Preparation method of epoxy coating with self-repairing performance

Abstract

The invention relates to a preparation method of an epoxy coating, in particular to a preparation method of an epoxy coating with self-repairing performance, which is a self-repairing epoxy coating based on the synergistic effect of siloxane modified graphene oxide (GOS) and boron-oxygen-containing six-ring modified polydimethylsiloxane (BP-AMINE). The preparation method comprises the following steps: grafting (3-aminopropyl) triethoxysilane to graphene oxide through a chemical condensation method to prepare GOS, and preparing a BP-AMINE monomer through a chemical substitution method. The coating is endowed with quick self-repairing capability by utilizing reversibility of siloxane exchange reaction of GOS and boron oxygen hexacyclic ester exchange reaction of BP-AMINE. The coating can be repaired within 30 minutes at the temperature of 70 DEG C after being scratched, the repairing efficiency is larger than or equal to 98%, the repaired coating still keeps excellent corrosion resistance after being soaked in a 3.5 wt% NaCl solution for 60 days, and the coating is suitable for the fields of metal protection, aerospace and the like.

Description

Technical Field

[0001] The invention belongs to a method for preparing a polymer coating, and in particular relates to a method for preparing an epoxy coating with self-repairing properties. Background Art

[0002] Epoxy materials are a type of polymer material containing at least two epoxy groups in the molecule. Due to their excellent physical and chemical properties, they are widely used in aerospace, transportation, medical, adhesives, coatings and anti-corrosion fields. After curing, epoxy resin forms a three-dimensional cross-linked network with high bonding strength, good dielectric properties, low curing shrinkage, and excellent acid, alkali and solvent resistance. However, epoxy materials will inevitably be subjected to stress or scratches during use, especially in the field of anti-corrosion coatings. The harsh external environment will accelerate the expansion of microcracks inside the material, resulting in a shortened material life or even scrapping. Therefore, the damage repair technology of epoxy materials is of great significance for improving the safety of material use and extending its service life.

[0003] At present, the repair technology of epoxy coatings is mainly divided into two categories: external aid and intrinsic. The external aid repair mechanism encapsulates the repair agent or corrosion inhibitor in microcapsules. When the material is damaged, the microcapsules rupture and release the repair agent to achieve self-repair. For example, epoxy resin and tetraethylenepentamine are encapsulated in microcapsules respectively, and repair is achieved by high-temperature curing. However, this method has problems such as complex microcapsule preparation and the dependence of repair efficiency on dispersion uniformity and external heating. It is not a true self-repair. Intrinsic self-repairing coatings are based on the unique molecular structure of the material and can be repaired without external aid materials, but it is often difficult to meet the rapid repair needs of anti-corrosion coatings. Therefore, how to develop a high-performance, fast-repairing and simple process self-repairing coating has become a key technical problem that needs to be solved in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an epoxy coating with self-healing properties, which combines the siloxane exchange reaction of GOS with the boro-oxygen hexacyclic ester exchange reaction of BP-AMINE to design an epoxy coating with self-healing properties. GOS enhances the shielding performance and underwater repair performance of the coating, and BP-AMINE provides dynamic reversible bond deep repair, and the two work together to achieve efficient repair.

[0005] The technical solution of the present invention is as follows: A method for preparing an epoxy coating with self-repairing properties, the method comprising the following steps: (1) Preparation of siloxane-modified graphene oxide (GOS) Graphene oxide was mixed with KH550 solution and reacted fully at 80 °C. Then the product was centrifuged, washed repeatedly with deionized water to remove residues, and vacuum-dried at 50 °C to obtain GOS. (2) Preparation of boron-containing six-membered ring modified polydimethylsiloxane (BP-AMINE) 10 mmol of 4-carboxyphenylboronic acid and 40 mL of thionyl chloride were added to a round-bottom flask and stirred at 80 °C for 12 hours for full reaction. The solution was evaporated to obtain white powder of phenylboroxine (AB). Under low-temperature conditions, 30 mmol of triethylamine was added to a dichloromethane solution of 10 mmol of amino-terminated polydimethylsiloxane and stirred for 1 hour. A dichloromethane solution of AB (6 mmol) was added dropwise, and the low-temperature system was maintained and stirred for another 6 hours. After standing for 5 hours, the cross-linked polymer formed would precipitate in the form of a gel, and the milky white BP-AMINE gel was collected. (3) Preparation of the coating Epoxy resin E51, D400, GOS, and BP-AMINE were stirred in proportion for 20 minutes, and the mixture was coated on a Q235 steel substrate using a coating rod and cured at high temperature to obtain a self-healing epoxy coating.

