Protein-based coupling agents for carbon fibers

Abstract

A composition comprising carbon fibers and a hydrolyzed protein, a curable resin or prepolymer component having at least one ethylenically unsaturated polymerizable group, and water in an amount of 0.0 to 10.0 wt% based on the total weight of the composition wherein the carbon fibers are present in an amount of 85.0000 to 99.9995 wt% based on the total amount of hydrolyzed protein and carbon fibers, and the hydrolyzed protein is present in an amount of 0.0005 to 15.0000 wt%.

Description

[0001] The present invention relates to a composition comprising carbon fibers and hydrolyzed proteins, wherein the carbon fibers are present in an amount of 85.0000 to 99.9995 weight-% and the hydrolyzed proteins are present in an amount of 0.0005 to 15.0000 weight-%, calculated on the total amount of hydrolyzed proteins and carbon fibers. Furthermore, the present invention relates to a method of manufacturing a carbon fiber composite and to said carbon fiber composite. The present invention further relates to an additive composition and to the use of said additive composition.

[0002] Carbon fiber reinforced composites comprise carbon fibers embedded in a polymer matrix. The polymer matrix acts as a binder between the fibers. The matrix polymer can be a thermoplastic polymer and / or a cross-linked polymer. The carbon fibers generally improve the mechanical properties of the composite compared to the matrix polymer alone. Improvements in tensile strength and stiffness have been achieved while the composite has a low density. Such materials have attractive properties for air and ground vehicles as their low weight enables low fuel or energy consumption of e.g. engine driven vehicles. Carbon fiber composites have also been used in other fields where a combination of high mechanical strength and low weight is desired, e.g. in the wind energy industry, e.g. rotor blades of windmills, in airplanes, in cars, in sports goods like tennis rackets and hockey sticks and in protective and safety clothing like safety shoes.

[0003] Additives acting as coupling agents between carbon fibers and a polymer matrix have been described. Such coupling agents can improve the bonding strength between carbon fibers and a polymer matrix and thereby improve the overall mechanical properties of carbon fiber composites.

[0004] WO 2014 / 071517 relates to a bio-composite. The composite is manufactured by embedding a fibrous material with a polymer matrix comprising animal proteins and a cross-linking agent and then curing. Several problems occur during mechanical testing. For example, the data sets show considerable standard deviations, many of the test specimens break outside the middle section, the sample surfaces are uneven, the actual sample thickness varies, delamination of the fiber layers occurs, the fiber distribution is problematic and the test specimens are wet or blistered (page 14,

[0065] -

[0066] ). These results are in line with the findings of the present invention that the use of large amounts of proteins does not lead to an improvement of the overall mechanical properties of the fiber composite but rather is detrimental.

[0005] There is a need for additives acting as coupling agents for carbon fibers used in composites which alleviate the above-mentioned drawbacks. Furthermore, the additives should effectively improve the mechanical properties of carbon fiber composites even in small amounts of application. It is a further object of the present invention to provide coupling agents which are ecologically friendly and easy to degrade. Furthermore, they should be cost-effective and easy to obtain.

[0006] In view of the above, the present application provides a composition comprising carbon fibers and a hydrolyzed protein, a curable resin or prepolymer component having at least one olefinically unsaturated polymerizable group and, optionally, water in an amount of 0.0 to 10.0 wt.-%, calculated on the total weight of the composition, wherein the carbon fibers are present in an amount of 85.0000 to 99.9995 wt.-% and the hydrolyzed protein is present in an amount of 0.0005 to 15.0000 wt.-%, calculated on the total amount of hydrolyzed protein and carbon fibers.

[0007] Hydrolysis is any chemical reaction in which a molecule of water breaks one or more chemical bonds. There are different types of hydrolysis, such as chemical hydrolysis, physical hydrolysis and enzymatic hydrolysis. "Hydrolysis" refers to the breaking of an amide bond in a polypeptide to produce shorter amino acid chains with carboxylic acid functional groups and amino groups. Hydrolysis of a protein typically results in the production of proteins and peptides with different molecular weights, as well as free amino acids. As used herein, the term "hydrolyzed protein" is a mixture of proteins, peptides and / or free amino acids resulting from the hydrolysis of a protein.

[0008] Typically, a mixture of different types of hydrolysis is used to obtain the hydrolyzed protein. For example, the protein can first be extracted by treatment with hot water, followed by further enzymatic hydrolysis. Parameters such as pH, temperature and pressure can be adjusted to obtain the desired result.

[0009] Enzymatic hydrolysis of a protein can be achieved by the catalytic action of enzymes. Hydrolytic enzymes are a class of enzymes that typically behave as biochemical catalysts that use water to break chemical bonds, which often results in the splitting of larger molecules into smaller molecules. Some common examples of hydrolytic enzymes are esterases, including lipases, phosphatases, glycosidases, peptidases and nucleases. Examples of peptidases are pepsin and trypsin.

[0010] In one embodiment, the hydrolysis step comprises alkaline hydrolysis, in which the protein is hydrolyzed in the presence of a base. In one embodiment, the base comprises an aqueous solution of an alkali metal hydroxide or an alkaline earth metal hydroxide. In one embodiment, the alkaline hydrolysis can be carried out at elevated temperature and pressure for a time sufficient to produce hydrolyzed proteins of the desired size. For example, the alkaline hydrolysis can be carried out at a temperature of about 150 °C and a pressure of about 400 kPa.

[0011] In another embodiment, the hydrolysis step comprises thermal hydrolysis. For example, the protein can be subjected to a temperature of at least about 180 °C and a pressure of about 1,200 kPa for a time sufficient to produce hydrolyzed proteins of the desired size.

[0012] The conditions and type of hydrolysis can be chosen by the person skilled in the art to produce a hydrolyzed protein with the desired degree of hydrolysis. More severe hydrolysis will result in relatively small peptides and more individual amino acids. Less severe hydrolysis will result in relatively large peptides.

