A method for preparing a halogen-free flame retardant

Abstract

The application provides a preparation method of a halogen-free flame retardant, and belongs to the technical field of flame retardants, and comprises the following steps: S1, microcrystalline cellulose is added into an acid solution, heated to 70-80 DEG C, and stirred and acidolysed for 4-6 h to obtain cellulose powder; S2, the cellulose powder is dispersed into water, 6-[3-(2-oxazoline group) benzene]-1, 3, 5-triazine ring-2, 4-diamine is added, ultrasonic treatment is carried out for 5-10 min, then the temperature is increased to 80-85 DEG C, and stirring reaction is carried out for 1-3 h, after cooling, washing and drying, modified cellulose is obtained; S3, the modified cellulose is added into ethanol, after adding a non-ionic surfactant, ultrasonic treatment is carried out for 5-10 min to obtain a modified cellulose dispersion liquid, a zinc salt solution is added into the modified cellulose dispersion liquid, stirring is carried out at room temperature for 5-10 h, after ending, washing and drying, a halogen-free flame retardant is obtained. The microcrystalline cellulose is acidolysed to obtain a reinforcing phase, 6-[3-(2-oxazoline group) benzene]-1, 3, 5-triazine ring-2, 4-diamine is grafted to the surface of the cellulose, and the coordination chelation of zinc ions is combined, so that the synergistic improvement of the flame retardation effect and the mechanical property is realized.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant technology, specifically relating to a method for preparing a halogen-free flame retardant. Background Technology

[0002] Flame retardants, as key additives for improving the fire resistance of polymer materials, effectively inhibit flame spread by altering the thermal degradation behavior and combustion process of the materials. Flame retardant systems are mainly divided into inorganic (such as aluminum hydroxide and magnesium hydroxide) and organic (such as halogenated, phosphorus-based, and nitrogen-based compounds). Among them, although halogenated flame retardants have high flame retardant efficiency, they release toxic gases during combustion, posing a significant environmental risk. Therefore, halogen-free flame retardants have gradually become the focus of research and development.

[0003] However, existing halogen-free flame retardants still have many problems. Most halogen-free systems require large addition amounts to achieve the desired flame retardant rating due to the inherent flame retardant properties of the materials themselves. This leads to a significant decrease in the material's mechanical properties. Therefore, how to achieve synergistic optimization between flame retardant efficiency and mechanical property maintenance, and how to synergistically improve both flame retardant efficiency and mechanical properties, is a problem that needs to be solved. Summary of the Invention

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

[0005] The technical solution adopted in this invention is as follows:

[0006] This invention proposes a method for preparing a halogen-free flame retardant, comprising the following steps:

[0007] S1. Add microcrystalline cellulose to an acid solution, heat to 70-80℃ and stir for 4-6 hours to obtain cellulose powder;

[0008] S2. Disperse cellulose powder in water, add 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, sonicate for 5-10 min, then heat to 80-85℃ and stir for 1-3 h. After cooling, wash and dry to obtain modified cellulose.

[0009] S3. Add modified cellulose to ethanol, add a nonionic surfactant, and sonicate for 5-10 minutes to obtain a modified cellulose dispersion. Add zinc salt solution to the modified cellulose dispersion and stir at room temperature for 5-10 hours. After the stirring is complete, wash and dry to obtain a halogen-free flame retardant.

[0010] 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).

[0011] 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.

[0012] In some embodiments of the present invention, in step S2, the amount of cellulose powder added to water is 5-10 g / L.

[0013] In some embodiments of the present invention, in step S2, the mass ratio of cellulose powder to 6-[3-(2-oxazolinyl)benzo]-1,3,5-triazinecyclo-2,4-diamine is 1:(1-3).

[0014] In some embodiments of the present invention, in step S3, the amount of modified cellulose added to ethanol is 10-15 g / L.

[0015] In some embodiments of the present invention, in step S3, the nonionic surfactant is one or a combination of several of sorbitan monooleate polyoxyethylene ether, octylphenyl polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0016] In some embodiments of the present invention, in step S3, the amount of nonionic surfactant added is 2-5 g / L.

[0017] 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).

[0018] 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%.

