Self-repairing fiber composite material and its use

Description

[0001] The invention relates to a self-repairing fiber composite material with hollow glass fibers embedded in a matrix and its use.

[0002] Fiber-reinforced composites (FRP) typically consist of a polymer matrix, usually a resin, into which high-strength / high-modulus fibers are embedded to enhance mechanical properties. Depending on the market segment and requirements, glass fibers (GFRP), aramid fibers (AFRP), or carbon fibers (CFRP) are primarily used. Target markets are those where weight and / or energy savings are important, such as in the automotive sector, aerospace, shipbuilding, architecture, or wind energy generation. Another area is sporting goods, which are generally marketable regardless of price.

[0003] A major problem arises from the formation of microcracks in the polymer matrix, caused by mechanical stress, climatic conditions, or other factors. If these structural defects propagate into macroscopic cracks, either the fibers are sheared off when the matrix breaks, or delamination occurs between two fiber layers. In the worst-case scenario, this leads to the total failure of the affected components. Such failures often occur spontaneously and without any prior visually detectable damage. Therefore, the components are usually designed very conservatively and thus over-dimensioned.

[0004] It is well known and documented that microcracks in polymer matrices can be repaired by incorporated, curable monomer systems. See, for example, Murphy EB, Wudl F: "The world of smart healable materials", Progr. Polym. Sci. 35 (2010), 223-251, and Hager MD, van der Zwaag S., Schubert S. (Eds.), Self-healing Materials, Adv. Polym. Sci. 273, Springer International Publishing Switzerland, 2016. A self-repairing or self-healing effect is achieved by protecting a crosslinkable monomer and incorporating it as homogeneously as possible into the composite material. Typically, microcapsules or hollow fibers filled with reactive monomer systems are used as reservoirs for this purpose. When microcracks occur, they are filled locally by the escaping monomer fluid, particularly due to the capillary forces at work, and the hardening process is triggered by a special catalyst distributed in the matrix.This can prevent or at least significantly delay the merging of microcracks into macrocracks and the delamination of fiber and matrix.

[0005] White et al. (Nature 409, 794-797 (2001)) describe microcapsules filled with a specific monomer as a depot. During manufacturing, these are homogeneously dispersed in the matrix. In the event of a microcrack, some microcapsules rupture, the monomer diffuses into the microcrack via capillary action, and crosslinks to form a solid polymer on a catalyst also present in the matrix. This prevents further propagation of the microcrack and thus component failure. The system used by White et al. utilizes the metathesis-based ring-opening polymerization of dicyclopentadiene (DCPD). The polymerization is initiated by a first-generation Grubbs catalyst. A disadvantage is that the matrix must be filled to a high degree with the microspheres, which negatively impacts the matrix properties and necessitates the use of an unnecessarily large number of microcapsules, resulting in high costs.

[0006] In US patent 2011 / 0118385 A1, hollow glass fibers (GHF) are used as a storage medium for polymerizable substances. The GHF are used as a composite of pre-impregnated E-glass layers and epoxy, with additional self-healing layers of hollow glass fibers at critical interfaces. This design allows the GHF to simultaneously fulfill the storage function for the self-healing agents and the reinforcement function. A second-generation Hoveyda-Grubbs catalyst is homogeneously mixed into the epoxy matrix. An advantage is that, due to the fibrous geometry of the GHF, rupture under shear stress and thus the release of the filling material is much more likely than with spherical microcapsules because of the high aspect ratio. Furthermore, the geometry of hollow fibers allows for a lower filler density.Matrix-rich areas are present in fabric-reinforced composites due to the undulation of the yarns in all inter-yarn spaces. Matrix-rich areas also dominate at the joint surfaces of fiber-reinforced composites (FRPs), so that in this configuration, the healing function of the glass-hollow fiber-filled matrix is ​​particularly effective at the critical joint surfaces. Following an initial reduction in strength of 16% for GFRP (glass fiber reinforced plastic) and 8% for CFRP (carbon fiber reinforced plastic), the incorporation of the glass-hollow fibers resulted in a 100% (GFRP) and 97% (CFRP) restoration of the original strength after loading. In both cases, however, the composites had to undergo heat treatment, which supports the transport of the healing agent to the damaged area and its curing, and therefore does not constitute truly autonomous self-healing.