[0013] Preferably, the hydrolyzed protein comprises or contains a hydrolyzed protein derived from animals or plants or mixtures thereof. Preferred are hydrolyzed proteins from animals such as pigs, chickens, cows. Furthermore, the hydrolyzed protein can be a bovine protein, a protein derived from bovine serum, pigskin and / or casein or other proteins derived from milk. Preferred plant-based proteins are derived from e.g. peas, soy, wheat, potatoes.

[0014] Further preferred is that the hydrolyzed protein is derived from collagen. Collagen is the major structural protein in the extracellular matrix present in various connective tissues of the body. As a major component of connective tissue, it is the most abundant protein in the mammalian body. Collagen is composed of amino acids that are bound together to form collagen helices. It is mainly present in connective tissues such as cartilage, bone, tendons, ligaments, and skin.

[0015] Gelatin, which is commercially available and used in food and industry, is a partially hydrolyzed collagen and typically has a molecular mass in the range of 100-500 kDa. Using the Bloom gel strength test, gelatin has a gel strength of about 30 to 300 grams Bloom and is capable of forming a gel. This gelling gelatin is also referred to as G-type gelatin. Gelatin as such should not be understood as a hydrolyzed protein according to the present application and it does not show the desired effects as shown by the experiments performed. Suitably, the hydrolyzed gelatin has a gel strength of below 30 grams Bloom, more preferably below 20 grams Bloom, even more preferably below 10 grams Bloom. Most preferably, the hydrolyzed gelatin has a gel strength between 0 and 20 grams Bloom, or even a gel strength of 0 grams Bloom. The non-gelling gelatin type is also referred to as F-type gelatin or collagen peptides and consists mainly of low molecular weight components. Preferably, the hydrolyzed protein is non-gelling, thus not capable of forming a gel.

[0016] Gel strength (jelly strength, Bloom) of gelatin is the mass in grams required to press a standard plunger (AOAC plunger, with a 12.70 mm (0.500 inch) diameter, flat surface and sharp edge, no measurable radius) 4 mm into a gel of concentration 6.67% and aged for 17 hours at 10.0°C. Suitable devices for testing gel strength are gel strength meters, such as Lloyd TA Plus, LFRA Texture Analyser (Brookfield), LFRA Texture Analyse CT3 (Brookfield), Texture Analyser TA-XTplus (Stable Micro Systems), Texture Analyser TA-XT2i (Stable Micro Systems), Zwick / Roell.

[0017] To assess gel strength, a 6.67% gelatin sample solution was prepared in a wide mouth test jar (capacity approximately 155 ml, inner diameter 59 mm + / - 1 mm, total height 85 mm and flat bottom) with 7.50 grams of gelatin and 105 milliliters of deionized water at 60°C, cooled to 10.0°C and kept at this temperature for 17 hours to age.

[0018] Preferably, the hydrolyzed protein has a molecular weight distribution wherein at least 50% by weight of the hydrolyzed protein is in the range of 1000 g / mol to 100000 g / mol. More preferably, the hydrolyzed protein has a molecular weight distribution wherein at least 50% by weight of the hydrolyzed protein is in the range of 1000 to 75000 g / mol. Again more preferably, the hydrolyzed protein has a molecular weight distribution wherein at least 50% by weight of the hydrolyzed protein is in the range of 1000 to 50000 g / mol, most preferably, the hydrolyzed protein has a molecular weight distribution wherein at least 50% by weight of the hydrolyzed protein is in the range of 5000 to 50000 g / mol.

[0019] Molecular weight was determined by high performance size exclusion chromatography (HPSEC).

[0020] Column: Medium: Silica; Particle: 5 microns; Pore size: 125 Angstrom; 7.8 mm I.D. x 30 cm length; (TSK G2000 SWXL 5 pm) (Ref. 0008540 Tosoh Bioscience GmbH)

[0021] Guard column: medium: silica; particle: 7 microns; 6 mm I.D. x 4 cm length (TSK SWXL Guardcol 7 microns (Ref. 0008543, Tosoh Bioscience GmbH)

[0022] As eluent, an aqueous solution of 1 L was prepared by dissolving 13.27 g KH2PO4, 0.445 g Na2HPO4 and 11.69 g NaCl.

[0023] Calibration standards: narrow calibration: FLLK calibration solution (CNBr bovine); wide calibration, commercially available GME porcine collagen peptide wide calibration standard (Gelita Eberbach).

[0024] In one embodiment, the hydrolyzed protein is part of an additive composition comprising the hydrolyzed protein and at least one polar solvent, wherein the polar solvent comprises at least one polymer based on ethylene oxide or propylene oxide and mixtures thereof, wherein optionally the end groups are etherified with alkyl having 1 to 6 carbon atoms. Preferably, the end groups are etherified with alkyl having 1 to 4 carbon atoms. A polymer is defined as a molecule having at least two repeating units.

[0025] Preferably, the additive composition comprises, calculated on the total weight of the hydrolyzed protein and the polar solvent,

[0026] 0.1 to 99.0 wt.-% of the hydrolyzed protein, and

[0027] 1.0 to 99.9 wt.-% of the polar solvent.

[0028] More preferably, the additive composition comprises, calculated on the total weight of the hydrolyzed protein and the polar solvent,

[0029] 0.1 to 75.0 wt.-% of the hydrolyzed protein, and

[0030] 25.0 to 99.9 wt.-% of the polar solvent.

[0031] Again more preferably, the additive composition comprises, calculated on the total weight of the hydrolyzed protein and the polar solvent,

[0032] 0.1 to 50.0 wt.-% of the hydrolyzed protein, and

[0033] 50.0 to 99.9 wt.-% of the polar solvent.

[0034] Most preferably, the additive composition comprises, calculated on the total weight of the hydrolyzed protein and the polar solvent,

[0035] 0.1 to 35.0 wt.-% of the hydrolyzed protein, and

[0036] 65.0 to 99.9 wt.% of a polar solvent.

