IMPROVEMENTS RELATING TO CARBON FIBRE PROCESSING

Abstract

Carbon fibre precursors for use in the formation of carbon fibre materials. The carbon fibre precursors comprise fibres of polymeric material which have a coating layer thereon, the coating layer comprising a material susceptible to dielectric heating, for example carbon nanotubes. The carbon fibre precursors may be suitable for forming into carbon fibres using a dielectric heating step, despite the fibres of polymeric material not being susceptible to dielectric heating, without adversely affecting the structure and physical properties of the main body of the carbon fibre so formed. A method of preparing a carbon fibre precursor for a carbon fibre formation process and a method forming a carbon fibre are also disclosed.

Claims

1. A carbon fibre precursor comprising a fibre of polymeric material and a coating layer on the fibre, the coating layer comprising a dielectric heating susceptor material.

2. The carbon fibre precursor according to claim 1, wherein the coating layer has a thickness of from 5 to 200 nm.

3. The carbon fibre precursor according to claim 1, wherein coating layer comprises a surfactant.

4. The carbon fibre precursor according to claim 1, wherein the coating later comprises a polymeric carrier material.

5. The carbon fibre precursor according to claim 1, wherein the fibre of polymeric material comprises lignin.

6. The carbon fibre precursor according to claim 1, wherein the dielectric heating susceptor material is formed of carbon nanotubes.

7. The carbon fibre precursor according to claim 1, wherein the dielectric heating susceptor material provides from 0.01 to 0.1 wt % of the carbon fibre precursor.

8. A method of preparing a carbon fibre precursor for a carbon fibre formation process, the method comprising the steps of: a) providing a fibre of polymeric material; b) coating the fibre of polymeric material with a composition comprising a dielectric heating susceptor material.

9. The method according to claim 8, wherein step b) involves dipping the fibre of polymeric material into a liquid comprising the dielectric heating susceptor material.

10. The method according to claim 9, wherein step b) involves the steps of: i) dipping the fibre of polymeric material into a liquid comprising a polymeric carrier material; ii) after step i) dipping the fibre of polymeric material into the liquid comprising the dielectric heating susceptor material.

11. The method according to claim 10, wherein after step i) and before step ii) the fibre of polymeric material is rinsed with a solvent.

12. The method according to claim 10, wherein the steps i) and ii) are repeated at least once.

13. The method according to claim 9, wherein the liquid comprising the dielectric heating susceptor material further comprises a surfactant.

14. The method according to claim 8, further comprising: c) exposing the carbon fibre precursor to electromagnetic radiation to heat the carbon fibre precursor to a temperature of at least 800° C. to carbonize the carbon fibre precursor to form the carbon fibre.

15. The method according to claim 14, wherein step c) involves exposing the carbon fibre precursor to microwave frequency radiation having a frequency of from 1 to 300 GHz for 2 to 60 minutes.

Description

EXAMPLES

[0080] Materials

[0081] Fibres of a 60/40 blend of lignin (TCC)/TPU were produced from modified (hydroxy propyl) Kraft hardwood (TCC) with a Mw of 11,357 g/mol obtained from Tecnaro co. (Germany) and the TPU (thermoplastic polyurethane) Pearlthane ECO 12T95 obtained from Veltox (France) (manufactured by Lubrizol). The blended 60/40 lignin (TCC)/TPU was extruded using an Xplore microcompounder MC15 twice, the first time to form pellets and the second time to form fibres to provide the fibres of polymeric material of the carbon fibre precursors of the present invention. In the first extrusion, the pellets were extruded in a counter-rotating mode using a separated heating control at temperatures of 175, 190, 200 and 190° C. to provide pellets with a diameter and/or length of approximately 5 mm. To form the fibres, the pellets were extruded using a single hole die with a diameter of 500 microns at temperatures of 155, 190, 200 and 190° C. This provided fibres having a diameter of from 100 to 200 μm. As they were formed, the fibres were wound onto bobbins using an automatic winder to provide fibres.

[0082] Spun PAN fibres were obtained from Dralon.

