CN117380104A

CN117380104A - Amine-containing microcapsules and process for their preparation

Info

Publication number: CN117380104A
Application number: CN202310775670.XA
Authority: CN
Inventors: 杨晶磊; 赵颖
Original assignee: Hong Kong University of Science and Technology HKUST
Current assignee: Hong Kong University of Science and Technology HKUST
Priority date: 2022-07-11
Filing date: 2023-06-28
Publication date: 2024-01-12

Abstract

The present invention relates to an amine-containing microcapsule comprising a liquid core material comprising an amine liquid having a viscosity in the range of of 100 mPa-s to 300 mPa-s; and a polymer shell material which is polyurea and/or the like and which surrounds the liquid core material. The amine liquid and diisocyanate and the analogues thereof are subjected to instant interfacial polymerization to form a core-shell structure, wherein the shell layer of the core-shell structure is a polyurea shell layer and/or a similar shell layer, and the core of the core-shell structure is an amine liquid core material. The invention also relates to a method for encapsulating hydrophilic amines by combining interfacial polymerization and microfluidic technology. The present invention describes an interfacial reaction mechanism in which the encapsulation process is optimized to produce amine microcapsules with adjustable aspect ratio, high core content and tight shells.

Description

Amine-containing microcapsules and process for their preparation

Cross Reference to Related Applications

The present application claims priority to U.S. patent application 63/359,901 filed on month 11 of 2022, 07, the disclosure of which is incorporated herein by reference.

Technical Field

The present invention relates generally to the technical fields of interfacial polymerization, microfluidic technology, encapsulation technology, and the like.

Background

The amino group has great potential for becoming an ideal carbon dioxide adsorbent and a multifunctional curing agent, and is suitable for various adhesives in high-end industrial application. Inspired by the widespread cellular systems in which physical boundaries (e.g., membrane structures) are established to contain internal substances and regulate efficient mass transfer to ensure efficient proper functioning, encapsulation of amines into microstructures facilitates the design of smart material systems with high adaptability, controllability and efficiency.

In recent years, researchers have made more and more efforts to microencapsulate amines, using various techniques. However, the main problems faced by encapsulated amines are (1) high affinity of the amine with water and most organic solvents, and (2) extremely high reactivity between the amine and various functional groups. The high solubility of the amine results in a substantial partitioning of the amine into the continuous phase, forming a thicker oil-oil emulsion interface, which prevents efficient adsorption of the surfactant molecules to form a stable viscoelastic surfactant film. Diffusion also severely promotes oswald ripening, reducing emulsion stability and leading to uneven particle distribution and impeding continuous interfacial polymerization. On the other hand, the high reaction kinetics of the two fast delivering monomers create severe localized kinetic turbulence, which is catastrophic for the fragile surfactant films, high probability of breaking the emulsion, leading to disruption of shell growth and complete encapsulation failure. For the reasons mentioned above, the high reactivity and good solubility in most solvents makes it difficult to form stable emulsions during encapsulation, resulting in a hindrance to efficient encapsulation of the amine.

To date, several strategies for encapsulating hydrophilic amines have been explored by researchers in the field, including microfluidic, vacuum infusion, and emulsion methods. The microfluidic method adopts a T-shaped joint to generate liquid drops, and can prepare amine microcapsules with stable performance. However, it is extremely inefficient in microcapsule production and is only suitable for small scale academic research. To expand the production of amine microcapsules, some researchers have used vacuum infiltration to infiltrate amine solutions into hollow porous micro-containers. However, the porous shell layer, which allows amine permeation, also causes leakage of the core during storage, thus producing microcapsules with poor shell properties. The third amine microcapsule production technique is emulsion-based interfacial polymerization, which has a high extended production potential. However, the compatibility of amines with water and most organic solvents is high. During the emulsification process, severe partitioning phenomena occur leading to the formation of large amounts of fines, which prevent successful microencapsulation. Therefore, the emulsion method is only applicable to very high polarity amines.

Disclosure of Invention

At present, there is no effective method for encapsulating hydrophilic amines in the art, and the main objective of the present invention is to solve these problems by exploring and developing an effective strategy for encapsulating expandable amines and to achieve desirable properties including high core content, good shell strength, thermal stability, proper shell thickness, high adaptability, and production efficiency, etc.

The present invention provides a high throughput platform that can produce amine microcapsules with adjustable aspect ratio, core content and shell thickness by integrating the process of amine filament breakage and simultaneous interfacial polymerization caused by spontaneous fluid instability. The aspect ratio and diameter of the resulting microcapsules were systematically investigated using hexamethylene diisocyanate (HMDI) concentration, injection rate and stirring rate as variables. HMDI concentration affects shell properties of the capsule, including compactness, thickness, morphology, thermal stability, and the like. The present invention describes an interfacial reaction mechanism in which the encapsulation process is optimized to produce amine microcapsules with adjustable aspect ratio, high core content and tight shells.

In one aspect, the present invention provides an amine-containing microcapsule comprising a liquid core material comprising an amine liquid having a viscosity in the range of from 100 mPa-s to 300 mPa-s; and a polymeric shell material comprising polyurea and the like and surrounding the liquid core material. The method comprises the steps of performing instant interfacial polymerization on amine liquid, diisocyanate and analogues thereof to form a core-shell structure, wherein a shell layer of the core-shell structure is a polyurea shell layer and/or an analogue shell layer, and a core of the core-shell structure is an amine liquid core material.

According to one aspect of the invention, the time scale for the splitting of the amine liquid jet into fragments or droplets is defined as τ _inst Whereas the reaction time of the amine liquid with the diisocyanate and its analogues to form the core-shell structure is defined as τ _frozen ,. When τ is _inst >τ _frozen Obtaining said microcapsules having an aspect ratio higher than 1.0; when τ is _inst≤ τ _frozen When the amine liquid jet breaks up into spherical droplets less than 200 microns in diameter before being solidified into the microcapsules.

