Process of melt-spinning polyacrylonitrile fiber

Abstract

Processes for producing carbon fiber, the filament thereof and pre-oxidized fiber are provided. In one embodiment, the gel spinning of polyacrylonitrile filament is achieved by using small-molecule gelling agent, and the carbon fiber obtained thereby is increased by 15% to 40% in tensile strength and by 20% to 35% in toughness. In another embodiment, the melt spinning process of polyacrylonitrile is conducted by using imidazole type ion liquid as plasticizer, the process reduces environment pollution, is suitable for industrial production and the fiber produced thereby is improved in its strength. In yet another embodiment, polyacrylonitrile pre-oxidized fiber is produced by melt spinning, so low cost and controllable pre-oxidization of polyacrylonitrile can be achieved. In a further embodiment, high strength carbon fiber is manufactured by using polymer thickening agent. In another further embodiment, low cost and controllable pre-oxidization of polyacrylonitrile is achieved by conducting pre-oxidization before spinning, minimizing skin-core structure, so as to produce high performance carbon fiber, and reduce the production cost of carbon fiber greatly.

Claims

1. A process for producing a carbon fibre, comprising the following steps: a) mixing 0.01-2 parts by weight of a carbon nanotube and 100 parts by weight of a solvent, and ultrasonic processing for 1.5-3 hrs with an ultrasonic cell disrupter at 300 w-600 w to obtain a mixture; b) adding 0.01-5 parts by weight of a polymer thickener to the mixture from step a) followed by ultrasonic processing for 1-2 hrs with an ultrasonic cell disrupter at 300 w-600 w to obtain another mixture; c) forming a coating of 100-300 nm on pre-oxidized fibre with the mixture obtained from step b), followed by carbonizing, to obtain the carbon fibre.

2. The process according to claim 1, characterised in that the carbon nanotube used in step a) is a carboxylated multi-walled carbon nanotube.

3. The process according to claim 1, characterised in that the solvent used in step a) is selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, dimethylacetamide, and distilled water.

4. The process according to claim 1, characterised in that the polymer thickener used in step b) is selected from the group consisting of polyacrylonitrile, polyvinyl alcohol, and -cyanoacrylate.

5. The process according to claim 1, characterised in that the coating in step c) is formed by immersing the pre-oxidized fibres in the mixture obtained from step b) in a pre-oxidized fibres-to-mixture ratio of 1:3-1:2 and standing for 1-2 hrs.

6. The process according to claim 1, characterised in that the coating in step c) is formed by electrostatic spraying the mixture obtained from step b) onto the surface of the fibre with a voltage of 80 kv-120 kv, a spray distance of 25 cm-40 cm, and a rotation speed of spray gun of 2800 r/min-3000 r/min.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The present invention will be further described in details in connection with certain preferred embodiments with reference to the accompanying drawings, in which

(2) FIG. 1 shows a SEM photograph of the cross-section of carbon fibre precursor based precursor fibre spun from a spinning solution containing 2 wt. % gelling agent based on the total weight of the solution;

(3) FIG. 2 shows a SEM photograph of the cross-section of carbon fibre precursor based precursor fibre spun from a spinning solution containing 3 wt. % gelling agent based on the total weight of the solution;

(4) FIG. 3 shows a SEM photograph of the cross-section of carbon fibre precursor based precursor fibre spun from a spinning solution containing 4 wt. % gelling agent based on the total weight of the solution;

(5) FIG. 4 shows a SEM photograph of the cross-section of carbon fibre precursor based precursor fibre spun from a spinning solution containing 5 wt. % gelling agent based on the total weight of the solution;

(6) FIG. 5-1 shows a SEM photograph of the cross-section of PAN fibre obtained when PAN/[BMIM]Cl is 1:1 after washed with water;

(7) FIG. 5-2 shows another SEM photograph of the cross-section of PAN fibre obtained when PAN//[BMIM]Cl is 1:1 after washed with water;

(8) FIG. 6 is a DMA curve diagram of the PAN fibre obtained when PAN/[BMIM]Cl is 1:1;

(9) FIG. 7-1 shows a SEM photograph of the cross-section of PAN fibre obtained when PAN/[BMIM]Cl is 1.2:1 after washed with water;

(10) FIG. 7-2 shows another SEM photograph of the cross-section of PAN fibre obtained when PAN/[BMIM]Cl is 1.2:1 after washed with water;

(11) FIG. 8 is a curve diagram illustrating the relationship between Tg and PAN content of the fibres obtained from PAN/[BMIM]Cl system before washed with water;

