EP1086144A1 - Methods for the preparation of polyamide nanocomposite compositions by in situ and solid state polymerizations - Google Patents

Abstract

In situ polymerization of polyamide monomers and silicate materials followed by solid state polymerization produces polyamide nanocomposite materials with desirable physical properties. The nanocomposite materials produced include homopolymers and copolymers. The properties of the nanocomposite materials may be varied by the choice of monomers, type of silicate, and polymerization conditions.

Description

METHODS FOR THE PREPARATION OF POLYAMIDE NANOCOMPOSITE COMPOSITIONS BY IN SITU AND SOLID STATE POLYMERIZATIONS

FIELD OF THE INVENTION This invention relates to a process to prepare a nanocomposite material comprising a polymer matrix having dispersed therein a silicate. More particularly, this invention relates to a process to prepare a nanocomposite material comprising forming a flowable mixture of a polyamide and a silicate material, dissociating the silicate, and subjecting the dissociated flowable mixture to a solid state polymerization step to produce the nanocomposite material. CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. Provisional Application Serial No. 60/074,639, filed February 13, 1998, and PCT Application Serial No. PCT US99/03097 filed February 12, 1999.

BACKGROUND OF THE INVENTION International Application WO 93/04118 discloses a process of preparing a polymer nanocomposite having platelet particles dispersed therein. The process involves melt-processing the polymer with a swellable and polymer-compatible intercalated layered material and subjecting it to a shear rate sufficient to dissociate the layers. The layered material is compatibilized with one or more "effective swelling/compatibilizing agents" having a silane function or an onium cation function.

International Application WO 93/04117 discloses a process of preparing a polymer nanocomposite having platelet particles dispersed therein, where the polymer and the swellable and polymer-compatible intercalated layered material are melt-processed; The layered material is compatibilized with one or more "effective swelling/compatibilizing agents" selected from primary ammonium, secondary ammonium and quaternary phosphonium ions. The selected swelling/compatibilizing agents "...render their surfaces more organophilic than those compatibilized by tertiary and quaternary ammonium ion complexes...", facilitate exfoliation, resulting in less shear in mixing and less decomposition of the polymer, and heat stabilize the composite more than other cations (such as quaternary ammonium cation) swelling/compatibilizing agents. International Patent Application WO 94/22430 discloses a nanocomposite composition having a polymer matrix comprising at least one gamma phase polyamide, and dispersed in the polyamide is a matrix of a nanometer-scale particulate material. The addition of the particulate material to nylon 6 resulted in an improvement of flexural modulus and fiexural strength (from 7 to 35%), when compared to unfilled nylon 6. The addition of the particulate material to nylon

6,6 resulted in very little improvement (1 to 3%) of flexural modulus and flexural strength when compared to unfilled nylon 6,6.

International Patent Application WO 93/10098 discloses a polymer composite made by melt-processing a polymer with swellable and polymer-compatible intercalated layered material comprising layers having reactive organo- silane species covalently bonded to their surfaces. International Patent Application WO 95/14733 discloses a method of producing a polymer composite that does not demonstrate melting or glass transition by melt-processing a polymer with a layered gallery-containing crystalline silicate. The examples include intercalated sodium silicate and a crystalline poly(ethylene oxide), montmorillonite intercalated with a quaternary ammonium and polystyrene, and montmorillonite intercalated with a quaternary ammonium and nylon 6.

International Patent Application WO 98/29499 discloses polyester nanocomposite compositions containing clay particles. The clay particles are preferably synthetic or chemically modified. U.S. Patent No. 4,889,885 (issued December 26, 1989) describes a composite of a non- polyamide resin and a dispersed layered silicate. The silicate is treated with an onium salt ion exchange, and added to a monomer or oligomer.

U.S. Patent No. 5,514,734 (issued May 7, 1996) describes polymer composites containing layered or fibrillar particles derivatized with organosilanes, organotitanates, or organozirconates. Composite materials are characterized by thickness, diameter, and interlayer distances.

International Patent Application WO 93/11190 describes a polymer composite containing an exfoliated material derivatized with a reactive organosilane. Polymers are added prior to mixing in an extruder. International Patent Application WO 94/11430 describes gamma crystalline phase polyamides containing dispersed layered inorganic materials. EPO application 0 358 415 A1 describes a polyamide resin containing a dispersed layered silicate which has been treated with an organic cation of a lactam as a swelling agent.

Japanese Kokai Patent No. SHO 62[1987]-252426 describes polymerization of a nylon 6 monomer in the presence of a silicate. The cooling rate of the polymer is controlled to achieve particular crystalline structures in the resulting composite.

None of the above references, alone or in combination, disclose the present invention, as claimed.

SUMMARY OF THE INVENTION

This invention relates to a process to prepare a polymer nanocomposite composition suitable for automotive, electronic, film and fiber applications, where a combination of tensile strength, tensile modulus and flexural modulus are required. Additionally, the claimed polymer nanocomposite composition has a desirable surface appearance, toughness, ductility and dimensional stability. The composition processes well and tolerates a wide range of molding conditions. The present invention relates to a process to prepare the above polymer nanocomposite composition comprising forming a flowable mixture of a polyamide and a silicate material and dissociating (as that term is described in more detail below) at least about 50% but not all of the silicate, and subjecting the polyamide in the dissociated flowable mixture to a solid state polymerization step. Optionally, the silicate is a silicate material treated with at least one ammonium ion of the formula: NR₁R₂R₃R₄ wherein:

Ri, R₂, R₃ and R_t are independently selected from a group consisting of a saturated or unsaturated Ci to C ₂ hydrocarbon, substituted hydrocarbon and branched hydrocarbon, or where Ri and R₂ form a N,N-cyclic ether. Examples include saturated or unsaturated alkyls, including alkylenes; substituted alkyls such as hydroxyalkyls, alkoxyalkyls, alkoxys, amino alkyls, acid alkyls, halogenated alkyls, sulfonated alkyls, nitrated alkyls and the like; branched alkyls; aryls and substituted aryls, such as alkylaryls, alkyoxyaryls, alkylhydroxyaryls, alkylalkoxyaryls and the like. Optionally, one of Ri, R , R₃ and R₄ is hydrogen. The milligrams of treatment per 100 grams of silicate (MER) of the treated silicate, described in more detail below, is preferably from about 10 milliequivalents/100 g below the cation exchange capacity of the untreated silicate to about 30 milliequivalents/100 g above the cation exchange capacity of the untreated silicate.

An additional embodiment of the invention relates to nanocomposite compositions comprising a polyamide and a silicate. The polyamide may have a concentration of amine groups at least 10 mole % greater than the concentration of the carboxylic acid end groups. Preferably the polyamide has a weight average molecular weight in the range of about 30,000 D to about 40,000 D. Alternatively, the polyamide may have a weight average molecular weight of at least 40,000 D.

A further embodiment is directed towards a nanocomposite composition comprising a polyamide and a silicate, wherein the silicate is treated with an ammonium ion of the formula: wherein R_a, R_D and Rς is hydrogen (H) and and R_d includes a carboxylic acid moiety.

The composite polymer matrix material of the present invention demonstrates, when tested, an improvement in tensile modulus and flexural modulus, without a substantial decrease in tensile strength or toughness when compared to that of the polymer without the silicate.

