Traitement en cours

Veuillez attendre...

Paramétrages

Paramétrages

Aller à Demande

1. WO2016092267 - NANOTUBES DE CARBONE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

Carbon Nanotube

The present invention relates to carbon nanotubes (CNTs), and in particular, to novel methods for growing CNTs, for example on carbon fibre fabric or carbon cloth. The invention extends to fuzzy carbon reinforced polymers (FCFRP) prepared using such methods, and to uses of FCFRP composites in a wide variety of applications, such as in the aerospace, transport, automobile and defence industries.

Carbon fibre fabric or carbon cloth is known, and is made up of carbon fibre or tows, which are woven together. Typically, each tow consists of approximately 1,000-12,000 fibres, and an example is shown in Figure 1, which is a scanning electron microscope (SEM) image is a collection of carbon fibres forming a section of a carbon fibre tow. As in traditional weaving, tows disposed orthogonally to each other create a warp and a weft which are interwoven.

Unfortunately, untreated carbon fibre is incredibly difficult to handle, therefore, polymer sizings are routinely applied thereto in order to improve fibre-polymer adhesion as well as fibre handleability. Various polymeric sizings can be used, but the most common sizing is epoxy. For instance, 'Carbon Fiber Composites' by Deborah D. L Chung 1994; 'Advanced Composite Materials' by Louis A. Pilato, Michael J. Michno; and 'Composite Materials in Aircraft Structures.' edited by D. H. Middleton all confirm that sizing is essential.

Carbon fibre fabric, including a polymer sizing interface, can be used to reinforce polymers, thereby providing a mechanically strong material without the potential weight penalty which would be caused by using metals, for example. There are two main methods of manufacturing a carbon fibre reinforced polymer (CFRP): the pre-impregnated method and the infusion method. In the infusion method, carbon fabric is stacked and then infused with a plastic to obtain the desired final composite. Such materials have revolutionised some industries.

However, it is desirable not only to improve the mechanical properties of CFRPs, but also to enhance their thermal and electrical properties. Accordingly, one solution is to fabricate CFRPs with carbon nanotubes (CNTs). The general trend has focused on in-situ growth of CNTs, or attaching CNTs to the carbon fibres in the CFRP. Carbon fabric which includes CNTs is referred to as "fuzzy fibres", as the fibres look fuzzy after the carbon nanotubes are grown/attached, as shown in the SEM image of Figure 2.

Attaching CNTs requires functionalization, either damaging carbon nanotubes (for instance, covalent functionalization) or adding insulating layer to the carbon nanotubes (for instance, non-covalent functionalization). It has been found that attaching CNTs also generally leads to poor density of CNTs on the surface of the carbon fibres and poor alignment. Therefore, growing CNTs is a preferred method and receives more attention in the research community.

Once the CNTs are grown or attached to the carbon fabric it is infused with the polymer matrix, and the composite then undergoes curing of the polymer matrix. For both instances, the resultant composite is referred to as a "fuzzy" carbon fibre reinforced polymer (FCFRP).

Incorporating the CNTs in the polymer matrix is still in its infancy, and as such, there are problems associated with poor carbon nanotube alignment, limitation to small weight percentage additions of CNTs, poor CNT graphitisation, the lack of morphology control and poor matrix infusion capability.

Previous researchers have attempted to solve the re-cycling problems which are inherent to carbon fabrics provided with polymer sizing by developing novel polymer sizings that degrade with the resin in the CFRP, or which can be burnt off to allow the carbon fibres to be recycled. This is discussed at http://www.gocarbonfibre.com/andy-brink-michelman-fiber-sizing.aspx and 'Recycling carbon fibre reinforced polymers for structural applications: Technology review and market outlook.' Pimenta, S. Waste Management. 2011. 31:2. 378-392. Additionally, previous work has involved the development of different polymer sizings to use with different resin combinations and for different fabrication processes. However, none of the above approaches have been successful.

The present invention arises from the inventors' work in trying to overcome the problems associated with the prior art.

In accordance with a first aspect of the invention, there is provided a method of growing a carbon nanotube (CNT) on a carbon fabric comprising at least one carbon fibre, the method comprising providing the carbon fabric with a catalyst on a first surface thereof, and growing a carbon nanotube from the catalyst, characterised in that the carbon fabric does not comprise polymer sizing during the nanotube growth step.

