WO2009015453A2

WO2009015453A2 - Process for obtaining a solid nanocomposite

Info

Publication number: WO2009015453A2
Application number: PCT/BR2008/000220
Authority: WO
Inventors: Heloisa Cajon Schumacher; Márcia Maria RIPPEL; Fernando Galemeck
Original assignee: Universidade Estadual De Campinas - Unicamp; Orbys Desenvolvimento De Tecnologia De Materiais Ltda
Priority date: 2007-07-27
Filing date: 2008-07-28
Publication date: 2009-02-05
Also published as: WO2009015453A3; BRPI0706080A2

Abstract

The present invention refers to a process for preparing solid nanocomposites, formed by elastomeric or thermoplastic latexes and layered compounds, synthetic or natural, intercalated or exfoliated. The novelty shown in the process of this invention is the obtainment of solid nanocomposites through the coagulation of latex and clay dispersions in coagulating agents, by thermal or mechanical means, thereby obtaining solid rubber/clay nanocomposites having a high clay intercalation and/or exfoliation degree. The solid nanocomposite produced by the process of this invention and dispensing with vulcanization has much higher mechanical properties than many conventional polymers or elastomers, as well as excellent properties of resistance to oils and solvents, which makes feasible its application in industrial fields such as in transportation equipment industry, in the manufacture of tires, dynamic and static seals, gaskets, sealants, hoses, belts, among other possible applications. The present invention still refers to articles produced with said solid nanocomposites.

Description

PROCESS FOR OBTAINING A SOLID NANOCOMPOSITE

The present invention refers to a process for preparing solid nanocomposites from an aqueous dispersion containing non-modified solid layered silicate and polymer latex, wherein said process is applicable, among other things, to the manufacture of adhesives, footwear, athletic articles, tires, and auto parts. Description of the prior art

Nanocomposites are hybrid materials which, in one of its components, have nanometric dimensions in at least one of the axes of the particles. Such as in conventional composites, one of the components serves as a matrix where particles from the second material are dispersed. The obtainment of nanocomposites through the incorporation of nanometric charges into polymeric matrices may give rise to materials having higher impact resistance and elastic modulus.

The layered silicate reinforced polymer or elastomer shows good mechanical, electrical, and thermal properties, as well as gas and liquid barrier properties, and chemical resistance to oils and solvents, as compared to conventional polymers or elastomers.

Layered silicates (clays) are phyllosilicates, which group includes montmorillonite, hectorite, saponite, mica, among others. The structure of a layered phyllόsflϊcate is formed by two tetrahedral silica layers and one octahedral aluminum layer. Due to the isomorphic substitution in the phylosilicate, where, for example,

AI^J ions are replaced with Si on the SiO₂ layer or sheet, the basal face has a negative charge which is balanced by exchangeable cations, such as Na⁺, K\ Li⁺, and Ca^~+.

In an aqueous suspension of clay, water molecules permeate into the interlayer space of clay, where repulsive hydration forces lead to the separation of layers on the order of up to tens of nanometers, which is known as osmotic swelling (Luckham, P. F & Rosi, S. Advances in Colloid Interface Science, 82, 43-92, 1999).

There are various processes for producing nanocomposites which include melt intercalation, in situ monomer polymerization, via solution, or via latex. The document owned by Southern Clay Products

Inc, GB2408048, discloses a method of preparing NBR and SBR rubbers, containing clays modified with onium ions, such as, for example, a dimethyl hydrogenated double-tailed quaternary amine compound. The mixture of rubber with the organically-modified clay is carried out in Babmury mixers, at 12O⁰C, being subsequently vulcanized at 15O⁰C.

The document owned by Nippon Petrochemicals, JP2005068237, also discloses the obtainment of a nanocomposite with onium salt modified clay, but in a system formed by isobutylene and butyl rubber. Two documents owned by ExxonMobil Chemical, US2005027058 and US2005027057, disclose the preparation of elastomeric nanocomposites with CIoisite clay, modified with onium, phosphonium, or sulphonium. The elastomer used is a halogenated elastomer, such as isobutylene containing units derived from styrene, such as para-bromo-methylstyrene. The halogenated elastomer is primarily mixed with a functionalized amine, which can be made in the presence of a solvent, and then mixed with the clay. A second elastomeric component may be added, such as natural rubber, SBR, NBR, PI, SIBR, EPM, EPDM, or even a thermoplastic resin. The mixture is carried out in a Bambury mixer, at between 120 and 300⁰C. The nanocomposite is subsequently vulcanized.

Document US2006 I 00339 owned by Exxon Mobil Chemical discloses the preparation of a f unctionalized elastomeric nanocomposite in which elastomers, specially those derived from poly-isobutylene-co-p-alkylstyrene and poly- isobutylene - isoprene, should be functionalized by reacting substances which produce free radicals and unsaturated carboxylic acids, or the like, with the elastomer. The clay is exfoliated by the treatment with organic substances, such as quaternary ammonium salts, silanes, phosphonium salts, phosphines and sulphides, but preferably, cationic surfactants. The amount of exfoliating agent may range from 0.1 to 20 phr. The exfoliated clay is mixed with the elastomer in the melt state, in a ratio which may range from 0. 1 to 50% by mass. The nanocomposite mixture may still contain a second elastomer, such as natural rubber, polybutadiene rubber, nitrile rubber, etc. The obtained nanocomposite is then vulcanized.

Document CN 1563181 owned by Huanan Technical University, discloses a nanocomposite prepared with rubber, organically-modified layered silicate, a monomer or monomer mixture, and an initiator. This process consists in adding modified layered silicate and reactive monomer in a rubber mixture and, it necessary, adding an initiator. These are examples which demonstrate the use of clays organically modified with onium salts (ammonium, phosphonium, etc.) However, the modification with such substances causes certain inconveniences related, for example, with the thermal instability of quaternary ammonium salts and the toxicity of phosphonium salts.