DESCRIPTION OF THE FIGURES

The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

DETAILED DESCRIPTION OF THE INVENTION

Polyamides of the present invention are synthetic linear polycarbonamides characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain which are separated from one another by at least two carbon atoms. Polyamides of this type include polymers, generally known in the art as nylons, which can be obtained from diamines and dibasic acids having the recurring unit represented by the general formula:

-NHCOR₅COHNR₆ - in which R₅ is an alkylene group of at least 2 carbon atoms, preferably from about 2 to about 11 or arylene having at least about 6 carbon atoms, preferably about 6 to about 17 carbon atoms; and R_<5 is selected from R₅ and aryl groups. Also, included are copolyamides, terpolyamides and the like obtained by known methods, for example, by condensation of hexamethylene diamine and a mixture of dibasic acids consisting of terephthalic acid and adipic acid. Polyamides of the above description are well-known in the art and include, for example, polyQiexamethylene adipamide) (nylon 6,6), poly(hexamethylene sebacamide) (nylon 6,10), poly(hexamethylene isophthalamide), poly(hexamethylene terephthalamide), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azelamide) (nylon 9,9), poly (decamethylene sebacamide) (nylon 10,9), poly(decamethylene sebacamide) (nylon 10,10), poly [bis(4-amino cyclohexyl)methane-l,10-decanecarboxamide)], poly(m-xylene adipamide), poly(p-xylene sebacamide), poly(2,2,2-trimethyl hexamethylene terephthalamide), poly(piperazine sebacamide), poly(p-phenylene terephthalamide), poly(metaphenylene isophthalamide), and copolymers and terpolymers of the above polymers. Additional polyamides include nylon 4,6, nylon 6,9, nylon 6,10, nylon 6,12, nylon 11, nylon 12, amorphous nylons, aromatic nylons and their copolymers.

Other useful polyamides are those formed by polymerization of amino acids and derivatives thereof, as for example, lactams. Illustrative of these useful polyamides are poly(caprolactam) (nylon 6), poly(4-aminobutyric acid) (nylon 4), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid) (nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(l 1-aminoundecanoic acid) (nylon 11), poly(12- aminodocecanoic acid) (nylon 12) and the like. The preferred polyamide is Vydyne® nylon, which is poly(hexamethylene adipamide)

(nylon 6,6), which gives a composite with the desired combination of tensile strength, tensile modulus and flexural modulus for the applications contemplated herein (Vydyne^® is a registered trademark of Solutia Inc.).

The preferred molecular weight of the polyamide is in the range of about 30,000 to about 80,000 D (weight average) with a more preferred molecular weight in the range of about 30,000 to about 40,000 D. The most preferred molecular weight of the polyamide is at least about 40,000 D (weight average). Increasing the weight average molecular weight of the polyamide from about 35,000 to about 55,000 D results in an unexpected increase in toughness as indicated by the notched Izod impact test. Whereas an increase in the weight average molecular weight of from about 35,000 to about 55,000 D in the polyamide neat results in a small increase in toughness, the same increase in molecular weight in the nanocomposite results about twice the increase in toughness. Therefore, the increase in toughness is enhanced in the nanocomposite when compared to that of the polyamide neat.

In a preferred embodiment, the polyamide has an amine end group/acid end group ratio greater than one (1). More preferably, the concentration of amine end groups is at least 10 mole % greater than the concentration of the carboxylic acid end groups. In an even more preferred embodiment, the polyamide has a concentration of amine end groups at least 20 mole % greater than the concentration of the carboxylic acid end groups, and in a most preferred embodiment, the polyamide has a concentration of amine end groups at least 30 mole % greater than the concentration of the carboxylic acid end groups. In another embodiment, the concentration of amine end groups is essentially equal to the concentration of carboxylic acid end groups.

Among the preferred embodiments is nylon 6, nylon 6,6, blends thereof and copolymers thereof. The range of ratios of the nylon 6/nylon 6,6 in the blends is from about 1/100 to 100/1. Preferably, the range is from about 1/10 to 10/1. The range of ratios of the nylon 6/nylon 6,6 in the copolymers is about 1/100 to 100/1. Preferably, the range is from about 1/10 to 10/1. Optionally, the nanocomposite composition comprises at least one additional polymer.

Examples of suitable polymers include polyethyleneoxide, polycarbonate, polyethylene, polypropylene, poly(styrene-acrylonitrile), poly(acrylonitrile-butadiene-styrene), poly(ethylene terephthalate), poly(butylene terephthalate), poly(trimethylene terephthalate), poly(ethylene naphthalate), poly(ethylene terephthalate-co-cyclohexane dimethanol terephthalate), polysulphone, poly(phenylene oxide) or poly(phenylene ether), poly(hydroxybenzoic acid-co- ethylene terephthalate), poly(hydroxybenzoic acid-co-hydroxynaphthenic acid), poly(esteramide), poly(etherimide), poly(phenylene sulfide), poly(phenylene terephthalamide).

The mixture may include various optional components which are additives commonly employed with polymers. Such optional components include surfactants, nucleating agents, coupling agents, fillers, impact modifiers, chain extenders, plasticizers, compatibilizers, colorants, mold release lubricants, antistatic agents, pigments, fire retardants, and the like.

Suitable examples of fillers include carbon fiber, glass fiber, kaolin clay, wollastonite, mica and talc. Suitable examples of compatibilizers include acid-modified hydrocarbon polymer, such as maleic anhydride-grafted propylethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylenebutylene-styrene block copolymer. Suitable examples of mold release lubricant includes alkyl amine, stearamide, and di-or tri- aluminum stearate.

Suitable examples of impact modifiers include ethylene-propylene rubber, ethylene- propylene diene rubber, methacrylate-butadiene-styrene (with core-shell morphology), poly(butylacrylate) with or without carboxyl modification, poly(ethylene acrylate), poly(ethylene methylacrylate), poly(ethylene acrylic acid), poly(ethylene acrylate) ionomers, poly(ethylene methacrylate acrylic acid) terpolymer, poly(styrene-butadiene)block copolymers, poly(styrene-butadiene-styrene)block terpolymers, poly(styrene-ethylene/butylene-styrene) block terpolymers and poly(styrene-ethylene/butylene-styrene carboxylate) block terpolymers. Suitable coupling agents include silane, titanate and zirconate coupling agents. Silane coupling agents are well-known in the art and are useful in the present invention. Examples of suitable coupling agents include octadecyltnmethoxysilane, gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropylphenyldimethoxysilane, gamma- glycidoxypropyl tripropoxysilane, 3,3-epoxycyclohexylethyl trimethoxysilane, gamma- proprionamido trithoxysilane, N-trimethoxysilylpropyl-N(beta-aminoethyl) amine, trimethoxysilylundecylamine, trimethoxysilyl-2-chloromethylphenylethane, trimethoxysilylethylphenylsulfonylazide, N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride, N-(trimethoxysilylpropyl)-N-methyl-N,N-diallylammonium chloride, trimethoxysilylpropylcinnamate, 3-mercaptopropyl trimethoxysilane, 3- isocyanatopropyltriethoxysilane, and the like. The preferred silane is gamma- aminopropyltriothexy silane. The silane coupling agent is optionally added to the polymer composite in the range of about 0.5 to about 5 weight % of the layered silicate. The preferred concentration range of silane coupling agent is about 1 to about 3 weight % of the layered silicate in the composite.

In one embodiment, the nanocomposite composition further comprises a composition wherein an end group of the polyamide is bonded to a surface of the treated silicate by a silane coupling agent.

