Flame-retardant and antibacterial bio-based epoxy resin as well as preparation method and application thereof

Abstract

The invention discloses flame-retardant and antibacterial bio-based epoxy resin as well as a preparation method and application thereof, and a bio-based epoxy resin system based on multiple hydrogen bonds and pi-pi accumulation is prepared from bifunctional cardanol-based epoxy resin, monomer methacrylic acid-2-hydroxyethyl phosphate, tannin and the like in a dual-curing manner. Mechanism research shows that the flame retardant property of the system is enhanced by a conjugated pi-pi bond system of a benzene ring, a phenolic hydroxyl group free radical scavenging effect and a dynamic phosphate carbonization effect together. The antibacterial activity of polyphenol enables the antibacterial efficiency of the cured epoxy resin on staphylococcus aureus to reach 99%, and meanwhile, the hydroxyl-phosphate structure in the structure endows the material with reprocessability. The efficient flame-retardant and antibacterial bio-based epoxy resin is prepared in a dual-curing manner.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus-containing flame-retardant bio-based materials technology, specifically relating to a flame-retardant and antibacterial bio-based epoxy resin, its preparation method, and its application. Background Technology

[0002] Epoxy resins are among the most widely produced thermosetting polymers globally. Due to their excellent mechanical and thermal properties, epoxy resins have attracted widespread attention in coatings, adhesives, composites, and electronic packaging. Traditional epoxy resins rely on petrochemical raw materials (such as bisphenol A), and prolonged exposure may pose health risks. Bio-based epoxy resins, including those derived from vegetable oils and natural phenol-based epoxy resins, are gaining attention due to their sustainable sources, abundant natural components, and low carbon emissions. However, bio-based epoxy resins are often flammable, difficult to recycle, and lack functionality, limiting their industrial applications.

[0003] To address the aforementioned issues, dynamic covalent chemistry is increasingly being applied in the field of flame-retardant epoxy resins. Its core lies in combining flame-retardant groups with dynamic covalent bonds to form a dynamic phosphate ester chemical system. By introducing epoxy curing agents containing dynamic phosphate esters into epoxy resins, a dynamic phosphate ester network structure that combines intrinsic flame retardancy with a "wide temperature range" characteristic can be constructed. The introduction of dynamic phosphate ester groups not only endows epoxy resins with flame-retardant properties but also, due to the high reversibility of phosphate ester bonds, allows the material to rapidly undergo network topology rearrangement under heating conditions, thus possessing dynamic properties such as self-healing. This effectively addresses the shortcomings of flame-retardant epoxy resins in extending service life and improving safety. However, although flame-retardant functionality is achieved through dynamic covalent bonds, integrating multiple functions such as antibacterial properties and intrinsic flame retardancy into a single epoxy resin material still faces challenges. Therefore, there is an urgent need to introduce novel non-covalent interactions to expand the functional dimensions of epoxy resins.

[0004] This invention, through the synergistic effect of reversible hydrogen bonds and dynamic phosphate ester bonds, further introduces phosphorus-containing and tannic acid structures into the cashew phenol epoxy monomer structure, simultaneously achieving reprocessability, antibacterial, and flame-retardant functions in bio-based epoxy curing resins, meeting key needs in the biomedical and food packaging fields. This invention establishes a paradigm for the rational design of next-generation multifunctional integrated bio-based materials, providing sustainable solutions for advanced engineering applications. Summary of the Invention

[0005] Technical problem solved: This invention provides a flame-retardant and antibacterial bio-based epoxy resin, its preparation method and application. The bio-based cured epoxy resin in this method contains dynamic phosphate ester bonds and polyphenol structures, thus possessing functions such as high-efficiency flame retardancy, recyclability and antibacterial properties.

[0006] Technical solution: A flame-retardant and antibacterial bio-based epoxy resin, the structure of which is shown below: Wherein, R2 is any one or a mixture of the following structures:

[0007]

[0008] x takes values ​​from 1 to 20, and y takes values ​​from 1 to 20.

[0009] A method for preparing flame-retardant and antibacterial bio-based epoxy resin includes the following steps: mixing a bifunctional cashew nut shell epoxy resin monomer (EDCS) with tannic acid (TA) and a solvent to obtain solution A. The structure of the bifunctional cashew nut shell epoxy monomer (EDCS) is shown below: R1 is any one or a mixture of the following structures. The tannic acid (TA) is Solution B is obtained by thoroughly mixing 2-hydroxyethyl methacrylate (HP) with a photoinitiator, a polymerization inhibitor, and a solvent. The HP is 2-hydroxyethyl methacrylate. Finally, all of the obtained solution B is added to solution A, and the mixture is thoroughly mixed and degassed. The mixture is poured into a mold and cured in a UV curing oven, followed by heat curing, to obtain a flame-retardant and antibacterial bio-based epoxy resin.

