WO2009038971A1

WO2009038971A1 - Erosion resistant impregnating resin systems and composites

Info

Publication number: WO2009038971A1
Application number: PCT/US2008/075101
Authority: WO
Inventors: James M. Nelson; Ryan E. Marx
Original assignee: 3M Innovative Properties Company
Priority date: 2007-09-18
Filing date: 2008-09-03
Publication date: 2009-03-26

Abstract

Impregnating resin systems exhibiting improved erosion resistance upon curing are described. The impregnating resin systems comprise a curable resin and surface-modified nanoparticles. The surface modified nanoparticles comprise a core, a surface, and a surface modifying agent attached to the surface. The composite articles comprise a fibrous layer impregnated with such impregnating resin systems. Methods of enhancing the erosion resistance of composite articles are also described.

Description

EROSION RESISTANT IMPREGNATING RESIN SYSTEMS AND COMPOSITES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 60/973,205, filed September 18, 2007, the disclosure of which is incorporated by reference herein in its entirety.

FIELD

[0002] The present disclosure relates to the use of surface modified nanoparticles in impregnating resin systems to improve the erosion resistance of composite articles. The present disclosure also relates to methods of improving the erosion resistance of composite articles. Composite articles having improved erosion resistance are also disclosed.

SUMMARY

[0003] Briefly, in one aspect, the present disclosure provides an erosion resistant composite article comprising a fibrous layer impregnated with a curable resin and surface modified nanoparticles comprising a core, a surface, and a surface modifying agent attached to the surface. In some embodiments, the fibrous layer comprises two or more fibrous plies. In some embodiments, the fibrous layer comprises at least one of glass fibers, inorganic fibers, organic fibers, natural fibers, or carbon fibers.

[0004] In some embodiments, the curable resin is a thermosetting resin. In some embodiments, the resin is selected from the group consisting of epoxy resins, polyester resins, acrylic resins, and vinyl esters. In some embodiments, the fibrous layer is impregnated with a reactive diluent. In some embodiments, the reactive diluent is styrene.

[0005] In some embodiments, the surface modified nanoparticles comprise silica. In some embodiments, the surface modified nanoparticles comprise an inorganic surface. In some embodiments, the inorganic surface comprises a metal oxide.

[0006] In some embodiments, the surface modifying agent is a reactive surface modifying agent. [0007] In another aspect, the present disclosure provides an impregnating resin system comprising a curable resin and surface modified nanoparticles. In some embodiments, when cured, the erosion resistance of the impregnating resin as measure according to the Rain Erosion Resistance Test is at least 2 times (in some embodiments, 5 times, and in some embodiments, 10 times) greater than the erosion resistance of the curable resin absent the surface modified nanoparticles when cured.

[0008] In yet another aspect, the present disclosure provides methods of improving the erosion resistance of a composite article. In some embodiments, the method comprises infusing a fibrous layer with any of the impregnating resin systems described herein and curing the curable resin to form a cured composite article.

[0009] In a further aspect, the present disclosure relates to the use of surface-modified nanoparticles in an impregnating resin system to improve the erosion resistance of a composite article.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 illustrates an exemplary composite article according some embodiments of the present disclosure.

[0011] FIG. 2 illustrates a cross-section of a surface-modified nanoparticle according to some embodiments of the present disclosure.

[0012] FIG. 3 illustrates a Rain Erosion Resistance apparatus.

[0013] FIG. 4 illustrates the feed portion of the Rain Erosion Resistance apparatus of FIG. 3.

[0014] FIG. 5 is an image of the surface of the composite article of Comparative Example 2.

[0015] FIG. 6 is an image of the surface of the composite article of Example 2.

DETAILED DESCRIPTION

[0016] Composite materials comprising a resin-impregnated fibrous matrix are used in a wide variety of applications. In many applications, e.g., aerospace, wind blade, architectural, sporting goods, marine and other transportation (i.e. rail cars) the composites suffer from limited erosion resistance in use environments. Helicopter blades, for example, see substantial deterioration of their composite structure upon flying in rainstorms. Bike frames on traditional road and off-road bikes experience considerable pitting and scratching through normal use that may lead to shortened product life due to composite fatigue. Composites used in wind towers see considerable rain exposure and will see increasing exposure to rough climates as more off-shore turbines are built and exposed to sea-air environments (e.g., salt).