The silicate materials of the present invention are selected from the group consisting of layered silicates and fibrous, chain-like silicates, and include phyllosilicates. Examples of fibrous, chain-like silicates include chain-like minerals, for example sepiolite and attapulgite, with sepiolite being preferred. Such silicates are described, for example, in Japanese Patent Application Kokoku 6-84435 published October 26, 1994.

Examples of layered silicates include layered smectite clay minerals such as montmorillonite, nontronite, beidellite, volkonskoite, Laponite^® synthetic hectorite, natural hectorite, saponite, sauconite, magadiite, and kenyaite; vermiculite; and the like. Other useful materials include layered illite minerals such as ledikite and admixtures of illites with one or more of the clay minerals named above. The preferred layered silicates are the smectite clay minerals such as montmorillonite, nontronite, beidellite, volkonskoite, Laponite^® synthetic hectorite, natural hectorite, saponite, sauconite, magadite, and kenyaite.

The layered silicate materials suitable for use in the present invention are well-known in the art, and are sometimes referred to as "swellable layered material". A further description of the claimed layered silicates and the platelets formed when melt processed with the polyamide is found in International Patent Application WO 93/04117, which is hereby incorporated by reference. The layered silicate materials typically have planar layers arrayed in a coherent, coplanar structure, where the bonding within the layers is stronger than the bonding between the layers such that the materials exhibit increased interlayer spacing when treated.

The layered silicate materials may be treated as described in more detail below with the subject ammonium ion to enhance the interlayer swelling and/or spacing useful for the performance of the treated silicate of the present invention. As used herein the "inter layer spacing" refers to the distance between the faces of the layers as they are assembled in the treated material before any delamination (or exfoliation) takes place. The preferred clay materials generally include interlayer or exchangeable cations such as Li⁺, Na⁺, Ca²⁺, K⁺, Mg²⁺ and the like. In this state, these materials have interlayer spacings usually equal to or less than about 4 A and only delaminate to a low extent in host polymer melts regardless of mixing. In the claimed embodiments, the cationic treatment is a ammonium species which is capable of exchanging with the interlayer cations such as Li⁺, Na⁺, Ca²⁺, K⁺, Mg²⁺ and the like in order to improve delamination of the layered silicate.

The treated silicate of the present invention is a silicate material as described above which is treated with at least one ammonium ion of the formula

" R₁R₂R₃R₄ wherein: Rj, R₂, R₃ and R are independently selected from a group consisting of a saturated or unsaturated Ci to C₂ hydrocarbon, substituted hydrocarbon and branched hydrocarbon, or where Ri and R₂ form a N,N-cyclic ether. Examples include saturated or unsaturated alkyls, including alkylenes; substituted alkyls such as hydroxyalkyls, alkoxyalkyls, alkoxys, amino alkyls, acid alkyls, halogenated alkyls, sulfonated alkyls, nitrated alkyls and the like; branched alkyls; aryls and substituted aryls, such as alkylaryls, alkyoxyaryls, alkylhydroxyaryls, alkylalkoxyaryls and the like. Optionally, one of Ri, R₂, R₃ and is hydrogen. A mixture of two or more ammonium ions is contemplated by the present invention.

In an embodiment of the present invention, Ri is selected from the group consisting of hydrogenated tallow, unsaturated tallow or a hydrocarbon having at least 6 carbons, and R₂, R₃ and R₄ independently have from one to eighteen carbons. Tallow is composed predominantly of octadecyl chains with small amounts of lower homologues, with an average of from 1 to 2 degrees of unsaturation. The approximate composition is 70% ₈, 25% C₁₆, 4% Cj and 1% C₁₂. In another preferred embodiment of the present invention, Rj and R₂ are independently selected from the group consisting of hydrogenated tallow, unsaturated tallow or a hydrocarbon having at least 6 carbons and R₃ and R₄ independently have from one to twelve carbons.

Examples of suitable Ri, R₂, R3 and R_ι groups are alkyl such as methyl, ethyl, octyl, nonyl, tert-butyl, ethylhexyl, neopentyl, isopropyl, sec-butyl, dodecyl and the like; alkenyl such as 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 1-heptenyl, 1-octenyl and the like; cycloalkyl such as cyclohexyl, cyclopentyl, cyclooctyl, cycloheptyl and the like; alkoxy such as ethoxy; hydroxyalkyl; alkoxyalkyl such as methoxymethyl, ethoxymethyl, butoxymethyl, propoxyethyl, pentoxybutyl and the like; aryloxyalkyl and aryloxyaryl such as phenoxyphenyl, phenoxymethyl, phenoxydecyl, phenoxyoctyl and the like; arylalkyl such as benzyl, phenylethyl, 8-phenyloctyl, 10-phenyldecyl and the like, alkylaryl such as 3-decylphenyl, 4-octylphenyl, nonylphenyl and the like.

Suitable ammoniums used in treating the silicate materials include oniums such as dimethyldi(hydrogenated tallow) ammonium, dimethylbenzyl hydrogenated tallow ammonium, dimethyl(ethylhexyl) hydrogenated tallow ammonium, trimethyl hydrogenated tallow ammonium, methylbenzyldi(hydrogenated tallow) ammonium, N,N-2- cyclobutoxydi(hydrogenated tallow) ammonium, trimethyl tallow ammonium, methyldihydroxyethyl tallow ammonium, octadecylmethyldihydroxyethyl ammonium, dimethyl (ethylhexyl) hydrogenated tallow ammonium and mixtures thereof. Particularly preferred ammoniums include quaternary ammoniums, for example, dimethyldi(hydrogenated tallow) ammonium, dimethylbenzyl hydrogenated tallow ammonium, methyldihydroxyethyl tallow ammonium, octadecylmethyldihydroxyethyl ammonium, dimethyl(ethylhexyl) hydrogenated tallow ammonium and mixtures thereof. The treatment with the ammonium ion(s), also called "cationic treatments", includes introduction of the ions into the silicate material by ion exchange. In the embodiment where the silicate material is a layered silicate, the cationic treatments may be introduced into the spaces between every layer, nearly every layer, or a large fraction of the layers of the layered material such that the resulting platelet layers comprise less than about 20 particles in thickness. The platelet layers are preferably less than about 8 particles in thickness, more preferably less than about 5 particles in thickness, and most preferably, about 1 or about 2 particles in thickness.

The treated silicate has a MER of from about 10 milliequivalents/100 g below the cation exchange capacity of the untreated silicate to about 30 milliequivalents/100 g above the cation exchange capacity of the untreated silicate. The MER is the milliequivalents of treatment per 100 g of silicate. Each untreated silicate has a cation exchange capacity, which is the milliequivalents of cations available for exchange per 100 g of silicate. For example, the cation exchange capacity of the layered silicate montmorillonite can be about 95, and the exchange capacity of sepiolite is in the range of about 10 to about 20. When the MER of the treated silicate substantially exceeds the cation exchange capacity, there is an excess of cationic treatment which may be available to react with the polyamide. This excess may cause degradation of the properties of the polyamide. The higher the MER, the lower the concentration of silicate in the treated silicate. Therefore, a first nanocomposite sample may have a higher concentration of treated silicate but a lower concentration of silicate, than a second nanocomposite sample, because the first sample has a higher MER than the second sample. If the MER value of the treated silicate is substantially less than its exchange capacity, for example about 85 MER for the preferred montmorillonite, there is too little of the cationic treatment to have a beneficial effect. If the MER exceeds about 125, the excess ammonium may be detrimental to the properties of the nylon. Preferably, when the untreated montmorillonite has an exchange capacity of about 95, the treated layered silicate has a cation exchange capacity of from about 85 to about 125.