According to one aspect of the invention, the liquid core material comprises a hydrophilic amine or an amine having a long hydrocarbon chain, including tetraethylenepentamine, polyetheramine, or a combination thereof. Amine solutions are very miscible with most solvents and are reactive with a wide variety of chemical groups.

According to one aspect of the invention, the liquid core material is present in an amount of 1wt% to 95wt% of the total amount of the amine-containing microcapsules, and the polyurea and/or analog thereof is present in an amount of 5wt% to 99wt% of the total amount of the amine-containing microcapsules.

According to one aspect of the invention, the amine-containing microcapsules have a thickness in the range of 1 micron to 40 microns.

According to one aspect of the invention, the amine-containing microcapsules have a diameter in the range of 1 micron to 200 microns.

According to one aspect of the invention, the amine-containing microcapsules have an aspect ratio in the range of 1-30.

According to one aspect of the invention, the amine-containing microcapsules are spherical, tubular, cylindrical or filiform.

In another aspect, the present invention provides a method of preparing an amine-containing microcapsule comprising directly injecting an amine liquid having a viscosity in the range of 100 mPa-s to 300 mPa-s into a continuous oil phase at room temperature by a microfluidic device; stirring the continuous oil phase for a duration of 10 to 30 minutes by means of a stirrer provided in the microfluidic device to perform interfacial polymerization to form a mixture containing primary microcapsules comprising amine; the mixture was reacted at 40 ℃ for 2 hours followed by 50 ℃ for 2 hours and finally 60 ℃ for 2 hours to form the amine-containing microcapsules.

According to one aspect of the invention, the continuous oil phase comprises an oil, a diisocyanate and/or its analogues and a surfactant, and the amine liquid and the diisocyanate and its analogues form a polyurea and its analogue shell structure by instant interfacial polymerization.

According to one aspect of the present invention, the oil comprises paraffin oil and/or an analogue thereof selected from one or more of mineral oil, n-hexane, cyclohexane, hexadecane, toluene, xylene, decalin or polyisobutylene, the diisocyanate and an analogue thereof selected from one or more of hydrogenated diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, lysine diisocyanate, polymethylene polyphenyl polyisocyanate, 2, 6-diisocyanatotoluene, 1, 3-diisophenylcyanate, 1, 4-diisocyanatobutane, terephthal-diisocyanate, 1, 4-dithioisocyanatobutane or hexamethylene diisocyanate, and the surfactant is selected from one or more of Span 80, span 85, TERGITOL alkoxypolyethylene hydroxyl ethanol, tridecyl polyoxyethylene stearyl ether, sodium dodecyl benzene sulfonate, 2-ethylhexanol EO-PO, polyvinyl alcohol, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan brown acid ester, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan tristearate or polyoxyethylene sorbitan tristearate.

According to one aspect of the invention, the concentration of the catalyst is 0.01 mL-min ^-1 To 5 mL-min ^-1 Is injected into the continuous oil phase.

According to one aspect of the invention, the stirring rate is between 10rpm and 700rpm.

According to one aspect of the invention, the method further comprises washing the amine-containing microcapsules at least twice with n-hexane, and then drying them.

In another aspect, the invention provides an apparatus for injecting an amine liquid comprising a stirring impeller integrated with a conduit outlet inserted below the surface of the solution.

Drawings

The invention will be more readily understood from the following description of exemplary embodiments, set forth in the accompanying drawings, in which:

FIG. 1 depicts a schematic diagram of droplet generation and shell formation according to one embodiment of the invention.

Figure 2 shows a picture of the formation of liquid filaments when amine liquid is injected into the continuous phase.

Figure 3a shows optical microscopy pictures of microcapsules produced by interfacial reactions between different amine combinations and HMDI.

FIG. 3b depicts the chemical structures of TEPA, jeffamine T403, and Jeffamine D2000.

Figure 4 shows optical microscopy pictures of microcapsules of different shapes according to one embodiment of the invention.

Figure 5a shows an SEM image of a complete spherical microcapsule.

Fig. 5b shows an SEM image of the complete tubular microcapsule.

Fig. 5c shows an SEM image of a cross-sectional view of a spherical microcapsule.

Figure 5d shows an SEM image of a cross-sectional view of a tubular microcapsule.

Fig. 6 depicts the normalized viscosity of the continuous phase, and the interfacial tension between deionized water and the continuous phase as a function of HMDI concentration, in accordance with one embodiment of the present invention.

Figure 7 depicts the effect of HMDI concentration on 7 a) aspect ratio and 7 b) diameter of microcapsules prepared with various amine sources.

Figure 8 depicts the effect of continuous phase agitation rate on 8 a) aspect ratio and 8 b) diameter of microcapsules prepared at different injection rates.

Fig. 9 shows optical microscopy pictures of reaction solutions with different HMDI concentrations. Scale bar = 200 microns.

Fig. 10 depicts the change in microcapsule shell thickness as the HMDI concentration increases.

Figure 11a depicts the morphology of the outer surface of microcapsules collected after injection for 5 minutes at room temperature, according to one embodiment of the present invention.

Figure 11b depicts the morphology of the outer surface of microcapsules collected after 10 minutes of injection at room temperature, according to one embodiment of the present invention.

Figure 11c shows the morphology of the inner surface of the microcapsules collected after injection for 10 minutes at room temperature.

Figure 12 shows the morphology of the outer surface of the microcapsules collected after different time intervals (1 h, 2h, 3h, 4h, 5h, 6 h) of the second step. Scale bar = 2 microns.

Fig. 13 shows the structural morphology of microcapsules collected after different time intervals (1 h, 2h, 3h, 4h, 5h, 6 h) of the second step. Scale bar = 50 microns.

Figure 14a depicts an isothermal profile of intact microcapsules produced with different HMDI concentrations, according to one embodiment of the present invention.