[0017] The use of protective coatings or films to impart erosion resistance has several deficiencies. For example, the coating or film can be expensive to apply and may require multiple additional steps. The coatings or films add weight to the structure, particularly when adhesives, primers, or adhesion promoters are used to bond the coatings or films to the surface of the composite. The coatings or films can interfere with desirable aesthetic features of the underlying composite, e.g., the visually striking and distinctive carbon weave pattern observed with in applications using carbon fiber based composites, e.g., sporting goods. Finally, coatings and films can craze and/or delaminate leading to failure or costly repairs.

[0018] In contrast to the use of coatings and films, the present inventors have discovered that the erosion resistance of a composite can be significantly enhanced through the use of nanoparticle-containing impregnating resin systems. One method of assessing erosion resistance is described herein as the "Rain Erosion Resistance" test. In some embodiments, upon curing the erosion resistance, as determined by the Rain Erosion Resistance test, of the nanoparticle-containing impregnating resin systems is at least 2 times greater, in some embodiments, at least 5 times greater, and in some embodiments, at least 10 times greater than the erosion resistance of the same cured resin system absent the surface modified nanoparticles. Similarly, in some embodiments, upon impregnating the resin system in a fibrous layer and curing to form a cured composite article, the erosion resistance (as determined by the Rain Erosion Resistance test) of the cured composite article is at least 2 times greater, in some embodiments, at least 5 times greater, and in some embodiments, at least 10 times greater than the erosion resistance of the same cured composite article absent the surface-modified nanoparticles. [0019] In some embodiments, these resin systems can be used in current composite infusion processes and with current fibrous matrices offering great design flexibility without drastically affecting cure kinetics or resin viscosity. In some embodiments, the use of resin systems of the present disclosure may result in lower weight composites while providing improved erosion resistance. For example, in some embodiments, the increase in mechanical properties obtained by using some resin systems of the present disclosure may enable a reduction in the number of fibrous plies while maintaining or enhancing the mechanical properties relative to part produced using traditional resin systems, i.e., resin systems lacking surface-modified nanoparticles.

[0020] Referring to FIG. 1, an erosion-resistant composite part according to some embodiments of the present disclosure is shown. Composite part 100 comprises fibrous layer 110 impregnated with an impregnating resin system. The impregnating resin system comprises resin 120, and surface-modified nanoparticles 130. In some embodiments, fibrous layer 110 includes multiple fibrous plies.

[0021] In some embodiments, the fibrous layer comprises inorganic fibers, e.g., glass fibers. In some embodiments, the fibrous layer comprises organic fibers, including, e.g., natural fibers. In some embodiments, the fibrous layer comprises carbon fibers. In some embodiments, combinations of these and other fibers may be used.

[0022] Generally the present disclosure relates to any composite part including e.g., those used in aerospace applications, architectural applications, marine and other transportation applications, and sporting goods. In some embodiments, surface 101 of the composite parts of the present disclosure exhibit improved erosion resistance relative to composite parts made with the same resin system absent the surface modified nanoparticles. In some embodiments, the erosion resistance is at least 2 times greater, in some embodiments, at least 5 times greater, and in some embodiments, at least 10 times greater

[0023] Generally, resin 120 is a curable resin, e.g., a thermosetting resin. Any curable resin may be used. Exemplary curable resins include epoxies, vinyl esters, polyesters, acrylics and the like. In some embodiments, the resin system may include a reactive diluent, e.g., styrene, in addition to the curable resin. Generally, reactive diluents co-react with the curable resin and/or with other components of the resin system. [0024] Referring to FIG. 2, generally nanoparticles 130 comprise core 131, having an inorganic surface 132. In some embodiments, the core comprises an inorganic material and the surface is integral to the core. In some embodiments, inorganic surface 132 may comprise a separate layer surrounding core 131. In such embodiments, the core may comprise organic and/or inorganic materials.

