PROCESS FOR PRODUCING CARBON NANOFIBRE PRECURSOR YARN AND CARBON NANOFIBRE YARN THEREFROM

TECHNICAL FIELD

[001] The present invention generally relates to a process of preparing a continuous carbon nanofibre yarn precursor and production of carbon nanofibre yarn therefrom. The invention is particularly applicable for production of polymer nanofibre yarns and carbon nanofibre yarns produced therefrom and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. However, it should be appreciated that the process could be applied to a variety of suitable carbon fibre precursor materials, such as SiC, inorganic oxide, C/C composite, metal/C composite, and inorganic oxide/C composite nanofibre yarns.

BACKGROUND OF THE INVENTION

[002] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[003] High-performance carbon fibres (HPCFs) are a new light and strong material that has a significantly higher mechanical strength than conventional carbon fibres. HPCFs have a high tensile strength (2 to 7 GPa) and high modulus (228 to 392 GPa) with a very light weight. HPCFs are widely used as a structural material where a high strength-to-weight ratio is required, including aerospace, wind turbine and automobiles. The recent increase in the demand for HPCFs has led to active development of new carbon fibre production technology.

[004] A significant proportion of HPCFs are made from PAN. In conventional HPCF formation processes, PAN precursor fibres are prepared by a wet spinning technique, and then subjected to a series of treatments, including drawing, stabilization and carbonization. Drawing orientates the polymer chains within the precursor fibres and reduces fibre diameter. The drawn fibres are then stabilized by heating at a temperature around 250 to 500 Ό in air to convert the polymer's linear chemical bonding structure to a more thermally stable ladder bonding structure. For PAN, this may in some processes be achieved by heating the fibres to a temperature of 300 °C for up to 120 minutes. Further carbonizing at higher temperatures (for example 1000 to 1500 ) in an inert environment expels any non-carbon atoms and form tightly bonded carbon crystals that are aligned generally parallel to the longitudinal axis of the fibre.

[005] The ultimate tensile strength of HPCFs in most cases does not exceed 25% of the theoretically estimated value largely due to structural defects generated in the carbon fibre production process. For example, contamination, fibre coagulation and associated solvent diffusion between polymer and coagulant during wet spinning may cause phase separation and formation of voids, cracks, or cavities within fibres. Core-sheath structure may occur when the inner core of fibre is oxidized incompletely during the stabilization step, and carbon fibres prepared from such a core-shell structure have poor mechanical properties due to burning off the core in the carbonization process.

[006] Reducing fibre diameter is one solution to minimize the structural defects and thus improve the mechanical properties of the resulting fibre. Reducing fibre diameter facilitates stabilization of precursor fibres, thus diminishing the formation of core-shell structures. Carbon nanofibres (CNFs) are one form of fibre that may offer a number of advantageous over existing fibres as the fibres of this material have a diameter several orders of magnitude smaller than existing carbon fibres.

[007] Electrostatic spinning, also known as electrospinning, has been previously used to prepare ultrafine PAN precursor fibres which have a diameter typically about hundreds of nanometre. Electrospinning involves drawing a polymer solution under a strong electric field to form dry filaments. Examples of previous electrospinning PAN nanofibre formation is published in for example J. Chen, H. Ge, H. Liu, G. Li, C. Wang, Journal of Wuhan University of Technology-Mater. Sci. Ed. 2010, 25, 200-205. Carbon fibres have also been reportedly formed from electrospun PAN nanofibres in for example S. Y. Gu, J. Ren, Q. L. Wu, Synthetic Metals 2005, 155, 157-161 , and United States Patent No. 8,608,992 B2.

[008] Previous studies have all used nanofibres that were collected in the form of a nonwoven fibre mat. The use of this form of nanofibre is problematic as it is difficult to uniformly stretch such a thin, low strength fibre web. In addition, the randomly-orientated fibrous structure does not provide sufficient unidirectional/ uniaxial mechanical properties desirable in carbon fibres and more particularly in HPCFs. The use of a nonwoven fibre mat also presents scalability problems, as the mat is generally produced as a discrete, typically short, length precursor product. A commercial scale fibre production line typically requires kilometres of substantially aligned fibre to be produced as a continuous length material, such as a yarn.

[009] It would therefore be desirable to provide a process of producing a continuous carbon nanofibre precursor yarn and a carbon nanofibre yarn having improved fibre properties.

SUMMARY OF THE INVENTION

[010] The present invention provides a process of preparing a continuous carbon nanofibre yarn precursor and production of carbon nanofibre yarns therefrom.

[01 1] The present invention provides in a first aspect a process of preparing a continuous carbon nanofibre precursor yarn comprising:

forming a continuous nanofibre yarn by electrospinning; and

drawing the nanofibre yarn under dry conditions to improve the fibre and molecular orientation of the nanofibre yarn,

thereby producing a continuous carbon nanofibre precursor yarn.

[012] The present invention provides an effective method to produce nanofibre yarns having improved fibre and molecular orientation. Nanofibres produced by electrospinning a fibrous mat normally have a randomly-orientated web structure which has poor mechanical strength and is difficult to be drawn evenly. In the present invention, continuous nanofibre yarns are produced using an electrospinning process. A yarn comprises a continuous nanofibre bundle with an interlocked structure, where the nanofibres have greater alignment than a fibrous mat. The nanofibre yarns are then subjected to a drawing treatment to improve the fibre and molecular orientation. The inventors consider that the present invention comprises the first process in which a continuous nanofibre yarn undergoes a drawing treatment to improve and/or otherwise affect the mechanical properties of a nanofibre yarn. This produces an improved carbon nanofibre yarn precursor, and following treatment step or steps (detailed below) an improved carbon nanofibre yarn.

[013] The process of the present invention produces a continuous carbon fibre precursor yarn. It should be understood that a continuous yarn comprises continuous nanofibre bundles with an interlocked structure which provides a continuous length of material. The process used to produce the fibre can operate continuously to produce the nanofibre yarn with the constant supply of production inputs, for example electricity and electrospinning polymer solution. This is in contrast to other processes, for example nanofibre mat processes, in which a discrete length or portion of material is produced which is then subsequently formed into a short length yarn. It should be appreciated that despite being continuously produced, the product carbon nanofibre precursor yarn can have a finite length typically a result of cutting the produced fibre at a particular point along the length of the yarn.

[014] A yarn is a long continuous length of interlocked fibres. In the present invention, the continuous yarn comprises multiple nanofibre bundles arranged together in a continuous length. The continuous nanofibre yarn produced by electrospinning preferably has an interlocked fibrous structure. In some embodiments, the continuous nanofibre yarn produced by electrospinning comprises a twisted yarn. The twisted yarn comprises fibres twisted along longitudinal length of the yarn.

[015] In the present invention, the precursor fibres are prepared by direct drying of the solution jet during electrospinning. In this respect, the nanofibre yarn is formed by fast evaporation of solvent from a polymer solution jet during electrospinning. The formed continuous nanofibre yarn is therefore formed without involving coagulation, as the fibres are dried using direct drying of that solution jet during electrospinning. Without involving any coagulation, the process of the present invention can substantially reduce and in some cases substantially eliminate fibre contamination and defects due to solvent diffusion, particularly when compared to fibres formed using traditional wet spinning processes. Furthermore, electrospinning is advantageous as it provides comparatively easy preparation of nanofibres, allows the integration of various components into the fibre and yarn, and provides precise control of fibre composition (as detailed below).

[016] The drawing step typically involves drawing or stretching the nanofibre yarn and constituent nanofibres preferably in a uniaxial direction, along the longitudinal axis/ length of the yarn. Drawing treatment reduces fibre diameter, and improves fibre uniformity and alignment of the nanofibres within the yarn, as well as alignment of polymer chains within the constituent nanofibres. In the present invention, in the drawing step, the nanofibre yarn is in a substantially dry condition. More particularly, in the drawing step, the nanofibre yarn may be drawn in air, preferably without the addition of any additives applied to the nanofibre yarn.

[017] The drawing step/process is preferably undertaken in hot, dry conditions. In comparison, drawing treatment of conventional carbon fibre precursors is often undertaken in liquid or steam, and additives are added to precursor fibres to improve the drawing performance. The drawing process/step is dry and therefore does not include the application of an aqueous solution or steam to the nanofibre yarn prior to or during drawing.

[018] Where the nanofibre yarn is a polymer nanofibre yarn, the drawing step is typically undertaken at least above the glass transition temperature (Tg) of the polymer, preferably between Tg and the degradation temperature of the polymer. In some embodiments, the temperature at which the drawing step is undertaken at least 20 , preferably at least 30 ° C higher than the Tg of the polymer. In this respect, the temperature for PAN nanofibre yarn at which the drawing step is preferably undertaken at least 90 °C, preferably greater than 100 °C. However, it should be appreciated that the specific drawing temperature use is dependent on the constituent polymer or polymers of the nanofibre yarn being drawn.

[019] The glass transition temperature (Tg) of a nanofibre and yarn composed thereof is dependent on the composition of those nanofibres. For example, PAN is a semi-crystal polymer with a glass transition temperature (Tg) in the range of 72 °C to 150 °C. Above Tg, polymer nanofib res become plastic and therefore can be drawn to a large ratio.

