Preparation method of halogen-free flame retardant

Abstract

The invention provides a preparation method of a halogen-free flame retardant, and belongs to the technical field of flame retardants, and the preparation method comprises the following steps: S1, adding microcrystalline cellulose into an acid solution, heating to 70-80 DEG C, and stirring for acidolysis for 4-6 hours to obtain cellulose powder; s2, dispersing the cellulose powder into water, adding 6-[3-(2-oxazolinyl) benzene]-1, 3, 5-triazino-2, 4-diamine, carrying out ultrasonic treatment for 5-10 minutes, heating to 80-85 DEG C, carrying out stirring reaction for 1-3 hours, cooling, washing, and drying to obtain modified cellulose; and S3, adding the modified cellulose into ethanol, adding a nonionic surfactant, carrying out ultrasonic treatment for 5-10 minutes to obtain a modified cellulose dispersion liquid, adding a zinc salt solution into the modified cellulose dispersion liquid, stirring at room temperature for 5-10 hours, and washing and drying after the stirring is finished to obtain the halogen-free flame retardant. According to the invention, microcrystalline cellulose is subjected to acidolysis to obtain a reinforced phase, 6-[3-(2-oxazolinyl) benzene]-1, 3, 5-triazinyl-2, 4-diamine is grafted to the surface of cellulose, and coordinated chelation of zinc ions is cooperated to realize synergistic improvement of flame retardant effect and mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardants, and particularly relates to a preparation method of a halogen-free flame retardant. Background Art

[0002] Flame retardants, as key additives for improving the fire resistance of polymer materials, effectively inhibit the spread of flames by modifying the thermal degradation behavior and combustion process of the material. Flame retardant systems are primarily categorized as inorganic (such as aluminum hydroxide and magnesium hydroxide) and organic (such as halogen, phosphorus, and nitrogen compounds). While halogen-based flame retardants offer high flame retardancy, they release toxic gases during combustion, posing significant environmental risks. Consequently, halogen-free flame retardants are becoming a research and development focus.

[0003] However, existing halogen-free flame retardants still present numerous challenges. Most halogen-free systems, due to inherent flame retardancy limitations, require a significant addition to achieve the desired flame retardancy level. This can significantly reduce the material's mechanical properties. Therefore, achieving a synergistic optimization between flame retardancy and mechanical performance remains a pressing challenge. Summary of the Invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a method for preparing a halogen-free flame retardant, so as to at least partially solve the problems raised in the above background technology.

[0005] The technical solution adopted by the present invention is as follows: The present invention provides a method for preparing a halogen-free flame retardant, comprising the following steps: S1. Add microcrystalline cellulose to an acid solution, heat to 70-80°C, stir and acid hydrolyze for 4-6 hours to obtain cellulose powder; S2. Dispersing cellulose powder in water, adding 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, and ultrasonically treating for 5-10 minutes, then heating to 80-85° C. and stirring for 1-3 hours, cooling, washing, and drying to obtain modified cellulose; S3. Add modified cellulose to ethanol, add a nonionic surfactant and then perform ultrasonic treatment for 5-10 minutes to obtain a modified cellulose dispersion, add zinc salt solution to the modified cellulose dispersion, stir at room temperature for 5-10 hours, wash and dry after completion to obtain a halogen-free flame retardant.

[0006] In some embodiments of the present invention, in step S1, the acid solution includes hydrochloric acid and citric acid, and the volume ratio of hydrochloric acid to citric acid is 1:(8-10).

[0007] In some embodiments of the present invention, in step S1, the amount of microcrystalline cellulose added to the acid solution is 5-20 g / L.

[0008] In some embodiments of the present invention, in step S2, the amount of cellulose powder added to water is 5-10 g / L.

[0009] In some embodiments of the present invention, in step S2, the mass ratio of cellulose powder to 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine ring-2,4-diamine is 1:(1-3).

[0010] In some embodiments of the present invention, in step S3, the amount of modified cellulose added to ethanol is 10-15 g / L.

