A self-curing, high-modulus and high-strength intrinsic flame-retardant sulfonamide epoxy resin and its preparation method

Abstract

The present invention provides a sulfonamide epoxy resin represented by Formula I and a method for preparing the same. Through ingenious process control, the present invention synthesizes a resin containing both epoxy and amino groups, enabling self-curing without the need for mixing with a curing agent or other components. Furthermore, the epoxy resin exhibits high and controllable reactivity, excellent physical and mechanical properties, and intrinsic flame retardancy, and has broad application prospects. #imgabs0#

Description

Technical Field

[0001] The invention belongs to the field of materials, and in particular relates to a self-curing, high-modulus and high-strength intrinsic flame-retardant sulfonamide epoxy resin and a preparation method thereof. Background Art

[0002] Epoxy resins are widely used in electronic packaging, coatings, adhesives, and composite materials due to their excellent processing properties, bonding properties, mechanical properties, electrical insulation properties, chemical stability, and other properties. When epoxy resins are used as composite material matrices, on the one hand, with the continuous development of electronic appliances, coatings, aircraft, and spacecraft, higher requirements are placed on the flame retardancy of epoxy resin-based composite materials, which requires the resin matrix to have good flame retardancy. On the other hand, for carbon fiber composites with epoxy resin as the matrix, their compressive strength is significantly affected by the modulus of the resin matrix. The introduction of a new generation of high-performance fibers requires a resin matrix with a higher modulus to match them. In addition, the preparation of prepregs requires the epoxy resin and curing agent to be heated and mixed, which is a relatively cumbersome process and faces the problem of precipitation of the curing agent during cooling.

[0003] In order to improve the flame retardant properties of epoxy resin, most people use the method of adding flame retardants, such as adding aluminum hydroxide, red phosphorus, silicone, and organic halogen flame retardants to the epoxy resin matrix to achieve flame retardancy. However, the compatibility issues between these flame retardants and the epoxy resin matrix will also have a significant impact on the mechanical properties of the epoxy resin. Although in addition to additive flame retardant epoxy resins, intrinsic flame retardant epoxy resins (reactive flame retardant epoxy resins) have also been developed, that is, flame retardant groups are introduced into the resin through chemical reaction to improve the flame retardancy of the resin, which can avoid the incompatibility problem caused by the addition of flame retardants, the existing intrinsic flame retardant epoxy resins often have complicated synthesis routes, expensive raw materials, high costs, and mechanical properties that are difficult to match the new generation of high modulus carbon fibers ([1] Qi Y, Wang J, Kou Y, et al. Synthesis of an aromatic N-heterocycle derived from biomass and its use as a polymer feedstock[J]. Nature Communications, 2019; [2] Qi Y, Weng Z, Kou Y, et al. Facile synthesis of bio-basedtetra-functional epoxy resin and its potential application as high-performance composite resin matrix[J]. Composites Part B Engineering, 2021, 214: 108749. [3] Yu QA, Zw A, Yan KB, et al. Synthesize and introduce bio-basedaromatic s-triazine in epoxy resin: Enabling extremely high thermal stability, mechanical properties, and flame retardancy to achieve high-performancesustainable polymers-ScienceDirect[J]. Chemical Engineering Journal, 2020, 406.).

[0004] Therefore, in order to further expand the application of epoxy resins, it is very important to develop epoxy resins with both good mechanical properties and intrinsic flame retardancy. Currently, there are no reports of intrinsic flame retardant epoxy resins with self-curing, high modulus and high strength. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a self-curing sulfonamide epoxy resin, comprising the steps of:

[0006] (1) mixing p-aminobenzenesulfonamide and epichlorohydrin at 110-130° C. and reacting for 22-26 hours;

[0007] (2) Cooling to 35-45°C, adding alkali and reacting for 3-5 hours;

[0008] The reaction formula is as follows:

[0009]

[0010] Furthermore, the alkali is sodium hydroxide or potassium hydroxide; preferably sodium hydroxide.

[0011] Furthermore, the molar ratio of epichlorohydrin to p-aminobenzenesulfonamide is (25-35):1, preferably 30:1;

[0012] The molar ratio of the aminobenzenesulfonamide to the base is 1:(2-3), preferably 1:2.25.

