Flame retardant and its preparation method and application

Abstract

The present invention provides a flame retardant and its preparation method and application, and is particularly related to the field of flame retardant technology. The present invention uses 3,4-diaminophenol and hexachloroacetone as raw materials to prepare 6,6'-dihydroxy-p-benzimidazole, and 6,6'-dihydroxy-p-benzimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) are mixed and reacted to prepare a DOPO-type flame retardant containing a p-benzimidazole structure. The flame retardant of the present invention is used in polylactic acid, which can improve the problem of poor compatibility between the flame retardant and the polylactic acid matrix and improve the flame retardant efficiency of the polylactic acid.

Description

Technical Field

[0001] The present invention relates to the field of flame retardant technology, and in particular to a flame retardant and a preparation method and application thereof. Background Art

[0002] Polylactic acid (PLA) boasts excellent mechanical, biocompatibility, and physical properties, making it one of the most representative biodegradable and bio-based polymers on the market. It is widely used in a variety of fields, including drug delivery, textiles, and packaging materials. PLA fibers offer a superior tactile feel compared to petroleum-based synthetic fibers, and fabrics made from them have a silky texture and the high wrinkle resistance of polyester fabrics. PLA also exhibits excellent UV resistance, resilience, and abrasion resistance. PLA contains few flammable substances, produces low levels of combustible smoke and dust, and produces no toxic gases upon ignition. However, PLA has a low limiting oxygen index (LOI), which makes it prone to dripping during combustion, which can easily cause fire to spread, resulting in poor flame retardancy. Typically, additive flame retardants used to modify PLA suffer from poor compatibility and reduced mechanical properties. Therefore, there is a need to develop new flame retardants for flame-retardant modification of PLA. Summary of the Invention

[0003] In view of the above shortcomings of the prior art, the present invention provides a flame retardant and a preparation method and application thereof, so as to improve the problem of poor compatibility of additive flame retardants when modifying polylactic acid.

[0004] To achieve the above-mentioned object and other related objects, the present invention provides a flame retardant, the structural formula of which is as follows:

[0005]

[0006] On the other hand, the present invention also provides a method for preparing a flame retardant, which comprises the following steps: mixing 3,4-diaminophenol and hexachloroacetone to react to prepare 6,6'-dihydroxy-p-benzimidazole (PBI); and reacting 6,6'-dihydroxy-p-benzimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) in the presence of a basic catalyst to prepare a flame retardant.

[0007] In one example of the present invention, the mixing reaction of 3,4-diaminophenol and hexachloroacetone to prepare 6,6'-dihydroxy-p-benzimidazole includes: adding 3,4-diaminophenol and a first solvent to a reactor, mixing and stirring under the protection of a nitrogen atmosphere; adding hexachloroacetone dropwise to the reactor under ice bath conditions, and ultrasonically reacting at 40°C to 60°C for 1 to 2 hours; filtering, washing, and drying to obtain 6,6'-dihydroxy-p-benzimidazole.

[0008] In one example of the present invention, the molar ratio of the 3,4-diaminophenol to the hexachloroacetone is (2-10):1.

[0009] In an example of the present invention, the first solvent includes at least one of water, ethanol, methanol, ethylene glycol, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, and tetramethyl sulfoxide.

[0010] In one example of the present invention, the flame retardant is prepared by reacting 6,6'-dihydroxy-p-benzimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide under the action of an alkaline catalyst, comprising: dissolving 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in a second solvent, adding an alkaline catalyst and 1,1'-p-benzimidazole, heating to 40°C to 80°C, reacting for 10 to 16 hours, filtering, washing, and drying to obtain a flame retardant.

[0011] In one example of the present invention, the molar ratio of the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the 6,6'-dihydroxy-p-benzimidazole is (2-2.5):1.

[0012] In one example of the present invention, the second solvent includes at least one of heptane, hexane, petroleum ether, methylcyclohexane, toluene, xylene, ethylbenzene, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, dimethylformamide, dimethylacetamide, acetonitrile, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

[0013] In one example of the present invention, the alkaline catalyst includes at least one of sodium hydroxide, sodium methoxide, potassium methoxide, lithium methoxide, sodium ethoxide, potassium ethoxide, and lithium ethoxide.

[0014] The present invention also provides an application of a flame retardant in polylactic acid, wherein the amount of the flame retardant added to the polylactic acid accounts for 0.4wt% to 2.5wt% of the total mass of the polylactic acid and the flame retardant, and the limiting oxygen index of the polylactic acid is 24% to 33%.

