Optimized process for production of composites from recycled carbon fibers and thermoplastic matrix

Abstract

To provide: a process to obtain a semi-finished product comprising recycled carbon fibers and a thermoplastic matrix comprising a thermoplastic polyamide; a semi-finished product; and uses thereof in production of composites.SOLUTION: A method for obtaining a recycled carbon fiber-reinforced semi-finished product comprises the following steps of: a) providing a nonwoven fabric comprising recycled carbon fibers; b) uniformly disposing a polymer powder comprising a thermoplastic polyamide on the nonwoven fabric comprising the recycled carbon fibers; and c) consolidating the nonwoven fabric obtained in the step b) to obtain a fiber-reinforced semi-finished product.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a process for obtaining a semi-finished product comprising recycled carbon fibres and a thermoplastic matrix comprising a thermoplastic polyamide, the semi-finished product obtained and its use in the manufacture of composite materials. [Background technology]

[0002] Carbon fibers are composed primarily of carbon atoms. Although carbon fiber is quite costly to produce, it has found wide application worldwide due to several highly sought-after properties such as high stiffness, high tensile strength, high strength-to-weight ratio, high chemical resistance, high temperature tolerance and low thermal expansion.

[0003] As a result, the amount of waste material containing carbon fibers is steadily increasing. To recycle these valuable fibers, the respective waste materials are typically shredded and the fibers are reclaimed from the composite materials using pyrolysis or solvolysis.

[0004] Another source of recycled carbon fibres are offcuts from semi-finished textiles. These recycled fibres are shortened to the required length depending on the respective application. The discontinuous waste carbon fibres obtained as cut waste can then be fed to a process for recycling carbon fibres.

[0005] Recycled carbon fiber (rCF) or cut waste carbon fiber can be processed into nonwoven fabrics.

[0006] However, nonwoven fabrics containing recycled carbon fibers have different and often inferior fabric properties compared to nonwoven fabrics containing virgin carbon fibers.

[0007] This is mainly due to the randomly oriented, discontinuous carbon fibers obtained by chopping waste carbon fibers or cutting virgin fibers. Common recycling methods such as solvolysis or pyrolysis also remove the sizing agents from the carbon fibers, reducing the protection of the fibers.

[0008] In particular, processing these recycled carbon fiber-containing nonwovens into semi-finished products with a thermoplastic matrix has historically been difficult, with issues such as lofting of the nonwovens causing oxidation of the polymer during consolidation, leading to poor impregnation of the semi-finished products.

[0009] Typically, thermoplastic polymer fibers are processed into nonwoven fabrics containing recycled carbon fibers, and each nonwoven fabric is consolidated to form a thermoplastic matrix, which can lead to a non-uniform distribution of the thermoplastic polymer in the semi-finished product and limit the usable thermoplastic polymers to those that can be spun into fibers.

[0010] There is therefore a need for a process that obtains semi-finished products with good properties comprising recycled carbon fibres and thermoplastic polymers, allowing the mass production of semi-finished products that can be used in the manufacture of composite materials.

[0011] After extensive research in the art, it has surprisingly been found that nonwoven fabrics containing recycled carbon fibers can be processed into recycled carbon fiber reinforced semi-finished products by utilizing a powder impregnation method to place thermoplastic polyamide powder into the nonwoven fabric before consolidating the nonwoven fabric into the respective semi-finished product.

[0012] The obtained recycled carbon fiber reinforced semi-finished products showed good homogeneity as evidenced by very small differences in fiber volume fraction at different points of the semi-finished products. Summary of the Invention [Means for solving the problem]

[0013] The present invention relates to a process for obtaining recycled carbon fiber reinforced semi-finished products, which process comprises the steps of: a) providing a nonwoven fabric comprising recycled carbon fibers; b) uniformly disposing a polymer powder comprising a thermoplastic polyamide on the nonwoven fabric comprising recycled carbon fibers; and c) consolidating the nonwoven fabric obtained in step b) to obtain a fiber-reinforced semi-finished product.