[0007] Disadvantages of the methods described in the prior art for the use of hollow fibers filled with curable substances are: The high viscosity of the starting materials used necessitates complex filling procedures for the glass capillaries during production, such as applying pressure or vacuum. Glass capillaries with a narrow cross-section are not available. The catalyst is mixed into the matrix, requiring very large quantities of expensive and often toxic catalyst. The monomer encapsulation is done manually; a technically desirable automation process is not feasible. To trigger demonstrable self-healing, unacceptably high quantities of curing agents are required for the entire fiber composite. Systems used for self-healing require activation via either UV irradiation or heat (e.g., the Diels-Alder reaction), which significantly limits the respective application range.

[0008] The object of the present invention is to overcome the disadvantages of the self-healing or self-repairing systems described in the prior art. According to the invention, this object is achieved by a self-repairing fiber composite material with hollow fibers embedded in a matrix, characterized in that the glass hollow fibers are continuous and closed at their ends, wherein glass hollow fibers (A) contain one or more polyisocyanates and glass hollow fibers (B) contain one or more polyols, and the polyisocyanates and the polyols leak out of the glass hollow fibers upon cracking within the matrix, react with each other to form polyurethane, and fill the cracks, wherein the polyols, optionally diluted, have a viscosity at 20°C of at least 0.01 Pa·s, and in particular of 0.02 Pa·s to 0.8 Pa·s.As a further preferred parameter for the viscosity of the polyol, in particular the diol, in the hollow glass fibers (B), the following could be specified: 0.01 to 0.7 Pa·s, in particular 0.02 to 0.5 Pa·s. A range of 0.02 to 0.3 Pa·s is considered particularly preferred. The viscosity, abbreviated as η, is determined using a rotational viscometer according to DIN EN ISO 3219, 1994-10 edition, at 20°C.

[0009] The advantageous embodiments of the self-repairing fiber composite material according to the invention will be discussed below: It is preferred that the matrix is ​​based on an organic material in the form of a thermoset or on an inorganic material in the form of ceramic or concrete. It is particularly preferred that the thermoset matrix is ​​based on an epoxy resin (EP), polyurethane (PUR), unsaturated polyester resin (UP), polyvinyl ester resin (VE), phenol-formaldehyde resin (PF), diallyl phthalate resin (DAP), methacrylate resin (MMA), polyurethane (PUR), amino resins, in particular melamine resin (MF / MP) and urea resin (UF).

[0010] A particular feature of the invention is that the hollow glass fibers embedded in the matrix are continuous and closed at their ends. Furthermore, it is advantageous that the continuous fibers have a length of more than 3 cm, in particular more than 5 cm, as filament yarn or filament bundles.

[0011] To fulfill their essential function, namely to fracture when cracks occur in the matrix, it is preferred that the hollow glass fibers exhibit a tensile strength (according to DIN 53842-1:1976-04) in the longitudinal direction of 5 to 80, particularly 20 to 60, and / or a tensile elongation (according to DIN 53842-1:1976-04) of 0.5 to 5, particularly 1 to 3.5, and / or a modulus of elasticity of less than 50 GPa (according to DIN 53842-1:1976-04). For determining the corresponding characteristic data, see R. Teschner: "Glasfasern" (Glass Fibers), Springer-Verlag Berlin, Heidelberg, 2013. These brittleness requirements are met by ordinary glass, particularly in the form of E-glass, which is composed of hollow glass fibers. E-glass is an aluminum borosilicate glass. E-glass is by far the most commonly used type of glass in GRP (glass fiber reinforced plastic).

[0012] The cracking in the matrix mentioned above can occur, for example, due to the following influences: deformation by impact, bending stress or delamination of fiber and matrix due to heat or weather influence, such as UV light.

[0013] To further optimize the self-repairing fiber composite material according to the invention, it is preferred that the inner diameter of the hollow glass fibers be between 2 µm and 200 µm, preferably between 5 µm and 100 µm, particularly between 5 µm and 30 µm, and their outer diameter be between 5 µm and 1 mm, preferably between 8 µm and 750 µm, particularly between 10 µm and 50 µm. It is equally advantageous if the ratio of outer diameter to inner diameter of the hollow glass fibers is 5 to 1.5, particularly 3 to 2.

