Do-it-yourself repair materials

Abstract

Disclosed herein is a self-healing material that includes microcapsules containing a monomeric or oligomeric repair agent, as well as a catalyst capable of catalyzing the polymerization of the monomeric or oligomeric repair agent.

Description

[Technical Field]

[0001] The present invention relates generally to self-healing materials and methods for enabling self-healing materials to heal themselves. [Background technology]

[0002] A self-healing material is a substance that has the ability to automatically repair damage to itself without external diagnosis of the problem or human intervention. Materials typically degrade over time due to fatigue, environmental exposure, or damage that occurs during the operation of the device that uses the material. Cracks and other types of damage are known to result in changes in the thermal, electrical, and acoustic properties of the material, ultimately leading to its failure (e.g., due to crack propagation within the material). In conventional materials, early detection of damage (e.g., cracks) is difficult, typically requiring periodic inspection and repair. Self-healing materials, in contrast, counteract degradation by initiating repair mechanisms in response to microscopic damage.

[0003] Self-healing materials have attracted significant commercial interest due to their potential for longer service lives and reduced maintenance costs compared to conventional materials. Self-healing materials have many promising applications in the built environment, and their importance is expected to grow in a carbon-constrained world as they enable improved resource efficiency. Humanity's reliance on fossil fuels and petrochemical feedstocks requires a well-connected and robust infrastructure. Therefore, infrastructure failures can have significant environmental impacts, such as oil spills and gas leaks. However, pipes transporting oil and CO2 at high pressures are exposed to highly corrosive environments, which can damage the materials used in the pipes. Furthermore, oil and gas pipes are often located underground (exposed to corrosion from soil) or underwater (exposed to corrosion from saltwater), making these locations difficult to access for inspection and repair. Incorporating self-healing mechanisms into these pipes to extend their lifespan would greatly benefit the industry.

[0004] Current pipeline technology uses a three-layer system, which is prone to failure under certain environmental conditions. The metal surface of the pipe is coated with an epoxy primer to facilitate adhesion of the polypropylene layer and inert polypropylene topcoat. The epoxy primer and polypropylene adhesive layer contain accessible functional groups that can be used for self-healing.

[0005] One class of self-healing materials involves encapsulating a healing agent (e.g., in microcapsules) within a polymer matrix. Capsule-based self-healing polymer composites were first reported by [1]. When a crack forms and propagates through the polymer matrix, the microcapsules rupture, releasing the healing agent at the crack plane. The catalyst is dispersed throughout the polymer matrix, and the healing agent eventually comes into contact with the dispersed catalyst. This triggers curing / polymerization, repairing the crack plane and restoring mechanical integrity (or cohesion).

[0006] Most self-healing materials reported to date are based on ring-opening metathesis polymerization (ROMP) using precious metal catalysts, such as Grubb's catalyst (ruthenium-based) or platinum nanoparticles. Grubb's catalysts are not only very expensive, but also do not exhibit long-term stability under environmental conditions where encapsulated self-healing materials would be useful (e.g., pipelines used for oil and gas). Thus, precious metal catalysts are impractical for use in self-healing materials that operate under harsh environmental conditions, such as those used in commercial oil and gas transportation.

[0007] Another method uses dual microcapsules that encapsulate the repair agent and the polymerizer / hardener separately. However, the process of encapsulating the hardener is very complicated, and this method is not commercially viable due to its high complexity and high cost. Furthermore, this method requires that both the repair agent and the polymerizer / hardener be homogeneously mixed by rupturing equal numbers of capsules. Furthermore, the amount of each capsule required to ensure self-healing approaches 30% by weight for each capsule type, so including two separate types of capsules may affect the properties of the material. Finally, the liquid reagents used in this method may not have the stability required for use in self-healing materials designed for long product life, especially when these materials are exposed to harsh environments.

[0008] In view of the above, there is a need for new and improved self-healing materials, particularly in the oil and gas industry. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] White et al., Nature 2001, 409, pp. 794-797 Summary of the Invention

[0010] The present inventors have surprisingly discovered that these challenges can be overcome by providing catalysts in the form of metal-organic frameworks (MOFs). Due to their stability and customizable functionality for anchoring within polymer matrices, MOFs are well suited for incorporation into various layers of petroleum pipelines and other polymer-based materials. For example, the inner layers of petroleum pipelines often contain functional groups such as hydroxyl, epoxy, maleimide, and anhydride, which can be used as anchor points for functionalized MOF backbones. Because inner layers are exposed to particularly harsh conditions, the use of self-healing materials in the construction of these layers is expected to be particularly useful for ensuring satisfactory product life.

[0011] Thus, the present invention provides the following: [1] Polymer matrix, a microcapsule comprising a shell portion and a hollow core portion, the microcapsules being dispersed within the polymer matrix, the hollow core portion being filled with a monomeric or oligomeric repair agent; and A metal-organic framework catalyst suitable for catalyzing the polymerization of the monomeric or oligomeric repair agent.

[0012] [2] The self-healing material according to item 1, wherein the metal-organic framework catalyst is dispersed within the polymer matrix.

[0013] [3] The self-healing material according to item 1 or 2, wherein the shell portion of the microcapsule is formed from one or more of the group consisting of urea-formaldehyde, polysulfone, and polymethyl methacrylate.