Figure 14b depicts the core content of intact microcapsules produced with different HMDI concentrations, according to one embodiment of the invention.

Figure 14c depicts an isothermal profile of complete microcapsules prepared at different stirring rates in the first stage, according to one embodiment of the present invention.

Figure 14d depicts the core content of the complete microcapsules prepared at different agitation rates in the first stage, according to one embodiment of the present invention.

Figure 15 shows SEM images of spherical and tubular 25TEPA75T403 microcapsules.

Fig. 16 depicts the TGA profile of pure 25TEPA75T403 and its microcapsules.

Detailed Description

In the following description, a method of encapsulating hydrophilic amines in combination with interfacial polymerization and microfluidic technology, which has a core-shell structure, will be exemplified. Those skilled in the art will appreciate that even modifications, additions and/or substitutions are possible, without departing from the scope and spirit of the invention and that the scope of the invention is therefore not limited. Specific details may be omitted so as not to obscure the invention; however, this disclosure is written in order to enable any person skilled in the art to practice the disclosed technology without undue experimentation.

Over several decades of effort, microencapsulation of amines with different hydrophilicities remains a challenge under simplified strategies and high throughput. Because of the high solubility of amines in most organic solvents, the use of emulsion processes to prepare amine microcapsules is unsuitable in most cases.

Once the amine drops into the immiscible phase containing the diisocyanate, a film forms almost immediately at the interface. This approach avoids precontacting, i.e. emulsification, between the amine and the pure organic phase. Thus, less amine is distributed into the continuous phase and less fragments are formed. However, the practical realization of microcapsules with this concept requires mass production of droplets. Chip-based microfluidics are widely used for controllable droplet generation, but suffer from its low production efficiency. Thus, the droplets of the present invention are produced by injecting the amine liquid directly into the agitated continuous phase through the microtubes. Without limitation, the amine liquid eventually breaks down into tiny droplets under the shear force of the continuous phase. In combination with the immobilization of the polymer shell formed around the amine liquid, it is expected that microcapsules with adjustable aspect ratios will be produced. Overall, the potential to mass produce custom amine microcapsules can overcome a long-standing and urgent need to address production challenges.

In view of this, the present invention provides an amine-containing microcapsule comprising a liquid core material comprising an amine liquid having a viscosity of from 100 mPa-s to 300 mPa-s of , utilizing the rapid reaction kinetics of the amine and diisocyanate; and a polymeric shell material comprising polyurea and the like, and surrounding the liquid core material. The method comprises the steps of performing instant interfacial polymerization on amine liquid, diisocyanate and analogues thereof to form a core-shell structure, wherein a shell layer of the core-shell structure is a polyurea shell layer and/or an analogue shell layer, and a core of the core-shell structure is an amine liquid core material.

According to one aspect of the invention, the amine-containing microcapsules are spherical, tubular, cylindrical or filiform. The time scale for the breaking up of an amine liquid jet into fragments or droplets is defined as τ _inst Whereas the reaction time of the amine liquid with the diisocyanate and its analogues to form the core-shell structure is defined as τ _frozen ,. When τ is _inst >τ _frozen Obtaining said microcapsules having an aspect ratio higher than 1.0; when τ is _inst≤ τ _frozen When the amine liquid jet breaks up into spherical droplets less than 200 microns in diameter before being solidified into the microcapsules.

In the present invention, the range of liquid core material content may be tailored to specific application requirements. In some embodiments, the content of the liquid core material may be varied within a specific chemical composition range to achieve desired material properties. These chemical components may comprise a single substance or a combination of substances to achieve desired properties and characteristics. According to one aspect of the invention, the liquid core material includes, but is not limited to, hydrophilic amines or amines having long hydrocarbon chains, such as tetraethylenepentamine, polyetheramine, or combinations thereof. The liquid core material is present in an amount of 1wt% to 95wt% based on the total amount of the amine-containing microcapsules. For example, the liquid core material is present in an amount of 25wt% to 95wt%, 50wt% to 95wt%, 75wt% to 95wt%.

According to one aspect of the invention, the polyurea and/or analogue thereof is present in an amount of 5 to 99wt% of the total amount of the amine-containing microcapsules. For example, the polyurea and/or analog thereof is present in an amount of 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%.

Preferably, the polyurea and/or analogue thereof is present in an amount of 5wt%, 8wt%, 12wt%, 16wt%.

According to one aspect of the invention, the amine-containing microcapsules have a thickness in the range of 1 micron to 40 microns. Has a thicker shell thickness (about 20 microns to 30 microns) when the HMDI concentration is low and a thinner shell thickness (less than 10 microns) when the HMDI concentration is high.

According to one aspect of the invention, the amine-containing microcapsules have a diameter in the range of 1 micron to 200 microns. For example, the amine-containing microcapsules have diameters of 1 micron, 2 microns, 3 microns, 4 microns, 5 microns, 10 microns, 20 microns, 30 microns, 40 microns, 50 microns, 60 microns, 70 microns, 80 microns, 90 microns, 100 microns, 110 microns, 120 microns, 130 microns, 140 microns, 150 microns, 160 microns, 170 microns, 180 microns, 190 microns, 200 microns.

According to one aspect of the invention, the amine-containing microcapsules have an aspect ratio in the range of 1 to 30.

In another aspect, the present invention provides a method of preparing an amine-containing microcapsule comprising directly injecting an amine liquid having a viscosity in the range of 100 mPa-s to 300 mPa-s into a continuous oil phase at room temperature by a microfluidic device; stirring the continuous oil phase for a duration of 10 to 30 minutes by means of a stirrer provided in the microfluidic device to perform interfacial polymerization to form a mixture containing primary microcapsules comprising amine; the mixture was reacted at 40 ℃ for 2 hours followed by 50 ℃ for 2 hours and finally 60 ℃ for 2 hours to form the amine-containing microcapsules. The method may further comprise washing the amine-containing microcapsules at least twice with n-hexane, and then drying them.