[0014] Within the scope of the invention, it is considered particularly preferred if the continuous hollow glass fibers are incorporated into a textile fabric, especially a woven fabric and / or a tape. It is particularly advantageous if the continuous hollow glass fibers are present in the form of rovings and / or incorporated into a textile fabric, especially a woven fabric and / or a tape. A roving is defined as a bundle, strand, or multifilament yarn made of parallel filaments and is usually provided with a sizing agent. A tape consists of flatly arranged filament bundles or rovings that are laid unidirectionally (UD) or multidirectionally. The tape laying technique enables the production of very lightweight components by laying matrix-impregnated high-performance fiber tapes in a defined manner along the forces acting within the component.The fibers are laid down in a plane, with the fiber tapes being laid down repeatedly until the component is built up with the required fiber orientations in each layer, up to the calculated component thickness. The fiber bundle is then formed into a three-dimensional structure in a subsequent forming process. This allows for high-speed fiber placement while simultaneously offering a high degree of design freedom in the component geometry.

[0015] It is advantageous to pay attention to the spacing of the hollow glass fibers in the respective matrix for optimization purposes. It is considered beneficial if the spacing of the hollow glass fibers is determined by the type of matrix and the microcracks occurring within it, which fracture the hollow glass fibers (A) and (B), allowing their contents to fill the cracks and form polyurethane. A further advantageous development of this concept is that the spacing of the hollow glass fibers (A) and (B) is in the dimension of a microcrack of approximately 1 to 5 µm, and particularly of approximately 2 to 4 µm.

[0016] The relevant reactants, in the form of polyisocyanates and polyols, are located in the aforementioned hollow glass fibers (A) and hollow glass fibers (B). As previously mentioned, upon glass breakage, these reactants escape from the hollow glass fibers and react within the crack, advantageously filling it and forming polyurethane. A further advantage of this process is that the reaction occurs at room temperature and therefore does not require initiation by external factors such as temperature, electromagnetic radiation, or electricity.

[0017] Regarding the reactants within the hollow glass fibers (A) and hollow glass fibers (B), it should be noted that these are, in abstract terms, polyisocyanates on the one hand and polyols on the other. It is advantageous if the polyisocyanate is in the form of a diisocyanate, in particular 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, pentamethylene diisocyanate, methylenediphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, 1,5-naphthalene diisocyanate, and / or xylene diisocyanate, and the polyol is preferably in the form of a diol, in particular polyethylene glycols, monoethylene glycol, diethylene glycol, 1,2- or 1,3-propanediol, 1,4-butanediol, or lower polypropylene glycols.

[0018] It is preferred that the molar ratio of polyisocyanate to polyol, in particular of diisocyanate to diol, based on the overall system, is approximately 1:1, and that, in the case of differences in the functionalities of the polyol and the diisocyanate, the respective equivalence ratio is also approximately 1:1. The aforementioned molar ratio or equivalence ratio may be subject to certain fluctuations in individual cases without significantly impairing the desired effect according to the invention. It is therefore advantageous that the deviation of the molar ratio or equivalence ratio does not exceed 10% and is particularly within the range of approximately 5 to 10%. It is permissible for those skilled in the art to add crosslinking tris- and higher-functionality isocyanates and / or alcohols to adjust specific mechanical properties, whereby the deviation of the molar ratio or equivalence ratio is not significantly impaired.The equivalence ratio of diisocyanate to diol should not exceed 10%, and in particular should be in the range of approximately 5 to 10%. Examples of polyols are trimethylolpropane, pentaerythritol, and sugar alcohols, especially sorbitol.

[0019] In the chemical processes mentioned, it is advantageous to include catalysts. Specifically, catalysts are used for the conversion of polyisocyanates in polyols in the event of cracking in the matrix, with the catalysts being, in particular, tin compounds, especially tin butyl laurate.

[0020] It is also advantageous that the catalyst is present together with the polyol in the hollow glass fiber (B). This leads to optimal chemical reactions. In principle, the catalyst can also be present in the matrix itself, i.e., outside the hollow glass fibers, but in specific cases, it can also be present in the polyisocyanate contained within the hollow glass fiber (A).

[0021] According to a preferred embodiment, the catalyst is added to the diol contained in the hollow glass fiber (A). This mixture is then filled into the corresponding capillaries. The catalyst concentration in the mixture can be between 5 and 2500 ppm, particularly between 5 and 1000 ppm, with the range of approximately 100 ppm to approximately 2500 ppm being especially preferred. It is preferred, with regard to homogeneous miscibility with the diol on the one hand and the effectiveness with respect to polymerization on the other, to use a catalyst concentration of approximately 100 ppm to approximately 2500 ppm. The required amount of catalyst in the overall composite is thus many times lower than according to the prior art, which is a significant advantage.

