FIELD OF THE INVENTION

[0001] The present disclosure relates to novel carbon fibre textile materials, a method for manufacturing the same and devices comprising these carbon fibre textile materials are described.

BACKGROUND OF THE INVENTION

[0002] Carbon fibre materials and especially polyacrylonitrile (PAN)-based fibre materials are utilised in a wide range of applications. In prior applications PAN-based precursors were employed to manufacture fibre materials, wherein the precursor structure is targeted to be very dense, having a low porosity or defects and a high orientation of the polymer chains, especially to take advantage of the later carbon fibre materials for reinforcement applications.

[0003] If these PAN-based precursors are later thermally processed and activated, such as by processing the precursors to a stabilized (oxidized) fibre, and/or further processing to carbon fibres and thermally activating the material in air atmosphere, the specific surface area according to the BET (Brunauer Emmett Teller) method is high, however the weight loss of the carbon fibre is also high during the thermal activation process. This method typically results in fibre materials with specific surface areas according to the BET method in a range of 500 to 1500 m ² /g wherein PAN fibres having a diameter of 7 to 15 pm are employed (M. Inagaki, F. Kang, Materials Science and Engineering of Carbon, Fundamentals, published by Elsevier, Second Edition, 2014, p. 367, table 3.27). These carbon fibres can be used for applications such as water purification or as filter.

[0004] The above-mentioned carbon fibres although having a high specific surface area have the disadvantage that the weight loss after the thermal activation step is also high and the underlying thermal activation step is time-consuming. The high weight loss causes high costs as not only a lot of carbon fibre material is lost but also that the thermal activation step is time-consuming. If these carbon fibres are used as a component of a carbon fibre textile material the costs for forming this fibre textile material are accordingly higher. Therefore, the object to be solved according to the present invention is the provision of a carbon fibre textile material comprising carbon fibres having a high specific surface area, but wherein the underlying carbon fibres are more cost-efficient.

BRIEF SUMMARY OF THE INVENTION

[0005] Surprisingly, the inventors have found that by employing polyacrylonitrile (PAN)- precursor fibres with a substantial specific surface area, in particular specific surface areas according to the BET method of at least 2 m ² /g and with a mean diameter of at least 5 pm, carbon fibres can be obtained with high specific surface area, in particular with specific surface areas according to the BET method of at least 50 m ² /g. However, it is necessary to thermally activate the carbon fibres in an oxidizing atmosphere to get carbon fibres with these high specific surface areas. The manufacturing of the carbon fibres comprises a stabilization process, a carbonisation process, optionally followed by a graphitization process. Furthermore, it was found that by employing PAN-precursor fibres with a substantial specific surface area, in particular specific surface areas according to the BET method of at least 2 m ² /g and a mean diameter of at least 5 pm, carbon fibres can be obtained with a particular and advantageous pore structure and morphology. For example, the obtained carbon fibres and consequently, the carbon fibre textile materials comprising those carbon fibres have a particularly high active surface area wherein the weight loss after the thermal activation step is low. Carbon fibre textile materials according to the present disclosure can therefore be beneficial in electrochemical applications, especially when a high electro-catalytic reactivity and/or performance is advantageous. Furthermore, the carbon fibre textile materials according to the present disclosure may be beneficial in a wide range of applications, for instance due higher catalytical activity and/or increased filtration behaviour and/or low weight and/or high temperature resistance and/or beneficial acoustic behaviour.

[0006] According to an embodiment of the present disclosure a method for manufacturing a carbon fibre textile material is provided. The method comprises the following sequence of steps:

A) providing PAN-precursor fibres with a specific surface area according to the BET method of at least 2 m ² /g and a diameter of at least 5 pm; B) carrying out a stabilizing process in air atmosphere in a temperature range between 200 °C and 300 °C on the PAN-precursor fibres for stabilizing the PAN- precursor fibres;

C) carrying out a high temperature heat treatment process for obtaining carbon fibres;

D) carrying out a thermal activation process for activating the carbon fibres in an oxidizing atmosphere, thereby obtaining carbon fibres exhibiting a specific surface area according to the BET method of at least 50 m ² /g and

E) using either the PAN-precursor fibres according to step A) or the stabilized PAN- precursor fibres according to step B) or the carbon fibres according to step C) for forming a fibre textile material.

