Mineral fibers grafted with amine functions

Abstract

The present invention relates to mineral fibers grafted with amine functions, characterized in that said fibers have a surface roughness defined by a root mean square deviation Rq greater than or equal to 0.70 nm, and in that they have a degree of grafting of at least 85 pmol of amine functions per mm2, to the use of said fibers as reinforcing material, to a composite comprising at least one organic material and such fibers, and to a process for producing said fibers, characterized in that it comprises at least one step of depositing, by plasma-enhanced chemical vapor deposition (PE-CVD), a layer of at least one precursor chosen from an aminosilane and a mixture of a primary amine and a source of silica on mineral fibers.

Description

[0001] Description

[0002] Title of the invention: Mineral fibers grafted with amine functions

[0003] The present invention relates to mineral fibers grafted with amine functions, characterized by a particular surface roughness and rate of grafting of amine functions, the use of said fibers as a reinforcing material, a composite comprising such fibers, as well as a method of manufacturing said fibers.

[0004] Composite materials are currently used in a wide range of sectors, including nautical, aeronautical, transport, energy (wind turbines, etc.), and even technical sports equipment. Their use is gradually increasing due to their lightness combined with high mechanical strength. Composite materials of this type are characterized by a very specific composition: the mixture of two immiscible materials, an organic, ceramic, or metallic phase, called a matrix, which gives the material its shape, and an inorganic phase (fibers or particles) which reinforces the material and, for example, provides better mechanical properties. In 2022, organic matrix composite materials accounted for 10 million tons of materials produced, and the market is growing every year.Companies are increasingly turning to these lightweight, mechanically efficient materials that are easy to shape and generally corrosion-resistant. However, mixing these two immiscible phases produces heterogeneous materials with high anisotropy. In particular, the interfaces in composite materials can be fragile and lead to a reduction in their lifespan. Indeed, during high mechanical stress, this stress must be efficiently transferred from the matrix to the reinforcements in order to obtain materials with high mechanical capacity. Otherwise, the composite materials will see their interfaces severely damaged and fractures appear. Interfaces are also sensitive in conditions of high humidity, where water tends to infiltrate these interfaces and hydrolyze the bonds formed between the matrices and the reinforcements.Several methods have been proposed to improve adhesion at interfaces such as physical, chemical or mechanical methods. In particular, it is known to modify the surface of fibers using coupling agents, isocyanates, silanes, oxidizing agents, esterification agents, etc. in a liquid medium. The use of coupling agents is the most widespread technique and allows the formation of bonds between the different phases thanks to the presence of chemical groups within the material, capable of binding with both phases.

[0005] Currently, liquid silanization of mineral fibers is used in industry to improve the mechanical properties of composite materials. However, these liquid treatments generally use solvents and / or toxic products that are harmful to the environment; the operating conditions can be difficult to control to achieve the expected performance, and require a drying step. Furthermore, these treatments use an excessive quantity of precursors for a result that is not entirely satisfactory in terms of adhesion.

[0006] There is therefore a need for composite materials with improved lifetime, and more particularly for composite materials in which the mineral fiber / organic matrix interface is improved and / or for composite materials with improved mechanical properties.

[0007] There is also a need for mineral fibers with better adhesion properties to organic matrices.

[0008] There is also a need for a simple, easy-to-implement mineral fiber manufacturing process with reduced environmental impact, while improving their adhesion properties to organic matrices.

[0009] The first subject of the invention is mineral fibers grafted with amine functions, characterized in that said fibers have a surface roughness defined by a quadratic mean deviation Rq greater than or equal to 0.70 nm, and preferably greater than or equal to 0.90 nm; and in that they have a grafting rate of at least 85 pmol of amine functions per mm 2 , and preferably at least 100 pmol of amine functions per mm 2 .