[0014] In another aspect, the present invention relates to a recycled carbon fiber reinforced semi-finished product comprising a nonwoven fabric comprising recycled carbon fibers and a thermoplastic matrix comprising a thermoplastic polyamide, the semi-finished product having an average fiber volume fraction (aFVF) and a fiber volume fraction difference (ΔFVF), The average fiber volume fraction (aFVF) is within a range of 5 to 50 volume %, preferably 10 to 40 volume %, and more preferably 17 to 30 volume %, based on the total volume of the recycled carbon fiber reinforced semi-finished product, and the average fiber volume fraction (aFVF) is obtained by measuring the fiber volume fractions of n 10 mm x 20 mm samples taken from points in the recycled carbon fiber reinforced semi-finished product that are 5 cm or more and 20 cm or less apart from each other, and calculating according to the following formula (i):

number

[0015] In a further aspect, the present invention relates to a process for obtaining a composite material, the process comprising the steps of: step I) of providing a recycled carbon fiber reinforced semi-finished product according to the invention; Step II) of heating the recycled carbon fiber reinforced semi-finished product; and III) forming the heated recycled carbon fiber reinforced semi-finished product into a composite material.

[0016] Finally, the invention relates to a composite material comprising a recycled carbon fiber reinforced semi-finished product according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention relates to a process for obtaining recycled carbon fiber reinforced semi-finished products, which process comprises the steps of: a) providing a nonwoven fabric comprising recycled carbon fibers; b) uniformly disposing a polymer powder comprising thermoplastic polyamide on the nonwoven fabric comprising recycled carbon fibers; and step c) of consolidating the nonwoven fabric obtained in step b) to obtain a fiber-reinforced semi-finished product.

[0018] Fiber-reinforced semi-finished products Fiber-reinforced semi-finished products are known in the prior art and consist of a polymer matrix reinforced with fibers. They are usually obtained in the form of sheets.

[0019] Nonwoven fabric containing recycled carbon fiber Methods for recycling carbon fibres are known in the prior art, typically by shredding each waste material containing carbon fibres and using pyrolysis or solvolysis to separate the fibres from the remaining waste material.

[0020] Shredding the waste destroys the oriented continuous carbon fibers present in the waste. Thus, the recycled carbon fibers obtained are randomly oriented discontinuous carbon fibers. The length of these recycled carbon fibers is usually less than 180 mm.

[0021] Additionally, both pyrolysis and solvolysis remove the sizing agents that are typically applied to carbon fibers (unsized fibers).

[0022] Fiber sizing is known in the prior art. It provides a thin, uniform coating on the surface of the fiber during the manufacturing process. Sizing helps prevent filament breakage during handling and processing, as well as during subsequent compounding and composite processing, and improves the compatibility of the fiber in subsequent processes.

[0023] Recycled carbon fibers cannot be woven into a woven fabric due to their short length and random orientation, but they can be processed into a nonwoven fabric.

[0024] Processes for obtaining nonwoven fabrics are known in the prior art, including wet processes, dry processes, etc.

[0025] The nonwoven fabrics containing recycled carbon fibers used in the processes according to the present invention preferably have one or more of the following properties:

[0026] The length of the recycled carbon fibers is preferably in the range of 20 mm to 180 mm, more preferably 25 mm to 150 mm, and even more preferably 30 to 100 mm.

[0027] The nonwoven fabric preferably comprises recycled carbon fibers in an amount of 80 to 100% by weight, more preferably 90 to 100% by weight, and even more preferably 98 to 100% by weight, based on the total weight of the nonwoven fabric.

[0028] The basis weight of the nonwoven fabric containing recycled carbon fibre is preferably 50 g m -2 ~250g·m -2 , more preferably 75 g m -2 ~150g·m -2 , and even more preferably 90 g m -2 ~110g·m -2 is within the range.

[0029] In one embodiment of the process according to the present invention, the recycled carbon fibers of the nonwoven fabric are discontinuous.

[0030] In another embodiment of the process according to the present invention, the recycled carbon fibers of the nonwoven fabric are discontinuous and unsized.

[0031] Polymer powders including thermoplastic polyamides For the impregnation of nonwoven fabrics containing recycled carbon fibers (rCF), as mentioned above, a polymer powder containing a thermoplastic polyamide is used.

[0032] Methods for obtaining polymer powders are known in the prior art. For example, suitable polymer powders can be obtained by grinding the respective polymers. Furthermore, the use of cryogenic grinding can be advantageous, for example, to increase the brittleness of the polymer and facilitate the grinding process of the polymer.

