WO2008068543A1

WO2008068543A1 - Process for making a nanocomposite material having an elastomeric matrix and nanocomposite material thus obtained

Info

Publication number: WO2008068543A1
Application number: PCT/IB2006/003460
Authority: WO
Inventors: Cinzia Della Porta; Valentina Ermini
Original assignee: Laviosa Chimica Mineraria SpA
Current assignee: Laviosa Chimica Mineraria SpA
Priority date: 2006-12-04
Filing date: 2006-12-04
Publication date: 2008-06-12
Anticipated expiration: 2009-06-04

Abstract

Process for making a nanocomposite material having an elastomeric matrix for applications in the field of tyres, in particular, mixtures for tyre treads, comprising the steps of: dispersing clay material in a softened acqueous solution obtaining an aqueous dispersion; purifying the aqueous dispersion of the impurities embedded therein obtaining a purified nanoclay; combining the purified nanoclay with an organic modifier obtaining an organophilic nanoclay; filtering the organophilic nanoclay for removing the part of organic modifier not reacted; drying and grinding the organophilic nanoclay; introducing the organophilic nanoclay in a mixer; introducing at least one elastomer in the mixer; mixing the organophilic nanoclay and the elastomer in the mixer obtaining a nanocomposite material having an elastomeric matrix.

Description

TITLE

PROCESS FOR MAKING A NANOCOMPOSITE MATERIAL HAVING an eLASTOMERIC MATRIX AND NANOCOMPOSITE MATERIAL THUS

OBTAINED DESCRIPTION

Field of the invention

The present invention relates to a process for making a composite material having an elastomeric matrix comprising a nanostructured montmorillonite as reinforcing material that can be used in the field of tyres, in particular, mixtures for tyre treads.

Furthermore, the invention relates to a nanocomposite material having an elastomeric matrix obtained through this process. Background of the invention

As well known, the ore known as "kaolin" is generally used as reinforcing filler and/or for stiffening a polymeric matrix, in particular for elastomers. With the name kaolin a wide class is covered of aluminium hydrated silicates (having various subclasses) , which are called also "clays" and comprise bentonites, whose typical examples are montmorillonites [R.J. Lewis, Hawley' s Condensed Chemical Dictionary, 13a ed. J. Wiley & Sons, New York, 1997] . A distinction within kaolin ores is made defining soft and hard clays, depending on whether compositions of such clays with a suitable polymeric matrix give rise to vulcanized materials having a low or high module. A practical classification also exists on the effects of kaolins in polymeric compounds [I. Franta, Elastomers and Rubber Compounding Materials, Vol. 1: Studies in Polymer Science, 1989, Elsevier, Amsterdam] . Naturally the less reinforcing kaolins, the soft ones, are characterized by particles having an average diameter larger than the more reinforcing kaolins. In particular, the diameters of the particles of soft kaolins are less than 5 microns whereas those of hard kaolins hard have average diameters less than 2 microns [Franta, op.cit.]. It is known to those skilled in the art that the performances of such filling or stiffening materials are much limited and their contribution to mechanical reinforcement is much less than that obtained with either silanized precipitated silica or carbon black [R. Magaraphan et al. Rubber Chemistry & Technology, vol. 76, p. 406, (2003)].

The current techniques provide the steps of collecting such ore from natural deposits and their use directly or after milling.

Also certain phyllosilicates, such as hectorite or montmorillonite, characterised by a silicate structure formed by layers, have never been used as reinforcing material but have been used as polymeric matrix filling material .

An essential aspect concerning reinforcement is the polymer-reinforcing charge interaction [F.Cataldo, Carbon, vol. 40, p.157, (2002); F.Cataldo, Polymer International, vol. 50, p.828, (2001); F.Cataldo, Macromolecular Symposia, vol. 228, p.91, (2005)]; evidently simple milling steps are not enough to improve in a radical way this interaction even in case of phyllosilicates.