[0014] [4] The self-healing material according to item 3, wherein the shell portion of the microcapsule is formed from urea-formaldehyde, and optionally, the urea-formaldehyde is melamine-modified urea-formaldehyde.

[0015] [5] The self-repairing material according to any one of items 1 to 4, wherein the microcapsules have an average diameter of about 20 μm to about 200 μm, optionally about 50 μm to about 100 μm.

[0016] [6] The self-repairing material according to any one of items 1 to 5, wherein the shell portion of the microcapsules has an average thickness of about 100 nm to about 500 nm, optionally about 200 nm to about 400 nm, more optionally about 250 nm to about 350 nm, for example about 300 nm.

[0017] [7] The self-repairing material according to any one of items 1 to 6, comprising about 10 to about 30 wt. % microcapsules, optionally about 12 to about 25 wt. %, more optionally about 15 to about 25 wt. %, for example about 20 wt. % microcapsules.

[0018] [8] The self-healing material according to any one of items 1 to 7, comprising about 1 to about 10 wt% of the metal-organic framework catalyst, optionally about 3 to about 8 wt%, more optionally about 4 to about 6 wt%, for example about 5 wt% of the metal-organic framework catalyst.

[0019] [9] The self-healing material of item 1, wherein the shell portion of the microcapsule comprises an inner portion and an outer portion, and the outer portion comprises a metal-organic framework catalyst.

[0020]

[10] The self-healing material of item 9, wherein the inner portion is formed from a polymerized monomeric or oligomeric repair agent.

[0021]

[11] The self-healing material of paragraph 9 or 10, wherein the outer portion is formed from a polymerized monomeric or oligomeric repair agent, or the outer portion is formed from one or more of the group consisting of urea-formaldehyde, polysulfone, and polymethyl methacrylate.

[0022]

[12] The self-healing material of item 11, wherein the outer portion is formed from a polymerized monomeric or oligomeric repair agent.

[0023]

[13] The self-healing material of paragraph 11, wherein the outer portion is formed from urea-formaldehyde, and optionally, the urea-formaldehyde is melamine-modified urea-formaldehyde.

[0024]

[14] The self-repairing material according to any one of items 9 to 13, wherein the average diameter of the microcapsules is about 20 to about 200 μm, optionally about 50 to about 100 μm.

[0025]

[15] The self-repairing material according to any one of items 9 to 14, wherein the shell portion of the microcapsules has an average thickness of about 100 nm to about 500 nm, optionally about 200 nm to about 400 nm, more optionally about 250 nm to about 350 nm, for example about 300 nm.

[0026]

[16] The self-repairing material according to any one of items 9 to 15, comprising about 10 to about 40 wt% of metal-organic framework-containing microcapsules, optionally about 15 to about 35 wt%, more optionally about 20 to about 30 wt%, for example about 25 wt% of metal-organic framework-containing microcapsules.

[0027]

[17] The self-healing material according to any one of items 9 to 16, comprising about 1 to about 10 wt% of the metal-organic framework catalyst, optionally about 3 to about 8 wt%, more optionally about 4 to about 6 wt%, for example about 5 wt% of the metal-organic framework catalyst.

[0028]

[18] The self-repairing material according to any one of items 1 to 17, wherein the monomeric or oligomeric repair agent comprises an epoxy resin, optionally a bisphenol-based epoxy resin.

[0029]

[19] The epoxy resin comprises an epoxy resin selected from the group consisting of bisphenol-based epoxy resins; glycidyl ether resins; glycidyl aniline resins; and novolac, aliphatic, cycloaliphatic, aromatic, and bio-based epoxy resins having 1 to 6, for example 1 to 4, epoxy groups; Optionally, the epoxy resin is selected from the group consisting of bisphenol F diglycidyl ether (DGEBF), bisphenol A diglycidyl ether (DGEBA), and "Araldite (registered trademark) LY564". The self-healing material according to any one of items 1 to 18.

[0030]

[20] The self-repairing material according to any one of items 1 to 19, wherein the metal-organic framework comprises a zeolite-imidazolate framework.

[0031]

[21] The self-healing material according to any one of items 1 to 20, wherein the metal-organic framework comprises a ligand selected from the group consisting of imidazole, 2-methylimidazole, 2-nitroimidazole, 4,5-dichloroimidazole, 2-imidazolecarboxaldehyde, and combinations thereof.

[0032]

[22] The self-repairing material according to any one of items 1 to 21, wherein the metal-organic framework comprises a zeolite-imidazolate framework selected from the group consisting of ZIF-2, ZIF-3, ZIF-4, ZIF-8, ZIF-67, ZIF-65, ZIF-77, ZIF-71, ZIF-72, ZIF-90 and combinations thereof.

[0033]

[23] The self-repairing material according to any one of items 1 to 22, wherein the metal-organic framework comprises ZIF-8.

[0034]

[24] A method for repairing a self-healing material according to any one of items 1 to 23, comprising exposing the self-healing material to conditions suitable for polymerization of the monomeric or oligomeric repair agent.

[0035]

[25] The method of claim 24, wherein the conditions suitable for polymerization of the monomeric or oligomeric repair agent of the self-healing material include a temperature of about 20°C to about 180°C.

[0036]

[26] The method of paragraph 24 or 25, wherein the self-healing material is exposed to conditions suitable for polymerization of the monomeric or oligomeric repair agent for at least 1 hour, optionally at least 2 hours, more optionally at least 6 hours, further optionally at least 10 hours, even further optionally at least 16 hours, for example at least 24 hours.