[0015] The flame retardant provided by the present invention contains p-benzimidazole, and the nitrogen atom of the imidazole ring in the p-benzimidazole structure contains a lone pair of electrons, which can enable it to interact with the polylactic acid resin base, thereby improving the compatibility of the flame retardant and polylactic acid.

[0016] Adding nitrogen-containing groups to the flame retardant can improve the flame retardant efficiency. In addition, a cross-linked network containing aromatic heterocycles is formed between the imidazole groups, which further enhances the anti-dripping effect of the flame retardant polylactic acid.

[0017] The preparation method of the flame retardant provided by the invention has simple process, short cycle, easy post-processing, and is easy to control and industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 The present invention is a flow chart of the method for preparing the flame retardant. DETAILED DESCRIPTION

[0020] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following examples and the features in the examples can be combined with each other unless they conflict. It should also be understood that the terms used in the examples of the present invention are for the purpose of describing specific embodiments, not for the purpose of limiting the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under the conditions recommended by the manufacturers.

[0021] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0022] Polylactic acid (PLA) has a limiting oxygen index (LOI) of 21%, which can easily produce dripping during combustion, causing fire to spread and resulting in poor flame retardancy. Currently, additive flame retardants suffer from poor compatibility with the PLA resin matrix and reduced mechanical strength. This application provides a flame retardant, its preparation method, and its application to address this issue.

[0023] The structural formula of the flame retardant provided in this application is as follows:

[0024]

[0025] The above structural formula contains a p-benzimidazole structure, which contains an imidazole ring. The nitrogen atom in the imidazole ring has a lone pair of electrons, which can interact with the polylactic acid resin base, thereby improving the compatibility of the flame retardant with polylactic acid. Furthermore, the addition of nitrogen-containing groups to the flame retardant can improve flame retardancy. In addition, the imidazole groups form a cross-linked network containing aromatic heterocycles, further enhancing the anti-drip effect of the flame-retardant polylactic acid.

[0026] See also Figure 1 The preparation method of the flame retardant of the present application comprises at least the following steps:

[0027] S1. Mixing 3,4-diaminophenol and hexachloroacetone to react to prepare 6,6'-dihydroxy-p-benzimidazole;

[0028] S2. 6,6'-dihydroxy-p-benzimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are reacted in the presence of a basic catalyst to prepare a flame retardant.

[0029] Specifically, the process for preparing 6,6'-dihydroxy-p-benzimidazole in step S1 is as follows: adding 3,4-diaminophenol and a first solvent to a reactor, and mixing and stirring them uniformly under the protection of a nitrogen atmosphere; adding hexachloroacetone dropwise to the reactor under ice bath conditions, and ultrasonically reacting at 40°C to 60°C for 1 to 2 hours; filtering, washing, and drying to obtain 6,6'-dihydroxy-p-benzimidazole.

[0030] The reactor includes a thermometer, a stirring device, and a container. For example, the reactor is a three-necked flask equipped with a thermometer and a magnetic stirrer. During the reaction, nitrogen is introduced into the three-necked flask as a protective gas. The first solvent is used to dissolve 3,4-diaminophenol. The amount of the first solvent is not limited, as long as it can completely dissolve 3,4-diaminophenol. The first solvent includes at least one of water, ethanol, methanol, ethylene glycol, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, and tetramethyl sulfoxide. That is, the first solvent can be any of the solvent types listed above, such as ethylene glycol or ethanol; it can also be a mixture of any two or more of the solvents listed above, such as a mixture of ethanol and ethylene glycol or a mixture of methanol and water, etc., which are not listed here one by one. When the first solvent is a mixture of two or more, the ratio between the components of the mixture is not limited, and any ratio can be mixed. Of course, the first solvent may also be other solvents not listed here that can completely dissolve 3,4-diaminophenol.