Recent studies [F. Gao, Material Today, vol.7, p.50, (2004); S. S. Ray, M. Okamoto, Progress in Polymer Science, vol.28, p.1539, (2003)] have shown that it is possible to demolish the multi-layered structure of phyllosilicates, in particular montmorillonites, with suitable methods, in order to obtain an intercalated material, or in particular an exfoliated material, i.e. a material in which the laminae that make up the multi-layered structure and that are kept together by Van of the Waals interactions, have been intercalated in a "sandwich-like" configuration by molecules of a "complexing agent", such that the laminae can in particular result completely separated from each other and dispersed, i.e. exfoliated. Such intercalation, or exfoliation, can be obtained by a treatment of the phyllosilicates or montmorillonites with alkylammonium or alkylphosphonium salts. It has been shown that with this treatment the alkaline cations present between the layers of the montmorillonitic structure are replaced by the cations organic derived from the alkylammonium or alkylphosphonium salts. Owing to this treatment the hydrophilic montomorillonites turn into organophilic montomorillonites, i.e. if in the natural status they had a considerable affinity to water and a low compatibility with the polymeric matrix, after the treatment with the ammonium salt, or phosphonium, acquire more affinity and then are more compatible and more dispersible in the organic matrix i.e. the polymeric matrix. The separation among the layers is achieved since the cations of alkylammonium enter between the layers and cause necessarily the attenuation of the Van of the Vaals forces and then the intercalation or exfoliation.

Since nanostructured material is a desirable material whose supramolecular structure is manipulated at a nanometric scale, also exfoliated montmorillonites can be defined as "nanostructured" since each silicate layer, i.e. each lamina, has an average thickness of about of a nanometer and a diameter set between 30 nm and several microns . As a consequence, the traditional and current technology provides a micronization of kaolin up to reaching a size of the aggregates about of microns but without however being able to exfoliate the multi-layered structure of the phyllosilicates. More recent technologies provide a combining montmorillonite with a suitable agent, for example an alkylammonium salt and a dispersion of the nanoclay in a polymeric matrix so that it is exfoliated avoiding phenomena of flocculation, i.e. of reaggregation of the laminae. With this technology, it is possible to reach much higher levels of dispersion of montmorillonite with respect to the traditional technology with surprising stiffening effects with a minimum amount of reinforcing nanostructured material [Gao, op.cit.; Ray & Okamoto, op. cit. ] .

There are some steps, however, that are critical in this process of making a composite polymeric material reinforced with a nanostructured montmorillonite: the step of dispersion of the phyllosilicates, in particular the montmorillonites, their reaction with alkylammonium or alkylphosphonium salts, and finally their exfoliation in the polymeric matrix. If only one of these steps is not correctly carried out the conditions are not fulfilled for intercalation, or in particular exfoliation, of montmorillonite in the polymeric matrix and therefore the desirable stiffening phenomena are not achieved.

In the literature of this field, in particular concerning processes of forming a nanocomposite material in an elastomeric matrix [S. Sadhu, A. K. Bhowmick, Rubber Chemistry & Technology, vol.78, p.321, (2005); S. Sadhu, A. K. Bhowmick, Rubber Chemistry & Technology, vol.76, p.860, (2003); S. S. Sternstein et al. Rubber Chemistry & Technology, vol.78, p.258, (2005); R. Magaraphan et al . Rubber Chemistry & Technology, vol.76, p.406, (2003);], as well as concerning processes of forming a nanocomposite material in an a plastic matrix [Gao, op.cit.; Ray & Okamoto, op. cit.], the described methods have low industrial potentiality, because they comprise the following steps: A) complexing of sodium montmorillonite with an alkylammonium salt that causes montmorillonite to swell in water and to react with the alkylammonium salt, and collecting the product by filtering and drying (see Magaraphan et al., op. cit . ) ;

B) dissolving in a suitable solvent (i.e. toluene) an elastomer along with a vulcanizing composition, and mixing in a toluenic dispersion the nanoclay prepared in (A) , and subsequent evaporation in a thin film or distillation of the solvent for collecting the composite.

With this process the desired result is obtained of dispersion exfoliated montmorillonite within the polymeric matrix achieving excellent mechanical features, but the use of solvents, beyond causing an additional environmental impact, is far from normal industrial practices of this field, where all the components are mixed without any solvents.