[0037]

[27] The method of any one of paragraphs 24 to 26, wherein the self-healing material forms part of an oil or gas pipeline maintained under conditions suitable for polymerization of the monomeric or oligomeric repair agent. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1 shows the general structure of a zeolite-imidazolate framework. [Figure 2] FIG. 1 is a diagram showing a polymerization reaction of imidazole and an epoxy resin. [Figure 3] FIG. 3 shows the propagation of a crack 301 through a self-healing material 302. As the crack propagates, microcapsules 303 containing a monomeric or oligomeric repair agent rupture, releasing the repair agent into the crack (step ii)). The repair agent comes into contact with a metal-organic framework catalyst 304 embedded in a polymer matrix, catalyzing the polymerization of the repair agent to produce solid polymers 305a, 305b in the crack and microcapsules, thereby repairing the crack. [Figure 4] FIG. 1 shows the XRD spectrum of ZIF-8 synthesized according to Preparation Example 1. [Figure 5] FIG. 1 is a SEM image of ZIF-8 particles synthesized according to Preparation Example 1. [Figure 6a] 1 is an SEM image of microcapsules synthesized according to Preparation Example 2. [Figure 6b] 1 is a high-magnification SEM image of a single microcapsule synthesized according to Preparation Example 2. [Figure 7]7 is an optical microscope image of ruptured microcapsules showing released epoxy as described in Preparative Example 2. Capsule 701 is ruptured to release epoxy 702. [Figure 8] 1 is a microscope image of a cured RIM935 / 936 epoxy matrix incorporated into a MUF / epoxy capsule, as described in Preparation Example 2. [Figure 9a] 1 is an SEM image of a cross section of a RIM935 / 936-MUF / epoxy composite showing ruptured capsules, as described in Preparation Example 2. [Figure 9b] 1 is a high-magnification SEM image of the shell portion of a microcapsule synthesized according to Preparation Example 2. [Figure 10] 1 is a graph showing an in-situ repair temperature profile as described in Example 1. [Figure 11] FIG. 1 shows the in situ repair process of a) untreated RIM935, b) 8% ZIF8 in RIM935, and c) 25% capsule-8% ZIF8 in RIM935, as described in Example 1. [Figure 12] Shown are microscopic images of a) untreated RIM935 sample, b) 8% ZIF8 sample in RIM935, and c) 25% capsule-8% ZIF8 sample in RIM935 before (left) and after (right) healing, as described in Example 2, where 1201 indicates released epoxy and 1202 indicates cured epoxy. [Figure 13] 1 shows the logarithm of |Z| at a frequency of 0.1 Hz for RIM935 untreated samples, and control and self-healing samples with different concentrations of MUF capsules and ZIF8 after scratching and healing at 60°C for 12 hours, as described in Example 3. [Figure 14] 1 is an optical microscope image of a sample after 20 hours of electrochemical impedance spectroscopy (EIS) testing as described in Example 3. [Figure 15] FIG. 10 shows the repair efficiency as a function of temperature for samples with 25% MUF capsules and 8% ZIF8, as described in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0039] In embodiments herein, the word "comprising" may be interpreted to require the recited features, but not to limit the presence of other features. Alternatively, the word "comprising" may relate to a situation where only the recited components / features are intended to be present (e.g., the word "comprising" may be replaced with the phrase "consists of" or "consists essentially of"). It is expressly contemplated that both broader and narrower interpretations may apply to all aspects and embodiments of the invention. In other words, the word "comprising" and its equivalents may be replaced with the phrases "consists of" or "consists essentially of" or their equivalents, and vice versa.

[0040] The present invention provides a self-healing material. As used herein, a "self-healing material" is a material that can at least partially repair defects formed in or on the material. For example, a self-healing material may be capable of at least partially repairing cracks and / or scratches formed in or on the material. In certain embodiments that may be described herein, the self-healing material can at least partially repair cracks formed in the material. Heating the material as described herein may be necessary to cause the self-healing process to occur. The self-healing ability of a material can be determined by any suitable method known in the art, such as electrical impedance spectroscopy (EIS) or a "Single Edge Notched Bend test" such as ASTM 5045. Measurements after self-healing can be compared to a control to determine the extent of repair. In embodiments described herein, when subjected to appropriate conditions, the self-healing material has a repair efficiency determined by these methods of at least 50%, e.g., at least 60%, at least 70%, at least 80%, or at least 90%, and references to at least partial repair should be interpreted accordingly.

[0041] The self-healing material includes microcapsules. As used herein, a microcapsule is a microparticle that includes a solid shell encapsulating a core.

[0042] The solid shell portion of the microcapsule may be formed from any suitable material, such as urea-formaldehyde resin, polysulfone, polymethyl methacrylate, and combinations thereof. In the embodiments of the present invention described above, the solid shell portion of the microcapsule comprises urea-formaldehyde resin. In the embodiments of the present invention described above, when the solid shell portion of the microcapsule comprises urea-formaldehyde resin, it may comprise a melamine-modified urea-formaldehyde resin (MUF), which is itself formed from a mixture of melamine, urea, and formaldehyde. The melamine-modified urea-formaldehyde resin has good thermal stability and barrier properties due to the triazine ring of melamine, and also improves stability in humid environments.