[0025] In some embodiments, surface 132 comprises a metal oxide. Any known metal oxide may be used. Exemplary metal oxides include silica, titania, alumina, zirconia, vanadia, chromia, antimony oxide, tin oxide, zinc oxide, ceria, and mixtures thereof. In some embodiments, the nanoparticle comprises an oxide of one metal (e.g., a surface layer) deposited on an oxide of another metal (e.g., a core). In some embodiments, the nanoparticle comprises a metal oxide surface deposited on a non-metal oxide core.

[0026] In some embodiments, the nanoparticles have a primary particle size of between about 5 nanometers to about 500 nanometers, and in some embodiments from about 5 nanometers to about 250 nanometers, and even in some embodiments from about 50 nanometers to about 200 nanometers. In some embodiments, the cores have an average diameter of at least about 5 nanometers, in some embodiments, at least about 10 nanometers, at least about 25 nanometers, at least about 50 nanometers, and in some embodiments, at least about 75 nanometers. In some embodiments the cores have an average diameter of no greater than about 500 nanometers, no greater than about 250 nanometers, and in some embodiments no greater than about 150 nanometers.

[0027] As used herein, "primary particle size" refers to the maximum cross-section dimension of a particle. Thus, for spherical particles, the primary particle size would correspond to the diameter of the spherical particle. As a further example, for elliptical particles, the primary particle size would correspond to the major axis of the particle. Particle size measurements can be based on, e.g., transmission electron microscopy.

[0028] Exemplary zirconias are available from Nalco Chemical Co. under the trade designation "Nalco 00SS008" and from Buhler AG Uzwil, Switzerland under the trade designation "Buhler zirconia Z-WO sol". Zirconia nanoparticle can also be prepared using known techniques such as described in U.S. Patent Application serial No. 11/027426 filed Dec. 30, 2004 and U.S. Patent No. 6,376,590. Exemplary mixed metal oxides for use in materials of the invention are commercially available from Catalysts & Chemical Industries Corp., Kawasaki, Japan, under the trade designation "Optolake 3. Commercially available silicas include those available from Nalco Chemical Company, Naperville, Illinois (for example, NALCO 1040, 1042, 1050, 1060, 2327 and 2329) and Nissan Chemical America Company, Houston, Texas.

[0029] In some embodiments, the core is substantially spherical. In some embodiments, the cores are relatively uniform in primary particle size. In some embodiments, the cores have a narrow particle size distribution. In some embodiments, the core is substantially fully condensed. In some embodiments, the core is amorphous. In some embodiments, the core is isotropic. In some embodiments, the core is at least partially crystalline. In some embodiments, the core is substantially crystalline. In some embodiments, the particles are substantially non-agglomerated. In some embodiments, the particles are substantially non-aggregated in contrast to, for example, fumed or pyrogenic silica.

[0030] Referring again to FIG. 2, nanoparticles 130 are surface-modified, i.e., surface treatment agent 134 is attached to inorganic surface 132. Generally, a surface treatment agent is an organic species having a first functional group capable of attaching (e.g., chemically (e.g., covalently or ionically) attaching, or physically (e.g., strong physisorptively) attaching) to the surface of a nanoparticle, wherein the attached surface treatment agent alters one or more properties of the nanoparticle. In some embodiments, surface treatment agents have no more than three functional groups for attaching to the core. In some embodiments, the surface treatment agents have a low molecular weight, e.g., a weight average molecular weight less than 1000.

[0031] In some embodiments, the surface-modified nanoparticles may be reactive; i.e., at least one of the surface treatment agents used to surface modify the nanoparticles of the present disclosure includes a functional group capable of reacting with one or more components of the impregnating resin system, e.g., the curable resin(s) and/or the optional reactive diluent(s).

[0032] In some embodiments, the surface treatment agent further includes one or more additional functional groups providing one or more additional desired properties. For example, in some embodiments, an additional functional group may be selected to provide a desired degree of compatibility between the reactive, surface modified nanoparticles and one or more of the additional constituents of the resin system, e.g., one or more of the crosslinkable resins and/or reactive diluents. In some embodiments, an additional functional group may be selected to modify the rheology of the resin system, e.g., to increase or decrease the viscosity, or to provide non-Newtonian rheological behavior, e.g., thixotropy (shear-thinning).

