GRAPHENE-REINFORCED POLYMERS, PROCESS FOR PRODUCING

GRAPHENE-REINFORCED POLYMERS AND THE USE OF SAID ADDITIVE

The present invention relates to a graphene-based composition, particularly in the form of dispersion, comprising at least one graphene-like filler material and at least one chemical, preferable, from at least one chlorinated paraffin. The present invention likewise relates to the use of the composition and to a process for preparing it.

Description

Graphene-based compositions based on chlorinated paraffin as filler for reinforcing polymers

The present invention relates to a graphene-based composition according to claim 1 , its use according to Claims 9 and 10 and a method for their preparation according to claim 11.

Polymer materials such as rubber, plastics, thermosets, binders, adhesives, varnishes or lacquers are widely used in many applications depend on their certain properties. However, usually polymer materials are thermal and electrical insulators. To increase the barrier of the polymer materials properties addition of the specific fillers to polymers is required. Graphene demonstrates excellent mechanical properties as it was measured by Atomic Force Microscopy (C. Lee, X. D. Wei, J. W. Kysar, J. Hone, Science, 2008, 321 , 3851 ). Thus, graphene can react as an excellent modification additive of the polymer properties, by mixing with polymer. However, graphitic structure of the graphene is extremely inert with weak wettability by either: hydrophilic and hydrophobic media. To date it has not been possible to produce polymer compositions with using pure graphene. Chemical modification of the graphene surface is required.

Graphene-based compositions are the dispersion of the graphene in the chemicals is using as component in plastics, thermosets, coatings, paints, varnishes, adhesives, lacquers in order to improve (stiffness, elasticity, toughness, hardness) or provide (electrical conductivity, thermal conductivity) properties. Mixing graphene and polymer themselves is not sufficient for improvement any properties of the polymer. This means that in case of bad contact at the interface graphene-matrix the effect of the filler addition drops down dramatically. For efficient graphene application the interface between graphene and matrix must have the right structure to provide most efficient compatibility between both components. Interfacial modification serves as the connection between graphene-based filler and polymer matrix and prevent the insulating the properties enhancement. Interfacial modification must transfer unique graphene properties with its good distribution to the macroscopic volumes of the materials.

Graphene-based composition is a mixture comprising a binder in the form of a liquid and a graphene material, for example, in the form of filler particles. Thus, the dispersion has a good processing and dissemination capability that is preferably characterized by an optimal compatibility with the polymer. Furthermore, the proportion of the graphene component must not exceed a certain limit, so that the dispersion composition has a good homogeneity.

Widely used polymer materials required reinforcement by graphene-based composition according to the present invention comprises but not limited are polyethylene, polypropylene, polyamide, polyether ketone, polysulphone, polyetylenethereph- thalate, polyurethane, polyvinylchloride (PVC), natural rubber, butadiene rubber, nitrile butadiene rubber, acrylonitrile butadiene rubber, styrene-butadiene rubber (SBR), isobutylene isoprene rubber, ethylene propylene diene monomer rubber, acrylic rubber, alkyl acrylate copolymer etc.

Commonly, carbon black is widely used filler for the reinforcement of the polymer compositions. However, disadvantage is the high filler content and poorer properties enhancement, below 20-30 %.

Because of polymer materials are not expensive, lightweight the demand in high efficient reinforced polymer materials is drastically increased last decades. To increase the reinforcement efficiency of the polymer materials various approaches have been described.

One approach is to provide a reinforced PVC plastisol resin which contains a reinforcing component, such as metal fibers, glass fibers, carbon fibers, ceramic fibers, aramid fibers, synthetic organic fibers, synthetic inorganic fibers, natural inorganic fibers and natural organic fibrous materials (US 20080,318,042 A1 ).

US 4,374,941 A describes the use of a carbon black (CB) dispersed in water and coagulated with SBR latex for SBR-CB particles size control and improvement of the composition properties. Electrically conductive SBR rubber composition filled with graphite is known from US 3,301 ,799. This composition is characterised by long term stable electrical resistance of 90,000 to 120,000 ohms after 1 month, which is based on the inclusion of the conductive graphite particles well dispersed in rubber by use of the wetting agent Triton X-100.

The carbon nanotube containing rubber composition described, however, have various disadvantages. As is used in US 2013 0 ,261 ,246 A1 as a reinforcing agent used carbon nanotube. That required significant mixing in two or more stages, and the mixing in different apparatus, for example one stage in an internal mixer and one stage in an extruder. Within proposed technology unwanted pre-crosslinking (=scorch) occurs during the mixing stage.