[0011] In some embodiments of the present invention, in step S3, the nonionic surfactant is one or a combination of sorbitan monooleate polyoxyethylene ether, octylphenyl polyoxyethylene ether, lauryl alcohol polyoxyethylene ether and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0012] In some embodiments of the present invention, in step S3, the amount of non-ionic surfactant added is 2-5 g / L.

[0013] In some embodiments of the present invention, in step S3, the volume ratio of the modified cellulose dispersion to the zinc salt solution is 1:(1-1.5).

[0014] In some embodiments of the present invention, in step S3, the zinc salt is zinc acetate, zinc nitrate, zinc chloride or zinc sulfate, and the concentration of the zinc salt solution is 5-15 wt%.

[0015] The beneficial effects achieved by the present invention are as follows: The present invention simultaneously obtains a nanoscale reinforcing phase through acid hydrolysis of microcrystalline cellulose and introduces high-density carboxyl sites. Through an esterification reaction, 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is grafted onto the cellulose surface, creating a covalently bonded interface and enhancing the mechanical strength of the polymer material. During combustion, the triazine ring releases non-flammable nitrogen gas, which catalyzes cross-linking to form carbon. Simultaneously, zinc ions form a composite ceramic layer through hydroxyl coordination and chelation, achieving a triple synergistic effect of condensed phase flame retardancy. This system overcomes the industry bottleneck of flame retardants impairing mechanical properties, combining the core advantages of interface reinforcement, gas-phase flame suppression, and ceramic barrier properties. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0018] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0019] In view of the deficiencies in the prior art mentioned in the background technology, the present invention provides a method for preparing a halogen-free flame retardant, comprising the following steps: S1. Add microcrystalline cellulose to an acid solution, heat to 70-80°C, stir and acid hydrolyze for 4-6 hours to obtain cellulose powder; S2. Dispersing cellulose powder in water, adding 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, and ultrasonically treating for 5-10 minutes, then heating to 80-85° C. and stirring for 1-3 hours, cooling, washing, and drying to obtain modified cellulose; S3. Add modified cellulose to ethanol, add a nonionic surfactant and then perform ultrasonic treatment for 5-10 minutes to obtain a modified cellulose dispersion, add zinc salt solution to the modified cellulose dispersion, stir at room temperature for 5-10 hours, wash and dry after completion to obtain a halogen-free flame retardant.

[0020] Acid hydrolysis of microcrystalline cellulose can produce nanoscale cellulose powder, which can enhance the mechanical properties of polymer materials. It can also introduce carboxyl groups onto the surface of the microcrystalline cellulose, providing sites for subsequent grafting. 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is then grafted onto the surface of the cellulose nanopowder via an esterification reaction. This creates a strong organic-inorganic hybrid interface, strengthening the interfacial bonding between the flame retardant and the polymer matrix. This allows for more efficient transfer of external loads from the matrix to the cellulose powder reinforcement phase, further enhancing the mechanical properties of the polymer. Furthermore, during combustion, the triazine ring of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine decomposes at high temperatures to produce non-flammable gases such as NH3. Its oxazoline structure also promotes carbonization, achieving both gas-phase and condensed-phase flame retardancy. Finally, the Zn²⁺ of the zinc salt can chelate with the hydroxyl groups on the surface of the cellulose powder through charge interaction to form a stable complex. During the combustion process, Zn²⁺ is converted into ZnO to form a continuous and dense ceramic carbon layer, thereby further enhancing the flame retardant effect.

[0021] In summary, the present invention simultaneously obtains a nanoscale reinforcing phase through acid hydrolysis of microcrystalline cellulose and introduces high-density carboxyl sites. 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is grafted onto the cellulose surface via an esterification reaction, constructing a covalently bonded interface and improving the mechanical strength of the polymer material. During combustion, the triazine ring releases nitrogen-based non-combustible gas (gas-phase flame retardant), the oxazoline group catalyzes cross-linking to form carbon, and the zinc ions simultaneously coordinate and chelate through the hydroxyl group to form a composite ceramic layer (thickness), achieving a triple synergistic effect of condensed phase flame retardancy. This system breaks through the industry bottleneck of flame retardants damaging mechanical properties, combining the core advantages of interface reinforcement, gas-phase flame suppression, and ceramic barrier.