Another method of limited industrial interest concerns the intercalation of montmorillonite with a suitable monomer that is then polymerized in order to obtain a composite, obtaining also in this case excellent dispersion and reinforcement [Ray & Okamoto, op. cit.], but still far from the current industrial practice and from an application and production. The only processes for having industrial interest comprise, instead, the mixing the elastomeric matrix with all the ingredients in a normal closed mixer, for example a "Banbury" mixer, well known by persons skilled in the art. When mixing mixing in banbury, the elastomeric or plastic mass becomes hot and fluid under the action of the mechanical energy of the rotor and of the flows of material, and then the stiffening agents (so called "charges") are added, both traditional and nanostructured, along with other co-formulants . In this process exfoliated rαontmorillonite has been prepared appropriately, otherwise the stiffening effects are disappointing. An example of the criticity of this situation been given in the scientific literature, where some authors had to treat the nanostructured montmorillonite with a solvent before mixing in the closed mixer, to ensure a minimum acceptable dispersion and to avoid flocculation of montmorillonite

[M. Ganter, W. Gronski et al . Rubber Chemistry &

Technology, vol. 74, p.221, (2001)]. Other authors have compared the different methods of preparation by either mixing with a solvent and in closed mixer, using the same types of elastomer and of montmorillonite or other type of charge and have shown that the better results are obtainable only by mixing in a solvent [Y. T. Vu, J. E. Mark, L. H. Pham, M. Engelhardt, Journal of Applied Polymer Science, vol. 82, p.1391, (2001) ] .

Moreover, a not appropriate mixing in the closed mixer causes regrettable drawbacks, like final nanocomposite material with inferior quality, for example in the tests of resistance to growth of cuts (crack growth tests) , presumably due to phenomena of flocculation of the nanostructured filler [K. Reinke, W. Grellmann, Rubber Chemistry & Technology, vol. 77, p.662, (2004)]. Summary of the invention

It is therefore a feature of the present invention to provide a process for the production of a nanocomposite material having an elastomeric matrix for applications in the field of tyres, in particular, mixtures for tyre treads, which present improved mechanical features with respect to the materials traditionally used.

These and other features are accomplished with one exemplary process for the production of a nanocomposite material having an elastomeric matrix for applications in the field of tyres, in particular, mixtures for tyre treads, whose main feature is that it comprises the steps of:

— dispersing clay material in a softened acqueous solution obtaining an aqueous dispersion;

— purifying the aqueous dispersion of the impurities embedded therein obtaining a purified nanoclay;

— combining the purified nanoclay with an organic modifier obtaining an organophilic nanoclay; — filtering the organophilic nanoclay for removing the part of organic modifier not reacted;

— drying and grinding the organophilic nanoclay;

— introducing the organophilic nanoclay in a mixer;

— introducing at least one elastomer in the mixer; — mixing the organophilic nanoclay and the elastomer in the mixer obtaining a nanocomposite material having an elastomeric matrix.

Advantageously, the purified nanoclay has a content of impurities less than 2% by weight, preferably less than 1%.

Advantageously, a vulcanization retardant is added selected from the group comprised of:

— a carboxylic acid;

— phtalic anhydride; — N-cyclohexyl-thiophtalimide ;

— a combination thereof

Preferably, the carboxylic acid used as vulcanization retardant is selected from the group comprised of:

— benzoic acid; — acetyl-salicylic acid;

— stearic acid;

— a combination thereof. In particular, the vulcanization retardant can be put in the mixer with the elastomer and the organophilic nanoclay before starting the mixing step.

Alternatively, the vulcanization retardant is premixed with the organophilic nanoclay before putting them in the mixer.

From tests carried out on natural rubber (cis-1,4- polyisoprene) , intercalated montmorillonite once embedded in the in the composite resulted to speed up the vulcanization kinetics. The increase of vulcanization speed is often undesired in the industrial practice, since it can bring to premature "burning" of the mixture.

The acceleration of the vulcanization kinetics is responsive to the presence of the cation of the used ammonium salt, in particular tetralkylammonium, which acts also by secondary accelerant.

The use of a vulcanization retardant is in contrast with this tendence to a higher vulcanization speed and allows then to avoid undesired phenomena, such as premature "burning" of the mixture, without affecting the improvements deriving from the use of the nanoclay in particular, such as increasing the hardness and reducing mechanical hysteresis.