[0033] In order to achieve good impregnation and dispersion of the polymer powder, the maximum particle size of the polymer powder containing the thermoplastic polyamide is preferably within the range of 1 μm to 1000 μm, and more preferably 10 μm to 600 μm.

[0034] Since the process according to the present invention uses a polymer powder containing a thermoplastic polyamide, suitable thermoplastic polyamides are not limited to polyamides that can be spun into fibers. Thus, polyamides having low viscosity and / or low molecular weight can be used as thermoplastic polyamides.

[0035] Thermoplastic describes the property of plastic polymeric materials that they are moldable at certain elevated temperatures and solidify upon cooling.

[0036] Suitable polyamides are, for example, polyamide 6 (PA6), polyamide 66 (PA66), polyamide 6I (PA6I), polyamide 66 / 6I (PA66 / 6I) and mixtures thereof.

[0037] Thermoplastic polyamide PA66 has a molecular weight of 18,000 to 24,000 g·mol -1 , preferably 19000 to 20000 g mol -1and / or 35,000 to 50,000 g mol -1 , preferably 38500 to 41000 g mol -1 The polymer may have a weight average molecular weight (Mw) in the range of

[0038] Thermoplastic polyamide PA66 / 6I has a molecular weight of 10,000 to 14,500 g mol -1 , preferably 12000 to 13000 g mol -1 and / or 18000-34000 g mol -1 , preferably 24000 to 28000 g mol -1 The polymer may have a weight average molecular weight (Mw) in the range of

[0039] Thermoplastic polyamide PA6I has a molecular weight of 8000 to 13000 g·mol -1 , preferably 10,000 to 12,000 g mol -1 Number average molecular weight (Mn) in the range of 17500 to 27000 g mol -1 , preferably 20,000 to 25,000 g mol -1 The polymer may have a weight average molecular weight (Mw) in the range of

[0040] Thermoplastic polyamide PA6 is 15000-20000g·mol -1 , preferably 17000 to 19000 g mol -1 and / or 29000-38000 g mol -1 , preferably 33000 to 36000 g mol -1 The polymer may have a weight average molecular weight (Mw) in the range of

[0041] The average molecular weight is measured in accordance with ISO 16014-1.

[0042] The polymer powder containing thermoplastic polyamide preferably contains more than 90% by weight, preferably in the range of 95% to 100% by weight, of thermoplastic polyamide, and more preferably consists of thermoplastic polyamide.

[0043] To impregnate the rCF-containing nonwoven fabric with the thermoplastic polyamide-containing polymer powder, the thermoplastic polyamide-containing polymer powder is uniformly placed on one side, preferably both sides, of the nonwoven fabric.

[0044] Techniques for depositing polymer powders are known in the prior art.

[0045] The polymer powder comprising thermoplastic polyamide is preferably disposed on the nonwoven fabric comprising rCF at a temperature within the range of 150°C to 350°C, preferably 200°C to 300°C, more preferably 225°C to 275°C.

[0046] The amount of polymer powder containing thermoplastic polyamide disposed on the nonwoven fabric containing rCF is preferably within the range of 30% by weight to 90% by weight, more preferably 40% by weight to 80% by weight, based on the total weight of the nonwoven fabric after impregnation.

[0047] The total amount of the polymer powder containing thermoplastic polyamide and the nonwoven fabric containing rCF is preferably within the range of 90% by weight to 100% by weight, more preferably 95% by weight to 100% by weight, and more preferably 98% by weight to 100% by weight, based on the total weight of the semi-finished product obtained.

[0048] Compaction Consolidation is a process in which heat and pressure are applied to a material or material composition.

[0049] By applying heat and pressure, a polymer powder containing thermoplastic polyamide is melted and forced into a nonwoven fabric containing rCF to obtain a recycled carbon fiber reinforced semi-finished product.

[0050] Compaction methods are known in the prior art. In a preferred embodiment, a double belt press is used for compaction. Even more preferably, a double steel belt press is used for compaction.

[0051] The amount of heat and pressure applied must be sufficient to cause the polymer powder, including the thermoplastic polyamide, to melt.