The method of the invention overcomes a technical prejudice because the longstanding understanding in the field is that a polymer sizing must always be applied to improve the handleability of the carbon fibre fabric. Surprisingly, the inventors of the invention have now found that the polymer sizing is not in fact needed to improve carbon fibre handling and reduce billowing of carbon fibre filaments in the tows of the carbon fabric. Additionally, as shown in Figure 8, removal of the electrically insulating polymer sizing that is used in the prior art methods significantly improves the electrical conductivity of the carbon fabric, and thereby allows the manufacture of fuzzy carbon fibre reinforced polymers with improved electrical properties. Furthermore, removal of the sizing from the fibres also eliminates one element which contributed to a reduced Tg in the final composite, which weakened the thermal stability of the fibre/matrix interface. Additionally, the lack of a polymer sizing should lead to reductions in material cost and processing steps, resulting in a shorter turnaround time and a much simplified manufacturing process.

Preferably, the method is characterised in that the carbon fabric does not comprise epoxy polymer sizing during the nanotube growth step. Other sizings not present in the carbon fabric (in an epoxy-matrix composite) include polyhydroxyether,

polyphenyleneoxide, copolymers of styrene and maleic anhydride (SMA), a block copolymer of SMA with isoprene, polysulfone, polybutadiene, silicone, a carboxy-terminated polybutadiene, and a copolymer of ethylene and acrylic acid. In addition, sizings not present in the carbon fabric (in a thermoplast-matrix composite) include polyimides and polyimide-PES blends.

The method preferably comprises providing the carbon fabric with a catalyst on a second surface of the carbon fabric, and growing a carbon nanotube therefrom.

Preferably, the second surface is on an opposite side of the carbon fabric to the first surface. The additional step of growing nanotubes on the catalyst on the second side may be carried out at the same time as, or after, the step of growing the carbon nanotubes on the catalyst provided on the first side of the carbon fabric.

The step of growing the carbon fibre from the catalyst deposited on the carbon fabric preferably comprises growing the carbon fibre from the catalyst deposited on a dry carbon fabric.

It may be understood that the carbon fabric is considered to be a dry carbon fabric if it is not disposed within a polymer matrix or resin.

Advantageously, a polymer matrix or resin may be applied to the carbon fabric subsequent to the step of growing the carbon fibre. Since this polymer matrix or resin is not present during the step of growing the carbon fibre it does not need to be stable under the conditions required to grow the carbon fibre. Accordingly, this allows a greater selection of polymers and resins. Additionally, the process of growing the carbon fibre from the catalyst deposited on a dry carbon fabric is easier to scale up than it would otherwise be if the carbon fabric was disposed with a polymer matrix or resin.

Preferably, the catalyst comprises a material selected from a group consisting of:

copper (Cu), nickel (Ni), ruthenium (Ru), cobalt (Co), iron (Fe), rubidium (Rd), platinum (Pt), iridium (Ir), palladium (Pd), rhodium (Rh), carbides, silver (Ag), gold (Au), manganese (Mn), molybdenum (Mo), chromium (Cr), Tin (Sn), magnesium (Mg), aluminium (Al), silicon carbide (SiC), germanium (Ge), silicon (Si), diamond, steel or a composite of any two or more of the aforementioned materials. A preferred catalyst comprises iron (Fe). Any of these catalyst materials may be used on the first and/ or second side of the carbon fabric. The step of providing the carbon fabric with a catalyst on the carbon fabric (which may be the first and/or second side thereof), may comprise sputter depositing a suitable material onto the carbon fabric, thereby creating a catalyst layer thereon. The catalyst layer may be between ι nm and 500 nm in cross-section. Preferably, the catalyst layer is between 1 nm and 9 nm in cross-section.

The method may comprise providing the carbon fabric (the first and/or second side thereof) with a support layer before the catalyst is deposited. Preferably, the support layer comprises copper (Cu), nickel (Ni), ruthenium (Ru), cobalt (Co), iron (Fe), rubidium (Rd), platinum (Pt), iridium (Ir), palladium (Pd), rhodium (Rh), carbides, silver (Ag), gold (Au), manganese (Mn), molybdenum (Mo), chromium (Cr), tin (Sn), magnesium (Mg), aluminium (Al), silicon carbide (SiC), germanium (Ge), silicon (Si), diamond, steel or a composite of any two or more of the aforementioned materials. A preferred support layer comprises aluminium (Al). The step of providing the carbon

fabric with a support layer may comprise sputter depositing a suitable material thereon. The support layer may be between 1 nm and 500 nm in cross-section. Preferably, the support layer is between 10 nm and 50 nm in cross-section.