[0022] It is generally advantageous if the self-repairing fiber composite material according to the invention additionally contains reinforcing fibers, in particular reinforcing fibers in the form of organic and / or inorganic fibers, especially glass fibers (GF), mineral fibers (MF), ceramic fibers, carbon fibers (CF) or natural fibers (NF) as one-dimensional fibers or rovings, two-dimensional textiles, in particular in the form of woven fabrics and non-woven fabrics, or three-dimensional reinforcing structures in the form of laminates. It is expedient that the additional reinforcing fibers are in the form of long fibers with a length of 1 ≥ L ≥ 50 mm or continuous fibers with a length of > 50 mm, in particular in the form of rovings, woven fabrics, non-woven fabrics, multiaxial non-woven fabrics and / or knitted fabrics.It is also advantageous if, in the case of the additional inclusion of reinforcing fibers of the aforementioned type, a quantitative relationship between the hollow glass fibers and the additional reinforcing fibers is considered. It is expedient that the total amount of fibers included be 5 to 30 wt.%, preferably 10 to 25 wt.%, and particularly 12 to 20 wt.%, hollow glass fibers, with the remainder consisting of the additional reinforcing fibers. Alternatively, a quantification could be made via the weight ratio of glass fibers to additional reinforcing fibers. Here, it is advantageous that the weight ratio of hollow glass fibers to additional reinforcing fibers is 1:10 to 1:1, particularly 1:5 to 3:5. The viscosity values ​​given above in connection with the filling of the hollow glass fiber (B) are to be applied accordingly.Preferably, the compounds already highlighted above as advantageous diisocyanates are used.

[0023] It is particularly advantageous in all cases involving continuous hollow glass fibers, especially when incorporated into a textile fabric, to seal the ends of the fibers using a fast-curing adhesive or laser beams. A standard cyanoacrylate-based superglue can be used as a fast-curing adhesive. Regarding laser sealing, the following applies: The filaments can be cut and simultaneously melted, i.e., sealed, with a laser. Pulsed lasers, such as a pulsed CO₂ laser, are preferred. It may be necessary to pass the laser over the cutting path several times to sever all fibers within a bundle of hollow glass fibers.Microscopic examinations show that no undesired polymerization reactions occur that would appear as gray flocculations or deposits after laser irradiation at the fused filament ends. Advantageous experimental conditions and laser settings can be found in the examples.

[0024] The self-repairing fiber composite material is particularly advantageously developed in that the polyols, optionally diluted with water and / or an alcohol, have a viscosity of at least 0.01 Pa·s. The preceding statements regarding the viscosity of the undiluted polyol in the glass hollow fiber (B) apply accordingly.

[0025] The self-repairing fiber composite material according to the invention can be used in a variety of applications where the matrix shown above is subject to external influences that lead to cracking and then permanently impair the service life of the system. It is particularly preferred that the self-repairing fiber composite material be used in the fields of vehicles, aerospace, shipbuilding, architecture, wind energy generation, or sporting goods.

[0026] As shown above, it has therefore proven advantageous to use diisocyanates in the glass hollow fiber (A) and diols in the glass hollow fiber (B). The selection of the diisocyanate is expediently based on its reactivity and / or stability. Preferably used are 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene-2,4-diisocyanate, pentamethylene diisocyanate, methylenediphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, 1,5-naphthalene diisocyanate, and / or xylene diisocyanate, particularly hexamethylene diisocyanate. The selection of the diol is expediently based on its viscosity. Excessively high viscosity is disadvantageous for filling the glass hollow bodies or glass capillaries. Diols with a comparatively low molecular weight are therefore preferred. Polyethylene glycols 200, 300, and 400 are particularly preferred, especially polyethylene glycol 200.The system uses a diisocyanate / diol catalyst, preferably a tin compound of the type described above.

[0027] As mentioned above, it is possible to dilute the polyols, especially diols, to some extent with water or an alcohol, particularly a monoalcohol, especially methanol. Dilution with water is considered preferred. If a polyisocyanate / polyol, especially a diisocyanate / diol, is incorporated into the polyol or diol as a catalyst in the system, then a tin compound, preferably tin dibutyl dilaurate, is preferably used for this purpose.

[0028] When selecting the polyisocyanate component of the hollow glass fiber (A), it is advantageous to consider that polymerization, i.e., curing at room temperature, only occurs after a latency period. This ensures that the monomers do not polymerize immediately upon release, but have sufficient time to diffuse into any microcracks or existing macrocracks via capillary action, allowing the desired polymerization to occur as locally as possible. The latency period serves as a selection criterion.

