The present invention relates to a method for preparing polymer composites comprising modified carbon nanotubes, polymer composite comprising modified carbon nanotubes and use of same in floor heating, heating of car seats, operating tables and clothing.

Carbon nanotubes are graphene layers rolled into hollow cylinders (typically single layer carbon atoms) . Due to their structure, they are also considered as one-dimensional objects, as the length to diameter ratio of nanotubes may be in the order of millions. Nanotubes have unusual properties, such as: very high tensile strength or unique electrical properties and very good thermal conductivity. With these unique characteristics they have a high application potential. Of particular interest are multi-walled carbon nanotubes made of concentric graphene layers. Due to the high chemical resistance, their properties can be modified by breaking some of the bonds between carbon atoms. The main challenge when using carbon nanotubes is the method of bonding them with the carrier material that may be subject to functionalization, such as polymer matrices . Solutions based on the use of carbon nanotubes as polymer fillers have been known for many years, however, a fundamental problem is to obtain a homogenous dispersion of carbon nanotubes in the polymer matrix. The existing solutions involve preparation of a dispersion by means of surfactants, followed by application of a mixture so obtained to the prepared polymer precursors or the final polymer dispersion. Because chemicals must be used to disentangle the fibres of carbon nanotubes, the composites are characterised by a limited mechanical strength and flexibility. Another solution is to disperse raw nanotubes in the polymer matrix, however, it is not possible to obtain a homogenous structure of composites so prepared. Such a system exhibits good electrical performance with limited applicability due to poor mechanical characteristics. Patent PL392221 discloses a method to prepare a carbon nanotubes incorporated cellulose nanocomposite . Such material has better current-voltage performance in the case of pure and modified cellulose fibres, and has better mechanical performance as compared with pure and modified carbon nanotubes. The said method involves preparation of first solution of cellulose in a hydrophilic ionic liquid, preparation of the second solution of carbon nanotubes in a hydrophilic ionic liquid with anionic surfactant, followed by precipitation of the said nanocomposite from the solution with water. Tubes are dispersed in a hydrophilic liquid in the presence of an anionic surfactant by ultrasonic treatment, resulting in breaking up the nanostructure agglomerations with carbon nanofibres becoming separated from each other. In addition, the surfactants reduce viscosity of the liquid and lower the surface tension of nanotube agglomerates. Patent PL391415 discloses a method for preparing carboxylated or carboxylated and hydroxylated carbon nanotubes without impurities of oxidizing agents that are difficult to remove, by pre-oxidising carbon nanotubes in the solid phase in air atmosphere to red glowing heat at 500-700 °C in a microwave field. Then, nanotubes are further oxidized by exposing them to a cooling or cooling-oxidizing liquid medium, and the suspension is subjected to ultrasonic treatment. After the suspension is dispersed, the oxidized carbon nanotubes are filtered or centrifuged, washed and dried until a loose, free-flowing product is obtained. The said method is characterized by purity combined with the presence of hydrophilic groups on the surface. The main challenge is posed by the complicated purification process, the need to ensure anaerobic atmosphere and a large amount of carbon on the surface of nanotubes. On the other hand, patent PL383273 discloses a method of using carbon nanotubes for the coating of fibres in particular intended for the manufacture of heating materials. The possess for using carbon nanotubes for fibre coating is characterized in that carbon nanotubes, after being purified from amorphous carbon, are enriched with hydrophilic functional groups, and then converted to the ammonium salt. The solution of modified carbon nanotubes is then used for coating fibres or fabrics. The method according to the said invention, only involves coating of cellulose or cellulose/polymer substrates. Due to the presence of hydroxyl groups on the surface of cellulose, they can be bonded with modified carbon nanotubes using a chemical catalyst. The patent application KR20120065494 presents a flexible heat mat of DC voltage, in the form of a thin fabric layer enriched with carbon nanotubes, eliminating the need for metallic conductors, such as copper. In the cited patent, carbon nanotubes are integrated with the fabric structure, which is characterized by a low mechanical strength, especially to puncture and tear, and is liquid-absorbing, thus offering limited applicability. The technical challenge of the present invention is to propose a polymer composition enriched with multi-walled carbon nanotubes to enable fabrication of low-voltage heating mats that would be resistant to mechanical and chemical damage, safe to use and at the same time flexible enough to allow for folding and unfolding in the full range from 0° to 360°, to apply and trim the heating module to suite the size of the area to be heated. The first object of the invention is a method for fabricating a polymer composite, comprising modified carbon nanotubes, involving the following steps: a) diaminobenzene is added to a dispersion of nanotubes in heptanes until the pH value of the solution is 9, b) halogenated silicon compounds with hydrocarbon systems attached are added to the solution from step a, c) mixture from step b) is stirred on a magnetic stirrer, d) preparation from step c) is dissolved in a nonpolar solvent, e) chemically inert silicone is dissolved in a nonpolar solvent, f) chemically inert silicone is mixed with the dissolved preparation comprising carbon nanotubes, wherein diaminobenzene from step a) is a 2% solution in isopentanol, halogenated silicon compounds from step b) are a 2% solution in heptane, stirring in step c) is carried out for 30 min at 2000 rpm, wherein the carbon nanotubes dispersed in heptanes in step a) are from 20 nm to 120 nm long and have a diameter from 5 nm to 15 nm. In a further preferred embodiment of the invention, the method is characterized in that up to 5 wt% of ethanol or isobutanol is added to the dispersion of nanotubes during stirring on the magnetic stirrer in step c) . In a further preferred embodiment of the invention the method is characterized in that in step b) the tri (tri , 4, 7, 9-pentyl ) nonane ethoxy silane is used as a silicon compound. Even more preferably, the method according to the invention is characterized in that the nonpolar solvent is selected from a group consisting of hexane, toluene, dearomatised gasoline, mixture of dearomatised gasoline and turpentine, turpentine oil, mixture of turpentine and butyl acetate. Most preferably, the method according to the invention is characterized in that the ratio of dissolved chemically inert silicone preparation containing dissolved carbon nanotubes is in the range from 1:1 to 1000:1.

