Preparation method of fluorine atom regulated bio-based epoxy resin with high mechanical strength and repair efficiency

Abstract

The invention discloses a preparation method of fluorine atom regulated bio-based epoxy resin with high mechanical strength and repair efficiency. A carboxyl-terminated curing agent with a dynamic disulfide bond (-S-S-) and epoxidized soybean oil are subjected to a cross-linking reaction, on one hand, fluorine atoms form hydrogen bonds, and the mechanical strength and toughness of the elastomer are effectively improved; on the other hand, dissociation and recombination of dynamic bonds are accelerated through the fluorine atom electron withdrawing effect, and therefore efficient self-repairing is achieved. The bio-based epoxy self-repairing material with high mechanical strength and high repairing efficiency is designed and synthesized, the material applicability is widened, the use of petrochemical resources is reduced, and the bio-based epoxy self-repairing material has potential application prospects in the fields of aerospace, transportation, electronic equipment and the like.

Description

Technical Field

[0001] The present invention belongs to the field of self - healing materials, and particularly relates to a preparation method of a bio - based epoxy resin with fluorine atom regulation and both high mechanical strength and repair efficiency. Background Art

[0002] In recent years, epoxy resins have been widely used in various fields due to their excellent mechanical properties, thermal stability and chemical corrosion resistance. However, the raw material bisphenol A of epoxy resin is a petroleum - based product, which is non - renewable and has a negative impact on the environment, and is not conducive to promoting sustainable development and low - carbon life. Vegetable oil, as an inexpensive and easily available renewable resource, is widely used in the preparation of sustainable polymer materials. As the most produced vegetable oil, soybean oil can be simply processed to prepare different soybean oil derivatives, such as epoxidized soybean oil, soybean oil polyol, vinyl fatty acid, etc., and is currently widely used in fields such as biodiesel, plasticizer, coatings, etc. Soybean oil is mainly composed of triglycerides, and after modification, it can form a three - dimensional cross - linked network structure, so as to prepare bio - based thermosetting resins to replace epoxy resins. However, due to the high cross - link density and short chain segment length between cross - link points of such epoxidized soybean oil resins, the prepared thermosetting resins are brittle and have low mechanical strength. For example, the fracture strength of the polybasic acid - cured epoxidized soybean oil resin is less than 1 MPa, and the fracture strain is less than 0.5% (Green Chem., 2013, 15, 3360 - 3366). In Chinese Patent 202411893140.6 (Bio - based epoxy resin composite material and its preparation method), the tensile strength of the epoxidized soybean oil - based composite material is 11 - 19 MPa.

[0003] On the other hand, due to its irreversible covalent cross-linking network, epoxy resin materials cannot be recycled and reprocessed after damage. Therefore, most aged and damaged epoxy resins are disposed of by incineration or landfilling, which causes serious environmental pollution and waste of resources. One very effective way to solve this problem is to introduce dynamically reversible covalent bonds during the synthesis process. Dynamically reversible cross-linking can trigger the reversible "breaking" and "binding" of covalent bonds under the stimulation of certain external conditions, realizing molecular dynamic exchange and recombination, regulating the cross-linking degree and resilience of polymers, constructing a dynamic cross-linking network, and endowing the material with self-healing and reprocessable properties by utilizing the reversibility of the reaction. Currently, the dynamically covalent bonds that have been studied more are imine bonds, disulfide bonds, Diels-Alder (DA) bonds, borate ester bonds, etc. However, there are still challenges in preparing epoxy resins with both high mechanical properties and repair efficiency. For example, in Chinese Patent 202211644410.0 (a self-healing flame-retardant soybean oil-based thermosetting resin and its preparation method), epoxy soybean oil is cross-linked through the esterification reaction of phosphoric acid and epoxy groups. The tensile strength of the cross-linked sample is 6-20 MPa, and it can only perform simple scratch repair at 140 °C. For self-healing materials with high mechanical strength, the conditions required for their reshaping and recycling are often more demanding, such as higher temperature and greater pressure. For example, the epoxy soybean oil cross-linked by a vanillin-derived dynamic curing agent has a tensile stress of about 38 MPa, but this material needs to be hot-pressed and reshaped at 190 °C and 20 MPa (ACS Sustainable Chem. Eng., 2020, 8, 15020-15029). Therefore, it is of great significance to develop a bio-based epoxy self-healing material with both high mechanical strength and repair efficiency. Summary of the Invention

[0004] Based on the deficiencies existing in the above current situation, the present invention provides a preparation method of a fluorine atom-regulated bio-based epoxy resin with both high mechanical strength and repair efficiency. The self-healing epoxy resin based on epoxy soybean oil of the present invention can have both good mechanical properties and rapid and effective self-healing properties under heating, broaden the applicability of the material, and reduce the use of petrochemical resources.

