ES2951704B2 - MEASUREMENT EQUIPMENT FOR IN-SITU SELF-REPAIR OF A MATERIAL AND MEASUREMENT METHOD - Google Patents

Description

DESCRIPTION

IN-SITU SELF-REPAIR MEASUREMENT EQUIPMENT A MATERIAL AND

MEASUREMENT METHOD

FIELD OF THE INVENTION

The present invention relates to the development of equipment for quantitative in situ measurement of the self-healing of materials and a method for quantifying the self-healing of materials.

STATE OF THE PRIOR ART

Inspired by living tissues, in recent years research into materials with self-healing ability has advanced significantly due to their potential in different fields of technology. This emerging and exciting area of research could significantly extend the life and safety of components made from different materials in a wide range of applications. The emerging new class of "self-healing materials" may allow the reconstruction of molecular structure from the fractured form to the intact form. However, most of the known self-healing processes require the application of external stimuli (heat, radiation or chemical reactions, among others), which can be a limiting aspect in some applications.

Depending on the self-healing mechanism, materials can exhibit extrinsic or intrinsic self-healing. In the case of extrinsic self-healing, the materials are regenerated due to the existence of capsules or microchannels, which are incorporated during the synthesis of said materials. Although the incorporation of microcapsules, fibers or low melting point components are efficient, the release of their active components generates chemical curing reactions that allow self-repair to be carried out only once and, in addition, the repaired area has a structure different from that of the original material. In contrast, intrinsic self-healing materials do not contain curing agents, but instead possess latent self-healing functionality that is activated by the action of damage or external agents.

Although different materials with self-healing capacity have been developed, one of the aspects that remains to be resolved, particularly in polymeric materials, is to find a method that allows it to be monitored in a quantitative, repetitive and precise manner. In the literature, various qualitative methods have been proposed that provide information about the time necessary for a material to self-heal and that allow us to visually establish how this process occurs. On the other hand, the quantitative methods that have been developed allow evaluating the efficiency of self-healing, but these methods evaluate self-healing indirectly through a characteristic property of the material, such as its mechanical resistance to traction and/or breakage, its properties rheological or its dynamic-mechanical properties, among others. Therefore, there is neither a method nor equipment that allows the self-healing process of materials, mainly polymeric materials, to be measured directly and quantitatively in situ.

Qualitative methods for evaluating self-repair

Optical methods

One of the most used qualitative methods due to its simplicity to monitor the degree of self-healing of a material, preferably a polymeric material, is optical microscopy. The procedure consists of cutting or scratching the sample with scissors or a blade, respectively, reassembling the cut pieces and placing them under the lens of the equipment. In some studies, the damaged sample needs to be heated to self-repair, which requires placing it on a heating stage on the microscope slide. One of the advantages of methods based on the use of optical microscopes is that they allow the self-healing process of materials to be followed for long periods of time.

Another optical method used for the qualitative analysis of the self-healing process of materials is the scanning electron microscope (SEM), which has the same characteristics as the use of an optical microscope. On the other hand, document CN108490130A proposes a method to evaluate the self-healing of materials used in cable insulation based on the use of a confocal laser microscope. To do this, a cut is made in the sample and the cross-sectional area of the cut is measured before and after self-repair.

With optical methods, only qualitative information can be obtained, without being able to know the efficiency or kinetics of the self-healing of the materials. Furthermore, the edges of the cut are never perfect, reproducibility is poor, self-healing cannot be evaluated consecutively in the same cut, and it is not distinguished whether self-healing occurs from the core of the material to the surface or from the surface. surface inwards.

Conductivity measurements

A less conventional method to track self-healing of materials is to measure conductivity by applying a coating of a conductive material. For example, a silver ink has been applied to a polyurethane, measuring its conductivity. After subsequently cutting the polyurethane film with a razor blade, its electrical conductivity is lost. Upon heating at 60 °C for 1 hour, the polyurethane film self-healed, which was detected by the recovery of conductivity.

In another study, an elastic galinstan (GaInSn) conductive wire was placed in a polyurethane. To examine the self-healing ability, the polyurethane with the gallinstan wire was cut into two pieces, bonding them at room temperature for 8 hours, during which time the gallinstan wire completely restored its original mechanical and conductive properties.

On the other hand, patent CN113484651A proposes a method to evaluate the degree of conductivity recovery of different materials. The initial resistivity of the materials that are subsequently cut is measured, we wait for them to self-heal and their resistivity is re-evaluated.

These methods require applying a conductive coating to the materials, so they are modified, and are also a very selective method that cannot be used on all materials. Additionally, conductivity measurements do not directly evaluate the self-healing of the material but rather that of the conductive materials that are incorporated.

Cutting with a metal wire

One of the few methods that allows determining the self-healing time of materials is the cutting method with a metal wire. The method consists of passing a 1 mm diameter metal wire, at the ends of which a certain weight is hung, through the center of a cylindrical or rectangular piece of material. As the wire passes through the material, the damaged area regains its shape and structural integrity at room temperature. Although a priori it is a fairly simple method, it requires complicated preparation, an adequate geometry of the material and selecting the weight to hang from the metal wire according to the mechanical properties of the material. Furthermore, the material must be rectangular or cylindrical with a significant thickness so that the metal wire can pass through the sample slowly. If the material is very soft, the deformation of the piece occurs and even its irreversible breakage, without self-repair occurring. Therefore, the method is restricted to materials with adequate mechanical properties.

Cutting with scissors

The simplest, fastest and easiest method to know if a material has self-healing capacity or not is to make a cut with scissors and join the cut parts; If the material needs temperature to self-heal, it can be placed in a stove. Once a certain time has passed, a manual tensile effort is applied to the sample to determine whether or not self-healing of the material has occurred. This method is indicative to know whether self-repair of a material occurs or not, as well as to estimate the approximate time it may take to self-repair; Furthermore, it does not allow the kinetics of self-healing to be quantified.

