Intrinsic flame-retardant bio-based epoxy resin and preparation method thereof

Abstract

The invention relates to intrinsic flame-retardant bio-based epoxy resin and a synthesis method thereof.The intrinsic flame-retardant bio-based epoxy resin takes magnolol as a main raw material, and the molecular structure contains biphenyl units and ester bonds, so that the intrinsic flame-retardant bio-based epoxy resin has excellent flame retardance and thermal performance. The synthesis method comprises the following three steps: firstly, reacting magnolol with halogenated alkane to generate a precursor; secondly, reacting the precursor with acyl chloride to generate an intermediate; finally, oxidizing the intermediate to generate the target epoxy resin. The method does not need to add a large amount of flame retardant, and avoids negative influence on the performance of the epoxy resin. The synthesized epoxy resin shows excellent flame retardance and heat resistance, has high carbon residue rate, glass transition temperature and thermal decomposition temperature, and has the flame retardant level reaching V-0 level which is superior to that of general epoxy resin.

Description

Technical Field

[0001] The invention belongs to the technical field of epoxy resins, and in particular relates to an intrinsic flame-retardant bio-based epoxy resin and a synthesis method thereof. Background Art

[0002] Epoxy resins are widely used in aerospace, electronics, automobiles, construction and other fields due to their good mechanical properties, electrical insulation and chemical corrosion resistance. The raw materials of traditional epoxy resins come from non-renewable resources such as petroleum. In particular, bisphenol A epoxy resin (DGEBA) accounts for about 90% of the total production of epoxy resins. Its main raw material, bisphenol A, comes from petroleum resources and is biologically toxic. Bio-based epoxy resins have broad development prospects.

[0003] In addition, epoxy resins generally have the disadvantage of being flammable, which greatly limits their application in the field of high flame retardancy and fire resistance. There are currently two main methods to improve the flame retardancy of epoxy resins: additive and reactive. The additive method uses flame retardant additives to improve the flame retardancy of epoxy resins. Among them, halogen-containing flame retardant additives have the best flame retardant effect, but their biological toxicity is high, posing a great threat to human health and the environment. Halogen-free flame retardants usually have low flame retardant efficiency and require increased dosage to achieve a better flame retardant effect, resulting in a decrease in the crosslinking density of the epoxy resin system. On the other hand, due to the poor compatibility of flame retardants with epoxy resins, migration and precipitation are prone to occur, thereby reducing the thermal stability of the epoxy resin system.

[0004] CN106633673A discloses a flame-retardant epoxy resin based on a phosphaphenanthrene derivative and an inorganic flame retardant and a preparation method thereof. The flame-retardant epoxy resin is prepared by compounding different phosphaphenanthrene derivative flame retardants with different inorganic flame retardants and then melt-blending them with bisphenol A diglycidyl ether epoxy resin. However, phosphorus-containing flame retardants usually have poor compatibility with polymers and have certain toxicity, which has adverse effects on the environment and human body.

[0005] CN102010569A discloses a halogen-free flame-retardant epoxy resin composition, which comprises: a flexible epoxy resin, a special epoxy resin, a synthetic rubber, a rubber-modified epoxy resin, an aromatic amine curing agent, an imidazole curing accelerator, an antioxidant, a phosphorus-containing flame retardant, a filler and an organic solvent, etc. However, the glass transition temperature (T g ) is lower.

[0006] Therefore, the use of biomass raw materials to prepare intrinsic flame-retardant epoxy resins with good thermal stability has important market value and application prospects. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for synthesizing a bio-based flame-retardant epoxy resin containing a polycyclic aromatic ring structure. By utilizing the high carbon-forming ability of the polycyclic aromatic rings, the residual carbon rate of the resin can be effectively improved, and higher heat resistance and high flame retardancy can be obtained.

[0008] The present invention is achieved through the following technical solutions:

[0009] An intrinsic flame retardant bio-based epoxy resin, wherein the epoxy resin has a structure shown in formula (I):

[0010]

[0011] Wherein R1 is one of -C6H4, -C4H8, -CH2, and R2 is a C1-C3 alkyl group.