In a preferred embodiment, the carbon fabric comprises polymer sizing which is removed before the carbon nanotube growth step, and preferably before the catalyst is deposited on the fabric. Optionally, the method may comprise annealing the support layer after it has been provided onto the sized carbon fabric. The step of annealing the support layer may comprise heating the carbon fabric to a temperature which is adequate to remove the polymer sizing. The carbon fabric may be heated to a temperature of between 300°C and 8oo°C for a suitable time. Preferably, the step of annealing the support layer comprises heating the carbon fabric to a temperature of between 400°C and 700°C, and more preferably between 500°C and 6oo°C for a suitable time. A suitable time may comprise at least 5 minutes, more preferably at least 10 minutes, and most preferably at least 15 minutes. It will be appreciated that any of the above temperatures may be combined with any of the above timings.

Preferably, the step of growing the carbon nanotubes comprises growing carbon nanotubes in a chemical vapour deposition (CVD) system. The process can be performed in any form of CVD system, including thermal CVD (TCVD), plasma enhanced CVD (PECVD) or photothermal CVD (PTCVD). Preferably, PTCVD is used in which optical energy is delivered to the carbon fabric as infrared radiation, preferably from above the carbon fabric. For example, IR lamps may be used while the carbon fabric sample is placed on a water-cooled chuck. Preferably, an upper surface of the carbon fabric is heated to a temperature of at least 400°C, 500°C or at least 6oo°C. An upper surface of the carbon fabric may be heated up to iioo°C. Preferably, the bulk of the carbon fabric remains at a temperature below 6oo°C, 470°C or below 250°C. The bulk temperature of the carbon fabric may be recorded by a pyrometer disposed towards a lower surface of the carbon fabric or a thermocouple placed alongside the sample. The temperature of the carbon fabric may be mainly controlled by the electrical power supplied to the optical lamps, the gases used and pressure of the gases in the chamber. If the power supplied to the chamber is by another means, this will need to be optimised to couple the correct energy to the system, which will be known to the skilled person. It will be appreciated that the heat capacities of the gases in the chamber will also play a role in the thermal energy kinetics. Preferably, the bulk temperature of the carbon fabric is in the range of 250 - 500°C, preferably with an upper surface temperature of between 350 - 850°C.

Preferably, the growth of CNTs comprises the step of treating the carbon fabric with the catalyst to a bulk temperature of below 470°C, preferably in flowing hydrogen (H2). However, other gases such as argon (Ar), nitrogen (N2), helium (He), ammonia (NH3), etc., can also be used. Plasma-assisted or chemical-based catalyst treatment may also be used. Preferably, the flowing H2 is delivered at between 25 - 500 seem (standard cubic centimetres per minute), most preferably about 200 seem. Preferably, this step is carried out at a pressure between 0.1 Torr and 7600 Torr, preferably about 10 Torr. Preferably, the preheating step is maintained for about 1-60 minutes, more preferably about 5-15 minutes, and most preferably about 10 minutes. It will be appreciated that any of the above pressures may be combined with any of the above timings.

Growth of CNTs may comprise using a carbon feedstock such as acetylene (C2H2), ethylene (C2H4), methane (CH4), carbon monoxide (CO), camphor, naphthalene, ferrocene, benzene, ethanol, or any other carbon feedstock. Preferably, the growth of CNTs comprises using C2H2 as the carbon feedstock. Preferably, this is maintained for about 0.1-60 minutes, more preferably about 2-30 minutes, and most preferably about 15 minutes. The carbon feedstock may be delivered between 5 - 500 seem. Preferably, the carbon feedstock is delivered at about 50 seem. Preferably, this step is carried out at a pressure between 0.1 Torr and 7600 Torr, preferably about 10 Torr. It will be appreciated that any of the above pressures may be combined with any of the above timings.

The carbon fabric CNT composite material, which is produced by the method of the first aspect is novel per se because the combination of the high density, alignment, length and quality lead to the possibility of fabricating a carbon fibre composite without the polymer sizing. The optical reflectance characteristics of the material of the invention differ from that which is produced using prior art methods. This can be observed in Figure 9, where the optical absorption is greater for the fuzzy fibre fabric (right) compared to the standard carbon fibre fabric (left).