Quantitative methods for evaluating self-healing

Tensile tests

Among the most used methods to quantitatively evaluate the self-healing capacity of materials are tensile tests carried out on universal testing machines. The properties determined are tensile strength, elongation at break, stress at a given elongation, elongation at a given stress, stress at the yield point and elongation at the yield point, among others. . The method consists of normalized specimens of the material, in the shape of a weightlifter or ring, stretched in a universal testing machine under tensile stress with constant travel speed. Both force and elongation are continuously monitored during the continuous deformation of the specimen until it breaks. The procedure for evaluating the self-healing of the material consists of cutting the standardized specimens into two equal parts with a sharp blade. The damaged surfaces are then carefully reattached and, if necessary, placed in an oven for the time required for the self-healing process. Different specimens of the same material in the shape of a halter are cut and joined several times, allowing different times to pass, after which new tensile tests are carried out under the same conditions used in the mechanical tests of the virgin material. With the data extracted from the mechanical tests, the self-repair efficiency is calculated using equation (1):

However, the tensile strength and self-healing efficiency gradually decrease with the increase of time because it is difficult to accurately join the two completely separated parts. This provides some insight into the drawbacks of this method for assessing the self-healing ability of a material.

In another study, the surface of a polyurethane is scratched and subsequently cured at different times at 80 °C for 24 hours to ensure that, during the tensile test, no cracks occur for an elongation of 700%.

In another study, tensile tests are carried out to compare the self-healing efficiency of a polyurethane at room temperature in and out of water. It was shown that increasing the mechanical properties of polyurethane decreased the self-healing efficiency because the migration of the polymeric segments to the damaged areas was slowed down.

One of the advantages of mechanical testing is that the self-healing mechanism of materials can be understood and/or predicted from their mechanical properties. For example, in a study carried out with polyurethanes synthesized with different percentages of aliphatic disulfide groups, it was observed that for a given content of soft segments, a high elongation at break and adequate self-healing occurred. When the content of disulfide groups increased, the percentage of hard segments of the polyurethane also increased, as well as the number of physical crosslinks, slowing down the self-healing process. In summary, higher stiffness and increased hard segment content of polyurethane decrease its self-healing efficiency.

In patent CN108445005A it is proposed to cut a sample of material into at least two pieces, immediately put the separated sections together, drop a few drops of water on the break and keep it at room temperature for 12-16 hours. The degree of self-healing of the material was evaluated by tensile tests. In patent CN108680431A of the same authors, a method is proposed to evaluate the self-repair of a cable, which consists of cutting the cable into two parts, joining it and, after different times, evaluating its mechanical properties through tensile tests.

Tensile tests to evaluate self-healing are usually very laborious and not very reproducible, and, furthermore, after joining the cut pieces, the tensile strength of the original material is not usually recovered, because it is difficult to join them sufficiently. precise. Therefore, these methods allow us to determine how the self-healing process affects the mechanical properties of the material.

Boot test

These methods consist of placing two separated/cut pieces of the same self-healing material in contact for a certain time, measuring the force necessary to separate them. Each specimen is cut in half into two equal parts with a razor blade and placed in a micro-testing machine. At the beginning of the test, the two halves of the material are aligned and the vertical displacement is assigned to the moving platform so that the two halves of the sample remain compressed. After compressing the sample for a specific period of time, the force required to separate the two joined halves is measured, which is taken as a measure of the degree of self-healing. To completely separate the two halves of the sample, the test is performed at high speeds and the separation distance must be quite long for complete separation to occur, since there is usually a thin strip of material between the two pieces. After 10 minutes from the joining of the separated pieces of a polyurethane material, 36-68% of the original resistance was recovered.

This method, like tensile testing methods, is usually very laborious and difficult to control. Additionally, the speed of separation, the size of the sample and the precise alignment of the two cut pieces affect the result obtained. Another limitation of the method is that it is required to use sample geometries with a very precise thickness and length. One of the advantages of this method is that it allows evaluating self-healing in samples that have been damaged under non-ideal conditions, that is, it allows simulating real conditions of damage to the material.

Thermomechanical properties

In patent CN108375657A, a method for evaluating the self-healing capacity of a material was proposed based on its dynamic thermal-mechanical and thermogravimetric properties. The self-healing of the material was visualized with an optical microscope and a transmission electron microscope (TEM), correlating the degree of self-healing with the properties evaluated by dynamic thermal-mechanical analysis (DMA), particularly with the elastic moduli. This method requires combining several experimental techniques that determine different properties and a defined correlation is not established between them. Furthermore, a very laborious preparation of the samples is required in order to adequately evaluate their viscoelastic properties, using different test conditions and different sample geometries.

The analysis of the literature shows that there is no method that allows quantifying the degree of self-healing and/or monitoring the self-healing kinetics of materials, particularly in situ. The procedures currently used are very laborious, are not reproducible, use an indirect measure of the property of the material to be able to evaluate the efficiency of self-repair and require performing the separation and re-union of the cut parts in two different stages.