[0043] The core of the microcapsule is filled with a monomeric or oligomeric repair agent, which is provided as a liquid. As used herein, "filled with" means that the hollow volume of the core is at least partially filled with the monomeric or oligomeric repair agent. For example, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, for example, about 100% of the volume of the core of the microcapsule may be filled with the monomeric or oligomeric repair agent. Typically, at least 90%, for example, at least 95%, at least 99%, for example, about 100% of the volume of the core of the microcapsule may be filled with the monomeric or oligomeric repair agent.

[0044] The monomeric or oligomeric repair agent is provided in a form that allows it to be released from the microcapsules when the shell is ruptured. Thus, when the microcapsules are ruptured by a scratch or crack, the monomeric or oligomeric repair agent can flow into or otherwise occupy the voids formed by the scratch or crack. Once the repair agent flows into the voids, it comes into contact with the metal-organic framework catalyst. The monomeric or oligomeric repair agent is compatible with the metal-organic framework catalyst such that the catalyst catalyzes the polymerization reaction of the monomeric or oligomeric repair agent. Thus, when the monomeric or oligomeric repair agent comes into contact with the metal-organic framework catalyst, a polymerization reaction occurs, forming a solid polymer within the voids. This fills the voids and repairs the self-healing material.

[0045] Any monomeric or oligomeric repair agent may be used as long as it flows into voids created by scratches or cracks to fill the voids. For this reason, liquid monomeric or oligomeric repair agents are particularly preferred. A specific class of monomeric or oligomeric repair agents that can be used in the embodiments described herein are epoxy resins, which are advantageously inexpensive and easy to polymerize using readily available catalysts such as amines and imidazoles. As used herein, epoxy resin refers to a composition containing a monomer and / or prepolymer containing epoxide functionality. Specific epoxy resins that can be used in the present invention include bisphenol-type epoxy resins; glycidyl ether resins; glycidyl aniline resins; and novolac, aliphatic, cycloaliphatic, aromatic, and bio-based epoxy resins having 1 to 6, e.g., 1 to 4, epoxy groups. Specific epoxy resins that may be used in the embodiments of the invention described herein are bisphenol F diglycidyl ether (DGEBF), bisphenol A diglycidyl ether (DGEBA), and Araldite® LY564.

[0046] Any metal-organic framework catalyst can be used as long as it is compatible with the monomer or oligomer repair agent. Metal-organic framework catalysts offer advantages over noble metal catalysts in terms of their ease of preparation, low cost, and stability over the lifetime of the self-healing material. Among metal-organic frameworks, zeolite-imidazolate frameworks (ZIFs) can be used because they are robust, easy to synthesize on a large scale, and significantly cheaper than noble metal catalysts. ZIFs can catalyze the polymerization of epoxy functional groups due to the presence of a nucleophilic nitrogen atom on the imidazole ring.

[0047] The general structure of ZIF is shown in Figure 1. This structure consists of a tetrahedrally coordinated transition metal ion surrounded by imidazolate or imidazolate derivative (i.e., imidazole or imidazole derivative with the nitrogen atom deprotonated) ligands. The imidazolate ligands are thought to coordinate to the transition metal ion through the nitrogen atom. The structures of imidazole and imidazolate are shown below. TIFF0007737394000001.tif2071Imidazole Imidazolate

[0048] As will be understood by those skilled in the art, the ZIFs used in the present invention may contain imidazolate ligands or imidazolate derivative ligands, which may be substituted at one or more positions on the imidazole ring as shown below. TIFF0007737394000002.tif4184Imidazole derivatives Imidazolate derivatives

[0049] In an embodiment of the present invention, the transition metal ion in the ZIF is selected from the group consisting of Fe, Co, Cu and Zn, and the transition metal ion has a 2+ charge.

[0050] Generally, the ratio of imidazolate / imidazolate derivative ligands to metal ions is such that the overall charge of the ZIF is neutral. For example, if the transition metal ion has a 2+ charge, the ratio of imidazolate ligands to metal ions is 2:1.

[0051] There are many ZIFs, and as shown in Figure 1, they share a common structure: a framework containing imidazolate ligands. The imidazolate ligands may be derived from imidazole (ZIF-2 to ZIF-4), 2-methylimidazole (ZIF-8 or ZIF-67), 2-nitroimidazole (ZIF-65 and ZIF-77), 4,5-dichloroimidazole (ZIF-71 and ZIF-72), or 2-imidazolecarboxaldehyde (ZIF-90). The functional groups on the imidazole ligands can be tailored to achieve desired properties. The key factor in the reactivity of the imidazolate ligands and their ability to catalyze the epoxy curing reaction is the steric hindrance of the tertiary amine. Controlling the side chains on the imidazolate ligands allows for tuning of the reactivity of the tertiary amine and, therefore, the reactivity of the ZIF catalyst.

[0052] Furthermore, the particle size of the resulting ZIF particles can be controlled by varying synthesis conditions such as the stirring speed of the ZIF precursor mixture, the ratio of ZIF precursors (ratio of imidazole to metal ions), the type of ZIF precursor, and the solvent. Higher stirring speeds result in smaller ZIF particle sizes, and higher imidazole to metal ion ratios also result in smaller particle sizes. The solvent used influences the rate of ZIF formation and the resulting particle size. Without being bound by theory, it is believed that the hydrogen bond-donating ability of the solvent influences the crystallization rate and the resulting particle size. Suspending the catalytic imidazole moiety in the solid state avoids the challenges associated with liquid reagents.