[0010] By "amine functions" we mean chemical groups corresponding to primary, secondary or ternary amines. These groups can be represented schematically as follows

[0011] [Chem 1]

[0012] Using mineral fibers grafted with amine functions, having a surface roughness defined by a mean square deviation Rq greater than or equal to 0.70 nm, and having a grafting rate of at least 85 pmol of amine functions per mm 2 , the grafted mineral fibers of the invention have improved adhesion properties compared to conventional mineral fibers, while guaranteeing good mechanical strength.

[0013] The mineral fibers grafted with amine functions have a surface roughness defined by a quadratic mean deviation Rq greater than or equal to approximately 0.70 nm, preferably greater than or equal to approximately 0.90 nm, and particularly preferably greater than or equal to approximately 1.00 nm.

[0014] According to a particularly preferred embodiment of the invention, the mean square deviation Rq is at most approximately 10 nm, and more preferably at most approximately 2 nm.

[0015] Mineral fibers grafted with amine functions may have an arithmetic mean roughness, noted Ra, greater than or equal to 0.50 nm, preferably greater than or equal to 0.70 nm, and particularly preferably greater than or equal to 0.80 nm.

[0016] The root mean square deviation Rq (respectively the arithmetic mean roughness Ra) for defining the roughness of mineral fibers grafted with amine functions can be measured using a contact or non-contact device, such as a probe profilometer, an optical profilometer, an optical cutting device or an atomic force device. It is preferably measured using an atomic force device such as an atomic force microscope (AFM).

[0017] The root mean square deviation of roughness Rq is defined in the international standard NF EN ISO 4287.

[0018] The fibers of the invention have a grafting rate of at least approximately 85 pmol of amine functions per mm 2 , preferably at least approximately 100 pmol of amine functions per mm 2 , and particularly preferably at least approximately 110 pmol of amine functions per mm 2 .

[0019] The grafting rate of amine functions can be determined by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), or by titration such as acid-orange titration, and preferably by titration such as acid-orange titration.

[0020] The fibers of the invention may be chosen from glass, quartz, silica and alumina fibers, and preferably glass fibers.

[0021] The fibers of the invention preferably comprise at least one layer containing oxygen, silicon, carbon, and nitrogen. The nitrogen of said layer is in particular provided by the grafted amine functions.

[0022] The fibers of the invention more particularly comprise at least one layer containing: one or more silicon-oxygen (Si-O) function(s), and - one or more carbon-nitrogen (CN) function(s).

[0023] The carbon-nitrogen (CN) functions of said layer can be provided by the grafted amine functions.

[0024] The fibers of the invention are obtained by plasma-enhanced chemical vapor deposition (PE-CVD) of at least one precursor chosen from an aminosilane and a mixture of a primary amine and a silica source, on mineral fibers.

[0025] The precursor is preferably an aminosilane, and particularly preferably an aminoalkyltrialkoxysilane. The aminosilane precursor may be chosen from (3-aminopropyl)triethoxysilane (APTES), (3-aminopropyl)trimethoxysilane (APTMS), N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, trimethoxylsilylpropylethylenediamine (TMSPED), 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane, and a mixture thereof.

[0026] The primary amine precursor can be ethylenediamine, allylamine, or butylamine.

[0027] The silica source precursor may be hexamethyldisilazane or a tetraalkoxysilane such as tetraethoxysilane or tetramethoxysilane.

[0028] (3-Aminopropyl)trimethoxysilane (APTMS) is preferred. It allows for an optimal grafting rate while ensuring good adhesion.

[0029] The fibers of the invention may be in the form of multi-filament fibers of 5 to 30 μm in diameter, and with a linear density ranging from 10 to 10,000 tex.

[0030] According to a preferred embodiment, the grafted fibers have an increase in adhesion to the interfaces of at least approximately 30%, particularly preferably of at least approximately 40%, and more particularly preferably of at least approximately 50%, compared to non-grafted mineral fibers (e.g. “bare” fibers or sized fibers as defined below).