According to one aspect of the invention, the continuous oil phase comprises an oil, a diisocyanate and/or its analogues and a surfactant, the amine liquid and the diisocyanate and its analogues forming a polyurea and/or its analogue shell structure by instant interfacial polymerization therebetween. "instant interfacial polymerization" involves the reaction of an amine liquid and a diisocyanate (or its analog) which occurs at the interface where the two materials come into contact during the reaction process because the reaction rate of the amine liquid and the diisocyanate is very fast. The rapidity of this interfacial polymerization reaction enables the polymer material to be formed in a short time and to be bonded at the interface.

According to one aspect of the invention, the oil includes, but is not limited to, paraffinic oil, mineral oil, n-hexane, cyclohexane, hexadecane, toluene, xylene, decalin, or polyisobutylene, and the like.

According to one aspect of the present invention, the diisocyanate and its analogs include, but are not limited to, 4' -diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, lysine diisocyanate, polymethylene polyphenyl polyisocyanate, 2, 6-toluene diisocyanate, 1, 3-diphenyl cyanate, 1, 4-diisocyanate butane, p-phenylene diisocyanate, 1, 4-dithioisocyanate butane, hexamethylene diisocyanate, or the like.

According to one aspect of the invention, the surfactant includes, but is not limited to Span 80, span 85, TERGITOL alkoxypolyethylene hydroxyl ethanol, trideceth, sodium dodecyl benzene sulfonate, 2-ethylhexanol EO-PO, polyvinyl alcohol, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan polyoxyethylene acid ester, polyoxyethylene sorbitan isostearate, polyoxyethylene sorbitan tristearate, or polyethoxy oleic acid sorbitol, and the like.

According to one aspect of the invention, the amine solution is injected into the continuous oil phase at an injection rate of 0.01mL min "1 to 5mL min" 1.

According to one aspect of the invention, the stirring rate is between 10rpm and 700rpm. For example, the stirring rate is 50rpm, 100rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm.

According to one aspect of the invention, the amine-containing microcapsules produced are stable under most storage/handling conditions. For example, the prepared amine-containing microcapsules are capable of maintaining their structural and performance stability at temperatures up to 140 degrees.

According to one aspect of the invention, the structural strength of the housing can be adjusted by controlling the reaction time of the housing. Observing morphological evolution of the shell through a Scanning Electron Microscope (SEM), and showing that the shell is deformed flatly in the SEM observation process due to short reaction time, so that the strength is lower; the long reaction time can maintain the three-dimensional structure of the shell and can bear the self weight under the high vacuum condition.

Examples

Example 1 Experimental design and microcapsule formation

The combination of liquid extrusion processes and interfacial polymerization is extremely complex involving many parameters and their coupling such as interfacial tension, viscous forces, inertial forces, mass diffusion and interfacial reaction kinetics. By adjusting these parameters, it is expected that microcapsules having different aspect ratios and diameters will be obtained.

The whole encapsulation process consists of the following steps: in the first step, the liquid amine is extruded directly into the continuous phase while forming a preliminary polyurea shell at room temperature by the instant interfacial polymerization between the amine and the diisocyanate and its analogues. In a second step, the polyurea shell is thickened at an elevated temperature to obtain the final microcapsule.

The design of the encapsulation device is shown in fig. 1. The pipe outlet for liquid amine injection is inserted below the surface of the continuous phase containing diisocyanate and around the rotating impeller so that the local impeller reynolds number (Re) and continuous phase velocity can be easily calculated. As shown in fig. 2, during injection, the liquid amine is forced through the outlet into the immiscible continuous phase at a rate. Once the amine is extruded, the flowing viscous continuous phase tends to stretch and drag it downstream by viscous drag, while the interfacial tension between the two phases tends to fix it at the tip. If no restraining force is applied, the liquid jet eventually breaks up into droplets due to fluid instability.

In one embodiment, the microfluidic device comprises a syringe pump and a polytetrafluoroethylene tube, the outlet of the polytetrafluoroethylene tube being located below the liquid surface, near the periphery of the impeller.

One key element in the design of the present invention is the addition of hydrogenated diphenylmethane diisocyanate (HMDI) in the continuous phase, which reacts instantaneously with the liquid amine at the two-phase interface to form a Polyurea (PU) film, which is typically accomplished in the microsecond to second range. Interfacial polymerization proceeds at infinite lateral dimensions, meaning that the reaction occurs as long as there are available reactants between the two phases. Thus, in theory, the polyurea film continues to form across the interface. When the film is in a certain growth stage against shear stress and instability, the amine liquid jets may delay splitting, forming short columns or fibers.

In addition to competing with liquid stability, successful encapsulation of amines into microcapsules by interfacial polymerization also plays a critical role. Because of the limited miscibility between the two phases, interfacial polymerization can only be performed in regions of miscibility having a limited thickness. Once the initial film is formed, the ability of the amine monomer to diffuse through the film toward the reaction zone decreases exponentially with the growth of the nanofilm, and this self-limiting property prevents excessive thickening of the film. Typically, for amine-isocyanate systems, the thickness of the film is in the range of nanometers to a few microns.

In addition, defects and relatively thin sites are prone to monomer diffusion breaches, which can lead to thickening of the newly formed polyurea film in such reaction areas. Overall, the self-limiting and self-completing properties of interfacial polymerization facilitate the formation of uniform and defect-free films of suitable thickness. Because of these properties, residual amine can be microencapsulated with a dense PU film.

The invention relates to the instability time (tau) _inst ) Defined as the time scale of the breaking up of the amine liquid jet into fragments or droplets. Freezing time (τ) _frozen ) Defined as the reaction time of the amine with HMDI to form the polyurea shell layer, to obtain a shell of a certain strength that allows the liquid to solidify without deformation. By comparing the two time scales, when τ _inst >τ _frozen When polyurea shells form faster, instability is delayed or exceeded. In this case, it is expected that microcapsules having an aspect ratio higher than 1.0 can be obtained. When τ is _inst <τ _frozen When the radius fluctuation causes the liquid jet to become unstable, the instability development is accelerated, and finally the liquid jet is positioned atSplit into small spherical droplets before being solidified into microcapsules.