[0006] In the preparation method of the epoxy coating with self-healing performance described above, in step (1): the mass ratio of graphene oxide to KH550 is 1:(5 - 30), preferably 1:15; the reaction time of the product at 80 °C is 6 - 24 hours, preferably 10 hours.

[0007] In the preparation method of the epoxy coating with self-healing performance described above, in step (2): the low-temperature reaction condition is -20 - 0 °C, preferably -5 °C; the molecular weight of amino-terminated polydimethylsiloxane is 500 - 3000 g / mol, preferably 1000 g / mol; the milky white BP-AMINE gel for collection is selected from one of tetrahydrofuran, dichloromethane, and chloroform, preferably dichloromethane.

[0008] In the preparation method of the epoxy coating with self-healing performance described above, in step (3): the mass ratio of GOS is selected from 0.1 - 3.0 wt%, preferably 0.75 wt%; the mass ratio of BP-AMINE gel is selected from 5 - 50 wt%, preferably 30 wt%; the high-temperature curing temperature range is 50 °C - 80 °C, preferably 70 °C, and curing is for 6 hours; the coating thickness is 20 - 200 μm, preferably 55 - 85 μm; the molar ratio of E51 to D400 can be selected as 1:(0.5 - 1.1), preferably 1:1.

[0009] The beneficial effects of the present invention are as follows: 1. Simple process, no need for complex encapsulation technology: The present invention abandons the microcapsule encapsulation process relied on by the foreign-aid type self-healing coating. By directly introducing silicone-modified graphene oxide (GOS) and modified polydimethylsiloxane containing boroxine ring (BP-AMINE), the preparation process is simplified and the production cost is reduced.

[0010] 2. Fast and efficient self-healing performance: Through the synergistic effect of the siloxane exchange reaction of GOS and the boroxine ring transesterification reaction of BP-AMINE, when microcracks or damages occur, the coating can quickly trigger the recombination of dynamic reversible bonds to achieve deep repair (as Figure 1 shown). The repair speed is significantly better than that of traditional intrinsic coatings, meeting the immediate protection requirements of anti-corrosion coatings.

[0011] 3. Multi-dimensional synergistic repair mechanism: GOS provides rapid closure and shielding protection for surface cracks, and BP-AMINE repairs deep damages through dynamic bond recombination. The two work together to achieve all-round repair from micro to macro, extending the service life of the coating. Description of the Drawings

[0012] Figure 1 : Optical image of the repair effect of the self-healing performance epoxy coating; Figure 2 : Electrochemical comparison images of the self-healing performance epoxy coating before and after repair. Detailed Embodiments

[0013] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention. For those not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase. Example 1

[0014] Graphene oxide was mixed with KH550 at a mass ratio of 1:15 and reacted at 80 °C for 10 hours. Then the product was centrifuged, washed repeatedly with deionized water to remove residues, and vacuum-dried at 50 °C to obtain GOS. 10 mmol of 4-carboxyphenylboronic acid and 40 mL of thionyl chloride were added to a round-bottom flask and stirred at 80 °C for 12 hours for a full reaction. The solution was evaporated to obtain a white powder of phenylboroxine (AB). At a low temperature of -5 °C, 30 mmol of triethylamine was added to a dichloromethane solution of 10 mmol of 1000 g / mol amino-terminated polydimethylsiloxane and stirred for 1 hour. A dichloromethane solution of AB (6 mmol) was added dropwise while maintaining the low-temperature system, and stirring was continued for 6 hours. After standing for 5 hours, the cross-linked polymer formed as a gel and precipitated out. The milky white BP-AMINE gel was collected. Epoxy resin E51 and D400 were mixed at a molar ratio of 1:1. Additionally, 0.75 wt% of GOS and 30 wt% of the BP-AMINE gel were mixed in, and the mixture was stirred for 20 minutes. The mixture was coated on a Q235 steel substrate with a coating rod and cured at 70 °C for 6 hours to obtain a self-healing epoxy coating.

