Method for preparing polyurethane microcapsule shell with controlled release properties affected by mechanical stimulation

Abstract

A method for preparing a polyurethane microcapsule shell with controlled release properties affected by mechanical stimulation, comprising mixing deionized water with polyvinyl alcohol to obtain an aqueous phase A; adding an oil phase 4,4'-diphenylmethane diisocyanate to the aqueous phase A and mixing these materials to obtain an emulsion; mixing deionized water with dibutyltin dilaurate and ethylene glycol to obtain an aqueous phase B; dropwise adding the emulsion to the aqueous phase B, and stirring these materials at a constant temperature to obtain a mixed liquid; and cooling the mixed liquid to room temperature, then carrying out suction filtration under vacuum, and performing washing with ethanol, suction filtration, and then drying in air at room temperature to obtain the polyurethane microcapsule shell. The prepared polyurethane microcapsule shell has relatively good controlled release properties when undergoing external mechanical stimulation, the release rate can be regulated and controlled on the basis of mechanical stimulation, the polyurethane microcapsule shell can stably play a role in an environment, and the primary development stage of micro-damage on a power device is effectively suppressed.

Description

A method for preparing a polyurethane microcapsule shell whose controlled release properties are affected by mechanical stimulation Technical Field

[0001] The invention belongs to the field of material science and engineering technology, and particularly relates to a method for preparing a polyurethane microcapsule shell whose controlled-release properties are affected by mechanical stimulation. Background Art

[0002] Microencapsulation technology is a surface modification technology that uses film-forming materials to coat the internal core material to form a stable core-shell structure. Due to its convenience, flexibility, uniform dispersion, easy storage and transportation of internal substances, and stable activity, it has gradually become a better material encapsulation method. In self-healing materials, using microcapsules as carriers for storing and releasing repair agents can provide the material with a more precise core material release and protection mechanism, thereby achieving self-repair of the material, effectively extending the service life of the substrate, and reducing the cost and expenses of equipment online monitoring and fault repair. The core and key link of microencapsulation technology is the formation of the microcapsule shell. The microcapsule shell not only determines the stability, protection performance and release characteristics of the microcapsule, but also directly affects the effectiveness of the microcapsule in different application fields.

[0003] Currently, the commonly used chemical preparation methods for microcapsule shells are mainly in-situ polymerization and interfacial polymerization. In-situ polymerization refers to a method in which monomers or precursors are polymerized directly inside the microcapsule to form the microcapsule shell. The in-situ polymerization method is characterized by mild reaction conditions, a relatively simple method, high reaction efficiency, and easy control of the molecular weight and distribution of the polymer. However, the microcapsule wall formed by this method is relatively hard, and part of the preparation process requires consideration of the compatibility and stability of the starting materials, which limits the material selection. Interfacial polymerization refers to a method in which polymers are polymerized at the interface of two immiscible liquids to form the microcapsule shell. The preparation of microcapsules using interfacial polymerization allows for more precise control of their size and morphology. The resulting microcapsule wall is relatively flexible, and a variety of different materials can be flexibly used for interfacial polymerization to meet different application requirements. Interfacial polymerization is commonly used to prepare shells such as polyamines, polyureas, polythioureas, and polyesters. However, their preparation may produce volatile organic compounds or involve toxic gas emissions, which can easily pollute the environment, have strict process requirements, and have high production costs. In order to reduce the impact on the environment and optimize the performance of microcapsules, there are currently some methods for preparing polyurethane microcapsule shells.

[0004] Existing polyurethane microcapsule shells generally possess excellent flexibility and wear resistance, effectively protecting the core material from environmental influences. However, their controlled-release properties are relatively slow and long-lasting, making them commonly used in fragrances, food additives, and other fields to prolong the substance's effect and improve its utilization. However, this slow controlled-release property is not suitable for rapidly inhibiting and repairing minor damage to insulating materials in the initial stages of damage development in the electrical industry. To ensure that microcapsules can respond promptly to damage self-repair in power equipment, it is necessary to improve the performance of polyurethane microcapsule shells.