[0037] The at least one polar solvent preferably has a molecular weight of 100 to 1000 g / mol, wherein the polar solvent comprises at least one polymer based on ethylene oxide or propylene oxide and mixtures thereof, wherein optionally the end groups are etherified with alkyl groups having 1 to 6 carbon atoms. More preferably, the polar solvent has a molecular weight of 100 to 800 g / mol, even more preferably of 200 to 800 g / mol, most preferably the polar solvent has a molecular weight of 200 to 700 g / mol. The molecular weight of the polar solvent can suitably be determined by measuring the hydroxyl content of the hydroxyl-terminated segment, for example by titration (ISO 4629-1 :2016).

[0038] Suitably, the polar solvent comprises at least one of methoxypolyethylene glycol, polyethylene glycol and polypropylene glycol.

[0039] All known kinds of carbon fibers, in addition to carbon nanofibers or other nanomaterials, can be used in the composition according to the present application. Preferably, the carbon fibers have a diameter of at least 1 micrometer based on the smallest extent in one dimension. More preferably, the carbon fibers have a diameter of at least 2 micrometers, even more preferably of at least 3 micrometers. Most preferably, the carbon fibers have a diameter in the range of 3 to 10 micrometers or 3 to 20 micrometers. Carbon fibers include amorphous carbon fibers and graphite fibers. Carbon fibers produced from various starting materials are likewise suitable, for example carbon fibers prepared from polyacrylonitrile, pitch or rayon or also from biobased sources. The carbon fibers can have undergone a chemical or mechanical surface pretreatment, for example with known sizing agents during the fiber production process. Carbon fibers which have not been specifically pretreated can likewise be used. It is advantageous if the carbon fibers have been subjected to a sizing treatment.

[0040] Depending on the intended end use, the carbon fibers can be present as filament fibers, staple fibers or chopped fibers. In some embodiments, the carbon fibers are present as a woven fabric or a nonwoven. In other embodiments, the carbon fibers are present as a roving.

[0041] The composition according to the present application is very suitable for the production of carbon fiber composites. Thus, the composition can comprise further components and materials which are typically used for the production of carbon fiber composites.

[0042] The composition further comprises a curable resin or prepolymer component having at least one ethylenically unsaturated polymerizable group. The curable resin or prepolymer component typically forms the matrix polymer of the carbon fiber composite material. Such curable resins are well known in the art. The presence of the resin in the composition typically renders the composition pasty or liquid at a temperature of 23°C. Examples include unsaturated polyester resins, for example polyester resins having unsaturated groups based on maleic acid or fumaric acid. In other embodiments, the curable resin can be a polyurethane resin having ethylenically unsaturated polymerizable groups, for example a polyurethane resin having one or more acrylate or methacrylate end groups or a polyurethane made by reacting isocyanates with polyols, typically in the presence of a catalyst or upon exposure to ultraviolet light. Other examples of suitable resins include epoxy acrylates (also known as vinyl ester resins, which are resins made by esterification of an epoxy resin with acrylic or methacrylic acid), dicyclopentadiene-based resins, epoxy resins and so-called (meth)acrylic syrup systems. Epoxy resins are a class of reactive prepolymers and polymers containing epoxy groups. Epoxy resins are produced, for example, by combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ether. Preferably, the curable resin or curable prepolymer comprises at least one of an epoxy resin, an epoxy acrylate (vinyl ester resin) or a polyurethane resin.

[0043] Other components can be present in the composition, in particular such components that are typically used in the manufacture of carbon fiber composite materials. Examples of such components include thermoplastic resins or polymers, organic or inorganic fillers and pigments, thickening agents, ultraviolet light stabilizers, mold release agents, defoamers and monomers or ss-linkers having ethylenically unsaturated polymerizable groups, such as acrylates and methacrylates or vinyl aromatic compounds. Curing initiators, such as organic peroxides, azo initiators or benzopinacol, or curing agents, such as amines, acid anhydrides or isocyanates can likewise be included in the composition.

[0044] Preferably, the composition comprises, calculated on the total amount of hydrolyzed protein, carbon fibers and curable resin or prepolymer,

[0045] 30.0000 to 89.9995 wt.-% of carbon fibers,

[0046] 0.0005 to 5.0000 wt.-% of hydrolyzed protein, and

[0047] 10.0000 to 69.9995 wt.-% of curable resin or curable prepolymer.

[0048] More preferably, the composition comprises, calculated on the total amount of hydrolyzed protein, carbon fibers and curable resin or prepolymer,

[0049] 40.0000 to 89.9995 wt.-% of carbon fibers,

[0050] 0.0005 to 5.0000 wt.-% of hydrolyzed proteins, and

[0051] 10.0000 to 59.9995 wt.-% of a curable resin or a curable prepolymer.

[0052] More preferably, the composition comprises, calculated on the total amount of hydrolyzed proteins, carbon fibers and curable resin or prepolymer,

[0053] 40.00 to 89.99 wt.-% of carbon fibers,

[0054] 0.01 to 3.00 wt.-% of hydrolyzed proteins, and

[0055] 10.00 to 59.99 wt.-% of a curable resin or a curable prepolymer.

[0056] Most preferably, the composition comprises, calculated on the total amount of hydrolyzed proteins, carbon fibers and curable resin or prepolymer,

[0057] 45.00 to 84.99 wt.-% of carbon fibers,

[0058] 0.01 to 3.00 wt.-% of hydrolyzed proteins, and

[0059] 15.00 to 54.99 wt.-% of a curable resin or a curable prepolymer.

[0060] The composition is a non-aqueous composition. A non-aqueous composition is essentially free of water. This means a paste-like or liquid composition comprising water in an amount in the range of 0.0 to 10.0 wt.-%, preferably in the range of 0.0 to 7.0 wt.-%, calculated on the total weight of the composition. More preferably, the non-aqueous composition comprises 0 to 5.0 wt.-% of water. For example, the composition comprises less than 3.0 wt.-% or less than 1.0 wt.-% of water, calculated on the total weight of the composition. Suitably, the composition comprises 0 to 3.0 wt.-% of water or 0 to 1.0 wt.-% of water, calculated on the total weight of the composition.