[0005] The preparation method of the fluorine atom-regulated bio-based epoxy self-healing resin of the present invention includes the following steps:

[0006] Dissolve epoxy soybean oil (ESO), curing agent and catalyst in a solvent, disperse them evenly by ultrasonic treatment, react for 5 h under the condition of an oil bath at 80 - 90 °C, transfer to a hot stage at 50 - 70 °C after the reaction to dry the solvent (preferably at 60 °C), then hot press the product into a film at 200 °C using a hot press, and finally sinter in a tubular furnace at 160 - 200 °C (preferably at 180 °C) to obtain a bio-based epoxy resin material containing dynamic disulfide bonds and ester bonds.

[0007] The epoxy value of the epoxy soybean oil is 7%.

[0008] The catalyst is 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

[0009] The solvent is tetrahydrofuran.

[0010] The ultrasonic frequency is 40 KHz, the ultrasonic power is 100 w, and the ultrasonic time is 5 min.

[0011] The curing agent contains dynamic disulfide bonds, and its structural general formula is as follows:

[0012]

[0013] Wherein R independently represents -H or -F respectively.

[0014] The molar ratio of the terminal carboxyl group of the curing agent to the epoxy group functional group of the epoxy soybean oil is 1:1, and the molar ratio of the terminal carboxyl group of the curing agent to the catalyst is 1:0.05.

[0015] In the present invention, by influencing the dissociation and recombination of dynamic bonds through the electron-withdrawing effect of fluorine atoms and the hydrogen bond effect formed by fluorine atoms, using curing agents DTFB and DTLB with or without fluorine atom substituents, and based on the esterification reaction of carboxyl groups and epoxy groups, the curing agent reacts with epoxy soybean oil (ESO) to obtain bio-based epoxy resin materials with different mechanical properties and different dynamic bond exchange rates. Both curing agents are commercially available. Among them, DTFB is 2,2'-dithiobis(6-fluorobenzoic acid), purchased from Tokyo Chemical Industry (Shanghai) Co., Ltd.; DTLB is 2,2'-dithiobisbenzoic acid, purchased from Shanghai Macklin Biochemical Co., Ltd. The catalyst TBD is also purchased from Shanghai Macklin Biochemical Co., Ltd.

[0016] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0017] The present invention introduces dynamic disulfide bonds and ester bonds into epoxy resin, and regulates the exchange rate of dynamic bonds through the electron-withdrawing effect of fluorine atoms. At the same time, fluorine atoms form hydrogen bonds with the generated hydroxyl groups, enabling the prepared epoxy resin to have excellent mechanical properties and self-healing properties. Moreover, the curing agent containing fluorine atom substituents endows the crosslinked epoxy resin with better tensile properties and self-healing properties. The tensile stress can reach 32 MPa, and the tensile strength recovery rate can reach 100% after the material is cut and reshaped at 160 °C for 40 min, showing excellent reshaping performance.

[0018] The following further elaborates on the present invention in detail in conjunction with the accompanying drawings and specific embodiments. Description of the Drawings

[0019] Figure 1 It is the infrared spectrogram of the epoxy resins obtained in Example 1 and Comparative Example 1 of the present invention.

[0020] Figure 2 It is the stress-strain curves of the initial samples and reshaped samples of the epoxy resins crosslinked by the two curing agents obtained in Example 1 and Comparative Example 1 of the present invention.

[0021] Figure 3 It is the dynamic thermomechanical analysis diagram of the epoxy resins crosslinked by the two curing agents obtained in Example 1 and Comparative Example 1 of the present invention.

[0022] Figure 4 It is the stress relaxation curves of the two cured epoxy resins obtained in Example 1 and Comparative Example 1 of the present invention and the linear fitting curves through the Arrhenius equation. Specific Embodiments

[0023] The following details the embodiments of the present invention. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0024] The method for material reshaping and recycling is as follows: The crushed pieces after cutting the epoxy film are hot-pressed at 160 - 180 °C and 15 MPa for 40 min to re-form a uniform and defect-free film, and its mechanical properties are tested.

[0025] Example 1:

[0026] The epoxy resin containing fluorine atoms is prepared in the following steps in this example:

[0027] 1. Preparation of the epoxy resin ESFB crosslinked by the fluorine atom-containing curing agent

[0028] 1.31 g (0.0032 mol) of epoxidized soybean oil and 30 mL of tetrahydrofuran were added to a 100 mL round-bottom flask and sonicated until completely dissolved to obtain solution A; 1 g (0.0032 mol) of DTFB was added to solution A and sonicated until completely dissolved to obtain solution B. 0.041 g (0.00016 mol) of TBD was added to solution B as a catalyst to obtain solution C. Solution C was refluxed in an oil bath at 85 °C for 5 hours. After the reaction was completed, the solvent was dried on a hot stage at 60 °C to obtain a sample. The sample was placed in a hot press at 200 °C and 15 MPa and hot-pressed for 30 min to obtain a pre-cured ESFB sample. The pre-cured sample was placed in a tube furnace and fired at 180 °C for 10 h under a nitrogen atmosphere to obtain an ESFB material.