[0005] Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a polyurethane microcapsule shell whose controlled-release properties are affected by mechanical stimulation.

[0009] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing a polyurethane microcapsule shell whose controlled release properties are affected by mechanical stimulation, characterized by comprising:

[0010] Deionized water and polyvinyl alcohol are mixed to obtain aqueous phase A;

[0011] Adding the oil phase 4,4'-diphenylmethane diisocyanate to the water phase A and mixing to obtain an emulsion;

[0012] Deionized water, dibutyltin dilaurate, and ethylene glycol are mixed to obtain aqueous phase B;

[0013] The emulsion is dropped into aqueous phase B and stirred at constant temperature to obtain a mixed solution;

[0014] The mixed solution was cooled to room temperature and then vacuum filtered, washed with ethanol, and dried in air at room temperature to obtain a polyurethane microcapsule shell.

[0015] As a preferred embodiment of the preparation method of the present invention, the deionized water and polyvinyl alcohol are mixed to obtain aqueous phase A, wherein the mass ratio of deionized water to polyvinyl alcohol is 100-150 ml:1-3 g.

[0016] As a preferred embodiment of the preparation method of the present invention, the deionized water and polyvinyl alcohol are mixed to obtain aqueous phase A, and the mixing temperature is 30-50°C.

[0017] As a preferred embodiment of the preparation method of the present invention, the oil phase 4,4'-diphenylmethane diisocyanate is added to the aqueous phase A and mixed to obtain an emulsion, wherein the volume ratio of the aqueous phase A to the oil phase 4,4'-diphenylmethane diisocyanate is 15-18:1.

[0018] As a preferred embodiment of the preparation method of the present invention, the deionized water is mixed with dibutyltin dilaurate and ethylene glycol to obtain aqueous phase B, wherein the volume ratio of deionized water to dibutyltin dilaurate and ethylene glycol is 40-60:0.4-0.6:1.5-2.

[0019] As a preferred embodiment of the preparation method of the present invention, the molar ratio of ethylene glycol to 4,4'-diphenylmethane diisocyanate is 1:1.

[0020] As a preferred embodiment of the preparation method of the present invention, the emulsion is dripped into the aqueous phase B and stirred at a constant temperature to obtain a mixed liquid, wherein the constant temperature is 60-80°C.

[0021] As a preferred embodiment of the preparation method of the present invention, the stirring time is 1.5 to 2 hours.

[0022] As a preferred embodiment of the preparation method of the present invention, wherein: the washing is performed with ethanol, wherein the mass fraction of ethanol is 30%.

[0023] As a preferred embodiment of the preparation method of the present invention, the washing times are 2 to 3 times.

[0024] Beneficial effects of the present invention:

[0025] (1) The present invention optimizes the synthesis method of microcapsules with polyurethane-based shells, reveals the structural performance relationship of the shell structure in the controlled release problem, and provides a method for preparing a polyurethane microcapsule shell whose controlled release characteristics are affected by mechanical stimulation, so as to effectively suppress the primary development stage of minor damage to power equipment.

[0026] (2) The present invention prepares a polyurethane microcapsule shell whose controlled release characteristics are affected by mechanical stimulation by interfacial polymerization. The molecular weight of the diol used in the preparation process directly affects the mechanical properties of the microcapsule and the release time of the core material coated therein. The higher the molecular weight of the diol used, the higher the mechanical strength of the microcapsule formed and the longer the release time of the core material inside.

[0027] (3) The present invention adopts interfacial polymerization to prepare a polyurethane microcapsule shell sample whose controlled release characteristics are affected by mechanical stimulation. The basic principle is that DPMDI prepolymer is dispersed in an aqueous phase and an emulsion is formed in water by an emulsifier. Under stirring, the prepolymer emulsion is slowly dripped into an aqueous phase containing a cross-linking agent. Under the action of the cross-linking agent, a cross-linking polymerization reaction occurs, thereby forming a polyurethane microcapsule shell structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0029] FIG1 is a schematic diagram of the shell-forming reaction process of the polyurethane microcapsules of the present invention.