[0029] Although it is readily possible for a person skilled in the art to produce the endless glass fibers used according to the invention, or thus the self-repairing fiber composite material according to the invention, based on their knowledge of the present technical field, it appears expedient to describe here a particularly advantageous embodiment of the self-repairing fiber composite material according to the invention, also with regard to its production, in connection with the advantageous use of a fabric incorporating the hollow glass fibers.

[0030] As mentioned, a fabric incorporating the aforementioned hollow glass fibers (A) and (B) can be used to particular advantage within the scope of the invention. Accordingly, the fabric contains hollow glass fibers in both the warp and weft directions. It is preferred that the hollow glass fibers (A) in the weft direction are filled with the polyisocyanate, in particular the diisocyanate, and the hollow glass fibers in the warp direction are filled with the polyol, in particular the diol, as well as with the catalyst, so that the polymerization desired according to the invention is triggered upon crack formation by the contact of the polyisocyanates and the polyols. Here are the details:

[0031] The glass hollow fibers are filled successively by vertically immersing the fabric in the corresponding polyisocyanates, in particular diisocyanates, and polyols, in particular diols (with the glass hollow fibers (A) and (B)). Advantageously, the capillary ends of the hollow fibers are first immersed in the warp direction into the preferably used diol / catalyst mixture, where they are filled by the resulting capillary action. The filling process can be visualized by adding a dye (e.g., CI Solvent Blue 63). The process can also be accelerated by increasing the temperature. The fabric is then rotated by 90° and the weft threads are filled with the diisocyanate in the same manner. It remains the responsibility of those skilled in the art to carry out the filling in reverse order or to introduce the diisocyanates in the warp direction and the diols in the weft direction.

[0032] Sealing the hollow glass fibers can be achieved in various ways, particularly using fast-curing adhesives or, in a particularly preferred application, by means of a laser. The advantage lies in the fact that the sealed components, stored in separate capillaries, retain good stability for many years. Premature inerting of the components in the absence of damage, for example due to diffusion phenomena during weathering, is therefore virtually impossible.

[0033] To produce the fiber composite body according to the invention, the finished glass hollow fiber material, sealed at the fiber ends, is inserted into a matrix using methods familiar to those skilled in the art, for which reference is made to the following examples. It should be noted here that, within the scope of the invention, thermosets preferably form the matrix; however, in individual cases, it is also possible to use thermoplastic matrices made of polymers with a low melting point. The melting point of the thermoplastic should be below the boiling points of the components (A) and (B) selected for filling the hollow fibers. In any case, good mechanical composite properties are achieved if the matrix is ​​based on thermoset epoxy resins.

[0034] From both a mechanical and economic perspective, combining the treated hollow glass fiber fabrics with layers of ordinary glass fabric (e.g., E-glass) is particularly advantageous, even in the production of multilayer fiber composites. In such composites, the proportion of ordinary glass fabric layers typically predominates. However, the treated hollow glass fiber fabric can also be used for composite production with other fiber types, as detailed in this description.

[0035] Although the above procedure is essentially aimed at specific embodiments of the invention for better explanation, it is readily apparent to the person skilled in the art that the respective procedures can be applied according to the embodiments of the invention described above.

[0036] The invention proves to be advantageous compared to the prior art from a variety of perspectives: A particular advantage is that, with regard to the entire composite body in general, a very small quantity of the self-healing or self-repairing system is sufficient. Consequently, a low degree of filling with latently reactive reactants is sufficient to achieve good self-repair in the composite body in the event of cracking.

[0037] This means that the mechanical properties are generally not affected, or only minimally affected, by the addition of these components. When the hollow glass fiber breaks, for example due to an impact and / or a crack in the fiber composite, the reaction components, in the form of the polyol and the diol, are released from the hollow glass fibers, come into contact with each other, and react within the crack. This process forms a polymeric, elastic cement that bonds the microscopically small crack surfaces. Polymerization is therefore only triggered when the hollow glass fibers break and the resulting contact between the reaction components. Because the catalyst becomes available simultaneously to initiate or at least promote the reaction, no further activation by heat, UV exposure, or other measures is required.The original mechanical strength of the fiber-reinforced composite material is fully or largely restored. This makes it possible to design lightweight fiber-reinforced composites with the same mechanical properties and a longer average service life. A particular advantage is that a very small amount of the self-repair system can be used.