[0061] Suitably, the hydrolyzed proteins are in a polar solvent. Examples of suitable polar solvents are methoxypolyethylene glycol, polyethylene glycol, polypropylene glycol and mixtures thereof.

[0062] Preferably, the polar solvent comprises at least one polymer based on ethylene oxide or propylene oxide and mixtures thereof, wherein optionally the end groups are etherified with alkyl having 1 to 6 carbon atoms. More preferably, the polar solvent comprises at least one of methoxypolyethylene glycol, polyethylene glycol and polypropylene glycol. Most preferably, the polar solvent comprises at least one of methoxypolyethylene glycol 350 (MPEG 350), methoxypolyethylene glycol 500 (MPEG 500) and polypropylene glycol 600 (PPG 600). In a further embodiment, the polar solvent contains methoxypolyethylene glycol, polyethylene glycol and / or polypropylene glycol.

[0063] Suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, carbon fibers and polar solvent,

[0064] 0.0005 to 15.0000 wt.-% of hydrolyzed protein,

[0065] 60.0000 to 99.9495 wt.-% of carbon fibers, and

[0066] 0.0500 to 25.0000 wt.-% of polar solvent.

[0067] More suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, carbon fibers and polar solvent,

[0068] 0.0005 to 15.0000 wt.-% of hydrolyzed protein,

[0069] 60.0000 to 99.9495 wt.-% of carbon fibers, and

[0070] 0.0500 to 25.0000 wt.-% of polar solvent.

[0071] Again more suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, carbon fibers and polar solvent,

[0072] 0.0005 to 15.0000 wt.-% of hydrolyzed protein,

[0073] 70.0000 to 99.9495 wt.-% of carbon fibers, and

[0074] 0.0500 to 15.0000 wt.-% of polar solvent.

[0075] Most suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, carbon fibers and polar solvent,

[0076] 0.01 to 10.00 wt.-% of hydrolyzed protein,

[0077] 75.00 to 99.94 wt.-% of carbon fibers, and

[0078] 0.05 to 15.00 wt. % of a polar solvent.

[0079] Further, the composition suitably comprises, calculated on the total weight of hydrolyzed protein, curable resin or curable prepolymer, carbon fibers and polar solvent,

[0080] 0.0005 to 5.0000 wt. % of a hydrolyzed protein,

[0081] 10.0000 to 69.9495 wt. % of a curable resin or curable prepolymer,

[0082] 0.0500 to 7.0000 wt. % of a polar solvent, and

[0083] 30.0000 to 89.9495 wt. % of carbon fibers.

[0084] More suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, curable resin or curable prepolymer, carbon fibers and polar solvent,

[0085] 0.01 to 3.00 wt. % of a hydrolyzed protein,

[0086] 10.00 to 69.94 wt. % of a curable resin or curable prepolymer,

[0087] 0.05 to 7.00 wt. % of a polar solvent, and

[0088] 30.00 to 89.94 wt. % of carbon fibers.

[0089] Yet more suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, curable resin or curable prepolymer, carbon fibers and polar solvent,

[0090] 0.01 to 3.00 wt. % of a hydrolyzed protein,

[0091] 15.00 to 59.94 wt. % of a curable resin or curable prepolymer,

[0092] 0.05 to 7.00 wt. % of a polar solvent, and

[0093] 40.00 to 84.94 wt. % of carbon fibers.

[0094] Most suitably, the composition comprises, calculated on the total weight of hydrolyzed protein, curable resin or curable prepolymer, carbon fibers and polar solvent,

[0095] 0.01 to 3.00 wt. % of a hydrolyzed protein,

[0096] 15.00 to 59.94 wt% of a curable resin or curable prepolymer,

[0097] 0.05 to 5.00 wt% of a polar solvent, and

[0098] 40.00 to 84.00 wt% of carbon fibers.

[0099] The present application also relates to a method of manufacturing a carbon fiber composite material. The method comprises the steps of:

[0100] - providing a composition comprising, calculated on the total weight of carbon fibers, hydrolyzed proteins and curable resin or curable prepolymer,

[0101] a) 30.0000 to 89.9995 wt% of carbon fibers,

[0102] b) 0.0005 to 5.0000 wt% of hydrolyzed proteins,

[0103] c) 10.0000 to 69.9995 wt% of curable resin or curable prepolymer, and

[0104] - curing the composition to produce a carbon fiber composite material.

[0105] Preferably, the method of manufacturing a carbon fiber composite material comprises the steps of:

[0106] - providing a composition comprising, calculated on the total weight of carbon fibers, hydrolyzed proteins and curable resin or curable prepolymer,

[0107] a) 40.00 to 84.99 wt% of carbon fibers,

[0108] b) 0.01 to 3.00 wt% of hydrolyzed proteins,

[0109] c) 15.00 to 59.99 wt% of curable resin or curable prepolymer, and

[0110] - curing the composition to produce a carbon fiber composite material.

[0111] The curing process can be carried out by any method known in the art. The curing can be carried out at room temperature or, preferably, at elevated temperature. The temperature increase can be initiated at ambient temperature and then achieved by the exothermic behavior of the system. The temperature increase can also be forced by external heating, optionally combined with pressure.

[0112] Typical processes include sheet molding compounding (SMC), bulk molding compounding (BMC), infusion molding (RIM - resin infusion molding, RTM - resin transfer molding), compression molding, VARI (vacuum applied resin infusion), filament winding, pultrusion, and autoclave curing.

[0113] In general, the same explanations provided above for the composition of the application apply to the composition used in the process of the application.

[0114] When preparing the composition for use in the process, the individual components can be added and mixed in any suitable order. Preferably, the hydrolyzed protein is added to the carbon fibers before, together with or after the curable resin or curable prepolymer.