Patent KR102105840 proposes a device and a method to determine the width of a crack in concrete materials based on the calculation of the diffusion coefficient of a gas. This patent also discloses the evaluation of the self-healing of concrete materials based on the diffusion of a gas towards the crack. The device proposed in patent KR102105840 is composed of a sample support, a hermetic chamber that is filled with gas, a gas concentration meter, a gas injection system and a gas discharge system, a controller of the opening and closing of valves, a gas supply source and a computer. On the other hand, the method proposed in patent KR102105840 consists of separately making a crack in the surface of a piece of concrete that is placed in the equipment, bringing the cracked area of the material into contact with the upper part of the hermetic container, so that the area with the crack is exposed to the gas exit from the closed chamber. Once the sample is fixed, the gas is injected into an airtight chamber at high pressure until a pre-established concentration is reached. The gas is then let out from the closed chamber into the fissure of the sample, so that the gas diffuses outwards. The changes in gas concentration over time are recorded to calculate the gas diffusion coefficient, with the same process repeated for different gas concentrations. From the variation of the diffusion coefficients of the gas at different initial concentrations, the degree of self-healing of the material is estimated.

The device and method proposed in patent KR102105840 for evaluating the degree of self-healing of concrete materials have several limitations. The equipment can only be used for materials damaged outside the equipment, so self-repair is not generated in situ. This means that the self-repair of the material would begin to be evaluated once it has already started. On the other hand, it is a discontinuous system because it requires a gas load at a given concentration while carrying out the measurements on the same sample. In other words, the measurement of material self-healing requires discontinuous measurements to be made. Another limitation of the device and method proposed in patent KR102105840 is that the opening of the hermetically closed gas chamber must coincide exactly with the crack of the material to prevent gas leaks from occurring, particularly considering that the morphology of the material crack is always uneven. Additionally, the method proposed in patent KR102105840 is valid for rigid and essentially elastic materials, which limits its use in flexible materials and in most polymeric materials since said materials would deform heterogeneously. Finally, the repeatability of the method is limited as the crack is made extrinsically to the equipment and manually, and since a part of the sample crack is exposed to the outside, it can cause the self-repair of the material to begin before it begins. to measure, and would be affected by factors external to the equipment.

The limitations of the devices and methods for evaluating the self-healing of materials previously described in the literature are resolved with the equipment and method proposed in the present invention.

Current methods require cutting or modifying the material to cut it and then join the separate pieces together. This means that with these methods the material cannot be cut/drilled in the same place where it is self-healing.

The present invention provides equipment that allows self-healing of materials, mainly polymeric materials, to be determined in situ, as well as to quantify the efficiency of self-healing and monitor the kinetics of the self-healing process. Furthermore, a procedure for evaluating and monitoring the self-healing of materials is proposed that consists of drilling the material in situ, letting a gas stream flow through the drilled hole. The decrease in gas flow through the borehole is directly related to the kinetics of the self-healing process. When the gas flow is interrupted, the self-healing process is complete. This method is simple, fast and reproducible, and allows several measurements to be carried out in situ on the same sample at different temperatures and with different geometry and size of the materials.

DESCRIPTION OF THE INVENTION

The present invention refers to equipment for measuring self-healing of materials that can be polymeric materials, composite materials, ceramic materials, materials based on cement, mortar or concrete, and textile materials. Within polymeric materials, we consider, for example, polyurethanes, polysiloxanes and derivatives (silicones), fluorinated polymers, polyamides, polyesters, epoxies, natural and synthetic rubbers, polyacrylates and polycyanoacrylates, polystyrene, polyvinyl chloride (PVC), polyolefins, polyethylene terephthalate (PET), polysulfides and polysulfones, polyanilines, polycaprolactones, polycarbonates, polyethylene oxides, polyureas, polyacetylenes, polypyrroles, polythiophenes, and copolymers such as acrylonitrile butadiene styrene (ABS) copolymers and styrene-butadiene-styrene copolymers ( SBS).

The present invention refers first of all to a device for measuring the self-repair of materials that comprises:

- a main body formed by an upper structure and a lower structure, separated by a space capable of housing a sample of material, and such that when joined together they form an airtight chamber,

- a gas inlet and a gas outlet, each located in one of the two structures that make up the main body,

- a stem arranged in the upper structure, capable of sliding vertically up and down, which holds and guides a piercing element and

- a piercing element arranged in the stem.

By airtight it means that there is no gas leak in the main body.

When "upper" is indicated, reference is made to the structure of the main body in which the stem with the piercing element is arranged.

When "lower" is indicated, it refers to the structure of the main body on which the measuring equipment rests.

The main body is divided into the upper structure and the lower structure, which when joined together form the hermetic chamber and can be heated to perform self-repair measures at temperatures different from room temperature.

In the space that separates the upper structure from the lower structure, a sample of material can be placed, which is static throughout the test.

According to particular embodiments, the measuring equipment comprises an adapter for the case in which the sample has a size smaller than the inner perimeter of the main body. In the event that the equipment includes an adapter, the adapter includes a sample holder that allows the sample to be placed between the upper structure and the lower structure, and elements for fixing the sample to the adapter.

Elements for securing the sample to the adapter can be, for example, washers, threaded rod washers, nuts and gaskets (such as O-rings).

The coupling sections of the upper and lower structure can have different, similar or identical geometries, which are joined to form the main body, ensuring an airtight seal, and in turn, the holding of the sample.

The geometry of the two structures that form the main body may be different, similar or identical, preferably, the two structures are of identical geometry.

The main body can have various shapes, such as prismatic or cylindrical, preferably it is cylindrical.

The two main body structures can be the same size or different sizes, preferably they are the same size.

According to preferred embodiments, the gas inlet is arranged in the lower structure and the gas outlet is located in the upper structure of the main body. In this way the gas inlet and outlet are located respectively below and above the sample.

The gas is arranged in a container connected to the main body, such as a bullet.

Any gas can be used, including nitrogen, helium, carbon dioxide, neon, or argon, among others, or combinations of them. Preferably, the gas is an inert gas. In a specific embodiment it is nitrogen and helium.

The stem that guides the drilling element can enter and exit vertically through the upper structure of the equipment to drill and withdraw from the material sample, respectively, which allows the gas flow that enters through the lower structure to flow towards the upper structure. or vice versa.

