CHIP MADE FROM RECYCLED COMPOSITE MATERIAL AND PRODUCTION METHOD THEREOF

Abstract

The present invention relates to a chip made from composite material containing carbon fibres in a cured adhesive, said chip having a substantially constant thickness defined between two parallel opposite faces of the chip, the surface of each face comprising carbon fibres that are at least partially not included in the cured adhesive.

Claims

1. A composite material chip comprising carbon fibers in a cured adhesive, said chip having a substantially constant thickness defined between two parallel opposite faces of the chip, each face including on the surface carbon fibers that are at least partially not included in the cured adhesive.

2. The chip according to claim 1, wherein a portion of the carbon fiber which is at least partially not included in the cured adhesive constitutes a bare fiber.

3. The chip according to claim 2, having a bare fiber area ratio which is greater than or equal to 22%, the percentage being related to the total surface area of the face of the chip which is analysed.

4. The chip according to claim 1, one face of which has a roughness measured by a mass loss which is greater than or equal to 0.008%, said mass loss being measured by an abrasion test performed on a linear abrasion meter using an H18 abrasive rubber for 100 cycles.

5. The chip according to claim 1, having a thickness between 200 m and 1 mm.

6. The chip according to claim 1, wherein said carbon fibers extend substantially parallel to said opposite faces of the chip.

7. The chip according to claim 1, wherein the carbon fibers are oriented in the same direction.

8. The chip according to claim 1, having a rectangular shape.

9. The chip according to claim 1, wherein each face of the chip has a surface area of at least 1 cm.sup.2.

10. A method for manufacturing a chip as defined according to claim 1, said method comprising the following steps: providing a composite material comprising carbon fibers which are oriented in a substantially parallel manner in a cured adhesive; and mechanically cutting the composite material with a blade device, said cutting being carried out by positioning the carbon fibers parallel to the direction of advancement of the blade of said blade device.

Description

[0097] Other characteristics and advantages of the invention will appear in the FIGURE and the following examples and which are given for illustrative purposes.

[0098] FIG. 1 represents, in the form of a graph, the flexural modulus of a panel comprising chips according to the invention which are organised in a unidirectional manner, the chips being obtained from composite material to be recycled, and that of a new panel containing unidirectionally oriented carbon fibres.

EXAMPLE 1: OBTAINING A CHIP ACCORDING TO THE INVENTION

[0099] The formation of chips is carried out from elements made from composite material based on carbon fibres which are to be recycled.

[0100] To do this, the chips are obtained by mechanically cutting said elements.

[0101] The chip cutting can be made using a cutting machine such as a blade device. The blade device may be a planer type system. A planer type system corresponds to a cutting machine including a blade allowing thin slices of regular thickness to be separated from the surface of an element over which it has passed.

[0102] When an element is cut to form chips, the blade of the blade device is positioned, in a conventional manner, such that the edge of the blade moves in a plane parallel to the direction of advancement of the blade of said blade device, the direction of advancement of the blade of the blade device being rectilinear.

[0103] The edge of the blade also called sharp edge corresponds to the edge of the blade which first penetrates the material to be cut.

[0104] The material to be cut is positioned in the cutting machine according to the organisation of the carbon fibres it contains.

[0105] If the fibres in the material to be cut are unidirectional, that is to say included in a matrix substantially parallel, in only one direction, then the fibres are positioned parallel to the direction of advancement of the blade of said blade device.

[0106] If the fibres are included in the form of woven web, the part will preferably be placed such that the weft or warp threads are substantially parallel to the direction of advancement of the blade of said blade device.

[0107] The fibres can also be disposed in a succession of layers, each layer including unidirectional fibres, but the layers having different fibre orientations. This is for example the case for materials called four-directional materials, the layers of which can have the following successive relative orientations: 0 (reference layer), 90, 45, 45. Thus, a four-directional material is a laminated material comprising several layers of unidirectional carbon fibre, the layers being oriented in four different directions: 0, 90, 45, 45.

[0108] The blade device can advantageously be adjusted so that the blade thereof attacks the element between two layers of fibres, whether they are two layers of unidirectional fibres or two woven webs.

[0109] The cutting plane will advantageously be maintained between the layers of fibres in order to maintain their integrity as much as possible.

[0110] Advantageously, the blade device can comprise a micrometric wedge system consisting of a superposition of elements disposed on either side of the material to be cut, said wedge system being positioned on a reference plane and having an accuracy of less than the 1/10.sup.th of a millimetre. Such a wedge system allows controlling the attack area of the blade and thus make a more accurate cut between the layers of fibres. This system thus allows controlling the thickness of the chips obtained while keeping the carbon fibres intact.