[0031] In the invention, adhesion is measured with a method based on a well-known method according to the Anglicism "pull out" or detachment method and more specifically micro-drop method developed by Miller et al. [Composites Science and Technology, 1991, 42, 207-219]. It consists of exerting a uniaxial stress on a monofilament on which a small amount of resin is deposited along the fiber until causing fiber-matrix decohesion and extraction of the filament. In other words, the filament is extracted from the drop of resin by traction. In the present invention, the samples are prepared by stretching a fiber on a cardboard frame, then a drop of resin is deposited on the fiber. The fiber is then slowly pulled out of the drop. Adhesion is measured using a polyester resin such as that marketed under the reference "POLYLITE 413-575" in the presence of a hardener marketed under the reference "NOR.OX MCP-75 ». The specified method allows obtaining an interface shear stress value in MPa (also known as "Interfacial Shear Strength" or the acronym "IFFS"). This value can be compared to an interface shear stress value in MPa of the ungrafted fibers (IFFS ref). An IFFS / IFFSref ratio can then be determined.

[0032] According to a preferred embodiment of the invention, the fibers have a mechanical strength by tensile test TM1 (in Newton) such that TM1 > TMO, or when TM1 < TMO, (TMO-TM1) / TMO < 0.2, with TMO (in Newton) representing the mechanical strength by tensile test of non-grafted mineral fibers (i.e. “bare” fibers or sized fibers).

[0033] In the invention, the mechanical strength is measured by tensile testing, preferably at a tensile speed of approximately 100 mm / min and / or with a fiber length of approximately 30 cm.

[0034] Use of fibers

[0035] The second object of the invention is the use of fibers in accordance with the first object of the invention, as reinforcing material.

[0036] In particular, the fibers can be used in the fields of construction, the automotive industry, space, or biomedicine.

[0037] The fibers of the invention make it possible in particular to design composite materials with good mechanical properties, thanks to their good adhesive properties.

[0038] This prevents fiber breakage and / or organic matrix / fiber delamination, and thus extends the lifespan of composite materials containing fibers as reinforcement material.

[0039] The corn material The third subject of the invention is a composite material, characterized in that it comprises at least one organic material, preferably a polymer material, and fibers in accordance with the first subject of the invention.

[0040] The polymer material may be a thermoplastic or thermosetting material, preferably a thermosetting polymer material, and particularly preferably chosen from unsaturated polyesters, polyepoxides, urea-formaldehyde, melamine-formaldehyde, phenol-formaldehyde resins, polybismaleimides, polyimides, crosslinked polyurethanes), polyvinyl esters, vulcanized elastomers, polyisocyanurates, polysiloxanes, and one of their mixtures.

[0041] According to a preferred embodiment of the invention, the composite material comprises from 60 to 95% by mass of fibers, and particularly preferably from 65 to 90% by mass approximately, relative to the total mass of the composite material.

[0042] The process

[0043] The fourth subject of the invention is a method for manufacturing fibers in accordance with the first subject of the invention, characterized in that it comprises at least one step of plasma-assisted chemical vapor deposition (PE-CVD), of at least one precursor chosen from an aminosilane and a mixture of a primary amine and a source of silica, on mineral fibers.

[0044] Plasma-enhanced chemical vapor deposition (PE-CVD) is well known as "Plasma-Enhanced Chemical Vapor Deposition" (PE-CVD) to refer to so-called "non-equilibrium" processes. PE-CVD deposition [with different sources: DC (direct current), LF (low frequency), MF (medium frequency), RF (radio frequency), or microwave] allows for the production of extremely crosslinked deposits at low temperatures. PE-CVD deposition guarantees better quality and precision in fiber grafting.

[0045] Generally speaking, during a PECVD process, one or more gases and / or one or more liquid precursors are introduced into an enclosure containing an element or part to be coated. The chemical reaction is assisted by an electrical discharge in direct current or at medium or high frequency, for example radiofrequency or microwave, which ionizes the gases and forms a plasma, the plasma being a generally electrically neutral mixture consisting of ions and electrons. The plasma promotes the dissociation of the gases and activates the chemical reaction in the vapor phase.

[0046] The mineral fibers used in the process of the invention are chosen from glass, quartz, and alumina fibers, and preferably glass fibers.