Document owned by the Sumitomo Rubber company, JP200332775 1 , discloses the production of a rubber composition containing rubber, a charge and a nanocomposite from rubber and clay, wherein the clay is dispersed in a diene-type rubber. The amount of clay is from 1 -50% by mass in the nanocomposite. The amount of charge is from 1 -99 parts by mass in 100 parts by mass of the sum of nanocomposite and rubber.

Document WO200701 1456 owned by ExxonMobil Chemical Patents, discloses the preparation of a nanocomposite from an halogenated elastomer in an organic medium, followed by the neutralization of the halogenated elastomer solution and the addition of an aqueous slurry of clay, forming a masterbatch emulsion which can be then mixed with a second portion of halogenated rubber. Various documents owned by the Yokohama

Rubber company disclose the preparation of rubber nanocomposites. Document JP2004250473 discloses the preparation of a rubber composition produced by mixing a rubber, containing epoxy groups, with layered clay organized through ionic bonding of an organic compound, having any one of carboxy, amino and, thiol groups. Document JP2004250245 discloses a nanocomposite produced from rubber with clay organically-modi fied with a compound containing a thiol group and an amino group in its molecule. Document JP2004155912 also discloses the preparation of a rubber from rubber and clay, wherein clay is organized through ionic bonding with an ammonium compound, which has a carboxyl group and a chain with 6 to 30 carbons in its molecule, and a halogenated butyl rubber. Document JP2003221473 discloses a rubber composition consisting of a nanocomposite from rubber and clay. The composition is prepared by mixing a compound, having a maleic anhydride group with a clay treated with primary and/or secondary ammonium ion having six or more carbons, with a solid rubber by means of ionic bonding. Document JP2003221452 discloses a nanocomposite-like masterbatch rubber composition consisting of rubber, carbon black, and mineral clay organically treated with a secondary and/or tertiary ammonium ion via ionic bonding. Document JP2003055514 relates to a nanocomposite-like rubber composition containing butyl rubber having a specific phosphonium salt structure, with a phenyl group as a functional group, and modified clay with onium salt.

Document JP2003292678 owned by the Bridgestone company discloses the preparation of a rubber composition from the dispersion of clay in a rubber latex mixture and a water-soluble coupling agent of the aminosilane type. The procedure consists in mixing the aqueous suspension of clay with the NBR, SBR, BR or NR latex, and then adding the coupling agent (N-[beta|(aminoethyI)[gamma]-aminopropylmethyldimetoxysilane, subsequently drying the mixture.

Document WO02070589 owned by the Southern Clay company discloses the preparation of polymer nanocomposites through the destabilization of a dispersion of polymer and clay. The preparation procedure consists in mixing a dispersion of polymer in latex form with a dispersion of clay. To this mixture a fiocculant agent is added. The flocculated material is separated by filtration, centrifugation, or evaporation. Polymers which can be used include polyester, polyurethane, PVC, styrene-butadiene, acrylic rubber, poly-isoprene, etc. The polymer dispersion may occur in an aqueous medium, in an organic medium, or in a mixture of both, at a concentration of up to 80% by mass. In all examples described in the document (WO02070589) synthetic commercial latexes, in concentration of 50% by mass, are used. Clay dispersion may occur in an aqueous medium, at a concentration in the range of 1 to 10% by mass.

The clay dispersion is added to the latex dispersion and the obtained mixture is flocculated by the addition of quaternary ammonium salts and amines or, alternatively, the clay dispersion itself may contain a quaternary ammonium salt, double metallic layered hydroxides, or inorganic salts. The clay dispersion containing quaternary ammonium salt is designated by the authors of the patents as organoclay. In this case latex flocculation requires even minutes to occur. The amount of flocculation agent ranges from 1 to 10% by mass.

Another method described by this document refers to the preparation of a clay dispersion with a quaternary ammonium compound, wherein this compound is at a concentration 3 times higher than the ion exchange capacity of clay. The obtained dispersion contains a portion of the quaternary ammonium compound which is not bounded to the clay. This dispersion is then mixed with a polymer dispersion, preferably in latex form, forming the flocculated nanocomposite.

The maximum amount of clay on prepared nanocomposites is of 30% by mass, that is, about 43 phr. However, in the examples described in the patent the maximum amount of clay on nanocomposites is of 5.7% with respect to the mass of the polymer. Among documents which describe the preparation of elastomeric nanocomposites from latex and aqueous dispersion of clay followed by coagulation are those owned by Exxon Research

Engineering, Goodyear, Beijing Chemical Engineering University, and ΓTRI.

There are two documents from Exxon Research Engineering regarding the production of elastomeric nanocomposites. Document TW419496 refers to the preparation of a montmorillonite dispersion in water, followed by the addition of a surfactant (alkyltrimethylammonium salt, dodecyltrimethylammonium bromide). Next, monomers (styrene, isoprene) are added by carrying out polymerization of the styrene- isoprene latex intercalated into the clay, and subsequently coagulated with methanol and dried. The solid nanocomposite is then mixed, by melting, with a SBR copolymer, together with zinc oxide, stearic acid, and tetramethylthiuram disulfide (accelerator) in a mixer at 13O⁰C followed by cross-linking. Another document from Exxon Research (US5883173) discloses the preparation of a solid nanocomposite (NCP) from latex, formed by in situ polymerization or from a previously formed latex. In in situ polymerization the process is the same as described in document TW419496. Conversely, the preparation of a solid NCP from the pre- formed polymer involves primarily dissolving the functional ized polymer (isobutylene-co-paramethyl isoprene triethylammonium copolymer) in a solvent (tetrahydrofiiran), subsequently adding water, a nonylphenol derived surfactant, hexadecanol, and stirring overnight. Then, dried montmorillonite is added and ultrasound is applied in order to coagulate the NCP, which is vacuum-dried.