[020] Drawing the nanofibre yarn generally includes applying a drawing or stretching force to the nanofibre yarn. The drawing regime and response of a nanofibre and yarn composed thereof is also dependent on the drawing/ stretching force applied to the yarn and nanofibres thereof. In some embodiments, and in particular for some polymer nanofibre yarns, the selection of the appropriate force to apply preferably causes a two-stage strain change when the polymer is heated to a temperature higher than the glass transition temperature (Tg) of the polymer. The polymer is preferably heated to a temperature of at least 20 , more preferably at I east 40 higher than the Tg of the polymer. In some embodiments, the two stage strain changes comprises a first stage occurring at or around Tg having a maximum elongation rate of 1 to10 %/min occurred, and a second stage occurring at, at least 20 , preferably 40 higher than the Tg of the polymer in which the elongation rate is from 50 to 200 %/min.

[021] It should be appreciated that the exact drawing force applied to the yarn and constituent nanofibres depends on the physical dimensions, composition and properties of the nanofibre yarn. For example, with polymer nanofibre yarns, polymer chain movement within the fibres is not accelerated by the drawing force when the force is not high enough. If the drawing force is too high, the yarn breaks before it is fully stretched. A force between the two extreme states could lead to an initially accelerated stretching at a relatively lower temperature followed by further fully stretching a higher temperature, showing a two-stage change in elongation rate. In some embodiments, the drawing force applied to the PAN nanofibre yarn of diameter 200 to 300 micrometres is from 2.0 cN to 10 cN, preferably from 3.0 cN to 7.5 cN. For example, for PAN nanofibre yarn having a yarn diameter of 279 ± 30 μηι and comprising PAN fibres of 812 ± 312 nm in diameter, it was found that at 140 a suitable stretching force of from 3.0 cN to 7.5 cN would meet these criteria.

[022] The drawing ratio (the drawn length/the original length of the nanofibre yarn) can influence the properties of the resulting precursor nanofibre yarn. The drawing ratio influences the diameter and material properties of the nanofibre and yarn.

[023] The yarn can be stretched/ drawn to any suitable drawing ratio. In some embodiments, the nanofibre yarns are drawn to at least 3 times the original length of the nanofibre yarn, preferably up to 6 times the original length of the nanofibre yarn. In some embodiments, the drawing ratio is from 3 to 10 times the original length of the nanofibre yarn, preferably from 4 to 7 times the original length of the nanofibre yarn. For example, the inventors have found that PAN nanofibre yarns can be drawn up to 6 times of its original length under a hot dry condition, without using an aqueous solution and steam.

[024] At higher drawing ratios, the yarns became more compact and curled fibres were straightened. Yarns and fibres both decrease in diameter after the drawing treatment. The reduction in average fibre diameter depends on the drawing ratio. For example, when the drawing ratio was 3 times, the average yarn diameter reduced by around 300% and nanofibre diameters reduced by around 200%. At a higher drawing ratio, for example 6 times, the average yarn diameter reduced by around 430% and nanofibre diameters reduced by around 240%. For example, for one PAN nanofibre yarn, the electrospun yarn had a diameter of 279 ± 30 μηι and the PAN fibres was 812 ± 312 nm in diameter. When the drawing ratio was 3 times, the average yarn and fibre diameters reduced to 91 ± 7 μηι and 408 ± 141 nm, respectively. Higher drawing ratio, such as 6 times, further reduced the yarn and fibre diameters to 64 ± 5 μηι and 336 ± 142 nm [025] As noted above, drawing the yarn affects the material properties of the yarn and the comprising nanofibres. In general, the higher the tensile properties are improved through drawing treatment, the higher the strength of carbon fibres achieved. In some embodiments, the drawing step increases the yarn tensile strength and modulus by at least 500 %, preferably at least 700 %, yet more preferably at least 800%, for example from 800 to 1800 %. In some embodiments in which the nanofibre yarn comprises PAN, the nanofibre yarn has a tensile strength of at least 200 MPa, preferably at least 300 MPa. For example, where the nanofibre yarn comprises PAN, the polymer nanofibre yarn has an initial diameter of 279 ± 30 μηι and the PAN fibres of 812 ± 312 nm in diameter have a tensile strength of 362 ± 37 MPa. After drawing treatment the tensile strength is improved up to five times the original undrawn tensile strength. The carbon nanofibre derived from this post drawn nanofibre yarn has the tensile strength at least 1 GPa.

[026] Drawing treatment can also facilitate the orientation of the constituent molecule, for example polymer molecule, along the fibre direction of the fibres in the yarn. Preferably, drawing decreases the fibre alignment angle along the yarn axis. Again, this effect is dependent on drawing ratio, with a higher drawing ratio increasing molecule orientation, for example for a polymer nanofibre yarn, the chain orientation of the polymer along the fibre direction of the fibres in the yarn. In some embodiments, drawing reduces the fibre alignment angle to between 15 and 40° preferably at most 30°.

[027] In some embodiments, the majority fibres of the nanofibre yarn after electrospinning (without drawing) typically have an alignment angle of 0°to 60°. At a drawing ratio of 2, the alignment angle is typically reduced to 30°. A higher drawing ratio (for example 6) preferably produces high alignment of fibres, in some cases with an alignment angle as small as 15°.

[028] In addition to the decreased diameter, the diameter distribution can become narrower after drawing treatment. In some embodiments, the nanofibre yarn has a diameter distribution substantially from 100 nm to 2.0 μηπ, preferably from 300 nm to 1 .6 μηπ. The resulting draw treated nanofibre precursor yarn preferably has a diameter distribution substantially from 50 nm to 1 .0 μηπ, preferably from 100 nm to 900 nm.

[029] The continuous nanofibre yarn can comprise any suitable material. In some embodiments, the continuous nanofibre yarn can comprise at least one of a polymer, copolymer, petroleum pitch, lignin, cellulose, or a sol from inorganic materials. The yarn may also include an additive, such as at least one of organic/inorganic salts, surfactants, organic compounds, macromolecules, copolymers, nanoparticles, nanotube/fibres, nano platelets, nanowires, quantum dots, etc. These nanofibre yarns can be subjected to further treatment to form the carbon nanofibre yarns.

[030] In other embodiments, the continuous nanofibre yarn may comprise a precursor nanofibre for at least one of SiC nanofibre yarns, inorganic oxide nanofibre yarns, composite carbon nanofibre yarns, C/C composite carbon nanofibre yarns, metal/C composite nanofibre yarns, or inorganic oxide/C composite nanofibre yarns. It should be appreciated that precursor nanofibre refers to the composition of the continuous nanofibre yarn prior to treatment such as stabilisation and carbonization treatment as described below.

[031] The carbon nanofibre formed from the process of the present invention can therefore have a conventional composition formed from a polymer type nanofibre precursor yarn or could have a special composition selected from at least one of SiC nanofibre yarns, inorganic oxide nanofibre yarns, composite carbon nanofibre yarns, C/C composite carbon nanofibre yarns, metal/C composite nanofibre yarns, or inorganic oxide/C composite nanofibre yarns.

[032] These other nanofibre yarns (such as SiC, inorganic oxide, C/C composite, metal/C composite, or inorganic oxide/C composite nanofibre yarns), are prepared from an electrospinning solutions which includes a precursor polymer (for example petroleum pitch, polycarbomethylsilane, inorganic sol gel or the like) or a mixture of precursor polymer with an additive or additives. The precursor polymer is dissolved in a suitable solvent, while the additives may be dispersed into the precursor solution. [033] This process of the present invention is therefore suitable for making SiC nanofibre yarns. SiC nanofibers and SiC nanofibre yarns can be prepared from electrospun poly(carbomethylsilane), a polysilane.

[034] The process of the present invention is also suitable for making composite nanofibre yarns, for example C/C composite carbon nanofibre yarns, metal/C composite nanofibre yarns, or inorganic oxide/C composite nanofibre yarns. Polymer based nanofibres containing a carbon nanomaterial (e.g. nanotube, graphene, C ₆ o, or nanowire) can be prepared by electrospinning a suitable polymer solution (for example PAN) containing the nanomaterial. Then C/C nanofibres are prepared from the resulting composite nanofibres and nanofibre yarn.

[035] Examples of suitable carbon nanomaterials for preparing C/C composite nanofibre yarns include at least one of: carbon nanotubes (single-walled, multi- walled); carbon nanowire; graphene; C60; or carbon nanoparticles.

[036] Examples of suitable metals for preparing Metal/C composite nanofibre yarns include at least one of: platinum; silver; gold; copper; or titanium.

[037] Examples of suitable inorganic oxide nanomaterials for preparing inorganic oxide/C composite nanofibre yarns include at least one of: silica; iron oxide; aluminium oxide; titanium dioxide; manganese oxide; zinc oxide; cobalt oxide; nickel oxide; vanadium oxide; chromium oxide; niobium oxide; zirconium dioxide; rubidium oxide; rhodium oxide, or mixtures thereof.

