has better bonding performance with the epoxy resin matrix. At the same time, it increases the viscosity of the epoxy resin mixture, which can avoid the problem of poor flame retardant performance of epoxy resin mixtures that are prone to falling off during long-term use.

[0010] Furthermore, the present application modifies DOPO, transforming it from a reactive flame retardant into a non-reactive flame retardant. This avoids the reaction between DOPO and ethylene oxide, thus resolving the issue that DOPO negatively affects the glass transition temperature of epoxy composites during use.

[0011] According to another aspect of this application, a method for preparing the above-mentioned phosphorus-based flame retardant is provided, characterized in that the preparation method includes the following steps:

[0012]

[0013] (1) Compound II reacts with compound III to produce compound IV;

[0014] (2) The phosphorus-based flame retardant is obtained by reacting the compound of formula IV with the compound of formula V, DOPO.

[0015] Optionally, in step (1), the compound of formula II and the compound of formula III are dissolved in an organic solvent and stirred at 60-80°C for 6-10 hours.

[0016] Optionally, a catalyst is also added to the organic solvent in step (1), wherein the catalyst is potassium bisulfate or sodium bisulfate.

[0017] Optionally, the organic solvent is one or more selected from toluene, xylene, trimethylbenzene, dichlorobenzene, and cyclohexane.

[0018] Optionally, in step (2), compound V is added to an organic solvent, and compound IV is slowly added under the condition of nitrogen gas being introduced and stirring, and the reaction is carried out for 2 to 6 hours to obtain the phosphorus-based flame retardant product.

[0019] Optionally, the organic solvent is a THF solvent.

[0020] Optionally, step (2) is followed by a purification step (3), in which the reaction solution obtained in step (2) is cooled to room temperature and the solvent is evaporated to obtain the phosphorus-based flame retardant.

[0021] According to another aspect of this application, an epoxy resin mixture is provided, the epoxy resin mixture comprising the following components in parts by weight:

[0022] 100 parts epoxy resin, 2-8 parts phosphorus flame retardant, 1-5 parts curing agent;

[0023] The phosphorus-based flame retardant is the phosphorus-based flame retardant described above or a phosphorus-based flame retardant prepared by any of the above preparation methods.

[0024] According to the last aspect of this application, the application of the above-described phosphorus-based flame retardant or the phosphorus-based flame retardant prepared by any of the above-described preparation methods in the flame retardancy of epoxy resins is provided.

[0025] The beneficial effects of this application include, but are not limited to:

[0026] 1. According to the phosphorus-based flame retardant of this application, DOPO is modified to change from a reactive flame retardant to a non-reactive flame retardant, so that it will not react with the ethylene oxide groups in the epoxy composite material and affect the performance of the matrix.

[0027] 2. The phosphorus-based flame retardant according to this application has better compatibility with epoxy resin, and can better bind and distribute in the epoxy resin matrix. It can not only improve the flame retardant effect of the phosphorus-based flame retardant in the flame retardant process, but also improve the viscosity and strength properties of the epoxy resin mixture, especially the aging resistance is significantly improved.

[0028] 3. According to the phosphorus-based flame retardant of this application, a long carbon chain structure is introduced, which can rapidly coke during the flame retardant process. The coke can drive DOPO groups to gather at the combustion interface and form a barrier, thereby improving the flame retardant effect. Furthermore, the nitrogen element can generate nitrogen free radicals during the flame retardant process and enter the gas phase, playing a quenching role in the combustion process. The phosphorus-based flame retardant provided by this application improves the condensed phase and gas phase involved in the combustion process, thereby improving the flame retardant effect of the phosphorus-based flame retardant. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0030] Figure 1 This is a schematic diagram of the reaction process in which the compound of formula II reacts with the compound of formula III to produce the compound of formula IV.

[0031] Figure 2 This is a schematic diagram of the reaction process by which the compound of formula IV and the compound of formula V involved in this application react to obtain phosphorus-based flame retardant products.

[0032] Figure 3 The image shows the infrared spectrum of the phosphorus-based flame retardant involved in this application. Detailed Implementation

[0033] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0034] Unless otherwise specified, the raw materials and catalysts used in the embodiments of this application were all purchased commercially.

[0035] The phosphorus-based flame retardant provided in this application is prepared by the following method:

[0036] The structure of phosphorus-based flame retardants is shown in Formula I:

[0037]

[0038] The reactants involved in the preparation process are shown in Formulas II, III, and V, respectively, where Formula IV is the intermediate product of the reaction.