Document US2005065266 owned by Goodyear discloses the preparation of nanocomposites from rubber and clay (smectite) swelled in water. It also refers to the production of rubber compounds containing this NCP, in the manufacture of tyres and other products such as conveyor belts, power transmission belts, and hoses. In the case of tyres, the tread is produced by the rubber compound containing NCP, which substitutes a significant amount of carbon black as a reinforcement, in order to achieve a reduced heat buildup for higher tyre durability, weight reduction, and fuel saving. NCP is prepared by adding clay (smectite) in hot water (6O⁰C) and subsequently adding rubber latex (for example, SBR or NR), but also includes synthetic latexes composed of isoprene, butadiene, isoprene and butadiene, isoprene-styrene, butadiene- styrene, butadiene-acrylonitrile, isoprene-butadiene, isoprene- acrylonitrile monomers) to form a mixture in which a cationic polymeric quaternary amine or ethylene polyamine solution is added, in order to intercalate or exfoliate the clay, with ion exchange and aiding in the coagulation of NCP. Coagulation may also be promoted through the addition of an acid solution or acid salt in order to reduce pH. The nanocomposite may still be prepared by adding a clay/latex mixture to a sulfuric acid solution followed by the addition of cationic polymeric quaternary amine, whereby coagulated NCP is obtained, which is dried. In preparing the nanocomposite from natural rubber, clay is added directly to the natural latex (20.3%TS, pH 10.8) diluted with demineralized water and containing the antioxidant Irganox. This mixture is gradually added to a sulfuric acid solution pH 3-4, together with a cationic polymeric quaternary amine solution. The obtained precipitate is centrifuged, washed, and dried at 66° C. This document also describes the production of rubber compositions which include the produced NCPs, diene-type rubber (polybutadiene, polyisoprene, or styrene/butadiene copolymer), charges (carbon black, silica, etc.) and a coupling agent. Those compositions are subsequently vulcanized with sulfur compounds.

Document EP 1321489 discloses the preparation of an elastomeric nanocomposite from cationic latex, which can be styrene-butadiene, styrene-isoprene, isoprene, butadiene, isoprene- butadiene, butadiene-acrylonitrile, and isoprene-acrylonitrile. The clay (montmorillonite) is dispersed in water, at 8O⁰C and under strong stirring, to which dispersion cationic latex is added, which coagulates forming the solid NCP. It also describes the preparation of a rubber composition which includes the produced NCP, a diene- type elastomer and additional reinforcing charge as carbon black, precipitated silica and/or silica-containing carbon black, and also a coupling and vulcanization agent having a vulcanizing agent containing sulfur. Document owned by Beijing Chemical Engineering University, CN1238353, discloses the preparation of a nm-class composite rubber-clay material by mixing the rubber latex with an aqueous clay suspension, coagulating, and subsequently removing water.

In the articles published by the authors of the document CN 1238353 (Zhang, L. et al. Polymer Engineering and Science, 78, 1873- 1878,200; Wang, Y. et al. Journal of Applied Polymer Science, 78, 1879- 1883, 2000; Wu, Y-P et al. Journal of Applied Polymer Science, 82, 2842-2848, 2001 ; Wu, Y-P. Journal of Applied Polymer Science, 89, 3855-3858, 2003; Wu, Y-P. et al. Composites Science and Technology, 65, 1 195-1202, 2005; Jia, Q- X. et al. Journal of Applied Polymer Science, 103, 1826- 1833, 2007), the described process involves the addition of rubber latex (SBR, SVBR, NBR or carboxylated NBR) to an aqueous suspension of bentonite clay (2%), followed by stirring. This mixture is then coagulated with a coagulating solution which may be hydrochloric acid, calcium chloride, or triethylenetetraammonium chloride, at concentrations between 1 and 2%. No mention is made as to the use of stirring during the coagulation process and the order of addition of the coagulating agent varies, either the coagulant is added in the latex and rubber mixture or the clay latex dispersion is added in the solution of the coagulating agent. However, patent CN 1238353 claims that the coagulant should be added on the latex and clay dispersion, that the preparation of the clay and latex mixture should be made using microwave or ultra-sound, and that substances able to cause the coupling of the rubber and clay macromolecules should be added to the clay mixture.

In the work developed by Wu, Y-P., et al. (Wu, Y- P., et al. Journal of Applied Polymer Science, 89, 3855-3858, 2003), mention is made to the use of a compatibilizer in the formation of the nanocomposite, which showed a low exfoliation degree of sheets with an increasingly higher clay content. According to the method described in these works, obtained nanocomposites are always vulcanized.