Hence, in a second aspect, there is provided a carbon fabric composite comprising a plurality of carbon fibres with one or more carbon nanotubes attached thereto, obtained or obtainable by the method of the first aspect.

It is possible to use the method of the first aspect to grow CNTs which are longer and more dense than is possible using the methods of the prior art, i.e. less than a 1% increase in mass.

Accordingly, in accordance with a third aspect there is provided a carbon fabric composite comprising a plurality of carbon fibres with one or more carbon nanotubes attached thereto, wherein the one or more carbon nanotubes comprise at least i%, 2%, 3%, 4%, and more preferably at least 5% of the mass of the carbon fabric composite.

Preferably, the one or more of carbon nanotubes comprise a plurality of carbon nanotubes with a density of at least 1 x 1010 CNTs/cm2.

In some embodiments, the method of the first aspect may comprise functionalising the carbon fibres which make up the carbon fabric with, for example, with or oxygen or n-doping with, for example, nitrogen.

Thus, in accordance with a fourth aspect there is provided a carbon fabric composite comprising a plurality of carbon fibres with one or more carbon nanotubes attached thereto, wherein one or more of the carbon fibres is functionalised with oxygen and/ or n-doped with nitrogen, and the or each carbon fabric composite was prepared by the method of the first aspect.

Advantageously, the oxygen functionalized carbon fibres may improve the

dispersability of plastic, leading to a composite with fewer voids. Oxygen is also used to improve the adhesion between the epoxy resin and carbon nanotubes as it makes the nanotubes and carbon fibre fabric more polar. Functionalising with oxygen may be achieved by exposing the carbon fibres to oxygen under thermally elevated, chemical or plasma treatment.

Advantageously, the n-doped carbon fibres may allow the fuzzy fibre fabric to have improved electrical conductivity. N-doping with nitrogen may be achieved by exposing the carbon fibres to nitrogen under thermally elevated, chemical or plasma treatment.

It will be appreciated that carbon fibre and FCFRP composites prepared in accordance with the present invention have a variety of far-reaching commercial applications.

Accordingly, in a fifth aspect, there is provided use of a composite according to the second, third or fourth aspect, in aerospace, automobile, transport, electronic and defence industries, decorative coatings, multifunctional and/ or smart materials, ablative coatings, camouflage and/ or stealth materials, adhesives, coatings, sensors, optoelectronics, fuel cells and/or membranes, optoelectronics, structures and magnetics.

Use of the composite in aerospace applications may include the use of components comprising a carbon fabric which has been prepared in accordance with the first aspect. The components may be used in civil aviation, military aviation, missiles, rockets and/ or satellite technology.

Advantageously, in the aerospace industry the composite could be used instead of metallic structures to handle the build-up of static charge imparted through air friction and lightning strikes. In particular, the composite could be provided in parts of the aircraft that are most susceptible to lightning strikes (i.e. the nose; lead-edge and trailing edge of wing and horizontal and vertical stabiliser and the engine nacelle). Advantageously, in the electronic and transport industry, the increased surface area of the carbon fibre due to the growth of CNTs on the surface is beneficial for storing electrical charge.

Advantageously, in the electronic industry, the controllability (e.g. through masking) of growing CNTs on the surface of the carbon fibre leads to the possibility of creating conductive paths or electrical circuits. This would allow the creation of multifunctional composite structures.

All features described herein (including any accompanying claims, abstract and drawings), and/ or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/ or steps are mutually exclusive.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which:-

Figure l is a scanning electron microscope (SEM) image of carbon fibres comprising a carbon cloth;

Figure 2 is an SEM image of a prior art fuzzy fibre (carbon fibres grown on carbon fibre);

Figure 3 is a schematic diagram of a photo-thermal chemical vapour deposition (PTCVD) growth system which may be used to grow carbon nanotubes in an embodiment of the invention;

Figure 4 is a graph showing the temperature against time for the growth of carbon nanotubes using one embodiment of the method of the present invention;

Figure 5a is an SEM image of carbon nanotubes grown on a carbon fabric in accordance with the present invention;

Figure 5b is a higher magnification image of Figure 5a;