[0039]

[0040]

[0041] (1) Compound II reacts with compound III to produce compound IV. The reaction process is as follows: Figure 1 As shown;

[0042] (2) The reaction of compound IV with compound V yields the phosphorus-based flame retardant, as follows: Figure 2 As shown.

[0043] The present invention will be specifically described below through specific embodiments, comparative examples, and test cases.

[0044] Example 1

[0045] (1) Add 50 ml of toluene solvent to a three-necked flask, add compound II 5,5',5”,5”'-(3,6-bis(dodecyloxy)benzene-1,2,4,5-tetrayl)tetra(2-bromothiophene) and compound III to the three-necked flask and mix well. Then add 2 g of potassium hydrogen sulfate crystals and stir to dissolve evenly. Then, under the condition of oil bath temperature of 75°C, turn on the magnetic stirrer and keep the stirring speed of 280 rpm for 8 h. The amount of compound II added is 50 g, and the molar ratio of compound II to compound III added is 1:4. After the reaction is completed, the oil bath temperature is raised to 120°C to evaporate the toluene solvent to obtain the crude product of compound IV.

[0046] (2) Add 75 ml of THF solvent to a three-necked flask, then add compound V and pre-treat with nitrogen for 10 min. Then continue to purge with nitrogen and adjust the stirring speed of the magnetic stirrer to 300 rpm. Slowly drop in the crude product of compound IV prepared in step (1) and react at room temperature for 3 h. The molar ratio of compound V to compound II is 4:1.

[0047] (3) After the reaction in step (2) is completed, the reaction solution is cooled to room temperature, 50 ml of saturated sodium chloride solution is added for washing, 10 g of sodium sulfate solid is added to remove water, and THF organic solvent is evaporated to obtain a dark brown viscous liquid, which is the phosphorus flame retardant product.

[0048] An epoxy resin mixture was prepared using the phosphorus-based flame retardant prepared above. The epoxy resin mixture included 100g of epoxy resin, 6g of phosphorus-based flame retardant, 0.5g of defoamer, 1g of leveling agent, and 5g of D-230 curing agent.

[0049] The infrared spectrum of the phosphorus-based flame retardant prepared in this embodiment is as follows: Figure 3 As shown, curve A represents compound II, curve B represents compound II and compound III, curve C represents compound II and DOPO, and curve D represents the phosphorus-based flame retardant prepared in the example. According to the infrared spectrum results, compound II reacted with compound III and DOPO to successfully prepare a phosphorus-based flame retardant compound with the structure of formula I.

[0050] Example 2

[0051] (1) Add 50 ml of xylene solvent to a three-necked flask, add compound II 5,5',5”,5”'-(3,6-bis(dodecyloxy)phenyl-1,2,4,5-tetrayl)tetra(2-bromothiophene) and compound III to the three-necked flask and mix well. Then add 2 g of potassium hydrogen sulfate crystals and stir to dissolve evenly. Then, under the condition of oil bath temperature of 65°C, turn on the magnetic stirrer and keep the stirring speed of 280 rpm for 10 h. The amount of compound II added is 50 g, and the molar ratio of compound II to compound III added is 1:4. After the reaction is completed, the oil bath temperature is raised to 145°C to evaporate the xylene solvent and obtain the crude product of compound IV.

[0052] (2) Add 75 ml of THF solvent to a three-necked flask, then add compound V and pre-treat with nitrogen for 10 min. Then continue to purge with nitrogen and adjust the stirring speed of the magnetic stirrer to 300 rpm. Slowly drop in the crude product of compound IV prepared in step (1) and react at room temperature for 2 h. The molar ratio of compound V to compound II is 4:1.

[0053] (3) After the reaction in step (2) is completed, the reaction solution is cooled to room temperature, 50 ml of saturated sodium chloride solution is added for washing, 10 g of sodium sulfate solid is added to remove water, and THF organic solvent is evaporated to obtain a dark brown viscous liquid, which is the phosphorus flame retardant product.

[0054] An epoxy resin mixture was prepared using the phosphorus-based flame retardant prepared above. The epoxy resin mixture included 100g of epoxy resin, 4g of phosphorus-based flame retardant, 0.5g of defoamer, 1g of leveling agent, and 1g of D-230 curing agent.