In one example, three amine sources (tetraethylenepentamine, polyetheramine Jeffamine T403, and Jeffamine D2000) were screened as feed models to prepare microcapsules. The structural formulae of the three amine sources are shown in FIG. 3 b. Tetraethylenepentamine (TEPA) is an aliphatic amine with extremely high reactivity, whereas polyetheramines Jeffamine T403 and Jeffamine D2000 are less reactive but have higher viscosity due to longer hydrocarbon chains. Thus, upon interfacial polymerization with an amine mixture, the amine source that is more reactive to HMDI will preferentially react at the interface. Typically, the interfacial tension between the amine and the paraffinic oil is very low. As shown in table 1, the difference in interfacial tension was almost negligible in these three samples.

On the other hand, viscosity plays an important role in the unstable development process. Higher viscosity may provide higher resistance to liquid jet break up. In Table 1, samples T403 and 25TEPA_75T403 have similar viscosity and interfacial tension, meaning that they have an instability time (τ _inst ) Similarly. However, the kinetics of the reaction between sample T403 and HMDI is too low to resist the unstable forces of the liquid before breaking into small droplets. Thus, spherical microcapsules were obtained at sample T403 (fig. 3 a). By adding TEPA, the shell is mainly formed by the reaction between TEPA and HMDI. Fast formation of shell (lower τ) _frozen ) Is sufficient to compete with the instability and lead to the formation of tubular microcapsules. When Jeffamine D2000 (having lower reactivity but higher viscosity) was added to increase the viscosity of the amine mixture from 147.7 mPas to 381.3 mPas, the development of instability was greatly prolonged (τ _inst Higher). Thus, in this case, the shell formation time between amine and HMDI is comparable to the instability time, thereby forming tubular microcapsules. In general, the aspect ratio of the predicted microcapsules to be formed is a relative concept. Only when a specific tau is _frozen Relative to a particular tau _inst In the case of (2), tubular microcapsules can be obtained.

TABLE 1

As shown in fig. 4, several geometries of the resulting microcapsules are shown. By varying the viscosity, interfacial tension, feed rate, shear rate, reactivity, etc., the final shape of the microcapsules can be adjusted, for example, from spheres to short cylinders or fibers.

Furthermore, there may be a large difference in microcapsule diameters. The microcapsules are dried and collected, and the spherical microcapsules can flow freely after collection. The tubular microcapsules of high aspect ratio have little entanglement but are loosely attached together and can be easily dispersed in practical applications. The detailed morphology of the microcapsules is shown in fig. 5a to 5 d. Both spherical and tubular microcapsules can be seen in fig. 5a-5b to exhibit a distinct core-shell structure. Fig. 5c-5d show SEM images of cross-sectional views of spherical microcapsules as well as tubular microcapsules, clearly showing that large voids are inside the structure, which can be used to store residual amine species.

Example 2-adjustment of aspect ratio and diameter of microcapsules by adjusting HMDI concentration

As previously mentioned, the destabilizing forces tend to break up the liquid filaments into tiny droplets. At the same time, the solid PU film produced by the rapid reaction between TEPA and HMDI creates a competitive force that keeps the liquid jet in its original shape. The competition between freezing time and destabilization time may lead to the formation of microcapsules of different shapes. To demonstrate this phenomenon, the present example aims at studying the effect of HMDI concentration.

By adjusting the HMDI content in the continuous phase, higher HMDI concentrations increase the reaction rate and reduce the shell formation time during encapsulation. Thus, the amine liquid should freeze at an earlier stage and the liquid filaments dominate the shape generation.

In one embodiment, fig. 6 depicts the normalized viscosity of the continuous phase, and the interfacial tension between deionized water and the continuous phase as a function of HMDI concentration. As the results in fig. 6 show, the viscosity of the continuous phase remained constant over the range studied. However, due toThe rapid reaction of amines with isocyanates makes it difficult to measure the interfacial tension of the two phases after HMDI addition. The kinetics of the reaction of deionized water with HMDI is low enough to provide enough time for hanging drop measurements. Accordingly, deionized water was chosen as an alternative for the present invention. Interfacial tension between deionized water and the continuous phase. The results of fig. 6 show that there is no significant change in interfacial tension after HMDI addition. The pattern of instability development and the time scale of a particular amine system remained substantially similar throughout the course of the study. Only tau due to different reaction kinetics _frozen The shape of the resulting microcapsules can be affected by variations in (a) and (b).

The effect of the change in aspect ratio and diameter of microcapsules prepared with different amines with HMDI concentration is shown in fig. 7, where fig. 7a depicts the effect of HMDI concentration on aspect ratio. Figure 7b depicts the effect of HMDI concentration on microcapsule diameter prepared with different amine sources. The results show that for each amine, there is a transition from spherical microcapsules (aspect ratio=1.0) to tubular microcapsules (aspect ratio > 1.0). As HMDI concentration increases, the rate of shell formation increases accordingly. Thus, the dispersed phase solidifies at an early stage where the amine liquid is still in a linear form, thereby forming tubular microcapsules. In addition, at higher HMDI concentrations, the aspect ratio of the tubular microcapsules also increases, mainly due to the faster formation rate, higher mechanical strength PU shells.

In other embodiments, the dispersed phase may also be prepared using TEPA mixed with varying amounts of Jeffamine T403. As shown in Table 2, T403 amine increased bulk viscosity, increased resistance to cracking, and increased τ _inst . It should be noted, however, that T403 is less reactive than TEPA and that at high viscosity of the dispersed phase, the diffusion of TEPA into the interface is reduced, which may lead to higher τ _frozen And a lower aspect ratio. As the T403 content increases, the aspect ratio increases, which indicates that in these cases the effect of higher viscosity outweighs the decrease in reactivity.