The edge or tip of the piercing element may have a thickness between 0.01 mm and 10 mm, for example, it may be a needle with a diameter of 1 mm. The piercing element must have the appropriate length so that it can completely pierce the material sample, for example, it can be a needle with a diameter of 1 mm.

In addition, the stem and the piercing element allow a 360° rotation of both elements.

The measuring equipment for self-repair of materials also includes a gas flow meter that allows precise control of the same, connected to the main body.

The material self-repair measurement equipment also comprises a pressure regulator arranged in a duct that connects the gas container with the main body, adjacent to the gas outlet of the container, which allows precise control of the gas pressure. that reaches the flow meter.

The material self-repair measurement equipment also comprises a gas supply cut-off valve, arranged in the duct that carries the gas to the main body, arranged between the pressure regulator and the gas flow control valve. .

The material self-repair measurement equipment also comprises a second gas flow control valve arranged in the duct that allows precise control of the gas flow rate towards the main body, between the gas supply cut-off valve. gas and the main body.

The material self-healing measurement equipment also includes a data acquisition device that continuously records the gas flow through the crack made in the sample as a function of time.

The self-repair measurement equipment may also comprise a bubbling device, arranged at the gas outlet of the main body, which allows continuous monitoring of the gas flowing through the outlet of the main body, while performing the self-repair measurement. self-repair.

The main body of the self-healing measurement equipment can be manufactured with any non-porous material that allows the generation of a cavity or hermetic chamber and that does not cause any contamination or alteration of the sample. These materials may be metals such as aluminum or titanium, alloys such as bronze or stainless steel, polymeric materials such as polytetrafluoroethylene or polypropylene, fiberglass or carbon fiber composite materials, ceramic materials, quartz, or glass.

The gas pipes of the measuring equipment must also be manufactured with a non-porous material, such as those mentioned for the manufacture of the main body.

The system of valves, fittings and accessories can be made of various materials, such as metals, alloys (for example, stainless steel or brass), polymeric materials (for example, rigid silicone, viton, rubber), glass, quartz, composite materials ( composites), and ceramic materials.

The two structures that make up the main body of the self-repair measurement equipment are joined by mechanical fastening elements such as screws, threaded elements, nuts, jaws, pins, guide sockets; or repositionable adhesives.

During the use of the equipment, the sample is placed between these two structures, such that when they join they form the hermetic cavity. If the size of the material sample is less than the perimeter of the main body cavity (internal diameter in case the main body is circular), the sample is placed inside a perimeter adapter (diameter in case the main body is circular). main body is circular) slightly larger than the perimeter (internal diameter in case the main body is circular) of the main body, which carries a sample holder into which it is inserted. The adapter is integrated between the upper and lower structures of the main body of the self-repair equipment. The operation of the equipment and the way of carrying out the self-repair measurement is the same for any size of the material sample. The adapter can be made of different materials, such as metals, alloys (for example, stainless steel or brass), polymeric materials (for example, rigid silicone, Viton, rubber), glass, quartz, composite materials, and materials ceramics

If it is desired to measure the self-healing of materials at a temperature higher than room temperature, the main body can be heated up to 150 °C, between 20 °C and 150 °C. The heating element can be an electrical resistance with a thermal sensor or thermocouple that allows measuring the temperature inside the main body, as well as an external temperature control system. In addition, the main body can be covered with a thermal insulating material to maintain a constant internal temperature, which must be made of materials with high thermal resistivity, such as natural and synthetic polymers, or mineral wool, so as to avoid heat dissipation and prevent the operator from getting burned.

According to preferred embodiments, the material self-repair equipment comprises:

- a main body formed by an upper structure and a lower structure, separated by a space capable of housing a sample of material, and such that when joined together they form an airtight chamber,

- a gas inlet and a gas outlet, each located in one of the two structures that make up the main body,

- a stem arranged in the upper structure, capable of sliding vertically up and down, which holds and guides a piercing element,

- a piercing element arranged in the stem,

- a bullet that supplies a gas,

- a regulator to precisely control the gas outlet pressure,

- a gas supply cut-off valve and a second valve that allows controlling the gas flow,

- a flow meter to accurately determine the gas flow,

- a data acquisition device that continuously records the variation of gas flow with time and

- a bubbling device, arranged at the gas outlet of the main body, which allows the continuous flow of gas to be continuously controlled during the performance of the self-repair measure.

The present invention also refers to a method of measuring the self-healing of a material using the self-healing measuring equipment defined above and comprising:

- arrange a sample between the upper and lower structures that make up the main body of the equipment,

- join the two structures by hermetically closing the space between them,

- slide the stem with the piercing element vertically until the material sample is pierced,

- remove the stem from the sample,

- make gas flow from the lower structure to the upper structure, or vice versa, through the perforation made in the material sample, during the time that the measurement test lasts, and

- continuously measure the gas flow and the time it takes for gas to stop passing through the perforation made in the material sample.

According to preferred embodiments, the sample is drilled eccentrically with the drilling element oriented by the stem.

The sample can be drilled as many times as necessary, in the same location or in a different location without the need to move or manipulate it.

The stem is removed from the sample, the gas flow is continuously measured and the time it takes for gas to stop passing through the fissure made in the sample, since the gas flow decreases as the fissure closes, so so that when the gas stops flowing, self-repair is considered to have occurred.

The sample can have any geometry, preferably circular or prismatic, and can have dimensions between 1 mm and 100 mm, and a thickness between 0.05 mm and 20 mm. In a particular embodiment, the dimensions of the sample are 19 mm and a thickness of 3 mm. However, both the geometry of the material and that of the equipment can be different, being a parameter that does not affect the extent of self-repair.