[0013] Furthermore, the reaction in step (1) is carried out at 120° C. for 24 hours.

[0014] Furthermore, the reaction in step (2) is carried out at 40° C. for 4 hours.

[0015] The present invention also provides a sulfonamide epoxy resin comprising a structure shown in Formula I:

[0016]

[0017] Furthermore, the above-mentioned sulfonamide epoxy resin is prepared by the above-mentioned method.

[0018] The present invention also provides a cured epoxy resin, which is obtained by curing the sulfonamide epoxy resin.

[0019] Furthermore, the cured epoxy resin is obtained by reacting the sulfonamide epoxy resin at 130-150° C. for 1-3 hours and then reacting at 190-210° C. for 2-4 hours to self-cure; preferably, the cured epoxy resin is obtained by reacting at 140° C. for 2 hours and then reacting at 200° C. for 3 hours to self-cure.

[0020] The present invention also provides application of the cured epoxy resin in flame retardant materials.

[0021] Beneficial effects of the present invention:

[0022] This invention uses the flame retardant sulfonamide as a raw material and exploits the differences in functional group activity to cleverly design a self-curing epoxy resin containing both amino and epoxy groups. This resin can be cured and formed simply by heating, significantly optimizing the carbon fiber composite molding process. This unique self-curing structure significantly increases the number of -SO2- groups in the system, resulting in a resin with both excellent mechanical properties and good intrinsic flame retardancy. Furthermore, the resin's synthesis method is very simple, the raw materials are inexpensive, and it has promising application prospects.

[0023] Obviously, based on the above contents of the present invention, according to common technical knowledge and customary means in this field, without departing from the above basic technical ideas of the present invention, other various forms of modifications, replacements or changes can be made.

[0024] The following further describes the above content of the present invention in detail through specific embodiments in the form of examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above content of the present invention fall within the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The following are the reaction formula, infrared spectrum and hydrogen nuclear magnetic resonance spectrum of the sulfonamide epoxy resin of the present invention.

[0026] Figure 2 It is the H NMR spectrum of the comparative example sulfonamide epoxy resin.

[0027] Figure 3 The vertical combustion test results of the sulfonamide epoxy resin cured by the present invention and the E51 / DDM cured epoxy resin are shown.

[0028] Figure 4 These are the results of micro combustion experiments on the epoxy resin cured with sulfonamide and the epoxy resin cured with E51 / DDM.

[0029] Figure 5 These are the thermogravimetric analysis results of the cured sulfonamide epoxy resin of the present invention and the E51 / DDM cured epoxy resin.

[0030] Figure 6 This is the result of thermogravimetric analysis experiment.

[0031] Figure 7 The DSC analysis results at different heating rates. DETAILED DESCRIPTION

[0032] The raw materials and equipment used in the present invention are all known products and are obtained by purchasing commercially available products.

[0033] Example 1. Preparation of sulfonamide epoxy resin of the present invention

[0034] Add 1 mol of p-aminobenzenesulfonamide to 30 mol of epichlorohydrin, and react at 120°C for 24 hours (no catalyst required). After the reaction, cool to 40°C, add 2.25 mol of sodium hydroxide, and react for 4 hours. Then filter, wash with water, and remove the solvent to obtain the product.

[0035] The obtained sulfonamide epoxy resin (SAASC) and the raw material p-aminobenzenesulfonamide (SAA) were subjected to infrared spectroscopy analysis and nuclear magnetic resonance hydrogen spectrum detection. The results are as follows Figure 1 As shown, it is proved that the sulfonamide epoxy resin SAASC of formula I of the present invention was successfully synthesized.

[0036] Example 2: Preparation of Cured Sulfanilamide Epoxy Resin

[0037] The sulfonamide epoxy resin solution obtained in Example 1 was reacted at 140° C. for 2 hours and then at 200° C. for 3 hours, and self-cured to obtain a cured sulfonamide epoxy resin SAASC.