[038] As noted above, the continuous nanofibre yarn can be formed from one or more polymers or copolymers. Polymer materials (polymer and/or copolymer (where applicable)) for making carbon fibres can be selected from at least one of Cellulose acetate (CA), Chitosan, Ligin, Nylon, Phenolic resin, Poly[(9,9-di-n- octylfluorenyl-2,7-diyl)-alt-(benzo[2,1 ,3] thiadiazol-4,8-diyl)], Poly(L-lactide-co- epsiloncaprolactone) P(LLA-CL), Polyamide (PA), Polyacrylic acid (PAA), Polyacrylonitrile (PAN), Polyaniline ( PANi), Polybenzimidazole (PBI), Polybutylene terephthalate (PBT), polycarbonate (PC), Polycaprolactone (PCL), polycarbonate urethane (PCU), Polydioxanone (PDS), Poly(3,4- ethylenedioxythiophene) (PEDOT), Polyether imide (PEI) , Poly ethlyene oxide (PEO), Polyethersulfone (PES), Polyethylene-co-vinyl acetate (PEVA), PFO-PBAB(Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N_-diphe nyl)-N,N_-di(p- butyloxy-phenyl)-1 ,4-diaminobenzene]), Poly(ferrocenylsilane) (PFS), polyglutamic acid) (PGA), Poly(glycolic acid) (PGCA), Poly(glycerol sebacate) (PGS), Poly(hydroxybutyrate-cohydroxyvalerate) (PHBV), 3-hydroxybutyric acid (PHB), Poly(hexamethylene adipate) (PHMA), Polyimide (PI), Polyisobutylene (PIB), Poly(L-lactide) (PLA), D,L-Lactide-polyethyleneglycol PLA-PEG, PLGA (Poly(lactic-co-glycolic acid)), PLLA (Poly(L-lactide)), PLLA-CL (Poly(L-lactide- co-_-caprolactone)), poly(2-acrylamido-2-methyl-1 -propanesulfonicacid) (PMAPS), Poly(methyl methacrylate) (PMMA), Polymethylsilsesquioxane (PMSQ), Poly(N-isopropylacrylamide) (PNIPAM), Poly Propylene carbonate (PPC), Poly (p-xylene tetrahydrothiophenium chloride), Poly(p- phenyleneterephthalamide) (PPTA), Polypyrrole (Ppy), Polystyrene (PS), Poly(sulfobetainemethacrylate) (PSBMA), Poly urethane (PU), Polyvinyl alcohol) (PVA), Polyvinyl acetate) (PVAc), Polyvinyl chloride (PVC), Poly(N- vinylcarbazole) (PVCz), Poly(vinylidenefluoride-co-hexafluoropropene) (PVDF- HFP), Poly(vinylidene fluoride) (PVDF), Poly(vinylidenefluoride- cotrifluoroethylene) (PVDF-TrFE), Polyvinylpyrrolidone (PVP). However, it should be understood that the process of the present invention should not be limited to the exemplified materials, and that other materials are possible. The inventors have found that any polymer that can stabilized before carbonation, for example through a crosslink, chemical reaction, radiation or the like can be formed via electrospinning into nanofibres that can be converted to carbon nanofibres.

[039] As can be appreciated, a polymer nanofibre is produced from a polymer solution having the desired composition. The polymer solution comprises a polymer and a solvent. The polymer solution can be produced from suitable monomer or monomers mixed with a suitable solvent and any desired additive or additive in a suitable polymerisation process, typically an addition polymerisation process such as solution or suspension polymerisation to produce a polymer solution from monomer. Alternatively, a suitable polymer, copolymer or the like can be dissolved into a suitable solvent to get a polymer solution for use in electrospinning. This polymer solution can be used directly in electrospinning, or mixed with further additives where desired. In this respect, additives are also dissolved/dispersed into the solution if needed.

[040] Suitable solvents for forming a polymer solution with a polymer include at least one of trichloroethane, trichloroethylene, methylene chloride, chloroform, carbon tetrachloride, tetrachlorethylene, methnol, ethanol, propanol, butanol, ethylene glycol, diethyl ether, ethylacetate, acetone, n,n-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, hexafluoroisopropanol, hexafluoroacetone, carbon disulphide, toluene, petroleum ether, acetic acid, formic acid, butanone, cyclohexane, dimethylacetamide, diethylene glycol, ethyl acetate or water.

[041] The process of the present invention is suitable for making multi- ingredient carbon fibre precursors. When wet spinning is used to prepare carbon fibre precursors in a conventional process, it is very difficult to control the fibre composition due to the complicated coagulation process. In comparison, electrospinning enables the inclusion of additives into the nanofibres and control the content precisely within nanofibres. Thus in some embodiments, the forming step involves electrospinning a polymer solution which includes a dissolved polymer and at least one additive. The additive can be added to the polymer solution through dissolving/dispersing the material in the polymer solution for co-electrospinning.

[042] Suitable additives include small molecules, polymers, nanomaterials or the like. Specific examples include organic/inorganic salts, surfactants, organic compounds, macromolecules, co-polymers, nanoparticles, nanotube/fibres, nano platelets, nanowires, quantum dots, or the like. The purpose of adding additives is to improve the properties of the nanofibre and/or resulting nanofibre yarn for example improving spinning ability, fibre uniformity, post- electrospinning drawing ability, stabilization, carbonization, or graphitization. A single additive may have multiple functions to improve some of the performances. Furthermore, as noted above the additive can also be used to produce other nanofibre yarns such as SiC, inorganic oxide, C/C composite, metal/C composite, or inorganic oxide/C composite nanofibre yarns. These nanofibre yarns can be prepared from an electrospinning solutions which includes a mixture of precursor polymer with an additive or additives. The resulting continuous nanofibre yarn will therefore include the polymer and the additive. Where additives are added to the polymer solution, the additive content can be controlled precisely by control of the ratio/ concentration of that additive in the polymer solution.

[043] A number of electrospinning devices can be used to produce suitable continuous nanofibre yarns. The electrospinning device includes least one, preferably at least two electrospinning spinnerets which cooperatively electrospin a precursor solution into a nanofibre which is deposited onto a rotary intermediate collector. In exemplary embodiments, electrospinning comprises producing a nanofibre yarn using two electrospinning spinnerets which cooperatively electrospin a precursor solution into a nanofibre which is deposited onto a rotary intermediate collector. Such an electrospinning apparatus may use a winder tube to collect the produced nanofibre yarn prior to the drawing step.

[044] Any suitable spinneret could be used. In some embodiments, the two electrospinning systems comprise needle spinnerets which are spaced apart about the intermediate collector. Any suitable needle spinneret could be used. In some embodiments, each of the needle spinnerets includes a back disc electrode so as to enhance fibre deposition of each system onto the intermediate collector. This ensures electrospinning of continuous nanofibre yarns in highly controlled manner.

[045] In other embodiments, the spinnerets can comprise one or more needleless spinnerets. Needleless systems can provide much higher nanofibre productivity. A number of needleless electrospinning systems are known in the art. Spinnerets for needleless electrospinning can be classified into two categories: rotating or stationary spinnerets. Rotating spinnerets can introduce mechanical vibration to the polymer solution, which assists in initiating jets. Rotating spinnerets mostly work continuously. The rotating spinneret can have at least one of a cylinder, ball, disc, coil, ring, roller or beaded chain configuration. The rotating spinneret is typically partially immersed with the electrospinning solution. These spinnerets are all connected with a high voltage power supply through the electrospinning solution. Nanofibers are electrospun upwardly towards a collector, which effectively prevents the polymer fluid from dropping onto the fibre collected. The rotation of the spinneret conveys polymer solution to the electrospinning sites, ensuring continuous production of nanofibre. For electrospinning using a stationary spinneret, an auxiliary force (for example magnetic field, gravity, or gas bubble) is often applied to initiate electrospinning process. The spinneret may have a plate, bowl, dome, cylinder cone or the like configuration. In these embodiments, the electrospinning solutions are fed from separate solution containers. Here electrospinning relies on the initiation of jets from an open liquid surface provided on the spinneret. A useful summary of needleless electrospinning systems that can be used in embodiments of the present invention is provided in Niu et al. Fiber Generators in Needleless Electrospinning. Journal of Nanomaterials, Volume 2012 (2012), Article ID 725950, the contents of which should be taken to be incorporated into this specification by this reference.

[046] The spinnerets and more particularly the nozzle (for needle electrospinning systems) of each electrospinning system are preferably arranged at an angle of between 30 and 90 degrees to a central axis running through the collector and between the two spinnerets of the electrospinning systems, preferably between 50 and 70 degrees, more preferably about 60 degrees. The spinnerets of the two electrospinning systems are preferably arranged on opposite sides of the collector. In such systems, the two electrospinning systems are preferably configured to have an opposite charge, i.e. one electrospinning system is positively charged and one electrospinning system is negatively charged.

[047] In other embodiments, electrospinning comprises producing a nanofibre yarn using multiple pairs of electrospinning spinnerets which cooperatively electrospin a precursor solution into a nanofibre which is deposited onto a rotary intermediate collector. Any number of spinnerets can be used, for example 4, 6, 8, 10 or more. The use of multiple pairs of spinnerets increases yarn productivity. Where the electrospinning system includes at least one pair of spinnerets, each pair of spinnerets has an opposite charge. Where multiple pairs of spinnerets are used, spinnerets of opposite charge (positively charged and negatively charged) are preferably placed in alteration manner (for example, a positively charged spinneret placed next a negatively charged spinneret).