The fibre textile material according to step E) preferably represents a woven fabric or a non- woven fabric. The non-woven fabric is preferably a dry laid non-woven and/or a wet laid non-woven; more preferably the dry laid non-woven or wet laid non-woven is selected from the group consisting of a felt, a fleece, a layered material, a paper, and any arbitrary combinations thereof.

[0007] According to another embodiment of the present disclosure, a device selected from the group consisting of a catalytic converter, a filter, a battery cell, a redox flow battery, a super capacitor, an electrolysis cell, a fuel cell, an advanced electrode material, a silencer, a noise or sound absorber, a reflector, a catalyst carrier material or a water purification device comprising a carbon fibre textile material according to any of the embodiments disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figures la to lc display scanning electron microscope (SEM) images of different PAN precursor fibres.

[0009] Figure la displays a SEM image of a cross section of known, comparative PAN- precursor fibres of the present disclosure having a BET of around 0.2 m ² /g. [0010] Figure lb displays a SEM image of a cross section of PAN-precursor fibres of the present disclosure having a BET of around 5 to 6 m ² /g.

[0011] Figure lc displays a SEM image of a cross section of PAN-precursor fibres of the present disclosure having a BET of around 15 to 20 m ² /g.

[0012] As can be seen the PAN-precursor fibres as shown in Figures lb and lc have a higher porosity and a rough surface structure compared to the known PAN-precursor fibres as shown in Figure la.

DETAILED DESCRIPTION OF THE INVENTION

[0013] As used herein, the terms "having", "containing", "including", "comprising" and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features.

[0014] It is to be understood that other embodiments may be utilised and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. The embodiments described herein use specific language, which should not be construed as limiting the scope of the appended claims.

[0015] The term "specific surface area according to the BET method" refers to the analysis technique according to Brunauer Emmett und Teller and describes measurements of the specific surface area carried out according to DIN ISO 9277; 2014-01 based on nitrogen gas adsorption.

[0016] For measuring the active surface area (ASA), temperature programmed desorption (TPD) tests are carried out, wherein a solid test sample is thermally treated in an inert gas atmosphere and the concentration of the desorbed gaseous species is recorded. For measurement, a device (AutoChem II 2920; Micrometries) was used. This device is a fully automated chemisorption analyser, including a gas feeding, a temperature controlled reaction zone and a gas analyser (OmniStar TM; Pfeiffer Vacuum). After a first calibration of the mass spectrometer by passing a gas mixture through it (consisting of 1% CO and 1% C0 ₂ dissolved in 98% Ar gas) the test sample is heated in a quartz reactor to 1000 °C with a heating rate of 10 K / min using Ar flow (50 mL / min). The desorbed gases are analysed by the mass spectrometer. After completing the heating step, a second calibration of the mass spectrometer is carried out.

Based on the first and the second calibration, the concentration of the desorbed gases CO / C0 ₂ (in vol-%) can be recorded as a function of the temperature.

The amount of detected CO and CO2 can be related to the number of active sites on the test sample surface. The active surface area (ASA; given in m ² /g) corresponds to the ratio of active sites to the total surface area. For calculation, the following equation is used:

ASA= No*o*NAvo/m, where No corresponds to the number of oxygen atoms desorbed calculated based on the concentration of CO and CO2 (Nco + 2 N _C 02), NAVO corresponds to Avogadro's number, m is the sample mass in gram and s is the cross-sectional area of the oxygen atom (s=0.083 nm ² ).