[0038] Example 3: Preparation of sulfonamide epoxy resin of the present invention

[0039] Add 1 mol of p-aminobenzenesulfonamide to 25 mol of epichlorohydrin, and react at 120°C for 24 hours (no catalyst required). After the reaction, cool to 40°C, add 2.25 mol of sodium hydroxide, and react for 4 hours. Then filter, wash with water, and remove the solvent to obtain the product.

[0040] The obtained sulfonamide epoxy resin (SAASC) and the raw material p-aminobenzenesulfonamide (SAA) were subjected to infrared spectroscopy analysis and nuclear magnetic resonance hydrogen spectrum detection. The results are as follows Figure 1 As shown, it is proved that the sulfonamide epoxy resin SAASC of formula I of the present invention was successfully synthesized.

[0041] Example 4: Preparation of sulfonamide epoxy resin of the present invention

[0042] Add 1 mol of p-aminobenzenesulfonamide to 35 mol of epichlorohydrin, and react at 120°C for 24 hours (no catalyst required). After the reaction, cool to 40°C, add 2.25 mol of sodium hydroxide, and react for 4 hours. Then filter, wash with water, and remove the solvent to obtain the product.

[0043] The obtained sulfonamide epoxy resin (SAASC) and the raw material p-aminobenzenesulfonamide (SAA) were subjected to infrared spectroscopy analysis and nuclear magnetic resonance hydrogen spectrum detection. The results are as follows Figure 1 As shown, it is proved that the sulfonamide epoxy resin SAASC of formula I of the present invention was successfully synthesized.

[0044] Comparative Example 1

[0045] Referring to the method of Example 1, the reaction conditions of p-aminobenzenesulfonamide and epichlorohydrin were adjusted as follows: 4-butylammonium bromide was added as a catalyst, the reaction was carried out at 100°C for 12 hours, the temperature was lowered to 40°C after the reaction, 2.25 mol parts of sodium hydroxide were added, and the reaction was carried out for 2 hours. The other conditions remained unchanged to obtain the product.

[0046] The obtained product was analyzed by infrared spectroscopy and nuclear magnetic resonance hydrogen spectrum. Figure 2 As shown in the spectrum of sequence number 1, it can be seen that accurate selective substitution cannot be achieved after adding the catalyst.

[0047] Comparative Example 2

[0048] Referring to the method of Comparative Example 1, the catalyst was replaced by benzyltrimethylammonium chloride, and the other conditions remained unchanged to obtain the product.

[0049] The obtained product was analyzed by infrared spectroscopy and nuclear magnetic resonance hydrogen spectrum. Figure 2 As shown in the spectrum of sequence number 2, it can be seen that after adding the catalyst to the reaction, accurate selective substitution cannot be achieved.

[0050] Comparative Example 3

[0051] Referring to the method of Example 1, the reaction conditions of p-aminobenzenesulfonamide and epichlorohydrin were adjusted to: reaction at 120°C for 12 hours, cooling to 40°C after the reaction, adding 2.25 mol parts of sodium hydroxide and reacting for 2 hours, while keeping the other conditions unchanged, to obtain the product.

[0052] The obtained product was analyzed by infrared spectroscopy and nuclear magnetic resonance hydrogen spectrum. Figure 2 As shown in the spectrum of sequence number 3, it can be seen that the product obtained after shortening the reaction time is incompletely substituted.

[0053] Comparative Example 4: E51 epoxy resin / aromatic amine curing agent system

[0054] 4,4'-Methylenediamine (DDM) was used to cure E51 epoxy resin. Curing of the epoxy resin adhered to a 1:1 molar ratio of reactive functional groups to amino hydrogens. A liquid mixture of neat epoxy resin and DDM, heated above 90°C, was poured into a PTFE mold. The resin was cured at 120°C for 2 hours, 150°C for 3 hours, and then 180°C for 3 hours. After the curing period, the sample was annealed to room temperature. This yielded an E51 / DDM-cured epoxy resin.

[0055] The beneficial effects of the present invention are demonstrated by experimental examples below.