[0022] In some embodiments, in step S1, the acid solution includes hydrochloric acid and citric acid, and the volume ratio of hydrochloric acid to citric acid is 1: (8-10). Among them, hydrochloric acid provides a strong proton source to improve the acidolysis efficiency of microcrystalline cellulose, and citric acid can impart carboxyl modification to the surface of microcrystalline cellulose through esterification reaction between carboxyl groups and cellulose hydroxyl groups. By setting the volume ratio of hydrochloric acid to citric acid to 1: (8-10), both the hydrolysis efficiency is guaranteed and the side reactions can be controlled.

[0023] In some embodiments, in step S1, the amount of microcrystalline cellulose added to the acid solution is 5-20 g / L. If the amount of microcrystalline cellulose added is less than 5 g / L, excessive acid will lead to excessive degradation of cellulose; if the amount of microcrystalline cellulose added is greater than 20 g / L, the amount of acid will be relatively insufficient, resulting in incomplete hydrolysis. Therefore, the amount of microcrystalline cellulose added to the acid solution needs to be set to 5-20 g / L.

[0024] In some embodiments, in step S2, the amount of cellulose powder added to water is 5-10 g / L, thereby allowing the cellulose powder to be fully dispersed in the water and preventing agglomeration of the cellulose powder.

[0025] In some embodiments, in step S2, the mass ratio of cellulose powder to 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is 1:(1-3). Excessive amounts of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine will prevent grafting due to steric hindrance and will exist in the form of physical adsorption. Excessive amounts of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine will result in insufficient coverage on the cellulose surface. Therefore, the mass ratio of cellulose powder to 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is set to 1:(1-3).

[0026] In some embodiments, in step S3, the amount of modified cellulose added to ethanol is 10-15 g / L, thereby allowing the modified cellulose to be fully dispersed in the ethanol and preventing agglomeration of the modified cellulose.

[0027] In some embodiments, in step S3, the nonionic surfactant is one or a combination of sorbitan monooleate polyoxyethylene ether, octylphenyl polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer. Nonionic surfactants can promote the dispersion of modified cellulose in ethanol and improve the chelation efficiency of Zn²⁺ on cellulose.

[0028] In some embodiments, in step S3, the amount of nonionic surfactant added is 2-5 g / L. If the amount of nonionic surfactant added is too little, the modified cellulose will be unevenly dispersed. If the amount of nonionic surfactant added is too much, it will introduce excess organic matter, interfere with the chelation reaction, and increase the difficulty of subsequent washing.

[0029] In some embodiments, in step S3, the volume ratio of the modified cellulose dispersion to the zinc salt solution is 1:(1-1.5). By setting the volume ratio of the modified cellulose dispersion to the zinc salt solution to 1:(1-1.5), it is possible to avoid insufficient Zn²⁺, which prevents it from fully combining with the cellulose, and to avoid excessive Zn²⁺, which increases the difficulty of washing.

[0030] In some embodiments, in step S3, the zinc salt is zinc acetate, zinc nitrate, zinc chloride, or zinc sulfate, and the concentration of the zinc salt solution is 5-15 wt %. By setting the concentration of the zinc salt solution to 5-15 wt %, localized supersaturation of Zn²⁺ can be avoided, Zn²⁺ aggregation can be prevented, and the binding efficiency of Zn²⁺ to cellulose can be improved.

[0031] The present invention will be further described below by way of specific embodiments.

[0032] The experimental methods in the following examples, unless otherwise specified, are all conventional methods available in the prior art; the experimental materials used in the following examples, unless otherwise specified, are all purchased from commercial channels.