[0033] In some embodiments, two or more different surface treatment agents may be used. In some embodiments, each surface treatment agent may provide a different property, e.g., one surface treatment agent may react with a component of the resin system, and one surface treatment agent may provide compatibility with the resin system. In some embodiments, two or more surface treatment agents will be selected to achieve a desired value for a particular property, e.g., a combination of polar and non-polar surface treatment agents may be selected to achieve the desired compatibility with the resin system.

[0034] Nanoparticle resin systems according to the present disclosure having a wide range of rheological behavior can be obtained by different combinations of particle surface treatment agents, curable resins and reactive diluents. Surface treatment agents that make the particles more compatible with the resins and/or reactive diluents tend to provide fluid, relatively low viscosity, substantially Newtonian compositions. Surface treatment agents that make the particles only marginally compatible with the curable resins and/or reactive diluents tend to provide compositions that exhibit one or more of thixotropy, shear thinning, and/or reversible gel formation, preferably in combination with low elasticity. Surface treatment agents that are more incompatible with the curable resins and/or reactive diluents generally provide formulations that tend to settle, phase separate, agglomerate or the like. Thus, it can be appreciated that the selection of the surface treatment agents offers tremendous control and flexibility over rheological characteristics.

[0035] Examples of surface treatment agents include alcohols, amines, carboxylic acids, sulfonic acids, phosphonic acids, silanes and titanates. The selection of a particular treatment agent is determined, in part, by the chemical nature of the metal oxide surface. In some embodiments, silanes may be used for silica and other for siliceous fillers. In some embodiments, silanes and carboxylic acids may be used for metal oxides such as zirconia. [0036] The surface modification can be done either prior to mixing with one or more of the other components of the resin system or after mixing. In some embodiments, it may be useful to react the silanes with the particle or nanoparticle surface before incorporation into the other components of the resin system.

[0037] The required amount of surface treatment agent is dependant upon several factors such particle size, particle type, particle surface area, surface treatment agent molecular weight, and surface treatment agent type. In some embodiments, approximately a monolayer of surface treatment agent is attached to the surface of the particle. The attachment procedure or reaction conditions required also depend on the surface treatment agent used. In some embodiments, e.g., with silanes, it may be useful to surface treat at elevated temperatures under acidic or basic conditions for from 1-24 hours. Surface treatment agents such as carboxylic acids may not require elevated temperatures or extended time.

[0038] Representative types of surface treatment agents suitable for the compositions of the present disclosure include compounds such as, for example, [2-(3-cyclohexenyl) ethyl] trimethoxysilane, trimethoxy(7-octen-l-yl) silane, isooctyl trimethoxy-silane, N-(3- triethoxysilylpropyl) methoxyethoxyethoxyethyl carbamate, N-(3- triethoxysilylpropyl) methoxyethoxyethoxyethyl carbamate, 3- (methacryloyloxy)propyltrimethoxysilane, allyl trimethoxysilane, 3- acryloxypropy ltrimethoxy silane ,

3-(methacryloyloxy)propyltriethoxysilane, 3-(methacryloyloxy) propylmethyldimethoxysilane, 3-acryloyloxypropyl)methyldimethoxysilane, 3 -(methacryloyloxy)propyldimethylethoxysilane, 3 -(methacryloyloxy) propyldimethylethoxysilane, vinyldimethylethoxysilane, phenyltrimethoxysilane, n-octyltrimethoxysilane, dodecyltrimethoxysilane, octadecyltrimethoxysilane, propy ltrimethoxy silane , hexy ltrimethoxy silane , viny lmethy ldiacetoxy silane , vinylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltrimethoxysilane, vinyltriphenoxysilane, vinyltri-t- butoxysilane, vinyltris-isobutoxysilane, vinyltriisopropenoxysilane, vinyltris(2- methoxyethoxy)silane, styrylethyltrimethoxysilane, mercaptopropyltrimethoxysilane, 3- glycidoxypropyltrimethoxysilane, acrylic acid, methacrylic acid, oleic acid, stearic acid, dodecanoic acid, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA), beta- carboxyethylacrylate, 2-(2-methoxyethoxy)acetic acid, methoxyphenyl acetic acid, and mixtures thereof. In some embodiments, a proprietary silane surface modifier identified by the trade name "Silquest A1230" (commercially available from OSI Specialties, Crompton South Charleston, West Virginia), may be used.