Ln another work developed by Wu, Y-P., et al. (Wu, Y-P., et al. Composites Science and Technology, 65, 1 195- 1202, 2005) it was observed the occurrence of a increase on the basal spacing in the NR and SBR nanocomposites, coagulated with triethylenetetraammonium chloride, as high as 1.34 nm, which is above the 1.25 mm of sodium montmorillonite. For NBR and CNBR nanocomposites, coagulated with calcium chloride, the basal spacing was as high as 1 .50 nm. Although the results were good, they did not reflect the formation of a nanocomposite, since by modifying the clay with calcium chloride or triethylenetetraammonium chloride, authors observed the same basal spacing, of 1.34 nm and 1.52 nm, for R-NHi⁺-IVTMT and Ca^"+- MMT, respectively. They came to the conclusion that the intercalation of rubber molecules in the interlayer spacing did not occur, but rather an ion exchange reaction between R-NH₃ ⁺ and Ca ⁺ ions with Na⁺ ions, during the coagulation. This means that most sheets reagregate themselves when in the presence of the electrolyte, and the coagulated and dried material was called a nanocompound. The work developed by Jia, Q-X., et al. (Jia, Q-X. et al. Journal of Applied Polymer Science, 103, 1826- 1833, 2007) describes the obtainment of nanocomposites from nanocompounds mixed with modifying agents, such as quaternary ammonium salt or silane. A nanocompound is obtained by adding latex on an aqueous dispersion of clay. This mixture is coagulated in an electrolytic solution, whereby the nanocompound is obtained. The dried nanocompound is mixed with modifying agents (quaternary ammonium salt or silane), vulcanizing agents, and other additives and vulcanized, whereby the nanocomposite is obtained. Therefore, authors of the Chinese document

CN 1238353 do not obtain nanocomposites by using what they call LCM (Latex Compound Method) with subsequent coagulation, without making the use of the post-addition of a quaternary surfactant, which is a widely-known procedure and described in the state of art and with vulcanization.

Document US67101 1 1 discloses the preparation of polymer nanocomposites from a mixture of negatively-charged polymer latex and a cationic polyelectrolyte. Actually, the clay suspension is added slowly to the cationic polyelectrolyte solution. The cationic polyelectrolyte must belong to poly(diallyldimethylammonium chloride) or poly(4-vinylpyridine chloride) group.

The clay, now positively-charged, as a result of the excess of positive charges from the polyelectrolyte, is mixed with an anionic latex, wherein the mixture coagulates due to the opposed charges of clay and latex.

Nevertheless, the examples described in this patent are prepared with SBR or PMMA latex dispersions at concentrations of 2.35% by solid content. The concentration of clay, a fluoromica, in the aqueous suspension should be of 0.5 m/v, and the concentration of the polyelectrolyte solution should be of 2%.

In the described patents, the coagulants used are saline solutions of di- or trivalent metals, in some cases associated with diluted solutions of strong acids. The use of polyelectrolytes may also be included, which raises the cost of the product. These coagulants are already commonly used in coagulation processes known in the industrial field.

There are numerous latex coagulation systems described in the literature and even well-known in the industrial field, which include solutions of electrolytes such as potassium chloride, calcium chloride, magnesium chloride, mixtures of sodium chloride and sulfuric acid, mixtures of sodium chloride, polyamine, and sulfuric acid, mixtures of aluminum sulfate and sulfuric acid, magnesium sulfate, acids such as sulfuric, hydrochloric, nitric, or phosphoric acid, sodium carbonate and sodium sulfate, as well as organic salts such as sodium or potassium acetates, sodium oxalate, sodium tartarate, calcium acetates, or magnesium. Some patents owned by big companies also disclose latex coagulation systems, such as from 3 M, which uses onium salts, such as tetrabutylphosphonium hydroxide. The use of quaternary ammonium salts and polyelectrolytes is also described.

In the preparation of elastomer-clay nanocomposites via latex, a dispersion containing clay and polymer latex is firstly obtained. In order to produce the solid nanocomposite, water needs to be removed. Recently, a new methodology for preparing polymer nanocomposites through the latex dispersion method was developed, wherein layers from the layered compound, a phyllosilicate, are intercalated and/or fully exfoliated (PI 0301 193-3), without the modification of the clay or addition of any additive.

The present invention refers to a process for obtaining solid nanocomposites from the coagulation of latex and clay dispersions prepared by the latex dispersion method, wherein layers from the layered compound, a phyllosilicate, are intercalated and/or fully exfoliated without modification of the clay or addition of any additive, whereby solid polymer (elastomer)-clay nanocomposites are obtained in which the layers of the phyllosilicate are intercalated and/or fully exfoliated.

The solid polymer (elastomer)-clay nanocomposite obtained by the process of this invention can be extruded, calendered, compression molded, injection molded, blow molded, molded in various forms including fibers, films, automotive industrial parts, household products, used in the manufacture of innerliners and innertubes for airplanes, automobiles, trucks, etc., due to its impact resistance, low vapor permeability, and resistance to oils and solvents.

Summary of the invention

The present invention refers to a process for obtaining a solid nanocomposite from a dispersion containing non- modified solid layered silicate and polymer latex wherein the solid nanocomposite is obtained through an electrolytic coagulation of the latex and clay dispersion.

This invention also refers to a solid nanocomposite obtained by means of the process described in the invention, said nanocomposite having from 60% to 99.999% by mass of polymer and 0.001 % to 40% of non-modified solid layered silicate.

This invention still refers to solid articles comprising said solid nanocomposite obtained by means of the process described in the invention, said nanocomposite having from 60% to 99.999% by mass of polymer and 0.001% to 40% of non- modified solid layered silicate.

Brief description of the drawings

Figure 1 - X-ray diffractograms of Cloisite® clay and natural rubber nanocomposites having 10 phr of Cloisite®, obtained through a coagulation process by the addition of the dispersion of clay and natural latex on the acetic acid solution, according to examples 1 to 4.

Figure 2 - X-ray diffractograms of Argel-T clay and the natural rubber nanocomposite having 10 phr of Argel-T, obtained through a coagulation process by the addition of the dispersion of clay and natural centrifuged latex on the acetic acid solution, according to example 5.

Figure 3 - X-ray diffractograms of Brasgel PBS 50 clay and the natural rubber nanocomposite having 10 phr of

Brasgel PBS 50, obtained through a coagulation process by the addition of the dispersion of clay and natural centrifuged latex on the acetic acid solution, according to example 6.