[0052] Consolidation is preferably carried out at a temperature in the range of 230° C. to 330° C., more preferably 250° C. to 310° C., and / or at a pressure in the range of 1 to 60 bar, preferably 5 to 30 bar, more preferably 8 to 20 bar.

[0053] During consolidation, the polymer powder, including the thermoplastic polyamide, is transformed into the thermoplastic matrix of the recycled carbon fiber reinforced semi-finished product.

[0054] Complete impregnation of the rCF-containing nonwoven fabric with thermoplastic polyamide can be achieved by the process according to the invention as described above.

[0055] semi-finished products The invention further relates to a semi-finished product reinforced with recycled carbon fibers that can be produced by the process according to the invention as described above, characterized in that it comprises a nonwoven fabric comprising recycled carbon fibers as described above and a polymer matrix comprising a thermoplastic polyamide as described above.

[0056] The average fiber volume fraction (aFVF) of this recycled carbon fiber reinforced semi-finished product is in the range of 5 to 50 volume %, more preferably 10 to 40 volume %, and even more preferably 17 to 30 volume %, based on the total volume of the recycled carbon fiber reinforced semi-finished product.

[0057] To measure the average fiber volume fraction (aFVF), multiple (n) samples are taken from different points of the semi-finished product and the fiber volume fraction of each sample is measured. In order to obtain representative samples, the points from which each sample is taken should be at least 5 cm apart. In the measurement method used in the present invention, the points are 5-20 cm apart from each other.

[0058] Techniques for measuring the fiber volume fraction of fiber-reinforced materials are known in the prior art.

[0059] One way to measure the fiber volume fraction is to remove the polymer matrix from the sample by heat or chemical treatment according to DIN EN 2564 or DIN 16459. The remaining fibers are then washed, dried and weighed. Knowing the initial weight and volume of the semi-finished product as well as the density of the fibers, the fiber volume fraction can be determined.

[0060] The average fiber volume fraction (aFVF) may be calculated according to equation (i) below:

number

[0061] Using the process according to the invention as described above, highly homogeneous recycled carbon fiber reinforced semi-finished products can be obtained.

[0062] According to the present disclosure, the homogeneity of the rCF reinforced semi-finished product can be determined by the measured fiber volume fraction (FVF n ) and the average fiber volume fraction of the semi-finished product (aFVF).

[0063] The fiber volume fraction difference (ΔFVF) may be calculated according to equation (ii) below: ΔFVF=FVF n -aFVF (ii)

[0064] According to the present invention, the ΔFVF of any sample n is ≦±3 vol.%, preferably ≦±2 vol.%, more preferably ≦±1.5 vol.%.

[0065] This small variation in fiber volume fraction indicates improved homogeneity of the recycled carbon fiber reinforced semi-finished product according to the present invention compared to other mixing and infiltration techniques known in the art.

[0066] composite material The recycled carbon fiber reinforced semi-finished products of the present invention can be processed into composite materials.

[0067] The process for obtaining the composite material according to the present invention comprises the steps of: I) providing a recycled carbon fiber reinforced semi-finished product as described above or obtained by any of the processes as described above; II) heating the recycled carbon fiber reinforced semi-finished product; III) forming the heated recycled carbon fiber reinforced semi-finished product into a composite material; Includes.

[0068] The heating in step II) may be carried out by any method known in the art. In a preferred embodiment, the recycled carbon fiber reinforced semi-finished product is heated in a convection oven or an infrared oven.

[0069] As described above, in order to completely impregnate the nonwoven fabric containing rCF with the thermoplastic polyamide, the recycled carbon fiber reinforced semi-finished product in step II) is heated at a temperature lower than the melting point of the thermoplastic polyamide, thereby reducing the amount of oxidation of the polymer due to the loft of the nonwoven fabric.

[0070] The heating in step II) is preferably carried out at a temperature lower than the melting point of the thermoplastic polyamide, more preferably at a temperature within the range of 150°C to 300°C, and even more preferably at a temperature within the range of 200°C to 250°C.

[0071] The forming of composite materials is known in the art. In a preferred embodiment, the composite material is formed by a heat press, where the blank is inserted into a heated tool.

[0072] Preferably, the shaping in step III) is carried out in a tool having a temperature in the range of 50°C to 150°C, preferably 60°C to 120°C.