[0019] The beneficial effects achieved by this invention are as follows:

[0020] This invention achieves a nanoscale reinforcing phase by simultaneously acid hydrolyzing microcrystalline cellulose and introducing high-density carboxyl sites. Following esterification, 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is grafted onto the cellulose surface to construct a covalently bonded interface, enhancing the mechanical strength of the polymer material. During combustion, the triazine ring releases nitrogen-based non-flammable gases, the oxazolinyl groups catalyze cross-linking to form char, and zinc ions coordinate with hydroxyl groups to form a composite ceramic layer, achieving a triple synergistic effect of condensed-phase flame retardancy. This system overcomes the industry bottleneck of flame retardants damaging mechanical properties, possessing the core advantages of interface reinforcement, gas-phase flame suppression, and a ceramic barrier. Detailed Implementation

[0021] 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.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0023] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] To address the shortcomings of the prior art mentioned in the background section, this invention provides a method for preparing a halogen-free flame retardant, comprising the following steps:

[0025] S1. Add microcrystalline cellulose to an acid solution, heat to 70-80℃ and stir for 4-6 hours to obtain cellulose powder;

[0026] S2. Disperse cellulose powder in water, add 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine, sonicate for 5-10 min, then heat to 80-85℃ and stir for 1-3 h. After cooling, wash and dry to obtain modified cellulose.

[0027] S3. Add modified cellulose to ethanol, add a nonionic surfactant, and sonicate for 5-10 minutes to obtain a modified cellulose dispersion. Add zinc salt solution to the modified cellulose dispersion and stir at room temperature for 5-10 hours. After the stirring is complete, wash and dry to obtain a halogen-free flame retardant.

[0028] Acid hydrolysis of microcrystalline cellulose can produce nanoscale cellulose powder, which can enhance the mechanical properties of polymer materials. Furthermore, it can introduce carboxyl groups onto the surface of microcrystalline cellulose, providing sites for subsequent grafting. Then, esterification is used to graft 6-[3-(2-oxazolinyl)benzo]-1,3,5-triazine-2,4-diamine onto the surface of the cellulose nanopowder, constructing a robust organic-inorganic hybrid interface. This enhances the interfacial bonding between the flame retardant and the polymer matrix, allowing external loads to be more effectively transferred from the matrix to the cellulose powder reinforcing phase, further enhancing the mechanical properties of the polymer material. During combustion, the triazine ring of 6-[3-(2-oxazolinyl)benzo]-1,3,5-triazine-2,4-diamine decomposes at high temperatures to produce non-flammable gases such as NH3. Its oxazoline structure can also promote char formation, thus achieving both gas-phase and condensed-phase flame retardant effects. Finally, the Zn²⁺ of the zinc salt can chelate with the hydroxyl groups on the surface of the cellulose powder through charge interaction, thereby forming a stable complex. During combustion, Zn²⁺ is converted into ZnO to form a continuous and dense ceramicized carbon layer, thereby further enhancing the flame retardant effect.

[0029] In summary, this invention achieves a triple synergistic effect of obtaining a nanoscale reinforcing phase and introducing high-density carboxyl sites through the simultaneous acid hydrolysis of microcrystalline cellulose. Following esterification, 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine is grafted onto the cellulose surface to construct a covalently bonded interface, thereby enhancing the mechanical strength of the polymer material. During combustion, the triazine ring releases nitrogen-based non-flammable gases (gas-phase flame retardancy), the oxazolinyl groups catalyze cross-linking to form char, and simultaneously, zinc ions coordinate and chelate through hydroxyl groups to form a composite ceramic layer (thickness), achieving synergistic flame retardancy in the condensed phase. This system overcomes the industry bottleneck of flame retardants damaging mechanical properties, possessing the core advantages of interface reinforcement, gas-phase flame suppression, and a ceramic barrier.

[0030] In some embodiments, in step S1, the acid solution includes hydrochloric acid and citric acid, with a volume ratio of hydrochloric acid to citric acid of 1:(8-10). Hydrochloric acid provides a strong proton source to improve the acid hydrolysis efficiency of microcrystalline cellulose, while citric acid can impart carboxylation modification to the surface of microcrystalline cellulose through esterification of the carboxyl groups with the hydroxyl groups of cellulose. By setting the volume ratio of hydrochloric acid to citric acid to 1:(8-10), both hydrolysis efficiency and side reactions can be controlled.

[0031] 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 <5 g / L, excessive acid will lead to excessive degradation of cellulose; if the amount of microcrystalline cellulose added is >20 g / L, the hydrolysis will be incomplete due to insufficient acid. Therefore, the amount of microcrystalline cellulose added to the acid solution needs to be set to 5-20 g / L.

[0032] In some embodiments, in step S2, the amount of cellulose powder added to the water is 5-10 g / L. This allows the cellulose powder to be fully dispersed in the water, preventing agglomeration.