Figure 4 - X-ray diffractograms of Viscogel Aco clay and the natural rubber nanocomposite having 10 phr of

Viscogel Aco, obtained through a coagulation process by the addition of the dispersion of clay and natural centrifuged latex on the acetic acid solution, according to example 7.

Figure 5 - X-ray diffractograms of Cloisite® clay and nitrile rubber nanocomposites having 10 phr of Cloisite®, obtained through a coagulation process by the addition of the dispersion of clay and nitrile latex on the aluminum sulphate solution, according to examples 8 and 9.

Figure 6 - X-ray diffractograms of Cloisite® clay and the nitrile rubber composite having 10 phr of Cloisite®, obtained through a coagulation process by the addition of the coagulating agent on the dispersion of clay and nitrile latex, according to example 10.

Figure 7 - Mass increase in pure natural rubber coagula and nanocomposites having 10 phr of clay, by xylene sorption, according to examples 1 to 7.

Figure 8 - Mass increase in pure nitrile rubber coagula, nanocomposites and composites having 10 phr of clay, by the sorption of an isooctane-toluene mixture, according to examples 8 and 10.

Figure 9 shows scanning electron microscopy micrographs of secondary and backscattered electrons of a cross- section of the nanocomposite obtained according to Example I .

Figure 10 shows clear-field images of cross- sections of the nanocomposite obtained according to Example 8 obtained by transmission electron microscopy. Nanocomposites were prepared according to procedures described in Examples I to 10. * - Clay sheets parallel to the plane.

Detailed description of the invention The present invention refers to a process for obtaining solid nanocomposites from the coagulation of latex and clay dispersions prepared by the latex dispersion method, where layers of the layered compound, a phyllosilicate, are intercalated and/or fully exfoliated without modification of the clay or addition of any additive. Latex and clay dispersions referred to herein are prepared according to teachings disclosed in document PI 0301 193-3.

The present process of the invention concerns the production of rubber nanocomposites with clay, through the coagulation of clay and latex dispersions, prepared according the teachings disclosed in document PI 0301 193-3, whereby solid nanocomposites are obtained.

The methodology developed and disclosed in document PI0301 193-3 for preparing polymer nanocomposites, describes that the layers of the layered compound, a phyllosilicate, are intercalated and/or fully exfoliated in the polymeric matrix, without modification of clay or addition of any additive. The novelty shown in the present invention is the method for coagulating latex and clay dispersions, such as, for example, natural rubber and nitrile rubber latexes, prepared according to teachings disclosed in document PI 0301 193-3, whereby rubber and clay solid nanocomposites are obtained where layers of the phyllosilicate are intercalated and/or fully exfoliated. The solid nanocomposite obtained through this process can be extruded, molded, thermopressed, calendered, and vulcanized.

The present invention refers to a process for obtaining a solid nanocomposite from an aqueous dispersion containing non-modified solid layered silicate and polymer latex, wherein said solid nanocomposite is obtained through an electrolytic coagulation of the latex and clay dispersion. The electrolytic coagulation process occurs by means of the addition of the latex and clay dispersion on a coagulating agent solution. Preferably, the addition of the latex and clay dispersion on a coagulating agent solution occurs under a shearing action over the coagulated latex and clay dispersion. The shearing action is preferably obtained by means of mechanical and/or magnetic and/or manual stirring. During the addition of the latex and clay dispersion on the coagulating agent solution, a temperature rise of the coagulated dispersion is preferably carried out. Layered silicates to which the present invention refers correspond to clays which, in the case of this invention, are selected from the types consisting of smectite, hectorite, mica, vermiculite, saponite, montmorillonite, or any mixture thereof. Preferably, the clay used in the present invention is montmorillonite. The polymer latex of the present invention is selected from natural rubber, nitrile rubber, carboxylated nitrile rubber, styrene-butadiene, styrene, carboxylated styrene-butadiene, synthetic polyisoprene, acrylic rubber, or any mixture thereof.

The coagulation method described in this process of the invention consists in adding the rubber latex dispersion with clay on the coagulating agent solution, under stirring. Coagulating agents which may be used in this coagulation process include weak and strong acid solutions, such as acetic, hydrochloric, sulfuric acid, salt solutions of monovalent (Na⁺, K⁺, NH₄ ⁺), divalent (Ca²⁺, Mg²⁺), and trivalent (Al ¹ , F-V ) cations, wherein the anion of the salt may be sulphate, chloride, nitrate, phosphate, acetate, among others, and can also be associated with the use of acid solutions from these anions. Some examples of salts which can be used in the coagulation process described herein are: aluminum sulphate, magnesium sulphate, calcium chloride, aluminum chloride, sodium chloride, and ammonium chloride. Coagulating agents can further be used in mixtures of one or more components, at concentrations comprised between 0.3 and 5 mol.L^"1.

The amount of layered clay or material in the rubber nanocomposite of the present invention may range widely, from 0.001 to 40% by mass of the nanocomposite, but preferably, from 0.5 to 30% by mass. The amount of clay will be determined by the use or application intended for the rubber nanocomposite.

Elastomers and polymers which can be used include, but are not limited to, natural rubber, nitrile rubber, carboxylated nitrile rubber, styrene-butadiene, carboxylated styrene- butadiene, synthetic polyisoprene, acrylic rubber.

The process for coagulating the nanocomposite prepared via latex makes feasible the production of elastomeric nanocomposites from its latexes, without the need of introducing an intercalant into clays, making them become organoclays, and without the need of using coagulated rubber and hot mixture processes for obtaining the nanocomposites.