The amount of silicate included in the composition is in the range of about 0.1 to about 12 weight % of the composite. The concentration is adjusted to provide a composite polymer matrix material which demonstrates, when tested, an increase in tensile modulus and flexural modulus, without a substantial decrease in tensile strength. Preferably, the increase in tensile modulus and flexural modulus is at least about 10%. More preferably, the increase in tensile modulus and flexural modulus is at least about 20%o. Too little silicate fails to provide the desired increase in tensile modulus and flexural modulus. Too much silicate provides a polyamide composite with a decreased tensile strength. Further, it may be desirable to have the crystalline regions of the polyamide in the nanocomposite composition be less than about 1.0 μm.

The particle size of the silicate is such that optimal contact between the polymer and the silicate is facilitated. The range of particle size can vary from about 10 microns to about 100 microns. Preferably, the particle size is in the range of from about 20 to about 80 microns. Most preferably, the particle size is below about 30 microns, such as those that pass through 450 mesh screens, in that the resulting polymer nanocomposite has improved performance properties.

Optionally, the silicate can be treated with one or more ammonium ions of the formula

^R_aR_bRcRd wherein at least one of R_a, R_D and R_c is hydrogen (H) and R_<j is selected from a group consisting of a saturated or unsaturated Ci to C ₂ hydrocarbon, substituted hydrocarbon and branched hydrocarbon. Examples include saturated or unsaturated alkyls, including alkylenes; substituted alkyls such as hydroxyalkyls, alkoxyalkyls, alkoxys, amino alkyls, acid alkyls, halogenated alkyls, sulfonated alkyls, nitrated alkyls and the like; branched alkyls; aryls and substituted aryls, such as alkylaryls, alkyoxyaryls, alkylhydroxyaryls, alkylalkoxyaryls and the like. As the definition of the Rd group for the ammonium ion above is generally the same as the definition for the I^_t group in the ammonium ion, the Examples set forth above for the R₄ group are also exemplary of the R_d group.

In a separate embodiment, R_a, R_D and R_c are hydrogen (H), and the R_d group contains a carboxylic acid moiety such that the ammonium ion

⁺NR_aR_bRcRd is an amino acid, for example 12-aminolauric acid ammonium. In this embodiment, it is particularly preferred that the amine end groups/acid end groups ratio of the polyamide is greater than one (1) .

Optionally, the above ammonium ions may be mixed with at least one quaternary ammonium ion, said mixture used to treat the silicate. The quaternary ammonium ion preferably has a hydrocarbon chain. The hydrocarbon chain may be saturated or unsaturated. The hydrocarbon chain may be obtained from a natural source such as tallow, or from a synthetic source such as a synthesized or purified C₁₂, Cj₄, C₁₆, or C₁₈ chain. A preferred mixture includes at least one of dimethyldi(hydrogenated tallow) ammonium, methyl dihydroxyethyl tallow ammonium, dimethylbenzyl hydrogenated tallow ammonium and/or dimethyl(ethylhexyl) hydrogenated tallow ammonium, either alone or in combination with 12-aminolauric acid ammonium.

Optionally, the silicate can be further treated with azine cationic dyes, such as nigrosines or anthracines. Said cationic dyes would impart color-fastness and uniformity of color in addition to increasing the intercalation of the polymer molecules.

It is further desirable to have a polymer composite that provides both the desired strength and flexibility, and yet is lightweight. This is accomplished by minimizing the concentration of silicate in the nanocomposite. The preferred nanocomposite contains a concentration of silicate of from about 0.1 to about 12.0 weight % of the composite. The most preferred nanocomposite contains a concentration of silicate of from about 0.5 to about 6.0 weight % of the composite. In a first embodiment of the present invention, the nanocomposite composition is prepared using a three step process. One step includes forming a flowable mixture of the polyamide as a polymer melt and the silicate material. The second step includes dissociating at least 50% but not all of the silicate material. The term "dissociating", as utilized herein, means delaminating or separating the silicate material into submicron-scale structures comprising individual or small multiple units. For the embodiment wherein layered silicates are utilized this dissociating step includes delaminating the silicate material into submicron scale platelets comprising individual or small multiple layers. For the embodiment wherein fibrous, chain-like silicates are utilized, this dissociating step includes separating the silicate material into sub- micron scale fibrous structures comprising individual or small multiple units.

As referred to in the mixture forming step, a flowable mixture is a mixture which is capable of dispersing dissociated silicate material at the submicron scale. A polymer melt is a melt processable polymer or mixture of polymers which has been heated to a temperature sufficiently high to produce a viscosity low enough for submicron scale mixing to occur. The process temperature should be at least as high as the melting point of the polyamide employed and below the degradation temperature of the polyamide and of the organic treatment of the silicate. The actual extruder temperature may be below the melting point of the polyamide employed, because heat is generated by the flow. The process temperature is high enough that the polymer will remain in the polymer melt during the conduct of the process. In the case of a crystalline polyamide, that temperature is above the polymer's melting temperature. For example, a typical nylon 6, having a melting point of about 225°C, can be melted in an extruder at any temperature equal to or greater than about 225°C, as for example between about 225°C and about 260°C. For nylon 6,6 a temperature of preferably from about 260°C to about 320°C is normally employed.

Conventional methods can be employed to form the flowable mixture. For example, the flowable mixture can be prepared through use of conventional polymer and additive blending means, in which the polymer is heated to a temperature sufficient to form a polymer melt and combined with the desired amount of the silicate material in a granulated or powdered form in a suitable mixer, as for example an extruder, a B anbury^® type mixer, a Brabender^® type mixer, Farrell continuous mixers, and the like.

In one embodiment, the flowable mixture may be formed by mixing the polyamide with a previously formed silicate-containing concentrate. The concentrate includes the silicate and a polymer carrier. The concentration of the silicate material in the concentrate, and the amount of concentrate are selected to provide the desired silicate concentration for the final nanocomposite composition. Examples of suitable polymers for the carrier polymer of the concentrate include polyamide, ethylene propylene rubber, ethylene propylene diene rubber, ethylene-ethylacrylate, ethylene-ethylmethacrylate or ethylene methacrylate. Examples include Iotek^® ionomer and Escor^® ATX acid terpolymer, both available from Exxon. The polyamide polymers suitable for the carrier polymer include nylons such as nylon 6, nylon 6,6, nylon 4,6, nylon 6,9, nylon 6,10, nylon 6,12, nylon 11, nylon 12, amorphous nylons, aromatic nylons and their copolymers. The polymer of the carrier may be the same as or different from the polyamide of the flowable mixture. For example, both polymers may be a polyamide, particularly nylon 6,6, but may have the same or different molecular weight. The preferred weight average molecular weight of the carrier polymer of the concentrate is in the range of about 5,000 D to about 60,000 D. The most preferred range of the weight average molecular weight for the carrier polymer is in the range of about 10,000 to about 40,000 D. In this embodiment, the dissociation step of the present process, as described below, may occur at least in part via the forming of the concentrate such that the dissociation step may precede the step of forming the flowable mixture. It is therefore understood that the process steps (e.g., forming and dissociating) may occur sequentially without regard to order, simultaneously or a combination thereof. In the second step, the flowable mixture is sufficiently mixed to form the dispersed nanocomposite structure of dissociated silicate in the polymer melt, and it is thereafter cooled. The silicate can be dissociated by being subjected to a shear having an effective shear rate. As used herein, an effective shear rate is a shear rate which is effective to aid in dissociation of the silicate and provide a composition comprising a polyamide matrix having silicate substantially homogeneously dispersed therein without substantially breaking the individual units (e.g., platelets or fibrous chains).