(12) FIG. 9 shows a SEM photograph of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and KMnO.sub.4/[BMIM]Cl is 0.01:100 after washed with water;

(13) FIG. 10 shows a SEM photograph of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and KMnO.sub.4/[BMIM]Cl is 0.1:100 after washed with water;

(14) FIG. 11 shows a SEM photograph of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and BPO/[BMIM]Cl is 0.01:100 after washed with water;

(15) FIG. 12 shows a SEM photograph of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and BPO/[BMIM]Cl is 0.1:100 after washed with water;

(16) FIG. 13 shows the infrared spectra of fibres obtained when PAN/[BMIM]Cl is 1:1 and KMnO.sub.4/[BMIM]Cl is 0.1:100;

(17) FIG. 14 shows the infrared spectra of fibres obtained when PAN/[BMIM]Cl is 1:1 and BPO/[BMIM]Cl is 0.1:100;

(18) FIG. 15 shows a filed emission SEM photograph at 10000 magnification for carbon fibres treated with polyacrylonitrile:multi-walled carbon nanotube:dimethylsulfoxide=0.05:0.5:100 by weight;

(19) FIG. 16 shows a filed emission SEM photograph at 10000 magnification for carbon fibres treated with polyvinyl alcohol:multi-walled carbon nanotube:N,N-dimethylformamide=0.05:0.5:100 by weight;

(20) FIG. 17 shows a filed emission SEM photograph at 10000 magnification for carbon fibres treated with polyvinyl alcohol:multi-walled carbon nanotube:water=5:0.05:100 by weight;

(21) FIG. 18 shows a filed emission SEM photograph at 10000 magnification for carbon fibres treated with -cyanoacrylate:multi-walled carbon nanotube:water=5:0.05:100 by weight;

(22) FIG. 19-1 is a flow diagram showing a process of producing PAN based carbon fibres in prior art;

(23) FIG. 19-2 is a flow diagram showing an improved process of producing PAN based carbon fibres;

(24) FIG. 20-1 shows the infrared spectra of PAN/IL pre-oxidized at 170 C. for different times, 1: not pre-oxidized; 2: 20 min; 3: 40 min; 4: 60 min; 5: 90 min;

(25) FIG. 20-2 shows the infrared spectra of PAN/IL pre-oxidized at 160 C. for different times, 1: 20 min; 2: 40 min; 3: 60 min; 4: 90 min; 5: 120 min; 6:150 min;

(26) FIG. 21 shows the infrared spectra of PAN/DMSO pre-oxidized at 175 C. for different times, 1: 4 hrs; 2: 5 hrs; 3: not pre-oxidized;

(27) FIG. 22 shows the infrared spectra of PAN precursor fibre pre-oxidized in oxidization furnace, 1: pre-oxidized at 250 C.; 2: not pre-oxidized.

EXAMPLES

(28) For a better understanding of embodiments of the present invention, together with the technical means, the characteristics and the purposes as well as effects thereof, reference is made to the following embodiments.

Example 1

(29) First, 5 g anhydrous PAN powder and 95 g DMSO solvent are uniformly mixed in a three-neck flask, while heated in an oil bath maintained at a temperature of 70 C., and stirred to completely dissolve PAN powder. After the PAN powder is dissolved, 2 g distilled water is added. Upon mechanical stirred for one hour, the slurry is transferred to a spinning machine for spinning, and the PAN based precursor fibre obtained by the gel spinning (in which the spinning temperature is 60 C., the coagulation bath temperature is 10-20 C., the primary washing temperature is 75 C., the secondary temperature is 100 C.) has a tensile strength of 4.31 GPa. FIG. 1 shows a SEM photograph (magnification factor of which is 15, 000) of PAN based precursor fibre spun from a spinning solution containing 2 wt. % gelling agent based on the total weight of the solution. It can be seen from FIG. 1 that the cross-section of the obtained PAN based precursor fibre is circle nearly without voids across the section and the precursor fibre is structural compact. Therefore, the tensile strength of the PAN based precursor fibre for carbon fibre is substantially increased.

Example 2

(30) First, 10 g anhydrous PAN powder and 90 g DMF solvent are uniformly mixed in a three-neck flask, while heated in an oil bath maintained at a temperature of 90 C., and stirred to completely dissolve the PAN powder. After the PAN powder is dissolved, 3 g ethylene glycol is added. Upon mechanical stirred for one hour, the slurry is transferred to a spinning machine for spinning, and the PAN based precursor fibre obtained by the gel spinning (the spinning condition is the same as those in example 1) has a tensile strength of 4.4 GPa. FIG. 2 shows a SEM photograph (magnification factor of which is 15, 000) of PAN based precursor fibre spun from a spinning solution containing 3 wt. % gelling agent based on the total weight of the solution. It can be seen from FIG. 2 that the cross-section of the obtained PAN based precursor fibre is circle nearly without voids across the section, and the precursor fibre is structural compact and skin-core structure is not observed.