[0033] Example 1: S1. Prepare an acid solution in a volume ratio of hydrochloric acid to citric acid of 1:8, add 5 g / L of microcrystalline cellulose to the acid solution, heat to 70° C., stir, and acid hydrolyze for 4 h to obtain cellulose powder; S2. Dispersing cellulose powder in water at an addition amount of 5 g / L, adding 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, with a mass ratio of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine to cellulose powder being 1:1, performing ultrasonic treatment for 5 minutes, then heating to 80° C. and stirring for reaction for 1 hour, cooling, washing, and drying to obtain modified cellulose; S3. Add 10 g / L of modified cellulose to ethanol, add 2 g / L of nonionic surfactant, and perform ultrasonic treatment for 5 minutes to obtain a modified cellulose dispersion. Add 5 wt% zinc acetate-ethanol solution to the modified cellulose dispersion in a volume ratio of 1:1. Stir at room temperature for 5 hours, wash, and dry to obtain a halogen-free flame retardant.

[0034] Example 2: S1. Prepare an acid solution in a volume ratio of hydrochloric acid to citric acid of 1:9, add 12 g / L of microcrystalline cellulose to the acid solution, heat to 80° C., stir, and acid hydrolyze for 6 h to obtain cellulose powder; S2. Dispersing cellulose powder in water at an addition amount of 7 g / L, adding 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, with a mass ratio of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine to cellulose powder being 2:1, performing ultrasonic treatment for 10 minutes, then heating to 85° C. and stirring for reaction for 3 hours, cooling, washing, and drying to obtain modified cellulose; S3. Add modified cellulose in an amount of 12 g / L to ethanol, add a non-ionic surfactant in an amount of 3 g / L, and then perform ultrasonic treatment for 10 minutes to obtain a modified cellulose dispersion. Add a zinc acetate-ethanol solution with a concentration of 10 wt% to the modified cellulose dispersion, and the volume ratio of the modified cellulose dispersion to the zinc acetate-ethanol solution is 1:1.2. Stir at room temperature for 8 hours, wash, and dry to obtain a halogen-free flame retardant.

[0035] Example 3: S1. Prepare an acid solution in a volume ratio of hydrochloric acid to citric acid of 1:10, add 20 g / L of microcrystalline cellulose to the acid solution, heat to 80° C., stir, and acid hydrolyze for 6 h to obtain cellulose powder; S2. Dispersing cellulose powder in water at an addition amount of 10 g / L, adding 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, with a mass ratio of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine to cellulose powder being 3:1, performing ultrasonic treatment for 10 minutes, then heating to 85° C. and stirring for reaction for 3 hours, cooling, washing, and drying to obtain modified cellulose; S3. Add 15 g / L of modified cellulose to ethanol, add 5 g / L of nonionic surfactant, and perform ultrasonic treatment for 10 minutes to obtain a modified cellulose dispersion. Add 15 wt% zinc acetate-ethanol solution to the modified cellulose dispersion in a volume ratio of 1:1.5 to the modified cellulose dispersion. Stir at room temperature for 10 hours, wash, and dry to obtain a halogen-free flame retardant.

[0036] Comparative Example 1: The components are the same as those in Example 1, except that the cellulose powder, 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine ring-2,4-diamine and zinc acetate are simply stirred and mixed.

[0037] Comparative Example 2: The method is consistent with Example 1, except that step S2 is not performed, and step S3 is performed using the cellulose powder obtained in step S1 instead of the modified cellulose.

[0038] Comparative Example 3: The same as Example 1, except that step S3 is not performed.

[0039] Examples 1-3 and Comparative Examples 1-3 were tested, and the test contents were as follows: The flame retardants prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with epoxy resin in an amount of 15 wt % to prepare samples.

[0040] Tensile performance test: According to the GB / T528-2009 test standard, a universal testing machine was used with a tensile rate of 500 mm / min, dumbbell-shaped specimens (75 mm × 2 mm) were used, and the gauge length was set to 20 mm. 3-5 specimens were tested for each set of formula specimens. The tensile strength of each specimen was recorded and the test results were averaged. The test temperature was room temperature.