[0047] The mineral fibers used in the process of the invention are ungrafted mineral fibers. They may be “bare” mineral fibers, i.e. without grafting and / or without surface treatment, or sized mineral fibers.

[0048] The glass fibers used in the process of the invention may in particular be those marketed by Saint-Gobain Vetrotex, such as type A fibers marketed under the reference “TD44C” and type S fibers marketed under the reference “1383”. They are generally manufactured by passing through a furnace at 1550°C then through platinum combs allowing the production of fine rods of a few μm, then undergo a sizing step.

[0049] The deposition step is preferably carried out on sized mineral fibers. Sizing prior to the deposition step can improve the mechanical properties and possibly the adhesion of the mineral fibers.

[0050] Mineral fibers, and in particular glass fibers, can be coated with a size, in particular one that has been added during their manufacture.

[0051] The size is generally an aqueous dispersion of one or more of the following chemical components: coupling agent(s), film-forming agent(s), lubricants), antistatic agent(s).

[0052] The size in the form of a dispersion can be deposited on the fibers using a liquid spray or by contact, for example using a roller.

[0053] Preferably, the size is applied in quantities of the order of approximately 1% by mass relative to the total mass of the fibers. The fineness of the glass fibers is defined by the tex (unit of linear mass), where 1 tex = 1 gram of fibers / km.

[0054] According to a preferred embodiment, the deposition step is carried out at atmospheric pressure (i.e. 1013 hPa at sea level). This allows in particular rapid treatment and avoids one or more vacuum steps implemented in low pressure plasma processes, e.g. using pressures of the order of approximately 1 to 10 Pa, i.e. 10 -2 at 10' 1 mbar approximately. The process of the invention can then be carried out continuously while ensuring good homogeneity of the deposit. A deposition step at atmospheric pressure also makes it possible to increase the quantities of material processed, to have a lower environmental impact, and to improve grafting control.

[0055] The deposition step is preferably carried out with a plasma torch, particularly an atmospheric pressure plasma jet (known by the acronym "APPJ"). This allows for better control of the deposited layers and functions.

[0056] Plasma jet treatment is a post-discharge treatment.

[0057] The deposition step can be carried out in the presence of a plasma gas, such as air, nitrogen, a nitrogen / hydrogen mixture, or argon, and preferably air. The use of air improves the grafting rate.

[0058] In the nitrogen / hydrogen mixture, the hydrogen may represent a content of approximately 5% by volume or less, relative to the total volume of gas.

[0059] Advantageously, the air used may comprise approximately 21% by volume of oxygen (O2).

[0060] The plasma gas flow rate during the deposition step can range from 30 l s / min to approximately 50 ls / min, and preferably 35 l s / min at 45 l s / min approximately.

[0061] The flow rate can be adapted according to the dimensions of the torch. The unit mls / min means "standard milliliter per minute", and the unit l s / min means “standard litre per minute”, with standard conditions corresponding to a pressure of 1013 mbar and a temperature of 20°C.

[0062] According to a preferred embodiment, the deposition step is carried out in dry air and / or on dry mineral fibers. Dry conditions make it possible to improve the grafting rate and / or the adhesion of the fibers.

[0063] In the invention, dry mineral fibers are mineral fibers having a residual water content of at most approximately 5% by mass relative to the total mass of the fibers, and preferably at most approximately 0.5% by mass.

[0064] The residual water content of mineral fibers can be determined by loss of mass at 120°C.

[0065] In the invention, dry air corresponds to a relative humidity RH of at most approximately 20%, and preferably at most 10%.

[0066] Relative humidity can be determined using hygrometric sensors in the air sent into the torch.

[0067] According to a preferred embodiment, the deposition step is carried out with a power of at most 1000 W, and particularly preferably at most 600 W. Such a maximum power makes it possible to increase the grafting rate and / or the adhesion of the fibers. Too high a power can decrease the grafting rate (grafting / ablation competition) and / or the adhesion of the fibers.

[0068] The power can be adapted according to the dimensions of the torch.

[0069] The power during the deposition step can be at least 450 W.