[0083] Multi-walled carbon nanotubes (MWCNTs) “Elicarb” were obtained from Thomas Swan and Co. Ltd.

[0084] Poly(diallyldimethylammonium chloride) (PDDA), with a molecular weight of 100,000-200,000 g/mol and sodium deoxycholate (DOC) (C.sub.24H.sub.39NaO.sub.4) were purchased from Sigma Aldrich.

[0085] Sample Preparation

Example 1

[0086] The 60/40 blend of lignin (TCC)/TPU polymer fibres were coated according to the following layer-by-layer process which is also summarized in schematic 100 of FIG. 1. 0.05 wt % of MWCNTs were dispersed in an aqueous solution comprising 1 wt % DOC to provide suspension 102. The MWCNT/DOC suspension 102 was sonicated for 30 min, followed by 20 min of 15 W tip sonication in an ice water bath, and another 30 min of bath sonication to homogenize. The MWCNT/DOC suspension was then centrifuged at 4000 rpm for 20 min and the supernatant was decanted. The polymer fibres were immersed in a cationic PDDA (0.25 wt) solution 101 for 5 min, followed by rinsing and drying, and then dipped into the anionic MWCNT/DOC suspension 102 for another 5 min. This process results in the deposition on the polymer fibres of a PDDA/MWCNT-DOC bilayer (BL). After the initial BL was deposited, all subsequent layers were deposited with 2 min dip times, with rinsing and drying in between. This cycle was repeated to deposit the desired number of bilayers. Deposited multilayer films were air-dried overnight and then stored in a desiccator prior to further processing or characterization. The Examples summarized in Table 1 are named 1.xy, with the number “x” denoting the number of coating cycles the sample has undergone. The “y” letter in the Example name denotes the sequence of steps involved in each coating cycle (shown in the “procedure” column), with “a” denoting a dip-rinse-rinse-dip-rinse-rinse sequence and “b” denoting a dip-rinse-dry-dip-rinse-dry sequence.

[0087] In order to improve the adhesion of the MWCNTs layers, the surface of the fibres can be treated using surface activation techniques such as microwave plasma surface modification, dielectric barrier discharge surface modification or atmospheric pressure jet plasma surface modification. These samples were treated using Dielectric Barrier Discharge (DBD) Plasma Remote in a System SURFX Atomflo 500 (13.56 MHz Tgas 90-110° C.).

TABLE-US-00001 TABLE 1 Lignin-TPU/MWCNTs coated samples. Surface Sample Susceptor modification Cycles Procedure Example 1.5a MWCNTs Yes 5 dip-rinse-rinse-dip- rinse-rinse Example 1.10a MWCNTs Yes 10 dip-rinse-rinse-dip- rinse-rinse Example 1.5b MWCNTs Yes 5 dip-rinse-dry-dip- rinse-dry Example 1.10b MWCNTs Yes 10 dip-rinse-dry-dip- rinse-dry Example 1.20b MWCNTs Yes 20 dip-rinse-dry-dip- rinse-dry Example 1.30b MWCNTs Yes 30 dip-rinse-dry-dip- rinse-dry

Example 2—PAN Coated Samples

[0088] PAN polymer fibres were coated with PDDA/MWCNT-DOC bilayers using the same procedure to provide the carbon fibre precursor of Example 2. During each bilayer coating process, the PAN fibers changed their colour to grey due to the presence of MWCNTs. Table 2 summarizes the PAN-based coated carbon fibre precursor examples. These Examples are numbered in the same way as described above for Example 1.

TABLE-US-00002 TABLE 2 Surface Sample Susceptor modification Cycles Procedure Example 2.5a MWCNTs Yes 5 dip-rinse-rinse-dip- rinse-rinse Example 2.4a MWCNTs Yes 4 dip-rinse-rinse-dip- rinse-rinse Example 2.3b MWCNTs Yes 3 dip-rinse-dry-dip- rinse-dry Example 2.2b MWCNTs Yes 2 dip-rinse-dry-dip- rinse-dry Example 2.1b MWCNTs Yes 1 dip-rinse-dry-dip- rinse-dry

[0089] After the coating process, the PAN fibres were not agglomerated—see SEM images of FIG. 2 which show control and PAN fibres coated with 5 cycles of the above process—indicating that the fibres were coated individually and homogeneously, which was desirable for the carbonization process.