[0115] In some embodiments, the additive is added to the carbon fibers before the curable resin or prepolymer component is included in the composition. The additive can be added directly to the carbon fibers after fiber manufacture, before or after any chopping, cutting or weaving of the fibers. The additive can be applied to the carbon fibers in any suitable manner, for example by spraying pure or diluted additive onto the fiber surface, or by dipping the fibers into the additive, which can optionally be diluted with a solvent. The additive can also be applied to a woven or non-woven fabric or roving of carbon fibers. In another preferred embodiment, the additive of the application is applied to the carbon fibers after the first sizing process has been completed.

[0116] Alternatively, the additive can be pre-mixed with the curable resin or prepolymer component and included in the composition together with the curable resin or prepolymer component. In still further embodiments, the additive is added to the composition after the carbon fibers have been combined with the curable resin or prepolymer component.

[0117] If desired, the composition can be shaped in any suitable form prior to curing. Examples of shaping operations include placing the composition in a suitable mold, and forming a sheet by a winding or rolling or pressing process, optionally followed by a cutting step.

[0118] Curing of the composition can be carried out by free radical polymerization; the term free radical polymerization can also include processes in which chain transfer reactions occur. In a preferred embodiment, to facilitate the curing reaction, a free radical generating curing agent can suitably be included in the composition. Organic peroxides, azo initiators and benzopinacol are well known and suitable free radical generators. In addition or instead of a free radical generator, the curing process can also be effected using radiation.

[0119] Epoxy resins can react with themselves by catalytic homopolymerization, or with a wide range of co-reactants, including polyfunctional amines, acids (and anhydrides), phenols, alcohols and thiols (often referred to as mercaptans). A common epoxy resin is based on reacting epichlorohydrin with bisphenol A to produce a chemical known as bisphenol A diglycidyl ether. Polyurethanes are made, for example, by reacting isocyanates with polyols in the presence of a catalyst or upon exposure to UV light.

[0120] Curing is preferably carried out at elevated temperature, for example by heating the composition for a sufficient time and temperature to achieve the desired degree of cure. Typically, curing can be carried out at a temperature in the range of 20 to 240 °C, preferably in the range of 40 to 220 °C, more preferably in the temperature range of 60 to 210 °C, and even more preferably in the temperature range of 80 to 200 °C.

[0121] Depending on the method used, curing can be achieved in a rather short time, such as 20 seconds to 3600 seconds, but can also take up to 4, 6, 12 or even 24 hours. Curing at elevated temperature can be carried out in an autoclave or a suitable oven or directly in a press.

[0122] The present invention further relates to a carbon fiber composite obtainable by any of the described methods.

[0123] The present invention further relates to the use of the described additive composition as a coupling agent for carbon fiber composites.

[0124] The present invention also relates to the use of the described additive composition for improving the mechanical properties of carbon fiber composites.

[0125] Experimental section

[0126] List of raw materials

[0127]

[0128]

[0129] List of abbreviations used:

[0130] kDa kilo Dalton

[0131] LDPE low density polyethylene

[0132] MPEG methoxypolyethylene glycol

[0133] PPG polypropylene glycol

[0134] SMC sheet molding compound

[0135] UD unidirectional

[0136] wt weight

[0137] General preparation of coupling agent

[0138] In a 250 mL glass flask equipped with a stir bar, weigh in 20 g of protein powder (typically ANiPept M). Add 80 g of solvent (typically MPEG 350). Mix the components on a magnetic stirrer at room temperature and 200 rpm until the protein is dispersed. Avoid sedimentation, store the sample under stirring until used for further processes.

[0139] General formulation and preparation of epoxy resin system:

[0140] Table 1 : Formulation

[0141]

[0142] Fill the resin into a 30 l hobbock, add internal mold release and mix thoroughly by hand. Add curing agent 1 to the mixture and mix again. Add the coupling agent to the formulation and mix again by hand. Weigh curing agent 2 separately and add to the formulation and mix in a dissolver (700 rpm, 4.4 m / s) until completely dissolved.

[0143] Mix the complete formulation in a dissolver at 2000 rpm (12.57 m / s) until a temperature of 30°C is reached.

[0144] Preparation of fabric for epoxy resin:

[0145] Cut the fabric (typically Zoltek PANEX 35-13 50K) into 950 x 600 mm layers. Place two layers on top of each other with the orientation of the rovings aligned at 0° and weigh after production to calculate the fiber weight content.

[0146] Preparation of chopped fibers for epoxy resin:

[0147] The SMC production line was started with the production parameters and the lid was weighed with dry fiber (usually Panex 35, 13 type sized). The diameter of the lid was 320 mm, which equals 1 m 2 . To achieve an areal weight of 3000 g / m 2 , the fiber content in the lid must be 125 g.

[0148] Production of epoxy SMC

[0149] Setup of the SMC production line:

[0150] Equipment: SMC-Lab 800 HM-LB-23, manufactured by Schmidt & Heinzmann in 1989

[0151] Linear speed: 3.4 m / min

[0152] Doctor blade width: 550 mm

[0153] Opening of the doctor blade: fiber layer: 1 mm;

[0154] Opening of the doctor blade: chopped fiber: 1.2 mm

[0155] Pressure belt: 1 bar

[0156] Pressure impregnation: 1 bar

[0157] The resin system was distributed onto two doctor blades.

[0158] Use of fabric as reinforcement material:

[0159] The package was inserted into the SMC production line and the procedure was repeated until all fabric was used up. At the end of the SMC production line, each package was individually cut off and laid flat on a table, after all packages had passed, it was packaged as a whole and stored in a heated storage chamber at 30°C for 14 days.

[0160] Use of chopped fiber as reinforcement material:

[0161] The chopped carbon fiber fell from the cutter onto the resin on the SMC production line (combination of lengths 25 and 50 mm). The compound was processed through the production line and wound up at the end and stored in a heated storage chamber at 30°C for 14 days.