EP 2070093 A1 describes functional graphene rubber composites with application of the graphene oxides as a reinforcing agent. However, graphene oxides contain oxygen functionalities up to 40 % at. Such significant amount of oxygen makes graphene oxide highly hydrophilic and extremely hygroscopic with significant water content depending on humidity, and remains in the structure even after drying. Such phenomenon is disadvantage for many applications of the rubber compositions.

The invention is therefore based on the problem to provide a rubber composition, which does not have the abovementioned disadvantages.

According to the authors overview, chloroparaffine is an excellent candidate in creation of the novel graphene based compositions. Korea Kumho Petrochemicals in US2013/ 020752 invented the method for preparing a carbon nanomateri- al/polymer composite using paraffin wax for pelletizing carbon nanomaterial and preparing polymer composite. However, such method is applied for carbon nano- tubes which are toxic materials and required making materials different from the powder stage. Thus, pelletizing carbon nanomaterials with additive really solves problem of dust in production processes, however dispersion improvement must be done by proper way.

KR 20130121294 discloses a modification of graphene used as a nanocomposite material. Graphene is modified by generation of the amino groups on the graphene surface followed by reaction with halogenated hydrocarbons, whereof the halogen type is chloride or bromide. However, modification is made with low molecular weight halides, such as alkyl chloride, vinylic chloride, aryl chloride. Modification by the compound with higher molecular weight (C ₁₀ - C ₃₀ ) and with high chlorination degree (30 - 70 %) may be very difficult with sterical effects during attachment of big molecules, on one hand, and possible crosslinking between graphene particles where to one chloroparaffine molecule number of graphene particles can be grafted destroying dispersion quality and properties of polymer composites.

The CN104151696 invention provides a method for preparing a graphite-modified polypropylene plastic composite pipe with use of paraffin wax as a dispersant in process of modifying graphene. However, in case of plastic composites by the inventor ^' s approach, process requires the stage of drying modified graphene powder on top of use of paraffin wax, which is different in chemical structure, and has melting point in range of 47 - 65 degree.

The CN101885881 invention relates to a heat resistant and flame retardant PVC cable production method by use chloroparaffine as flame-retardant plasticizer in combination with graphite particles, which have mesh size greater than 2000 meshes. According to Ken Kosanke table there are really big graphite particles of greater than 2.4 mm size, when enhancement of the mechanical properties is achievable with graphene of 1 to 2 nanometers in thickness.

This object is achieved by a graphene-based composition with the features of claim 1.

Accordingly, graphene-based composition in the form of dispersion, comprising at least one graphene-like filler material and at least one chemical, preferable, from at least one chlorinated paraffin.

The graphene-based composition the invention allows rapid improvement of the mechanical properties of the rubber composites due to the good dispersion of the graphene-like filler material in rubber and stress transfer from the polymer matrix to monolayer graphene, showing that the graphene acts as a reinforcing phase. In one embodiment, the graphene-based composition comprises 0.01 to 99.99% by weight, preferably 0.1 to 80% by weight, particularly preferably 1 to 65 wt% of at least one graphene-like filler material, and 0.01 to 99.99 wt %, preferably 20 to 99.9% by weight, particularly preferably 35 to 99% by weight of at least one chemical, preferable, from at least one chlorinated paraffin.

The mechanical properties enhancement of the polymer materials with application of the inventive composition includes increasing the modulus. In one embodiment, the improving the mechanical properties of a polymer materials with application of the inventive composition includes increasing strength. In an embodiment, the improving the mechanical properties of a polymer materials with application of the inventive composition includes increasing toughness. In an embodiment, the im- proving the mechanical properties of polymer materials with application of the inventive composition includes increasing the modulus and the modulus is increased by 10% or more, preferably the modulus is increased by 100% or more, more preferably the modulus is increased by 200% or more and further preferably the modulus is increased by 300% or more.

The particle size of the used graphene-like filler materials will vary and have different sizes in X-Y direction and different thickness said number of graphitic layers. Thus, the graphene-like filler materials are the combination of particles in the nanometer and micrometer range, in particular less than 5 μιη. The thickness of the graphene-like filler materials can be chosen differently, from 0.345 nm for single layer graphene (SLG) up to 100 nm for graphene nanoplatelet (GNP) or nanograph- ite (NG). Almost all fillers are commercially available from specialty dealer Ceal- Tech, XG Sciences, Graphenea, Angstron Materials, Thomas Swan, Applied Graphene Materials, but not limited in above mentioned companies.