[0111] Thin slices of composite material are thus obtained. These slices may in particular have a thickness comprised between 200 m and 1 mm, preferably between 200 m and 500 m.

[0112] The elements to be cut are brought to the desired length for the chips before being cut into slices by the cutting machine, such that the chips having the desired length are directly obtained at the outlet of the cutting machine.

[0113] Alternatively, the slices are then recut to obtain chips. Typically, they are cut transversely by any suitable cutting means, for example by sawing, in order to form fine rectangular chips of regular length. Other shapes of chips can of course be cut from the obtained slices.

[0114] For example, for the production of flat panels, chips of 10 cm to 20 cm in length were obtained and allowed obtaining very good results in terms of mechanical performance as exemplified below. Greater lengths can also be used, such as in the range of 50 cm or even 1 m.

[0115] Obviously, the cutting method described above can be adapted according to the considered application and the amounts to be produced.

[0116] Once the chips are formed, they therefore take the form of fine elements including carbon fibres which are, at least partially, included in a cured resin. The chips are therefore in the form of substantially two-dimensional parts (in that their thickness is very small compared to the other dimensions thereof). The surface of the chips is advantageously of at least 1 cm.sup.2, and preferably greater than 3 cm.sup.2, in the range of 10 cm.sup.2, or even greater, for example up to approximately 100 cm.sup.2.

[0117] The carbon fibres are oriented in the cured resin of the chips. Preferably, they are substantially parallel, orthogonal to each other, and/or oriented at 45 from each other.

[0118] The fibres of the chips having a substantially constant thickness, they include two opposite faces (between which the thickness is defined). The cutting of the chips is carried out so as to keep the carbon fibres intact as much as possible. To do this, the chips are cut such that the fibres (the majority, or even almost all or all of them) extend parallel to the opposite faces of the chips. The fibres thus extend in planes which are parallel to the general plane of extension of the chip, and can have a great length despite the small thickness of the chips.

[0119] The term majority, means more than 50% in number.

[0120] The term almost all, means more than 90% in number.

EXAMPLE 2: CHARACTERISATION OF THE CHIPS ACCORDING TO THE INVENTION

[0121] The applicant has carried out tests allowing characterising the chips according to the present invention. These tests were carried out using the materials listed in table 1.

[0122] These materials are in the form of composite rod, plate or web.

[0123] A composite rod is a cylinder obtained by pultrusion of a composite material.

[0124] A composite web is distinguished from a composite plate by its thickness. Indeed, the web has a thickness in the range of 0.2 mm while the composite plate has a thickness of several millimetres.

[0125] The partially consolidated composite webs are webs whose carbon fibres are integrated into a matrix or resin whose polymerisation has started, but is not completed. They are therefore distinguished from composite webs including carbon fibres in a non-polymerised matrix because for the latter the polymerisation has not started.

[0126] When no details are provided on the state of polymerisation of the matrix of the materials presented in table 1 above, this means that the matrix is polymerised.

TABLE-US-00001 TABLE 1 List of the used materials Composition of the Technique for No composite material obtaining the chips 1 Composite rod Cutting according to including carbon Example 1 with a blade fibres in an epoxy device matrix, with a UD* arrangement 2 Composite rod Cutting according to including carbon Example 1 with a blade fibres in an epoxy device then sanding matrix, with a UD* the surface with P1000 arrangement grit sandpaper 3 Composite plate Cutting according to including carbon Example 1 with a blade fibres in an epoxy device matrix, with a UD* arrangement 4 Composite plate No cutting, smooth including carbon chips fibres in an epoxy matrix, with a UD* arrangement 5 Composite plate No cutting, sanding including carbon with P80 grit fibres in an epoxy matrix, with a UD* arrangement 6 0.15 mm thick No cutting composite web including carbon fibres in an epoxy matrix, with a UD* arrangement 7 Composite web No cutting including carbon fibres in an unpolymerised epoxy matrix, with a UD* arrangement 8 Composite web No cutting, sanding including carbon with P80 grit fibres in an unpolymerised epoxy matrix, with a UD* arrangement 9 Partially No cutting, smooth consolidated chips composite web including carbon fibres in an epoxy matrix, with a UD* arrangement 10 Partially No cutting, sanding consolidated with P80 grit composite web including carbon fibres in an epoxy matrix, with a UD* arrangement 11 Composite web No cutting including carbon fibres in a thermoplastic polyphenylene sulphide (PPS) resin, with a UD* arrangement 12 Composite sheet No cutting including carbon fibres in a thermoplastic matrix, with a UD* arrangement *UD: unidirectional arrangement of the carbon fibres

[0127] The materials 1 to 12 have all been sized to have the same width: 9 mm and the same length: 100 mm. To do this, the materials 1 and 2 were sized using a mitre saw, the material 3 was sized using a paper trimmer and materials 4 to 12 were sized either via a paper trimmer or using scissors.