According to preferred embodiments of the method, when the size of the material sample is less than the internal perimeter of the main body (internal diameter in case the main body is circular), the adapter with a cavity can be used to support the sample with dimensions between 0.5 mm and 99 mm, and a thickness between 0.01 mm and 19 mm. In a particular embodiment, the dimensions of the sample are 10 mm and a thickness of 3 mm.

The sample can be heated between 20 °C and 150 °C. In a particular embodiment, the sample temperature is between 35°C and 80°C.

The stem and piercing element allow 360° rotation.

Two different variables of the gas must be controlled, one is the pressure when it leaves the container or container (such as a bullet) and the other is the flow of gas. Both are checked and fixed before passing through the sample. The pressure is the same throughout the test, but the gas flow will decrease as the sample self-heals (the crack made in the material closes and less gas flow passes through). This gas flow is what leaves the upper structure (or the lower one, depending on the configuration of the main body) and goes to the data acquisition device.

According to preferred embodiments of the method, the pressure of the gas when it leaves the container or container (such as a bullet) can be varied between 1 mbar and 2 bars. In a specific embodiment, the pressure is 750 mbar.

According to preferred embodiments of the method, the gas flow leaving the container can be varied between 0.1 mL/min and 500 mL/min. In a particular embodiment, the flow is varied between 8 mL/min and 65 mL/min.

The sample can be drilled at any point on its surface, but preferably it is drilled eccentrically to be able to perform different repetitions in situ on the same sample. According to particular embodiments of the method, drilling is done 0.5 mm from the center of the sample.

The gas flow outlet of the main body of the self-repair measuring equipment is continuously monitored by a flow sensor. Gas flow variations over time are recorded continuously.

In addition to recording the data digitally, at the exit of the gas flow, the equipment can have a bubbling system attached to observe the passage of the gas continuously and additionally detect when complete self-repair of the material has been carried out.

The method according to the invention allows monitoring the kinetics of the self-healing process of the materials, carrying out consecutive and repetitive measurements, and provides an estimate of the time necessary to achieve complete self-healing, all in situ and without manipulating the sample, self-healing being able to be carried out at temperatures between 20 °C and 150 °C, and for samples of different sizes and geometries. More specifically, this invention provides new equipment for measuring the self-healing of materials, including polymeric materials, and a new method for quantitatively monitoring the self-healing process over time.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Scheme of the measurement equipment for self-repair of materials. In the figure the references mean: 1- Gas bullet; 2- Pressure regulator; 3- Shut-off valve; 4- Gas flow control valve; 5- Main body; 6- Flow meter; 7-Data acquisition device.

Figure 2: Schematic of the main body of the self-repair measurement equipment and its components with the sample. In the figure the references mean: 8- Upper structure; 9-Gas inlet; 10- Lower structure; 11- Stem; 12- Drilling element; 13- Gas outlet; 14- Sample or sample holder with the sample.

Figure 3: Adapter diagram for samples of different sizes: (I) Arrangement of adapter elements where 12- Drilling element; 15- Upper washer with threaded rods; 16- O-rings; 14- Sample; 17- Sample holder; 18- Lower washer; 19-Nuts. (II) Insertion of auxiliary elements. (III) Closing position of the adapter assembly.

Figure 4: Movement of the stem to pierce the sample.

Figure 5: Example of eccentric drilling of a material sample.

Figure 6: Sample of material placed in the self-repair measurement equipment.

Figure 7: Scheme of the measurement method for self-healing of materials.

Figure 8: Variation of gas flow with time after the different stages of the self-healing process of YP polyurethane.

Figure 9: Self-healing kinetics of YP polyurethane.

Figure 10: Variation of gas flow with time after the different stages of the self-healing process of 20%PCD80%PCD2 polyurethane.

Figure 11: Variation of gas flow with time after the different stages of the self-healing process of 100% PCD2 polyurethane.

Figure 12: Self-healing kinetics of 100%PCD, 60%PCD40%PCD2, 20%PCD80%PCD2 and 100%PCD2 polyurethanes.

Figure 13: Self-healing kinetics of YP polyurethane using different nitrogen gas flows.

Figure 14: Self-healing kinetics of YP polyurethane in different repetitions.

EXAMPLES

Example 1: Measurement and monitoring of the self-healing process of a polyurethane material.

To measure and follow the self-healing process of a material, one of the polyurethanes described in patent EP3103846A has been used, which has the ability to intrinsically self-heal at room temperature.

YP polyurethane synthesis

The polyurethane called YP has been synthesized using the one-shot method that is well known in the literature. The “one-shot” method consists of simultaneously mixing all the components necessary to synthesize a polymer.

The ingredients necessary to synthesize YP polyurethane are a polycarbonate polyol and 1,6 hexanediol with a molecular weight of 1000 Da (Eternacoll® UH-100, UBE Chemical Europe S.A., Castellón, Spain), 4,4'-methylenebis (cyclohexyl isocyanate) ( HMDI) with 90% purity (Sigma Aldrich Co., St. Louis, MO, USA), and 1,4 butanediol (BD) with 99% purity (Panreac Applichem®, Darsmstadt, Germany). The NCO/OH ratio used was 1.1.

To obtain YP polyurethane, the required amount of polyol and 1,4 butanediol is added to a 60 mL polypropylene bottle, stirring the mixture in a SpeedMixer at 2,400 rpm for 1 minute. The mixture is placed in an oven at 80 °C for 10 minutes. Subsequently, the required amount of HMDI isocyanate is added to the mixture and stirred again in a SpeedMixer at 2,400 rpm for 1 minute. Finally, the mixture is placed in a vacuum oven for 9 hours consecutively following the following steps: 50 °C for 30 min; 60 °C for 30 min; 70 °C for 30 min; and 80 °C for 6 hours. After 24 hours, a post-curing process ("annealing") is carried out at 85 °C for 1 hour to stabilize the structure of the YP polyurethane.