[0039] The surface modification of the particles in the colloidal dispersion can be accomplished in a variety of ways. Generally, the process involves mixing an inorganic dispersion with surface treatment agents. Optionally, a co-solvent may be added, e.g., l-methoxy-2-propanol, ethanol, isopropanol, ethylene glycol, N,N-dimethylacetamide, ethyl acetate, and/or l-methyl-2-pyrrolidinone. The co-solvent can enhance the solubility of the surface treatment agents as well as the surface modified particles. The mixture comprising the inorganic sol and surface treatment agents is subsequently reacted at room or an elevated temperature, with or without mixing. In some embodiments, the mixture can be reacted at about 80⁰C for about 16 hours, resulting in the surface modified sol. In some embodiments, e.g., where heavy metal oxides are surface modified, the surface treatment of the metal oxide may involve the adsorption of acidic molecules to the particle surface. The surface modification of the heavy metal oxide may take place at room temperature.

[0040] The surface modification of zirconia with silanes can be accomplished under acidic conditions or basic conditions. In some embodiments, silanes are heated under acid conditions for a suitable period of time, at which time the dispersion is combined with aqueous ammonia (or other base). This method allows removal of the acid counter ion from the zirconia surface as well as reaction with the silane. In some embodiments, the particles are precipitated from the dispersion and separated from the liquid phase.

[0041] The surface modified particles can then be combined with the other components of the resin system (e.g., the curable resin and/or the reactive diluent) using any of a variety of methods. In some embodiments, a solvent exchange procedure is used whereby the curable resin and/or the reactive diluent is added to the surface modified sol, followed by removal of the water and co-solvent (if used) via evaporation, thus leaving the particles dispersed in the curable resin and/or the reactive diluent. The evaporation step can be accomplished for example, via distillation, rotary evaporation or oven drying. In some embodiments, the surface modified particles can be extracted into a water immiscible solvent followed by solvent exchange, if so desired.

[0042] Alternatively, another method for incorporating the surface modified nanoparticles in one or more of the other components of the resin system involves the drying of the modified particles into a powder, followed by the dispersion of this powder into one or more of the reactive diluent, curable resin and a solvent. The solvent can be acetone or ethanol. The drying step in this method can be accomplished by conventional means suitable for the system, such as, for example, oven drying, gap drying or spray drying.

[0043] Generally, any known technique may be used to create composite parts according to the present disclosure. For example, composite parts may be assembled by a variety of infusion techniques which include vacuum assisted resin transfer molding (VARTM) and resin transfer molding (RTM). A composite part made by the VARTM process are created with the fibrous layer placed in a suitable open mold, vacuum bag containing a fibrous layer, with peel ply and flow aids in place to easily infuse the resin system containing surface modified nanoparticles. A detailed description of an exemplary VARTM process is outlined in the Examples Section. Alternatively RTM employs a closed mold geometry typically made of 316 stainless steel, wherein composite parts are made by using a combination of vacuum and pressure to infuse a fibrous layer. Pressure is used to deliver (via pump) the resin system containing surface modified nanoparticles to the closed and often heated mold.

Examples

[0044] Materials

[0045] Rain Erosion Resistance Test

[0046] A schematic of the apparatus used to test for Rain Erosion Resistance Test is shown in FIGS. 3 and 4. This apparatus is described in detail in pending U.S. Patent Application No. 11/680,784, filed June 26, 2007 ("METHOD OF TESTING LIQUID DROP IMPACT AND APPARATUS" Daniels, et. al).

[0047] With reference to FIGS. 3 and 4, pellets 31 were fed to gun 10 via hopper 30 that allows for continuous feeding for the pellets. The hopper consisted of a 50.8 cm long by 5.7 cm wide by 3.8 cm deep container with a V-shaped bottom ending in channel 32 for dispensing pellets to the gun. When the channel is closed, the width of the channel has an opening smaller than the diameter of the pellet (e.g. 3.2 mm). When the channel is open, the channel has an opening slightly larger than the diameter of a single pellet (e.g. 4.8 mm) yet narrower than the diameter of two pellets to allow a single row of pellets to enter the channel.