Any method which can be used to apply a shear to a flowable mixture or any polymer melt can be used. The shearing action can be provided by any appropriate method, such as by mechanical means, by thermal shock, by pressure alteration, or by ultrasonics. Preferably, the flowable polymer mixture is sheared by mechanical methods in which portions of the melt are caused to flow past other portions of the mixture by use of mechanical means such as stirrers, Banbury^® type mixers, Brabender^® type mixers, Farrel^® continuous mixers, and extruders. Most preferably, the mixture is subjected to multiple shearings. In addition to the increased shear provided by multiple shearing, increased residence time is also provided, which results in improved performance properties. Another procedure employs thermal shock in which shearing is achieved by alternatively raising or lowering the temperature of the mixture causing thermal expansions and resulting in internal stresses which cause the shear. In still other procedures, shear is achieved by sudden pressure changes in pressure alteration methods; by ultrasonic techniques in which cavitation or resonant vibrations which cause portions of the mixture to vibrate or to be excited at different phases and thus subjected to shear. These methods of shearing flowable polymer mixtures and polymer melts are merely representative of useful methods, and any method known in the art for shearing flowable polymer mixtures and polymer melts may be used.

Shearing can be achieved by introducing the polymer pellets at one end of the extruder (single or twin screw) and receiving the sheared polymer at the other end of the extruder. A preferred twin screw extruder is a co-rotating fully intermeshing type, such as the ZSK series manufactured by Werner and Pfleiderer Company. The silicate can be fed into the twin screw extruder at the feed throat or at the downstream vent. The preferred method is to feed the silicate at the downstream vent, which produces a composite polymer with improved performance properties.

Another preferred continuous compounder is the Farrel Continuous Mixer (FCM). For composites using Vydyne 21 nylon, the preferred temperature of the melt is in the range from about 275 to 315°C, with the most preferred range being from about 275 to 295°C.

The polymer melt containing nano-dispersed dissociated silicate material may also be formed by reactive extrusion in which the silicate material is initially dispersed as aggregates or at the nanoscale in a liquid or solid monomer and this monomer is subsequently polymerized in an extruder or the like. Alternatively, the polymer may be granulated and dry mixed with the treated silicate material, and thereafter, the composition may be heated in a mixer until the polymer is melted forming the flowable mixture. The third process step is a solid state polymerization step, wherein the compounded pellets are held for several hours at a high temperature at least about 20°C below the melting or softening point of the polymer. For example, for nylon 6 and nylon 6,6, typical solid state polymerization conditions are heating the solid polymer in the range of about 200°C to about 240°C for a period of from about 2 to about 5 hours. It is desirable to remove water produced during polymerization, e.g. by a dry nitrogen stream. Said additional process step results in an increase in molecular weight and an improvement in toughness, ductility and tensile strength of the nanocomposite.

The solid state polymerization step can be further effected with a catalyst that increases the molecular weight of the polyamide, e.g., a phosphorous-containing catalyst such as monosodium phosphate. Such phosphorous-containing catalysts are disclosed in U.S. Patent No. 4,966,949. For the composites that include a catalyst, milder treatment conditions are needed to effect the desired polymerization. For example, the treatment temperature can be below the temperature used in solid state polymerization absent the catalyst using the same polyamide, i.e., more than 20°C below the melting or softening point of the polyamide. The treatment time can be lowered to the range of about 0.5 hours to about 5 hours.

An optional processing step is a heat treatment step, where the composition is heated to improve intercalation of the nylon molecules into the silicate structure. Said heat treatment step is performed by heating the composition at a temperature in the range of about 200°C to about 240°C for a period of about 2 to about 5 hours. The heat treatment step can optionally be incorporated into the dissociating step by increasing the residence time of the mixture in the mixer or extruder, thereby heat treating under melt conditions.

The process to form the nanocomposite is preferably carried out in the absence of air, as for example in the presence of an inert gas, such as argon, neon or nitrogen. The process can be carried out in a batchwise or discontinuous fashion, as for example, carrying out the process in a sealed container. Alternatively, the process can be carried out in a continuous fashion in a single processing zone, as for example, by use of an extruder, from which air is largely excluded, or in a plurality of such reaction zones in series or in parallel.

In another embodiment of the present invention, the process to prepare a polymer nanocomposite composition comprises forming a first flowable mixture of a polyamide, at least one monomer and a silicate material; dissociating at least 50% but not all of the silicate material; polymerizing the monomer; and subjecting the polyamide in the mixture to solid state polymerization. It is to be understood that the polymerization of the monomer step can occur simultaneously or sequentially with one or more other steps in the process of this embodiment. Preferably, at least one monomer of the this embodiment includes monomers such as ε- caprolactam, lauryllactam, and their corresponding lactones. In yet another embodiment of the present invention, the process to prepare a polymer nanocomposite composition comprises forming a flowable mixture of a polyamide and a treated silicate material; dissociating the at least about 50% but not all of the treated silicate material; adding an additional amount of said polyamide, most preferably during said dissociating step; and subjecting the polyamide in the mixture to solid state polymerization.

Each of the above embodiments of the process to prepare the polymer nanocomposite composition can be followed by additional steps or treatments, or additional melt polymerization of the composition by increasing the residence time in the mixer with the removal of water condensation product. The increased residence time can also improve the intercalation of the polyamide into the silicate, as discussed above.

The composition of the present invention may be made into, but is not limited to, the form of a fiber, film or a molded article.

Solid state polymerization increases toughness, strength, and ductility of the produced polymer, while generally maintaining processability and modulus. Solid-state polymerization may improve properties such as elongation at yield, tensile elongation at break, flexural modulus, elastic modulus and both notched and unnotched Izod impact strength. Additional catalysts may be added, but are not required. Acid-functional clay treatments are particularly amenable to SSP (e.g., SCPX 1016 and SCPX 1255). They may serve to build polymer-clay linkages by tethering nylon molecules to the adsorbed acid moieties. The stoichiometric balance of amine and acid groups can impact the properties of the resulting polymer. A higher amine:acid ratio in the nylon is desirable, especially in the case of aminoacid-treated silicates. The use of solid state polymerization to finish the nanocomposite would allow starting with a lower RV nylon that would enhance intercalation, leading to greater exfoliation of the clay layers. The inherent brittleness of nanocomposites compounded on the FCM may be overcome with SSP finishing, to make the FCM a viable low cost process alternative.

The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

EXAMPLES

Materials:

The following types of nylon 6,6 polymers have been employed in nanocomposites described herein.

NYLON MATRIX RESINS

The montmorillonite clay used has an exchange capacity of about 95 millieqivalents per 100 g of silicate.