Monitoring of the self-healing process of YP polyurethane

A sample of YP polyurethane is cut in a circular shape with a diameter of 19 mm and a thickness of 3 mm. The circular sample is placed in the self-healing measuring equipment and sealed tightly. A continuous flow of nitrogen gas is passed through at a pressure of 750 mbar and a flow rate of 8 mL/min throughout the duration of the process. The YP polyurethane sample is completely pierced 0.5 mm from the center with a 1 mm diameter needle, which is attached to a shank. Immediately thereafter, the needle is removed from the polyurethane sample, continuously monitoring the gas flow over time until the gas stops flowing, at which point complete self-healing is considered to have occurred. During the test, the variation of the gas flow passing through the crack made in the YP polyurethane with time is continuously recorded.

Figure 8 shows the variation of the gas flow that passes through the crack made in the YP polyurethane with time after the different stages of the self-healing process. Three different processes are distinguished: (i) Drilling of the sample that generates a sharp increase in the gas flow from the bottom of the sample to the top; (ii) the removal of the needle that pierces the YD polyurethane piece, which generates a slight overpressure due to the gas accumulated during the time in which the needle pierces the YP polyurethane; (iii) The self-healing process in which the gas flow passing through the crack made in the YP polyurethane continually decreases over time.

To follow the self-healing kinetics of the YP polyurethane, the gas flow that passes through the crack made in the sample has been represented as a function of time, expressing the flow as a percentage reduction with respect to the initial flow (the flow at the beginning of the repair process). self-repair is taken as time zero). Figure 9 shows that the self-healing of YP polyurethane is continuous and homogeneous and is completed in 1.4 seconds.

Example 2: Polyurethanes with different kinetics and self-healing capacity.

To determine the sensitivity of the method for quantitative evaluation of self-healing, three polyurethanes with different self-healing times and one polyurethane that does not present self-healing were synthesized.

Synthesis of polyurethanes

All polyurethanes have been synthesized using the one-shot method that is well known in the literature. The “one-shot” method consists of simultaneously mixing all the components necessary to synthesize a polymer.

The ingredients necessary to synthesize polyurethanes are a polycarbonate polyol and 1,6 hexanediol of molecular weight 1000 Da (Eternacoll® UH-100, UBE Chemical Europe S.A., Castellón, Spain), a polycarbonate polyol and 1,6 hexanediol of weight molecular 2000 Da (Eternacoll® UH-200, UBE Chemical Europe S.A., Castellón, Spain), 4,4'-methylenebis (cyclohexyl isocyanate) (HMDI) with 90% purity (Sigma Aldrich Co., St. Louis, MO, USA) , and 1,4 butanediol (BD) with 99% purity (Panreac Applichem®, Darsmstadt, Germany). The NCO/OH ratio used was 1.1.

The composition of the four polyurethanes differs in the molecular weight of the polyol or in the composition of the mixture of polyols of different molecular weights used in the synthesis and is indicated below:

100% PCD polyurethane - Formulated only with polycarbonate polyol and 1,6 hexanediol with a molecular weight of 1000 Da.

100% PCD2 polyurethane - Formulated only with polycarbonate polyol and 1,6 hexanediol with a molecular weight of 2000 Da.

Polyurethane 60%PCD40%PCD2 - Formulated with a mixture of 60% polycarbonate polyol and 1,6 hexanediol with a molecular weight of 1000 Da and 40% polycarbonate polyol and 1,6 hexanediol with a molecular weight of 2000 Da.

Polyurethane 20%PCD80%PCD2 - Formulated with a mixture of 20% polycarbonate polyol and 1,6 hexanediol with a molecular weight of 1000 Da and 80% polycarbonate polyol and 1,6 hexanediol with a molecular weight of 2000 Da.

To obtain the polyurethanes, the required amount of polyol or a mixture of polyols and 1,4 butanediol is added to a 60 mL polypropylene bottle, stirring the mixture in a SpeedMixer at 2,400 rpm for 1 minute. The mixture is placed in an oven at 80 °C for 10 minutes. Subsequently, the required amount of isocyanate is added to the mixture and shaken again in a SpeedMixer at 2,400 rpm for 1 minute. Finally, the mixture is placed in a vacuum oven for 9 hours consecutively following the following steps: 50 °C for 30 min; 60 °C for 30 min; 70 °C for 30 min; and 80 °C for 6 hours. After 24 hours, a post-curing process ("annealing") is carried out at 85 °C for 1 hour to stabilize the structure of the polyurethanes.

Monitoring of the self-healing process of YP polyurethane

A sample of YP polyurethane is cut with a circular shape of 19 mm in diameter and a thickness of 3 mm. It is placed in the self-repair measuring equipment and closed tightly. A continuous flow of nitrogen gas is passed through at a pressure of 750 mbar and a flow rate of 8 mL/min throughout the duration of the process. The polyurethane sample is completely pierced 0.5 mm from the center with a 1 mm diameter needle, which is attached to a shank. Immediately thereafter, the needle is removed from the polyurethane sample, continuously monitoring the flow of gas passing through the crack made in the polyurethane over time until the gas stops flowing, at which point self-healing is considered to occur. complete. During the test, the variation in the gas flow passing through the crack made in the polyurethane over time is continuously recorded.