In contrast to the BET method during the ASA measurement a gas is used which is bonded chemically on the active sites of the materials. During the described measurements two isotherms are obtained. First one measuring the total sum on chemically and physically bonded active gas (CO/CO2) and second one, after evacuation of the system, measuring the reversion of the physically bonded gas. The difference yield the isotherm for the

chemisorption which can be converted to the ASA value.

[0017] The term "carbonisation process" corresponds to a heat treatment process performed at a temperature of at least 600 °C in an inert gas atmosphere, preferably in a temperature range of 600 °C to 1600 °C, more preferably in a temperature range of 800 °C to 1400 °C.

[0018] The term "graphitisation process" corresponds to a heat treatment process performed at a temperature of greater than 1600 °C in an inert gas atmosphere, preferably in a temperature range of greater than 1600 °C to 2800 °C, more preferably in a temperature range of 1700 °C to 2200 °C. [0019] The term "stabilizing process" corresponds to a heat treatment process performed at a temperature between 200 °C and 300 °C in air atmosphere.

[0020] The term "thermal activation process" relates to a treatment process preferably carried out at temperatures no larger than 900 °C, more preferably no larger than 500 °C and wherein the treatment process is preferably carried out in the presence of air and/or C0 ₂ and/or water vapour.

[0021] PAN represents the polymer of acrylnitrile and is often used as textile fibre. PAN can be in the form of a homopolymer or of a copolymer. A copolymer usually contains acryl nitrile with a proportion of more than 85 % and a comonomer such as methylmethacrylate or vinylchloride. PAN fibres can be used as precursors for manufacturing carbon fibres.

[0022] According to an embodiment, the present disclosure relates to a carbon fibre textile material. The carbon fibre textile material may comprise carbon fibres with a specific surface area according to the BET method of at least 50 m ² /g, preferably of at least 100 m ² /g, and more preferably of at least 200 m ² /g. The carbon fibres may be obtained from heat treated and thermally activated PAN-precursor fibres, wherein the heat treatment may include a stabilization process and a carbonization process or a stabilization process, a carbonisation process and graphitization process, and wherein thermally activated describes that a thermal activation process has been carried out. The PAN-precursor fibres utilised to obtain the carbon fibres may exhibit a specific surface area according to the BET method of at least 2 m ² /g, preferably of at least 5 m ² /g, more preferably of at least 10 m ² /g, most preferably of at least 15 m ² /g and a mean diameter of at least 5 pm. Preferably, the diameter of the PAN- precursor fibres is in a range of 5 pm to 50 pm, more preferably in a range of 5 pm to 30 pm, most preferably in a range of 5 pm to 25 pm. The mean diameter of the PAN-precursor fibres is determined by measuring with the help of a microscope.

[0023] In an embodiment of the present disclosure the thermal activation process may reduce the weight of the carbon fibres. The carbon fibres may have been thermally activated after having been heat treated, wherein the weight of the heat treated and thermally activated carbon fibres may be preferably no more than 10 %, more preferably no more than 5 %, and most preferably no more than 3 % less than the weight of heat treated and non- activated carbon fibres prior to thermal activation. It can be said that these carbon fibres show a low weight loss after the thermal activation step. [0024] The carbon fibres may exhibit an active surface area (ASA) of at least 10 m ² /g, preferably of at least 15 m ² /g, more preferably of at least 20 m ² /g, even more preferably of at least 25 m ² /g. Furthermore, the carbon fibres may exhibit an activated surface area corresponding to at least 0.15, preferably at least 0.20, more preferably at least 0.25 and most preferably at least 0.30 of the specific surface area according to the BET method.

[0025] According to a further embodiment of the present disclosure, the carbon fibre textile material represents a woven fabric or a non-woven fabric. The non-woven fabric is preferably a dry laid-non-woven or a wet laid non-woven. More preferably the dry laid-non- woven or wet laid non-woven are selected from the group consisting of a felt, a fleece, a layered material, a paper, and any arbitrary combinations thereof.