[0012] The present invention also provides a method for synthesizing an intrinsic flame retardant bio-based epoxy resin, characterized in that the method comprises the following steps:

[0013] (1) dissolving magnolol and the catalyst in a solvent 4 to 8 times the mass of magnolol in a molar ratio of magnolol to catalyst = (1:0.1) to (1:1), mixing uniformly, then adding a halogenated alkane, the molar ratio of magnolol to halogenated alkane being (1:0.5) to (1:2), reacting at 10 to 30° C. for 16 to 24 hours, and washing and drying to obtain a precursor after the reaction is completed;

[0014] (2) According to the molar ratio of precursor: acid binding agent = (1:1) to (1:2), the precursor and the acid binding agent are dissolved in a solvent of 4 to 8 times the mass of the precursor, mixed evenly, and then the acyl chloride is added, the molar ratio of precursor: acyl chloride is (1:0.5) to (1:1), and the reaction is carried out at 0 to 40° C. for 16 to 24 hours. After the reaction is completed, the intermediate is washed and dried;

[0015] (3) dissolving the intermediate and the oxidant in a solvent 4 to 6 times the mass of the intermediate according to a molar ratio of intermediate: oxidant = (1:1) to (1:3), reacting at 0 to 30° C. for 18 to 30 hours, and washing and drying to obtain the intrinsic flame retardant bio-based epoxy resin after the reaction is completed;

[0016] Wherein, the catalyst is at least one selected from 15-crown-5, 18-crown-6, polyethylene glycol dialkyl ether, benzyltriethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride,

[0017] The halogenated alkane is at least one selected from ethyl bromide, dibromomethane, ethyl chloride, 2-chloropropane, methyl iodide, and ethyl iodide,

[0018] The acid binding agent is at least one selected from pyridine, N,N-diisopropylethylamine, triethylamine, imidazole, ammonium sulfate, sodium carbonate, potassium carbonate, and sodium acetate.

[0019] The acyl chloride is at least one selected from adipic acid chloride, terephthaloyl chloride, malonyl chloride and isophthaloyl chloride.

[0020] The oxidant is at least one selected from hydrogen peroxide, peracetic acid, m-chloroperbenzoic acid, monoperphthalic acid, and trifluoroperacetic acid.

[0021] The solvent used in step (1), step (2) and step (3) is at least one selected from diethyl ether, dichloromethane, ethyl acetate, tetrahydrofuran, acetone, methyl isobutyl ketone, n-hexane and ethylene dichloride.

[0022] The present invention is beneficial in that:

[0023] Generally speaking, the addition of large amounts of flame retardant additives will affect the crosslinking density of epoxy cured products. In addition, flame retardant additives are usually poorly compatible with epoxy resins, and migration and precipitation will occur when added in high amounts, resulting in a decrease in the thermal stability of epoxy resins.

[0024] The bio-based flame-retardant epoxy resin synthesized by the present invention not only contains polycyclic aromatic ring structural units with high charring ability, but is also a tetrafunctional epoxy resin, which ensures the rigidity and cross-linking density of the cross-linking network, and is conducive to the cured resin to obtain higher heat resistance and flame retardancy.

[0025] The thermal stability of the cured resin was tested using a NETZSCH 209F1 comprehensive thermal analyzer in a nitrogen atmosphere at a heating rate of 10°C / min. The thermal decomposition temperatures (T d30％ ) and residual carbon rate (R 800 ); using FTT-00001 microcalorimeter, heating rate 1℃ / s, test temperature range 50-750℃, to test the flame retardancy of cured resin, compare the heat release rate (PHRR) and total heat of combustion (THR) of cured material; using FTT0082 vertical combustion tester, refer to GB / T2408-2008 standard to test the combustion performance of cured resin; using FTT0077 limiting oxygen index tester, refer to GB / T2406 standard to compare the limiting oxygen index (LOI) of cured resin; using METTLER TOLEDO DMA1 dynamic thermomechanical analyzer, in nitrogen atmosphere, heating rate: 10℃ / min, frequency: 1Hz, measure the glass transition temperature (T g ). DETAILED DESCRIPTION

[0026] Example 1

[0027] A method for synthesizing a bio-based flame-retardant epoxy resin comprises the following steps:

[0028] 20.0 g of magnolol, 0.6 g of benzyltriethylammonium chloride and 150 g of acetone were added to a reaction bottle and mixed evenly, and then 10.0 g of iodomethane was added and reacted at 15±5° C. for 20 h. After the reaction was completed, the precursor was washed and dried.