Example 3

(31) First, 10 g anhydrous PAN powder and 90 g DMAc solvent are uniformly mixed in a three-neck flask, while heated in a sand bath maintained at a temperature of 90 C., and stirred to completely dissolve the PAN powder. After the PAN powder is dissolved, 4 g ethylene glycol is added. Upon mechanical stirred for one hour, the slurry is transferred to a spinning machine for spinning, and the PAN based precursor fibre obtained by the gel spinning (the spinning condition is the same as those in example 1) has a tensile strength of 4.2 GPa. FIG. 3 shows a SEM photograph (magnification factor of which is 25,000) of PAN based precursor fibre spun from a spinning solution containing 4 wt. % gelling agent based on the total weight of the solution. It can be seen from FIG. 3 that the cross-section of the obtained PAN based precursor fibre is circle nearly without voids across the section and the precursor fibre is structural compact.

Example 4

(32) First, 5 g anhydrous PAN powder and 95 g NaSCN solvent are uniformly mixed in a three-neck flask, while heated in an oil bath maintained at a temperature of 100 C., and stirred to completely dissolve the PAN powder. After the PAN powder is dissolved, 5 g urea is added. Upon mechanical stirred for one hour, the slurry is transferred to a spinning machine for spinning, and the PAN based precursor fibre obtained by the gel spinning (the spinning condition is the same as those in example 1) has a tensile strength of 4.5 GPa. FIG. 4 shows a SEM photograph (magnification factor of which being 15, 000) of PAN based precursor fibre spun from a spinning solution containing 5 wt. % gelling agent based on the total weight of the solution. It can be seen from FIG. 4 that the cross-section of the obtained PAN based precursor fibre is uniform nearly without skin-core structure and voids, and the precursor fibre is structural compact. Therefore, the tensile strength of the PAN based precursor fibre for carbon fibre is substantially increased.

Example 5

(33) First, 5 g anhydrous PAN powder and 95 g ZnCl.sub.2 solvent are uniformly mixed in a three-neck flask, while heated in an oil bath maintained at a temperature of 100 C., and stirred to completely dissolve the PAN powder. After the PAN powder is dissolved, 2 g thiourea is added. Upon mechanical stirred for one hour, the slurry is transferred to a spinning machine for spinning, and the PAN based precursor fibre obtained by the gel spinning (the spinning condition is the same as those in example 1) has a tensile strength of 4.51 GPa.

Example 6

(34) First, PAN powder and [BMIM]BF4 are uniformly mixed in a mass ratio of 1:1 in a high speed mixer. Then the mixture is transferred to a twin-screw spinning machine for melt spinning (in which screw speed is 50 r/min, the temperatures for feeding section, plasticizing section and melting section are set at 185 C., 190 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter). The spun fibre is subjected to a primary dry-heat drawing, a secondary dry-heat drawing, washing with water, oiling and thermosetting (in which the drawing ratio is 2-10 times, the drawing temperature is 90 C.-120 C. and the washing temperature is 25 C.-40 C.) to give PAN fibre. The obtained PAN fibre has a tensile strength of 2.8 cN/dtex and an elongation at break of 19.0%.

Example 7

(35) First, PAN powder and [BMIM]BF4 are uniformly mixed in a mass ratio of 1.2:1 in a high speed mixer. Then the mixture is transferred to a twin-screw spinning machine for melt spinning in which the screw speed is adjusted to 75 r/min, the temperatures for feeding section, plasticizing section and melting section are set at 180 C., 185 C. and 180 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to a primary dry-heat drawing, a secondary dry-heat drawing, washing with water, oiling and thermosetting to give PAN fibre. The obtained PAN fibre has a tensile strength of 3.6 cN/dtex and an elongation at break of 8.9%.