Figure 10 shows the variation of the gas flow that passes through the crack made in the sample with time after the different stages of the self-healing process of the 20%PCD80%PCD2 polyurethane. Three different processes are distinguished: (i) Drilling of the sample that generates a sharp increase in the gas flow from the bottom of the sample to the top; (ii) the removal of the needle that pierces the 20%PCD80%PCD2 polyurethane, which generates a slight overpressure due to the gas accumulated during the time in which the needle pierces the polyurethane; (iii) The self-healing process of 20%PCD80%PCD2 polyurethane in which the gas flow passing through the crack made in the polyurethane continuously decreases.

Figure 11 shows the variation of the gas flow that passes through the crack made in the sample with time after the different stages of the self-healing process of the 100% PCD2 polyurethane. Three different processes are distinguished: (i) Drilling of the sample that generates a sharp increase in the gas flow from the bottom of the sample to the top; (ii) the removal of the needle that pierces the 100% PCD2 polyurethane, which generates a slight overpressure due to the gas accumulated during the time in which the needle pierces the polyurethane; (iii) The self-healing process of 100% PCD2 polyurethane does not occur because the gas flow that passes through the crack made in the polyurethane remains constant over time.

To follow the self-healing kinetics of polyurethanes, the gas flow that passes through the crack made in each sample has been represented as a function of time, expressing the flow as a percentage reduction with respect to the initial flow (the flow at the beginning of the repair process). self-repair is taken as time zero). Figure 12 shows that the self-healing of 100%PCD and 60%PCD40%PCD2 polyurethanes is continuous and homogeneous and is completed in 1.4 seconds and 2.5 seconds, respectively (Table 1). However, the self-healing of 20%PCD80%PCD2 polyurethane is slower (completed in 8.5 seconds - Table 1) and occurs in several stages, being faster at the beginning and then slowing down for times greater than 3 seconds. Finally, 100%PCD2 polyurethane does not show self-healing.

Table 1: Self-healing times of different polyurethanes.

Example 3: Influence of gas flow on the extent of self-healing of a polyurethane.

YP polyurethane synthesis

The polyurethane called YP has been synthesized using the one-shot method that is well known in the literature. The “one-shot” method consists of simultaneously mixing all the components necessary to synthesize a polymer.

The ingredients necessary to synthesize YP polyurethane are a polycarbonate polyol and 1,6 hexanediol with a molecular weight of 1000 Da (Eternacoll® UH-100, UBE Chemical Europe S.A., Castellón, Spain), 4,4'-methylenebis (cyclohexyl isocyanate) ( HMDI) with 90% purity (Sigma Aldrich Co., St. Louis, MO, USA), and 1,4 butanediol (BD) with 99% purity (Panreac Applichem®, Darsmstadt, Germany). The NCO/OH ratio used was 1.1.

To obtain YP polyurethane, the required amount of polyol and 1,4 butanediol is added to a 60 mL polypropylene bottle, stirring the mixture in a SpeedMixer at 2,400 rpm for 1 minute. The mixture is placed in an oven at 80 °C for 10 minutes. Subsequently, the required amount of HMDI isocyanate is added to the mixture and stirred again in a SpeedMixer at 2,400 rpm for 1 minute. Finally, the mixture is placed in a vacuum oven for 9 hours consecutively following the following steps: 50 °C for 30 min; 60 °C for 30 min; 70 °C for 30 min; and 80 °C for 6 hours. After 24 hours, a post-curing process (“annealing”) is carried out at 85 °C for 1 hour to stabilize the structure of the YP polyurethane.

Monitoring of the self-healing process of YP polyurethane using different nitrogen gas flows

A sample of YP polyurethane is cut in a circular shape with a diameter of 19 mm and a thickness of 3 mm. The circular sample is placed in the self-healing measuring equipment and sealed tightly. A continuous flow of nitrogen gas is passed at a pressure of 750 mbar throughout the duration of the process. In two different experiments, the nitrogen gas flow was varied between 8 and 65 mL/min. The YP polyurethane sample is completely pierced 0.5 mm from the center with a 1 mm diameter needle, which is attached to a shank. Immediately thereafter, the needle is removed from the polyurethane sample, continuously monitoring the flow of gas passing through the crack made in the polyurethane over time until the gas stops flowing, at which point self-healing is considered to occur. complete. During the test, the variation in the gas flow passing through the crack made in the polyurethane over time is continuously recorded.

To follow the self-healing kinetics of the YP polyurethane using different nitrogen gas flows, the gas flow that passes through the crack made in the sample has been represented as a function of time, expressing the flow as a percentage reduction with respect to the initial flow (the flow at the beginning of the self-healing process is taken as time zero). Figure 13 shows that increasing the gas flow increases the time required for complete self-healing of the YP polyurethane from 1.4 to 21 seconds (Table 2). Furthermore, when the flow of nitrogen gas is small, the self-healing of YP polyurethane is continuous and homogeneous, while when the flow is large, the self-healing is gradual and slows down over 18 seconds.

Table 2: Self-healing times of YP polyurethane obtained using different nitrogen gas flows.

Example 4: Repeatability of the self-healing measurement of a polyurethane.

YP polyurethane synthesis

The polyurethane called YP has been synthesized using the one-shot method that is well known in the literature. The “one-shot” method consists of simultaneously mixing all the components necessary to synthesize a polymer.

The ingredients necessary to synthesize YP polyurethane are a polycarbonate polyol and 1,6 hexanediol with a molecular weight of 1000 Da (Eternacoll® UH-100, UBE Chemical Europe S.A., Castellón, Spain), 4,4'-methylenebis (cyclohexyl isocyanate) ( HMDI) with 90% purity (Sigma Aldrich Co., St. Louis, MO, USA), and 1,4 butanediol (BD) with 99% purity (Panreac Applichem®, Darsmstadt, Germany). The NCO/OH ratio used was 1.1.