[0073] Finally, the present invention relates to a composite material, characterized in that it comprises a nonwoven fabric comprising recycled carbon fibers and a thermoplastic matrix comprising thermoplastic polyamide, preferably comprising a recycled carbon fiber reinforced semi-finished product obtained by or according to any of the processes as described above or as described below.

[0074] This composite material can be further functionalized by any known method, an example of a suitable method is the injection molding process.

[0075] Furthermore, the present invention can be described by the following numbered clauses:

[0076] 1. Step a) of providing a nonwoven fabric comprising recycled carbon fibers; b) uniformly disposing a polymer powder comprising thermoplastic polyamide on the nonwoven fabric comprising recycled carbon fibers; step c) of consolidating the nonwoven fabric obtained in step b) to obtain a fiber-reinforced semi-finished product; 2. A process for obtaining recycled carbon fiber reinforced semi-finished products, comprising:

[0077] 2. Nonwoven fabric containing recycled carbon fiber is 50-250g m -2 , preferably 75 to 150 g m -2 , more preferably 90 to 110 g m -2 The process of claim 1, characterized in that the grammage is in the range of

[0078] 3. The process according to clause 1 or 2, characterized in that the nonwoven fabric comprises recycled carbon fibers in an amount in the range of 80-100% by weight, preferably 90-100% by weight, more preferably 98-100% by weight, based on the total weight of the nonwoven fabric.

[0079] 4. The process according to any one of clauses 1 to 3, characterized in that the recycled carbon fibres of the nonwoven fabric are discontinuous carbon fibres having a length in the range of 20mm to 180mm, preferably 25mm to 150mm, more preferably 30mm to 100mm.

[0080] 5. The process according to claim 4, characterized in that the nonwoven recycled carbon fibre is unsized.

[0081] 6. The process according to any one of clauses 1 to 5, characterized in that the polymer powder comprising thermoplastic polyamide comprises a polyamide selected from the list consisting of polyamide 6 (PA6), polyamide 66 (PA66), polyamide 6I (PA6I), polyamide 66 / 6I (PA66 / 6I) and mixtures thereof.

[0082] 7. Thermoplastic polyamides are 18000~24000g mol -1 , preferably 19000 to 20000 g mol -1 and / or 35,000 to 50,000 g mol -1 , preferably 38500 to 41000 g mol -1 PA66 having a weight average molecular weight (Mw) in the range 10000~14500g mol -1 , preferably 12000 to 13000 g mol -1 and / or 18000-34000 g mol -1 , preferably 24000 to 28000 g mol -1 PA66 / 6I having a weight average molecular weight (Mw) in the range 8000~13000g mol -1 , preferably 10,000 to 12,000 g mol -1 Number average molecular weight (Mn) in the range of 17500 to 27000 g mol -1 , preferably 20,000 to 25,000 g mol -1 PA6I having a weight average molecular weight (Mw) in the range 15000~20000g mol -1 , preferably 17000 to 19000 g mol -1 and / or 29000-38000 g mol -1 , preferably 33000 to 36000 g mol -1 PA6 having a weight average molecular weight (Mw) in the range and mixtures thereof The process according to clause 6, characterized in that the compound is selected from the list consisting of:

[0083] 8. The process according to any one of clauses 1 to 7, characterized in that the maximum particle size of the polymer powder comprising thermoplastic polyamide is in the range of 1 μm to 1000 μm, preferably 10 μm to 600 μm.

[0084] 9. The process according to any one of clauses 1 to 8, characterized in that the amount of thermoplastic polyamide in the thermoplastic polyamide-containing polymer powder is in the range of 80 to 100% by weight, preferably 90 to 100% by weight, more preferably 98 to 100% by weight, based on the total weight of the thermoplastic polyamide-containing polymer powder.

[0085] 10. The process according to any one of clauses 1 to 9, characterized in that the amount of polymer powder comprising thermoplastic polyamide is in the range of 30% to 90% by weight, preferably 40% to 80% by weight, based on the total weight of the semi-finished product obtained.

[0086] 11. The process according to any one of clauses 1 to 10, characterized in that the weight ratio of the polymer powder comprising thermoplastic polyamide to the nonwoven fabric comprising recycled carbon fibers is in the range of 0.5 to 5, preferably 0.7 to 3, more preferably 0.8 to 2.