Example 8

(36) First, PAN powder and [BMIM]BF4 are uniformly mixed in a mass ratio of 1:1 in a high speed mixer. Then the mixture is transferred to a twin-screw spinning machine for melt spinning in which the screw speed is adjusted to 70 r/min, the temperatures for feeding section, plasticizing section and melting section are set at 185 C., 190 C. and 190 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to a primary dry-heat drawing, a secondary dry-heat drawing, washing with water, oiling and thermosetting to give PAN fibres. The obtained PAN fibre has a tensile strength of 4.0 cN/dtex and an elongation at break of 16.9%. FIG. 5 shows a SEM photograph of the cross-section of PAN fibre after washed with water. It can be concluded from the SEM photograph that the cross section of the fibre is circle without skin-core structure. FIG. 6 is the DMA curve diagram of the PAN fibre obtained with PAN/[BMIM]Cl of 1:1. It can be deduced from FIG. 6 that the glass transition temperature of PAN is decreased upon the addition of plasticizer and it is beneficial to drawing of macromolecule chain.

Example 9

(37) First, PAN powder and [BMIM]Cl are uniformly mixed in a mass ratio of 1.2:1 in a high speed mixer. Then the mixture is transferred to a twin-screw spinning machine for melt spinning in which the screw speed is adjusted to 60 r/min, the temperatures for feeding section, plasticizing section and melting section are set at 180 C., 185 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to a primary dry-heat drawing, a secondary dry-heat drawing, washing with water, oiling and thermosetting to give PAN fibres. The obtained PAN fibre has a tensile strength of 4.0 cN/dtex and an elongation at break of 14.3%. FIG. 7 shows a SEM photograph of the cross-section of PAN fibre after washed with water. It can be seen from the SEM photograph that the cross section of the fibre is nearly circle and the core is relatively structural compact resulting in the PAN based precursor fibre with relatively excellent physical and mechanical properties. FIG. 8 is a curve diagram illustrating the relationship between Tg and PAN content of the fibres obtained from PAN/[BMIM]Cl system before washed with water. It can be deduced from FIG. 8 that the glass transition temperature of PAN decreases with the decrease of the PAN content, i.e. [BMIM]Cl functions as a plasticizer during the melt spinning, the higher the [BMIM]Cl content, the lower the glass transition of the melt, and the more beneficial to drawing of the fibre during subsequent procedure.

Example 10

(38) First, Cobalt dichloride, a catalyst of PAN pre-oxidization is dissolved in an ionic liquid (1-butyl-3methyl-imidazolium chloride) in a weight ratio of 1:100. Then anhydrous PAN powder is added with the weight ratio of PAN powder to ionic liquid being 1:1. The obtained mixture is feed into a twin-screw spinning machine for melt spinning while blowing air through the melting section of the twin-screw spinning machine, wherein the air flow is 1 ml/min, the screw speed is 40 r/min, the temperatures for the feeding section, plasticizing section and melting section are 170 C., 185 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is directly subjected to dry-heat drawing (wherein the drawing temperature is 110 C., the total drawing ratio is 4 times). The drawn fibre is washed with water at 70 C., followed by thermoset in dry and hot air at 150 C. to give PAN pre-oxidization fibre with a pre-oxidization degree of 31%.

Example 11

(39) First, cobalt sulphate, a catalyst of PAN pre-oxidization is dissolved in an ionic liquid (1-butyl-3-methyl imidazolium tetrafluoroborate) in a weight ratio of 0.01:100. Then anhydrous PAN powder is added with the weight ratio of PAN powder to ionic liquid being 1:1. The obtained mixture is feed into a twin-screw spinning machine for melt spinning while blowing oxygen through the melting section of the twin-screw spinning machine, wherein the oxygen flow is 5 ml/min, the screw speed is 120 r/min, the temperatures for the feeding section, plasticizing section and melting section are 185 C., 220 C. and 220 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is directly subjected to dry-heat drawing (wherein the drawing temperature is 140 C., the total drawing ratio is 6 times). The drawn fibre is washed with water at 90 C., followed by thermoset in dry and hot air at 150 C. to give PAN pre-oxidization fibre with a pre-oxidization degree of 31%.

Example 12

(40) First, potassium permanganate particles and [BMIM]Cl are uniformly mixed in a three-neck flask in a weight ratio of 0.01:100. After the potassium permanganate is completely dissolved, the dried PAN powder and [BMIM]Cl are uniformly mixed in a high speed mixer in a weight ratio of 1:1, followed by transferred to a twin-screw spinning machine for melt spinning while blowing oxygen through the melting section of the twin-screw spinning machine, wherein the oxygen flow is 2 ml/min, the screw speed is 50 r/min, the temperatures for the feeding section, plasticizing section and melting section are 185 C., 190 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to dry-heat drawing (wherein the drawing temperature is 120 C., the total drawing ratio is 45 times). The drawn fibre is washed with water at 80 C., followed by thermoset in dry and hot air at 120-150 C. to give PAN pre-oxidization fibre with a pre-oxidization degree of 31%. FIG. 9 shows a SEM photograph of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and KMnO4/[BMIM]Cl is 0.01:100 after washed with water. It can be seen from FIG. 9 that the cross section of the pre-oxidized fibre is very compact in structure and nearly circle in shape, and that there is nearly no voids in the core, the density is increased and the pre-oxidized fibre has relatively excellent physical and mechanical properties.