[048] In some embodiments, each spinneret includes an air jet. Air-jet enhanced electrospinning can increase nanofibre productivity, hence the yarn productivity.

[0041] The voltage applied on the spinnerets are preferable to be between 10 to 80 kV, preferably between 20 and 60 kV, more preferably about 25 kV. In embodiments where the spinneret, particularly a needle type spinneret does not include back discs, the voltage can be lowered, preferable to be between 10 to 20 kV. It is noted that the above voltage range is applicable to both needle and needleless spinnerets. The voltage applied is preferably in opposite polarity for the spinnerets on opposite sides of a central axis running through the collector and between the individual spinnerets of the one or more pairs of spinnerets of the electrospinning system.

[049] The intermediate collector is preferably configured to rotate to produce a twist in the produced nanofibre yarn. The rotary intermediate collector can comprise any suitable rotary body that includes an opening, for example a funnel, tube, ring, annulus or cylinder. In some embodiments, the rotary intermediate collector comprises a metal funnel. However, it should be appreciated that the intermediate collector can be made from any suitable material, for example one or more metals or plastics. Where the collector comprises a funnel, ring, tube, cylinder or the like, the collector is generally aligned with the base of the collector (for example for a funnel, the end of the collector with the largest diameter) generally facing the nozzle (i.e. the nanofibre applicator end of the spinneret) of each electrospinning system, and rotating about a central longitudinal axis of the collector. A funnel shaped intermediary collector typically has a conical or frustoconical shape, though it should be appreciated that other suitable shapes such as spherical and frustospherical shapes could also be used.

[050] Where electrospinning includes two or more electrospinning systems/ two or more electrospinning spinnerets are used for the yarn production, the individual spinnerets can be fed with different electrospinning/ precursor solutions to produce nanofibres of different compositions. This enables the process to produce composite nanofibre yarns in which the yarn contains two different types of fibres. A single carbon nanofibre yarn can be produced from two different nanofibre precursor solutions. For example, a nanofibre yarn can be produced by electrospinning two different polymer solutions. This can produce a yarn in which one carbon nanofibre has a high tensile strength and another has a high modulus, the carbon nanofibre yarn should have a high toughness. This can also allow tailoring the mechanical properties of carbon nanofibre yarn through the two types of carbon nanofibres.

[051] In some embodiments, each spinneret is configured to feed at least two different fluids to form a bicomponent fluid. Bicomponent electrospinning uses a spinneret which allows feeding at least two different fluids to form a bicomponent fluid, for example side-by-side, core-shell, or islands-in-a-sea, nanofibre yarns made of bicomponent nanofibres (e.g. side-by-side, core-shell, and sea-island) can be prepared. These nanofibre yarns can be used for making carbon nanofibre yarns with tailored composition, morphology or/and mechanical performance.

[052] The precursor nanofibre yarn can be subjected to stabilization and carbonization treatments to produce continuous carbon nanofibres in the form of a filament bundle or yarn. Therefore, a second aspect of the present invention provides a process of preparing a continuous carbon nanofibre yarn comprising:

forming a continuous carbon nanofibre precursor yarn according to the first aspect of the present invention;

subjecting the precursor yarn to at least one stabilization process to form a stabilised nanofibre yarn; and subjecting the stabilised nanofibre yarn to at least one carbonization process thereby producing a continuous carbon nanofibre yarn.

[053] The stabilization process converts the material of the nanofibres in the yarn (for example a polymer such as PAN) linear chemical bonding structure to a more thermally stable ladder bonding structure. The temperature used for the stabilisation process is material dependent. For PAN, this may in some processes be achieved by heating the fibres to a temperature of 300 °C. The stabilization process typically involves oxidation of the precursor yarn at a temperature in the range from 100 to 500 Ό, prefer ably in an oxidative environment, for example air. In some embodiments, the stabilization process has a temperature in the range from 200 Ό to 400 ° C, preferably about 300 Ό. Furthermore, the stabilization process preferably holds the precursor yarn at the stabilisation temperature for at least 10 minutes, preferably at least 30 minutes, preferably in the range from 10 to 180 minutes. The stabilization is normally carried out under tension for making high strength carbon fibres.

[054] The stabilisation functions to construct a highly cross-linked polymer network within fibres. This allows the fibres withstanding high temperature without losing their physical shape due to melting. A wide list of chemical/physical techniques (for example chemical crosslinking, hydrolysis, plasma treatment, or radiation) can be chosen for stabilization treatment of polymer fibres depending on chemical structure of the polymers used.

[055] Once the fibres have been stabilised, they can then be carbonized. Again, the temperature used for the carbonization process is material dependent, and the overall carbonization process can be between 600 to 3000 °C. In some embodiments, particular for PAN, this involves heating the fibres at a temperature in the range from 600 Ό to 3000 Ό, preferably from 600 Ό to 2000 Ό, 800 Ό to 1600 Ό an inert atmosphere, for example in the presence of an inert gas (e.g. argon or the like). The extreme heat treatment causes the fibres to expel any non-carbon atoms and form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fibre. [056] It should however be appreciated that the overall carbonization process can typically be divided into three parts:

• Pyrolysis: temperature up to 600 °C, which leads t o generation of large gas;

• Carbonation: 600 to 1800 to remove all other el ements apart from carbon.

• Graphitization: temperature above 1800 °C to make carbon crystallize into graphite.

[057] The process of the second aspect of the present invention may include at least one further treatment step. For example, in some embodiments following carbonisation, a surface treatment, for example oxidation may be used to improve the binding properties of the surfaces. This can be achieved using an electrolytic process, for example passing the carbonised fibre through an electrolytic bath. Additives or other elements may also be added to the fibre following carbonisation. Furthermore, the produced carbon nanofibre yarns may be washed, dried and coated with a coating material, for example an epoxy or the like, prior to winding on a product reel or spool. This process creates a rough surface and formation of high adhesion resin layer. In some embodiments, plasma treatment could also be used to surface functionalization of carbon nanofibres

[058] In some embodiments, a coating, for example an inorganic coating, can also be used to protect carbon fibres, for example forming a dense SiC layer on fibre surface. This can be achieved by surface treatment of carbon fibres, or coating carbon fibres with a thin layer of Si-containing polymer (e.g. polysilane) followed by a high temperature treatment. It should be appreciated that the coating could be applied prior to the carbonisation process or as a separate heat treatment step.

[059] The present invention also relates to a continuous carbon nanofibre precursor yarn produced from a process according to the first aspect of the present invention, and a continuous carbon nanofibre yarn produced from a process according to the second aspect of the present invention. [060] It should be appreciated that the described method is scalable between a laboratory set up and industrial set up for continuous production of carbon nanofibre precursor yarn and associated carbon nanofibre yarn.

BRIEF DESCRIPTION OF THE DRAWINGS

[061] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[062] Figure 1 provides a general process schematic of a carbon nanofibre production process according to one embodiment of the present invention.

[063] Figure 2 provides a) a schematic illustration of a yarn electrospinning setup, b) an illustration of the actual setup and yarn electrospinning process, c) photo of the fibrous cone, d) nanofibre yarn collected on a spool.

[064] Figure 3 provides SEM images of nanofibre yarn and fibre, histogram of fibre diameter distributions and angles of nanofibres along the yarn axis.

[065] Figure 4 provides a) Storage modulus (Ε') to temperature curve of PAN nanofibre yarns (heating rate 5 O/min, frequency v ibration 10 Hz), b) the strain and breaking stress with temperature (yarn was drawn under constant displacement 400 μηΊ/min), c) Strain to temperature curves of nanofibre yarns drawn under different forces, d) Strain rate to temperature curves of nanofibre yarns drawn with 3.0 cN, 5.0 cN and 7.5 cN force. (Heating rate for c and d is 1 ^• C/min).

[066] Figure 5 provides a) Dichroic ratio at different beam angles, b) effect of drawing ratio on orientation factor, c) strain to stress curves of nanofibre yarns under different drawing ratios, d) effect of drawing ratio on yarn tensile strength and Young's modulus. [067] Figure 6 provides a) SEM images of PAN nanofibre yarn after stabilization and carbonization treatments (embedded picture shows the cross section of carbon nanofibres, b) stress to strain curve of resultant CNF yarn.

[068] Figure 7 provides a schematic illustration of a needleless (disc) electrospinning that can be used to prepare a carbon nanofibre yarn precursor according to one embodiment of the present invention.

DETAILED DESCRIPTION

[069] Firstly referring to Figure 1 , there is shown a schematic process flow diagram showing the general process step of the process of the present invention. As shown in Figure 1 , the process is a two stage process, firstly forming a precursor nanofibre yarn (involving both forming and drawing processes, see below), and then subjecting that yarn in a further process involving stabilization and carbonization treatments to form the carbon nanofibre yarn. Referring to Figure 1 , the steps set out for this process are generally:

(1 ) forming a continuous nanofibre yarn by electrospinning;

(2) drawing the nanofibre yarn, thereby producing a continuous carbon nanofibre precursor yarn;

(3) subjecting the precursor yarn to at least one stabilization process to form a stabilised nanofibre yarn; and

(4) subjecting the stabilised nanofibre yarn to at least one carbonization process thereby producing a continuous carbon nanofibre yarn.