[0070] The frequency used can range from approximately 80 to 200 kHz.

[0071] The frequency can be adapted depending on the system electronics.

[0072] According to a preferred embodiment, the deposition step is carried out for 25 to 300 ms, and particularly preferably for 50 to 150 ms. Such a deposition time makes it possible to increase the grafting rate. In the case of a deposition step carried out continuously, the time corresponds to the time of exposure of the fibers to the plasma.

[0073] The deposition step can be carried out with a flow rate of said aminosilane precursor or primary amine / silica source mixture ranging from 0.05 ml s / min to approximately 3 mls / min, and preferably 0.05 ml s / min at 1 ml s / min approximately.

[0074] The step of depositing the aminosilane precursor or the primary amine / silica source mixture can make it possible to form at least one layer containing oxygen, silicon, carbon, and nitrogen. This specific layer is capable of interacting with at least one organic matrix and thus creating strong interactions between the mineral fibers and said organic matrix forming a composite material.

[0075] The step of depositing the aminosilane precursor or the primary amine / silica source mixture makes it possible in particular to obtain at least one layer containing: one or more silicon-oxygen (Si-O) function(s), and - one or more carbon-nitrogen (CN) function(s).

[0076] According to the method according to the fourth subject of the invention, the deposition step can be carried out in the presence of a volume i of a plasma gas, and a volume 2 of said aminosilane precursor in the form of an aerosol (suspension of droplets in a gas). The volume V2 corresponds to the total volume of droplets.

[0077] According to a preferred embodiment, the volume ratio V1 / V2 ranges from 10,000 to 100,000, and particularly preferably from approximately 15,000 to 45,000.

[0078] This allows a good compromise to be obtained between a high grafting rate and a deposition speed high enough to be in line with industrial production rates.

[0079] The aminosilane precursor is as defined in the first subject of the invention.

[0080] The primary amine precursor is as defined in the first subject of the invention.

[0081] The silica source precursor is as defined in the first subject of the invention.

[0082] The deposition step is preferably carried out continuously. In other words, mineral fibers (“bare” mineral fibers or sized fibers) pass continuously through an enclosure containing a plasma torch.

[0083] The deposition step can be carried out at a fiber travel speed ranging from approximately 0.7 m / min to 12 m / min, and preferably from approximately 1.3 m / min to 6 m / min. These speed ranges make it possible to improve fiber adhesion and / or fiber roughness while avoiding degradation of any fiber sizing.

[0084] During the deposition step, the fibers are preferably kept at a distance from a plasma torch of at least approximately 5 cm, preferably ranging from approximately 5.2 cm to 20 cm, and particularly preferably ranging from 5.2 to 10 cm. Such a distance makes it possible to increase the grafting rate.

[0085] The volume of aminosilane precursor relative to the length of the fibers can range from about 0.004 ml / m to about 4.3 ml / m, and particularly preferably from about 0.008 to about 1.5 ml / m.

[0086] The method may further comprise repeating the deposition step as defined above.

[0087] The method may further comprise, prior to this deposition step, a step of plasma-enhanced chemical vapor deposition (PE-CVD), of at least one organosilane precursor, and preferably of at least one tetraalkoxysilane precursor, on mineral fibers.

[0088] The tetraalkoxysilane precursor can be tetraethoxysilane, or hexamethyldisiloxane.

[0089] In this embodiment, the fibers obtained may further comprise an underlayer containing silicon, oxygen and optionally carbon.

[0090] Other features and advantages of the present invention will become apparent from the description of non-limiting examples given solely for illustrative and non-limiting purposes. Brief description of the drawings

[0091] Figure 1 is an atomic force microscopy image of "bare" fibers not in accordance with the invention and of grafted fibers in accordance with the invention.