Advantages provided by the method for preparation of rubber nanocomposites via coagulation described in this invention are: a) absence of organic solvents; b) clay is not required to be chemically modified nor undergo purifying processes in order to be used in the preparation of nanocomposites, when compared to documents described in the state of art; c) the elastomer does not need to be modified; d) does not make the use of the addition of intercalating agents in order to aid the intercalation of the elastomer into the clay; e) does not make the use of surface modifying agents for obtaining nanocomposites, whether in pre- or post-addition conditions, such as quaternary ammonium salt in order to achieve good properties of resistance to solvents and exfoliation of clay sheets; f) does not make the use of rubber vulcanization through any known method.

The present invention still refers to a process for obtaining a solid nanocomposite as described above, wherein said process comprises a step of drying the coagulated nanocomposite dispersion.

The present invention also refers to a step of diluting the solid and dried nanocomposite, obtained according the process of the invention, in a polymeric matrix processable in fluid state.

The invention also refers to a process for obtaining a solid nanocomposite which comprises a process for obtaining a solid nanocomposite from the coagulation of an aqueous dispersion containing non-modified layered silicate and polymeric latex, as described in the invention. The solid nanocomposite obtained by the process described in the present invention comprises from 60% to 99.999% by mass of polymer and 0.001% to 40% by mass of a non-modified solid layered silicate. Also as an object of the present invention are included solid articles comprising a solid nanocomposite obtained from the coagulation of an aqueous dispersion containing non- modified layered silicate and polymeric latex as described in the invention.

Some specific examples are described in the following in order to illustrate the present invention more particularly. Examples described herein show some preferred embodiments of the present invention and are not intended to limit the scope of protection thereof.

Example 1 : Preparation of the Coagulated Nanocomposite from Centrifuged Natural Rubber Latex with Sodium Montmorillonite Clay 10 phr.

An aqueous dispersion of sodium montmorillonite clay (Cloisite®-Na available from Southern Clay Products), prepared according to teachings disclosed in document PI0301 19-3, was added to 145.7 of centrifuged natural rubber latex having a high ammonium content with 64% solids, by mass. The mixture was homogenized and left to rest for 24 hours. About 40.0 g of the clay and latex dispersion were added to 3.0 g of acetic acid solution 10%, by volume, thereby obtaining a coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water.

Example 2: the same procedure as described in Example 1, differing only in that coagulation of 40.0 g of the clay and latex dispersion occurred by addition into 10,0 g of acetic acid solution 10%, by volume, thereby obtaining the coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water. Example 3: the same procedure as described in

Example 1 , except that solid content of the clay and latex dispersion was of 12% by mass. Coagulation of 40.0 g of the clay and latex dispersion occurred by addition into 40,0 g of acetic acid solution 1%, by volume, thereby obtaining a coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water.

Example 4: Preparation of the Coagulated Nanocomposite from Raw Natural Rubber Latex with Sodium Montmorillonite Clay 10 phr. An aqueous dispersion of sodium montmorillonite clay (Cloisite®-Na available from Southern Clay Products), prepared according to teachings disclosed in document PI0301 19-3, was added to 125Og of raw natural rubber latex having a high ammonium content with 36% solids, by mass. The flocculated mixture was then added slowlv to 730 mL of acetic acid solution ( 10%, by volume), thereby obtaining the coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water. Example 5: The same procedure as described in

Example 1 , except that a dispersion of Argel-T clay (Bentonit Uniao Nordeste) was prepared, thereby obtaining the coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water.

Example 6: The same procedure as described in Example I , except that a dispersion of Brasgel PBS-50 clay (Bentonit Uniao Nordeste) was prepared, thereby obtaining the coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water.

Example 7: The same procedure as described in Example 1 , except that a dispersion of Viscogel Aco 50 clay (Uniao Brasileira de M ineraςao) was prepared, thereby obtaining the coagulated nanocomposite. The coagulated nanocomposite was washed until the pH of the washing water was neutral, pressed and dried to remove all water.

Example 8: Preparation of the nanocomposite from Nitrile Rubber Latex with Sodium Montmorillonite Clay 10 phr. An aqueous dispersion of sodium montmorillonite clay (Cloisite®-Na available from Southern Clay Products), prepared according to teachings disclosed in document PI0301 19-3, was added to 144,3 g of nitrile rubber latex (25.2% non-volatiles, 3 1 -34% acrylonitrile, and Mooney viscosity of 20-30 MML l +4@ 100°C) with 24% solids, by mass. The dispersion was homogenized and left to rest for 24 h, thereafter being added to 1000 niL of aluminum sulphate solution 0.84% m/v, thus obtaining the coagulated nanocomposite. The coagulated nanocomposite was filtered, washed until the pH of the washing water was neutral, pressed and dried to remove all water.

Example 9: The same procedure as described in Example 6, except that nitrile rubber latex has 25.7% of non- volatiles, 3 1 -34% of acrylonitrile, and a Mooney viscosity of 42-52 MML 1+4 @ 100⁰C. The clay and latex dispersion obtained was added to 1000 niL of aluminum sulphate solution 0.84% m/v, thus obtaining the coagulated nanocomposite. The coagulated nanocomposite was filtered, washed until the pH of the washing water was neutral, pressed and dried to remove all water. Example 10: Preparation of a composite from

Nitrile Rubber Latex with Sodium Montmorillonite Clay 10 phr.