[0031] 3,4-diaminophenol and the first solvent are added to a three-necked flask equipped with a thermometer, a magnetic stirrer, and a nitrogen atmosphere, and stirred. After the 3,4-diaminophenol is completely dissolved, hexachloroacetone is added dropwise in an ice bath. The dropwise addition of hexachloroacetone can control the reaction process of 3,4-diaminophenol and hexachloroacetone, thereby ensuring a more complete reaction. The dropwise addition time is controlled to be 30 to 40 minutes, such as 30 minutes, 35 minutes, or 40 minutes. The reaction is then ultrasonically reacted at 40° C. to 60° C., such as 40° C., 50° C., or 60° C., for 1 to 2 hours, such as 1 hour, 1.5 hours, or 2 hours. After the reaction is completed, the resulting solid is collected, washed with ethanol, and dried to obtain 6,6'-dihydroxy-p-benzimidazole as a white solid.

[0032] The molar ratio of 3,4-diaminophenol to hexachloroacetone is (2-10):1, such as 2:1, 5:1 or 10:1. The reaction process of 3,4-diaminophenol and hexachloroacetone is as follows:

[0033]

[0034] Step S2: The flame retardant of the present application is prepared by reacting the 6,6'-dihydroxy-p-benzimidazole (PBI) prepared in step S1 with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The specific process is as follows: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is dissolved in a second solvent, an alkaline catalyst and 6,6'-dihydroxy-p-benzimidazole are added, the temperature is raised to 40°C to 80°C, the reaction is carried out for 10 to 16 hours, and the flame retardant is obtained by filtering, washing, and drying.

[0035] The second solvent is used to dissolve DOPO. The amount of the second solvent used is not limited, as long as it can completely dissolve DOPO. The second solvent includes at least one of heptane, hexane, petroleum ether, methylcyclohexane, toluene, xylene, ethylbenzene, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, dimethylformamide, dimethylacetamide, acetonitrile, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether. The second solvent can be any of the aforementioned types, such as tetrahydrofuran, dimethylacetamide, or heptane. It can also be a mixture of any two or more of the aforementioned types, such as a mixture of heptane and hexane, a mixture of tetrahydrofuran and dimethyl sulfoxide, a mixture of dimethylformamide and dimethylacetamide, or a mixture of acetonitrile, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether, etc. These are not listed here. When the second solvent is a mixture, the ratio of the components in the mixture is not limited; any ratio can be used. Of course, solvents not listed here that can completely dissolve DOPO can also be used.

[0036] The role of the alkaline catalyst is to neutralize the H+ Therefore, the amount of alkaline catalyst used is sufficient to completely neutralize the H + The alkaline catalyst includes at least one of sodium hydroxide, sodium methoxide, potassium methoxide, lithium methoxide, sodium ethoxide, potassium ethoxide, and lithium ethoxide. That is, the alkaline catalyst can be any one of the types listed above, such as sodium hydroxide, sodium methoxide, potassium ethoxide, etc.; it can also be a combination of any two or more of the types listed above, such as a combination of sodium methoxide and potassium methoxide, or a combination of sodium methoxide and sodium ethoxide, or a combination of sodium hydroxide, sodium methoxide, and sodium ethoxide, etc., which are not listed here one by one. When the alkaline catalyst is a combination of two or more, there is no restriction on the ratio of the components in the combination, and any ratio can be used. Of course, other alkaline catalysts not listed here that meet the experimental requirements and do not affect the main reactions of PBI and DOPO can also be used.

[0037] Step S2 involves dissolving DOPO in a second solvent, adding a basic catalyst and PBI, and reacting at 40-80°C for 10-16 hours. The molar ratio of DOPO to PBI is (2-2.5):1, such as 2:1, 2.3:1, or 2.5:1. The reaction temperature is, for example, 40°C, 60°C, or 80°C; and the reaction time is, for example, 10 hours, 13 hours, or 16 hours. The reaction process of PBI and DOPO is as follows:

[0038]

[0039] After the above reaction is completed, the reaction liquid is filtered, dried, washed and dried to obtain a white solid PBI-DOPO flame retardant monomer.

[0040] The PBI-DOPO flame retardant prepared by the invention is used in polylactic acid, can improve the limiting oxygen index of the polylactic acid, and has an obvious anti-melting dripping effect.

[0041] Furthermore, the amount of flame retardant added to the polylactic acid accounts for 0.4wt% to 2.5wt% of the total mass of the flame retardant and the polylactic acid. Accordingly, the limiting oxygen index of the modified polylactic acid is increased to 24% to 33%. Within a certain range (0.4wt% to 2.5wt), as the amount of flame retardant added increases, the limiting oxygen index of the polylactic acid gradually increases.

[0042] The present application is described in detail below through several specific examples. The chemicals used in the following examples can all be obtained through general commercial channels.