[0010] Preferably, the mass ratio of the above-mentioned bifunctional cashew phenolic epoxy resin monomer: tannic acid: 2-hydroxyethyl methacrylate phosphate is (14-16):(4-6):1.

[0011] Preferably, the solvent is at least one of hydroxyethyl methacrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate phosphate, tripropylene glycol diacrylate, and tert-butylaminoethyl methacrylate.

[0012] Preferably, the photoinitiator is one of triphenylphosphine, phenylbis(2,4,6-trimethylbenzoyl)phosphine, and 2-hydroxy-2-methylphenylacetone.

[0013] Preferably, the polymerization inhibitor is one of hydroquinone, p-phenylenediamine, and 2,6-di-tert-butyl-p-cresol.

[0014] Preferably, the amount of the above photoinitiator is 1% of the total mass of the reactants.

[0015] Preferably, the amount of the above-mentioned polymerization inhibitor is 0.5% of the total mass of the reactants.

[0016] The above curing method adopts a dual curing method of UV curing and thermal curing; the UV curing light source has a wavelength of 365nm and a curing time of 3-10 minutes, and the thermal curing temperature is 100-130℃ and the time is 20-50 minutes.

[0017] The above-mentioned bio-based epoxy resin is used in the preparation of products that are both flame-retardant and resistant to Staphylococcus aureus.

[0018] Beneficial effects: (1) The cashew phenol-based epoxy monomer structure provided by the present invention has both rigid benzene ring and flexible aliphatic chain structure, and the mechanical properties of the cured resin are strong and tough; (2) The bio-based epoxy cured material provided by the present invention is mainly derived from bio-based resources (cashew phenol and tannic acid), which can improve the added value of small molecule bio-based resources; (3) The bio-based epoxy cured material provided by the present invention has high-efficiency flame retardant, antibacterial and recyclable properties, and provides a new strategy for preparing multifunctional bio-based epoxy materials. Attached Figure Description

[0019] Figure 1 The image shows the infrared spectrum of the cured resin obtained in Example 1.

[0020] Figure 2 The limiting oxygen index analysis curves obtained in Examples 1, 2, and 3 are shown.

[0021] Figure 3 The UL-94 vertical burning test results obtained in Examples 1, 2, and 3 are shown.

[0022] Figure 4 Thermogravimetric-Infrared (TG-IR) combined with other methods in Examples 1, 2, and 3.

[0023] Figure 5 Thermogravimetric analysis curves of Examples 1, 2, and 3 in air.

[0024] Figure 6 Thermogravimetric analysis curves of Examples 1, 2, and 3 in nitrogen.

[0025] Figure 7 Analysis curves of cone calorimetry test changes in Examples 1, 2, and 3.

[0026] Figure 8 Antibacterial tests of Examples 1, 2, and 3. Detailed Implementation

[0027] The following embodiments are merely illustrative of the invention and should not be construed as limiting the scope or content of the invention. The invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1

[0029] Solution A was prepared by mixing bifunctional cashew nut shell epoxy resin monomer with tannic acid and solvent tripropylene glycol diacrylate. Solution B was then prepared by thoroughly mixing 2-hydroxyethyl methacrylate phosphate with photoinitiator 2-hydroxy-2-methylphenylacetone (1% of total reactant mass), polymerization inhibitor p-phenylenediamine (0.5% of total reactant mass), and solvent tripropylene glycol diacrylate. The mass ratio of cashew nut shell epoxy resin, tannic acid, and 2-hydroxyethyl methacrylate phosphate was 16:6:1. Solution B was then added entirely to solution A, stirred for 10 minutes, and degassed. The mixture was poured into a mold and cured in a UV curing oven for 10 minutes, followed by heat curing at 100°C for 30 minutes to obtain a flame-retardant bio-based epoxy resin.

[0030] Its chemical structure is shown in the figure, and its infrared characterization is shown in [reference needed]. Figure 1 The disappearance of the epoxy group absorption peak near 831 cm⁻¹ in the bifunctional cashew phenol-based epoxy resin monomer structure confirms that the epoxy groups in the cured resin have been completely consumed. Simultaneously, a characteristic broad absorption peak belonging to hydroxyl groups appears at 3340 cm⁻¹, and a strong absorption peak belonging to POC appears at 990 cm⁻¹.