[0038] The invention will be explained in more detail below using examples. Examples: Example 1 (Filling of glass hollow fibers and rovings)

[0039] Glass hollow fibers are used in the form of fiber bundles (rovings) (distributed by Polotsk-Stekklovolokno (Belarus), designated ECP 11 18.8 x 2Z100). These consist of 208 individual filaments. The total titer per filament bundle is 342 dtex (individual filament titer: 1.64 dtex). The average inner diameter of a filament is 5 µm, and the average outer diameter is 10 µm. The fiber bundles are coated with an aminosilane sizing.

[0040] To fill the rovings, one end is dipped into the monomer solution. To prevent unwanted diffusion of the monomer along the siliceous outer layer of the hollow glass fiber, a capillary barrier was installed. For this purpose, the rovings were first embedded in a block of epoxy resin, perpendicular to the fiber direction, at a distance of 10 cm from the immersion zone. A corresponding epoxy block was then cast at the other end of the roving, 5 cm from the end. This ensures that the monomer solution reaching the capillary end or the roving end does not flow back down the filament surface. Filling with Diol (Polyethylene glycol 200) :

[0041] The filling process was carried out horizontally by immersing one end of the roving in an open container filled with diol. Filling was performed at room temperature. To accelerate the filling process, the temperature can be increased. Alternatively, the filling can be accelerated by applying pressure at the capillary inlet and creating a vacuum at the capillary outlet. For this, the capillary inlet was connected to a syringe filled with diol. A vacuum pump was connected to the capillary outlet. The overpressure of 1.5–1.8 bar generated at the capillary inlet and the vacuum of 10–50 mbar generated at the capillary outlet by the vacuum pump accelerate the filling process with diol. This pressure / vacuum filling can be performed at room temperature as well as in a drying oven at 80–90°C.

[0042] (Similarly, vertical filling can be carried out at room temperature by suspending the roving with the epoxy blocks on appropriate rods and supports).

[0043] To control the filling process, the dye CI Solvent Blue 63 was added to the diol at a concentration of 20 mg / l.

[0044] After filling with Diol, the epoxy blocks were cut off and the roving ends were sealed with superglue.

[0045] Table 1 below shows the capillary filling times depending on the diol and its viscosity at 20°C, as well as the time required to fill a capillary bundle to a length of 0.5 m using the described method. For comparison, the result for dicyclopentadiene as described according to the prior art is also shown. Table 1 Diol Viscosity (20°C) [Pa·s] Filling time [h] Monoethylene glycol 0,0213 2-3 Diethylene glycol 0,0440 5-7 1,3-Propanediol 0,0418 5-7 1,4-Butanediol 0,0768 7-9 PEG 200 0,0669 6-8 PEG 300 0,0983 7-9 PEG 400 0,1290 10-12 PEG 600 0,1540 12-14 PEG 1000 firmly not possible PPG 425 0,1080 10-12 PPG 2000 0,4350 not possible DCPD 0,1640 not possible Note: PEG = Polyethylene glycol, PPG = Polypropylene glycol, DCPD = Dicyclopentadiene Filling with diisocyanate (hexamethylene diisocyanate) :

[0046] The same test conditions regarding filling apply as for the diols, whereby the corresponding safety regulations for working with isocyanates must be observed. After filling with isocyanate, the epoxy blocks were cut off and the roving ends were sealed with cyanoacrylate adhesive.

[0047] The filling process can be monitored by adding small amounts of a fluorescent dye to the diisocyanate (checked with a UV lamp). Example 2 (Filling a hollow glass fiber fabric)

[0048] A glass hollow fiber fabric (distributed by Polotsk-Stekklovolokno (Belarus) with the designation T-15(P)-76) was used, basis weight = 160 g / m². The fabric consists of hollow fiber filament yarns in the warp and weft with the same fineness as described in Example 1.

[0049] Starting at the edge of the fabric, an epoxy resin block was poured in the warp direction at a distance of approximately 10 cm from the weft direction. This "capillary barrier" thus runs across the entire width of the fabric. A corresponding capillary barrier was also poured at the opposite end of the fabric at a distance of 50 cm. Atmospheric filling with diol was carried out in a drying oven at 80-90°C by suspending the fabric with the capillary barriers vertically in the oven. The filling was done vertically with a previously prepared mixture of polyethylene glycol 200 (PEG 200) containing 1,000 ppm tin dibutyl laurate as a catalyst. After filling was complete, the capillary barriers were cut off and the warp threads at both ends were sealed with cyanoacrylate adhesive.