In a particularly preferred embodiment single layer graphene can be used as graphene-like filler materials. CVD synthesized graphene, CCVD synthesized graphene, PECVD synthesized graphene, reduced graphene from graphene oxide, exfoliated graphene are preferably used as a graphene-like filler materials. Graphene filler materials may also be in form a single graphitic layer sheet and / or multi graphitic layer sheets. The graphene have in particular thickness between 0.345 and 100 nm. In a preferred embodiment, the graphene is uniformly distributed in the dispersion and is under shear forces forming graphene network in composition. By this configuration, the mechanical and thermal of the composition is increased. The graphene may also be present in a modified form. Thus, graphene edges may be func- tionalized with carboxyl, hydroxyl, epoxy, halogen, amino groups or mixture of thereof. Functionalized graphene may be decorated, for example, with metal or metal oxide particles.

However, it is preferred if they are not decorated or modified with the use of metal- containing component.

Patent WO 2005/ 006403 A2 described thermal paste overfilled with the carbon particles. In such case, it produces a problem with the viscosity of the paste, its handling and application.

In the inventive composition graphene-like filler materials is dispersed in chemical, preferable chlorinated paraffin. Chlorinated paraffin in the inventive composition is linear or cyclic hydrocarbons with a carbon chain length above C ₁₀ and particularly of C10-30 and including a random substitution of chlorine atoms in the hydrocarbon chain wherein the substitution ratio is up to 70 % based on the number of carbon atoms in the olefin chain.

EP0114300 A1 described liquid developer for the development of electrostatic charge images based on carbon black. Chlorinated paraffin was used in the composition increasing homogeneity of the paint coatings.

Chlorinated paraffin in the inventive composition is having a viscosity between 60 mPa and 5000 mPa, preferably between 280 and 2200 mPa. The viscosity values apply at 60° C.

Chlorinated paraffin (CP) in the inventive composition is combined with graphene in a ratio 0.01 to 99.99% by weight, preferably 0.1 to 80% by weight, particularly preferably 1 to 65 wt% of at least one graphene material.

During composition processing, graphene-like filler materials in raw or modified form is treated mechanically or chemically with chlorinated paraffin to provide the uniform dispersion. The viscosity of the dispersion of the graphene-like filler material in CP can be in a wide range of 60 mPa to 50000 mPa, preferably 280 to 20000 mPa, depending on the need and depending on the filler concentration and composition in final polymer / rubber composite. During processing, no additional solvent, catalyst or initiator is required.

The use of chlorinated paraffin has a number of advantages over the typically used chemicals in functionalization of the graphene surface. Processing does not require additional stage of the precipitation, filtration, centrifugation or any other mechanical processes for extract graphene-like filler materials from the chlorinated paraffin media. The graphene-like filler materials modified with CP is in form of dispersion which is traditionally used in polymer of rubber materials production. Chlorinated paraffin has many versatile applications as plasticisers mainly in plastics and coatings, binders in varnishes, as an additive in joint sealants, in metal processing, in fat liquors for leather and fur goods and as a flame retardant in plastics, rubber, paper and textiles. Graphene-like filler materials dispersed in CP may improve the specific properties in all abovementioned applications of chlorinated paraffin. Additionally, CP is chemically grafted to graphene surface via Friedel-Craft alky la- tion of graphitic structure, by use of with aluminum trichloride, AICI ₃ , a Lewis acid catalyst. Georg Olah and his team (G.A. Olah, I . Busci, D.S. Ha, R. Aniszfeld, C.S. Lee, G.K.S. Prakash, Fullerene Sci. and Technol., 1997, 5:2, 389) synthesized polyhalogenated fullerenes which were used in further organic synthesis.

In another work authors (N. Tagmatarchis, V. Georgakilas, M. Prato, H. Shi- nohara, Chem Commun. 2002, 2010) reported covalent functionalization based on the reaction of the single-wall carbon nanotubes with chloroform in the presence of AICI ₃ . Such nanotubes are used for further modification work.

Hu and team (F. Hu, M. Patel, F. Luo, C. Flach, R. Mendelsohn, E. Garfunkel, H. He, M. Szostak, J. Am. Chem. Soc, 2015, 137(45), 14473) used transition- metal-alkylation of arenes catalyzed by graphene to produce valuable diarylalkane products in high yields and excellent regioselectivity.