Example 13

(41) First, potassium permanganate particles and [BMIM]Cl are uniformly mixed in a three-neck flask in a weight ratio of 0.1:100. After the potassium permanganate is completely dissolved, the dried PAN powder and [BMIM]Cl are uniformly mixed in a high speed mixer in a weight ratio of 1:1, followed by transferred to a twin-screw spinning machine for melt spinning while blowing oxygen through the melting section of the twin-screw spinning machine, wherein the oxygen flow is 2 ml/min, the screw speed is 50 r/min, the temperatures for the feeding section, plasticizing section and melting section are 185 C., 190 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to dry-heat drawing (wherein the drawing temperature is 120 C., the total drawing ratio is 45 times). The drawn fibres is washed with water at 80 C., followed by thermoset in dry and hot air at 150 C. to give PAN pre-oxidization fibre with a pre-oxidization degree of 67%. FIG. 10 shows a SEM photograph of part of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and KMnO4/[BMIM]Cl is 0.1:100 after washed with water. FIG. 13 shows the infrared spectra of fibres obtained when PAN/[BMIM]Cl is 1:1 and KMnO4/[BMIM]Cl is 0.1:100, wherein curve 1 is for pre-oxidized fibre and curve 2 is for precursor fibre. It can be concluded from FIG. 13 that the absorption peak of cyano group (2240 cm-1) upon oxidization decreases while the absorption peak of CN (1630 cm-1) increases, indicating that part of cyano groups are converted to CN upon pre-oxidization, facilitating the formation of intramolecular ring. It can be seen from FIG. 10 that the cross section of the pre-oxidized fibre is very compact in structure and there is no skin-core structure and no voids, the pre-oxidized fibre is structural uniform from surface to inside, and without skin-core structure as obtained by wet spinning

Example 14

(42) First, benzoyl peroxide and [BMIM]Cl are uniformly mixed in a three-neck flask in a weight ratio of 0.01:100. After the benzoyl peroxide is completely dissolved, the dried PAN powder and [BMIM]Cl are uniformly mixed in a high speed mixer in a weight ratio of 1:1, followed by transferred to a twin-screw spinning machine for melt spinning while blowing oxygen through the melting section of the twin-screw spinning machine, wherein the oxygen flow is 2 ml/min, the screw speed is 50 r/min, the temperatures for the feeding section, plasticizing section and melting section are 185 C., 190 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to dry-heat drawing (wherein the drawing temperature is 120 C., the total drawing ratio is 45 times). The drawn fibres is washed with water at 80 C., followed by thermoset in dry and hot air at 150 C. to give PAN pre-oxidization fibre with a pre-oxidization degree of 47%. FIG. 11 shows a SEM photograph of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and BPO/[BMIM]Cl is 0.01:100 after washed with water. It can be seen from FIG. 11 that the cross section of the pre-oxidized fibre is nearly circle in shape and is relatively compact in core and, and the pre-oxidized fibre has relatively excellent physical and mechanical properties.

Example 15

(43) First, benzoyl peroxide and [BMIM]Cl are uniformly mixed in a three-neck flask in a weight ratio of 0.1:100. After the benzoyl peroxide is completely dissolved, the dried PAN powder and [BMIM]Cl are uniformly mixed in a high speed mixer in a weight ratio of 1:1, followed by transferred to a twin-screw spinning machine for melt spinning while blowing oxygen through the melting section of the twin-screw spinning machine, wherein the oxygen flow is 2 ml/min, the screw speed is 50 r/min, the temperatures for the feeding section, plasticizing section and melting section are 185 C., 190 C. and 185 C., respectively, the aspect ratio of the spinneret is 1:3 and the orifices in the spinneret is 0.5 mm in diameter. The spun fibre is subjected to dry-heat drawing (wherein the drawing temperature is 120 C., the total drawing ratio is 45 times). The drawn fibres is washed with water at 80 C., followed by thermoset in dry and hot air at 150 C. to give PAN pre-oxidization fibre with a pre-oxidization degree of 73%. FIG. 12 shows a SEM photograph of part of the cross section of the fibre obtained when PAN/[BMIM]Cl is 1:1 and BPO/[BMIM]Cl is 0.1:100 after washed with water. It can be seen from FIG. 12 that the cross section of the pre-oxidized fibre is very compact in structure and there is no skin-core structure and no voids, the pre-oxidized fibre is structural uniform from surface to inside, and without skin-core structure as obtained by wet spinning FIG. 14 shows infrared spectra of fibres obtained when PAN/[BMIM]Cl is 1:1 and BPO/[BMIM]Cl is 0.1:100, wherein curve 1 is for pre-oxidized fibre and curve 2 is for precursor fibre. It can be concluded from FIG. 14 that the absorption peak of cyano group (2240 cm-1) upon oxidization decreases while the absorption peak of CN (1630 cm-1) increases, indicating that part of cyano groups are converted to CN upon pre-oxidization, facilitating the formation of intramolecular ring.