[0087] 12. The process according to any one of clauses 1 to 11, characterized in that the total amount of polymer powder comprising thermoplastic polyamide and nonwoven fabric comprising rCF is in the range of 90% by weight to 100% by weight, more preferably 95% by weight to 100% by weight, more preferably 98% by weight to 100% by weight, based on the total weight of the semi-finished product obtained.

[0088] 13. The process according to any one of clauses 1 to 12, characterized in that in step b) the polymer powder comprising thermoplastic polyamide is uniformly distributed on the nonwoven fabric at a temperature in the range of 150°C to 350°C, preferably 200°C to 300°C, more preferably 225°C to 275°C.

[0089] 14. The process according to any one of clauses 1 to 13, characterized in that the consolidation in step c) is carried out at a temperature in the range of 230°C to 330°C, preferably 250°C to 310°C.

[0090] 15. The process according to any one of clauses 1 to 14, characterized in that the consolidation in step c) is carried out at a pressure in the range of 1 to 60 bar, preferably 5 to 30 bar, more preferably 8 to 20 bar.

[0091] 16. The process according to any one of clauses 1 to 15, characterized in that the consolidation in step c) is carried out in a double belt press, preferably in a double steel belt press.

[0092] 17. A recycled carbon fiber reinforced semi-finished product comprising a nonwoven fabric comprising recycled carbon fibers as described in any one of clauses 1 to 16 and a thermoplastic matrix comprising a thermoplastic polyamide as described in any one of clauses 1 to 16, wherein the semi-finished product has an average fiber volume fraction (aFVF), the average fiber volume fraction (aFVF) being in the range of 5 to 50 vol.%, preferably 10 to 40 vol.%, more preferably 17 to 30 vol.%, based on the total volume of the recycled carbon fiber reinforced semi-finished product, the average fiber volume fraction (aFVF) being obtained by measuring the fiber volume fraction of n 10 mm x 20 mm samples taken from points at least 5 cm and no more than 20 cm apart from each other in the recycled carbon fiber reinforced semi-finished product and calculating according to the following formula (i):

number

[0093] 18. Measured fiber volume fraction (FVF) of sample n n The fiber volume fraction difference (ΔFVF) between the fiber volume fraction (aFVF) and the average fiber volume fraction (aFVF) is calculated according to the following equation (ii): ΔFVF=FVF n -aFVF (ii) 18. Recycled carbon fiber reinforced semi-finished product according to clause 17, wherein the fibre volume fraction difference (ΔFVF) is ≦±3 vol.%, preferably ≦±2 vol.%, more preferably ≦±1.5 vol.%.

[0094] 19. A recycled carbon fiber reinforced semi-finished product according to claim 17 or 18, characterized in that the total amount of the nonwoven fabric containing recycled carbon fibers and the thermoplastic matrix containing thermoplastic polyamide in the semi-finished product is in the range of 80-100% by weight, preferably 90-100% by weight, more preferably 98-100% by weight, based on the total weight of the semi-finished product.

[0095] 20. A recycled carbon fiber reinforced semi-finished product according to any one of claims 17 to 19, characterized in that it comprises a nonwoven fabric containing recycled carbon fibers and a thermoplastic matrix containing thermoplastic polyamide.

[0096] 21. A recycled carbon fiber reinforced semi-finished product according to any one of clauses 17 to 20, characterized in that it is obtained by the process according to any one of clauses 1 to 16.

[0097] 22. Step I) of providing a recycled carbon fiber reinforced semi-finished product obtained according to any one of clauses 1 to 16 or according to any one of clauses 17 to 21, II) heating the recycled carbon fiber reinforced semi-finished product; III) forming the heated recycled carbon fiber reinforced semi-finished product into a composite material.

[0098] 23. A process for obtaining a composite material according to clause 22, characterized in that the heating in step II) is carried out at a temperature below the melting point of the thermoplastic polymer, preferably in the range of 150°C to 300°C, more preferably 200°C to 250°C.

[0099] 24. Process for obtaining a composite material according to clause 22 or 23, characterized in that the shaping in step III) is carried out in a heated tool having a temperature in the range of 50°C to 150°C, preferably 60°C to 120°C.

[0100] 25. A composite material comprising a recycled carbon fiber reinforced semi-finished product according to any one of clauses 17 to 21.