This example serves to demonstrate that, by adding the coagulating agent on the latex and clay dispersion, a nanocomposite is not obtained, but rather a composite material. An aqueous dispersion of sodium montmorillonite clay (Cloisite®-Na available from Southern Clay Products), prepared according to teachings disclosed in document P10301 19-3, was added to 144.3 g of nitrile rubber latex (25.7% non-volatiles, 31-34% acrylonitrile, and Mooney viscosity of 42-52 MML 1 +4@ 100⁰C) with 24% solids, by mass. The dispersion was homogenized and left to rest for 24 h, thereafter being slowly coagulated with an aluminum sulphate solution 0.84% m/v. The coagulated material was filtered, washed until the pH of the washing water was neutral, pressed and dried to remove all water. What evidences the intercalation or exfoliation of clay in the rubber is the displacement of the diffraction peak 0001 , which corresponds to the basal spacing for lower angles (that is, increase of the interlayer distance) or the absence of the peak corresponding to the basal spacing in the X-ray diffractogram of the nanocomposites. Figures 1 to 5 show X-ray diffractogram s of nanocomposites coagulated in different electrolyte solutions, according to procedures described in Examples 1 to 9.

According to Figures 1 to 5, natural rubber and nitrile rubber nanocomposites with Cloisite, Argel-T, Brasgel PBS 50, and Viscogel Aco clays were obtained with all coagulating agent solutions utilized by the method of adding the clay and latex dispersion on the coagulating agent solution. This positive evaluation is accomplished by determining the intensity and angle of the peak corresponding to the basal spacing, or in the absence of a basal spacing in the X-ray diffractogram of the sample. In all cases, a reduction in the intensity of the basal peak and a displacement of the peak angle to a low angle has occurred, suggesting that intercalation of the elastomer between the clay layers and/or exfoliation thereof has occurred. Tables 1 and 2 show interlayer distances of rubber and clay nanocomposites, coagulated in different coagulating agent solutions, according to Examples I to 9, computed from X-ray diffractograms.

Table I . Interlayer distances of Cloisite-Na⁺ and nanocomposites from natural rubber and nitrile rubber obtained by coagulation, according to examples 1 to 5 and 8 to 9.

Table 2. Interlayer distances of Argel-T, Brasgel PBS 50, Viscogel Aco and nanocomposites from natural rubber obtained by coagulation, according to examples 5 to 7.

According to Table 1 nanocomposites prepared with Cloisite and coagulated by adding the latex and clay dispersion on the coagulating agent solution showed an increase on the basal spacing between 1.49 and 1.57 nm, demonstrating the intercalation of the elastomer in the clay.

Table 2 shows interlayer distance values of nanocomposites prepared with Argel-T and Viscogel Aco clays and coagulated by adding the latex and clay dispersion on the coagulating agent solution, in which an increase on the basal

I O spacing of clay was observed, which was between 1 .44 and 1 .50 nm, demonstrating the intercalation of the elastomer in the clay. In the case of the nanocomposite prepared with Brasgel PBS 50 clay, no diffraction peak of clay below 10 degrees was observed, which demonstrates the high exfoliating degree of clay in the nanocomposite. Xylene sorption tests were carried out with coagulated natural rubber nanocomposites, obtained according to examples 1 to 7, as a function of time. As a reference a natural rubber coagulum without clay coagulated with an acetic acid solution 2% by volume was used. Figure 7 shows sorption curves as a function of time.

By the end of 2 hours of swelling the natural rubber coagulum had a mass increase as high as 1354%. Coagulated nanocomposites, prepared according to examples 1 to 7, showed a decrease on the solvent sorption which in these coagula reached over 995%.

Sorption tests of an isooctane and toluene mixture ( 1 : 1 ) were carried out with coagulated nitrile rubber nanocomposites, obtained according to examples 8 and 10, as a function of time. As a reference a nitrile rubber coagulum without clay coagulated with an aluminum sulphate solution 0.84% m/v was used. Figure 8 shows sorption curves as a function of time.

At the end of 2 hours of swelling the nitrile rubber coagulum had a mass increase as high as 70%, at which it starts dissolving. The coagulated nanocomposite, prepared according to example 8, showed a reduction on the solvent sorption of 1 5%. On the other hand, the coagulum prepared according to example 10 swelled as much as the pure rubber, what demonstrates the inefficacy of the coagulation carried out by adding the coagulating solution on the clay and latex dispersion. Scanning electron microscopy images, obtained in the secondary electron (SEI) mode, of cross-sections of coagula prepared according to Example 1 , are shown in Figure 8. Quantitative analysis of silicon and carbon through X-ray energy- dispersive spectrometry were carried out in different points from cross-sections of the coagulum and images A and B show various points in which this analysis was carried out and are representative of the pattern observed in various fields and demonstrate the state of art. Table 2 shows concentration values for silicon and carbon in every point analyzed in cross-sections of images A and B. Generally, silicon is well distributed in analyzed cross-sections, and since this element is the main constituent of clay, it follows that clay is well distributed in the coagulated nanocomposite and that there are no buildup points of this mineral.

Table 3. Quantitative analysis of carbon and silicon in cross-sections of the coagulum obtained according to Example 1 , through EDX.

Clear-field images of the coagulum from Example 8 were obtained by Transmission Electron Microscopy (TEM). Figure 9 shows the four images which were chosen and analyzed to demonstrate the state of art.

The set of images shown in Figure 9 is representative of patterns observed in various fields of the sample in which distribution of clay on the elastomeric matrix can be seen. This set of images was obtained from cross-sections of coagula from Example 8 and observed by means of transmission electron microscopy in various fields. As a result of coagulation, two predominant domains were observed in the images: 1 - some little aggregates and isolated clay layers, as can be seen in images A and B. Dark lines are the edges of individual clay layers or aggregates from various layers. The spacing measured between layers is in the range from 1 .6 to 2.4 nm, at measured points. Still referring to image A it is possible to see clay layers parallel to the plane, due to the geometry and gray level of the drawing, which shows that clay is distributed randomly on the matrix, without a preferred orientation.