Examples 16-20

(44) Examples 16-20 are performed as Example 15 except that using different catalyst for PAN pre-oxidization and ionic liquids, as listed in the following table 1.

(45) TABLE-US-00001 TABLE 1 The catalyst for PAN pre-oxidization and ionic liquids as well as the pre-oxidization degree of the obtained fibres Catalyst for PAN Pre-oxidization No. preoxidization Ionic liquid degree (%) Example 16 K2S2O8 [EMIM]Cl 50 Example 17 Succinic acid [BMIM]Br 63 Example 18 Hydrogen peroxide [EMIM]BF4 82 Example 19 Ammonia [EMIM]BF6 68 Example 20 Hydroxylamine [BMIM]BF4 79 hydrochloride

Example 21

(46) 0.05 parts by weight of carboxylated multi-walled carbon nanotube (available from Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences, with length of 10-30 m, inner diameter of 10-20 nm, outer diameter of 5-10 nm) and 100 parts by weight of dimethylsulfoxide solvent are mixed, ultrasonic processed for 3 hrs in an ultrasonic cell disrupter operating at 300 w; to the resulting solution is added 0.05 parts by weight of polymer thickener PAN (with polymerization degree of 88,000 and particle size of 230 nm-250 nm) and ultrasonic processed for 2 hrs in an ultrasonic cell disrupter operating at 300 w. The oxidized PAN pre-oxidized fibre is dipped into the obtained solution in a solid-to-liquid ratio of 1:3 for 1 hr, and a coating of 200 nm is formed on the surface of the oxidized PAN pre-oxidized fibre. The oxidized PAN pre-oxidized fibre is carbonized at 1000 C. to give high strength carbon fibre. FIG. 15 shows a filed emission SEM photograph (magnification factor of which is 10,000) of carbon fibres treated with PAN:multi-walled carbon nanotube:dimethylsulfoxide=0.05:0.05:100 by weight. It can be seen from FIG. 15 that carbon nanotubes are uniformly attached to the surface of fibres and can repair voids on the surface of fibre so that the tensile strength of carbon fibre can be effectively increased.

Example 22

(47) 0.5 parts by weight of carboxylated multi-walled carbon nanotube (available from Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences, with length of 10-30 m, inner diameter of 10-20 nm, outer diameter of 5-10 nm) and 100 parts by weight of N,N-dimethylformamide solvent are mixed, ultrasonic processed for 1.5 hrs in an ultrasonic cell disrupter operating at 600 w. To the resulting solution is added 0.05 parts by weight of polymer thickener polyvinyl alcohol (with polymerization degree of 88,000 and particle size of 230 nm-250 nm) and ultrasonic processed for 1 hrs in an ultrasonic cell disrupter operating at 600 w. The oxidized PAN pre-oxidized fibre is dipped into the obtained solution in a solid-to-liquid ratio of 1:2 for 2 hrs; a coating of 200 nm is formed on the surface of the oxidized PAN pre-oxidized fibre. The oxidized PAN pre-oxidized fibre is carbonized at 1000 C. to give high strength carbon fibre. FIG. 16 shows a filed emission SEM photograph (magnification factor of which is 10,000) of carbon fibres treated with polyvinyl alcohol:multi-walled carbon nanotube:N,N-dimethylformamide=0.05:0.5:100 by weight. It can be seen from FIG. 16 that multi-walled carbon nanotubes are uniformly attached to the surface of carbon fibre and repair voids on the surface of carbon fibre, which is beneficial to increase of the tensile strength of carbon fibres.