Figure 6 is a schematic diagram showing the dimensions of a carbon fibre - CNT composite material which was made using the method of the present invention and was tested for electrical conductivity;

Figure 7 is a schematic diagram showing the three different electrical conductivity testing configurations that were applied to the carbon fibre CNT composite material of Figure 6 to test for electrical conductivity;

Figure 8 shows the electrical conductivity of the carbon fibre CNT composite material of Figure 6 compared to previous prior art composites;

Figure 9 shows two Petri dishes containing: the standard (sized) carbon fibre (left), with the fuzzy fibre fabric (right) in accordance with the present invention;

Figure 10a is an SEM image of carbon nanotubes grown on a carbon fabric in accordance with the present invention;

Figure 10b is a further SEM image of carbon nanotubes grown on a carbon fabric in accordance with the present invention;

Figure 11 are high magnification SEM images of carbon nanotubes grown on a carbon fabric in accordance with the present invention;

Figure 12 is an SEM image of a single carbon nanotube grown on a carbon fabric in accordance with the present invention, the length of the carbon nanotube has been extrapolated above and below the SEM image for clarity;

Figure 13 is an SEM image of carbon nanotube arrays grown on a carbon fabric in accordance with the present invention; and

Figure 14 shows how the mass of a carbon fabric changes as the carbon fabric underwent the various steps of the method of the invention.

Example l: Growth of carbon nanotubes (CNTs) on carbon fibre using the method of the invention

A piece of conventional (i.e. sized) 2/2 twill carbon fabric, where a warp tow cross two weft tows, was placed in a magnetron sputtering system (JLS MPS 500 DC) and aluminium (Al) was sputter deposited on both sides of the fabric to a thickness of 35 nm under argon (Ar) gas at a pressure of 2 Torr.

The sample was then placed in a sample holder in a photo-thermal chemical vapour deposition (PTCVD) system, such as that shown in Figure 3, and heated at 500°C under hydrogen gas (H2), which was injected into the system with a flow rate of 100 standard cubic centimetres per minute (seem) for 15 minutes. This stage removed the polymer sizing.

The sample was then returned to the magnetron sputtering system where iron (Fe) was sputter deposited on the first side of the carbon fabric to a thickness of 4 nm under Ar gas at a pressure of 2 Torr. The fabric was then returned to the sample holder in the PTCVD system with the first side of the carbon fabric face-up. In the time interval that elapsed between the iron being sputter deposited onto the first side of the carbon fabric and the fabric then being placed in the PTCVD system some of the iron oxidised to form iron oxide.

Heating of the system commenced at time t0, as shown in Figure 4. In this example optical heating with a power of 4.8 kW was used with fans and nitrogen gas being employed to cool the optical lamps. However, it will be appreciated that other methods could also be used. The system was heated to a temperature of 6oo-650°C over a period of ten minutes, meanwhile the sample holder was water-cooled by a chiller system which maintained the water temperature at io°C, thus ensuring that the bulk temperature of the sample was lower than the overall temperature of the system.

During this time the pressure was maintained at 10 Torr and hydrogen gas (H2) was injected into the system with a flow rate of 200 seem. These conditions caused the iron oxide to be reduced, leaving a layer of pure iron (Fe) on the first side of the fabric. The heating and reduction step occurred over the time period ti, as shown in Figure 4.

After ten minutes the growth stage commenced. The temperature was maintained in the range of 6oo-650°C, the pressure was maintained at 10 Torr, the flow of H2 also remained constant to reduce the overall temperature of the system, and the chiller

system maintained the water temperature at io°C. Additionally, acetylene was injected into the system with a flow rate of 50 seem. The acetylene acted as a carbon source and caused carbon nanotubes to grow on the carbon fibres on the first side of the fabric. The growth stage lasted for fifteen minutes, as show by time t2 in Figure 4.

It will be understood that length of the carbon nantubes is dependent upon how long the growth stage lasts for. In other words, a short growth time would lead to relatively short carbon nanotubes and long growth times would lead to relatively long carbon nanotubes. Accordingly, the length of time the growth stage lasts may be controlled to produce carbon nanotubes of a desired length.

Once the growth stage was completed the optical heating ceased and the sample was allowed to cool. The cooling stage is shown by time t3 and lasted for around 10 minutes. Due to the water-cooling this process is short, allowing many growth processes to be carried out in the same period as a standard TCVD system.