TABLE 2

Fig. 7b shows the change in microcapsule diameter with HMDI concentration. The diameter initially increases and then decreases, and then increases further. The size reduction corresponds to the first sign of tubular microcapsules. The largest diameter spherical microcapsules are closest to the initial droplet break off from the amine liquid filament. The smaller diameter microcapsules are formed by the primary dispersed droplets undergoing secondary rupture due to τ _froze n is equal to tau _inst Lower results.

Example 3-aspect ratio and diameter of microcapsules were adjusted by adjusting injection rate and stirring rate

In the present inventive system, the rate of the dispersed phase was much lower than the rate of the continuous phase (table 2). Thus, the spray pattern is driven by the flow rate of the external fluid. The injected amine is stretched and thinned by the inertial drag force downstream. At the end of the flow, spherical droplets of a size larger than the filaments are eventually formed due to the rayleigh-taylor instability driven fluctuations. Amine droplets can break off when the viscous drag exceeds the surface tension that maintains the droplet at the end of the linear object. These parent droplets are the largest in size and decrease due to secondary breakup before application of sufficient confinement.

Next, the present invention investigated the effect of injection rate and rotation rate of the dispersed phase and continuous phase, respectively, on aspect ratio and diameter of the microcapsules, and the results are shown in fig. 8a-8b. As the rate ratio increases, both the diameter and aspect ratio tend to increase. The capillary number (Caout) of the external fluid is defined as:

Ca _out ＝η _out v _out /γ，

wherein eta _out And v _out Representing the viscosity and rate of the continuous phase, respectively. It represents a balance between viscous drag and surface tension acting on the liquid-liquid interface.

The importance of the intrinsic force of the inner stream with respect to the force of the surface is represented by its primary (Wein), primary being defined as:

We _in ＝ρ _in Lv _in ² /γ，

wherein ρ is _in Is the density of the disperse phaseL is a characteristic length equal to the jet diameter, v _in Is the rate of the dispersed phase.

We when increasing the rate of the dispersed phase _in And (3) increasing. Thus, the amine drop dome due to surface tension shrinkage is pushed downstream due to the enhanced inertial effect. In addition, the higher flow means the thread. The continuous phase stretches the amine liquid into the linear material easily due to the low surface tension between the two phases. At higher rates of continuous phase, shear stress increases and disturbances such as agitator vibration are also increased. Thus, the filaments become thinner and break, resulting in a lower aspect ratio.

Example 4-adjustment of Shell tightness and thickness of microcapsules by adjusting HMDI concentration

HMDI concentration affects not only tau of microcapsules _frozen In addition, the diffusion and interfacial polymerization of TEPA are affected, which in turn affects the properties of the shell. In this example, TEPA is selected as the model amine. FIG. 9 shows optical microscopic images of the reaction solution after 10 minutes of amine injection at room temperature and after completion of the reaction. The microcapsules obtained after the completion of the second step are much darker than the microcapsules after injection, due to the thickening of the microcapsule shell after long polymerization.

In addition, microcapsules prepared using high levels of HMDI are more transparent than microcapsules prepared with low levels of HMDI, possibly due to the thinner PU shell layer formed. More importantly, the reaction system varied significantly with the HMDI content. In batches with HMDI content of 0.99wt%, a large amount of fragments were formed in the continuous phase during the initial phase after injection, whereas at high HMDI content the continuous phase was very clear with very few fragments. The fragments highlight the reaction between the free TEPA molecules and the HMDI molecules diffusing in the paraffin oil. And a higher proportion of fragments indicates that TEPA diffuses more severely towards the interface.

Referring to fig. 10, SEM was used to characterize the shell thickness of PU-TEPA microcapsules. The thickness of the rough and smooth polyurea shells was estimated to be the same, and the average of the shell thicknesses at multiple locations was used as the apparent thickness. The results show that the thickness of the polyurea shell decreases dramatically with increasing HMDI content. The shell thickness of the microcapsules with 0.99wt% hmdi is too high leaving little room for the TEPA core. When the HMDI concentration was increased from 0.99wt% to 16.67wt%, the polyurea shell thickness was reduced from 29.0.+ -. 1.9 μm to 1.9.+ -. 0.3. Mu.m. The thickness of the shell layer reflects the thickness of the interfacial reaction zone. Low HMDI concentrations are not sufficient to limit the spread of TEPA because PU network formation is not tight. However, at very high HMDI concentrations, the PU shell layer is sufficiently dense to substantially reduce the diffusion of TEPA molecules into the continuous phase and further limit shell growth.

EXAMPLE 5 morphological evolution of the microcapsules at different reaction stages

In order to better control the production of microcapsules with optimized properties, it is necessary to study the morphological evolution of the microcapsules. Thus, several experiments were performed under different conditions. The samples were prepared at a HMDI concentration of 10.71 wt%. First, a sample of microcapsules was collected after injection for 5 minutes at room temperature. As shown in fig. 11a, the outer surface of the sample is smooth with discrete protrusions. In addition, the shell is partially broken under electron beam damage, which is caused by insufficient reaction resulting in low shell strength. When the reaction was prolonged to about 10 minutes, the outer surface of the microcapsules became coarser, but there was no sign of loose particles (fig. 11 b). Furthermore, from an estimation of the complete surface morphology (fig. 11 c), it can be concluded that the mechanical strength of the housing is sufficient to withstand the damage caused by the electron beam during observation of the sample.

Referring to fig. 12, the present invention further extends the observation time, recording morphology and structure evolution every 1 hour. After 1 hour a large amount of attached nanoparticles can be observed. Furthermore, over time, the particles of the outer surface become larger and larger. However, it is difficult to determine the variation in the number density of particles due to the complex surface structure and agglomeration of particles.