[0128] Then, the materials 1 to 3 were cut in order to obtain chips according to the invention. The chips according to the invention are obtained by the method as described in Example 1.

[0129] The mechanical cutting with a plane is carried out such that it favours the cuts along the axis of the fibres. Indeed, the materials 1-3 consisting of mainly unidirectional fibres, that is to say fibres oriented in a single direction, these are positioned parallel to the direction of advancement of the blade of the mechanical blade cutting device.

[0130] Cutting as described above allows obtaining chips of regular thickness, to keep the carbon fibres intact as much as possible and obtaining chips comprising longer fibres.

[0131] The chips obtained from the materials 1 to 4 have a thickness comprised between 0.3 and 0.5 mm.

[0132] The materials 4 to 12 are used as comparative examples and have not been cut.

1. Surface Analysis: Determination of the Bare Fibre Area Ratio

[0133] Surface analyses were performed on all chips obtained from the materials 1 to 12 according to the procedure detailed below.

[0134] The bare fibre area ratio is defined as the surface occupied by bare carbon fibres, that is to say by carbon fibres which are not included in or not coated with resin, relative to the total surface which is analysed.

[0135] The bare fibre area ratio was determined for each of the materials 1 to 12 using a VHX-970F digital microscope marketed by the Keyence brand. The latter is provided with a VH-Z20T zoom objective capable of providing magnifications of 20 to 200. The image processing was carried out with ImageJ software, version 2.1.0/1.53c.

[0136] The principle of the measurement is to carry out an image processing with the microscope by selecting the brightest areas, theoretically corresponding to the carbon fibres, and extracting them to measure the surface area they occupy. The protocol is as follows: [0137] a) Sample arrangement

[0138] The sample or chip is placed horizontally on the microscope stage such that the orientation of the fibres on the images taken is vertical. The microscope is oriented at an angle of 30 relative to the straight line normal to the plane of the sample or chip (preferably to the right) and a LED type partial annular light (preferably a right partial annular light relative to the microscope objective) is applied such that the light beam reaches the surface of the fibres in a direction orthogonal to the axis of the fibres. This configuration allows, on the one hand, avoiding taking into account fibres which are coated in transparent resins and, on the other hand, preventing the reflection of the resin areas. [0139] b) Pixel selection

[0140] A selection of the pixels is made by the software by performing the following steps in the Image>Adjust>Color Threshold tab. This option allows selecting the brightness from which the pixels will be selected. For all tested materials the grey level was set to 50 (Brightness parameter). All areas whose grey level is greater than or equal to 50 have thus been selected. [0141] c) Results

[0142] Once the pixels have been selected, they are counted by going to the Analyze>Analyze Particles tab. The size of the pixels is set from 0 and their circularity is set between 0 and 1. The software then gives as a result the percentage of occupied surface area by the selected pixels relative to the total surface area of the image, which corresponds to the value of the bare fibre area ratio.

[0143] For each material, three chips are analysed and ten measurements are performed per chip. The bare fibre area ratio per chip is obtained by averaging these 10 measurements. The bare fibre area ratio per material is obtained by averaging the rates obtained by each of the three chips. The results are presented in Table 2 below.

TABLE-US-00002 TABLE 2 Bare fibre area ratio of the materials 1 to 12 Average standard CV No (%) deviation (%) Interval (%) 1 33.27 1.17 3.50% 32.10 34.43 2 30.34 4.06 13.38% 26.28 34.40 3 40.68 2.44 6.01% 38.23 43.12 4 11.90 2.01 16.87% 9.89 13.91 5 13.66 2.23 16.35% 11.43 15.90 6 10.47 2.87 27.39% 7.60 13.34 7 2.31 0.75 32.30% 1.56 3.06 8 11.00 1.25 11.32% 9.76 12.25 9 4.77 2.11 44.31% 2.66 6.88 10 3.41 0.36 10.70% 3.04 3.77 11 15.70 5.50 35.05% 10.20 21.21 12 0.72 0.07 9.16% 0.66 0.79

[0144] The chips obtained from the materials 1 to 3 (according to the invention) all have a bare fibre area ratio greater than or equal to 22% (taking into account the standard deviation) which is not the case for comparative chips of the materials 4 to 12.