[0031]

[0032] Wherein, R2 is any one or a mixture of the following structures:

[0033]

[0034] Example 2

[0035] Solution A was prepared by mixing bifunctional cashew nut shell epoxy resin monomer with tannic acid and hydroxybutyl acrylate solvent. Solution B was then prepared by thoroughly mixing cashew nut shell epoxy resin, tannic acid, and hydroxybutyl acrylate solvent. The mass ratio of cashew nut shell epoxy resin, tannic acid, and hydroxyethyl methacrylate was 15:5:1. Finally, solution B was added entirely to solution A, stirred for 10 minutes, and degassed. The mixture was poured into a mold and cured in a UV curing oven for 7 minutes, followed by heat curing at 100°C for 20 minutes to obtain a flame-retardant bio-based epoxy resin.

[0036] Example 3

[0037] Solution A was prepared by mixing bifunctional cashew nut shell epoxy resin monomer with tannic acid and solvent hydroxyethyl methacrylate. Solution B was then prepared by thoroughly mixing 2-hydroxyethyl methacrylate phosphate with photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (1% of the total reactant mass), polymerization inhibitor hydroquinone (0.5% of the total reactant mass), and solvent hydroxyethyl methacrylate. The mass ratio of cashew nut shell epoxy resin, tannic acid, and 2-hydroxyethyl methacrylate phosphate was 14:4:1. Finally, solution B was completely added to solution A, stirred for 10 minutes, and degassed. The mixture was poured into a mold and cured in a UV curing oven for 5 minutes, followed by heat curing at 100°C for 20 minutes to obtain a flame-retardant bio-based epoxy curable resin.

[0038] The properties of the flame-retardant bio-based epoxy curing resins obtained in the above embodiments are shown in Table 1.

[0039] Table 1

[0040]

[0041] From Table 1 and Figure 2 It can be seen that the oxygen index of Example 3 is 30.3%, which is higher than that of Example 1 and Example 2 (28.5% and 29.3%, respectively). This indicates that the increase of phosphorus (2-hydroxyethyl methacrylate phosphate) content is beneficial to improving the flame retardant properties of bio-based cured epoxy resin. Figure 3 Further vertical combustion experiments were conducted on the prepared bio-based epoxy curing resin, and all samples passed the V0 rating test, indicating they are flame-retardant materials. Furthermore, they exhibited self-extinguishing properties during combustion and did not produce molten droplets. The phosphorus-containing compound provided by this invention generates phosphate derivatives during combustion, promoting dehydration and carbonization, while the benzene ring structure enhances the stability of the char layer. The low thermal conductivity of the benzene ring-containing resin effectively inhibits heat penetration into the material matrix, thereby improving the flame-retardant properties of the material. In addition, the epoxy resin structure provided by this invention contains multiple hydrogen bonds and dynamic phosphate ester bonds. Reprocessing by hot pressing at 160°C and 5 MPa for 1 hour allows the cured fragments to be hot-pressed into rectangular shapes. Due to the structural rearrangement of β-hydroxyphosphate esters and the rearrangement of intermolecular hydrogen bonds under heating conditions, the reprocessing of the cross-linked network is achieved.

[0042] from Figure 4As can be seen from the TG-IR analysis of the cured resin, when the epoxy resin provided by this invention is exposed to high temperature, the hydroxyl, phosphate and phenolic hydroxyl groups in the copolymer first undergo a dehydration reaction to form a stable cross-linked network; as the temperature further increases, high-temperature decomposition produces volatile gases such as H2O, CO2 and ·H2PO3 free radicals, which suppress the flame in the gas phase and promote the volume expansion of the char layer; finally, through multiple complex chemical reactions, a char layer with high mechanical strength, micro-expansion and complete structure is formed, which effectively blocks heat and mass transfer and oxygen penetration, and achieves fire protection.

[0043] As shown in Table 1, the glass transition temperatures of the cured resins are quite similar, all above 40°C. Example 1 exhibits the highest crosslinking density, reaching 132.58 mol·m⁻¹. -3 This indicates that appropriately extending the double curing time can increase the crosslinking density of the cured resin. In addition, as can be seen from Table 1, the variation pattern of gel content is consistent with the variation pattern of crosslinking density.