Once the cooling stage had finished the sample was again returned to the magnetron sputtering system where Fe was then sputter deposited on a second side of the carbon fabric to a thickness of 4 nm under Ar gas at a pressure of 2 Torr. The fabric was then immediately returned to the sample holder in the photo-thermal chemical vapour deposition (PTCVD) system such that the second side of the carbon fabric was face-up. CNTs were then grown on the second side of the fabric using the same process as set out above.

SEM images showed that the CNTs which grew on the carbon fabric were dense, long and aligned, as can be seen in Figure 5a. Unlike in the prior art, the carbon fibres are barely visible under the CNTs, and this is emphasised by Figure 5b which is a close-up of Figure 5a. The left hand side of Figure 5b shows an area where CNTs have not grown and the carbon fibres which form part of the tow can be seen, this is a result of the warp tow masking the weft tow and serves to highlight how dense and long the CNTs are which have grown on the rest of the fabric, and are seen on the right hand side of Figure 5b.

In one experiment the resulting growth of CNTs led to a 5.7% increase in the mass of the carbon fibre fabric. Accordingly, it will be understood that the CNTs comprised about 5.4% of the total mass of the carbon fabric composite.

A further experiment measuring the difference in mass of carbon fabric was carried out and the results are shown in Figure 14. The mass of the carbon fabric decreases substantially when the fabric undergoes the "Thermal Treatment". This loss of mass is explained as the "Thermal Treatment" step when removing the polymer sizing.

It can be seen from Figure 14 that CNT growth on the first side caused a mass increase of 1.15% (which means that the CNTs comprised about 1.14% of the total mass). Additionally, similar proj ected CNT growth on the second side would cause a total mass increase of 2.24% (which would mean that the CNTs would comprise about 2.19% of the total mass).

The presence of these CNTs gives the carbon fabric structural integrity. The sample on the right of Figure 9 is a fuzzy carbon fabric made according to the above method. It will be noted that, unlike the standard carbon fabric on the left, the fuzzy carbon fabric has retained its shape with all the yarns running orthogonal/parallel.

Additionally, individual tows were removed from the fabric and the fibres remained held in the complete tow. This is not possible with a sized removed carbon fabric. The improved structural integrity is due to the high density of CNT growth on the carbon fibre. The growth is so great that the material curls as a result of the van der Waals forces between the CNTs.

Additionally, the removal of the epoxy size from the fibres also eliminates one element of the composite which contributed to a reduced Tg in the final composite, potentially a weakening of the thermal stability of the fibre/matrix interface. Additionally, the quality of CNTs used vastly surpasses the quality that was obtainable in the prior art. This results in more confidence in batch to batch quality, reduction of structural irregularities and this results in more consistent properties for the FCFRPs (fuzzy carbon fibre reinforced plastics).

Example 2: Measuring electrical conductivity of fuzzy carbon fibre reinforced polymers Four pieces of fuzzy carbon fabric, made according to the method detailed in Example 2, were stacked to make a four ply structure. The structure was then infused with a polymer matrix using a vacuum assisted resin transfer moulding (VARTM) system to

make the benchmark CFRP and a FCFRP in accordance with the present invention. Silver DAG, an electrically conductive paint, was applied to an initial and final 10 mm on the first side and an initial and final 10 mm on the first side on the second side to provide a range of electrical conductivity configurations. A view of the first side of the FCFRP, with Silver DAG applied, is shown in Figure 6 and the different configurations are shown in Figure 7.

The electrical conductivity of the surface, volume and thickness was then measure by attaching a Keithley 4200 parameter analyser with two needle probes to the areas where the Silver DAG had been applied, as shown in Figure 7. The results are shown in the graph of Figure 8 and in Table 1 (below), where the standard CFRP is a carbon fibre reinforced polymer without any CNTs, FCFRP (V:i) is a fuzzy carbon fibre reinforced polymer where CNTs were grown on the carbon fibres in accordance with the teachings of the prior art and FCFRP (V:2) is a fuzzy carbon fibre reinforced polymer where CNTs were grown on the carbon fibres in accordance with the teachings of the present invention.