The second object of the invention is a method for fabricating a polymer composite, comprising modified carbon nanotubes, involving the following steps: a) phenylhydrazine with ammonia is added a dispersion of nanotubes in heptane until the pH value of the solution is 9, b) halogenated silicon compounds with hydrocarbon systems attached are added to the solution from step a, c) mixture from step b) is stirred on a magnetic stirrer, d) preparation from step c) is dissolved in a nonpolar solvent, e) chemically inert silicone is dissolved in a nonpolar solvent, f) chemically inert silicone is mixed with the dissolved preparation comprising carbon nanotubes, wherein the solution added in step a) is 5% phenylhydrazine with 27% concentrated ammonia solution, halogenated silicon compounds are a 2% solution in heptane, stirring in step c) is carried out for 30 min at 2000 rpm, wherein the carbon nanotubes dispersed in heptane are from 20 nm to 120 nm long and have a diameter from 5 nm to 15 nm. Equally preferably, phenylhydrazine is dissolved in butyl acetate. More preferably, the method according to the invention is characterized in that the organosilicon system is enriched with fatty acid chains. In the further preferred embodiment of the invention, the nonpolar solvent is selected from a group consisting of hexane, toluene, dearomatised gasoline, mixture of dearomatised gasoline and turpentine, turpentine oil, mixture of turpentine and butyl acetate. Most preferably, the method according to the invention is characterized in that the ratio of dissolved chemically inert silicone preparation containing dissolved carbon nanotubes is in the range from 1:1 to 1000:1.

The third object of the invention is a modified polymer composite comprising carbon nanotubes, wherein it has been prepared by a method as defined in the first or second object of the invention.

Also preferably, the composite according to the invention is characterized in that the content of carbon nanotubes is from 0.5% to 15%, by weight. More preferably, the composite according to the invention is characterized in that it has a texture which is suitable for application to substrate by spray, roller, brush or other known method.

The fourth object of the invention is the use of a polymer composite comprising modified carbon nanotubes as defined in any previous object of the invention for fabrication of flexible heating mats.

The polymer composition with integrated multi-walled carbon nanotubes according to the invention allows to smoothly achieve the working temperature, depending on the applied voltage, current, and heating layer thickness and the type of nanotube medium applied to polymer matrix. The invention may be used to fabricate a heating film on the surface of hydrophobic silicones and mixtures of the same with other polymers. The specific surface structure and the dispersion method allow to fabricate nanostructured materials with very good electrical performance.

Exemplary embodiments of the invention are illustrated on the drawing, where Fig. 1 shows a heating mat with a power supply system, described in the third embodiment and Fig. 2 shows a heating mat with a power supply system as described in the fourth embodiment .