[070] Each of these process steps will now be described in more detail:

Electrospinning

[071] In the present invention, continuous nanofibre yarns are produced using an electrospinning process. A schematic illustration of a preferred embodiment of the yarn electrospinning process setup 100 is shown in Figure 2a. It should be appreciated that one form of this electrospinning process is described in general in AN et al (2012) Direct electrospinning of highly twisted, continuous nanofibre yarns. The Journal of The Textile Institute, Vol. 103, No. 1 , pp 80 to 88, the contents of which are to be understood to be incorporated into this specification by this reference.

[072] Referring to Figure 2a, the illustrated electrospinning setup 100 comprises the use of a rotary funnel collector 102 and two oppositely charged electrospinning spinnerets 104A and 104B which are spaced apart about the collector 102. The electrospinning spinnerets 104A and 104B comprise needle spinnerets electrospinning systems. Each of the electrospinning spinnerets 104A and 104B include a back disc electrode 105 to enhance fibre deposition of each system onto the collector 102. This ensures electrospinning of continuous nanofibre yarns in highly controlled manner. The two electrospinning spinnerets 104A and 104B are connected to separate DC power supplies 106A and 106B, though providing opposite charge to each nozzle 107A and 107B of the electrospinning spinnerets 104A and 104B, i.e. one electrospinning spinneret 104B is positively charged and one electrospinning spinneret 104A is negatively charged. The nozzles 107A and 107B of each electrospinning spinneret 104A and 104B are arranged at an angle of between 30 and 90 degrees, preferably about 60 degrees, to the funnel axis X-X running through the collector 102 and between the two electrospinning spinnerets 104A and 104B.

[073] The collector 102 comprises a funnel, and is configured to rotate to produce a twist in the produced nanofibre yarn 1 10. The funnel collector 102 is not earthed. In the illustrated example the collector 102 is metal. However, it should be appreciated that the setup 100 could function with the collector 102 formed from another material, for example a plastic/polymeric collector.

[074] The continuous nanofibre yarn 1 10 can comprise any suitable material, including at least one polymer suitable for making carbon nanofibres. The polymer may be a copolymer, petroleum pitch, lignin, cellulose, or a sol from inorganic materials. The continuous nanofibre yarn 1 10 can also comprise one or more additive, such as organic/inorganic salts, surfactants, organic compounds, macromolecules, co-polymers, nanoparticles, nanotube/fibres, nano platelets, nanowires, quantum dots, etc. The materials are simply spun from a suitable precursor solution (dissolved and/or dispersed precursor material plus solvent) fed from the electrospinning spinnerets 104A and 104B. These nanofibre yarns can be subjected to further treatment to form carbon nanofibre yarns, SiC nanofibre yarns, inorganic oxide nanofibre yarns, composite carbon nanofibre yarns, C/C composite carbon nanofibre yarns, metal/C composite nanofibre yarns, or inorganic oxide/C composite nanofibre yarns (of course depending on the composition of the continuous nanofibre precursor yarn).

[075] Where the nanofibre yarn is a polymer nanofibre yarn, the polymer nanofibre is produced from a polymer solution comprising a polymer, solvent and any desired additive or additives. The polymer solution can be produced from suitable monomer or monomers mixed with a suitable solvent and any desired additive or additive in a suitable polymerisation process, typically an addition polymerisation process such as solution or suspension polymerisation to produce a polymer solution. Alternatively, a suitable polymer, copolymer or the like is dissolved into a suitable solvent to get a polymer solution for use in electrospinning. This polymer solution can be used directly in electrospinning, or mixed with further additives where desired. In this respect, additives are also dissolved/dispersed into the solution if needed. This polymer solution can be used directly in electrospinning, or mixed with further additives (where desired).

[076] With other nanofibre yarns, such as SiC, inorganic oxide, C/C composite, metal/C composite, or inorganic oxide/C composite nanofibre yarns, the solutions are prepared from a precursor polymer (for example petroleum pitch, polycarbomethylsilane, inorganic sol gel) or a mixture of precursor polymer with the selected an additive or additives. The precursor polymer is dissolved in a suitable solvent, while the additives may be dispersed into the precursor solution. For example, a polymer based nanofibres containing a carbon nanomaterial (e.g. nanotube, graphene, C ₆ o, or nanowire) can be prepared by electrospinning a suitable polymer solution (for example PAN) containing the nanomaterial. Then C/C nanofibres are prepared from the resulting composite nanofibres and nanofibre yarn.

[077] The precursor solution is loaded into the spinnerets 104A and 104B and dispensed from nozzles 107A and 107B as a precursor solution jet. The nanofibres are formed by fast evaporation of the solvent from each precursor solution jet.

[078] In operation, the electrospinning spinnerets 104A and 104B cooperatively electrospin the precursor solution into a nanofibre which is deposited onto a rotary intermediate collector 102. The nanofibres are formed by fast evaporation of a solvent from a precursor solution jet which is dispensed from each of the nozzles 107A and 107B of each electrospinning spinnerets 104A and 104B. The nanofibers electrospun from the oppositely charged nozzles 107A and 107B deposit onto the rotary collector 102 to form a nanofibres web that covers the funnel end of the collector 102. The deposition of nanofibres onto the collector 102 is largely due to electrostatic attractions. Nanofibres cover the collector 102 forming a fibrous membrane on the mouth of the funnel of the collector 102. By initially inducing the formation of a "cone"- shaped hollow fibre assembly 1 12 on the distal funnel edge of the collector 102, a continuous yarn can be produced by withdrawing and twisting the nanofibre "cone". A driven yarn winder 108 (typically driven by an electric motor (not illustrated)) is used to collect the produced nanofibre yarn 1 10.

[079] It should be appreciated that in some embodiments, each electrospinning spinnerets 104A and 104B can be fed with different precursor solution to produce nanofibres of different compositions. This enables the process to produce composite nanofibre yarns in which the yarn contains two different types of fibres. A single carbon nanofibre yarn can be produced from two nanofibre precursor solutions. Similarly, in some embodiments each spinneret is configured to feed at least two different fluids to form a bicomponent fluid. Bicomponent electrospinning uses a spinneret which allows feeding at least two different fluids to form a bicomponent fluid, for example side-by-side, core-shell, or islands-in-a-sea, nanofibre yarns made of bicomponent nanofibres (e.g. side- by-side, core-shell, and sea-island) can be prepared. These nanofibre yarns can be used for making carbon nanofibre yarns with tailored composition, morphology or/and mechanical performance.

[080] A needleless electrospinning system could be used as an alternate to the electrospinning system shown in Figures 2a and 2b. Figure 7 illustrates one form of a needleless electrospinning system comprising a disc electrospinning system 200 that can be used to prepare a carbon nanofibre yarn precursor according to one embodiment of the present invention. The two spinnerets 104A, 104B in the yarn electrospinning system 100 described and illustrated in relation to Figures 2a and 2b are replaced by two rotating disc electrospinning systems 204A, 204B having disc spinnerets 207A, 207B as shown in Figure 7. The rest of the electrospinning system 200 is generally the same as described in relation to Figures 2a and 2b, and therefore like components in Figure 7 to Figure 2a have been given the same reference numeral PLUS 100.

[081] As shown in Figure 7, the disc spinnerets 207A, 207B are partially immersed in a PAN solution held in a reservoir (container) 220 underneath each disc spinnerets 207A, 207B. The rotation of disc spinnerets 207A, 207B brought the PAN solution to the disc top, where PAN nanofibres were generated when positive and negative high voltage was applied to the two disc spinnerets 207A, 207B, respectively. The formed nanofibres were collected on a funnel collector 202, with the PAN nanofibre yarn prepared by winding the nanofibre from the apex of the fibrous cone as shown in Figure 7 on a yarn winder 208. The yarn was then subjected to drawing, stabilisation, and carbonization treatment to get carbon nanofibre yarn. This electrospinning system 200 typically has higher yarn productivity relative to the needle spinneret electrospinning system 100 shown in Figure 2a.

[082] It should be appreciated that other needleless electrospinning systems and more particularly spinneret configurations could be used, for example cylinder, plate, rings, coils or the like. Examples of other suitable needleless electrospinning systems are provided in Niu et al. Fiber Generators in Needleless Electrospinning. Journal of Nanomaterials, Volume 2012 (2012), Article ID 725950, again the contents of which should be taken to be incorporated into this specification by this reference.

Drawing treatment

[083] As shown in Figure 1 , following formation of the nanofibre yarn, that nanofibre yarn is subjected to a drawing treatment step to improve the fibre and molecular orientation. In some embodiments, the drawing step may occur immediately after the electrospinning step, for example in a continuous process, where the electrospinning process feeds directly into a drawing process. In other embodiments, the drawing treatment step may form a separate process, where the nanofibre yarn formed from the electrospinning process is collected, for example on a spool, and then feed into the process at a suitable time.

[084] Drawing treatment reduces fibre diameter, but considerably improves fibre uniformity and alignment of the nanofibre yarn. Drawing the nanofibre yarn generally includes applying a drawing or stretching force to the nanofibre yarn.