[0162] Molding of the cured epoxy SMC

[0163] Molding parameters.

[0164] Equipment: Elast 200V from Engel, No. 207371, manufactured in 2016

[0165] Pressure: 1000 KN / 83 bar

[0166] Time: 300 sec

[0167] Temperature: 150°C

[0168] Closing speed: 12 mm / s

[0169] Thickness: 2.5 mm

[0170] Mold size: 300 x 400 mm

[0171] After maturing, the SMC was cut to a size of 390 x 290 mm. The SMC with fabric was molded in four layers and the SMC with chopped fibers was molded in two layers. All layers were weighed to calculate the fiber weight content of the final part.

[0172] Before molding, the prepared SMC was stored overnight at 20°C in order to process better during molding.

[0173] The mold was applied with release agent using a brush. The release agent was also applied to the substrate. The plate was molded for 300 seconds to heat it to the processing temperature.

[0174] Both the SMC and the substrate were placed in the mold and molded for 200 seconds. After 200 seconds, the substrate was removed and molded for another 90 seconds.

[0175] All panels were weighed and the fiber weight content of the final part was calculated. The panels were optically inspected.

[0176] Table 2: Formulation and preparation of the vinyl ester resin system:

[0177]

[0178] The vinyl ester resin was weighed into a 30 l hobbock and the saturated polyester was mixed in thoroughly by hand. The processing additives were added to the formulation and mixed by hand. The peroxide was then added and mixed by hand. The coupling agent and the LDPE were added and mixed separately. The formulation was then mixed in a dissolver at 2000 rpm (12.57 m / s) until a temperature of 30°C was reached. Finally, the magnesium oxide paste for thickening was added during mixing at 700 rpm (4.4 m / s) until complete dissolution. The formulation was then mixed at 700 rpm (4.4 m / s) for 1 minute.

[0179] For spray application, the vinyl ester resin was prepared accordingly, but without the coupling agent.

[0180] Preparation of fabric for vinyl ester:

[0181] The fabric (ZOLTEK PANEX 35-13 50K) was cut into 950 x 600 mm layers. Two layers were placed on top of each other with the orientation of the rovings aligned at 0° and weighed after production to calculate the fiber weight content.

[0182] Preparation of fabric for vinyl ester resin, spray application:

[0183] The fabric (Mitsubishi TR50S 12K) was cut into square pieces with a side length of 600 mm. The additive was spray applied to both sides of the square pieces using a spray gun SAT Jet 30 HVLP Digital using a 1.3 mm nozzle. The amount of coupling agent applied was 6.5 grams per piece (18.05 g / m 2 ).

[0184] The carbon fiber composition was stored for 24 hours at 23 °C before impregnation with the curable resin.

[0185] Preparation of chopped fibers for vinyl ester resin:

[0186] The SMC production line was started with the production parameters and the dry fiber (Panex 35, type 13 sizing) was weighed with the lid. The diameter of the lid was 320 mm, which equals 1 m 2 . To achieve an area weight of 3000 g / m 2 , the fiber content in the lid has to be 125 g.

[0187] Production of vinyl ester SMC

[0188] Setup of the SMC production line:

[0189] Equipment: SMC-Lab 800 HM-LB-23, manufactured by Schmidt & Heinzmann in 1989

[0190] Line speed: 3.4 m / min

[0191] Scraper width: 550 mm

[0192] Opening of the scraper: fiber layers: 1 mm

[0193] Opening of the scraper: chopped fibers: 1.2 mm

[0194] Pressure belt: 1 bar

[0195] Pressure impregnation: 1 bar

[0196] The resin system was dispensed onto two doctor blades.

[0197] Use of fabric as reinforcement material:

[0198] The packs were inserted on the SMC line and the procedure was repeated until all fabric was used. At the end of the SMC line, each pack was cut individually and laid flat on a table, after all packs had passed, it was packed together and stored in a heated storage chamber at 30°C for 1 day.

[0199] Use of chopped fibers as reinforcement material:

[0200] Chopped carbon fibers were dropped from a chopper onto the resin on the SMC line (combination of lengths 25 and 50 mm). The compound was processed through the line and wound up at the end and stored in a heated storage chamber at 30°C for 1 day.

[0201] Molding of cured vinyl ester SMC

[0202] Molding parameters.

[0203] Equipment: Elast 200V from Engel, No. 207371, manufactured in 2016

[0204] Pressure: 1000 KN / 83 bar

[0205] Time: 300 sec

[0206] Temperature: 150°C

[0207] Closing speed: 12 mm / s

[0208] Thickness: 2.5 mm

[0209] Mold size: 300 x 400 mm

[0210] After curing, the SMC was cut to a size of 390 x 290 mm.

[0211] The SMC with fabric was molded in four layers and the SMC with chopped fibers was molded in two layers.

[0212] All panels were weighed and the fiber weight content of the final part was calculated.

[0213] Molding of cured vinyl ester SMC, spray application

[0214] The above stack was molded using a press model PYXZ from Zeulenroda and cured at 150°C for 120 seconds at a pressure of 133 bar.

[0215] Mechanical testing of reinforced samples

[0216] The face sheets were cut with a saw (Diamant Boart DV 27, diamond blade). For measuring the tensile strength according to DIN EN ISO 527-4:1997-07, the carbon fiber composite sheet was cut into specimens with edge length of 150 mm x 2-10 mm. For measuring the transverse tensile strength according to DIN EN ISO 527-5B, the carbon fiber composite sheet was cut into specimens with edge length of 250 mm x 25 mm. For measuring the flexural strength according to DIN EN ISO 14125, the carbon fiber composite sheet was cut into specimens with edge length of 80 mm x 15 mm. The flexural strength measurement was performed parallel to the fiber direction.

[0217] Bending test DIN-EN-ISO 14125:2011 unidirectional fabric and chopped fibers

[0218] Tensile test DIN-EN-ISO 527-4:1997 chopped fibers

[0219] Transverse tensile test DIN-EN-ISO 527-5B:2010 unidirectional fabric

[0220] Before testing, all specimens were stored for 24 hours at 23 °C, 50% relative humidity.