[0053] Another advantage associated with the use of MOFs is their ability to form Pickering emulsions (liquid / liquid emulsions stabilized by the presence of solid particles at the liquid / liquid interface). Advantageously, microcapsules can be fabricated from Pickering emulsions to produce microcapsules with a MOF catalyst in the microcapsule shell and a monomeric or oligomeric repair agent in the microcapsule core. This can be achieved by adding the repair agent to the oil phase of an oil / water emulsion. When the solid MOF catalyst is added, it collects at the oil / water interface. This results in polymerization of the repair agent at the oil / water interface, forming a solid shell containing the polymerized repair agent and MOF surrounding the liquid repair agent core. This shell physically separates the MOF from the liquid repair agent, forming a multifunctional capsule containing the repair agent with a catalytic shell. Rupture of the capsule releases the repair agent, ensuring contact with the ZIF catalyst. This advantageously results in improved consistency and reliability of self-healing compared to self-healing materials in which the catalyst and healing agent particles are separate.

[0054] When microcapsules are formed from Pickering emulsions as described above, the shell is formed from the polymerization of the liquid monomeric or oligomeric repair agent. As the polymerization reaction progresses, a thin layer of polymer forms, separating the passive MOF from the liquid repair agent core. This prevents further polymerization of the liquid repair agent core. Thus, the microcapsule shell comprises an inner layer or portion of a brittle polymer (which may include other components from the oil phase, such as polystyrene or divinylbenzene) that separates the MOF from the liquid core, and an outer brittle shell layer or portion containing the MOF. Given that the MOF may not be uniformly distributed around each oil droplet in the Pickering emulsion, there may not be a clear boundary between the inner and outer shell layers / portions. The MOF may be present in the outer layer (i.e., the outer layer is a thin layer partially permeated by the MOF), or the MOF may be dispersed within the outer layer (i.e., the outer layer is thicker and completely covers the MOF).

[0055] Thus, in embodiments of the present invention disclosed herein, the shell portion of the microcapsule may contain a metal-organic framework catalyst. As will be understood by those skilled in the art, when the shell of a microcapsule containing a MOF catalyst is prepared from a Pickering emulsion, the formed shell prevents contact between the monomeric or oligomeric repair agent and the MOF catalyst. Thus, in embodiments of the present invention, the shell portion of the microcapsule may include an inner portion in contact with the monomeric or oligomeric repair agent and an outer portion containing the MOF catalyst. The inner portion of the shell (in contact with the monomeric or oligomeric repair agent) is formed from polymerized monomeric or oligomeric repair agent and does not contain the MOF catalyst (i.e., some of the polymerized repair agent is present between the monomeric or oligomeric repair agent and the MOF catalyst). The inner portion is a thin portion of the microcapsule shell that separates the MOF catalyst from the liquid monomeric or oligomeric repair agent within the core of the microcapsule. The outer portion may also be formed from polymerized monomeric or oligomeric repair agent and is the portion of the shell containing the MOF catalyst. In this case, the MOF catalyst may be present on the outer surface of the outer shell portion or may be present within the outer shell portion. Furthermore, when the inner and outer portions are formed from a polymeric repair agent, there does not necessarily need to be a clear boundary between the inner and outer shell portions.

[0056] The outer shell portion may be formed from one or more of a different material, such as urea-formaldehyde, polysulfone, and polymethyl methacrylate. In this case, the microcapsule shell will be composed of an inner shell portion that does not contain a MOF catalyst and is in contact with the monomeric or oligomeric repair agent corresponding to the inner shell portion described above. The microcapsule shell will also be composed of an outer shell portion formed from the different material and an intermediate portion between the inner and outer portions. The MOF catalyst will be located in the intermediate portion, for example, dispersed within or on the portion of the polymeric repair agent that does not form part of the inner shell portion. In this case, there may be a clear boundary between the outer shell portion and the remainder of the microcapsule.

[0057] In some embodiments of the invention disclosed herein, the microcapsule shell portion may comprise a ZIF catalyst and the core may comprise a monomeric or oligomeric epoxy resin curing agent.

[0058] The self-healing material may comprise a polymer matrix, and the microcapsules may be dispersed within the polymer matrix. In embodiments of the invention that may be described herein, the self-healing material may comprise a polymer matrix, and the microcapsules may be dispersed approximately uniformly throughout the self-healing material, such as throughout substantially all or all of the polymer matrix. When the metal-organic framework catalyst is present in a polymer matrix separate from the microcapsules, the metal-organic framework catalyst may be dispersed approximately uniformly throughout the self-healing material, such as throughout substantially all or all of the polymer matrix.

[0059] As will be appreciated by those skilled in the art, there will be some variation in the shape and size of microcapsules. In the embodiments of the present invention described hereinabove, the average diameter of the microcapsules may be about 20 to about 200 μm, for example, about 50 to about 100 μm. Typically, the solid shell portion of the microcapsules in the self-healing material may have an average thickness of about 100 nm to about 500 nm, for example, about 200 nm to about 400 nm, such as about 300 nm. As used herein, average diameter and average thickness refer to the arithmetic mean diameter and arithmetic mean thickness of all of the microcapsules and microcapsule shell portions in a sample.