[085] Drawing treatment can be a batch process or a continuous process:

[086] In a continuous process, the nanofibre yarn can be drawn over a number of spaced apart rollers which grip and move to draw the yarn and constituent nanofibre to a specified draw ratio. The nanofibre yarn is heated to a suitable drawing temperature in the process. For example, for a polymer nanofibre yarn the drawing temperature is preferably between Tg and the degradation temperature of the polymer. A number of continuous drawing processes are known in the art, particular fibre production art. It should be appreciated that a person skilled in the art would be able to use the teachings of the present invention in combination with known drawing processes to arrange a suitable continuous fibre drawing process.

[087] In a batch process, yarn drawing is carried out on discrete lengths of yarn in an oven or other heated enclosure. The nanofibre yarn is heated to a suitable drawing temperature in the process. Again, for a polymer nanofibre yarn this drawing temperature is preferably between Tg and the degradation temperature of the polymer. In such a process, a drawing force is applied to discrete lengths of the yarn to draw the yarn and constituent nanofibre to a specified draw ratio. It should be appreciated that a person skilled in the art would be able to use the teachings of the present invention in combination with known drawing processes to arrange a suitable batch fibre drawing process. [088] Following the drawing process, the post drawn nanofibre yarns can be cooled down, for example to room temperature, and collected for further treatment, for example on a suitable spool or other collection device.

Stabilization and carbonization treatments

[089] As shown in the process flow diagram of Figure 1 , a continuous carbon nanofibre yarn can be formed by applying at least one stabilization process followed by at least one carbonization process to the formed continuous carbon nanofibre precursor yarn.

[090] In some embodiments, these steps may occur immediately after the drawing step, for example in a continuous process, where the nanofibre yarn produced from the drawing process feeds directly into the stabilization and carbonization treatment. In other embodiments, the stabilization and carbonization steps may form a separate process, where the drawn nanofibre yarn is collected, for example on a spool, and then feed into these processes at a suitable time.

[091] The stabilization process converts the linear polymer structure of a precursor nanofibre yarn (for example a polymer such as PAN) to a more thermally stable ladder bonding structure. The stabilization process typically involves oxidation of the precursor yarn at a temperature of from 100 to 500 °C, preferably in air for at least 60 minutes, preferably at least 100 minutes. The stabilisation process can be achieved in a suitably designed oven or furnace arrangement.

[092] Once the fibres have been stabilised, they can then be carbonised. The overall carbonisation process involves heating them from 600 °C to 2000 Ό in an inert environment, for example argon or the like. It should be noted that nitrogen can be used as protective gas under 2000 °C, but will react with carbon above 2000 °C and therefore should not be used at t hose temperatures. It should however be appreciated that carbonization in inert environment is divided into three steps: 1 ) Low temperature carbonization (Pyrolysis) in temperature range from 400 to 1000 , where small molecules are releas ed;

2) High temperature carbonization (Carbonation) from 1000 to 1800 Ό to remove all other elements apart from carbon; and

3) Graphitization at a temperature above 1800 to increase graphite content in the carbon fibre.

[093] The extreme heat treatment causes the fibres to expel any non-carbon atoms and form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fibre. Again, the carbonisation process can be achieved in a suitably designed oven or furnace arrangement.

[094] The stabilization step or steps is normally carried out under tension for making high strength carbon fibres. The tension on fibres is not a necessary requirement during carbonization.

[095] The process of the second aspect of the present invention may include at least one further treatment step. For example, in some embodiments following carbonisation, a surface treatment, for example oxidation may be used to improve the binding properties of the surfaces. This can be achieved using an electrolytic process, for example passing the carbonised fibre through an electrolytic bath. Additives or other elements may also be added to the fibre following carbonisation. Furthermore, the produced carbon nanofibre yarns may be washed, dried and coated with a coating material, for example an epoxy, prior to winding on a product reel.

[096] It should be appreciated that the described method is scalable between a laboratory set up and industrial set up for continuous production of carbon nanofibre precursor yarn and associated carbon nanofibre yarn.

EXAMPLES

[097] The following examples describe laboratory scale embodiments of the process of the present invention. It should be appreciated that the results of this example is generally scalable to larger processes, and that the process of the present invention should not be limited to the specific arrangements used in the experimental process steps.

Example 1 : Needle electrospinning system

Experimental

Electrospinning nanofibre yarns:

[098] A purpose-made electrospinning system 100 was used for producing PAN nanofibre yarns. As illustrated in Figures 2a and 2b, the electrospinning setup consists of two electrospinning spinnerets 104A, 104B, a metal funnel collector 102 and a yarn winder 108 as described above. Each electrospinning spinnerets 104A include a back metal electrode 105 (diameter 8 cm, thickness 2 mm) on each electrospinning nozzle 107A, 107B. The electrospinning spinnerets 104A, 104B are powered by two separate power supplies 106A, 106B, one having a positive electrode 106B (ES30P, Gamma High Voltage Research), and the other having a negative electrode 106A (ES30N, Gamma High Voltage Research). The two electrospinning nozzles 107A, 107B were orientated 60 degrees to the funnel axis X-X on opposite sides of the funnel collector 102. Nozzle to funnel distance was set at 25 cm.

[099] Polyacrylonitrile (PAN, Mw 150,000 g/mol) and N, N'-dimethylformide (DMF) from Sigma-Aldrich were used as received for electrospinning. PAN solution (10 wt%) was prepared by dissolving PAN in DMF at 80 .

[100] To prepare a nanofibre yarn, both positively and negatively charged nanofibres were electrospun and deposited to the large end of the funnel 102 to form a thin nanofibre web thereon. The nanofibre web was then initially manually deformed to be a 3D cone, a nanofibre yarn can be stretched from the apex of the cone. A fibre bundle was then drawn from the cone apex. The rotating speed of funnel 102 was adjusted so that a fibrous cone is formed stably on the funnel 102. Figure 2c shows the fibrous cone formed on the funnel collector 102, and nanofibre yarn collected on a spool of the yarn winder 108 is shown in Figure 2d. Twists were inserted through the rotation of the funnel collector 102. A continuous PAN nanofibre yarn could be produced using this method and wound on the yarn winder 108 for hours without breaking. Drawing treatment:

[101] Batch yarn drawing was carried out in an oven (not illustrated). Ten pieces of nanofibre yarns (with gauge length 20 mm) were firstly with both ends mounted onto opposite sides on a paper frame using double side tapes. The paper frame was then cut on adjacent sides to the yarn mounting edges to release the load to the yarns. Nanofibre yarns were drawn under a constant load at 140 . One edge of the paper frame was fix ed at the top grate of the oven and another was applied with the weight load. Drawn by the gravity, the yarn stopped at a pre-set length (drawing ratio). The post drawn nanofibre yarns were then cooled down to room temperature for various characterizations.

Stabilization and carbonization:

[102] The stabilization treatment of nanofibre yarns was carried out under constant load (0.5 cN) at 250 Ό for 4 hours in an oven. Yarn was clamped at one end and hanged on top grate of the oven, and another end was clamped and was applied with the load. The carbonization was conducted in a tube furnace at 800 °C for 1 hour without tension. Nitro gen was purged initially and maintained a constant flow rate through the carbonization process.

Characterizations:

[103] The morphology of nanofibres and yarns was observed under a scanning electron microscope (Jeol, Neoscope SEM). Fibre and yarn diameters were measured based on SEM images using an image analysis software (lmagePro+4.5, Media Cybernetics Co.). Glass transition temperature was measured using the Q800 Dynamic Mechanical Analyser (DMA) (TA instruments) under a vibration frequency of 10 Hz and a heating rate of 5 /min from 40 to 200 . The thermal mechanical properties were examined in three methods: 1 ) constant displacement (400 μηΊ/ηΊίη) at holding temperatures and 2) constant force at elevating temperature from 40 to 300 (heating rate, 1 /min). The molecular orientat ion in nanofibre was characterized using Fourier transform infrared spectroscope (FTIR) (Brucker Vertex 70) at 64 scan rate. A polarized IR lens was used to obtain polarized IR beam. Tensile properties were examined using FAVIMAT single fibre tester (Textechno). Yarn samples were tested with the gauge length of 20 mm and the crosshead speed of 2 mm/min. The cross-sectional area of nanofibre yarns was calculated from denier of the yarns and density of PAN. Young's modulus and strain at break were average value of five repeated measurements.

Results

[104] Figure 3a provides an SEM image of nanofibre yarns and nanofibres showing the typical morphology of nanofibre yarns prepared. A good proportion of fibres in the yarn aligned in an angle along the yarn axis. Fluffy fibre coils and curled fibres were also found on yarn surface. The yarn had a diameter of 279 ± 30 μηι and the PAN fibres was 812 ± 312 nm in diameter. The large fibre diameter and diameter distribution were attributed to the use of two power supplies to produce oppositely charged nanofibres, strongly interfered with local electrostatic field.

[105] PAN fibres have a low strain level at room temperature, while the mobility of PAN chains increases considerably when it is in a temperature about the Tg. However, when the temperature is higher than 250 °C , degradation takes place. In the present study, the temperature for drawing PAN fibres was chosen above the Tg but lower than the degradation temperature. Before batch drawing treatment, the Tg of PAN nanofibre yarn was examined using DMA. Figure 4a shows the storage modulus (Ε') to temperature curve. The maximum storage modulus indicated that Tg was 105 °C, which was con sistent with the value reported in the art.