[0221] After testing, the results were evaluated and converted into an average fiber weight content within one experimental setup.

[0222] Concentration in the epoxy resin system

[0223] The coupling agent was prepared according to "General preparation of coupling agents" with 20% ANiPept M and 80% MPEG 350. Reinforced samples were prepared with the resin according to "General formulation and preparation of epoxy resin systems" and with the fabric according to "Preparation of fabrics for epoxy resins". The epoxy SMC was prepared according to "Production of epoxy SMC" and molded according to "Molding of epoxy SMC after curing". The mechanical properties were tested according to "Mechanical testing of reinforced samples".

[0224] The improvement of the mechanical properties is indicated in the following table 3 as % difference compared to the control panel without coupling agent.

[0225] Table 3

[0226]

[0227] With increasing concentration of the medium hydrolyzed protein, the transverse tensile strength, the flexural strength and the E-Modulus flexural strength also increased.

[0228] Physical form of the coupling agent

[0229] The coupling agent was prepared according to “General preparation of coupling agents” and applied at 5 wt% on the resin. Reinforced samples were prepared with the resin according to “General formulation and preparation of epoxy resin systems” and with the fabric according to “Preparation of fabric for epoxy resins”. As curing agent 2, TRAC 0061 H was used. Epoxy SMC was prepared according to “Production of epoxy SMC” and moulded according to “Moulding of epoxy SMC after maturation”. Mechanical properties were tested according to “Mechanical testing of reinforced samples”. The improvement of the mechanical properties is expressed in % difference compared to the control panel without coupling agent in Table 4 below.

[0230] Table 4

[0231]

[0232] Table 4 shows that the addition of hydrolyzed protein in powder form as well as hydrolyzed protein dispersion leads to an improvement of the tensile strength in the transverse direction and the flexural strength.

[0233] Alternative carbon fabric for epoxy resins

[0234] The coupling agent was prepared according to “General preparation of coupling agents”. The concentration of the protein in the solvent is listed in Table 5 below. The coupling agent was applied at 5 wt% on the resin. Reinforced samples were prepared with the epoxy resin according to “General formulation and preparation of epoxy resin systems” and according to “Preparation of fabric for epoxy resins”. As curing agent 2, TRAC 0061 H was used. The differences in fabric are listed in the table below.

[0235] The improvement of the mechanical properties is expressed in % difference compared to the control panel without coupling agent in Table 5 below.

[0236] Table 5

[0237]

[0238] On epoxy carbon composites with different carbon fabrics, a significant improvement of the mechanical properties by the addition of hydrolyzed protein dispersion can be shown.

[0239] Alternative curing systems, internal release agents and fabrics

[0240] The coupling agent was prepared according to “General preparation of coupling agents” with 20% ANiPept M and 80% MPEG 350 and applied at 5 wt% on the resin. Reinforced samples were prepared with the epoxy resin according to “General formulation and preparation of epoxy resin systems” and according to “Preparation of fabric for epoxy resins”. The differences in curing agent, internal release agent and fabric are listed in Table 6 below.

[0241] The increase in mechanical properties is expressed in the following table as the difference compared to a control plate containing no coupling agent.

[0242] Table 6

[0243]

[0244] Table 6 shows the significant increase in mechanical properties brought by the addition of the hydrolyzed protein dispersion, even with different curing systems, internal mold release agents and carbon fabrics.

[0245] Variation of the reinforcing material

[0246] The coupling agent was prepared according to "General preparation of coupling agents" with 20% ANiPept M and 80% MPEG 350 and applied at 5% by weight on the resin. The reinforced samples were prepared according to "General formulation and preparation of epoxy resin systems" and according to "Preparation of fabrics for epoxy resins" with carbon fibers Panex 35, type 13 sizing.

[0247] The increase in mechanical properties is expressed in the following table 7 as the difference compared to a control plate containing no coupling agent.

[0248] Table 7

[0249]

[0250] Table 7 shows the significant increase in mechanical properties brought by the addition of the hydrolyzed protein to the application system.

[0251] Size distribution of the protein hydrolysate

[0252] The coupling agent was prepared according to "General preparation of coupling agents" with 20% protein hydrolysate (listed in the following table 8) and 80% MPEG 350 and applied at 5% by weight on the resin. The reinforced samples were prepared according to "General formulation and preparation of epoxy resin systems" and according to "Preparation of fabrics for epoxy resins" with epoxy resins.

[0253] The increase in mechanical properties is expressed in the following table as the difference compared to a control plate containing no coupling agent.

[0254] Table 8

[0255]

[0256] The hydrolyzed proteins with different size distributions (1-100 kDa) all showed an effect on the increase in mechanical properties of the epoxy carbon composites.

[0257] Alternative solvents

[0258] Coupling agents were prepared according to "General preparation of coupling agents" with 20% ANiPept M and 80% solvent and applied at 5 wt% on the resin. Different solvents are listed in Table 9 below. Reinforced samples were prepared with epoxy resin according to "General formulation and preparation of epoxy resin systems" and according to "Preparation of fabrics for epoxy resins".

[0259] The increase in mechanical properties is expressed in Table 9 below as the % difference compared to a control plate without coupling agent.

[0260] Table 9

[0261]

[0262] Table 9 shows that in different polar solvents, the effect of hydrolyzed proteins on the increase in mechanical properties can be obtained.

[0263] Alternative protein sources

[0264] Coupling agents were prepared according to "General preparation of coupling agents" with 20% protein and 80% MPEG 350 and applied at 5 wt% on the resin. The protein sources are listed in Table 10 below. Reinforced samples were prepared with epoxy resin according to "General formulation and preparation of epoxy resin systems" and according to "Preparation of fabrics for epoxy resins".

[0265] The increase in mechanical properties is expressed in Table 10 below as the % difference compared to a control plate without coupling agent.