[0048] The channel was designed such that when closed, the pellets within the channel were pushed with finger 33 freely, single file, toward the gun while preventing other pellets from entering the channel. The row of pellets was advanced forward toward the front of the hopper by attaching finger 33 to cable 34 that was tensioned with hanging weight 35. The 0.9 kg (2 pound) weight was used to advance the pellets up feeding tube 36 into magazine 12, which fed gun 10. This weight provided sufficient force to advance the pellets up the tube, but not excessive force such that the pellets bypassed the propulsion site.

[0049] With reference to FIG. 3, the apparatus included stainless steel barrel 11. Pellets fired from gun 10 travel along barrel 11, ultimately exiting the barrel inside chamber 50. After the pellets leave the barrel of the gun, they travel less than about 5 centimeters (2 inches) before impacting the test sample.

[0050] The test samples 55 were mounted within 10.2 cm long by 13.3 cm wide by 17.8 cm tall chamber 50 that contained the muzzle of the gun. A single test sample was mounted within the chamber for each test. The test sample is stationary during impact, and was mounted at an angle of about 85 degrees relative to the path of the pellets. This ensured that the pellets would not be deflected back into the path of a subsequent pellet and allowed the pellet to fall into a collection receptacle.

[0051] The test sample was fixed in a substantially vertical position. Re-circulating pump 60 ((Part No. 23609-170, VWR, West Chester, Pennsylvania) was used to deliver a continuous film of water to the surface of the test sample at a rate of 600 milliliters per minute. Polyethylene tube 65, having a diameter of 6.4 mm (1/4 inch), extended from the pump to the surface of the test sample. The end of the tube that delivered water to the test specimen was cut at an angle such that when the tube was pressed against the test specimen, a sheet or film of water covered the test sample.

[0052] The Rain Erosion Resistance Apparatus was assembled using 0.177 caliber air gun 10 ("Drozd Air Gun", European American Armory Corporation, Cocoa, Florida,) and 6.4 mm (1/4 inch) diameter stainless steel hose as barrel 11 (Swagelok Company, Solon, Ohio). 4.5 mm Grade II acetate pellets 31 (Engineering Laboratories, Inc, Oakland, New Jersey) were propelled through use of pellet gun 10 which was connected to a tank of compressed nitrogen (Oxygen Service Company, St. Paul, Minnesota) (not shown) via tube 20. The pressure was set at 620 kPA (90 psi).

[0053] The force of the impacting pellets in combination with the liquid layer on the surface of the test sample is believed to create a pressure that is at least as high as water hammer pressure. In contrast, power washing produces about 1/10 of the pressure created by the impacting pellets.

[0054] General Procedure for the Rain Erosion Resistance Test. Fiber composite samples with dimensions of 7.6 cm (length) by 7.6 cm (width) by 0.26 cm (thickness) and neat resin samples with dimensions of 7.6 cm (length) by 7.6 cm (width) by 0.15 cm (thickness) were held in the target holder by metal clips to avoid slippage. Samples were tested with a flow of water over the surface of the composite to mimic rain damage as described in pending U.S. Patent Application No. 11/680,784.

[0055] Procedure for Fiber Infusion Process. Fiber composites were generated via infusion of fiberglass fabrics employing vacuum infusion techniques and materials as outlined in "VIP: Vacuum Infusion Process; Lite Version" DVD with Andre Cocquyt, produced by Jumby Bay studios and released in 2002. A representative example of this technique follows.

[0056] Fiberglass fibers of various plies and configurations were stacked on a flat glass plate which has been treated with a release coating such as (Safelease #30, Airtech International, Inc., Huntington Beach, California.). The plate was heated from the underside by use of a heating pad (Stock Composite Curing Heaters, Watlow, Anaheim, California.) which was temperature controlled (Digi-Sense Temperature Controller, Chicago Illinois) and equipped with a type J thermocouple which was taped to the glass panel. Single layers of peel ply (Econo Bleeder Lease B, Airtech International, Inc.) and flow aid (Resin Infusion Flow Netting, Green Flow 75, Airtech International, Inc.) were stacked on top of the fiberglass followed by a glass plaque cut to match the dimensions of the fibers.