[0092] Examples

[0093] Protocol for measuring the grafting rate of amine functions

[0094] The principle of acid orange titration is based on the electrostatic interaction of the sulfonate anion of an acid azo dye well known under the trade name "acid orange 7" or "Orange II" or "2-naphthol orange"

[0095] (IUPAC name: sodium 4-[(2£)-2-(2-oxonaphthalen-l-ylidene)hydrazinyl]benzene sulfonate), and amine functions, protonated in an acidic medium. Once the material to be tested has been immersed in an acidic solution of acid-orange, passing through a basic bath deprotonates the amine function and desorbs the originally absorbed acid-orange. The quantity of grafted amine, then corresponding to the quantity of acid-orange released into solution, is subsequently calculated by measuring the absorbance of the different solutions.

[0096] Directly after the deposition step according to the invention, the fibers are immersed in 1.5 ml of 14 mg / mL acid orange solution at pH 3 (adjusted with a 1 mol / L hydrochloric acid solution) for 30 min and at 40°C. Then, the samples are rinsed in several baths of a pH=3 hydrochloric acid solution (until the solutions are clear). After drying the samples, the fibers are immersed in a pH 12 solution (adjusted with a 1 M NaOH solution) for 15 min to desorb the dye. Finally, the solution is filtered to recover the fibers, and the pH of the solution containing the desorbed dye is adjusted to pH 3 using 1 mol / L hydrochloric acid.

[0097] The acid-orange solution is then analyzed in UV-visible at 484 nm.

[0098] In order to be able to trace the mass concentration of orange acid absorbed on the surface of the fibers, a calibration curve is made using solutions of known orange acid concentrations previously prepared, and their absorbance is recorded. Thus, knowing the absorbance of the analyzed solutions, the quantity of grafted amines can be directly calculated. Roughness was measured using an atomic force microscope sold under the trade name "AFM Dimension Icon" by Veeco in "tapping" mode. To allow AFM analysis, a fiber is fixed on a support.

[0099] Fiber adhesion measurement protocol

[0100] The principle of the test is to measure the adhesion between a filament of a fiber (single fiber) and a drop of resin.

[0101] The test consists of stretching a fiber on a cardboard frame using two stickers. The diameter of each fiber is measured under a microscope. A drop of resin, with a diameter of around 500 μm maximum, is placed on the fiber, in contact with a glass. After baking the samples for 24 hours at 60°C, a drop of glue such as ethyl cyanoacrylate is added to the fiber opposite the drop of resin. This prevents any slippage of the fiber during the tensile test. The samples are placed in a tensile machine sold under the trade name "Shimadzu EZ / LX", mounted with a 10 N sensor, capable of giving forces ranging from 0.02 to 10 N. A "Dino-Lite" microscope is used to observe the samples during the tensile tests and to record the detachment of the fibers from the drops of resin. The tensile speed is 0.1 mm / min.The cardboard is then cut, the fiber is then simply glued to the top glass and embedded in a drop of resin on the bottom glass. When pulled, the fiber pulled upwards must gradually detach from the resin and exit the drop. The force exerted to detach it from the resin is then used to calculate what is called the interfacial shear stress, well known by the English term "Interfacial Shear Stress" or the acronym "IFSS".

[0102] The resin used in the adhesion tests is a polyester resin marketed under the reference “POLYLITE 413-575” in the presence of a hardener marketed under the reference “NOR.OX MCP-75”.

[0103] Holding measurement protocol Tensile tests are carried out. To do this, the fibers are stretched until they break, the force required to pull them out gives the resistance or mechanical strength of the fibers by tensile testing.

[0104] The fibers are cut into 30 cm pieces. To prevent breakage at the jaws, pieces of tape are added to each end. The fibers are then placed in the jaws. The traction takes place at a speed of 100 mm / min. The jaws used are equipped with 2 kN sensors. A tensile testing machine sold under the trade name "MTS Insight Electromechanical" is used, and the results are processed on the "TW Elite" software.

[0105] Materials used in the examples

[0106] The fibers used in the examples below are type A fibers with a diameter of 16 pm (300 Tex) having a size containing aminosilanes marketed under the reference “TD44C”.

[0107] The aminosilane precursor used in the examples below is (3-aminopropyltrimethoxysilane (APTMS) marketed by Sigma-Aldrich (purity > 97%, CAS: ; 13822-56-5).