[106] Figure 4b shows the maximum strain and breaking stress curves of nanofibre yarn drawn at different temperatures. At 30 °C, the yarn can only be drawn up to a strain of 69% before breaking. The strain increased gradually with increasing the temperature when the temperature was below 90 , while a large increase with increasing the temperature took place in the temperature range from the Tg to 140 . At a higher temperatur e, the strain then showed a rapid reduced trend. It was noted that the strain at the Tg was about 330% when the yarn and the highest strain value of 543% was obtained at 140 . The drawing stress decreased obviously with increasing the temperature. [107] Figure 4c shows strain changes when drawing a nanofibre yarn under a constant force and meanwhile heating up the yarn at a constant rate (1 /min). When different loading forces were applied, the highest temperature which the yarn can be heated varied. The nanofibre yarn can be drawn continuously under 2.0 cN of force until the temperature reached 250 Ό. Higher drawing force between 2.0 and 10.0 cN led to reduced temperature upper limit, to 180 °C. Further increasing the drawing force led to con siderable reduction of the temperature range. In addition, the drawing force also affected the strain maximum. Low drawing force led to a small strain value. With increasing the force, the maximum strain increased. At a 7.5 cN constant force, the strain reached the maximum value (530%), suggesting the nanofibre yarn can be drawn at the largest drawing ratio.

[108] A two-stage strain change with temperature increase occurred when the yarn was drawn under a force of 3.0 to 7.5 cN. The first stage took place between the Tg and 130 , and the 2nd started at a round 140 until the upper temperature limit. The low temperature stage was attributed to movement of short chain segments under stretching, while longer chain segments move at a higher temperature. Such a two-stage strain change suggested that elongation rate changed when the yarn was drawn under a constant force while being heated.

[109] Figure 4d shows elongation rate changes with heating temperature (rate 1 /min) when the yarn is stretched under a consta nt force. At 3.0 cN, a maximum elongation rate (7 %/min) occurred at around 1 12 °C, which is in the 1 st stage elongation. The elongation rate then reduced gradually to a minimal value (4 %/min) at around 128 , and then increase d monotonously (up to 150 %/min) until the yarn broke at 145 . At higher dr awing force, the maximum elongation rate moved to a lower temperature. However, the elongation rate at the upper temperature limit was little affected.

[1 10] The drawing treatment reflects the competition of molecule movement and chain relaxation under an external drawing force. Under a small force (e.g. lower than 3.0 cN), polymer chains cannot be drawn to move unless the temperature is above the Tg. The gentle elongation allows sufficient chain movement with temperature increase. Increasing the drawing force facilitates the chain movement. When the force is not high enough, the chain movement is not accelerated by the drawing force. In this case, the temperature upper limit is not affected by variation of drawing force much. On the contrary, if the drawing force is too high (e.g. above 10.0 cN in our case), the yarn breaks before it is fully stretched. A force (e.g. 3.0 cN to 7.5 cN) between the two extreme states could lead to an initially accelerated stretching at a relatively lower temperature followed by further fully stretching a higher temperature, showing a two-stage change in elongation rate. Drawing under a suitable force at a temperature close to 140 Ό is effective to elongate the PAN na nofibre yarn to a high strain value.

[1 1 1] Yarn morphology after drawing treatment is also shown in Figure 3. Here, drawing ratio (i.e. ratio between the elongated and the initial yarn lengths) was employed to represent the elongation length. At a higher drawing ratio, the yarns became more compact and curled fibres were straightened. Yarns and fibres both decreased in diameter after the drawing treatment. When the drawing ratio was 3 times, the average yarn and fibre diameters reduced to 91 ± 7 μηι and 408 ± 141 nm, respectively. Higher drawing ratio, such as 6 times, further reduced the yarn and fibre diameters to 64 ± 5 μηι and 336 ± 142 nm.

[1 12] In addition to the decreased diameter, the diameter distribution became narrower after drawing treatment (Figure 3). In the as-spun yarn, the PAN fibres had a wide diameter distribution in a range between 300 nm and 1 .6 μηπ. After drawing treatment (drawing ratio, 6 times), the fibre diameter range changed to 100 nm to 900 nm. Higher drawing ratio did not further narrow the fibre diameter range much, except that the average fibre diameter decreased.

[1 13] After drawing treatment, the fibre alignment angle along the yarn axis (also referred as alignment angle) decreased (Figure 3). Without drawing, the majority fibres had an alignment angle of 0°to 60° . After drawing for 2 times of the yarn length, the alignment angle reduced significantly to 30°. Higher drawing ratio led to high alignment of fibres with an alignment angle as small as 15°.

[1 14] The effect of drawing treatment on polymer chain orientation within nanofibres was also examined by measuring the nitrile group vibration band (C≡N, peak wavenumber 2244 cm ^"1 ) in polarized FTIR. Chain-orientation factor (f) was calculated according to equations:

(D-l)(Do+2)

f = (D ₀ -l)(D+2) (2)

where D is the dichroic ratio of C≡N vibration peak intensity (A) under parallel ( || ) and perpendicular (- ¹ -) IR beams. D ₀ is the dichroic ratio of the polymer with perfect orientation.

[1 15] Figure 5a shows the D at different beam angle. Drawing treatment increased the D value, indicating that the drawing process facilitated the PAN molecule orientates along the fibre direction. The effect of drawing ratio on chain orientation is shown in Figure 5b. The f at 0 and 1 indicates random and perfectly orientated states, respectively. The f value increased with increasing the drawing ratio. The highest f, 0.63, was found on the nanofibre yarn drawn to 6 times of its length.

[1 16] Figure 5c & d show the stress-strain curves and effect of drawing ratio on the tensile strength and Young's modulus of nanofibre yarns. With increasing the drawing ratio, both tensile strength and Young's modulus increased until the drawing ratio was 5 times. The 5-times drawn yarns had a tensile strength and Young's modulus of 362 ± 37 MPa and 9.2 ± 1 .4 GPa, respectively, which were more than 800% and 1800% of as-spun yarns. In addition, the drawing treatment significantly decreased the strain level, which was attributed to the increased nanofibre alignment and polymer chain after drawing treatment. [1 17] To prove the feasibility of forming HPCFs from nanofibre yarn, a PAN nanofibre yarn after 5 times drawing treatment was subjected to stabilization and carbonization treatments. Figure 6a shows the SEM images of the carbonized nanofibre yarn, which has similar morphology to the precursor yarn. After carbonation, nanofibre and yarn diameters changed to 44.29 ± 0.09 μηι and 190.02 ± 31.79 nm respectively. The stress-strain curve of the CNFY showed some elongation and its modulus was 3 GPa at 1 % strain, but significantly increased to 40 GPa at 2.5% strain (Fig 5b). The relatively low tensile strength, 1.12 ± 0.18 GPa, was due to the un-optimized treatment condition. Optimization of the stabilization and carbonization conditions in further work would significantly increase the strength value.

Conclusion

[1 18] Continuous electrospun PAN nanofibres yarns were prepared. The yarns can be drawn up to 6 times of their original length at a dry condition, and the drawing treatment improves in yarn and fibre uniformity, fibre alignment, polymer chain orientation, and yarn tensile strength, but decreases yarn and fibre diameter and elongation at break.

[1 19] The drawing temperature and drawing force show influences on yarn drawing behaviour. The highest strength and modules were found on the yarn drawn by 5 times the length, which increased by more than 800% and 1800% when compared to the as-spun yarns. The nanofibres yarns after stabilization and carbonization treatments maintain the uniformity, and the CNF yarns prepared show comparable tensile properties to the commercial carbon fibres.

Example 2: PAN/PVDF bicomponent nanofibre yarn and carbon fibre

[120] A PAN solution and a PVDF solution were electrospun separately by the two electrospinning spinnerets 104A and 104B in the yarn electrospinning system 100 described in Example 1 and illustrated in Figures 2a and 2b.

[121] During electrospinning, positive and negative high voltages were applied to each of the spinneret heads 105. The PVDF and PAN nanofibres were deposited simultaneously onto the funnel collector 102, to form a fibrous cone. By stretching a fibre bundle from the apex of the cone, and meanwhile inserting twists to the bundle, a bicomponent yarn composed of PAN and PVDF nanofibres was formed, which was easily wound by the yarn winder 108. The as-spun yarn had a yarn diameter of 54 ± 8 μηπ, and a fibre diameter of 428 ± 236 nm, respectively. After drawing treatment, stabilization and carbonization following the method described in Example 1 , carbon nanofibre yarn was prepared from this bi-component yarn.

Example 3: PAN/pitch bicomponent nanofibre yarn and carbon fibre

[122] A PAN solution and a pitch solution were electrospun separately by the two electrospinning spinnerets 104A and 104B in the yarn electrospinning system 100 described in Example 1 and illustrated in Figures 2a and 2b. A PAN/pitch bicomponent yarn was obtained. After drawing treatment, stabilization and carbonization following the method described in Example 1 , carbon nanofibre yarn was prepared from this bi-component yarn.

Example 4: Core-sheath C-SiC nanofibre yarn

[123] Core-shell electrospinning spinnerets were used to replace the needle spinnerets 104A and 104B in the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. Polyacrylonitrile (PAN) solution and polycarbomethylsilane solution were fed separately into the core channel and the sheath fluidic channel of each spinneret. Solution jets with PAN/polycarbomethylsilane core-sheath structure were generated and a PAN/polycarbomethylsilane core-sheath nanofibre yarn was prepared from the system. After drawing treatment, stabilization and carbonization following the method described in Example 1 , a core-sheath C-SiC nanofibre yarn resulted.