[0101] 26. A composite material according to clause 25, characterized in that it is obtained by the process according to any one of clauses 22 to 24. EXAMPLES

[0102] Experimental Procedure Recycled carbon fiber reinforced semi-finished products PA66 polyamide with a maximum particle size of <600 μm (Mw: 8000 g mol -1 ) powder (D99.9%) at 250°C, 0.5 bar, coating speed 2 m / min, basis weight 100 g m -2 Each side of the nonwoven fabric is made of recycled but unsized discontinuous carbon fibers (total 160 g m -2 The nonwoven fabric was then consolidated in a double steel belt press at 280 °C, 15 bar and a speed of 0.5 m / min. The resulting rCF-reinforced semi-finished product in the form of an organosheet had a weight of 260 g m -2 and an average fiber volume fraction (aFVF) of 22.67 volume%.

[0103] Six 10 mm × 20 mm samples were taken from points 5 cm–20 cm apart from each other on the rCF-reinforced semi-finished products, and the fiber volume fraction was measured after removing the polymer matrix.

[0104] [Table 1]

[0105] The largest fiber volume fraction difference (ΔFVF) was found in sample 3 with FVF3 of 21.50 vol.%, which resulted in a fiber volume fraction difference (ΔFVF) between FVF3 and aFVF of -1.17 vol.%.

[0106] The obtained semi-finished product is therefore very homogeneous compared to other mixing and infiltration techniques.

[0107] composite material The rCF reinforced semi-finished products were heated in an infrared oven to 225 °C for 6 min. The heated rCF reinforced semi-finished products were then placed in a heated tool and molded into composites in a heat press at 80 °C.

Claims

1. a) providing a nonwoven fabric comprising recycled carbon fibers; b) uniformly disposing a polymer powder comprising thermoplastic polyamide on the nonwoven fabric comprising recycled carbon fibers; step c) of consolidating the nonwoven fabric obtained in step b) to obtain a fiber-reinforced semi-finished product; A method for obtaining a recycled carbon fiber reinforced semi-finished product, comprising:

2. The nonwoven fabric containing the recycled carbon fiber has a weight of 50 to 200 g / m －２ , preferably 75 to 150 g m －２ , more preferably 90 to 110 g / m －２ and / or the nonwoven fabric comprises the recycled carbon fibers in an amount in the range of 80 to 100 wt.%, preferably 90 to 100 wt.%, more preferably 98 to 100 wt.%, based on the total weight of the nonwoven fabric; and / or the recycled carbon fibers are discontinuous carbon fibers having a length in the range of 20 mm to 180 mm, preferably 25 mm to 150 mm, more preferably 30 mm to 100 mm.

3. 2. The method according to claim 1, characterized in that the polymer powder comprising thermoplastic polyamide comprises a polyamide selected from the list consisting of polyamide 6 (PA6), polyamide 66 (PA66), polyamide 6I (PA6I), polyamide 66 / 6I (PA66 / 6I) and mixtures thereof, and / or the maximum particle size of the polymer powder comprising thermoplastic polyamide is in the range of 1 μm to 1000 μm, preferably 10 μm to 600 μm, and / or the amount of the polymer powder comprising thermoplastic polyamide arranged in step b) is in the range of 30% to 90% by weight, preferably 40% to 80% by weight, based on the total weight of the semi-finished product obtained.

4. 2. The method according to claim 1, characterized in that the weight ratio between the polymer powder comprising thermoplastic polyamide and the nonwoven fabric comprising recycled carbon fibers is in the range of 0.5 to 5, preferably 0.7 to 3, more preferably 0.8 to 2, and / or the total amount of the polymer powder comprising thermoplastic polyamide and the nonwoven fabric comprising rCF is in the range of 90% to 100% by weight, more preferably 95% to 100% by weight, more preferably 98% to 100% by weight, based on the total weight of the semi-finished product obtained.

5. 2. The method according to claim 1, characterized in that in step b) the polymer powder comprising the thermoplastic polyamide is uniformly disposed on each side of the nonwoven fabric and / or is disposed at a temperature in the range of 150°C to 350°C, preferably 200°C to 300°C, more preferably 225°C to 275°C.