[0050] The fabric, filled with PEG 200 plus catalyst in the warp direction, was rotated 90°. After attaching the capillary barriers, it was filled in the weft direction with diisocyanate (hexamethylene diisocyanate) at 20°C under a fume hood. The filling was checked with a fluorescent dye (Fluorol Yellow 086). After removing the capillary barrier, the weft thread ends were sealed with cyanoacrylate adhesive. Example 3 (Production of a fiber-reinforced plastic)

[0051] A fabric made of hollow glass fibers was used, which was filled analogously to Example 2. In a modification to Example 2, a pulsed CO2 laser was used to cut the fabric and seal the filled hollow fibers. Laser performance characteristics :

[0052] 10 kHz, 25 W, multiple (up to 10x) passes at v = 500 mm / sec of the cutting path to separate all threads

[0053] The pre-cut, filled hollow glass fiber fabrics were layered alternately with standard glass fiber fabrics of the same dimensions to form a composite structure. All layers of glass fabric were precisely aligned on top of each other.

[0054] Specimen A : Glass fiber reinforced plastic (GFRP) with 10 layers of fabric: 8 layers of glass fabric (0° / 0°) as a base and on top of that 2 layers of filled hollow glass fiber fabric also in 0° / 0° orientation

[0055] Specimen B : Glass fiber reinforced plastic (GFRP) with 10 layers of fabric: Top layers: 4 layers of fiberglass fabric (0° / 0°) Middle layers: 2 layers of GHF filled (0° / 90°) Bottom layers: 4 layers of fiberglass fabric (0° / 0°)

[0056] Specimen C : Glass fiber reinforced plastic (GFRP) with 10 layers of fabric: Top layer: 1 layer of fiberglass fabric (0° / 0°) below: 2 layers of GHF filled (0° / 90°) below: 4 layers of fiberglass fabric (0° / 0°) below: 2 layers of GHF filled (0° / 90°) bottom layer: 1 layer of fiberglass fabric (0° / 0°)

[0057] These were impregnated with an epoxy matrix that was initially liquid.

[0058] Both the VARI (Vacuum Assisted Resin Infusion) and VAP (Vacuum Assisted Process) methods were used. In both methods, liquid epoxy resin and amine hardener were mixed and applied in a 5:2 ratio. Vacuum infiltration in both methods was performed at 100 mbar, generated by a vacuum pump; the liquid resin / hardener mixture cured overnight at room temperature. The vacuum of 100 mbar was maintained throughout the entire curing phase using hose clamps.

[0059] After the impregnated resin had cured, the entire structure was first separated from the metal plate. Then, using a peel ply, the structure was separated from the fiberglass fabric layers. The specimens were then removed from the resulting plate using a oscillating saw. Dimensions: 5-10 cm in the warp direction, preferably 6 cm; 11-3 cm in the weft direction, preferably 2 cm. The fiber-reinforced composite (FRP) thickness was 1.2-1.3 mm.

[0060] The test specimens (dimensions 6 x 2 cm) were then damaged using a drop test rig. A cylindrical impactor with a circular impact surface measuring 8 mm in diameter and 50.3 mm² was used. The mass of the impactor was 1.4633 kg, and the drop height was 18 cm (acceleration due to gravity). The impact energy per impact was 2.58 J.

[0061] Five impacts were triggered per impact surface. Four adjacent impact surfaces were created across the 2 cm width of the test specimen.

[0062] Self-healing or self-repair was mechanically verified on the test specimens using a three-point bending test. The specimens were positioned on two stationary cutting edges with a support distance of 50 mm. After a pre-force of 1 N was applied, the specimen was subjected to a 1% elongation. The force [N] was then measured during a 15-minute load test. Measuring device: Zwick universal testing machine. Table 2 Recovery time [days] Force impact 0 min 15 min undamaged 50,2 44,9 0 (initial after damage) 38,7 27,8 3 40,5 33,9 6 40,9 35,7 13 40,2 35,5 27 40,6 35,6

[0063] Table 2 shows measured values ​​from the 3-point bending test according to ASTM D790 for the impact-loaded self-repairing GRP as a function of the recovery time using specimen C as an example.