[0060] For the avoidance of doubt, when any numerical range is used herein, the higher and lower values ​​of any relevant range may be combined to provide new ranges, all of which are specifically contemplated herein. For example, the solid shell portion of the microcapsules in the self-healing material may fall within the following numerical ranges: about 100nm to about 200nm, about 100nm to about 300nm, about 100nm to about 400nm, about 100nm to about 500nm; Approximately 200nm to approximately 300nm, approximately 200nm to approximately 400nm, approximately 200nm to approximately 500nm; Approx. 300nm ~ approx. 400nm, approx. 300nm ~ approx. 500nm; Approximately 400nm~approximately 500nm; The thickness may be defined by:

[0061] The present invention also provides a method of repairing the self-healing material described herein, the method comprising the step of exposing the self-healing material to conditions suitable for polymerization of the monomeric or oligomeric repair agent.

[0062] The healing of the self-healing materials disclosed herein can occur over a wide range of temperatures. For example, polymerization of the monomeric or oligomeric healing agent may occur at temperatures ranging from room temperature to about 200°C. Furthermore, as will be appreciated by those skilled in the art, the healing process generally becomes faster when the self-healing material is heated to a higher temperature. Thus, if a lower temperature is used, the healing process is expected to take longer, while if a higher temperature is used, the healing process is expected to be shorter. This is evident from the following examples. While healing at room temperature is slower than healing at higher temperatures, this is generally not a problem because the self-healing material heals in situ and healing times are often not significant. Depending on the environment in which the self-healing material is used, non-limiting examples of temperatures and applications for the self-healing material include room temperature (for general construction applications), approximately 40°C to 80°C (for oil pipeline applications), and approximately 100°C to 180°C (for industrial processes requiring high temperatures). In some embodiments of the present invention, the self-healing material is capable of self-healing at temperatures of about 20°C to about 180°C.

[0063] In many cases, the self-healing material will heal at the ambient temperature of the environment in which it will be used, whether that be room temperature or a much higher temperature, such as about 150° C. However, as will be understood by those skilled in the art, if the repair process involves heating the material to an elevated temperature, the self-healing material will be exposed to the elevated temperature for an extended period of time. In such embodiments of the invention described hereinabove, the self-healing material may be heated to the elevated temperature for at least 1 hour, at least 2 hours, at least 6 hours, at least 10 hours, or at least 16 hours, for example, about 24 hours.

[0064] In certain embodiments, the self-healing material forms part of an oil or gas pipeline. In this embodiment, normal operating conditions of the oil or gas pipeline may be sufficient to polymerize the healing agent upon contact with the MOF catalyst. In other words, the oil or gas pipeline may operate at a temperature sufficient for polymerization to occur, and the self-healing material will be exposed to this temperature long enough to ensure healing occurs.

[0065] The present invention is illustrated by the following examples which should not be construed as limiting. [Example]

[0066] The "Epikote RIM935" and "Epikure RIMH936" resin systems used in the following examples were obtained from Hexion, Inc. (Columbus, Ohio).

[0067] Preparation Example 1: Synthesis of ZIF-8 5.9 g of Zn(NO3)2-6H2O was dissolved in 400 mL of water to form solution A, and 113 g of 2-methyl-1H-imidazole was dissolved in 400 mL of water to form solution B. The two solutions were mixed and vigorously stirred at room temperature for 1 h. The resulting ZIF-8 particles were collected by centrifugation at 10,000 rpm for 30 min and then washed three times with water. The resulting ZIF-8 particles were dried in air or in a vacuum oven at room temperature.

[0068] The XRD (Figure 4) shows characteristic peaks consistent with the literature, confirming the successful synthesis of ZIF-8. The SEM image (Figure 5) shows that the average particle size of ZIF-8 is approximately 100 nm.

[0069] Preparation Example 2: Synthesis of melamine-modified urea formaldehyde (MUF) / epoxy microcapsules Microcapsules were prepared from emulsions by in situ polymerization. The manufacturing process involves three steps: emulsion preparation, prepolymer synthesis, and microencapsulation.

[0070] In a 250 mL three-neck flask, 1.35 g of gum arabic (GA) and 0.45 g of sodium dodecylbenzenesulfonate (SDBS) were dissolved in 60 mL of deionized water, to which bisphenol F diglycidyl ether (DGEBF) epoxy resin (7.2 g) was added under propeller stirring at a speed of 500 rpm for 1 h to reach a stable emulsion.

[0071] Melamine (0.42 g), urea (2 g), and 37 wt% formaldehyde solution (5.4 g) were first dissolved in a 100 mL two-neck flask under stirring, and triethanolamine was then added dropwise to raise the pH of the solution to 8.5 to obtain a shell prepolymer. The temperature was then raised to 70 °C and the mixture was stirred under reflux for 1 hour to obtain a colorless, transparent, viscous prepolymer, which was then cooled to room temperature.

[0072] For the microencapsulation process, the prepolymer was added dropwise to the epoxy emulsion under continuous stirring at 500 rpm. Ammonium chloride (NH4Cl) (0.25 g) was added as a pH buffer and catalyst, and the pH was set to approximately 3 by adding 10 wt% hydrochloric acid solution dropwise while the temperature was raised to 65 °C. The emulsion was stirred for 3 h, then cooled to room temperature and neutralized with a 10 wt% aqueous solution of sodium hydroxide (NaOH). The slurry was washed with deionized water, filtered, rinsed with acetone to remove unencapsulated epoxy, and air-dried to yield a white or pale yellow, free-flowing powder.