6. 2. The method according to claim 1, characterized in that the consolidation in step c) is carried out at a temperature in the range of 230° C. to 330° C., preferably 250° C. to 310° C. and / or at a pressure in the range of 1 to 60 bar, preferably 5 to 30 bar, more preferably 8 to 20 bar, and / or in a double steel belt press.

7. A recycled carbon fiber reinforced semi-finished product comprising a nonwoven fabric comprising recycled carbon fibers and a thermoplastic matrix comprising a thermoplastic polyamide, the semi-finished product having an average fiber volume fraction (aFVF) and a fiber volume fraction difference (ΔFVF), said average fiber volume fraction (aFVF) is in the range of 5-50 vol%, preferably 10-40 vol%, more preferably 17-30 vol%, based on the total volume of said recycled carbon fiber reinforced semi-finished product, said average fiber volume fraction (aFVF) being obtained by measuring the fiber volume fraction of n 10 mm x 20 mm samples taken from points in said recycled carbon fiber reinforced semi-finished product that are 5 cm or more and 20 cm or less apart from each other, and calculating according to the following formula (i): [0010] where n is the number of samples taken, n is ≧2, preferably ≧4, and FVF ｎ is the fiber volume fraction of sample n, The fiber volume fraction difference (ΔFVF) is the fiber volume fraction (FVF) of the measured sample n. ｎ ) and the average fiber volume fraction (aFVF), calculated according to the following formula (ii): ΔFVF=FVF ｎ -aFVF (ii) 5. A recycled carbon fiber reinforced semi-finished product, characterized in that the fiber volume fraction difference (ΔFVF) is ≦±3 vol.%, preferably ≦±2 vol.%, more preferably ≦±1.5 vol.%.

8. 8. The recycled carbon fiber reinforced semi-finished product according to claim 7, characterized in that the nonwoven fabric comprises the recycled carbon fibers in an amount in the range of 80 to 100% by weight, preferably 90 to 100% by weight, more preferably 98 to 100% by weight, based on the total weight of the nonwoven fabric, and / or the recycled carbon fibers are discontinuous carbon fibers having a length in the range of 20 mm to 180 mm, preferably 25 mm to 150 mm, more preferably 30 mm to 100 mm.

9. 8. A recycled carbon fiber reinforced semi-finished product according to claim 7, characterized in that the polymer matrix comprising thermoplastic polyamide comprises a polyamide selected from the list consisting of polyamide 6 (PA6), polyamide 66 (PA66), polyamide 6I (PA6I), polyamide 66 / 6I (PA66 / 6I) and mixtures thereof, and / or the amount of the polymer matrix comprising thermoplastic polyamide is in the range of 30% to 90% by weight, preferably 40% to 80% by weight, based on the total weight of the semi-finished product, and / or the weight ratio of the polymer matrix comprising thermoplastic polyamide to the nonwoven fabric comprising recycled carbon fibers is in the range of 0.5 to 5, preferably 0.7 to 3, more preferably 0.8 to 2, and / or the total amount of the polymer matrix comprising thermoplastic polyamide and the nonwoven fabric comprising rCF is in the range of 90% to 100% by weight, more preferably 95% to 100% by weight, more preferably 98% to 100% by weight, based on the total weight of the semi-finished product.

10. A recycled carbon fiber reinforced semi-finished product according to claim 7, characterized in that it is obtained by the method according to any one of claims 1 to 6.

11. I) providing a recycled carbon fiber reinforced semi-finished product obtained according to claim 1 or according to claim 7; Step II) of heating the recycled carbon fiber reinforced semi-finished product; III) forming the heated recycled carbon fiber reinforced semi-finished product into a composite material; A method for obtaining a composite material, comprising:

12. A method for obtaining a composite material according to claim 11, characterized in that the heating in step II) is carried out at a temperature below the melting point of the thermoplastic polyamide, preferably in the range of 150°C to 300°C, more preferably 200°C to 250°C.

13. A method for obtaining a composite material according to claim 11, characterized in that the shaping in step III) is carried out in a heated mould having a temperature in the range of 50°C to 150°C, preferably 60°C to 120°C.

14. A composite material comprising the recycled carbon fiber reinforced semi-finished product according to claim 7.

15. 15. A composite material according to claim 14, characterized in that it is obtained by the method according to claim 11.

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