[0108] The deposition step is carried out under dry air comprising 21% by volume of dioxygen, as plasma gas (relative humidity less than 20%).

[0109] Device for carrying out the deposition step

[0110] The deposition step is implemented using an atmospheric plasma torch marketed by AcXys Technologies. A cold plasma at atmospheric pressure is generated between two electrodes: a first high-voltage electrode (Hafnium), a second electrode consisting of the torch wall (ground electrode). An arc is generated between these metal electrodes, clinging to a central electrode and extending to the central slot, called the silent pin. The plasma gas arrives in the form of a vortex around the central electrode, this circular circulation of gases favoring the anchoring of the arc at the tip of the electrode. An alternating current is used to frequently reverse the polarity of the electrodes and avoid reaching local thermodynamic equilibrium. The deposition step carried out with this torch is a post-discharge treatment, with the most stable species of the plasma.The glass fibers are not in direct contact with the generated arc but with the plasma species blown by the plasma gas. To implement the process continuously, a "swagelock" type connection or circuit was used between the fibers and the torch in order to modulate the torch / fiber distance which ranges from 5.8 to 20 cm. An atomizing nozzle was added for the introduction of the precursors. Two small motors [DC geared motors sold by Mdp with reference "1.13.021.3xx / GS28", reduction ratios 30 and 200], whose modulation of the voltage and current intensity produces different rotation speeds are added in order to modulate the fiber travel speed which ranges from 0.5 to 12 m / min. The residence time (i.e. the duration of the deposition step) is calculated by dividing the width of the "Swagelock" connection by the travel speed.A ceramic part is added to prevent the atomizing nozzle from overheating. The fibers are thus treated continuously. The generator frequency can vary from 80 kHz to 200 kHz.

[0111] Example 1 of preparation of grafted fibers in accordance with the invention

[0112] The type A fibers marketed under the reference “TD44C” were treated by PE-CVD according to the process in accordance with the invention using an atmospheric plasma torch as described above.

[0113] The generator frequency is set at 200 kHz, the applied voltage is set at 1000 volts, the current is of the order of IA, the power is 450 W, the torch / fiber distance is 5.8 cm, the fiber travel speed relative to the torch is 8 meters per minute. The temperature of the injected plasma gas is around 20°C and the temperature at the torch is estimated at 950-1000 K.

[0114] The flow rate of the APTMS precursor is 1 ml s / min and the plasma gas flow rate (air) is 35 l s / min.

[0115] The volume ratio of plasma gas to APTMS aminosilane precursor in gas form is 35000. The volume of aminosilane precursor relative to the fiber length is 0.125 ml / m.

[0116] This produces a layer of silicon, carbon, oxygen and nitrogen.

[0117] Figure 1 is an atomic force microscopy image of the type A fibers used in the process according to the invention (Figure 1 a) and of grafted type A fibers according to the invention or obtained according to the process according to the invention (Figure 1 b).

[0118] The grafted type A fibers in accordance with the invention or obtained according to the process in accordance with the invention have a grafting rate of 100 pmol / mm 2The type A fibers used in the process according to the invention have a grafting rate of only 37 pmol / mm 2 This initial grafting rate is linked to sizing with aminosilanes.

[0119] Roughness was measured using an atomic force microscope sold under the trade name “AFM Dimension Icon” by Veeco in “tapping” mode. To enable AFM analysis, a fiber is fixed on a support.

[0120] The grafted type A fibers according to the invention or obtained according to the process according to the invention have a mean square deviation Rq of approximately 1.19 nm. The type A fibers used in the process according to the invention have a mean square deviation Rq of approximately 0.62 nm.

[0121] The results of adhesion tests lead to an interfacial shear stress of 2.4 MPa for the grafted type A fibers in accordance with the invention or obtained according to the process in accordance with the invention and an interface shear stress of 1.32 MPa for the type A fibers used in the process in accordance with the invention, i.e. an increase of 80%.