In particular, the organophilic nanoclay can be added directly to the elastomer in a closed mixer, for example of "Banbury" type.

The step of purifying the aqueous dispersion can advantageously comprise the steps of:

— primary separation of the impurities from the aqueous dispersion by a vibrating sieve;

— secondary separation of the impurities from the aqueous dispersion at the outlet of the vibrating sieve by a hydrocyclone; — decantation of the aqueous dispersion at the outlet of the hydrocyclone;

— centrifugation at a high speed of the decanted aqueous dispersion. In particular, during the primary and secondary- separation macroscopic impurities are removed from the aqueous dispersion such as sand or stone particles, and the content of impurities turns from a starting 13% by weight to about 9%. After the decantation the nanoclay has a content of impurities lessthan, or equal to, about 4%. During this step the separation is obtained of the heavy particles of quartz and feldspar. Finally, after centrifugation at a high speed the nanoclay has a content of impurities less than 1% by weight owing to the removal of the light particles of quartz and cristobalite.

Advantageously, the organic modifier is selected from the group comprised of:

— an alkylammonium salt;

— an alkylphosphonium salt. Preferably, the alkylammonium salt used is the hexadecyltrimethylammonium chloride .

Preferably, the alkylphosphonium salt used is the tetradecyl (tributyl)phosphonium chloride.

In particular, the elastomer may be selected from the group comprised of:

— natural rubber;

— synthetic rubber;

— a combination thereof.

If the elastomer is synthetic rubber, it can be selected from the group comprised of:

— copolymer styrene-butadiene;

— polybutadiene;

— butyl rubber, polyisobutylne copolymerized with isoprene; — halobutyl rubber, such as chlorobutyl and bromobutyl;

— a combination thereof.

Preferably, the clay material is a smectitic clay selected from the group comprised of:

— montmorillonite,

— hectorite,

— saponite.

In particular, the content of the purified nanoclay in the nanocomposite material having an elastomeric matrix can be set between 0,1% and 50% of the overall weight, advantageously, between 0,4% and 30% of the overall weight, preferably between 1% and 20% of the overall weight . According to another aspect of the invention, a nanocomposite material having an elastomeric matrix for applications in the field of tyres is obtained through the process above described.

Hereafter some examples are given of possible methods of synthesis of a nanocomposite material, according to the present invention.

EXAMPLE 1

In a reactor having a mechanical stirrer 100 Kg are loaded of sodium montmorillonite in 3 m³ of demineralized water that are stirred for 12 hours obtaining a suspension of montmorillonite swollen of water. In particular, the sodium montmorillonite has a content of impurities less than 1% by weight. The mass is then heated up to 8O⁰C and to it slowly and under stirring 85 Kg are added of hexadecyl- trimethylammonium in 1,2 m³ of demineralized water. The wholed is for two hours and the nanoclay thus obtained, also -called Dellite, is filtered, washed with 2 m³ of water and dried at 9O⁰C.

The dried Dellite is put in a closed 2 litres mixer with an elastomer and various charges. Then, to the mixture Dellite/elastomer accelerating agents and vulcanizing agents are added. EXAMPLE 2

Starting from the Dellite obtained as described in example 1 the following nanocomposites are made: NO, Nl, N2 and N3, having the following formula: 100 parts for 100 parts of resin (phr) of natural rubber (standard indonesian rubber type 10) , 50 parts of carbon black N330, 5 parts of oil of process (distilled aromatic extract) , 2 parts of stearic acid, 4 parts of zinc oxide and a variable amount of Dellite for different nanocomposites: 0; 2.5; 5; and 7.5 parts for NO, Nl, N2 and N3, respectively.

In the second mixing step the following components have been added: 1 part of antioxidant type 6PPD (alkylphenylparaphenylendiamine) , 0.8 parts of TBBS (t- butyl-benzothiazylsulphenamide accelerant), and 1.3 parts of sulphur, and a variable amount of benzoic acid for each nanocomposite, and precisely: 0; 1, 2 and 3 parts for NO, Nl, N2 and N3 respectively. After mixing in two steps in the closed mixer the mixtures have been exfoliated in a open mixer, and vulcanized in special moulds in a vapour press at 150⁰C for 35 minutes. All the tests have been made according to the normal standard procedures ASTM or ISO. The nanocomposite material NO, Nl, N2 and N3 have been then subject to some tests, according to normal standard procedures ASTM or ISO, for evaluating the suitibility to use them in the field of tyres. The results are given in the following table 1.