[0026] According to yet another embodiment, the present disclosure relates to a method for manufacturing a carbon fibre textile material according to the present invention. This method comprises the following steps:

A) Providing PAN-precursor fibres with a specific surface area according to the BET method of at least 2 m ² /g and a mean diameter of at least 5 pm;

B) carrying out a stabilizing process in air atmosphere in a temperature range

between 200 °C and 300 °C on the PAN-precursor fibres for stabilizing the PAN- precursor fibres;

C) carrying out a high temperature heat treatment process for obtaining carbon fibres;

D) carrying out a thermal activation process for activating the carbon fibres in an oxidizing atmosphere, thereby obtaining carbon fibres exhibiting a specific surface area according to the BET method of at least 50 m ² /g and

E) using either the PAN-precursor fibers according to step A) or the stabilized PAN- precursor fibers according to step B) or the carbon fibers according to step C) for forming a fibre textile material. [0027] Preferably, the PAN-precursor fibres according to step A) have a specific surface area according to the BET method of at least 5 m ² /g and a mean diameter of at least 5 pm, more preferably the PAN-precursor fibres have a specific surface area according to the BET method of at least 10 m ² /g and a mean diameter of at least 5 pm, most preferably the PAN- precursor fibres have a specific surface area according to the BET method of at least 15 m ² /g and a mean diameter of at least 5 pm.

[0028] Preferably, the thermal activation process of step D) may be carried out in the presence of air and/or C0 ₂ and/or water vapour. The thermal activation process may result in a weight loss of the carbon material, wherein the weight loss may be less than 10 %, preferably less than 5 % and most preferably less than 3 %.

[0029] According to yet another an embodiment, the present disclosure relates to a device from the group consisting of a catalytic converter, a filter, a battery cell, a redox flow battery, a super capacitor, an electrolysis cell, a fuel cell, an advanced electrode material, a silencer, a noise or sound absorber or reflector, a silencer, a catalyst carrier material or a water purification device which comprises a carbon fibre textile material according to the present invention.

EXAMPLES

[0030] The following are non-limiting examples of carbon fibre textile materials and methods for manufacturing carbon fibre textile materials of the present invention. In addition, some examples are presented for comparison. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention, which would be recognised by one of ordinary skill in the art.

[0031] Comparative example 1: Using PAN-precursor fibres with a specific surface area according to the BET method of approximately 0.2 m ² /g and a mean diameter of 17 pm, a non-woven was produced using spunlace technology. The obtained non-woven exhibited an area weight of 45 g/m ² and a density of 0.13 g/cm ³ and a stabilising heat treatment process in oxygen atmosphere was carried out at a temperature no larger than 300 °C. Subsequently, the non-woven was carbonised under an inert gas atmosphere at 900 °C. The non-woven is then thermally activated (at 500 °C under air atmosphere) until a weight loss of 5% was measured to obtain the carbon fibre textile material. According to the BET method a specific surface area of 44 m ² /g was measured (based on Nitrogen gas adsorption) for the carbon fibre textile material. Figure la displays a SEM image of the PAN- precursor fibres used for the comparative example 1. As can be seen these PAN precursor fibres have a low porosity.

[0032] Inventive Embodiments 1:

Inventive Embodiment la: A sample comprising continuous PAN-precursor fibres (with a specific surface area according to the BET method of approximately 6 m ² /g and a mean diameter of 20 pm) was provided. Subsequently, a stabilizing heat treatment process in oxygen atmosphere was carried out at a temperature no larger than 300 °C. Afterwards the sample was carbonised under an inert gas atmosphere at 900 °C. The obtained sample was then thermally activated (at 500 °C under air atmosphere) until a weight loss of 5 % was measured to obtain the carbon fibre. According to the BET method a specific surface area of 150 m ² /g was measured (based on Nitrogen gas adsorption) for the carbon fibre. Figure lb displays a SEM image of the used PAN-precursor fibre material according to the inventive embodiment la.