[0057] The fibers and flow media were then bagged by positioning double-sided sealant tape (AT-200Y, Airtech International, Inc.) around the perimeter of the stack, installing ports for a vacuum source and resin infusion and applying the plastic vacuum bag (Econolon, Airtech International, Inc.) securely around the taped area. A vacuum pump (DD- 100 model, Precision Scientific, Chicago, Illinois) equipped with a pressure pot (Lagrange Products, Freemont Illinois) was attached at this point and the bagged area was checked for leakage by closing off the vacuum to the bagged area and reestablishing vacuum at 5 minutes and 30 minutes and monitoring vacuum levels (ca. 30 mm Hg). [0058] Once a leak-free assembly was established, resin was infused into the multi-ply glass fiber stack, typically over 60 minutes. The resin entrance and vacuum ports were then sealed and the resin was allowed to cure for 18 hours.

[0059] Comparative Example 1. Test specimens were generated by mixing 230 g of Hexion 135i with 69 g of Hexion Epikote MGS® RIMH 137 and pouring approximately 17 g of the resultant solution between two 10 cm by 10 cm glass sheets with rubber gasket spacers to generate a plaque of thermoset material. After 18 hours the panel was demolded and post cured at 60 ⁰C for 15 hours. The plaque was cut to yield test specimens with dimensions of 7.6 cm (length) by 7.6 cm (width) by 0.15 cm (thick) specimens. The sample was subjected to the test outlined in the General Procedure for Rain Erosion testing and was ablated to break after 61 rounds of pellets.

[0060] Example 1. Test specimens were generated by mixing 275 g of Silica Nanoparticles in Epoxy with 47.5 g of Hexion Epikote MGS® RIMH 137 and pouring approximately 17 g of the resultant solution between two 10 cm by 10 cm glass sheets with rubber gasket spacers to generate a plaque of thermoset material. The plaque was cut to yield test specimens with dimensions of 7.6 cm (length) by 7.6 cm (width) by 0.15 cm specimens. The sample was subjected to the test outlined in the General procedure for Rain Erosion testing and was ablated to break after 950 rounds of pellets.

[0061] Comparative Example 2. A blend of 165 g of HYDREX® IOOHF and 2.5 g Superox® 46727 (1.5 wt % vs. resin portion) was mixed using a DAC 600 FVZ Speedmixer™ (Flacktek, Inc., Landrum, South Carolina) at 2000 rpm for 2 minutes at room temperature. This solution was then infused according to the Procedure for Fiber Infusion Process into a 17.8 cm by 30.5 cm, 4 ply (+/-45, 0,0 -/+45) fiberglass-containing vacuum mold. Vacuum was maintained for approximately one hour at which time the resin inlet and vacuum outlets were closed and the panel was allowed to cure over a period of 18 hours. The panel was demolded and post cured at 65 ⁰C for 2 hours and at 121 ⁰C for 2 hours. The sample was cut to yield test specimens with dimensions of 7.6 cm (length) by 7.6 cm (width) by 0.26 cm (thickness) and subjected to the test outlined in the General Procedure for Rain Erosion testing. After 100 rounds of pellets the sample was badly delaminated as shown in FIG. 5. [0062] Example 2. A solution of 235 g of Silica Nanoparticles in Vinyl Ester and 2.1 g of Superox® 46727 (1.5 wt % vs. resin portion of nanocomposite) was mixed using a DAC mixer at 2000 rpm for 2 minutes at room temperature. This solution was then infused via the Procedure for Fiber Infusion Process into a 17.8 cm by 30.5 cm, 4 ply (+/- 45, 0, 0 -/+45) fiberglass-containing vacuum mold. Vacuum was maintained for approximately one hour at which time the resin inlet and vacuum outlets were closed and the panel was allowed to cure over a period of 18 hrs. The panel was demolded and post cured at 65⁰C for 2 hours and at 121⁰C for 2 hours. The sample was cut to yield test specimens with dimensions of 7.6 cm (length) by 7.6 cm (width) by 0.26 cm (thickness) and subjected to the test outlined in the General Procedure for Rain Erosion testing. After 1000 rounds of pellets the sample displayed only minor surface abrasion as seen in FIG. 6.