[0043] Example 1

[0044] 10 ml of ethylene glycol and 1.24 g (10 mmol) of 3,4-diaminophenol were added to a three-necked flask equipped with a thermometer and a magnetic stirrer, and stirred under the protection of a nitrogen atmosphere until the 3,4-diaminophenol was completely dissolved; then, 0.265 g (1 mmol) of hexachloroacetone was added dropwise under ice bath conditions for 30 minutes; after the addition was completed, the reaction was continued under ultrasonication at 50°C for 1 hour; after the reaction was completed, the obtained solid was filtered, washed with ethanol three times, and dried to obtain 6,6'-dihydroxy-p-benzimidazole as a white solid.

[0045] 0.216 g (1 mmol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in tetrahydrofuran, 0.04 g (1 mmol) of sodium hydroxide and 0.133 g (0.5 mmol) of 6,6'-dihydroxy-p-benzimidazole (PBI) were added to the tetrahydrofuran containing DOPO, the temperature was raised to 60°C, and the reaction was carried out for 13 hours. After the reaction was completed, the mixture was filtered and dried to obtain a white solid PBI-DOPO flame retardant monomer.

[0046] Example 2

[0047] 10 ml of ethylene glycol and 1.24 g (10 mmol) of 3,4-diaminophenol were added to a three-necked flask equipped with a thermometer and a magnetic stirrer, and stirred under a nitrogen atmosphere until the 3,4-diaminophenol was completely dissolved; then, 1.325 g (5 mmol) of hexachloroacetone was added dropwise under ice bath conditions for 30 minutes; after the addition was completed, the reaction was continued under ultrasonication at 60° C. for 1.5 hours; after the reaction was completed, the obtained solid was filtered, washed with ethanol three times, and dried to obtain 6,6'-dihydroxy-p-benzimidazole as a white solid.

[0048] 0.216 (1 mmol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in tetrahydrofuran, 0.04 g (1 mmol) of sodium hydroxide and 0.106 g (0.4 mmol) of 6,6'-dihydroxy-p-benzimidazole (PBI) were added to the tetrahydrofuran containing DOPO, the temperature was raised to 80°C, and the reaction was carried out for 10 hours. After the reaction was completed, the mixture was filtered and dried to obtain a white solid PBI-DOPO flame retardant monomer.

[0049] Example 3

[0050] 10 ml of ethylene glycol and 1.24 g (10 mmol) of 3,4-diaminophenol were added to a three-necked flask equipped with a thermometer and a magnetic stirrer, and stirred under a nitrogen atmosphere until the 3,4-diaminophenol was completely dissolved; then, 0.53 g (2 mmol) of hexachloroacetone was added dropwise under ice bath conditions for 30 minutes; after the addition was completed, the reaction was continued under ultrasonication at 40°C for 2 hours; after the reaction was completed, the obtained solid was filtered, washed with ethanol three times, and dried to obtain 6,6'-dihydroxy-p-benzimidazole as a white solid.

[0051] 0.216 (1 mmol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in tetrahydrofuran, 0.04 g (1 mmol) of sodium hydroxide and 0.121 g (0.455 mmol) of 6,6'-dihydroxy-p-benzimidazole (PBI) were added to the tetrahydrofuran containing DOPO, the temperature was raised to 40°C, and the reaction was carried out for 16 hours. After the reaction was completed, the mixture was filtered and dried to obtain a white solid PBI-DOPO flame retardant monomer.

[0052] Example 4

[0053] The PBI-DOPO flame retardant monomer and polylactic acid pellets prepared in Example 1 were melt-blended at 180° C., wherein the mass of the PBI-DOPO flame retardant monomer accounted for 0.4% of the total mass of the PBI-DOPO flame retardant monomer and the polylactic acid pellets; then spun to obtain polylactic acid fibers; and then the polylactic acid fibers were spun and woven to obtain polylactic acid fabrics.

[0054] The flame retardant performance of the fabric was tested in accordance with GB / T5454-1997 "Textile Combustion Performance Test Oxygen Index Method", and the test results showed that the limiting oxygen index LOI was 24%.

[0055] Example 5

[0056] The difference between this embodiment and embodiment 4 is that the mass of the PBI-DOPO flame retardant monomer accounts for 1.0% of the total mass of the PBI-DOPO flame retardant monomer and the polylactic acid pellets.