Example 1

Raw carbon nanotubes (10 g) were placed in a round bottom flask (2 litres) and 300 ml of nitric acid was added. The whole was mixed in a high-speed mixer at 22 000 rev/min for 2 hours. 200 ml of 30% hydrogen peroxide was added to the dispersion so obtained and mixed again for 30 minutes. After this time the solution was placed in ultrasonic reactor for 6 hours. 200 ml of concentrated nitric acid and 150 ml of concentrated sulphuric acid were added to the obtained mixture. The whole was placed under a return cooler and then boiled for 4 hours. The obtained mixture was filtered, the precipitate was transferred to a flat bottom flask (2 litres) poured over with 3% hydrobromic acid solution (1 litre) and placed in ultrasonic reactor for 20 minutes. Subsequently, the mixture was filtered, the precipitate was placed in a 500 ml flat-bottomed flask and 100 ml of concentrated HBr was added. The mixture was placed in a microwave reactor for 1 hour. After filtration, neutralization of excess HBr with ammonia to pH 10, re-filtration and drying - the material serves as an input material for further applications. Example 2

Raw carbon nanotubes (10 g) were placed in a round bottom flask (2 litres) and 300 ml of nitric acid and 100 ml of sulphuric acid was added. The whole was mixed in a high-speed mixer at 15 000 rev/min for 1 hour. 500 ml of water was added to the dispersion so obtained and filtered. Then, the precipitate was placed in a flat bottom flask, 200 ml of 30% hydrogen peroxide was added and placed in ultrasonic reactor for 30 min. After filtration, washing with water, the precipitate was placed in a 2000 ml round bottom flask and 400 ml of concentrated nitric acid and 150 ml of concentrated sulphuric acid was added. The whole was placed under a return cooler and boiled for 4 hours. The obtained mixture was filtered, the precipitate was transferred to a flat bottom flask (2 litres), poured over with demineralised water (600 ml), placed in ultrasonic reactor for 120 min. Subsequently, the mixture was filtered, the precipitate was placed in a 500 ml flat-bottomed flask and 100 ml of concentrated HBr was added. The mixture was placed in a microwave reactor for 2 hours. After filtration, neutralization of excess HBr with ammonia solution to pH 10, re-filtration and drying - the material serves as input material for further applications.

Example 3

50 ml of 2% diaminobenzene dissolved in isopentanol was added to the dispersion of nanotubes in 200 ml 4% heptane solution obtained in the first embodiment. After stirring and achieving pH 9 by means of diaminobenzene, halogenated silicon compounds containing triethylchlorosilane, dichlordimethylsilane, triheksylobromosilan with attached hydrocarbon systems in 20 ml of 2% heptane solution. Then, the prepared solution was stirred with magnetic stirrer for 30 min at 2000 revolutions per minute to form an input material for bonding with inert silicon, not containing acidic and basic functional groups, but only methyl, ethoxyl and hydroxyl functional groups. During stirring on magnetic stirrer, 5 wt% ethanol was added to the nanotubes dispersion. Then, the Protectosil product, i.e. tri (tri , 4, 7, 9-pentyl ) nonane ethoxy silane was used in the reaction. The so obtained preparation was dissolved in a nonpolar solvent, a 1:1 mixture of turpentine and dearomatised gasoline. The chemically inert FD80 silicone, built of chains enriched with ethoxy groups, was dissolved in the same nonpolar solvent. Preparation with carbon nanotubes dissolved in nonpolar solvent was mixed with silicone dissolved in nonpolar solvent in a 1:1 ratio, and then applied to the desired surface by a roller and dried to produce a finished product. Supplying electrodes (E), spaced at a distance K of 10 cm, were arranged on the obtained mat with two layers of heating composite, as shown in Fig. 1. The mat composite saturation with nanotubes was between 1% to 1.5%, with the layer thickness of 2 mm. The mat is supplied with 24V/3A AC voltage at a frequency of 50 Hz, using voltage control. The composite so obtained had a working range from 20 °C to 80 °C and 30 s time of reaching 80 °C.

Example 4 100 ml of 5% phenylhydrazine in concentrated 27% ammonia solution was added to the dispersion of nanotubes in 200 ml of 4% heptane solution obtained in the second embodiment. After stirring and achieving pH 9 by means of diaminobenzene, halogenated silicon compounds with hydrocarbon systems attached were added, as in embodiment 3. Then, the prepared solution was stirred with magnetic stirrer for 30 min at 2000 revolutions per minute to form an input material for bonding with inert silicon, not containing acidic and basic functional groups, but only methyl, ethoxyl and hydroxyl functional groups. The so obtained preparation was dissolved in a nonpolar solvent, a 1:1 mixture of turpentine and butyl acetate. The chemically inert E80 silicone, built of chains enriched with ethoxy groups, was dissolved in the same nonpolar solvent. Preparation with carbon nanotubes dissolved in nonpolar solvent was mixed with silicone dissolved in nonpolar solvent in a 100:1 ratio, and then applied to the desired surface by spraying and dried to produce a finished product. The achieved resistance of the applied layer was 20Ω. Supplying electrodes (E) , spaced at a distance L = 15 cm, were arranged on the obtained mat with 4 layers of heating composite, as shown in Fig. 2. The mat is supplied with 24V/3A AC voltage at a frequency of 50 Hz, using voltage control. The composite so obtained enabled working temperatures up to 100 °C reached in no more than 20 seconds .