Example 1 : Conventional compounding without SSP

A high molecular weight in the nylon matrix of nanocomposites has been found to be even more beneficial for the ductility and toughness of the nanocomposites than for the neat nylon polymer. The smectic silicates reduce nylon molecular weight during the compounding operation, especially in the first pass, resulting in a loss of ductility and toughness. For example, the molecular weight of nylon b was observed to drop from 36,500 to 31,500 D in a single pass of 7% montmorillonite treated with dimethyl di(hydrogenated tallow) ammonium cation (2M2HT-montmorillonite) through a 40 mm ZSK twin screw extruder manufactured by Krup Werner & Pfleiderer Company. A second pass reduced the MW further to only 21,000 D. The second pass under dry conditions could instead improve mechanical performance both due to molecular weight building as well as enhanced exfoliation and dispersion of the nano-platelets. Solid state polymerization (SSP) can be implemented in compounded nanocomposites under similar conditions used for the neat polymer as a more efficient method for building molecular weight. Improvements are obtained in tensile strength and elongation, as well as notched and un-notched Izod impact strength. Slight losses in modulus sometimes occur, perhaps due to breakage of the thin delaminated platelets during flow of the higher viscosity nylon matrix.

Effects of molecular weight

The effects of the nylon 6,6 molecular weight or its equivalent relative solution viscosity (RV) on mechanical properties are shown in Figures 1 and 2 for nanocomposites prepared by conventional compounding in a twin screw extruder without subsequent SSP. The nylon RV is that of the raw material fed to the extruder. PI and P2 in Figure 2 refer to the first and second passes through the compounder.

A higher amine/ carboxyl end group ratio on the nylon is preferable for nanocomposites, including those that are later subjected to SSP. The inherent Lewis acidity of the clay surface in combination with any acidity introduced from clay treatment, either in the form of an aminoacid cation or the polyacrylate peptizer used on some clay grades, could alter the end group balance of the nylon, resulting in some degree of depolymerization. For example, an acidity of 40 μequiv/g (4.0 mequiv/lOOg clay) -COOH was measured for both acrylate-coated Na- montmorillonite and the 2M2HT-montmorillonite. Amino acid exchanged grades would have higher acid levels according to the degree of substitution, as measured by the milliequivalenet exchange ratio (MER) in milliequivalents of cation per 100 g of silicate. Thus, nylons a, and c are preferred to nylon b. The higher amine end group concentration of nylon d would be especially important in the case of silicates treated with amino acid cations, which can react with the amine end groups of the nylon. These treated silicates show a stronger response to the effects of SSP, resulting in larger increases in the above properties than nanocomposites containing pristine silicates or those treated with unreactive moieties.

The molecular weight changes to the high amine nylon d due to compounding with 4% montmorillonite exchanged with 12-aminolauric acid (ALA-montmorillonite) and subsequent solid state polymerized have been analyzed via GPC.

The symbols used in this table have the following meaning:

Mw: weight-average molecular weight

Mn: number-average molecular weight

IV: intrinsic viscosity measured in formic acid Example 2: Solid state polymerization (SSP)

The extrusion process is seen in the above table to not change the molecular weight or its distribution in the nylon significantly. While a large increase in molecular weight of the nanocomposite does occur during SSP, it is reduced from that of the neat resin (which gels) by the presence of the acid moieties on the clay. There is, furthermore, evidence that the nylon matrix is being bound to the clay even during the compounding operation. During solid state polymerization, the nylon either branches or couples further with the organosilicate to form very high molecular weight species that become insoluble.

Solid state polymerization was practiced by heating the plastic pellets to 200-240°C (typically 220°C) with a dry nitrogen sweep to remove the water of condensation for a period of 2-4 hours (typically 4 hours). It was not necessary to add additional catalysts above those present from the initial melt polymerization, although mono- or di- sodium phosphate could have been added at 100-500 ppm. In one instance, adding 1 ,000 ppm monosodium phosphate resulted in an increase of compounded molecular weight from 27,400 to 30,600 D (SSP was not performed). Typically, the SSP dryer is set to 470°F (243 °C) oil temperature and the nylon nanocomposite is heated for four hours at 220°C (230°C shell temperature) following an approximately 2-hour heat-up period. The resulting time-temperature profiles are shown below for representative nanocomposite solid state polymerization runs.

6.6% wt. 2M2HT-montmorillontie in nylon a solid-state polymerized for five hours

3.7% wt. 2M2HT-montmorillonite in nylon a solid-state polymerized for four hours

3.7% wt. 2M2HT-montmorillonite in nylon a solid-state polymerized for five hours

4.0% wt. ALA-montmorillonite in nylon a solid-state polymerized for three hours

12.2% wt. montmorillonite treated with dimethyl benzyl hydrogenated tallow ammonium cation (2MBHT-montmorillonite) in nylon c, solid-state polymerized for four hours

8.4% wt. 2MBHT-montmorillonite in nylon c solid-state polymerized for two hours

6.2% wt. 2M2HT-montmorillonite in nylon b solid-state polymerized for three hours 650 ppm of monosodium phosphate, monobasic, as catalyst

Example 3: Introduction of ductility

An example of the introduction of ductility through SSP is shown by the stress-strain curves (Figures 3 and 4) for 4.0 w/o ALA-montmorillonite in nylon a.

Example 4: Increase in molecular weight

Increasing molecular weight of the nylon matrix is indicated by the intrinsic viscosity measurements shown in the table below.

Intrinsic viscosity vs. SSP Time

Intrinsic viscosity builds linearly with time in the SSP dryer, as for example shown by the following data and graph (Figure 5).

The rate of increase is faster for acid-terminated ammonium cations at long residence times in a high-amine nylon matrix, as shown by the ALA-montmorillonite data in the graph below (Figure 6).

Example: 5: Injection molding of solid state polymerized nanocomposites

Solid-state polymerized nanocomposites based on nylons c and d mold easier with higher temperature setpoints than at lower temperature. Among these two nylons, the nylon d-based nanocomposites mold more easily than those based on the nylon c, perhaps because the nylon c matrix reaches a higher viscosity level than the nylon d. Lower pack and hold pressures can also be used.

In both cases, however, higher pack pressures and hold pressures than conventionally used to injection mold nylon 6,6 are preferred to better pack out the mold.

Molding Comparisons

Such higher pack and hold pressures usually also tend to increase tensile modulus and strength. Without SSP, lower molding temperatures are preferred for higher ductility in the molded parts due to less thermal degradation of the polymer. However, the higher ductility with SSP is instead achieved by higher molecular weight, thus allowing the use of the higher temperatures that are known to benefit the stiffness of the molded nanocomposite. In this way, an additional degree of processing freedom is introduced via the SSP process by which injection molding parameters can be adjusted to optimize the overall molding process and property spectrum.

Example 6: Mechanical properties for concentrate route using high amine nylon matrix The use of a high amine end carrier nylon in a concentrate to enhance the properties induced by solid state polymerization of the final nanocomposite composition was evaluated. A high amine nylon concentrate comprising 17% ALA-montmorillonite in nylon d was then let down into three different resins having a range in molecular weight and amine/acid end group concentration, with and without subsequent solid-state polymerization prior to molding. A fairly intense screw design was used in the ZSK 40mm twin screw extruder with a feed rate of 100 lbs/hr (43.5 kg/hr) and screw speed of 250 rpm. The barrel zone temperatures were set at 270°C. For the solid-state polymerization the polymerization dryer was set to 470°F (243 °C) oil temperature from start to finish, giving a residence time of up to four hours at a 220°C resin temperature and 230°C shell temperature. Sample descriptions and mechanical properties are given in the table below.