[0030] FIG2 is a SEM image of the undamaged polyurethane microcapsule shell of Example 1 of the present invention.

[0031] FIG3 is a particle size distribution diagram of Example 1 of the present invention.

[0032] FIG4 is an FT-IR image of the polyurethane microcapsule shell of Example 1 of the present invention.

[0033] FIG5 is a graph showing the weight percentage change of the microcapsules of the present invention over 30 days.

[0034] FIG6 is a graph showing the rate of release of essential oils from the microcapsules of the present invention into the atmosphere. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0038] The manufacturers and purities of the chemical reagents used in the preparation of polyurethane microcapsule shell samples in the method of the present invention are shown in Table 1:

[0039] Table 1

[0040] The models and manufacturers of the main experimental instruments for preparing polyurethane microcapsule shell samples in the method of the present invention are shown in Table 2:

[0041] Table 2

[0042] Example 1

[0043] The present invention provides a method for preparing a polyurethane microcapsule shell whose controlled release properties are affected by mechanical stimulation:

[0044] (1) Preparation of aqueous phase A

[0045] Add 130 mL of deionized water and 2.2 g of polyvinyl alcohol ( PVA-103), set the temperature of the CNC magnetic stirrer to 40°C and the speed to 400 r / min, and perform magnetic stirring to mix thoroughly.

[0046] (2) Add the oil phase to the water phase A

[0047] 7.5 mL of 4,4'-diphenylmethane diisocyanate (DPMDI, as the oil phase) was added to the aqueous phase A, and the mechanical stirrer was set to a speed of 3500 r / min and stirred for 10 min. The mixed solution was poured into a glass reactor to obtain an emulsion.

[0048] (3) Preparation of aqueous phase B

[0049] To a 100 mL beaker were added 60 mL of deionized water, 0.6 mL of dibutyltin dilaurate (DBDTL), and 1.8 mL of ethylene glycol (EG, equimolar mass to DPMDI).

[0050] (4) Add the emulsion to the aqueous phase B

[0051] The emulsion in the glass reactor (2) was slowly dripped into the aqueous phase B, and the reaction mixture was placed in a constant temperature water bath, the temperature was raised to 70°C, the speed of the mechanical stirrer was set to 200 r / min, and the mixture was stirred for 2 h.

[0052] (5) Washing and drying

[0053] After the mixed solution was cooled to room temperature, it was vacuum filtered, washed with 30% ethanol three times, and then placed in air to dry at room temperature for 24 hours.

[0054] The dried polyurethane microcapsule shell sample is placed on a sample stand, and it is sprayed with platinum to prepare a sample. Then, a scanning electron microscope (SEM) test is adopted to observe and obtain its SEM figure as shown in Figure 2. As can be seen from the figure, the microcapsule presents a full spherical shape, and the particle size is relatively uniform, and the profile is relatively complete, and no damage occurs, which embodies the good mechanical properties of the polyurethane microcapsule shell. In terms of dispersibility, the prepared microcapsule core-shell structure is mostly a single individual, without obvious adhesion, which proves that its dispersibility is good. By carrying out electron microscope scanning to the damaged microcapsule shell, it can be obtained that its shell thickness is about 6.73 μ m, and it is observed that the core-shell outer surface is not completely smooth, but has more subtle projections, which may be due to the incomplete reaction of the prepolymer. This relatively rough outer surface can enhance the interaction between matrix material and the microcapsule when preparing composite material, making it more tightly meshed.

[0055] The particle size distribution of Example 1 was calibrated using an optical microscope observation system, and then the image was measured using sampling software. The particle size distribution curve was plotted using Origin plotting software, as shown in Figure 3. As can be seen from the figure, the particle size of the prepared sample is concentrated in the range of 10 to 30 μm, with a relatively uniform particle size distribution, successfully achieving a unimodal distribution within a relatively narrow particle size range, which is beneficial for its practical application in insulating composite materials.