[0090] FIG. 3 shows SEM images of Lignin based precursor fibres coated with MWCNTs. The top three images are of Example 1.5a; the middle images are of Example 1.10a; and the bottom images are of Example 1.20b. The SEM images of FIG. 3 show a very homogeneous coating on the surface of the Example 1 lignin-based carbon fibre precursors. Several regions of the fibre were analysed observing the same degree of coating in all of the zones. Where the fibres were coated with 20 cycles (Example 1.20b), the relatively high amount of MWCNTs produced agglomerates, as can be seen in FIG. 3. Therefore, the optimum number of coating cycles, at least for these fibres, may be between 5 and 10.

[0091] FIG. 4 shows the heating profile of the carbon fibre precursors of Example 2.5a under microwave heating using a modified domestic microwave oven with an IR-sensor incorporated for temperature monitoring. This heating profile shows it is possible to reach a temperature of above 900° C., which is sufficient to carbonize the carbon fibre precursors to produce carbon fibres.

[0092] FIG. 5 shows the heating profiles at maximum microwave power of the Examples of Table 2. In these heating profiles, the temperature increases until 1000° C. is reached (1000° C. is the limit of the temperature detector). The heating profiles show a rapid increase in the initial phase of heating. However, after a certain amount of time the temperature decreases slowly to below 1000° C. It is possible to observe that the temperature decreases faster when the samples have been coated with a fewer number of cycles. The anomalous behaviour of the sample 4C may be attributed to some experimental errors during sample preparation.

[0093] FIG. 6 shows heating profiles of Example 2.5a as a function of MW power—33%, 55% and 77% of the maximum 700 W power for the medium high, medium and medium low levels, respectively (in the order from top to bottom).

[0094] The carbon fibre produced from Example 2.5a as described above (PAN fibres coated with 5 cycles after 10 minutes of microwave heating) was analyzed by Raman in order to assess whether the microwave heating carbonized the polymer fibres of the carbon fibre precursors successfully. FIG. 7 shows the Raman spectrum of the carbon fibres produced from Example 2.5a after 10 minutes of microwave heating. This spectra has the typical features observed for carbon fibres—the D band located at 1351 cm.sup.−1 and the G band located at 1583 cm.sup.−1. In addition, SEM images were taken of these carbon fibres. These images, shown in FIG. 8, show that the fibres kept their fibrous shape during carbonization and would therefore be suitable for industrial use.

[0095] In summary, the present invention provides carbon fibre precursors for use in the formation of carbon fibre materials. The carbon fibre precursors comprise fibres of polymeric material which have a coating layer thereon, the coating layer comprising a material susceptible to dielectric heating, for example carbon nanotubes. The carbon fibre precursors may be suitable for forming into carbon fibres using a dielectric heating step, despite the fibres of polymeric material not being susceptible to dielectric heating, without adversely affecting the structure and physical properties of the main body of the carbon fibre so formed. A method of preparing a carbon fibre precursor for a carbon fibre formation process and a method forming a carbon fibre are also provided.

[0096] Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0097] Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of” or “consists essentially of” means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1% by weight of non-specified components.

[0098] The term “consisting of” or “consists of” means including the components specified but excluding addition of other components.

[0099] Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to encompass or include the meaning “consists essentially of” or “consisting essentially of”, and may also be taken to include the meaning “consists of” or “consisting of”.

[0100] For the avoidance of doubt, wherein amounts of components in a composition are described in wt %, this means the weight percentage of the specified component in relation to the whole composition referred to. For example, “wherein the liquid comprises 0.1 to 1.0 wt % polymeric carrier material” means that from 0.1 to 1.0 wt % of the liquid is provided by the polymeric carrier material.

[0101] The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

[0102] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0103] All of the features disclosed in this specification (including any accompanying claims, and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0104] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0105] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.