[0029] Comparative Example 1:

[0030] This comparative example provides a method for preparing a fluorine-free crosslinked epoxy resin ESLB:

[0031] 1.46 g (0.0032 mol) of epoxidized soybean oil and 30 mL of tetrahydrofuran were added to a 100 mL round-bottom flask and sonicated until completely dissolved to obtain solution A; 1 g (0.0032 mol) of DTLB was added to solution A and sonicated until completely dissolved to obtain solution B. 0.046 g (0.00016 mol) of TBD was added to solution B as a catalyst to obtain solution C. Solution C was refluxed in an oil bath at 85 °C for 5 hours. After the reaction was completed, the solvent was dried on a hot stage at 60 °C to obtain a sample. The sample was placed in a hot press at 200 °C and 15 MPa and hot-pressed for 1 h to obtain a pre-cured ESLB sample. The pre-cured sample was placed in a tube furnace and fired at 180 °C for 3 h under a nitrogen atmosphere to obtain an ESLB material.

[0032] Figure 1 FIG. is the infrared spectrum of the crosslinked epoxy resins obtained in Example 1 and Comparative Example 1 of the present invention. As can be seen from the figure, the characteristic peak of the epoxy group at 823 cm -1 disappeared after curing was completed, and the stretching vibration peak of the carbon-oxygen double bond of the carboxyl group was at 1690 cm -1 , and a new hydroxyl peak of β-hydroxy ester appeared at around 3450 cm -1 .

[0033] Figure 2 FIG. is the stress-strain curves of the initial samples and the reshaped samples of the epoxy resins crosslinked with the two curing agents obtained in Example 1 and Comparative Example 1 of the present invention. As can be seen from the figure, the tensile stress and elongation at break of the sample crosslinked with the curing agent containing fluorine atoms were significantly improved, and its stress reshaping efficiency at 160 °C could reach 100%, while the reshaping effect of the sample without fluorine at 160 °C was poor, and the stress reshaping efficiency could only reach about 70%.

[0034] Figure 3 These are the dynamic thermomechanical analysis diagrams of the two curing agent cross-linked epoxy resins obtained in Example 1 and Comparative Example 1 of the present invention. It can be seen from the figures that the sample cross-linked with the fluorine atom-containing curing agent has a higher storage modulus and a higher glass transition temperature. The glass transition temperature T g of ESFB is 50.1 °C, and the glass transition temperature T g of ESLB is 47.6 °C.

[0035] Figure 4 These are the stress relaxation curves of the two cross-linked epoxy resins obtained in Example 1 and Comparative Example 1 of the present invention and the linear fitting curves through the Arrhenius equation. The fluorine-containing sample has a lower activation energy, 44.3 kJ / mol for ESFB, and 62.7 kJ / mol for the fluorine-free sample ESLB.

[0036] The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a bio-based epoxy resin with regulated fluorine atoms and both high mechanical strength and repair efficiency, characterized in that It includes the following steps: Dissolve epoxidized soybean oil, curing agent and catalyst in a solvent, ultrasonically disperse evenly, carry out an oil bath reaction. After the reaction is completed, place it on a hot stage to remove the solvent. Then use a hot press to pre-cure the product, and finally use a tube furnace for firing and curing to obtain a bio-based epoxy resin material containing dynamic disulfide bonds and ester bonds; The structural general formula of the curing agent is as follows: ； Wherein R independently represents -F or -H respectively.

2. The preparation method according to claim 1, wherein: The epoxy value of the epoxidized soybean oil is 7%.

3. The preparation method according to claim 1, wherein: The catalyst is 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

4. The preparation method according to claim 1, wherein: The solvent is tetrahydrofuran.

5. The preparation method according to claim 1, wherein: The ultrasonic frequency is 40 KHz, the ultrasonic power is 100 w, and the ultrasonic time is 5 min.

6. The preparation method according to claim 1, wherein: The reaction temperature of the oil bath reaction is 80 - 90 °C, and the reaction time is 5 h.

7. The preparation method according to claim 1, wherein: The pre-curing temperature is 200 °C, the pressure is 15 MPa, and the time is 0.5 - 1 h.

8. The preparation method according to claim 1, wherein: The temperature of the tube furnace is set at 160 - 200 °C.

9. The preparation method according to claim 1, wherein: The molar ratio of the terminal carboxyl group of the curing agent to the epoxy group functional group of the epoxidized soybean oil is 1:1, and the molar ratio of the terminal carboxyl group of the curing agent to the catalyst is 1:0.

05.

10. The recycling and reshaping method of the bio-based epoxy self-healing material prepared by the preparation method according to any one of claims 1 - 9, wherein: Cut the bio-based epoxy self-healing material into pieces and hot press it at 160 - 180 °C and 15 MPa for 40 min to obtain the recycled and reshaped bio-based epoxy self-healing material.

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