[0145] This technical characteristic defining the chips according to the invention allows obtaining a composite material having high mechanical properties, as demonstrated below.

2. Abrasion Test

[0146] An abrasion test was performed in order to determine the mass loss of the chips, with a view to characterising their roughness.

[0147] This test was performed using a Taber linear abrasion meter (5750) provided with an H18 abrasion rubber. This test is carried out according to the procedure detailed below:

[0148] The sample is fixed on a support then subjected to the action of the H18 abrasive rubber (characteristic of a non-resilient material) mounted on the linear abrasion meter.

[0149] The following parameters are used: [0150] No load applied in addition to the support; [0151] Number of abrasion cycles: 100; [0152] Cycle length: 10 cm; [0153] Cycle speed: 25 cycles/minute.

[0154] The samples are weighed initially, then after 50 cycles, and finally after 100 cycles, to determine the total mass loss. For each material, at least three samples were tested and the average of the obtained values was calculated.

[0155] The mass loss provides information on the surface condition of the chips. Indeed, the action of the abrasion rubber on a smooth surface will result in a lower mass loss compared to its action on a rough surface comprising asperities. This is explained by the fact that the action of the abrasion rubber will lead to the elimination of these surface asperities.

[0156] Thus, the greater the mass loss, the rougher the surface and therefore contains asperities.

[0157] The results presented in Table 3 are expressed in grams, and as a percentage of mass lost relative to the initial mass.

TABLE-US-00003 TABLE 3 Abrasion test results standard No Loss (%) deviation CV (%) Interval (%) 1 0.065 0.0361 55.87% 0.10 0.029 2 0.026 0.0071 27.50% 0.033 0.019 3 0.019 0.00473 25.02% 0.024 0.014 4 0.015 0.01246 81.18% 0.028 0.003 5 0.068 0.08410 124.41% 0.152 0.016 6 0.005 0.00067 14.83% 0.005 0.004 7 0.024 0.02271 94.96% 0.047 0.001 8 0.063 0.01174 18.69% 0.075 0.051 9 0.012 0.00478 40.86% 0.016 0.007 10 0.017 0.01267 72.83% 0.030 0.005 11 0.002 0.00191 79.62% 0.004 0.0488% 12 0.001 0.000593 66.70% 0.001 0.0296%

[0158] It follows from Table 3 that the chips obtained from the materials 1 to 3 have a roughness measured by a mass loss which is greater than or equal to 0.008% by taking into account the standard deviation.

[0159] These technical characteristics defining the chips according to the invention allow obtaining a composite material having high mechanical properties as demonstrated below.

EXAMPLE 3: MECHANICAL PROPERTIES OF A COMPOSITE MATERIAL PART

[0160] The Applicant has carried out characterisation tests, in terms of mechanical characteristics, of the materials obtained from chips according to the present invention.

[0161] The tests whose results are described below, were carried out on prototype plates measuring 23 cm by 23 cm and having a thickness comprised between 3.5 mm and 3.6 mm.

[0162] The chips used in the tests presented here are from composite material elements including carbon fibres in a unidirectional arrangement included in an epoxy resin type adhesive. The used elements are from the aeronautical industry. The composite material had characteristics which are identical or similar to the UD carbon plate material, the characteristics of which are indicated in Table 4 below.

[0163] The chips are cut according to Example 1 from a starting composite material including carbon fibres in a unidirectional arrangement included in an epoxy resin type adhesive.

[0164] The obtained chips are rectangular, and have a length l of 100 mm, a width b of 9 mm and a thickness comprised between 0.3 mm and 0.5 mm.

[0165] From these chips, the plates are made according to the method as described below: [0166] coating the chips: the chips are mixed with a liquid adhesive in order to coat them, with a view to moulding them; [0167] moulding the chips in the form of flat panels; [0168] pressing the mould; [0169] unmoulding the part; and [0170] curing the part.

[0171] The mould is coated with a mould release agent and is topped so as to create a layer of adhesive on the surface of the mould.

[0172] The used adhesive is the ADEKIT H9011 system used according to the manufacturer's recommendations.

[0173] The chips are manually positioned in the mould.

[0174] The ratio of chips to adhesive is, unless otherwise stated, 65/35 by mass in the finished plate.

[0175] The moulding is carried out under a press, by applying a force of 20 ton-force, and by controlling the temperature to approximately 70 C.

[0176] After unmoulding, the plates are kept for a week at ambient temperature (20 C.) to finalise the curing before being used for measurements.