As can be seen from the structural integrity image shown in fig. 13, the earlier stage polyurea shell had a weaker mechanical strength during sample preparation and the shell collapsed rather than retaining its original spherical shape. The microcapsules with mechanically strong polyurea shells cannot be obtained until the reaction time is increased to 4 hours in step II and remain free-standing after drying. In summary, a reaction time of at least 4-5 hours is required to produce an amine capsule with the desired mechanical strength.

EXAMPLE 6 preparation of core ingredients of amine microcapsules

Referring to fig. 14, the large hollow area in the microcapsule indicates a high proportion of the core. The complete microcapsules were subjected to an isothermal TGA test at 140 ℃ to measure core content. At this temperature, TEPA decomposes severely, while the PU shell generally remains relatively stable. Thus, the TEPA core content can be accurately calculated by weight drop at 140 ℃. For the effect of HMDI content, it has been previously demonstrated that shell thickness decreases with increasing HMDII content. But for core content, there was a peak of 90.0wt% at an HMDII content of 13.79wt% (fig. 14a-14 b). Whereas at HMDI levels below 13.79wt%, the core content increases accordingly due to the formation of thinner shells. However, at higher HMDI levels, TEPA core levels decreased slightly despite shell thinning. This is probably due to the beginning of the formation of tubular microcapsules in the HMDI range and the higher specific surface area. At the lowest HMDI content of 0.99 wt.%, the core content was 0, indicating that the shell was extremely loose under this condition, and all TEPA diffused out for interfacial reaction.

During encapsulation, HMDI content plays a key role in shell thickness and compactability regulation. The stirring rate of the first stage stirrer had only a small effect on the core content, as shown in fig. 14c-14 d. When the stirring rate was increased from 50rpm to 650rpm, the core content was reduced from 91.8wt% to 84.5wt% mainly due to the larger specific surface area and shell ratio at the smaller microcapsule size. Microcapsules prepared using HMDI at a concentration higher than 3.85wt% HMDI have good core fraction. These results provide important guidance for the preparation of microcapsules with tunable properties.

EXAMPLE 7 microencapsulation of amines with longer Hydrocarbon chains

In this type , the spray of fluid is not connected to the oil phase before injection, and the second isocyanate in the phase immediately after injection is reacted. The golden mold can avoid the mutual scattering of two phases and the formation of a large amount of scraps, and is very beneficial to the compound of the aqueous amine coating of the carbon hydro- which is provided for sealing the components.

In this example, amine species with higher hydrophobicity, such as Jeffamine T403, are selected for encapsulation of the microcapsules. Since T403 has a longer carbon chain and a lower amine density, which may result in a lower crosslinking density of the gum shell, 25wt% TEPA (labeled 25TEPA75T 403) is added to T403 to increase the compactness of the gum shell. Referring to fig. 15, 25TEPA75T40 microcapsules having both spherical and tubular shapes can be prepared by adjusting parameters. The TGA profile of the pure core material and microcapsules is shown in figure 16. Due to the complex composition of the core material, it is difficult to determine the core content by isothermal processing. Only the microcapsules and the residual gum shell need to be weighed, a core content of about 86.3wt% can be obtained, which proves to be very effective for encapsulating highly hydrophobic amines.

Definition of the definition

Throughout this specification, unless the context requires otherwise, the term "comprise" or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure, particularly in the claims or the period, terms such as "comprise" or "include" or "comprise" have the meaning given to them in U.S. patent law. For example, they allow elements not recited to be defined, but exclude elements found in the prior art or that affect the basic or novel features of the invention.

Furthermore, throughout the specification and claims, unless the context requires otherwise, the term "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

As used herein, the terms "substantially", "essentially", "about" and "approximately" are used to describe and explain a minor variation. When used in connection with an event or circumstance, the term can refer to the instance in which the event or circumstance occurs accurately, as well as the instance in which the event or circumstance occurs approximately. For example, when used with a numerical value, these terms may encompass a variation of less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

Reference in the specification to "one embodiment," "an example embodiment," and the like, means that a particular feature, structure, or characteristic may be included in the described embodiments, but every embodiment may not necessarily include the particular feature, structure, or characteristic, and may not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

In the preparation methods described herein, the steps may be performed in any order without departing from the principles of the invention unless a temporal order or an order of operation is explicitly recited. In one claim, it should be noted that one step is performed before several other steps are performed, meaning that the first step is performed before any other step, but the other steps may be performed in any suitable order unless a sequence is further recited in the other steps. For example, claim elements listing "step a, step B, step C, step D, and step E" should be understood to mean that step a is performed first, step E is performed last, steps B, C and D can be performed in any order between steps a and E, and that the order is still within the literal scope of the claim process. A given step or subset of steps may also be repeated.

The term "TEPA (Triethylenetetramine)" is an organic compound, also known as TEPA amine, which is obtained from the reaction of four ethanolamine molecules via the synthesis of a mutually halogenated amine. TEPA has a chemical structure comprising a main amine group (NH) ₂ ) And three secondary amine groups.

The term "Jeffamine T403" is a polyetheramine having a low molecular weight. It is prepared by condensation reaction of trimeric propanol and tri-polyether amine. Jeffamine T403 has multiple functional groups and can be used as a cross-linking agent, an amine catalyst or an auxiliary agent in the fields of polymers, coatings, adhesives and the like. It has lower viscosity and high reactivity and can be used to improve the properties of certain materials, such as enhanced elasticity, heat resistance and chemical resistance.

The term "Jeffamine D2000" is a polyetheramine having a high molecular weight. It is prepared by condensation reaction of diisocyanate and polyether amine. Jeffamine D2000 has a relatively high viscosity and long chain structure and can be used as a softener, a cross-linking agent, an adhesive and a thickener in coatings. Because of its relatively high molecular weight, it has relatively high softness, viscosity and adhesion properties in some applications.