Table 1: The electrical conductivity of the surface, volume and thickness of a standard carbon fibre reinforced polymer (CFRP), a fuzzy carbon fibre reinforced polymer as taught in the prior art (FCFRP (V:i)) and a fuzzy carbon fibre reinforced polymer in accordance with the present invention (FCFRP (V:2))

Given the vastly improved conductivity of the FCFRP (V :2) sample the only way that the data could meaningfully be compared to the prior art samples was by showing the data on a graph with a logarithmic axis. It is observed that the FCFRP (V :2) is over one hundred times more conductive than standard CFRP and nearly one hundred times more conductive than FCFRP (V:2) for all three measurements.

The standard CFRP and FCFRP (V: i) samples only really have any degree of electrical conductivity across the surface. Accordingly, these materials can be described as two-dimensional anisotropic materials. However, the FCFRP (V :2) sample, which was made according to the teachings of the present invention, not only exhibits enhanced electrical conductivity across its surface but also exhibits electrical conductivity across its thickness and volume. Accordingly, this material can be described as a three-dimensional isotropic material where the CNTs form electrical percolation pathways between each carbon fibre.

Example 3: Functionalised fuzzy carbon fibres

It is possible to use a range of materials to functionalise the CNTs depending on the property that is to be enhanced. For instance, oxygen is typically used to improve the adhesion between the epoxy resin and the carbon nanotubes as it makes the carbon nanotubes and carbon fibre fabric more polar. Generally, functionalisation can be achieved by exposing the sample to a gas (containing the functional material of choice) under thermally elevated, chemical or plasma treatment.

Oxygen functionalizing the carbon fibres will improve the dispersability of plastic. Accordingly, when the polymer matrix is infused into the stacked carbon fabric it will be better able to disperse through the stack leading to a composite with fewer voids.

The process of functionalising the material (carbon nanotubes on carbon fibre) proceeds with the material being loaded into a Plasma Asher Emitech K1050X. 02 is introduced at a flow rate of 10 seem (10-15 seem is a sensible range) and the radio frequency generated plasma is set at 30 W. The process is carried out for 10 seconds (5 - 10 seconds is a sensible range). To complete, the plasma is terminated, 02 flow rate is stopped and then the chamber is vented to allow the material to be removed.

Alternatively, the carbon fibres which make up the carbon fabric can be nitrogen n-doped.

Nitrogen treatment of the fuzzy fibres will improve the electrical conductivity of the N-doped material, by injecting more charge carriers. As it will also polarise the material, the hydrophilicity will improve.

- ι5 -

Essentially, carbon atoms are replaced with nitrogen atoms. The nitrogen atoms have an extra electron per atom - the extra electron contributes to the conductivity of the material. The process of n-doping the material (carbon nanotubes on carbon fibre) would proceed with the material being loaded into a Plasma Asher Emitech K1050X. N2 is introduced at a flow rate of 10 seem (10-15 seem is a sensible range) and the radio frequency generated plasma is set at 30 W. The process is carried out for 10 seconds (5 - 10 seconds is a sensible range). To complete the plasma is terminated, N2 flow rate is stopped and then the chamber is vented to allow the material to be removed.

Example 4: Patterned fuzzy carbon fabrics

The density and pattern of growth of CNTs can be easily controlled via masking of the carbon fabric during the catalyst deposition stage i.e. by controlling the concentration of catalyst used and the nature of the metal employed

This allows the engineer greater design flexibility. Since the growth of the carbon nanotubes can be controlled it is possible to control where the electrical conductivity will be highest allowing the engineer to design a circuit within the composite where differential conductivity might be introduced. Thus, the fabric could be partially modified/functionalized. For instance, for components that are deemed most susceptible to charge build-up, the carbon fibre can be modified for a section to be electrically conductive due to the positioning of carbon nanotubes within the component. Additionally, by introducing chemical functionalisation to the carbon nanotubes (e.g. by introducing carboxyl, carbonyl, amino or hydroxyl groups) and thereby controlling polar (hydrophilic) and non-polar (hydrophobic) sections, it could be possible to alter the fibre-volume ratio in particular sections creating isotropy in the component.

Example 5: Density, diameter and length of the carbon nanotubes

The density, length and diameter of the carbon nanotubes which are grown on carbon fabric in accordance with the present invention can be estimated using SEM images.