Example 23

(48) 0.05 parts by weight of carboxylated multi-walled carbon nanotube (available from Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences, with length of 10-30 m, inner diameter of 10-20 nm, outer diameter of 5-10 nm) and 100 parts by weight of water solvent are mixed, ultrasonic processed for 2 hrs in an ultrasonic cell disrupter operating at 500 w. To the resulting solution is added 5 parts by weight of polymer thickener polyvinyl alcohol (with polymerization degree of 88,000 and particle size of 230 nm-250 nm) and ultrasonic processed for 1.5 hrs in an ultrasonic cell disrupter operating at 600 w. The obtained solution is electrostatically sprayed onto the surface of the oxidized PAN pre-oxidized fibre with a voltage of 80 kv, a spray distance of 25 cm and a rotation speed of spray gun of 2800 r/min to form a coating of 300 nm thereon. The oxidized PAN pre-oxidized fibre is carbonized at 1000 C. to give high strength carbon fibre. FIG. 17 shows a filed emission SEM photograph (magnification factor of which is 10,000) of carbon fibres treated with polyvinyl alcohol:multi-walled carbon nanotube:water=5:0.05:100 by weight.

Example 24

(49) 0.05 parts by weight of carboxylated multi-walled carbon nanotube (available from Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences, with length of 10-30 m, inner diameter of 10-20 nm, outer diameter of 5-10 nm) and 100 parts by weight of water solvent are mixed, ultrasonic processed for 1.5 hrs in an ultrasonic cell disrupter operating at 500 w. To the resulting solution is added 5 parts by weight of polymer thickener -cyanoacrylate (with molecular weight of 400-800, available from Shanghai Tailuo Company Ltd.) and ultrasonic processed for 1 hr in an ultrasonic cell disrupter operating at 500 w. The obtained solution is electrostatically sprayed onto the surface of the oxidized PAN pre-oxidized fibre with a voltage of 120 kv, a spray distance of 40 cm and a rotation speed of spray gun of 3000 r/min to form a coating of 100 nm thereon. The oxidized PAN pre-oxidized fibre is carbonized at 1000 C. to give high strength carbon fibre. FIG. 18 shows a filed emission SEM photograph (magnification factor of which is 10,000) of carbon fibres treated with -cyanoacrylate:multi-walled carbon nanotube:water=5:0.05:100 by weight. It can be seen from FIG. 18 that multi-walled carbon nanotubes are uniformly attached to the surface of carbon fibres and repair voids on the surface of carbon fibres, which is beneficial to increase of the tensile strength of carbon fibre.

Example 25

(50) 0.01 parts by weight of carboxylated Multi-walled Carbon nanotube (available from Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences, with length of 10-30 m, inner diameter of 10-20 nm, outer diameter of 5-10 nm) and 100 parts by weight of water solvent are mixed, ultrasonic processed for 1.5 hrs in an ultrasonic cell disrupter operating at 500 w. To the resulting solution is added 0.01 parts by weight of polymer thickener -cyanoacrylate and ultrasonic processed for 1 hr in an ultrasonic cell disrupter operating at 500 w. The obtained solution is electrostatically sprayed onto the surface of the oxidized PAN pre-oxidized fibre with a voltage of 100 kv, a spray distance of 30 cm and a rotation speed of spray gun of 2900 r/min to form a coating of 100 nm thereon. The oxidized PAN pre-oxidized fibre is carbonized at 1000 C. to give high strength carbon fibre.

Example 26

(51) 2 parts by weight of carboxylated multi-walled carbon nanotube (available from Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences, with length of 10-30 m, inner diameter of 10-20 nm, and outer diameter of 5-10 nm) and 100 parts by weight of dimethylacetamide solvent are mixed, ultrasonic processed for 1.5 hrs in an ultrasonic cell disrupter operating at 500 w. To the resulting solution is added 2 parts by weight of polymer thickener -cyanoacrylate and ultrasonic processed for 1 hr in an ultrasonic cell disrupter operating at 500 w. The obtained solution is electrostatically sprayed onto the surface of the oxidized PAN pre-oxidized fibre with a voltage of 120 kv, a spray distance of 30 cm and a rotation speed of spray gun of 2900 r/min to form a coating of 100 nm thereon. The oxidized PAN pre-oxidized fibre is carbonized at 1000 C. to give high strength carbon fibre. The mechanical properties of carbon fibres obtained from Examples 21-26 are shown in table 2.