To obtain YP polyurethane, the required amount of polyol and 1,4 butanediol is added to a 60 mL polypropylene bottle, stirring the mixture in a SpeedMixer at 2,400 rpm for 1 minute. The mixture is placed in an oven at 80 °C for 10 minutes. Subsequently, the required amount of HMDI isocyanate is added to the mixture and stirred again in a SpeedMixer at 2,400 rpm for 1 minute. Finally, the mixture is placed in a vacuum oven for 9 hours consecutively following the following steps: 50 °C for 30 min; 60 °C for 30 min; 70 °C for 30 min; and 80 °C for 6 hours. After 24 hours, a post-curing process ("annealing") is carried out at 85 °C for 1 hour to stabilize the structure of the YP polyurethane.

Monitoring of the self-healing process of YP polyurethane

A sample of YP polyurethane is cut in a circular shape with a diameter of 19 mm and a thickness of 3 mm. The circular sample is placed in the self-healing measuring equipment and sealed tightly. A continuous flow of nitrogen gas is passed at a pressure of 750 mbar and a flow of 65 mL/min throughout the duration of the process. The YP polyurethane sample is completely pierced 0.5 mm from the center with a 1 mm diameter needle, which is attached to a shank. Immediately thereafter, the needle is removed from the polyurethane sample, continuously monitoring the flow of gas passing through the crack made in the polyurethane over time until the gas stops flowing, at which point self-healing is considered to occur. complete. During the test, the variation in the gas flow passing through the crack made in the polyurethane over time is continuously recorded.

To determine the repeatability of the self-healing evaluation test on the same in situ sample, the stem with the piercing element is rotated and the sample is completely drilled again in a different part, the YP polyurethane needle is removed, and it is monitored. and records the variation of the gas flow that passes through the crack made in the polyurethane over time until the self-healing of the material occurs again. This step has been repeated consecutively in three different parts of the same sample.

To follow the self-healing kinetics of the YP polyurethane in the different repetitions, the gas flow that passes through the crack made in the sample has been represented as a function of time, expressing the flow as a percentage reduction with respect to the initial flow (the flow at start of the self-repair process is taken as time zero). Figure 14 shows that the time necessary for the sample to self-repair in the different repetitions is 24-26 seconds, being very similar in all repetitions. (Table 3).

Table 3: Self-healing times of YP polyurethane obtained by drilling it in three different areas of the same polyurethane.

Claims (21)

1. A material self-repair measurement equipment that includes: - a main body formed by an upper structure and a lower structure, separated by a space capable of housing a sample of material, and such that when joined together they form an airtight cavity, - a gas inlet and a gas outlet, each located in one of the two structures that make up the main body, - a stem arranged in the upper structure, capable of sliding vertically up and down, which holds and guides a piercing element and - a piercing element arranged in the stem. 2. The material self-repair measurement equipment according to claim 1, wherein the two structures of the main body are of the same or different size. 3. The material self-repair measurement equipment according to claim 1, wherein the main body is cylindrical in shape. 4. The material self-healing measurement equipment according to claim 1, wherein the gas inlet is arranged in the lower structure and the gas outlet is located in the upper structure of the main body. 5. The equipment for measuring the self-healing of materials according to claim 1, which also comprises an adapter that allows the sample to be adapted to the perimeter of the cavity between the upper and lower structures. 6. The self-healing materials measuring equipment according to claim 5, wherein the adapter comprises a sample holder and elements for securing the sample to the adapter. 7. The material self-healing measurement equipment according to claim 1, further comprising a pressure regulator arranged in the conduit that carries the gas to the main body, adjacent to the gas outlet of a container. 8. The material self-repair measurement equipment according to claim 1, further comprising a gas supply cut-off valve, arranged in a conduit that carries the gas to the main body, between the pressure regulator and the flow control valve. 9. The material self-repair measurement equipment according to claim 1, further comprising a second gas flow control valve arranged in the conduit that carries the gas to the main body, between the supply cut-off valve. gas and the main body. 10. The material self-repair measurement equipment according to claim 1, further comprising a gas flow meter, connected to the main body. 11. The material self-healing measurement equipment according to claim 1, wherein the main body is made of a non-porous material that allows the generation of an airtight cavity. 12. The material self-healing measurement equipment according to claim 11, wherein the main body is made of a material selected from aluminum, titanium, bronze, stainless steel, polymeric materials, fiberglass or fiber composite materials carbon, ceramic materials, quartz, glass or combinations of them. 13. The equipment for measuring self-healing of materials according to claim 1, which comprises a heating element that allows it to be heated between 20 °C and 150 °C. 14. Use of the material self-repair measurement equipment defined in one of claims 1 to 13 to perform in situ self-repair measurements. 15. A method for measuring the self-healing capacity of a material with the equipment defined in one of claims 1 to 13, comprising: - arrange a sample between the upper and lower structures that make up the main body of the equipment, - join the two structures by hermetically closing the space between them, - slide the stem with the piercing element vertically until the material sample is pierced, - remove the stem from the sample, - make gas flow from the lower structure to the upper one, or vice versa, through the perforation made in the material sample, for the duration of the measurement test, - continuously measure the gas flow and the time it takes to stop passing gas through the perforation made in the material sample. 16. A method according to claim 15, wherein the sample is drilled eccentrically. 17. A method according to claim 15, wherein the piercing element pierces and is removed from the sample repeatedly consecutively. 18. A method according to claim 15, wherein the pressure of the gas entering the main body varies between 1 mbar and 2 bars. 19. A method according to claim 15, wherein the gas flow entering the main body varies between 0.1 mL/min and 500 mL/min. 20. A method according to claim 15, wherein the gas flow outlet of the main body is continuously monitored. 21. A method according to one of claims 15 to 20, comprising heating the main body of the equipment between 20 °C and 150 °C.