Figures 10a and 10b show two SEM images of carbon nanotubes grown on carbon fabric. An area of the image that allowed the carbon nanotubes to be resolved was chosen and a line was drawn in this area perpendicular to the direction of the carbon nanotubes. The carbon nanotubes that crossed the line were counted. Accordingly, the length of the line and number of carbon nanotubes which crossed it allowed the density to be estimated. The inventors found that the density of the carbon nanotubes ranged from about 1 x 1010 CNTs/cm2 to 2 x 1010 CNTs/cm2.

Figure 11 shows five different high magnification images of carbon nanotubes which have been grown according to the present invention. Using these images it is possible to estimate the diameters of the carbon nanotubes. This can be done directly measuring the width of the carbon nanotubes, as shown in Figure 11. Figure 12 has been added to illustrate this method clearly, and shows a carbon nanotube where the length has been extrapolated. In Figure 12, it is clear where the walls of the carbon nanotube are and it is easy to see how the width can be measured. There is a certain degree of error using SEM images at these dimensions for the geometry of the CNTs, in that the emission of secondary electrons is high at the edges - this is known as the 'edge glow' effect. However, the inventors estimate that the diameters all fall in the ranges of between 10 nm and 30 nm.

Finally, as shown in Figure 13, it is also possible using SEM images to estimate the length of the carbon nanotubes. While carbon nanotube arrays with lengths of about 200 nm have been observed, this is unusual. By analysing SEM images the inventors have found the lengths of the carbon nanotubes to generally be in the range of 10 to 5θμπι.

Example 6: Applications of the fuzzy carbon fibre fabrics

As described in the previous examples, the fuzzy carbon fibre fabric manufactured using the method of the invention exhibits several key advantages not realised using prior art methods involving the use of polymer sizing, such as epoxy. As such, the inventors envisage the fuzzy carbon fibre fabric being used in a wide variety of applications, including aerospace, automobile, transport, electronic and defence industries, decorative coatings, multifunctional and/ or smart materials, ablative coatings, camouflage and/ or stealth materials, adhesives, coatings, sensors,

optoelectronics, fuel cells and/or membranes, optoelectronics, structures and magnetics.

For instance, in the aerospace industry the FCFRP could be employed instead of relying of metallic structures, dealing with the build-up of static charge imparted through air friction and lightning strikes. Components comprising the carbon fibre composite could be used for the parts of the aircraft that are most susceptible to lightning strikes (i.e. the nose; lead-edge and trailing edge of wing and horizontal and vertical stabiliser and the engine noise cowl). Alternatively, the carbon fibre composite could be used throughout the aircraft and components comprising a greater number of layers of the carbon fibre composite could be used in the parts of the aircraft that are most susceptible to lightning strikes.

The improvements in the thermal conductivity could again be beneficial to the aeronautical industry. Considering an aircraft travelling at cruising altitude, the thermally insulating CFRP wings act as thermal resistors and prevent the fuel inside the wings from being at a lower temperature. This leads to vapours forming in the fuel tanks compared to the last generation aircrafts, whereby the fuel is kept cool by the relatively low thermal resisting metallic wings.

An early issue with aircrafts was that they built up fuel vapour in their tanks and in one instance it resulted in an explosion. They have since added nitrogen-purging systems to prevent another occurance ihttp: //www.airspacemag.com/how-things-work/safer-fuel-tanks-588 Qi6/?no-ist). With the last generation of metallic aircrafts, the high thermal conductivity of the metals allowed the fuel to reach low ambient temperatures when in flight, resulting in minimal vapour build-up (although enough for the explosion, as mentioned). Carbon fibre composites have poor thermal conductivity (especially through-plane, i.e. in the z-direction), so, although they have the means to remove vapour, it is ideal to reduce the vapours from forming in the first place.

Another advantage is the capability of a thermally and electrically conducting composite material allowing de-icing. Either as a large heating element or providing a heat source at one end and allowing it to conduct throughout the material (the heat source which is commonly employed being the jet engine). Ice forming on the wings (especially the control surfaces, such as flaps and ailerons) can obviously lead to a loss of control of the aircraft.

The enhancement of the specific surface area of the carbon fibre through the growth of carbon nanotubes and the short interlaminar distances is ideal for fabricating a capacitor. The unprecedented enhancement in the surface area is proportional to capacitance.

The controllability (or masking) of growing CNTs on the surface of the carbon fibre leads to the possibility of creating conductivive paths or electrical circuits. This would allow the creation of multifunctional composite structures.