Example 5: Post-electrospinning crosslinking of polyvinyl alcohol) (PVA)

[124] A PVA solution was placed into the spinnerets 104A and 104B or the two electrospinning spinnerets in the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b and the solution was then delivered to the tip of the nozzles at a flow rate 1 .0 mL/h. 25 kV positive and negative voltages were applied to the back discs 105. A nanofibre yarn was produced and wound onto the winder 108. The nanofibre yarn had a diameter of 1 14 ± 23 μιτι.

[125] PVA nanofibres in the yarn had a diameter of 367 ± 1 13 nm. The yarn was then drawn under a drawing force of 0.1 to 0.2 cN/tex at 220 Ό in air. After drawing, the yarn was elongated to 6 times of its original length. The stabilization of PVA nanofibre yarns was carried out by placing the yarn in glutaraldehyde vapour for 15 minutes. During the process, the yarn was under a tension of 0.1 to 0.2 cN/tex. The yarn was then carbonized at 1200 Ό to get a carbon nanofibre yarn.

Example 6: Post-electrospinning hydrolysis of cellulose acetate (CA)

[126] A CA solution was placed into the spinnerets 104A and 104B in the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b and electrospun into a nanofibre yarn. The yarn was then drawn under a drawing force of 0.1 to 0.2 cN/tex at 220 in air . After drawing, the yarn was elongated to 3 times of its original length.

[127] The stabilization of CA nanofibre yarns was carried out by immersing the yarn in sodium hydroxide/ethanol solution (0.05M), and then rinsing with water. During the process, the yarn was under a tension of 0.1 to 0.2 cN/tex. After this treatment, CA converted to cellulose without changing the fibre morphology. The yarn was carbonized at 900 °C to get a carbon n anofibre yarn.

Example 7: Dehydrofluorination of polyvinylidene fluoride (PVDF) nanofibre yarn

[128] Electrospun PVDF nanofibre yarns was produced using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The electrospun PVDF nanofibre yarns were stabilized at a low temperature of 50 °C by immersing in a 8- iazabicyc lo [5.4.0]undec-7-ene(DBU) solution (solvent DMF- methanol mixture). During immersion, the yarn was under a tension of 0.1-0.2 cN/tex. After the treatment, the nanofibre yarns were rinsed with methanol and dried. They were finally carbonized at 1000 to get carbon nanofibre yarns. Example 8: Post-electrospinning plasma stabilization of polyacrylonitrile (PAN) [129] A PAN nanofibre yarn produced following the method described in Example 1 was passed through a plasma chamber. The yarn was subjected to an Ar 02 plasma treatment under a tension of 0.1-0.2 cN/tex. The plasma treated yarn can be directly carbonized without thermal stabilization.

Example 9: Carbon nanotube/carbon composite nanofibre yarn

[130] A PAN solution containing well-dispersed carbon nanotubes (3% by weight of PAN) was electrospun into a composite nanofibre yarn using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The yarn was then subjected to drawing treatment (drawing ratio 600%), stabilisation, and carbonization treatment following the method described in Example 1 to get carbon nanotube/carbon composite nanofibre yarn.

Example 10: Graphene/carbon composite nanofibre yarn

[131] A PAN solution containing graphene oxide (5% by weight of PAN) was electrospun into a nanofibre yarn using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The produced yarn was then subjected to drawing treatment (drawing ratio 500%), stabilisation, and carbonization treatment following the method described in Example 1 . Graphene oxide was reduced to graphene during carbonization, and a graphene/carbon composite nanofibre yarn finally resulted.

Example 1 1 : Pd/carbon nanofibre yarn

[132] Palladium acetate and PAN were dissolved in DMF solution to get a homogeneous solution. The solution was electrospun into nanofibre yarns using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The produced yarn was then subjected to drawing treatment, stabilisation, and carbonization treatment (1 100 ) following the method described in Example 1 . The Pd ²⁺ reduced to Pd element during the carbonization process. A Pd/carbon composite nanofibre yarn finally resulted. Example 12: SiC nanofibre yarns

[133] Polycarbomethylsilane solution was prepared by dissolving polycarbomethylsilane in solvent mixture containing toluene and dimethylformamide. Polystyrene (PS) was added into the electrospinning solution to improve the spinnability. The solution was electrospun into a nanofibre yarn using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The produced yarn was then subjected to drawing treatment following a similar method as described in Example 1 , pyrolysis, and high temperature treatment at 1200 °C in a furnace. During pyrolysis, the PS component decomposed, while the polycarbomethylsilane was converted into SiC at high temperature, resulting in a SiC nanofibre yarn.

Example 13: Al ₂ 0 ₃ nanofibre yarns

[134] Aluminum nitrate and polyvinyl alcohol (PVA) were dissolved in deionized water. Then ethanol was added to the prepared solution under stirring at 60°C to get a solution for electrospinning. The solution was then electrospun into nanofibre yarn using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The yarn was then subjected to drawing treatment following a similar method as described in Example 1 , pyrolysis treatment at 700 in a furnace to get an Al ₂ 03 nanofibre yarn. The PVA was removed during the pyrolysis process.

Example 14: Al ₂ 03/Zr0 ₂ nanofibre yarns

[135] Aluminum nitrate, chromium nitrate, and polyvinyl alcohol (PVA) were dissolved in deionized water. Then ethanol was added to the prepared solution under stirring at 60 to get a solution for elect rospinning. The solution was electrospun into nanofibre yarns using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The yarn was then subjected to drawing treatment following a similar method as described in Example 1 , pyrolysis treatment at 700 in a furnace to get a n Al ₂ 0 ₃ /Zr0 ₂ nanofibre yarn. Example 15: Air-jet enhanced electrospinning to prepare carbon nanofibre yarn precursor

[136] Air jets can be introduced into the yarn electrospinning setup to improve the yarn productivity of the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b.

[137] The yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b was modified (not illustrated) to introduce a jet flow in the direction of from spinneret 104A to collector 102 and from spinneret 104B to collector 102, respectively. The addition of air jets allowed considerable increase in the flow rate of PAN solution (e.g. dozens of times). As a result, the yarn productivity was increased significantly. The yarn was then subjected to drawing treatment, stabilisation, and carbonization treatment following a similar method as described in Example 1 to get carbon nanofibre yarn.

Example 16: Tetra-spinneret to electrospin carbon nanofibre yarn precursor [138] Instead of using two spinnerets for electrospinning of nanofibre yarns, more spinnerets can be used. For example, four spinnerets can be used to produce nanofibres.

[139] The four spinnerets were arranged symmetrically around the collector 102 in an experimental set up similar to that illustrated in Figure 1 . The tetra- spinneret setup increases (doubles) nanofibres yarn productivity compared with the dual spinneret system. The yarn was then subjected to drawing treatment, stabilisation, and carbonization treatment following a similar method as described in Example 1 to get carbon nanofibre yarn.

Example 17: Yarn electrospinning of phase separated PVP/PAN solution

[140] A polyvinylpyrrolidone (PVP)/DMF solution and a PAN/DMF were mixture with a proper (polymer weight ratio <1/9). Polymer phase separation took place in the solution mixture. The solution was then electrospun into a nanofibre yarn using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The resulting yarn was then subjected to drawing treatment, stabilisation, and carbonization treatment following a similar method as described in Example 1 . During this process, PVP melted at high temperature and inter-fibre connections were formed between the carbon nanofibres. In this way, carbon nanofibre yarn prepared have a densely packed structure.

Example 18: Emulsion electrospinning of nanofibre yarn

[141] A silicone oil was added into PAN/DMF solution and the mixture was emulsified with a high speed shear-mixing homogenizer to get an emulsion. Silicone oil distributed in PAN solution as a form of tiny droplets. The emulsion was then electrospun into a nanofibre yarn using the yarn electrospinning setup described in Example 1 and illustrated in Figures 2a and 2b. The produced yarn was then subjected to drawing treatment, stabilisation, and carbonization treatment following a similar method as described in Example 1 . During this process, silicone oil converted to silica nanowires which dispersed within carbon nanofibres. Silica nanowire reinforced carbon nanofibre yarn is formed.

APPLICATIONS

[142] Carbon fibre yarn formed from the process of the present invention can be used in the following areas:

• Aircrafts: The most sophisticated commercial aircraft, Boeing 787, was constructed of 80% carbon fibres in volume. With significantly reduced in weight, the Boeing 787 is 20% more fuel efficient than aircraft in the same class.

• Gas tanks: A gas tank made of carbon fibres could reduce 50% to 75% in weight than those made of glass fibre.

• Automobiles: Carbon fibres help cars in reducing weight thus improving fuel efficiency, and in improving safety during car crash.

• Construction: building, bridges, beams, roads and the like.

[143] It should be appreciated that when carbon nanofibres are used for the above applications purposes, a smaller amount of carbon nanofibres is required to achieve the same mechanical properties as conventional materials. Alternatively, the material can achieve a much higher mechanical strength when an equivalent weight of carbon nanofibres (compared to conventional material) is used. [144] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[145] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.