[0029] 12.3 g of the precursor, 5.1 g of potassium carbonate and 70 g of dichloromethane were added to a reaction bottle and mixed evenly, and then 4.2 g of isophthaloyl chloride was added and reacted at 5±5° C. for 24 h. After the reaction was completed, the intermediate was washed and dried to obtain.

[0030] 11.1 g of the intermediate, 9.8 g of peracetic acid and 50 g of dichloromethane were added to a reaction bottle and mixed evenly, and reacted at 25±5° C. for 20 h. After the reaction was completed, the bio-based flame-retardant epoxy resin was washed and dried to obtain the bio-based flame-retardant epoxy resin.

[0031] Example 2

[0032] A method for synthesizing a bio-based flame-retardant epoxy resin comprises the following steps:

[0033] 20.0 g of magnolol, 0.6 g of 18-crown ether-6 and 120 g of acetone were added to a reaction bottle and mixed evenly, and then 12.0 g of ethyl chloride was added and reacted at 20±5° C. for 16 h. After the reaction was completed, the precursor was washed and dried to obtain.

[0034] 12.3 g of the precursor, 5.1 g of triethylamine and 70 g of dichloromethane were added to a reaction bottle and mixed evenly, and then 4.2 g of terephthaloyl chloride was added and reacted at 15±5° C. for 20 h. After the reaction was completed, the intermediate was washed and dried to obtain.

[0035] 2.8 g of the intermediate, 1.1 g of hydrogen peroxide and 10 g of dichloromethane were added to a reaction bottle and mixed evenly, and reacted at 20±5° C. for 24 h. After the reaction was completed, the bio-based flame-retardant epoxy resin was washed and dried to obtain the bio-based flame-retardant epoxy resin.

[0036] Example 3

[0037] A method for synthesizing a bio-based flame-retardant epoxy resin comprises the following steps:

[0038] 20.0 g of magnolol, 0.6 g of tetrabutylammonium chloride and 150 g of acetone were added to a reaction bottle and mixed evenly, and then 12.0 g of ethyl iodide was added and reacted at 20±5° C. for 16 h. After the reaction was completed, the precursor was washed and dried to obtain.

[0039] 12.3g of the precursor, 5.1g of triethylamine and 68g of dichloromethane were added to the reaction bottle and mixed evenly, and then 4.2g of malonyl chloride was added and reacted at 15±5°C for 20h. After the reaction was completed, the intermediate was washed and dried. 33.1g of the intermediate, 66.6g of m-chloroperbenzoic acid and 120g of dichloromethane were added to the reaction bottle and mixed evenly, and reacted at 15±5°C for 28h. After the reaction was completed, the bio-based flame-retardant epoxy resin was washed and dried.

[0040] Example 4

[0041] A method for synthesizing a bio-based flame-retardant epoxy resin comprises the following steps:

[0042] 20.0 g of magnolol, 0.6 g of tetrabutylammonium chloride, 0.6 g of 18-crown ether-6 and 150 g of acetone were added to a reaction bottle and mixed evenly, and then 11.0 g of ethyl iodide was added and reacted at 15±5° C. for 24 h. After the reaction was completed, the precursor was washed and dried to obtain.

[0043] 12.3 g of the precursor, 5.1 g of triethylamine and 75 g of dichloromethane were added to a reaction bottle and mixed evenly, and then 4.2 g of isophthaloyl chloride was added and reacted at 20±5° C. for 17 h. After the reaction was completed, the intermediate was washed and dried to obtain.

[0044] 33.1 g of the intermediate, 66.6 g of m-chloroperbenzoic acid and 125 g of dichloromethane were added to a reaction bottle and mixed evenly, and reacted at 10±5° C. for 30 h. After the reaction was completed, the bio-based flame-retardant epoxy resin was washed and dried to obtain the above-mentioned.

[0045] The bio-based flame-retardant epoxy resin synthesized by the present invention and the commonly used heat-resistant tetrafunctional glycidylamine epoxy resin: N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) and the general petroleum-based epoxy resin: bisphenol A diglycidyl ether (E51) are cured with 4,4'-diaminodiphenyl sulfone (DDS) to compare their performance.

[0046] The bio-based flame-retardant epoxy resin synthesized in Example 1 was cured using DDS to obtain Sample 1.

[0047] The bio-based flame-retardant epoxy resin synthesized in Example 4 was cured using DDS to obtain Sample 2.