[0073] Figure 6 shows the SEM morphology of the synthesized MUF / epoxy microcapsules; the capsule size was 50-100 μm. To confirm that the epoxy was successfully encapsulated, a capsule 701 was manually ruptured and the released epoxy 702 was observed under a microscope (Figure 7). The capsules were well dispersed in the epoxy matrix (RIM935 / RIMH936) and were stably retained in the epoxy matrix after curing at room temperature for 2 days and post-curing at 60°C for 24 hours (Figure 8).

[0074] The shell thickness was determined by incorporating the capsules into a RIM935 / RIMH936 rod and observing the cross section. As shown in Figure 9, the shell thickness was approximately 300 nm and was observed to be well dispersed in the matrix. The capsules on the fracture surface appeared to be broken, which is positive for the release of epoxy.

[0075] Preparation example 3: Preparation of self-repairing material The self-healing agent MUF / epoxy microcapsules and the MOF catalyst ZIF-8 were incorporated into a RIM935 / RIMH936 (RIM935) epoxy matrix and tested for self-healing. The sample composition and cure profile are shown in Table 1. [Table 1]

[0076] Example 1: In-situ repair process for scratch damage Untreated RIM935 (a) and control samples of 8% ZIF8 in RIM935 (b), as well as the self-healing sample of 25% MUF capsules-8% ZIF8 in RIM935 from Preparation Example 3 (c), were cast onto glass slides. After curing, the samples were scratched and allowed to heal in situ on a temperature-controlled stage under an optical microscope in transmittance mode. Figure 10 shows the temperature profile. The samples were heated from 23.5 °C to 60 °C at a 10 °C ramp rate and then held for 12 hours. Figure 11 shows images taken from the in situ healing video. The control samples of untreated RIM935 (a) and 8% ZIF8 in RIM935 (b) show no change during the healing process. In contrast, the healed sample (c) with 25% capsules-8% ZIF8 in RIM935 shows healing along the scratch.

[0077] Example 2: Scratch Microscopy Test Control samples of untreated RIM935 (a) and 8% ZIF8 in RIM935 (b), as well as the self-healing sample of 25% MUF capsules in RIM935 and 8% ZIF8 (c) from Example 3, were cast onto carbon steel plates and scratched with a sharp razor. Figure 12 shows micrographs of the samples before and after healing at 60 °C for 12 hours. For untreated RIM935 (a) and 8% ZIF8 in RIM935 (b), there is no change before and after healing. For the 25% MUF capsules in RIM935 and 8% ZIF8 (c) sample, it can be seen that epoxy resin 1201 was released from the ruptured microcapsules before healing. After healing, the released epoxy resin 1202 is clearly cured.

[0078] Example 3: Electrochemical Impedance Spectroscopy (EIS) The self-healing ability of the polymer matrix, catalyzed by ZIF-8 and encapsulated epoxy as the healing agent, was evaluated by electrochemical impedance spectroscopy (EIS). Carbon steel plates were coated with samples (a)–(d) from Preparation Example 3 as described in Example 2 above. The coated carbon steel plates were scratched (approximately 5 mm long) with a razor blade. The samples were then healed at 60°C for 12 hours before being tested in an EIS setup. A 0.5 M NaCl solution was used as the electrolyte. Tests were performed at an open-circuit potential with a voltage amplitude of 20 mV over a range of 0.05–10,000 Hz. The frequency response at 0.1 Hz was considered for evaluating the coating performance.

[0079] To quantify the repair performance, the repair efficiency parameter was calculated using the following equation:

number

[0080] Figure 13 and Table 2 show the healing performance of the control sample and the self-healing samples with 15% capsules-5% ZIF8 in RIM935 and 25% capsules-8% ZIF8 in RIM935. For reference, the untreated sample had a log |Z| 0.1Hz is about 8, and the log |Z| of the unhealed scratched sample 0.1Hz is approximately 4. Figure 13 and Table 2 show that the untreated RIM935 sample (a) and ZIF8% in RIM935 (b) showed no healing at all. The 15% capsule-5% ZIF8 in RIM935 (d) and 25% capsule-8% ZIF8 in RIM935 (c) samples had healing efficiencies of 50% and 92%, respectively. After 20 hours of EIS exposure to saltwater, the self-healing sample containing microcapsules and ZIF8 showed no signs of corrosion, while the non-self-healing control sample showed signs of corrosion. These results support the EIS findings. [Table 2]

[0081] An optical microscope image of the sample is shown in FIG.