[0033] In some embodiments, 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). Excessive amounts of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine ring-2,4-diamine would prevent grafting due to steric hindrance and exist only in a physically adsorbed form. Insufficient amounts of 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine ring-2,4-diamine would result in insufficient coverage of the cellulose surface. Therefore, the mass ratio of cellulose powder to 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine ring-2,4-diamine is set to 1:(1-3).

[0034] In some embodiments, in step S3, the amount of modified cellulose added to ethanol is 10-15 g / L. This allows the modified cellulose to be fully dispersed in ethanol, preventing its aggregation.

[0035] In some embodiments, in step S3, the nonionic surfactant is one or a combination of several selected from 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 between Zn²⁺ and cellulose.

[0036] In some embodiments, the amount of nonionic surfactant added in step S3 is 2-5 g / L. Insufficient addition of nonionic surfactant will result in uneven dispersion of the modified cellulose, while excessive addition will introduce excess organic matter, interfering with the chelation reaction and increasing the difficulty of subsequent washing.

[0037] 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 would prevent it from fully binding with cellulose, while also avoiding excessive Zn²⁺, which would increase the difficulty of washing.

[0038] 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%, local supersaturation of Zn²⁺ can be avoided, Zn²⁺ aggregation can be prevented, and the binding efficiency of Zn²⁺ with cellulose can be improved.

[0039] The present invention will be further described below by way of specific embodiments.

[0040] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods already existing in the art; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0041] Example 1:

[0042] S1. Prepare an acid solution with a volume ratio of hydrochloric acid to citric acid of 1:8. Add microcrystalline cellulose to the acid solution at a rate of 5 g / L. Heat to 70°C and stir for 4 hours to obtain cellulose powder.

[0043] S2. Disperse cellulose powder in water at a dosage of 5 g / L, add 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 of 1:1, sonicate for 5 min, then heat to 80℃ and stir for 1 h, cool, wash and dry to obtain modified cellulose;

[0044] S3. Modified cellulose was added to ethanol at a concentration of 10 g / L, and a nonionic surfactant was added at a concentration of 2 g / L. The mixture was then sonicated for 5 min to obtain a modified cellulose dispersion. A 5 wt% zinc acetate-ethanol solution was added to the modified cellulose dispersion, with a volume ratio of 1:1 between the modified cellulose dispersion and the zinc acetate-ethanol solution. The mixture was stirred at room temperature for 5 h. After stirring, the mixture was washed and dried to obtain a halogen-free flame retardant.

[0045] Example 2:

[0046] S1. Prepare an acid solution with a volume ratio of hydrochloric acid to citric acid of 1:9. Add microcrystalline cellulose to the acid solution at a dosage of 12 g / L. Heat to 80°C and stir for 6 hours to obtain cellulose powder.

[0047] S2. Disperse cellulose powder in water at a dosage of 7 g / L, add 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 of 2:1, sonicate for 10 min, then heat to 85℃ and stir for 3 h, cool, wash and dry to obtain modified cellulose;

[0048] S3. Modified cellulose was added to ethanol at a concentration of 12 g / L, and a nonionic surfactant was added at a concentration of 3 g / L. The mixture was then sonicated for 10 min to obtain a modified cellulose dispersion. A 10 wt% zinc acetate-ethanol solution was added to the modified cellulose dispersion, with a volume ratio of 1:1.2 between the modified cellulose dispersion and the zinc acetate-ethanol solution. The mixture was stirred at room temperature for 8 h. After stirring, the mixture was washed and dried to obtain a halogen-free flame retardant.

[0049] Example 3:

[0050] S1. Prepare an acid solution with a volume ratio of hydrochloric acid to citric acid of 1:10. Add microcrystalline cellulose to the acid solution at a dosage of 20 g / L. Heat to 80°C and stir for 6 hours to obtain cellulose powder.

[0051] S2. Disperse cellulose powder in water at a dosage of 10 g / L, add 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 of 3:1, sonicate for 10 min, then heat to 85℃ and stir for 3 h, cool, wash and dry to obtain modified cellulose;

[0052] S3. Modified cellulose was added to ethanol at a concentration of 15 g / L, and a nonionic surfactant was added at a concentration of 5 g / L. The mixture was then sonicated for 10 min to obtain a modified cellulose dispersion. A 15 wt% zinc acetate-ethanol solution was added to the modified cellulose dispersion, with a volume ratio of 1:1.5 between the modified cellulose dispersion and the zinc acetate-ethanol solution. The mixture was stirred at room temperature for 10 h. After stirring, the mixture was washed and dried to obtain a halogen-free flame retardant.