[0056] The FT-IR spectrum of Example 1 is shown in FIG4 , from which some main peak distributions (-CH, etc.) can be seen. By comparing it with the FT-IR spectra of other compounds, it can be determined whether the polyurethane microcapsules are successfully prepared.

[0057] Example 2

[0058] In order to study the controlled-release properties of the prepared polyurethane microcapsule shell affected by mechanical stimulation, a certain amount of self-healing core material can be added to the inside before the shell is formed. By comparing the FT-IR images and weight change percentage curves of the microcapsules after adding the self-healing core material before and after controlled release, the changes in the controlled-release properties of the microcapsule shell after mechanical stimulation can be obtained.

[0059] As shown in Figure 5, without external mechanical stimulation (such as scratches or other damage), the microcapsule shell's stability keeps its weight percentage essentially unchanged. However, when the microcapsules are mechanically stimulated once every 10 days, the polyurethane shell ruptures on the second day after the stimulation, accelerating the release of the self-healing core material. The core material solidifies within a very short time, achieving self-healing. The FT-IR image of the released microcapsules is similar to that of the polyurethane shell, confirming the successful release of the core material.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that the oil phase in step (2) contains toluene-2,4-diisocyanate (TDI).

[0062] Comparative Example 2

[0063] The difference from Example 1 is that the oil phase in step (2) contains isophorone diisocyanate (IPDI).

[0064] Table 3 shows the encapsulation efficiency of the microcapsules obtained in Example 1 and Comparative Examples 1-2:

[0065] As shown in FIG5 , the DPMDI-EG (Example 1) interaction resulted in higher core material encapsulation and release efficiencies than the other two diisocyanate-EG (Comparative Examples 1-2) interactions.

[0066] Comparative Example 3

[0067] The difference from Example 1 is that ethylene glycol is not added in step (3).

[0068] Comparative Example 4

[0069] The difference from Example 1 is that in step (3), the molar ratio of ethylene glycol to 4,4'-diphenylmethane diisocyanate is 1:2.

[0070] Comparative Example 5

[0071] The difference from Example 1 is that in step (3), the molar ratio of ethylene glycol to 4,4'-diphenylmethane diisocyanate is 2:1.

[0072] In order to compare the effects of different ethylene glycol molecular weights on the release control characteristics, a certain amount of essential oil was added to the inside of the microcapsule for encapsulation before shell formation. The thickness of the encapsulation shell is shown in Table 4 below. The essential oil atmosphere release rate curve in the formed microcapsules is shown in Figure 6. The release rate of the microcapsule with the thinnest shell is the fastest. The experimental molar ratio selected is 1:1, which can achieve a certain shell thickness while ensuring a certain encapsulation rate. The innovation of the present invention is that the film thickness is determined by the molecular weight of ethylene glycol, which affects the release characteristics. The limit value is a molar mass ratio of 1:1 without affecting the encapsulation rate. In specific practical applications, microcapsules with a release rate that varies with the film thickness can be prepared according to one's own needs to meet the needs. Exceeding 1 may affect the use of the core material. Ethylene glycol affects its controlled-release properties. The mechanism is that the molecular weight of glycol directly affects the mechanical properties of the microcapsules and the release time of the core material coated therein. The higher the molecular weight of glycol used, the tighter the network structure formed by the cross-linking reaction. At the same time, the mutual attraction and bonding between molecules are stronger, thus forming a more uniform and thicker wall layer, resulting in higher stability and mechanical strength of the formed microcapsules, longer release time of the core material inside, and effective prevention of core material leakage.

[0073] Table 4

[0074] The thicker the shell, the higher the mechanical strength and stability, but at the same time the lower the internal encapsulation rate. Therefore, the thicker the shell is, the better, and the encapsulation rate of the internal core material must be considered.