[0041] LOI test: Plastic combustion performance - oxygen index method is used in a dynamic gas distribution device. The top of the sample is fixed vertically in the center of the combustion tube. The oxygen / nitrogen mixture ratio is adjusted (accuracy ±0.1%). A methane flame (height 20mm) is used to ignite the top of the sample. The minimum oxygen concentration required to maintain stable combustion for 3 minutes or more or to burn 50mm is measured. Each group is repeated 5 times and the average value is taken.

[0042] UL-94 combustion test: Secure the specimen in a vertical clamping device, lay a layer of dry absorbent cotton on the bottom, and ignite the lower edge of the specimen twice with a Bunsen burner (flame height 20mm, gas flow 105ml / min). Afterflame duration t1 is recorded 10 seconds after the first ignition. Immediately after extinguishment, a second ignition is performed, recording t2 for 10 seconds. The total afterflame time (t1 + t2) and whether the molten droplet ignites the absorbent cotton are used to determine the V-0 / V-1 / V-2 rating.

[0043] The test results are shown in Table 1.

[0044] Table 1

[0045] Referring to the test results in Table 1, the tensile strength, LOI index, and UL-94 flammability rating of Comparative Example 1 all decreased to varying degrees compared to Example 1, indicating that simple mixing can reduce the flame retardant efficiency of the flame retardant and the mechanical properties of the epoxy resin. The tensile strength of Comparative Example 2 decreased significantly compared to Example 1, indicating that the grafting of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine onto the cellulose surface via esterification creates a covalently bonded interface and enhances the mechanical strength of the polymer. The LOI index and UL-94 flammability rating of Comparative Example 2 decreased significantly compared to Example 1, indicating that the introduction of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine can improve the flame retardancy of the epoxy resin. The LOI index and UL-94 flammability rating of Comparative Example 3 decreased significantly compared with those of Example 1, indicating that the introduction of Zn²⁺ can further enhance the flame retardant effect by converting it into ZnO during the combustion process to form a continuous and dense ceramic carbon layer.

[0046] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a halogen-free flame retardant, characterized in that: The following steps are involved: S1. Add microcrystalline cellulose to an acid solution, heat to 70-80°C, stir and acid hydrolyze for 4-6 hours to obtain cellulose powder; S2. Dispersing cellulose powder in water, adding 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, and ultrasonically treating for 5-10 minutes, then heating to 80-85° C. and stirring for 1-3 hours, cooling, washing, and drying to obtain modified cellulose; S3. Add modified cellulose to ethanol, add a nonionic surfactant and then perform ultrasonic treatment for 5-10 minutes to obtain a modified cellulose dispersion, add zinc salt solution to the modified cellulose dispersion, stir at room temperature for 5-10 hours, wash and dry after completion to obtain a halogen-free flame retardant.

2. The preparation method according to claim 1, characterized in that In step S1, the acid solution includes hydrochloric acid and citric acid, and the volume ratio of hydrochloric acid to citric acid is 1:(8-10).

3. The preparation method according to claim 1, characterized in that In step S1, the amount of microcrystalline cellulose added to the acid solution is 5-20 g / L.

4. The preparation method according to claim 1, characterized in that In step S2, the amount of cellulose powder added to water is 5-10 g / L.

5. The preparation method according to claim 1, characterized in that In the step S2, the mass ratio of cellulose powder to 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine ring-2,4-diamine is 1:(1-3).

6. The preparation method according to claim 1, characterized in that In step S3, the amount of modified cellulose added to ethanol is 10-15 g / L.

7. The preparation method according to claim 1, characterized in that In step S3, the nonionic surfactant is one or a combination of sorbitan monooleate polyoxyethylene ether, octylphenyl polyoxyethylene ether, lauryl alcohol polyoxyethylene ether and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

8. The preparation method according to claim 1, characterized in that In step S3, the amount of non-ionic surfactant added is 2-5 g / L.

9. The preparation method according to claim 1, characterized in that In step S3, the volume ratio of the modified cellulose dispersion to the zinc salt solution is 1:(1-1.5).

10. The preparation method according to claim 1, characterized in that In step S3, the zinc salt is zinc acetate, zinc nitrate, zinc chloride or zinc sulfate, and the concentration of the zinc salt solution is 5-15 wt%.

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