Several embodiments and detailed features of the present disclosure are briefly described above. The embodiments described in this disclosure may be readily used as a basis for designing or modifying other processes and structures to achieve the same or similar objects and/or to obtain the same or similar advantages introduced in the embodiments of this disclosure. Such equivalent constructions do not depart from the spirit and scope of the present disclosure, and various changes, substitutions, and modifications may be made therein without departing from the spirit and scope of the present disclosure.

Claims

1. An amine-containing microcapsule, wherein the amine-containing microcapsule comprises:

a liquid core material comprising a

An amine liquid having a seed viscosity range of 100 to 300 mPas; a kind of electronic device with high-pressure air-conditioning system

A polymer shell material is polyurea and/or polyurea

An analogue thereof, and said polymeric shell material surrounding the liquid core material,

wherein, the amine liquid and diisocyanate and the analogues thereof are subjected to instant interfacial polymerization to form a core-shell structure, the shell layer of the core-shell structure is a polyurea shell layer and/or a similar shell layer, the core of the core-shell structure is an amine liquid core material,

the time scale for the amine liquid jet to break up into fragments or droplets is defined as τ _inst Whereas the reaction time of the amine liquid with the diisocyanate and its analogues to form the core-shell structure is defined as τ _frozen When τ _inst >τ _frozen Obtaining said microcapsules having an aspect ratio higher than 1.0; when τ is _inst≤ τ _frozen When the amine liquid jet breaks up into spherical droplets less than 200 microns in diameter before being solidified into the microcapsules.

2. The amine-containing microcapsule of claim 1, wherein the liquid core material comprises a hydrophilic amine or an amine having a long hydrocarbon chain.

3. The amine-containing microcapsule of claim 2, wherein the liquid core material comprises tetraethylenepentamine, polyetheramine, or a combination thereof.

4. The amine-containing microcapsule according to claim 2, wherein the liquid core material is present in an amount of 1 to 95wt% of the total amount of the amine-containing microcapsule, and the polyurea and/or analogue thereof is present in an amount of 5 to 99wt% of the total amount of the amine-containing microcapsule.

5. The amine-containing microcapsule of claim 1, wherein the amine-containing microcapsule has a thickness in the range of 1 micron to 40 microns.

6. The amine-containing microcapsule of claim 1, wherein the amine-containing microcapsule has a diameter in the range of 1 micron to 200 microns.

7. The amine-containing microcapsule according to claim 1, wherein the amine-containing microcapsule has an aspect ratio in the range of 1-30.

8. The amine-containing microcapsule of claim 1, wherein the amine-containing microcapsule is spherical, tubular, cylindrical, or filamentous.

9. A process for preparing an amine-containing microcapsule according to claim 1, characterized in that it comprises:

directly injecting an amine liquid with a viscosity ranging from 100 mPa-s to 300 mPa-s into the continuous oil phase at room temperature by means of a microfluidic device;

Stirring the continuous oil phase for a duration of 10 to 30 minutes by means of a stirrer provided in the microfluidic device to perform interfacial polymerization to form a mixture containing primary microcapsules comprising amine;

the mixture was reacted at 40 ℃ for 2 hours followed by 50 ℃ for 2 hours and finally 60 ℃ for 2 hours to form the amine-containing microcapsules.

10. The method of claim 9, wherein the continuous oil phase comprises an oil, a diisocyanate and/or its analogues and a surfactant, the amine liquid and the diisocyanate and its analogues forming a polyurea and/or its analogue shell structure by instant interfacial polymerization therebetween.

11. The method of claim 10, wherein the time scale for the amine liquid jet to break up into fragments or droplets is defined as τ _inst The reaction time of the amine solution with the diisocyanate and the like to form the shell layer is defined as τ _frozen When τ _inst >τ _frozen Obtaining said microcapsules having an aspect ratio higher than 1.0; when τ is _inst≤ τ _frozen When the amine liquid jet breaks up into spherical droplets having a diameter of less than 200 microns before being solidified into the microcapsules.

12. The method of claim 10, wherein the oil comprises one or more of a paraffinic oil and/or an analog thereof selected from mineral oil, n-hexane, cyclohexane, hexadecane, toluene, xylene, decalin, or polyisobutylene, the diisocyanate and analog thereof selected from one or more of hydrogenated diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, lysine diisocyanate, polymethylene polyphenyl polyisocyanate, 2, 6-diisocyanatotoluene ester, 1, 3-diisobenzocyanate, 1, 4-diisocyanatobutane, terephthalyl diisocyanate, 1, 4-dithioisocyanatobutane, or hexamethylene diisocyanate, and the surfactant is selected from one or more of Span 80, span 85, TERGITOL alkoxypolyethylene hydroxyl ethanol, tridecyl polyoxyethylene stearyl ether, sodium dodecyl benzene sulfonate, 2-ethylhexanol EO-PO, polyvinyl alcohol, polyoxyethylene sorbitol anhydride brown acid ester, sorbitol sorbitan stearate, polyoxyethylene sorbitan tristearate, or polyoxyethylene sorbitan tristearate.

13. The method of claim 10, wherein the amine liquid is present in an amount of 1wt% to 95wt% of the total amount of the amine-containing microcapsules and the polyurea and/or analog thereof is present in an amount of 5wt% to 99wt% of the total amount of the amine-containing microcapsules.

14. The method of claim 9, wherein the amine liquid comprises tetraethylenepentamine, polyetheramine, or a combination thereof.

15. The method of claim 9, wherein the concentration of the active agent is 0.01 mL/min ^-1 To 5.0 mL-min ^-1 Is injected into the continuous oil phase.

16. The method of claim 9, wherein the stirring rate is 10rpm to 700rpm.

17. The process of claim 9, wherein the process further comprises washing the amine-containing microcapsules at least twice with n-hexane, and then drying them.