[0055] Example 3

[0056] (1) Add 50 ml of cyclohexane solvent to a three-necked flask, add compound II 5,5',5”,5”'-(3,6-bis(dodecyloxy)benzene-1,2,4,5-tetrayl)tetra(2-bromothiophene) and compound III to the three-necked flask and mix well. Then add 2 g of sodium bisulfate crystals and stir to dissolve evenly. Then, under the condition of oil bath temperature of 80°C, use a magnetic stirrer and maintain a stirring speed of 280 rpm for 6 h. The amount of compound II added is 50 g, and the molar ratio of compound II to compound III added is 1:4. After the reaction is completed, the oil bath temperature is raised to 105°C to evaporate the cyclohexane solvent to obtain the crude product of compound IV.

[0057] (2) Add 75 ml of THF solvent to a three-necked flask, then add compound V and pre-treat with nitrogen for 10 min. Then continue to purge with nitrogen and adjust the stirring speed of the magnetic stirrer to 300 rpm. Slowly drop in the crude product of compound IV prepared in step (1) and react at room temperature for 5 h. The molar ratio of compound V to compound II is 4:1.

[0058] (3) After the reaction in step (2) is completed, the reaction solution is cooled to room temperature, 50 ml of saturated sodium chloride solution is added for washing, 10 g of sodium sulfate solid is added to remove water, and THF organic solvent is evaporated to obtain a dark brown viscous liquid, which is the phosphorus flame retardant product.

[0059] An epoxy resin mixture was prepared using the phosphorus-based flame retardant prepared above. The epoxy resin mixture included 100g of epoxy resin, 8g of phosphorus-based flame retardant, 0.5g of defoamer, 1g of leveling agent, and 3g of D-230 curing agent.

[0060] Comparative Example 1

[0061] The difference between the epoxy resin mixture in this embodiment and that in Example 1 is that the phosphorus-based flame retardant is replaced with an equal mass of DOPO, the structural formula of which is shown below.

[0062]

[0063] Comparative Example 2

[0064] The difference between the epoxy resin mixture in this embodiment and that in Example 1 is that the phosphorus flame retardant is replaced by a mixture of compound III, compound II and DOPO of equal total mass, and the molar ratio of compound III, compound II and DOPO in the mixture is 4:1:4.

[0065] Comparative Example 3

[0066] The difference between the epoxy resin mixture in this embodiment and that in Example 1 is that the phosphorus-based flame retardant is replaced with an equal mass of DOPI, the structural formula of which is shown below.

[0067]

[0068] Comparative Example 4

[0069] The difference between the epoxy resin mixture in this embodiment and that in Example 1 is that the phosphorus-based flame retardant is replaced with an equal mass of DOPP, the structural formula of which is shown below.

[0070]

[0071] Test Example 1

[0072] The epoxy resin mixtures containing phosphorus-based flame retardants prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to particle size analysis and centrifugal stability tests to evaluate the uniformity of phosphorus-based flame retardant distribution in the epoxy resin mixtures. In the centrifugal stability test, the mixtures were continuously centrifuged at 3000 rpm for 5 minutes and then observed. The results of each test were recorded and statistically analyzed, as shown in Table 1.

[0073] Table 1

[0074] serial number Average particle size (nm) Centrifugal stability Example 1 352 No layering Example 2 360 No layering Example 3 348 No layering Comparative Example 1 955 Clear stratification Comparative Example 2 620 Clear stratification Comparative Example 3 544 No layering Comparative Example 4 460 No layering

[0075] As shown in Table 1, unmodified DOPO exhibited the worst distribution uniformity in epoxy resin and easily separated from the epoxy resin matrix during stability testing. Furthermore, particle size analysis suggests that unmodified DOPO may be prone to aggregation in epoxy resin, resulting in weak dispersibility. This is presumably due to the small molecular weight and large specific surface area of ​​DOPO, and the presence of phosphorus and oxygen atoms in DOPO, which facilitates aggregation and weakens adhesion to epoxy resin. Modified DOPO showed significantly improved performance in centrifugal stability testing, exhibiting less stratification, indicating better bonding strength with epoxy resin. Additionally, the phosphorus-based flame retardant provided in the embodiments of this invention has the smallest average particle size, demonstrating its ability to bond well with the epoxy resin matrix, reduce aggregation, and achieve better distribution uniformity.