[0053] Comparative Example 1:

[0054] The composition is consistent with that of Example 1, except that the cellulose powder, 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine and zinc acetate are simply mixed by stirring.

[0055] Comparative Example 2:

[0056] Consistent with Example 1, except that step S2 is omitted, and the cellulose powder obtained in step S1 is used instead of the modified cellulose in step S3.

[0057] Comparative Example 3:

[0058] Consistent with Example 1, except that step S3 is omitted.

[0059] The tests were conducted on Examples 1-3 and Comparative Examples 1-3, and the specific test contents are as follows:

[0060] The flame retardants prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with epoxy resin at an addition amount of 15 wt% to prepare samples.

[0061] Tensile property 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 with a gauge length of 20 mm. 3-5 specimens were tested for each formulation sample. The tensile strength of each specimen was recorded. The average value of the test results was taken. The test temperature was room temperature.

[0062] LOI test: The plastic combustion performance-oxygen index method was used and carried out in a dynamic gas mixing device. The top of the sample was vertically fixed at the center of the combustion cylinder. The oxygen / nitrogen mixing ratio was adjusted (accuracy ±0.1%). The top of the sample was ignited with a methane flame (height 20 mm). The minimum oxygen concentration required to maintain stable combustion for ≥3 minutes or burn 50 mm of length was measured. Each group was repeated 5 times and the average value was taken.

[0063] UL-94 Combustion Test: The sample is fixed by a vertical clamping device, and a layer of dry degreased cotton is laid at the bottom. The lower edge of the sample is burned twice with a Bunsen burner (flame height 20mm, gas flow rate 105ml / min): the afterflame time t1 is recorded after 10 seconds of the first ignition, and t2 is recorded immediately after the extinguishing of the burner. The V-0 / V-1 / V-2 rating is determined based on the total afterflame time (t1+t2) and whether the molten droplets ignite the degreased cotton.

[0064] The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] 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 reduces 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 6-[3-(2-oxazolinyl)phenyl]-1,3,5-triazine-2,4-diamine was grafted onto the cellulose surface via esterification, constructing a covalently bonded interface and improving the mechanical strength of the polymer material. 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 retardant properties of the epoxy resin. The LOI index and UL-94 flammability rating of Comparative Example 3 decreased significantly compared to Example 1, indicating that the introduction of Zn²⁺ can further enhance the flame retardant effect by converting it into ZnO during combustion to form a continuous and dense ceramicized carbon layer.

[0068] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A process for the preparation of a halogen-free flame retardant, characterized in that, The method comprises the following steps: S1, adding microcrystalline cellulose into an acid solution, heating to 70-80℃, stirring acidolysis for 4-6h to obtain cellulose powder, wherein the acid solution comprises hydrochloric acid and citric acid, and the volume ratio of hydrochloric acid to citric acid is 1:(8-10); S2, dispersing the cellulose powder into water, adding 6-[3-(2-oxazoline group) benzene]-1,3,5-triazine ring-2,4-diamine, ultrasonic treatment for 5-10min, then heating to 80-85℃, stirring for 1-3h, and then cooling, washing and drying to obtain modified cellulose; S3, adding the modified cellulose into ethanol, adding a non-ionic surfactant, ultrasonic treatment for 5-10min to obtain a modified cellulose dispersion, adding a zinc salt solution to the modified cellulose dispersion, stirring at room temperature for 5-10h, and then washing and drying to obtain a halogen-free flame retardant.

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

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

4. The method of claim 1, wherein, In the step S2, the mass ratio of cellulose powder to 6-[3-(2-oxazoline group) benzene]-1,3,5-triazine ring-2,4-diamine is 1:(1-3).

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

6. The method of claim 1, wherein, In the step S3, the non-ionic surfactant is one or a combination of sorbitan monooleate polyoxyethylene ether, octylphenyl polyoxyethylene ether, lauryl polyoxyethylene ether and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

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

8. The method of claim 1, wherein, In the step S3, the volume ratio of the modified cellulose dispersion to the zinc salt solution is 1:(1-1.5).

9. The method of claim 1, wherein, In the step S3, the zinc salt is zinc acetate, zinc nitrate, zinc chloride or zinc sulfate, and the concentration of the zinc salt solution is 5-15wt%.

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