2- Large regions containing a great number of clay aggregates, as can be seen in images C and D, but also having some individual layers and some aggregates from a few layers. The width of aggregates ranges from 4.9 to 20.3 nm. Particularly in Image D it is possible to see that between two very thin clay aggregates (~5 nm), there is rubber and the spacing between these layers is of 42.5 nm, which suggests there is a quite exfoliated inorganic material. Another very important result taken from these images is the high adhesion degree between clay layers and the elastomer, which demonstrates the formation of the nanocomposite.

Claims

1. A process for obtaining a solid nanocomposite from an aqueous dispersion containing non- modified solid layered silicate and polymer latex, characterized in that it comprises an electrolytic coagulation of the latex and clay dispersion.

2. Process for obtaining a solid nanocomposite, according to Claim 1, characterized in that the electrolytic coagulation of the latex and clay dispersion occurs by adding the dispersion on a coagulating agent solution.

3. Process for obtaining a solid nanocomposite, according to Claim 2, characterized in that the addition of the latex and clay dispersion on a coagulating agent solution occurs under a shearing action over the coagulated nanocomposite dispersion.

4. Process for obtaining a solid nanocomposite, according to Claim 3, characterized in that the shearing is obtained by means of mechanical and/or magnetic and/or manual stirring.

5. Process for obtaining a solid nanocomposite, according to any one of Claims 2 to 4, characterized by rising the temperature after the addition of the latex and clay dispersion on a coagulating agent solution.

6. Process for obtaining a solid nanocomposite, according to any one of Claims 1 to 5, characterized in that, in the latex and clay dispersion, solid layered silicates comprise clay.

7. Process for obtaining a solid nanocomposite, according to Claim 6, characterized in that clay is selected from the types consisting of smectite, hectorite, mica, vermiculite, saponite, montmorillonite, or any mixture thereof.

8. Process for obtaining a solid nanocomposite, according to Claim 6, characterized in that the clay is montmorillonite.

9. Process for obtaining a solid nanocomposite, according to any one of Claims 1 to 8, characterized in that the polymer latex is selected from natural rubber, nitrile rubber, carboxylated nitrile rubber, styrene-butadiene, carboxylated styrene- butadiene, synthetic polyisoprene, acrylic rubber, or any mixture thereof.

10. Process for obtaining a solid nanocomposite, according to any one of Claims 2 to 9, characterized in that the coagulating agent solution is selected from weak acid solutions.

1 1. Process for obtaining a solid nanocomposite, according to Claim 10, characterized in that the weak acid is acetic acid.

12. Process for obtaining a solid nanocomposite, according to any one of Claims 2 to 9, characterized in that the coagulating agent solution is selected from strong acid solutions.

13. Process for obtaining a solid nanocomposite, according to Claim 12, characterized in that the strong acid used is hydrochloric acid.

14. Process for obtaining a solid nanocomposite, according to Claim 12, characterized in that the strong acid used is sulfuric acid.

15. Process for obtaining a solid nanocomposite, according to any one of claims 2 to 9, characterized in that the coagulating agent solution is selected from salt solutions of monovalent cations.

16. Process for obtaining a solid nanocomposite, according to Claim 15, characterized in that the monovalent cation used is selected from Na⁺, K⁺ e NH₄ ⁺.

17. Process for obtaining a solid nanocomposite, according to any one of claims 2 to 9, characterized in that the coagulating agent solution is selected from salt solutions of divalent cations.

18. Process for obtaining a solid nanocomposite, according to Claim 1 7, characterized in that the divalent cation used is selected from Ca^+" e Mg^{+^}.

19. Process for obtaining a solid nanocomposite, according to any one of claims 2 to 9, characterized in that the coagulating agent solution is selected from salt solutions of trivalent cations.

20. Process for obtaining a solid nanocomposite, according to Claim 19, characterized in that the trivalent cation used is selected from Al ^J and Fe \

21 . Process for obtaining a solid nanocomposite, according to any one of claims 15 to 20, characterized in that the anion of the salts used is selected from sulphate, chloride, nitrate, phosphate, and acetate.

22. Process for obtaining a solid nanocomposite, according to any one of claims 2 to 21, characterized in that the coagulating agent solution may comprise the salts as defined in claims 15 to 21 associated with acids.

23. Process for obtaining a solid nanocomposite, according to claim 22, characterized in that acids are selected from sulfuric acid, nitric acid, phosphoric acid, and acetic acid.

24. Process for obtaining a solid nanocomposite, according to any one of claims 2 to 23, characterized in that the coagulating agent solution has a molar concentration of the solute from 0.3 mol/L to 5 mol/L.

25. Process for obtaining a solid nanocomposite, according to any one of claims 1 to 24, characterized in that it further comprises a step of diluting the solid nanocomposite in a polymeric matrix processable in fluid state.

26. Process for obtaining a solid nanocomposite, according to any one of claims 1 to 25, characterized in that it further comprises a step of drying the coagulum obtained from the latex and clay dispersion.

27. Process for obtaining a solid nanocomposite, characterized in that it comprises a process for obtaining a solid nanocomposite as defined in any one of claims 1 to 26.

28. Process for obtaining a solid nanocomposite, according to any one of claims 1 to 26, characterized in that the resulting nanocomposites are formed by 60% to 99.999% by mass of polymer and 0.001 % to 40% of non-modified solid layered silicate.

29. A solid nanocomposite obtained by a process as defined in any one of claims 1 to 27, characterized in that it comprises from 60% to 99.5% by mass of polymer and from 0.5% to 40% of non-modified solid layered silicate.

30. Solid article, characterized in that it comprises a solid nanocomposite as defined in claim 29.