Claims

1. Self-repairing fiber-reinforced composite material comprising hollow glass fibers embedded in a matrix, characterized in that the hollow glass fibers are continuous and closed at their ends, wherein the hollow glass fibers (A) contain one or more polyisocyanates and the hollow glass fibers (B) contain one or more polyols, and the polyisocyanates and polyols flow out of the glass hollow fibers upon fracture of the fibers when cracks form within the matrix, react with one another to form polyurethane, and fill the cracks, wherein the polyols, optionally diluted, have a viscosity at 20°C of at least 0.01 Pa·s (measured according to DIN EN ISO 3219).

2. Self-repairing fiber-reinforced composite material according to claim 1, characterized in that the matrix is based on an organic material in the form of a thermoset or on an inorganic material in the form of ceramic or concrete, in particular the thermoset matrix is based on an epoxy resin (EP), polyurethane (PUR), unsaturated polyester resin (UP), polyvinyl ester resin (VE), phenolformaldehyde resin (PF), diallyl phthalate resin (DAP), methacrylate resin (MMA), polyurethane (PUR), amino resin, in particular melamine resin (MF / MP), and urea resin (UF).

3. Self-repairing fiber-reinforced composite material according to any of the preceding claims, characterized in that the continuous hollow glass fibers are incorporated into a textile fabric.

4. Self-repairing fiber-reinforced composite material according to at least one of claims 1 to 3, characterized in that the continuous fibers have a length of more than 3 cm as filament yarn or filament bundles.

5. Self-repairing fiber-reinforced composite material according to any one of the preceding claims, characterized in that the hollow glass fibers have a breaking strength (according to DIN 53842-1:1976-04) of 5 to 8 and / or a tensile elongation (according to DIN 53842-1:1976-04) of 0.5 to 5 and / or a modulus of elasticity (according to DIN 53842-1: 1976-04) of less than 50 GPa.

6. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the inner diameter of the hollow glass fibers is between 2 µm and 200 µm and their outer diameter is between 5 µm and 1 mm.

7. A self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the outer diameter-to-inner diameter ratio of the hollow glass fibers is 5 to 1.5.

8. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the spacing of the hollow glass fibers is determined by the type of matrix and the microcracks occurring therein, which break the hollow glass fibers (A) as well as hollow glass fibers (B), so that the cracks are filled by the formation of polyurethane, in particular, the spacing of the hollow glass fibers (A) and hollow glass fibers (B) is within the dimension of a microcrack of approximately 1 to 5 µm.

9. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the polyisocyanate is present in the form of diisocyanate as 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, pentamethylene diisocyanate, methylenediphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, 1,5-naphthalene diisocyanate, and / or xylene diisocyanate, and the polyol is present as polyethylene glycols, monoethylene glycol, diethylene glycol, 1,2- or 1,3-propanediol, 1,4-butanediol, or low-molecular-weight polypropylene glycol.

10. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the molar ratio of diisocyanate to diol, based on the total system, is approximately 1:1, and in the event of differences in the functionalities of the polyol and the polyol, the respective equivalence ratio is approximately 1:1, in particular the deviation of the molar ratio or the equivalence ratio is no more than 10%.

11. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that, in the event of crack formation in the matrix catalysts are incorporated for the reaction of the polyisocyanates and the polyols, wherein the catalysts are tin compounds, in particular the catalyst is present together with the polyol in the hollow glass fiber (B).

12. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the fiber composite material additionally contains reinforcing fibers in the form of organic and / or inorganic fibers, in particular the additional reinforcing fibers are present in the form of long fibers having a length of 1 ≥ L ≥ 50 mm or continuous fibers having a length of > 50 mm.

13. Self-repairing fiber-reinforced composite material according to claim 12, characterized in that 5 to 30 wt% of the total fibers incorporated consist of hollow glass fibers, with the remainder consisting of the additional reinforcing fibers.

14. A self-repairing fiber-reinforced composite material according to claim 12 or 13, characterized in that the weight ratio of hollow glass fibers to other reinforcing fibers is from 1:10 to 1:1.

15. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the continuous hollow glass fibers are sealed at their ends using a fast-curing adhesive or laser beams.

16. Self-repairing fiber-reinforced composite material according to at least one of the preceding claims, characterized in that the polyols, diluted with water and / or an alcohol, have a viscosity of at least 0.01 Pa·s at 20°C according to DIN EN ISO 3219.

17. Use of the self-repairing fiber-reinforced composite material according to at least one of the preceding claims in the fields of automotive engineering, aerospace, shipbuilding, architecture, wind power generation, or sporting goods.