(52) TABLE-US-00002 TABLE 2 Mechanical properties of carbon fibres obtained Mechanical properties Tensile strength Elongation at break Variation Elongation Variation Strength/GPa range (%) (%) range % Contrast (untreated) 3.18 8.90 Example 21 3.80 +22.64 13.5 +51.6 Example 22 4.35 +36.79 14.3 +60.6 Example 23 4.40 +38.36. 15.0 +68.5 Example 24 4.67 +46.85 16.3 +83.1 Example 25 4.78 +50.30 16.9 +89.8 Example 26 4.71 +48.11 16.0 +79.7

Example 27

(53) 1-butyl-3-methylimidazolium chloride ionic liquid and PAN powder are added in a reactor with mechanical stirrer. Upon the polymer is completely dissolved, a catalyst KMnO4 is added to facilitate cyclization of PAN. The weight percent of the above material are as follows: PAN, 5%; solvent, 95%. KMnO.sub.4 is added at 0.05 wt. % of PAN. The mixture is stirred at 170 C., oxygen is blown into the reactor at certain flow rate. The temperature and time of pre-oxidization is controlled and samples are collected when the reaction time is 20 min, 40 min, 60 min and 90 min, respectively, to get PAN spinning solutions with different pre-oxidization degree. FIG. 19-2 shows an improved process of producing PAN based carbon fibre used in this example. FIG. 20-1 shows infrared spectra of PAN/IL pre-oxidized at 170 C. for different time. It can be seen from the spectra that as the pre-oxidization time increases, the intensity of the absorption peak of CN group decreases and that of CN group increases, and the intramolecular cyclization degree increases.

Example 28

(54) 1-butyl-3-methylimidazolium chloride ionic liquid and PAN are added in a reactor with mechanical stirrer. Upon the polymer is completely dissolved, a catalyst KMnO4 is added to facilitate cyclization of PAN. The weight percent of the above material are as follows: PAN, 5%; solvent, 95%. KMnO.sub.4 is added at 0.05 wt. % of PAN. The mixture is stirred at 160 C., oxygen is blown into the reactor at 5 ml/min. The temperature and time of pre-oxidization is controlled and samples are collected when the reaction time is 20 min, 40 min, 60 min, 90 min, 120 min and 150 min, respectively, to get PAN spinning solutions with different pre-oxidization degree. FIG. 20-2 shows infrared spectra of PAN/IL pre-oxidized at 160 C. for different time. It can be seen from the spectra that as the pre-oxidization time increases, the intensity of the absorption peak of CN group decreases and that of CN group increases, and the intramolecular cyclization degree increases. However, the cyclization degree at 160 C. is lower than that at 170 C.

Example 29

(55) DMSO and PAN are added in a reactor with mechanical stirrer. Upon the polymer is completely dissolved, a catalyst KMnO4 is added to facilitate cyclization of PAN. The weight percent of the above material are as follows: PAN, 10%; DMSO, 90%. KMnO.sub.4 is added at 0.05 wt. % of PAN. The mixture is stirred at 175 C., oxygen-containing gas is blown into the reactor at a rate of 5 ml/min. The temperature and time of pre-oxidization is controlled, and pre-oxidization is proceeded for about 4-5 hrs to get PAN spinning solution. FIG. 21 shows infrared spectra of PAN/DMSO pre-oxidized at 175 C. for different time. It can be seen from the spectra that as the pre-oxidization time increases, the intensity of the absorption peak of CN group decreases and that of CN group increases, and the intramolecular cyclization degree increases.

Comparative Example 1

(56) First, a PAN/DMSO spinning solution is wet spun by conventional process. Then PAN precursor fibres are obtained after a series of post-treatments. PAN precursor fibre is pre-oxidized in a pre-oxidization furnace with 6 heating sections with the onset temperature of 170 C., the temperature is warmed up 10 C./10 min, while samples of pre-oxidized fibres are collected at different temperature, and finally maintained at 260 C. for 0.5 hr. The samples of pre-oxidized fibres are subjected to infrared analysis and compared with that obtained from the above two systems in terms of pre-oxidization degree. It has been found that the new process of spinning after the spinning solution being pre-oxidized can reach the same pre-oxidization degree as that obtained from conventional process, however, the pre-oxidization cost of the new process can be substantially decreased, and therefore the manufacturing cost of carbon fibres is decreased. FIG. 22 shows infrared spectra of PAN precursor fibre pre-oxidized in oxidization furnace. Compared with Examples 27, 28 and 29, the oxidization degree of comparative example 1 is comparative with that of Examples 27, 28 and 29, however the oxidization effect of examples 27, 28 and 29 is better and the process is simpler, therefore the cost of the subsequent carbon fibres manufacturing can be decreased.

(57) The basic principle, main characteristics and advantages of the invention are illustrated and described above. It should be understood by the skilled in the art that the examples and description are used to illustrate the principle of the invention and should not be taken as limiting the scope of the invention, and there will be various changes and modifications without departing the sprit and scope of the invention and those changes and modifications fall within the scope of the invention. The scope of the invention is defined by the accompanying claims and equivalents thereof.