[0266] Table 10

[0267]

[0268] Protein hydrolysates from various sources (plant or animal) bring a significant increase in the mechanical properties of carbon fiber composites. Non-hydrolyzed proteins, such as gelatin (type G gelatin) cannot be incorporated into the system and it is therefore not possible to measure the mechanical properties.

[0269] Vinyl ester resin system

[0270] Coupling agents were prepared according to "General preparation of coupling agents" with 20% ANiPept M and 80% MPEG 350. Different concentrations on the resin system are listed in Table 11 below. Reinforced samples were prepared with vinyl ester resin according to "Formulation and preparation of vinyl ester resin systems" and with fibers according to "Preparation of chopped fibers for vinyl esters".

[0271] The increase in mechanical properties is expressed in Table 11 below as the % difference compared to a control plate without coupling agent.

[0272] Table 11

[0273]

[0274] Table 11 shows that for the vinyl ester carbon composites, an improvement in mechanical properties can also be obtained.

[0275] Vinyl ester resin system, spray applied

[0276] The coupling agent was prepared according to "General preparation of coupling agents" with 20% ANiPept M and 80% MPEG 350. The reinforced samples were prepared with the vinyl ester resin according to "Formulation and preparation of vinyl ester resin systems" (for spray application) and with the fabric according to "Preparation of fabric for vinyl ester, spray application".

[0277] The improvement in mechanical properties is expressed in the following table 12 as % difference compared to the control panel without coupling agent.

[0278] Table 12

[0279]

[0280] By first spray applying the coupling agent on the fabric and then adding the vinyl ester resin, an improvement in mechanical properties can be obtained.

Claims

1. A composition comprising a) carbon fiber, b) a curable resin or prepolymer component having at least one ethylenically unsaturated polymerizable group, c) water in an amount of 0.0 to 10.0 wt. %, based on the total weight of the composition, and d) hydrolyzed protein, The carbon fiber is present in an amount of 85.0000 to 99.9995 wt %, and the hydrolyzed protein is present in an amount of 0.0005 to 15.0000 wt %, based on the total amount of the hydrolyzed protein and the carbon fiber.

2. The composition according to claim 1, comprising, calculated based on the total amount of hydrolyzed protein, carbon fiber and curable resin or prepolymer, 30.0000 to 89.9995% by weight of carbon fibers, 0.0005 to 5.0000% by weight of hydrolyzed protein, and 10.0000 to 69.9995 wt. % of a curable resin or curable prepolymer.

3. The composition of any preceding claim, wherein the curable resin or curable prepolymer comprises at least one of an epoxy resin, a vinyl ester resin, or a polyurethane resin.

4. A composition according to any one of the preceding claims, wherein the hydrolysed protein is in a polar solvent.

5. Composition according to any one of the preceding claims, wherein the polar solvent comprises at least one polymer based on ethylene oxide or propylene oxide and mixtures thereof, wherein the terminal groups are optionally etherified with alkyl groups having 1 to 6 carbon atoms.

6. A composition according to any one of the preceding claims, wherein the hydrolysed protein comprises or contains hydrolysed protein derived from an animal or plant, or a mixture thereof.

7. A composition according to any preceding claim, wherein the hydrolysed protein is derived from collagen.

8. The composition according to any one of the preceding claims, wherein the hydrolyzed protein has a molecular weight distribution wherein at least 50% by weight of the hydrolyzed protein is in the range of 1000 g / mol to 100000 g / mol.

9. The composition according to any one of the preceding claims, wherein the composition comprises, calculated based on the total weight of the hydrolyzed protein, the carbon fibers and the polar solvent, 0.0005 to 15.0000% by weight of hydrolyzed protein, 60.0000 to 99.9495 wt% carbon fibers, and 0.0500 to 25.0000 wt% polar solvent.

10. A composition according to any one of the preceding claims comprising, calculated based on the total weight of the hydrolysed protein, the curable resin or curable prepolymer, the carbon fibres and the polar solvent, 0.0005 to 5.0000% by weight of hydrolyzed protein, 10.0000 to 69.9495% by weight of a curable resin or curable prepolymer, 0.0500 to 7.0000 wt% of a polar solvent, and 30.0000 to 89.9495 wt% carbon fibers.

11. A method for manufacturing a carbon fiber composite material, comprising the steps of: i) providing a composition comprising, calculated based on the total weight of carbon fibers, hydrolyzed protein and curable resin or curable prepolymer, a) 30.0000 to 89.9995% by weight of carbon fibers, b) 0.0005 to 5.0000% by weight of hydrolyzed proteins, c) 10.0000 to 69.9995 wt. % of a curable resin or curable prepolymer, and ii) curing the composition to produce a carbon fiber composite material.

12. The method of claim 11, wherein the hydrolyzed protein is added to the carbon fibers before, together with, or after the curable resin or curable prepolymer.

13. A carbon fiber composite material obtainable by the method according to any one of claims 11 to 12.

14. An additive composition comprising hydrolyzed protein, and At least one polar solvent, wherein the polar solvent comprises at least one polymer based on ethylene oxide or propylene oxide and mixtures thereof, wherein the terminal groups are optionally etherified with alkyl groups having 1 to 6 carbon atoms.

15. The additive composition of claim 14, wherein the composition comprises, based on the total weight of the hydrolyzed protein and the polar solvent, 0.1 to 50.0% by weight of hydrolyzed protein, and 50.0 to 99.9 wt% polar solvent.

16. The additive composition according to any one of claims 14 to 15, wherein the polar solvent has a molecular weight of 100-1000 g / mol.

17. The additive composition according to any one of claims 14 to 16, wherein the polar solvent comprises at least one of methoxypolyethylene glycol, polyethylene glycol, and polypropylene glycol.

18. Use of the additive composition according to any one of the preceding claims as a coupling agent for carbon fiber composite materials.

19. Use of the additive composition according to any one of the preceding claims for improving the mechanical properties of carbon fiber composite materials.

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