The tests on natural rubber, cis-1, 4-polyisoprene, given in the table show that intercalated montmorillonite

(Dellite) once embedded in the composite speeds up the vulcanization kinetics as shown by the reometric data (MH, ML and MH-ML) . The increase of the vulcanization speed is often undesirable in the industrial practice because it can bring to a premature burning of the mixture. The acceleration of the vulcanization kinetics as stated above is given just to the presence of the cation of tetralkylammonium that acts also as secondary accelerant (see Franta, op. cit.) .

In case of the nanocomposite materials Nl, N2 and N3 the vulcanization speed decreases for use of the vulcanization retardant, which in the specific case is carboxylic acid.

The efficiency of the action of Dellite and of the desired dispersion can be measured as the stiffening effect of the composite, which is excellent and can be obtained for example from the data of hardness that increase from 60 points to 73 points, whereas even if with not much higher effects on the breaking load, a very high increase is observed instead of the modules at a low extension; this effect that is attenuated gradually at the modules at high extension up to the breaking load which corresponds to a reduction of the stretch to Break, is a clear effect of a stiffening in the composite.

The aging does not modify the stiffening features just discussed, whereas the De Mattia test on triggering and on propagating crack, shows that the Dellite not any detrimental effect both on triggering and on propagating cracks in the composite material. Finally, the ratio between viscous modulus and elastic modulus (so called tanD) in dynamic conditions shows that the presence of the Dellite assists reduction of mechanical hysteresis, encouraging many applications where these features are specifically required. In case of application in the field of tyres, the reduction of hysteresis is desirable since it causes a reduction of fuel consumption. The use of Dellite in mixtures for tyre treads, for example trucks, is advantageous on the basis of the available data, to reduce the amount of traditional "fillers", for example carbon black, with a subsequent reduction of the hysteresis, while maintaining high the elastic modulus and other mechanical features. The reduction of hysteresis is also desirable in composite materials used in the production of solid tyres and of vehicle parts. The high elastic modulus expecially, at low extension, is desirable in the production of rubber ducts.

EXAMPLE 3

Starting from the Dellite obtained as described in example 1, the following composite materials are made: N4, N5, N6 and N7 having the following formula: 50 parts (phr) of natural rubber (standard Indonesian rubber type 10), 50 parts of copolymer styrene-butadiene (type S1500), 50 parts of carbon black N330, 5 parts of oil of process

(distilled aromatic extract) , 2 parts of stearic acid, 3 parts of zinc oxide, and variable amount of Dellite for different nanocomposite materials and precisely: 0; 2.5; 5; and 7.5 parts for N4, N5, N6 and N7 respectively. In the second mixing step 1 part of antioxidant type 6PPD (alkylphenylparaphenylendiamine) , 0.8 parts of TBBS (accelering t-butyl-benzothiazylsulphenamide) , 0.2 parts of MBTS (accelering mercaptobenzotiazole disulphide) and 1.5 parts of sulphur have been added. For each composite N4, N5, Nβ and N7 variable amounts of benzoic acid have been used and respectively: 0; 1, 2 and 3 portions. After mixing in two steps in the closed mixer the mixtures have been exfoliated in a open mixer, and vulcanized in special moulds in a vapour press to 15O⁰C for 35 minutes.

Also the nanocomposite material N4, N5, Nβ and N7 have been subject to some tests, made according to the normal standard procedures ASTM or ISO. The results are given in the following table 2.

Table 2

Also in this case an acceleration of the vulcanization kinetics is seen. It is apparent that the ammonium salt used for preparing intercalated montmorillonite (Dellite) has an effect in the kinetic as in case of the example 2.