Any of those scientific works are focused on organic synthesis reactions in presence or on the carbon nanotubes and fullerenes surface. However, there is no evidence of the using alkylation reactions as creation organic compatibilizing layers onto graphene surface. Sun and Baker (Y. J. Sun, W. E. Baker, J Appl. Polym. Sci., 1997, 65, 1385) realized the Friedel-Crafts alkylation in a polyethylene / polystyrene (PE/ PS) melt blend, which resulted in improved compatibility between PE and PS. A number of Lewis acid compounds were tested as catalysts, among which the AICI3 was the most efficient. It was found in this study that the presence of a co-catalyst, such as a cationically polymerizable monomer or a halogenated alkane, significantly enhances the formation of PE-g-PS copolymer. The effects of blending parameters, such as temperature and blending time, on the in situ copolymer formation were investigated. The mechanical properties of compatibilized PE/PS blends were improved considerably. Such an in situ compatibilization technique has potential in the recycling of mixed polymer wastes.

A very important advantage of these dispersions is their excellent flame retardant properties due to a cleavage of non-combustible hydrogen chloride at high temperatures, which is combined with ability of the graphene-like filler materials significantly increase heat absorption resulting in decrease of time to ignition and minimizing flame. The addition of further additives such as dispersing agent and / or at surface-active substance and other substances may improve the quality of the graphene-like filler materials dispersion in chlorinated paraffin.

In the embodiment, the dispersing agent is selected from the group consisting of non-ionic and ionic surfactants, in particular polyisobutenesuccinimide.

In the further embodiment, Friedel-Craft alkylation of the graphene surface with chlorinated paraffin for grafting reaction of the CP followed by self-compatibilizing of Chloroparaffinated graphene in CP for plasticizing rubber- and /or polymer- based materials.

The invention composition is preferably used as additive for enhancement of the mechanical, thermal, electrical, optical, antibacterial properties in the processing of plastics, coatings, varnishes, joint sealants, leather and fur goods, paper and textiles, said host matrix.

Another major advantage of the compositions according to the invention is the low thermal expansion coefficient of the graphene. Due to the modified interface between graphene-like filler materials and host matrix the matrix polymer adheres to the surface of the graphene-like filler materials. This minimizes the thermal expansion as particular graphene fillers has very negative coefficients of thermal expansion of approximately -8 ^* 10 ^"6 K ^"1

The object of the present invention is also achieved by a method having the features of claim 11. Thereafter, the process for preparing a graphene-based composition, in particular in form of dispersion, the following steps: a) preparing graphene- like filler materials by modifying its form by mechanical or chemical treatment, and b) dispersion preparation by mixing with chlorinated paraffin, where step (a) optionally in part repeated mechanical homogenization of the composition. Thus, there is an in-situ embedding the at least one graphene-like filler materials in the at least one chlorinated paraffin forming dispersion.

The preparation of the graphene-like filler materials in step a) may conveniently be effected by ultrasonic treatment of the sample, by a ball mill or a roll mill.

The method may also be preferred for part of the in situ dispersion manufacturing step. Thus, the graphene-like filler materials in the chlorinated paraffin are dispersed.

The method leads to formation of a long-term stable composition by manufacturing the in situ graphene-like filler materials dispersion in chlorinated paraffin. While graphene-like filler materials in hydrocarbons produced in the way different from the invention show phase separations after one month of preparing, the graphene- like filler materials dispersion in chlorinated paraffin prepared by in situ manufacturing demonstrates high stability. This stability indicates that, in the case of using in situ mechano-chemical treatment graphene-like filler materials with chlorinated paraffin strong interaction between Graphene and CP may occur. The steric effects created by molecules of chlorinated paraffin prevent from interaction between graphene-like filler materials and as result from aggregation and sedimentation of the solid particles from dispersion.

The invention will now be described in connection with embodiments using several figures. In the drawings:

Figure 1 is a graphical representation of the stability test of the 0.1% wt. graphene-like filler materials dispersion in chlorinated paraffin.

Figure 2 is a schematic representation of the Friedel-Craft alkylation of graphene with chlorinated paraffin.

Figure 3 is a XPS spectrum of the graphene-like filler materials after Friedel-Craft alkylation with chlorinated paraffin.

Figure 4 is a graphical representation of the pressure change during dispersion processing.

Figure 5 is a comparative image of the dispersion of the graphene-like filler materials before and after functionalization with chlorinated paraffin.

The diagram in Figure 1 illustrates the change intensity of the different graphene- like filler materials in chlorinated paraffin dispersion obtained through sonication with 0.1 mg/ml of graphene. After 30 min sonicating and 5 min rest, UV-vis spectra were collected and the dispersions absorbance change over 60 min (from 200 to 1100 nm) were recorded. As figure 1 indicates, the curves of the UV-vis spectra are parallel in a wide range for different times as it was expected. The spectra are just shifted due to the absorbance changing in time as a result of the change of optical density of the dispersion which strongly depends on graphene concentration in dispersion. Neighbouring wavelengths have a comparable absorbance. The interaction between graphene-like filler materials with the chlorinated paraffin via Firedel-Craft Alkylation in presence of aluminium chloride is shown in Figure 2. Reaction preferably is occurred by enhancement of the electrophilicity of the CP by complexing of the AICI ₃ with chlorinated paraffin following by rearrangement of the carbocation and deposition long chloro-containing CP chains onto graphene surface building the sterical barrier of stabilization against agglomeration and giving good performance in dispersion quality.