[0044] Thermogravimetric analysis curves of the cured products of Examples 1, 2, and 3 in air are shown below. Figure 5 As shown, all of them have good carbon-forming ability, with the highest residual carbon content reaching 28% at 600℃, and the initial decomposition temperature is also above 250℃, indicating that the prepared epoxy resin has good carbon-forming ability. Figure 6 The thermogravimetric analysis (TGA) curves of the cured products from Examples 1, 2, and 3 in nitrogen atmosphere show that the residual carbon content (T5%) is consistently around 17%. Two distinct peaks appear on the DTG curves, at 290°C and 430°C, indicating a two-step weight loss process: matrix pyrolysis (300-400°C) and carbon layer oxidative degradation (400-500°C). This demonstrates that phosphorus (P) in the epoxy resin promotes the carbonization of the cured resin, acting as a good barrier to protect the substrate and inhibit heat and gas transfer between the two phases. This is beneficial for protecting the internal matrix and inhibiting further degradation, thus playing a role in the formation of condensed phase carbon and the thermal barrier structure. Compared to the data under N2 atmosphere, the trends in residual carbon content and T5% of the resin in air atmosphere are similar.

[0045] Figure 7 The graphs show the changes in total heat release, heat release rate, and CO2 release rate over time of the cured products obtained in Examples 1, 2, and 3, as measured using a cone calorimeter. The flame-retardant bio-based epoxy resin cured product provided by this invention exhibits excellent char-forming properties, thus showing a significantly reduced total heat release during combustion. Examples 1, 2, and 3 show a total heat release of 55.6 MJ / m³. 2 74.1 MJ / m 2 63.2 MJ / m 2 It is significantly lower than that of commercially available bisphenol A type epoxy resin cured products (typically around 100 MJ / m³). 2The above (indicating excellent flame retardant properties) demonstrates the superior flame retardant performance of the bio-based epoxy resin cured product provided by this invention. The product exhibits a low peak heat release rate (501.1 kW / m³). 2 481.2kW / m 2 and 309.5kW / m 2 Furthermore, the flame-retardant bio-based epoxy curing material provided by this invention has excellent char-forming properties and exhibits an extremely low CO2 release rate during combustion. The CO2 release rate in Example 1 is 0.15 g / s, indicating that it has a good smoke suppression effect.

[0046] Figure 8 The results of antibacterial experiments on epoxy resin show that the catechol and phosphate ester structures provided by this invention are introduced into the cashew phenol group crosslinking network structure to exert a synergistic antibacterial effect. Quantitative antibacterial experiments show that this resin has excellent antibacterial effects against Staphylococcus aureus, with an inhibition rate of 99%, confirming its ability to rapidly kill microorganisms and demonstrating broad application prospects in the fields of medical devices, food preservation, and daily chemical products.

[0047] Example 4

[0048] Solution A was prepared by mixing bifunctional cashew nut shell epoxy resin monomer with tannic acid and solvent tripropylene glycol diacrylate. Solution B was then prepared by thoroughly mixing 2-hydroxyethyl methacrylate phosphate with photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (1% of the total reactant mass), polymerization inhibitor hydroquinone (0.5% of the total reactant mass), and solvent tripropylene glycol diacrylate. The mass ratio of cashew nut shell epoxy resin, tannic acid, and 2-hydroxyethyl methacrylate phosphate was 14:4:1. Finally, solution B was completely added to solution A, stirred for 10 minutes, and degassed. The mixture was poured into a mold and cured in a UV curing oven for 5 minutes, followed by heat curing at 100°C for 20 minutes to obtain a flame-retardant bio-based epoxy curable resin.

[0049] Example 5

[0050] Solution A was prepared by mixing bifunctional cashew nut shell epoxy resin monomer with tannic acid and solvent hydroxyethyl methacrylate. Solution B was then prepared by thoroughly mixing 2-hydroxyethyl methacrylate phosphate with photoinitiator triphenylphosphine (1% of total reactant mass), polymerization inhibitor hydroquinone (0.5% of total reactant mass), and solvent hydroxyethyl methacrylate. The mass ratio of cashew nut shell epoxy resin, tannic acid, and 2-hydroxyethyl methacrylate phosphate was 14:4:1. Finally, solution B was completely added to solution A, stirred for 10 minutes, and degassed. The mixture was poured into a mold and cured in a UV curing oven for 5 minutes, followed by heat curing at 100°C for 20 minutes to obtain a flame-retardant bio-based epoxy curable resin.

[0051] Example 6

[0052] Solution A was prepared by mixing bifunctional cashew nut shell epoxy resin monomer with tannic acid and solvent hydroxyethyl methacrylate. Solution B was then prepared by thoroughly mixing 2-hydroxyethyl methacrylate phosphate with photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (1% of the total reactant mass), polymerization inhibitor p-phenylenediamine (0.5% of the total reactant mass), and solvent hydroxyethyl methacrylate. The mass ratio of cashew nut shell epoxy resin, tannic acid, and 2-hydroxyethyl methacrylate phosphate was 14:4:1. Finally, solution B was completely added to solution A, stirred for 10 minutes, and degassed. The mixture was poured into a mold and cured in a UV curing oven for 5 minutes, followed by heat curing at 100°C for 20 minutes to obtain a flame-retardant bio-based epoxy curable resin.