Inventive Embodiment lb: In addition, subsequently, a second thermal activation process was carried out (at 400°C under air atmosphere) using the obtained carbon fibre from Inventive Embodiment la until an additional weight loss of 5 % was measured. According to the BET method a specific surface area of 175 m ² /g was measured (based on Nitrogen gas adsorption) for the PAN-based fibre material.

[0033] Inventive Embodiments 2:

Inventive Embodiment 2a: A sample comprising PAN-precursor fibres (with a specific surface area according to the BET method of approximately 15 m ² /g and a mean diameter of 22 pm) was provided and a non-woven was produced from the sample using spunlace technology. The obtained non-woven exhibited an area weight of 40 g/m ² and a density of 0.12 g/cm ³ and a stabilising heat treatment process in oxygen atmosphere was carried out at a temperature no larger than 300 °C. Afterwards the non-woven was carbonised under an inert gas atmosphere at 900°C. The obtained non-woven was then thermally activated (at 500°C under air atmosphere) until a weight loss of 5 % was measured to obtain the carbon fibre textile material. According to the BET method a specific surface area of 260 m ² /g was measured (based on Nitrogen gas adsorption) for the carbon fibre textile material. Figure lc displays a SEM image of the used PAN-precursor fibre material according to the inventive embodiment 2a.

Inventive Embodiment 2b: A thermal activation process was carried out using the carbonised non-woven of the inventive embodiment 2a (at 400°C under air atmosphere) until a weight loss of 5 % was measured. According to the BET method a specific surface area of 310 m ² /g was measured (based on Nitrogen gas adsorption) for the carbon fibre textile material.

The active surface area of the carbon fibre textile material according to inventive

embodiment 2b was measured, which resulted in a value of ASA=141 m ² /g· The rate of ASA/BET is therefore approximately 0.45.

[0034] Inventive Embodiment 3: A sample comprising PAN-precursor fibres (with a specific surface area according to the BET method of approximately 15 m ² /g and a mean diameter of 22 pm) was provided and a non-woven was produced from the sample using spunlace technology. The obtained non-woven exhibited an area weight of 40 g/m ² and a density of 0.12 g/cm ³ and a stabilising heat treatment process in oxygen atmosphere was carried out at a temperature no larger than 300 °C. Afterwards the non-woven was carbonised under an inert gas atmosphere at 900°C. Afterwards the carbonized non-woven was graphitised under an inert gas atmosphere at 1700°C. The obtained non-woven was then thermally activated (at 500°C under air atmosphere) until a weight loss of 5 % was measured to obtain the carbon fibre textile material. According to the BET method a specific surface area of 90 m ² /g was measured (based on Nitrogen gas adsorption) for the carbon fibre textile material.

The active surface area of the carbon fibre textile material according to inventive

embodiment 3a was measured, which resulted in a value of ASA=29 m ² /g. The rate of ASA/BET is therefore approximately 0.32.

[0035] Comparative Embodiment 4: Using PAN-precursor fibres with a specific surface area according to the BET method of approximately 0.2 m ² /g and a diameter of 17 pm, a non- woven was produced using spunlace technology. The obtained non-woven exhibited an area weight of 45 g/m ² and a density of 0.13 g/cm ³ and a stabilising heat treatment process in oxygen atmosphere was carried out at a temperature no larger than 300 °C. Subsequently, the non-woven was carbonised under an inert gas atmosphere at 900°C. Afterwards the carbonized non-woven was graphitised under an inert gas atmosphere at 1700°C. The obtained non-woven was then thermally activated (at 500°C under air atmosphere) until a weight loss of 5 % was measured to obtain the carbon fibre textile material. According to the BET method a specific surface area of 26 m ² /g was measured (based on Nitrogen gas adsorption) for the carbon fibre textile material.

[0036] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "1700 °C" is intended to mean "about 1700 °C".