Furthermore, an increase of the hardness responsive to the amount of Dellite added, grows from 60,9 for nanocomposite material N4 without Dellite to 70 for N7 with the highest content of Dellite. Another aspect to take into account is the high stiffening effect expecially in the modules at low extension, nad lower even if significant also in the modules at high extension. The breaking load is slightly improved. Even after aging the effect of the Dellite on the reinforcement is unchanged and phenomena of reduced resistance against start and propagation of cracks in tha same dynamic conditions (test of De Mattia) have not been observed. The barrier effect offered by the addition of Dellite is apparent from the Goodrich test of permeability to air. Taking 100 the permeability to air of a composite of reference Q, the permeability is reduced to less than H of the original value with only 2.5 phr of Dellite and, in particular, to 2/3 of the original value with the addition of 5 phr of Dellite. This result is good for the application of Dellite also as component adapted to reduce the permeability to air and to gases elastomeric composite material. In applications in the field of tyres this effect is desirable expecially in mixtures for "innerliner" i.e. tubeless tyre treads.

EXAMPLE 5

Starting from the Dellite obtained as described in the example 1, the following composites are made: N8, N9, NlO and Nil having the following formula: 137.5 parts (phr) of copolymer styrene-butadiene (type S1712, extended oil with 37,5 parts of aromatic oil), 80 parts of carbon black N330, 5.5 parts of oil of process (distilled aromatic extract), 1.5 parts of stearic acid, 3 parts of zinc oxide, and variable amount of intercalated montmorillonite of the Dellite type for different nanocomposites: 0; 2.5; 5; and 7.5 parts respectively. In the second mixing step 1 part of paraffin wax, 1 part of antioxidant type 6PPD

(alkylphenylparaphenylendiamine) , 0.6 parts of TBBS (t- butyl-benzothiazylsulphenamide accelerant), 0.6 parts of

MBTS (mercaptobenzothiazole disulphide accelerant) and 2.2 parts of sulphur and variable amount of benzoic acid (0 for N8, N9 and NlO and 1 part for Nil, as shown in table 2) have been added. After mixing in two steps in the closed mixer the mixtures have been exfoliated in a open mixer, vulcanized in special moulds in a vapour press to 15O⁰C for 35 minutes. Table 3

Also in this case an acceleration is known of the vulcanization kinetics.

The stiffening effect is apparent but is maximum for 5 parts of Dellite, whereas higher amounts maggiori do not give further effects. Evidently in this mixture rich of plastifying oil an excess of Dellite (>5 parts) causes the flocculation of the nanocharges.

In line with what seen in examples M-P, also in the present case with a composite of sole synthetic rubber the hysteresis determined as tanD decreases with the increase of the amount of Dellite added. All this is very interesting in potential applications where this features is strongly desirable and it is not always available.

EXAMPLE 6

In a reactor having mechanical 100 Kg of sodium montmorillonite stirrer are loaded in 3 m³ of demineralized water that are kept under mechanical stirring for 12 hours obtaining a suspension of montmorillonite swollen of water.

The mass is then heated up to 80⁰C and to it slowly and under stirring 85 Kg are added of tetradecyl (tributyl) phosphonium chloride in 1,2 m³ of demineralized water. The wholeis stirred vigorously for two hours and the nanoclay thus obtained, hereafter "Nanoclay-P", is filtered, washed with 2 m³ of water and dried at 90⁰C. The dried Nanoclay-P is put in a closed 2 litres mixer with an elastomer and various charges. Then, to the mixture Nanoclay-P/elastomer accelerant agents and vulcanization agents are added. As shown in the examples from 2 to 5, the Dellite has the desired phenomenon of accelerating the vulcanization kinetics of the composites where it is included. For opposing to this phenomenon it has been then proposed the use of carboxylic acids and other substances as vulcanization retardants .

Instead, from the data relative to the tests carried out on the nanocomposite material N12, N13, N14 and N15, starting from the Nanoclay-P, it is apparent that in addition to the relevant stiffening andimpermeability to air already measured for the nanocomposite materials of the examples by the 2 to the 5, there is the further advantage of eliminating the drawbacks of an excessive and problematic acceleration of the vulcanization speed.

In fact, in this case the cations of alkylphosphonium do not affect the speed of vulcanization.