[0053] The limiting oxygen index and coating properties of the flame-retardant bio-based epoxy curing resins obtained in Examples 3-6 above are shown in Table 2.

[0054] Table 2

[0055]

[0056] Table 2 shows that the limiting oxygen index values ​​of Examples 3 and 4 are very close, but the coating performance differs. This is because the solvent in Example 4, tripropylene glycol diacrylate, contains multifunctional unsaturated double bonds. These multifunctional unsaturated double bonds increase the crosslinking density of the cured epoxy resin, resulting in a higher pencil hardness than the monofunctional hydroxyethyl methacrylate, but a decrease in flexibility. Compared to Example 3, the flexibility of Example 3 decreased by 4 mm. The coating performance of Examples 5 and 6 provided by this invention is excellent, indicating that the photoinitiators triphenylphosphine and phenylbis(2,4,6-trimethylbenzoyl)phosphine have little effect on the performance of the cured coating. However, the limiting oxygen index of Example 6, 30.6%, is slightly higher than the other examples because its polymerization inhibitor, p-phenylenediamine, contains nitrogen, a flame-retardant element, which to some extent exerts a synergistic flame-retardant effect of nitrogen and phosphorus through the gas and condensed phases. Compared with conventional polymerization inhibitors, polymerization inhibitors containing flame-retardant elements are beneficial for improving the flame-retardant performance of epoxy-cured resins. The epoxy resin cured products of Examples 4-6 provided by this invention all exhibit excellent antibacterial effects, and... Figure 7 The experimental results are consistent.

Claims

1. A flame-retardant and antibacterial bio-based epoxy resin, characterized in that, The structure of the bio-based epoxy curing resin is shown below: Wherein, R2 is any one or a mixture of the following structures: x takes values ​​from 1 to 20, and y takes values ​​from 1 to 20.

2. The method for preparing the flame-retardant and antibacterial bio-based epoxy resin according to claim 1, characterized in that, The steps are as follows: A solution A is obtained by mixing a bifunctional cashew nut shell epoxy monomer (EDCS) with tannic acid (TA) and a solvent. The structure of the bifunctional cashew nut shell epoxy monomer (EDCS) is shown below: R1 is any one or a mixture of the following structures. The tannic acid (TA) is Solution B is obtained by thoroughly mixing 2-hydroxyethyl methacrylate (HP) with a photoinitiator, a polymerization inhibitor, and a solvent. The HP is 2-hydroxyethyl methacrylate. Finally, all of the obtained solution B is added to solution A, and the mixture is thoroughly mixed and degassed. The mixture is poured into a mold and cured in a UV curing oven, followed by heat curing, to obtain a flame-retardant and antibacterial bio-based epoxy resin.

3. The preparation method according to claim 2, characterized in that, The mass ratio of bifunctional cashew phenol-based epoxy resin monomer: tannic acid: 2-hydroxyethyl methacrylate phosphate is (14-16):(4-6):

1.

4. The preparation method according to claim 2, characterized in that, The solvent is at least one of hydroxyethyl methacrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate phosphate, tripropylene glycol diacrylate, and tert-butylaminoethyl methacrylate.

5. The preparation method according to claim 2, characterized in that, The photoinitiator is triphenylphosphine, phenylbis(2,4,5-) One of 6-trimethylbenzoyl)phosphine and 2-hydroxy-2-methylphenylacetone.

6. The preparation method according to claim 2, characterized in that, The polymerization inhibitor is one of hydroquinone, p-phenylenediamine, and 2,6-di-tert-butyl-p-cresol.

7. The preparation method according to claim 2, characterized in that, The amount of photoinitiator used is 1% of the total mass of the reactants.

8. The preparation method according to claim 2, characterized in that, The amount of the polymerization inhibitor is 0.5% of the total mass of the reactants.

9. The preparation method according to claim 2, characterized in that, The curing method employs a dual curing approach combining UV curing and thermal curing. The UV curing light source has a wavelength of 365nm and a curing time of 3-10 minutes. The thermal curing temperature is 100-130℃ and the curing time is 20-50 minutes.

10. The use of the bio-based epoxy resin of claim 1 in the preparation of a product that is both flame-retardant and resistant to Staphylococcus aureus.

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