X-ray Photoeiectron Spectroscopy (XPS is the most widely used surface analysis technique. It provides valuable quantitative and chemical state information from the surface of the studying materials. I n our case, XPS measurements confirm functionalizing graphene-like filler materials with chlorinated paraffin due to the presence of organic chlorides on graphene surface. Figure 3 showed deconvoiution of the Cls and Chl2p peaks in the graphene study.

Repeated mechanical treatment of the graphene-like filler materials with chlorinated paraffin leads to the change of viscosity of the dispersion due to the individualizing of the graphene particles and improvement dispersion, resulting in changing pressure on the rolls during milling process. Figure 4 showed graphical representation of the pressure changes.

Figure 5 presents the comparative picture of the multilayer graphene dispersion in CP before and after functionalization with chlorinated paraffin. Samples were kept in laboratory for 4 months. Graphene after functionalization is still homogeneously dispersed, while bulk material is unstable and forms sediment on the bottom of flask.

Example 1

5 g of single layer graphene (SLG, CealTech AS) and 20 g of nitric acid (65 % wt, density 1.34 g/cm ³ ) were mixed in 50 ml conical flask and heated at 60°C for 4 hours to generate carboxyl (COOH) and hydroxyl (OH) functionalities at the SLG edges. Dispersion was filtrated and repeatedly washed with distilled water up to pH=7. Presence of carboxyl and hydroxyl function was confirmed by XPS analysis. 1 g of the graphene-like filler materials from the stage 1 was dispersed in 99 g of chlorinated paraffin (Chloroparaffin 112, LEUNA-Tenside GMbH) by ultrasound machine followed by roll milling (three-roll mill Exakt with gap distances 12 μιτι and 7 μιη) to give a homogeneous dispersion.

Example 2 25 g of multilayer graphene (TSG, Thomas Swan Ltd.) and two hundred fifty grams of the rapeseed oil (Coop Norge SA) were weighed and placed in the 1 I flask. The flask was initially sonicated for 2 hour followed by roll milling (three-roll mill Exakt with gap distances 8 μιη and 5 μιη) to give homogeneous dispersion. Dispersion was transferred to 1 I reactor und under torogously mixing and heated up to the reaction temperature - 303K. The desired amount 1 ,12 g of KOH catalyst was dissolved in the desired amount 112 g of methanol. To this solution was added the desired amount 258 g of co-solvent diethyl ether, and the resulting solution was added to the agitated reactor. The reaction was carried out until it reached the desired reaction time, 120 min. After finishing the reaction, the mixture was placed in separatory funnel and allowed to stand overnight to ensure that the separation of methyl esters and glycerol phase occurred completely. Glycerol phase (dark bottom phase) was removed and diluted with N-methyl pirrolidone for removal of the free standing organics from modified graphene-like filler materials. Functionalized graphene was filtered and dried at 60 degree C for 72 hours. 10 g of functionalized graphene was mixed with 100 g of chlorinated paraffin giving stable homogeneous dispersion.

Example 3

The resulting dispersion from example 2 is mixed and homogenized mechanically repeatedly with the 890 g of PHD GelCoat Ral9010 resin. Composite mixture was cured with 20 g of Benzoyl Peroxide. Graphene dispersion in matrix was evaluated by SEM and TEM.

Example 4

10 g of multilayer graphene (Thomas Swan) were dispersed in chlorinated paraffin (LEUNA-Tenside GMbH) by three roll-milling (EXAKT Three Roll Mill 80E, EXAKT Advanced Systems GMbH). The graphene/CP mixture was inserted in a three necks round bottom reactor equipped with a magnetic stirring, condenser, thermometer and Nitrogen purging line. Then 0.5 g of AICI _3: as catalyst, was added into the reactor. The mixture iwas heated to 60°C and kept for 2hrs to complete dispersion of aluminum chloride in the reaction mixture, followed by heating up to 120°C and keeping overnight under constant temperature and stirring. Reaction mixture was cooled to the room temperature, diluted with chloroform, filtrated and washed several times with chloroform to remove unreacted chloroparaffin and catalyst.