[0063] Generally, the particle loading may be selected based in part on the desired erosion resistance. For example, comparing FIGS. 5 and 6, Generally, performance enhancements of at least 1000% (10X) were seen when standard composites were infused with formulations containing engineered nanoparticles at loadings of about 30-40 wt% (based on resin usage). In fact, FIGS. 5 and 6 illustrate a substantially greater degree of erosion resistance associated with the composites of the present disclosure, as the sample of FIG. 6 indicates a far lower degree of erosion even though it was subject to impact by ten times as many particles as the comparative example of FIG. 5.

[0064] Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention.

Claims

What is Claimed is:

1. An erosion resistant composite article comprising a fibrous layer impregnated with an impregnating resin system comprising a curable resin and surface modified nanoparticles, wherein the surface-modified nanoparticles comprise a core, a surface, and a surface modifying agent attached to the surface; wherein the erosion resistance of the composite article when cured as measured according to the Rain Erosion Resistance Test is at least 2 times greater than the erosion resistance of the composite article absent the surface modified nanoparticles.

2. The composite article according to any one of the preceding claims, wherein fibrous layer comprises at least one of glass fibers, inorganic fibers, or carbon fibers.

3. The composite article according to any one of the preceding claims, wherein the curable resin is a thermosetting resin.

4. The composite article according to any one of the preceding claims, wherein the resin is selected from the group consisting of epoxy resins, polyester resins, acrylic resins, and vinyl esters.

5. The composite article according to any one of the preceding claims, wherein the impregnating resin system further comprises a reactive diluent.

6. The composite article according to any one of the preceding claims, wherein the surface modified nanoparticles comprise silica.

7. The composite article according to any one of the preceding claims, wherein the surface modifying agent is a reactive surface modifying agent.

8. The composite article according to any one of the preceding claims, wherein the erosion resistance of the composite article when cured as measured according to the Rain Erosion Resistance Test is at least 5 times greater than the erosion resistance of the composite article absent the surface modified nanoparticles.

9. The composite article according to any one of the preceding claims, wherein the composite article is a wind blade, a helicopter blade, a wind tower, or a bike frame.

10. An impregnating resin system comprising a curable resin and surface modified nanoparticles wherein the surface-modified nanoparticles comprise a core, a surface, and a surface modifying agent attached to the surface; and wherein when cured the erosion resistance of the impregnating resin as measured according to the Rain Erosion Resistance Test is at least 2 times greater than the erosion resistance of the curable resin absent the surface modified nanoparticles when cured.

11. The impregnating resin system according to claim 10, wherein the resin is selected from the group consisting of epoxy resins, polyester resins, acrylic resins, and vinyl esters.

12. The impregnating resin system according to any one of claims 10 or 11, wherein the impregnating resin system further comprises a reactive diluent.

13. A method of improving the erosion resistance of a composite article comprising infusing a fibrous layer with the impregnating resin system according to any one of claims 10 to 12, and curing the curable resin to form a cured composite article; wherein the erosion resistance is measured according to the Rain Erosion Resistance Test..

14. The method according to claim 13, wherein the erosion resistance of the cured composite article as measured according to the Rain Erosion Resistance Test is at least 5 times greater than the erosion resistance of a cured composite article absent the surface modified nanoparticles.

15. Use of surface-modified nanoparticles to provide erosion resistance to a composite article, wherein the surface-modified nanoparticles comprise a core, a surface, and a surface modifying agent attached to the surface.

16. Use according to claim 15, wherein the composite article comprises a fibrous layer infused with a cured impregnating resin system comprising a curable resin and the surface modified nanoparticles.

17. Use according to claim 16, wherein the erosion resistance of the composite articles as measured according to the Rain Erosion Resistance Test is at least 5 times greater than the erosion resistance of the composite article absent the nanoparticles.

18. Use according to any one of claims 15 to 17, wherein the composite article is a wind blade, a helicopter blade, a wind tower, or a bike frame.