[0076] Test Example 2

[0077] The epoxy resin mixtures containing phosphorus-based flame retardants prepared in Examples 1-3 and Comparative Examples 1-4 were tested for adhesion, impact strength, aging resistance, hardness, and flame retardancy. Hardness was determined using the pencil method according to GB / T6739 / 2006; adhesion was tested according to the cross-cut adhesion test method for varnishes, paints, and coatings according to GB / T9286 / 1998; and the LOI (Limiting Oxygen Index, the minimum percentage of oxygen required to sustain combustion in a nitrogen-oxygen mixture, used to characterize the flame retardant effect) was determined using an oxygen index meter according to ASTM D2863 / 2000. The sample size was 140mm × 6mm × 3mm. In the aging resistance test, the epoxy resin mixture was evenly applied to a 50cm... 2 Place the sample on a piece of iron, then heat it in an oven at 120℃ for 2 hours, cool it to room temperature, and expose it outdoors for 120 hours. Observe whether the color turns yellow, record the various tests and statistically analyze the results as shown in Table 2.

[0078] Table 2

[0079]

[0080] Based on the results of Examples 1-3 and Comparative Examples 1-2, the phosphorus-based flame retardant obtained by modifying DOPO in the embodiments of the present invention has better pre-curing viscosity properties than unmodified DOPO. This reduces the problem of epoxy resin peeling during use, improves the service life of epoxy resin materials, and enhances the aging resistance of epoxy resin. The epoxy resin can still maintain good impact strength after exposure treatment. Compared with the phosphorus-based flame retardants in Comparative Examples 3 and 4, the pre-curing viscosity properties and the impact strength after 120 hours of exposure are significantly improved, while maintaining good flame retardant properties.

[0081] In the phosphorus-based flame retardant provided by the present invention, DOPO is modified to form a phosphorus-based flame retardant with a larger molecular weight by bonding multiple DOPOs. The introduction of long carbon chains can significantly improve the adsorption capacity of the phosphorus-based flame retardant to the epoxy resin matrix, reduce the aggregation of DOPO and thus improve its distribution uniformity in the epoxy resin matrix, and significantly improve the impact strength performance of the epoxy resin.

[0082] The phosphorus-based flame retardant provided by this invention introduces long carbon chains that can promote the coke content in the condensed phase during the flame retardant process, thereby improving the flame retardant effect by increasing the coking rate. The introduced nitrogen element can form nitrogen free radicals that enter the gas phase and play a quenching role, thus having a very good flame retardant effect.

[0083] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A phosphorus-based flame retardant, characterized in that, The molecular structure of the phosphorus-based flame retardant is shown in Formula I:

2. The method for preparing the phosphorus-based flame retardant as described in claim 1, characterized in that, The preparation method includes the following steps: (1) Compound II reacts with compound III to produce compound IV; (2) The phosphorus-based flame retardant is obtained by reacting the compound of formula IV with the compound of formula V, DOPO.

3. The preparation method according to claim 2, characterized in that, In step (1), compound II and compound III are dissolved in an organic solvent and stirred at 60-80°C for 6-10 hours.

4. The preparation method according to claim 3, characterized in that, In step (1), a catalyst is also added to the organic solvent. The catalyst is potassium bisulfate or sodium bisulfate.

5. The preparation method according to claim 3, characterized in that, The organic solvent is one or more of toluene, xylene, trimethylbenzene, dichlorobenzene, and cyclohexane.

6. The preparation method according to claim 2, characterized in that, In step (2), compound V is added to an organic solvent, and compound IV is slowly added while nitrogen is introduced and stirring is maintained, and the reaction is carried out for 2 to 6 hours to obtain the phosphorus-based flame retardant product.

7. The preparation method according to claim 6, characterized in that, The organic solvent is THF solvent.

8. The preparation method according to claim 2, characterized in that, The step (2) is followed by a purification step (3), in which the reaction solution obtained in step (2) is cooled to room temperature and the solvent is evaporated to obtain the phosphorus-based flame retardant.

9. An epoxy resin mixture, characterized in that, The epoxy resin mixture comprises the following components in parts by weight: 100 parts epoxy resin, 2-8 parts phosphorus flame retardant, 1-5 parts curing agent; Wherein, the phosphorus-based flame retardant is the phosphorus-based flame retardant as described in claim 1 or the phosphorus-based flame retardant prepared by the preparation method described in any one of claims 2 to 8.

10. The application of the phosphorus-based flame retardant as described in claim 1 or the phosphorus-based flame retardant prepared by the preparation method according to any one of claims 2 to 8 in the flame retardancy of epoxy resin.

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