[0122] The tensile test results lead to a mechanical strength ranging from 650 to 750 N for the grafted type A fibers in accordance with the invention or obtained according to the process in accordance with the invention and to a mechanical strength of 750 N for the type A fibers used in the process in accordance with the invention.

[0123] Example 2 of preparation of grafted fibers not in accordance with the invention - liquid route The type A fibers marketed under the reference “TD44C” were treated by liquid route according to a process not in accordance with the invention.

[0124] The liquid treatment consists of silanization (APTMS) in an ethanol / water medium (95 / 5 volume ratio), with a pH adjusted to 6 by the gradual addition of acetic acid. The solution initially comprises 0.4 g of APTMS in 50 ml of ethanol / water and must stand for 3 hours for hydrolysis. 20 g of fibers are then soaked in this solution for 2 hours, after which they are dried in a vacuum oven for 2 hours at 120 °C.

[0125] The grafted fibers obtained have a grafting rate of 50 pmol / mm 2 , a root mean square deviation Rq of approximately 4.5 nm and an interfacial shear stress of 1 MPa. The liquid route reduces the adhesion of the original fibers and provides an insufficient grafting rate.

Claims

CLAIMS 1. Mineral fibers chosen from glass, quartz, silica and alumina fibers, grafted with amine functions, characterized in that said fibers are obtained by plasma-enhanced chemical vapor deposition (PE-CVD) on mineral fibers of at least one precursor chosen from an aminosilane and a mixture of a primary amine and a silica source, and have a surface roughness defined by a mean square deviation Rq greater than or equal to 0.70 nm, and in that they have a grafting rate of at least 85 pmol of amine functions per mm 2 .

2. Fibers according to claim 1, characterized in that they are glass fibers.

3. Fibers according to claim 1 or 2, characterized in that they comprise at least one layer containing oxygen, silicon, carbon, and nitrogen.

4. Fibers according to any one of the preceding claims, characterized in that they comprise at least one layer containing: one or more silicon-oxygen (Si-O) function(s), and - one or more carbon-nitrogen (CN) function(s).

5. Fibers according to any one of the preceding claims, characterized in that they are obtained by plasma-assisted chemical vapor deposition (PE-CVD) of at least one aminoalkyltrialkoxysilane precursor on mineral fibers.

6. Fibers according to any one of the preceding claims, characterized in that they are in the form of multi-filament fibers of 5 to 30 μm in diameter, and with a linear mass ranging from 10 to 10,000 tex.

7. Fibers according to any one of the preceding claims, characterized in that they exhibit an increase in adhesion to the interfaces of at least 30%, compared to non-grafted mineral fibers.

8. Fibers according to any one of the preceding claims, characterized in that they have mechanical strength by TM1 tensile test (in Newton) such that TM1 > TMO, or when TM1 < TMO, (TM0-TMl) / TM0 < 0.2, with TMO (in Newton) representing the mechanical strength by tensile testing of ungrafted mineral fibers.

9. Use of fibers as defined in any one of the preceding claims, as reinforcing material.

10. Composite material, characterized in that it comprises at least one organic material, preferably a polymer material, and fibers as defined in any one of claims 1 to 8.

11. Composite material according to claim 10, characterized in that it comprises from 60 to 95% by mass of fibers relative to the total mass of the composite material.

12. Method for manufacturing fibers as defined in any one of claims 1 to 8, characterized in that it comprises at least one step of depositing a layer by plasma-enhanced chemical vapor deposition (PE-CVD), of at least one precursor chosen from an aminosilane and a mixture of a primary amine and a source of silica, and preferably of at least one aminoalkyltrialkoxysilane precursor, on mineral fibers chosen from glass, quartz, silica and alumina fibers.

13. Method according to claim 12, characterized in that the deposition step is carried out in dry air and / or on dry mineral fibers.

14. Method according to claim 12 or 13, characterized in that the deposition step is carried out on sized mineral fibers.

15. Method according to any one of claims 12 to 14, characterized in that the deposition step is carried out with a power of at most 1000 W and / or for 25 to 300 ms.

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