[0057] The flame retardant performance of the fabric was tested in accordance with GB / T5454-1997 "Textile Combustion Performance Test Oxygen Index Method", and the test results showed that the limiting oxygen index LOI was 28%.

[0058] Example 6

[0059] The difference between this embodiment and embodiment 4 is that the mass of the PBI-DOPO flame retardant monomer accounts for 2.5% of the total mass of the PBI-DOPO flame retardant monomer and the polylactic acid pellets.

[0060] The flame retardant performance of the fabric was tested in accordance with GB / T5454-1997 "Textile Combustion Performance Test Oxygen Index Method", and the test results showed that the limiting oxygen index LOI was 33%.

[0061] The limiting oxygen index (LOI) is an important indicator of flame-retardant materials; the higher the LOI, the better the material's flame retardancy. The test results of Examples 4 to 6 show that applying the flame retardant prepared in this application to polylactic acid increases its LOI to 24% to 33%, significantly improving flame retardancy.

[0062] The flame retardant provided by the present invention contains p-benzimidazole. The nitrogen atom of the imidazole ring in the p-benzimidazole structure contains a lone pair of electrons, which can interact with the polylactic acid resin base, thereby improving the compatibility of the flame retardant with polylactic acid. In addition, adding nitrogen-containing groups in the flame retardant can improve the flame retardant efficiency. In addition, a cross-linked network containing aromatic heterocycles is formed between the imidazole groups, further enhancing the anti-melting dripping effect of the flame retardant polylactic acid. The preparation method of the flame retardant provided by the present invention is simple in process, short in cycle, and easy in post-processing, easy to control and industrially produced. Therefore, the present invention effectively overcomes some practical problems in the prior art and has high utilization value and use significance.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A flame retardant, characterized in that The structural formula of the flame retardant is as follows:

2. A method for preparing the flame retardant according to claim 1, characterized in that: The steps include: 3,4-diaminophenol and hexachloroacetone are mixed and reacted to prepare 6,6'-dihydroxy-p-benzimidazole; The 6,6'-dihydroxy-p-benzimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are reacted under the action of a basic catalyst to prepare a flame retardant.

3. The preparation method according to claim 2, characterized in that The method of preparing 6,6'-dihydroxy-p-benzimidazole by mixing 3,4-diaminophenol and hexachloroacetone for reaction comprises: 3,4-diaminophenol and a first solvent are added to a reactor, and mixed and stirred under the protection of a nitrogen atmosphere; hexachloroacetone is added dropwise to the reactor under ice bath conditions, and ultrasonic reaction is carried out at 40° C. to 60° C. for 1 to 2 hours; after filtering, washing, and drying, 6,6'-dihydroxy-p-benzimidazole is obtained.

4. The preparation method according to claim 3, characterized in that The molar ratio of the 3,4-diaminophenol to the hexachloroacetone is (2-10):

1.

5. The preparation method according to claim 3, characterized in that The first solvent includes at least one of water, ethanol, methanol, ethylene glycol, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, and tetramethyl sulfoxide.

6. The preparation method according to claim 2, characterized in that The method comprises reacting 6,6'-dihydroxy-p-benzimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide under the action of a basic catalyst to prepare a flame retardant, comprising: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is dissolved in a second solvent, an alkaline catalyst and 1,1'-p-benzimidazole are added, the temperature is raised to 40-80° C., the reaction is carried out for 10-16 hours, and the flame retardant is prepared after filtering, washing and drying.

7. The preparation method according to claim 2, characterized in that The molar ratio of the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the 6,6'-dihydroxy-p-benzimidazole is (2-2.5):

1.

8. The preparation method according to claim 6, characterized in that The second solvent includes at least one of heptane, hexane, petroleum ether, methylcyclohexane, toluene, xylene, ethylbenzene, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, dimethylformamide, dimethylacetamide, acetonitrile, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

9. The preparation method according to claim 2, characterized in that The alkaline catalyst includes at least one of sodium hydroxide, sodium methoxide, potassium methoxide, lithium methoxide, sodium ethoxide, potassium ethoxide, and lithium ethoxide.

10. Use of the flame retardant according to claim 1 in polylactic acid, characterized in that: The amount of the flame retardant added to the polylactic acid accounts for 0.4wt% to 2.5wt% of the total mass of the polylactic acid and the flame retardant, and the limiting oxygen index of the modified polylactic acid is 24% to 33%.

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