[0056] Experimental Example 1: Performance Characterization of the Sulfonamide Epoxy Resin of the Present Invention

[0057] 1. Experimental methods

[0058] Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AV II (Switzerland) at 600 MHz using tetramethylsilane (TMS) as the internal standard and DMSO-d6 as the solvent. Fourier transform infrared (FTIR) spectra were measured using a Nicolet 570 (ThermoScientific, USA) with a scanning range of 600 cm -1 to 4000cm -1 . The above tests were all conducted on the resin before curing (Example 1). Mechanical property tests were conducted on the cured resin (Example 1) and Comparative Example 4. The sample size was 80×10×4 mm. The three-point bending test was conducted at room temperature with a loading speed of 2 mm / min and a span of 64 mm using a universal testing machine Instron 5567 (Instron, USA) in accordance with ASTM D7264. The UL-94 vertical combustion test was conducted on a vertical combustion test machine with sample size of 80×10×3 mm. Microscale combustion calorimetry (MCC) was conducted on an FTT0001 microscale combustion calorimeter (UK) in accordance with ASTM D7309-13. A sample of approximately 5 mg was heated from 70-700°C at a heating rate of 1°C / s under a nitrogen flow rate of 80 cm3 / min. The decomposition temperature and residue of the cured products were studied using a TG290-F1 (NETZSCH, Germany) in a nitrogen environment. These products were heated from 40°C to 800°C.

[0059] 2. Experimental results

[0060] from Figure 1 907 cm in infrared spectrum -1 The peak at 5.9 ppm indicates the successful introduction of epoxy groups. The disappearance of the peak at 5.9 ppm and the residual peak at 6.9 ppm of p-aminobenzenesulfonamide (SAA) in the NMR spectrum indicate the selective substitution of amino groups, confirming the successful synthesis of the epoxy resin SAASC with sulfonamide structure.

[0061] The mechanical properties test results of cured SAASC and E51 / DDM are shown in Table 1. It shows that the mechanical properties of cured SAASC are very excellent and significantly stronger than those of E51 / DDM.

[0062] Table 1

[0063]

[0064] Figure 3 The results of the vertical combustion test show that SAASC extinguishes quickly after both the first and second ignitions, demonstrating good intrinsic flame retardancy.

[0065] Figure 4 The results of the micro-combustion test show that the peak heat release and total heat release of SAASC are significantly lower than those of the E51 / DDM system, showing good flame retardancy.

[0066] Figure 5 The results of the cone combustion test show that the peak heat release and total heat release of SAASC are significantly lower than those of the E51 / DDM system, and the smoke release rate and total smoke volume are significantly lower than those of the E51 / DDM system, showing good flame retardancy.

[0067] Figure 6 This is the result of the thermogravimetric analysis experiment. It can be seen that the SAASC system has a higher thermal residual weight, indicating better thermal stability.

[0068] Figure 7 These are the DSC analysis results at different heating rates. It can be seen that SAASC has moderate activity and does not react at room temperature.

[0069] In summary, the present invention cleverly designs and synthesizes an epoxy resin containing both epoxy groups and amino groups through process control, which can achieve self-curing without mixing the epoxy resin and the curing agent, greatly improving the processing efficiency; and the epoxy resin of the present invention has high reactivity while also having excellent mechanical properties (flexural modulus reaches 5154.9 MPa, flexural strength reaches 125.7 MPa) and intrinsic flame retardancy, as well as excellent thermal stability, and has broad application prospects.

Claims

1. A use of a cured epoxy resin in the preparation of a flame retardant material; characterized in that, The cured epoxy resin is of the structural formula It is cured with sulfonamide epoxy resin; The preparation of the sulfonamide epoxy resin comprises the following steps: (1) p-Aminobenzenesulfonamide and epichlorohydrin were mixed and reacted at 120°C for 24 hours; (2) Cool down to 40°C and add alkali to react for 4 hours; The reaction formula is as follows: ； The base is sodium hydroxide; The molar ratio of epichlorohydrin to p-aminobenzenesulfonamide is 30:1; The molar ratio of aminobenzenesulfonamide to base is 1:2.25; The preparation method of the cured epoxy resin is to react the sulfonamide epoxy resin at 140° C. for 2 h and then react at 200° C. for 3 h for self-curing.

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