[0177] The plates thus obtained correspond to plates of composite material whose chips, and therefore the fibres, are positioned in a unidirectional arrangement.

[0178] Table 4 below compares the mechanical characteristics of the plates UD1 and UD2 s to reference plates (UD carbon plate, wooden plate, aluminium plate).

TABLE-US-00004 TABLE 4 Mechanical properties Longitudinal Transverse direction direction performance performance Performance (0) (90) 45 Flexural Tensile Flexural Tensile Flexural Tensile Density modulus strength modulus strength modulus strength Material (g/cm.sup.3) (en GPa) (en MPa) (en GPa) (en MPa) (en GPa) (en MPa) Aluminium 2.7 70 300 70 300 70 300 (5754 H22) Wood (Beech) 0.8 14 110 10 100 12 100 UD carbon 1.45 150 1500 5 40 10 100 plate Plate UD1 1.3 57 616 (50% wt. of chips) Plate UD2 1.3 85 750 4 40 10 100 (65% wt. of chips)

[0179] The UD carbon plate corresponds to a plate made from a composite material based on new unidirectional carbon fibres.

[0180] The Plate UD1 and Plate UD2 correspond to composite material plates in accordance with embodiments of the invention, obtained as described above, and whose chips, and therefore the fibres, are positioned according to a unidirectional arrangement.

[0181] It is notable that the flexural modulus and the tensile strength of the Plate UD2 (with 650 of chips by mass) is significantly greater than 500 of the values obtained for the reference UD Carbon Plate, i.e. a composite material based on comparable new unidirectional fibres (from which the used chips can be extracted). In particular, the flexural modulus obtained, in the longitudinal direction, is equal to 57% of the flexural modulus of the comparable new unidirectional material based on carbon fibres. By bringing these results to equal masses of the panels (taking into account the differences observed in terms of density), the flexural modulus of the Plate UD2 (with 65% of chips by mass) is equal to 63% of the flexural modulus of the reference UD Carbon Plate.

[0182] The results presented above demonstrate the production of recycled materials with high mechanical performance. These results are obtained for materials including a proportion of chips which can be further increased relative to the added amount of adhesive (ratio of 65/35 by mass at most in the represented examples). However, the Applicant has observed that the percentage of chips directly influences the obtained mechanical performance, because it induces the percentage of fibres within the material. In particular, the flexural modulus of the Plate UD2 (containing 65% of chips by mass) is almost 50% higher than that of the Plate UD1 (containing 50% of chips by mass). The tensile strength is increased by more than 20%.

[0183] The chips according to the invention therefore allow obtaining a recycled material which has approximately 70% of the mechanical performances, in particular 70% of the flexural modulus, and (up to 75% to 80% of the performance at identical masses) of the comparable materials based on new fibres, with a simple manufacturing method, and having a low environmental impact compared to the chemical or thermal recycling methods.

[0184] Furthermore, even higher performances can be achieved, the Applicant having successfully produced parts containing more than 65% by mass of chips (in this case up to 78% by mass, and a panel containing approximately 85% by mass of chip seems feasible).

EXAMPLE 3: MECHANICAL PROPERTIES OF A COMPOSITE MATERIAL PART

[0185] FIG. 1 represents the flexural modulus of a panel made from chips according to the invention (obtained from a composite material to be recycled), the chips being organised in a unidirectional manner, and that of a panel obtained from new composite material containing unidirectionally oriented carbon fibres.

[0186] The flexural modulus is plotted on the ordinate.

[0187] The abscissa shows the angle at which the measurement is carried out. An angle of 0 corresponds to the direction of extension of the fibres or the chips, and 90 corresponds to the direction transverse to the fibres and/or chips.

[0188] The triangles correspond to the measurements made on a plate of a material comprising chips according to the invention including unidirectional carbon fibres, said chips being organised in a unidirectional manner. The flexural modulus of this plate, measured in the direction of extension of the chips and the fibres they contain, is 47 GPa.

[0189] The circles represent the theoretical bending moduli calculated for an equivalent plate, formed from a new composite material based on unidirectional carbon fibres whose flexural modulus in the direction of the fibres it contains would be 47 GPa.

[0190] It appears that, surprisingly, the measurements carried out for a composite material comprising chips according to the invention correspond perfectly to the theoretical values obtained for the new material formed with equivalent continuous fibres.

[0191] Thus, the mechanical properties of an element formed with the chips according to the invention are predictable according to the knowledge generally applied to new composite materials based on equivalent continuous carbon fibres.