[0015] Examples 2 to 9 The experimental procedure was the same as in Example 1. Among them, the specific feeding ratios of each of E51, D400, GOS, and BP-AMINE are shown in Table 1.

[0016] Table 1 Formulations of Examples Number E51 D400 GOS (wt%) BP-AMINE (wt%) Example 2 100 100 0.75 10 Example 3 100 100 0.75 20 Example 4 100 80 0.75 30 Example 5 100 80 0.75 20 Example 6 100 80 0.75 10 Example 7 100 100 0.25 30 Example 8 100 100 0.25 20 Example 9 100 100 0.26 10

Claims

1. A method for preparing an epoxy coating with self-repairing properties, characterized in that: The method comprises the following steps: (1) Preparation of siloxane-modified graphene oxide (GOS) Graphene oxide was mixed with KH550 solution and fully reacted at 80°C, and then the product was centrifuged, repeatedly washed with deionized water to remove the residue, and vacuum dried at 50°C to obtain GOS; (2) Preparation of modified polydimethylsiloxane containing hexaborane (BP-AMINE) 10 mmol 4-carboxyphenylboronic acid and 40 mL thionyl chloride were added to a round-bottom flask and stirred at 80°C for 12 hours for a full reaction. The solution was evaporated to obtain a white powder of phenylboroxane (AB). Under low temperature conditions, 30 mmol triethylamine was added to a dichloromethane solution of 10 mmol amino-terminated polydimethylsiloxane and stirred for 1 hour. The dichloromethane solution of AB (6 mmol) was added dropwise, the low temperature system was maintained, and stirring was continued for 6 hours. After standing for 5 hours, the cross-linked polymer generated by the reaction will precipitate in the form of gel, and the milky white BP-AMINE gel was collected. (3) Preparation of coating The four components of epoxy resin E51, D400, GOS, and BP-AMINE were stirred in proportion for 20 minutes, and the mixed liquid was applied to a Q235 steel substrate using a coating rod and the coating was cured at high temperature to obtain a self-healing epoxy coating.

2. The method for preparing an epoxy coating with self-repairing properties according to claim 1, characterized in that: In the step (1), the mass ratio of graphene oxide to KH550 is 1:(5-30), preferably 1:15; and the reaction time of the product at 80° C. is 6-24 hours, preferably 10 hours.

3. The method for preparing an epoxy coating with self-repairing properties according to claim 1, characterized in that: In the step (2), the low temperature reaction condition is -20-0°C, preferably -5°C; the molecular weight of amino-terminated polydimethylsiloxane is 500-3000 g / mol, preferably 1000 g / mol; and the solvent used to collect the milky white BP-AMINE gel is selected from tetrahydrofuran, dichloromethane, and chloroform, preferably dichloromethane.

4. The method for preparing an epoxy coating with self-repairing properties according to claim 1, characterized in that: In the step (3), the mass ratio of GOS is 0.1-3.0 wt%, preferably 0.75 wt%; the mass ratio of BP-AMINE gel is 5-50 wt%, preferably 30 wt%; the high temperature curing temperature range is 50°C-80°C, preferably 70°C, and the curing time is 6 hours; the coating thickness is 20-200 μm, preferably 55-85 μm; the molar ratio of E51 and D400 can be selected from 1: (0.5-1.1), preferably 1: 1.

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