Samples N12-N15 have been prepared exactly as in case of the examples N4-N7, but replacing the Dellite with the Nanoclay-P. As shown in table 4, the vulcanization kinetics, in this case, is retarded with respect to the composite of reference, as can be desumere by the reometric data, however the high increase of the modules, especially at low extensions, the increase of the hardness and the waterproofing effect of the Nanoclay are completely preserved. This shows that also the alkylphosphonium salts are effective in the intercalation and in complexing of montmorillonite like alkylammonium salts. Table 4

In case of the elastomeric matrix based on Styrene- butadiene, the effect of the Nanoclay-P does not appear to affect the kinetic of the vulcanization.

However, in case of a different elastomeric matrix, it has been shown that the use of the Nanoclay-P speeds up the process for vulcanization. Therefore, in these cases it is suitable to resort to vulcanization retardants as above cited and described in the examples from 2 to 5.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

1. Process for making a nanocomposite material having an elastomeric matrix for applications in the field of tyres, in particular, mixtures for tyre treads, characterised in that it comprises the steps of:

— purifying said aqueous dispersion of the impurities in it present obtaining a purified nanoclay; — combining said purified nanoclay with an organic modifier obtaining an organophilic nanoclay;

— filtering said organophilic nanoclay for removing the part of said organic modifier not reacted;

— drying and grinding said organophilic nanoclay; — introducing said organophilic nanoclay in a mixer;

— introducing at least one elastomer in said mixer;

— mixing said organophilic nanoclay and said elastomer in said mixer obtaining a nanocomposite material having an elastomeric matrix.

2. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said purified nanoclay has a content of impurities less than 2% by weight, preferably less than 1%.

3. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, where a vulcanization retardant is added selected from the group comprised of:

— a carboxylic acid;

— phtalic anhydride; — N-cyclohexyl-thiophtalimide ;

— a combination thereof.

4. Process for making a nanocomposite material having an elastomeric matrix, according to claim 2, wherein said carboxylic acid used as vulcanization retardant is selected from the group comprised of:

— benzoic acid;

— acetyl-salicylic acid; — stearic acid;

— a combination thereof.

5. Process for making a nanocomposite material having an elastomeric matrix, according to claim 2, wherein said vulcanization retardant is put in said mixer before starting said mixing step.

6. Process for making a nanocomposite material having an elastomeric matrix, according to claim 2, wherein said vulcanization retardant is premixed with said organophilic nanoclay before their introduction in said mixer.

7. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said organophilic nanoclay is added directly to said elastomer in a closed mixer.

8. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said purifying step of said aqueous dispersion comprises the steps of:

— primary separation of said impurities from said aqueous dispersion by a vibrating sieve;

— secondary separation of said impurities from said aqueous dispersion exiting from said vibrating sieve by a hydrocyclone;

— decantation of said aqueous dispersion exiting from said hydrocyclone;

— centrifugation at a high speed of said decanted aqueous dispersion.

9. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said organic modifier used is selected from the group comprised of: — an alkylammonium salt;

— an alkylphosphonium salt.

10. Process for making a nanocomposite material having an elastomeric matrix, according to claim 8, wherein said alkylammonium salt used is the hexadecyltrimethylammonium chloride.

11. Process for making a nanocomposite material having an elastomeric matrix, according to claim 8, wherein said alkylphosphonium salt used is the tetradecyl (tributyl)phosphonium chloride.

12. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said elastomer used is selected from the group comprised of:

— natural rubber; — synthetic rubber;

— a combination thereof.

13. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said elastomer is selected from the group comprised of:

— styrene;

— butadiene;

— polybutadiene;

— polyisobutylne; — isoprene;

— chlorobutyl;

— bromobutyl;

— a combination thereof.

14. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, wherein said clay material is a smectitic clay selected from the group comprised of: — montmorillonite,

— hectorite,

— saponite.

15. Process for making a nanocomposite material having an elastomeric matrix, according to claim 1, where the content of said purified nanoclay in said nanocomposite material having an elastomeric matrix is set between 0,1% and 50% of the overall weight, preferably between the 0,5% and 30% of the overall weight .

16. Nanocomposite material having an elastomeric matrix for applications in the field of tyres, in particular, mixtures for tyre treads, characterised in that it is obtained through the process described in the claims from 1 to 15.