The previous table shows the beneficial effect of solid state polymerization in improving the ultimate mechanical properties of tensile strength and elongation, as well as both notched and un-notched Izod impact strength. Its strong effect on nanocomposites comprising the ALA- montmorillonite compensates any molecular weight degradation of the nylon that might have occurred during compounding. The effects of the parameters can be analyzed more quantitatively by use of the neural network CAD/Chem software (AlWare, Cleveland, OH). In this approach, the nylons are described by their nominal weight-average molecular weight and the nominal ratio of amine/acid end groups. The mineral content of the nanocomposite is retained as a correlating variable to account for the minor differences between samples. On this basis, the following linear correlation coefficients are obtained. SSP refers to the solid state polymerization time, in hours.

These results show that solid state polymerization generally increases tensile properties along with both types of Izod impact strength, while having a negligible overall effect on flex properties. A higher initial molecular weight in the nylon (prior to compounding) could also be somewhat beneficial for notched Izod impact strength, but does not positively affect properties. A higher amine/acid end group ratio is seen to be generally advantageous for ductility (elongation) and toughness (un-notched Izod impact strength) as it helps to maintain nylon molecular weight by counteracting the additional acidity introduced by the clay treatment.

However, strong parameter interactions not apparent in the above table do occur and can be seen in the following response surfaces. With 4 hours solid state polymerization time, a nanocomposite comprising 4.9% by weight ALA-montmorillonite (3.9% mineral ash) in a 40,000 Mw nylon having balanced end groups is predicted to have the following properties: 14.00 Kpsi tensile strength, 612 Kpsi Young's modulus, 21.6% ultimate elongation, 558 Kpsi flex modulus, 18.68 Kpsi flex stress at 5% strain (below breaking strain), 0.91 ft-lb/in notched Izod, 43.9 ft-lb/in un-notched Izod and 9.5 mil/in shrinkage.

Figure 7 shows increasing tensile strength with SSP time when nanoclay is present, but not in the neat nylon. The ductility and toughness of nanocomposites, however, are increased significantly by solid state polymerization and to a lesser extent by higher amine/acid ratio and initial molecular weight of the nylon (Figures 8, 9 and 10). The ALA-montmorillonite concentration in the last two figures is 4.9%. Stiffness (tensile modulus) is slightly increased by solid state polymerization, perhaps through network formation between the high MW nylon and the clay by reactive tethering of the nylon polymer molecules to the ammonium ions adsorbed on the clay surface (Figure 11).

Example 7: Data Tabulation

A comprehensive listing of composition, SSP time and mechanical property data is given in the table below for all of the ALA-montmorillonite, 2M2HT-montmorillonite, 2MBHT- montmorillonite and sepiolite nanocomposite preparations involving solid state polymerization.

Mineral Total Silane S.S.P. Max Tens Tens Brk Tensile Flexural Flexural IZOD IZOD Breaks Mold f\on Clay Ash Clay (wt% on Time Strength Elongat. Modulus Modulus Strength Not. Unnot. / Shrinkage ype Type (% t) (%wt) Clay) (Hrs.) (kpsi) i_ (kpsi) (kpsi) (kpsi) (ft lbin) (ft lb/in) Non-Breaks (mils/in) a 2M2HT-mont 41 66 00 0 1212 44 590 531 178 052 162 (5/0) a 2M2HT-mont 41 66 00 5 1171 195 548 549 177 080 630 a 2M2HT-mont 23 37 00 0 1187 171 522 494 173 069 316 (4/1) a 2M2HT-mont 23 37 00 4 1196 966 481 507 171 096 506 a 2M2HT-mont 23 37 00 5 1160 733 513 541 177 084 631 a ALA-mont 32 40 00 0 1281 46 548 507 179 037 34 (5/0) a ALA-moπt 32 40 00 3 1202 243 528 515 173 076 451 c 2MBHT- ont 51 84 20 0 1397 59 687 701 206 052 115 (5/0) c 2 BHT-mont 51 84 20 2 1353 117 653 695 211 059 109 c 2MBHT-mont 75 122 20 0 1286 20 754 626 204 069 145 (5/0) c 2MBHT-mont 75 122 20 4 1324 22 734 615 197 071 383 b 2M2HT-mont 39 62 00 0 1116 54 544 524 164 050 129 (5/0) b 2M2HT-mont 39 62 00 3 1191 74 537 540 176 057 229 b OO 00 0 1138 477 455 450 160 079 396 (1/3) 194 b ALA-mont 38 48 20 0 1185 25 592 562 191 045 38 (5/0) 107 b ALA-mont 38 48 20 4 1363 226 587 560 186 087 191 (3/0) 98 c ALA-mont 40 50 20 0 1329 157 570 554 190 060 54 (5/0) 105 c ALA-mont 40 50 20 4 1364 204 587 548 185 092 503 (0/4) 106 d ALA-mont 40 50 20 0 1212 24 622 570 196 044 40 (5/0) 79 d ALA-mont 40 50 20 4 1427 181 647 577 193 079 422 (2/3) 74 d Sepiolite 35 41 00 0 1294 33 543 504 179 058 55 (5/0) n a d Sepiolite 35 41 00 4 1268 106 473 466 169 095 423 (1/4) 137 c Sepiolite 25 29 20 0 1181 283 467 446 158 091 426 (1/4) 168 c Sepiolite 25 29 20 4 1156 362 413 401 148 122 453 (0/5) 165

Aminoacid organoclay is seen to provide the most favorable combination of nanocomposite properties following SSP. However, it may cause more embrittlement than other clay types if SSP is not practiced. The acid functionalization is believed to compete for the amine end groups on the nylon chains, thus upsetting the end group balance and degrading nylon molecular weight during compounding. Higher initial molecular weight or amine/acid end group ratio in the selected nylon would help to counteract this effect, but SSP preferably would be performed following compounding to restore or even further increase the nylon molecular weight. Pristine sepiolite is observed to be less destructive to ductility and toughness than is the montmorillonite. Nanocomposite material compounded with a single pass through the Farrell Continuous

Mixer, which tends to impart high modulus but embrittlement in nanocomposites, could be solid-state polymerized to restore ductility and toughness along with possible increase in tensile strength. The combination of FCM compounding with SSP would represent a low cost process to a ductile and tough, yet stiff, nanocomposite. IN-SITU POLYMERIZATION OF NYLON NANOCOMPOSITES

Process Description:

In-situ polymerization holds great promise for improving clay dispersion and enhancing the strength of the silicate-nylon interface over that obtained by melt compounding. Efficient reinforcement comprising more than 20% increase in modulus has been found for a nanocomposite containing only 0.1 % by weight nano-silicate. Silane may be added to the reactor feed to improve interfacial bonding in the final nanocomposite.

Polyamide nanocomposite compositions may be formed by a process comprising forming an aqueous mixture of a treated silicate material and a polyamide monomer, treating the mixture to polymerize the polyamide monomer, and dissociating at least about 50% of the silicate material to form a polyamide nanocomposite composition.

In a specific embodiment, layered (montmorillonite, saponite, hectorite, laponite) and chain-like (sepiolite) silicates may be incorporated into nylon 6,6 and nylon 6,6/6 copolymers by exfoliating and dispersing the clay in the hexamethylene adipamide (HMA) nylon 6,6 salt solution prior to polymerization. Nylon 6,6/6 copolymers may be produced by including a component of epsilon-caprolactam in the monomer feed. The process has been demonstrated in both laboratory and pilot (250 pound (113 kg)) scale autoclaves.