[0048] A commonly used heat-resistant tetrafunctional glycidylamine epoxy resin: N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) was taken and cured with DDS to obtain sample 3.

[0049] General petroleum-based bisphenol A diglycidyl ether (E51) was taken and solidified with DDS to obtain sample 4.

[0050] The performances of Sample 1, Sample 2, Sample 3 and Sample 4 were compared and the results are listed in Table 1.

[0051] Table 1 Comparison of properties of several epoxy curing materials

[0052] Sample 1 Sample 2 Sample 3 Sample 4 <![CDATA[Residual carbon ratio (R 800 ) / %]]> 56.23 58.66 25.4 18.3 PHRR(W / g) 105.2 91.0 150.3 423.0 THR(KJ / g) 11.3 8.5 15.0 27.3 Limiting oxygen index / % 31.0 31.5 21.2 24.6 <![CDATA[Glass transition temperature (T g ) / °C]]> 240 251.2 234 178 <![CDATA[Decomposition temperature (T d30％ ) / °C]]> 489.6 503.3 393.0 407.5 Flame retardant grade V-0 V-0 No level No level

[0053] It can be seen from the table that the bio-based flame retardant epoxy resin synthesized by the present invention has excellent flame retardancy and heat resistance. Compared with samples 3 and 4, the glass transition temperature of sample 2 increased by 17.2°C and 73.2°C respectively. In addition, the residual carbon rate and decomposition temperature also increased by 231%, 321% and 110.3°C, 95.8°C respectively. Compared with samples 3 and 4, which have no flame retardancy level, the flame retardant level of the bio-based flame retardant epoxy resin synthesized by the present invention has reached the highest V-0 level.

[0054] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. An intrinsic flame retardant bio-based epoxy resin, characterized in that the epoxy resin has a structure shown in formula (I): Wherein R1 is one of -C6H4, -C4H8, -CH2, and R2 is a C1-C3 alkyl group.

2. A method for synthesizing an intrinsically flame-retardant bio-based epoxy resin, characterized in that: The method comprises the following steps: (1) dissolving magnolol and the catalyst in a solvent 4 to 8 times the mass of magnolol in a molar ratio of magnolol to catalyst = (1:0.1) to (1:1), mixing uniformly, then adding a halogenated alkane, the molar ratio of magnolol to halogenated alkane being (1:0.5) to (1:2), reacting at 10 to 30° C. for 16 to 24 hours, and washing and drying to obtain a precursor after the reaction is completed; (2) According to the molar ratio of precursor: acid binding agent = (1:1) to (1:2), the precursor and the acid binding agent are dissolved in a solvent of 4 to 8 times the mass of the precursor, mixed evenly, and then the acyl chloride is added, the molar ratio of precursor: acyl chloride is (1:0.5) to (1:1), and the reaction is carried out at 0 to 40° C. for 16 to 24 hours. After the reaction is completed, the intermediate is washed and dried; (3) dissolving the intermediate and the oxidant in a solvent 4 to 6 times the mass of the intermediate according to a molar ratio of intermediate: oxidant = (1:1) to (1:3), reacting at 0 to 30° C. for 18 to 30 hours, and washing and drying to obtain the intrinsic flame retardant bio-based epoxy resin after the reaction is completed; Wherein, the catalyst is at least one of 15-crown-5, 18-crown-6, polyethylene glycol dialkyl ether, benzyltriethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride. The halogenated alkane is at least one of ethyl bromide, dibromomethane, ethyl chloride, 2-chloropropane, methyl iodide and ethyl iodide, The acid binding agent is at least one of pyridine, N,N-diisopropylethylamine, triethylamine, imidazole, ammonium sulfate, sodium carbonate, potassium carbonate, and sodium acetate. The acyl chloride is at least one of adipoyl chloride, terephthaloyl chloride, malonyl chloride and isophthaloyl chloride. The oxidant is at least one selected from hydrogen peroxide, peracetic acid, m-chloroperbenzoic acid, monoperphthalic acid, and trifluoroperacetic acid.

3. The preparation method according to claim 2, characterized in that: The solvent in step (1), step (2) and step (3) is at least one of ether, dichloromethane, ethyl acetate, tetrahydrofuran, acetone, methyl isobutyl ketone, n-hexane and ethylene dichloride.

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