[0075] Comparative Example 6

[0076] In CN 107903877 A, (1) n-octadecane and TDI are dissolved in cyclohexane solvent to prepare a uniformly mixed oil phase system; (2) emulsifier and OP-10 are weighed and added to a beaker filled with distilled water, and stirred to prepare a uniformly mixed water phase system; (3) the oil phase is poured into the water phase beaker and stirred under a homogenizer.

[0077] Stir to form a uniform O / W emulsion; (4) transfer the emulsion to a three-necked flask and reduce the speed; (5) mix DETA and distilled water evenly, and add them dropwise to the above emulsion at a uniform speed. After the addition is completed, slowly heat it to 60°C and keep it warm for 3 hours to obtain a microcapsule suspension; (6) filter the obtained product, wash it with distilled water and ethanol, and filter it. Finally, dry the filter cake in a vacuum drying oven to obtain n-octadecane / polyurea resin phase change microcapsules.

[0078] In Comparative Example 6, the oil phase system is a mixture of n-octadecane, TDI, and cyclohexane solvents, while in the present invention, the oil phase is 4,4'-diphenylmethane diisocyanate, and the addition of ethylene glycol influences its controlled-release properties. The mechanism is that the molecular weight of the glycol directly affects the mechanical properties of the microcapsules and the release time of the core material they encapsulate. The higher the molecular weight of the glycol used, the greater the mechanical strength of the microcapsules formed and the longer the release time of the core material within them. As shown in Table 1 and Figure 5, the DPMDI-EG interaction (Example 1) results in higher core material encapsulation and release efficiency than the other two diisocyanate-EG interactions (Comparative Examples 1-2).

[0079] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all of these should be included in the scope of the present invention.

Claims

1. A preparation method of a polyurethane microcapsule shell whose controlled release property is affected by mechanical stimulation, characterized in that: including Mix deionized water and polyvinyl alcohol to obtain aqueous phase A; Add the oil phase 4,4'-diphenylmethane diisocyanate to aqueous phase A and mix to obtain an emulsion; Mix deionized water with dibutyltin dilaurate and ethylene glycol to obtain aqueous phase B; Drop the emulsion into aqueous phase B and stir at a constant temperature to obtain a mixed solution; After the mixed solution is cooled to room temperature, vacuum filter it, wash it with ethanol, and place it in the air to dry at room temperature to obtain the polyurethane microcapsule shell.

2. The preparation method according to claim 1, characterized in that: The deionized water and polyvinyl alcohol are mixed to obtain aqueous phase A, wherein the mass ratio of deionized water to polyvinyl alcohol is 100 - 150 ml: 1 - 3 g.

3. The preparation method according to claim 2, characterized in that: The deionized water and polyvinyl alcohol are mixed to obtain aqueous phase A, and the mixing temperature is 30 - 50 °C.

4. The preparation method according to claim 1, characterized in that: The oil phase 4,4'-diphenylmethane diisocyanate is added to aqueous phase A and mixed to obtain an emulsion, wherein the volume ratio of aqueous phase A to the oil phase 4,4'-diphenylmethane diisocyanate is 15 - 18:

1.

5. The preparation method according to claim 1, characterized in that: The deionized water is mixed with dibutyltin dilaurate and ethylene glycol to obtain aqueous phase B, wherein the volume ratio of deionized water to dibutyltin dilaurate and ethylene glycol is 40 - 60: 0.4 - 0.6: 1.5 - 2.

6. The preparation method according to claim 1, characterized in that: The molar ratio of ethylene glycol to 4,4'-diphenylmethane diisocyanate is 1:

1.

7. The preparation method according to claim 1, characterized in that: The emulsion is dropped into aqueous phase B and stirred at a constant temperature to obtain a mixed solution, wherein the constant temperature is 60 - 80 °C.

8. The preparation method according to claim 7, characterized in that: The stirring time is 1.5 - 2 h.

9. The preparation method according to claim 1, characterized in that: Wash with ethanol, wherein the mass fraction of ethanol is 30%.

10. The preparation method according to claim 9, characterized in that: The number of washing times is 2 - 3 times.

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