[0082] Example 4: Single Edge Notch Bend Test (SENB) The SENB test (ASTM 5045) was performed to further demonstrate the healing ability of the samples by quantitatively recovering their mechanical properties. The results are shown in Table 3 and Figure 15. The RIM935 control sample (a) did not heal at both room temperature and 60°C. The sample with 25% capsules and 8% ZIF8 in RIM935 (c) had mechanical healing efficiencies of 14%, 37%, and 53% at room temperature, 60°C, and 100°C, respectively, indicating a higher healing efficiency at higher temperatures. [Table 3]

[0083] Example 5: Preparation of microcapsules with a catalyst embedded in the shell An oil-in-water Pickering emulsion was prepared from an aqueous phase containing distilled water and ZIF-8, and an oil phase containing epoxy resin, styrene, divinylbenzene, azobisisobutyronitrile, and dichloromethane. The aqueous and oil phases were mixed together under vigorous shear to obtain a Pickering emulsion stabilized by ZIF-8 nanoparticles at the oil-water interface. N2 gas was bubbled through the emulsion to remove air. The reaction mixture was then heated to 65°C and polymerized at that temperature under nitrogen and reflux for 16 hours. The final product was isolated by centrifugation, washed repeatedly, and then dried in air. [Explanation of symbols]

[0084] 301... Crack 302 … Self-healing materials 303 ... Microcapsules 304 … Metal-organic framework catalyst 305a, 305b ... solid polymer 701... Capsule 702 ... Epoxy 1201 ... released epoxy 1202...hardened epoxy

Claims

1. polymer matrix, a microcapsule comprising a shell portion and a hollow core portion, the microcapsules being dispersed within the polymer matrix, the hollow core portion being filled with a monomeric or oligomeric repair agent; and a metal-organic framework catalyst suitable for catalyzing the polymerization of said monomeric or oligomeric repair agent; Including, The self-healing material, wherein the metal-organic framework comprises a zeolite-imidazolate framework.

2. 10. The self-healing material of claim 1, wherein the metal-organic framework catalyst is dispersed within the polymer matrix.

3. The self-healing material of claim 1 , wherein the shell portion of the microcapsules is formed from one or more of the group consisting of urea-formaldehyde, polysulfone, and polymethyl methacrylate.

4. The self-healing material of claim 3 , wherein the shell portion of the microcapsules is formed from urea-formaldehyde.

5. The self-healing material of claim 1 , wherein the microcapsules have an average diameter of about 20 μm to about 200 μm.

6. The self-healing material of claim 1 , wherein the shell portion of the microcapsules has an average thickness of about 100 nm to about 500 nm.

7. The self-healing material of claim 1 comprising about 10 to about 30 weight percent microcapsules.

8. 10. The self-healing material of claim 1, comprising about 1 to about 10 wt. % of the metal-organic framework catalyst.

9. 10. The self-healing material of claim 1, wherein the shell portion of the microcapsule comprises an inner portion and an outer portion, the outer portion comprising the metal-organic framework catalyst.

10. The self-healing material of claim 9 , wherein the inner portion is formed from a polymerized monomeric or oligomeric repair agent.

11. 10. The self-healing material of claim 9, wherein the outer portion is formed from a polymerized monomeric or oligomeric repair agent, or the outer portion is formed from one or more of the group consisting of urea-formaldehyde, polysulfone, and polymethyl methacrylate.

12. The self-healing material of claim 11 , wherein the outer portion is formed from a polymerized monomeric or oligomeric repair agent.

13. The self-healing material of claim 11 , wherein the outer portion is formed from urea-formaldehyde.

14. 10. The self-healing material of claim 9, wherein the microcapsules have an average diameter of about 20 to about 200 μm.

15. The self-healing material of claim 9, wherein the shell portion of the microcapsules has an average thickness of about 100 nm to about 500 nm.

16. 10. The self-healing material of claim 9, comprising about 10 to about 40 wt. % of the metal-organic framework-containing microcapsules.

17. 10. The self-healing material of claim 9, comprising about 1 to about 10 wt. % of the metal-organic framework catalyst.

18. The self-healing material of claim 1 , wherein the monomeric or oligomeric repair agent comprises an epoxy resin.

19. 20. The self-healing material of claim 18, wherein the epoxy resin comprises an epoxy resin selected from the group consisting of bisphenol-based epoxy resins; glycidyl ether resins; glycidyl aniline resins; and novolac, aliphatic, cycloaliphatic, aromatic, and bio-based epoxy resins having 1 to 6 epoxy groups.

20. 10. The self-healing material of claim 1, wherein the metal-organic framework comprises a ligand selected from the group consisting of imidazole, 2-methylimidazole, 2-nitroimidazole, 4,5-dichloroimidazole, 2-imidazolecarboxaldehyde, and combinations thereof.

21. 2. The self-healing material of claim 1, wherein the metal-organic framework comprises a zeolite-imidazolate framework selected from the group consisting of ZIF-2, ZIF-3, ZIF-4, ZIF-8, ZIF-67, ZIF-65, ZIF-77, ZIF-71, ZIF-72, ZIF-90, and combinations thereof.

22. 10. The self-healing material of claim 1, wherein the metal-organic framework comprises ZIF-8.

23. 10. A method of repairing a self-healing material according to claim 1, comprising subjecting the self-healing material to conditions suitable for polymerization of the monomeric or oligomeric repair agent.

24. 24. The method of claim 23, wherein the conditions suitable for polymerization of the monomeric or oligomeric repair agent of the self-healing material include a temperature of from about 20°C to about 180°C.

25. 24. The method of claim 23, wherein the self-healing material is subjected to conditions suitable for polymerization of the monomeric or oligomeric repair agent for at least 1 hour.

26. 24. The method of claim 23, wherein the self-healing material forms part of an oil or gas pipeline that is maintained under conditions suitable for polymerization of the monomeric or oligomeric repair agent.

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