In an alternative embodiment directed towards the preparation of copolymers, the silicates may be pre-dispersed in the caprolactam component prior to its addition to the salt solution. Alternatively, concentrates may be made in nylon 6 or in its precursor caprolactam solution, preferably with the addition of a peptizer, for later addition to the nylon 6,6 polymerization mixture. Low molecular weight liquid polyamides may be used as carriers for the nanoclay. Concentrates of the nanoclay exfoliated in these carriers by high shear homogenization may be added later in the nylon 6,6 polymerization cycle after the aqueous ionic environment is driven off.

The following parameters may affect the performance of the process: a. Prior dispersion of the clay in water, or use of wet never-dried clay, before introduction to the polymerization mixture; b. Application of high shear, ultrasonic energy or venturi cavitation flow to enhance exfoliation of the clay layers prior to polymerization; c. Salt concentration; d. pH; e. Diamine/acid ratio in the HMA salt solution; f. Ion exchange of cations on the clay surface to alter its hydrophobicity and reactivity or physical interaction with the nylon polymer matrix; g. Clay concentration; h. Type of silicate; i. Molecular weight of the nylon at the point clay is added to the polymerization; and j. Composition of the nylon polymer/copolymer.

It may be preferable to perform the process with a "diamine spike", i.e., a higher molar concentration of hexamethylene diamine (HMD) than adipic acid in the mixture to counter any acidity due to the clay or its treatment, as well as to compensate for the loss of HMD by vaporization during the polymerization cycles. The resulting higher viscosity of the polymerized melt indicates a greater molecular weight build in the polymer matrix. Silicate materials

Certain mineral types are preferable for use in the in-situ polymerization process, including synthetic Laponite, commercially available from SCP under the trade name Laponite®, hectorite, sepiolite, saponite, and montmorillonite at various points in the reaction cycle. It has been found to be preferable to first achieve a good dispersion of the exfoliated silicate layers in water prior to contact with the salt solution. In this regard it may be useful to start with a never-dried aqueous dispersion or aqueous suspension instead of dry silicate. Alternatively, dry silicate may be hydrated prior to its participation in the polymerization process. Silicate may be dispersed through high shear homogenization or cavitation generated ultrasonically or by throttling the aqueous suspension through a venturi tube or other methods known in the art.

The silicate material may be organically modified to produce a stronger interface with the nylon matrix phase of the final nanocomposite. Such organoclays are more hydrophobic than the pristine minerals and so may not form stable colloidal dispersions in water or in the nylon 6,6 salt solution. However, as in the melt compounding approach of the earlier patent application, polymer can intercalate the layered clay structure later in the polymerization cycle after the aqueous phase has been largely removed by vaporization. In fact, its lower molecular weight should actually enhance the rate of intercalation, leading to a more complete state of layer exfoliation and higher reinforcement of the final composite by the resulting smaller particle thicknesses than is obtained by direct melt compounding with a pre-polymerized nylon resin. Non-ionic conditions

In an embodiment designed to completely avoid an ionic environment, the silicate material may be added later in the polymerization cycle after the salt has been converted to oligomers or low molecular weight polymers. An alternate approach to avoiding ionic effects is to start the process with molten anhydrous salt in place of the salt solution. Peptizers

In order to avoid gelling, it may be preferable to limit concentration to 2% or possibly up to 4% of the other minerals. Higher concentrations up to about twice these limits may be feasible when a peptizer is also present in the mixture. These contain phosphate ions which may retard the buildup of structure in aqueous suspensions. The phosphates also act as buffers to control pH, which may also be desirable in achieving a high degree of clay dispersion. Examples:

Four clay types received from Southern Clay Products, Inc., Gonzales, TX - Mineral Colloids BP and MO along with Claytone types AF and APA, were dispersed in water, a 70% solution of caprolactam in water and a 50% aqueous solution of hexamethylene adipamide (HMA) at 1% using a Dispermat mixer running at 50 cycle/sec for 60 seconds. Of these four clays, only the dispersion of BP in water was stable. The high shear mixing is preferred. An Omni mixer is an example of a commercially available machine capable of achieving high shear mixing.

It was found that aminolauric acid clay treatment provides improved stability to the colloidal clay suspension in salt solution. Indeed, a macroscopically uniform product of 4% aminolauric acid treated montmorillonite was polymerized into nylon 6,6 in a lab autoclave. However, transmission electron microscopy (TEM) and wide angle x-ray scattering (WAXS) revealed that the silicate of this composite is not fully exfoliated. The mechanical properties of injection molded specimens were not enhanced by the presence of the clay. Foaming was experienced during in-situ polymerization in a lab autoclave with tallow- based (e.g., dimethyl-dihydrogenated tallow ammonium (2M2HT)) organoclay, while untreated (pristine) sodium and calcium montmorillonites did not exfoliate, according to clumps visible by optical microscopy. Use of tertiary ammonium silicate treatment rather than their quaternary counterparts were found to reduce foaming. A 97.5/2.5 nylon 6/6,6 copolymer was polymerized in the presence of 4% by weight 12- aminolauric acid organomontmorillonite. The product displayed considerably enhanced toughness and ductility over the nylon 6,6 homopolymer nanocomposite. Optical microscopy indicated the absence of any micron-sized clay residue, suggesting a higher degree of clay delamination than for the earlier homopolymer. This was confirmed by transmission electron microscopy (TEM). Injection molded properties of this sample were high, showing a 25% increase in tensile modulus and 50% increase in yield strength, with only about 1% silicate on a volume basis - a high reinforcement efficiency.

Alkoxy-modified organoclays comprising the more polar ammonium ions synthesized from alkoxy-functional Jeffamines were observed to produce more stable colloidal suspensions in mixed HMA/caprolactam solutions. In-situ polymerization was successfully performed with an ethoxy-modified montmorillonite. Initially, temperature was kept low (< 260°C) to safeguard against degradation of the clay coating. Smaller test tube sized polymerizations were performed without stirring in a Parr reactor over a range in ethylene oxide / propylene oxide sequencing on the ammonium cation of the treated montmorillonite. WAXS measurements showed the same degree of polymer intercalation into the silicate structure as in samples made with stirring in a lab autoclave. Coating compositions allowed the nylon 6,6 content to be raised as high as 12% without obstructing the silicate intercalation.

One polypropylene oxide quat produced a particularly stable colloidal suspension in a 50/50 mixture of nylon 6,6 salt solution and caprolactam solution that did not phase separate for several days at room temperature. In contrast, pristine sodium montmorillonite suspensions were found not to be stable at room temperature across a range of HMA/caprolactam mixture compositions, though in-situ polymerization of straight nylon 6 nanocomposite from caprolactam solution comprising Gelwhite pristine Ca-montmorillonite supplied by Southern Clay Products, Inc. produced a smooth-flowing concentrate that could later be let down into nylon 6,6 to form a blended nanocomposite.

Gelwhite L nanocomposites of 5, 10 and 15% concentration in nylon 6 prepared in a lab autoclave were let down in nylon 6,6 by adding them to the hexamethylene adipamide salt solution prior to nylon 6,6 polymerization. Although the resulting blend fibers were bright and smooth, indicating the absence of clay clumps, no improvement of physical properties was noted.

Hvdration of silicates

It was discovered that when montmorillonite is fully pre-hydrated, either as a never-dried slurry or by first completely suspending dry clay in water, it forms a more stable colloidal suspension in hexamethylene adipamide salt solution. The following types were found to produce stable 3% colloidal suspensions in water following high shear mixing with an Omni homogenizer: Gelwhite H and Gelwhite L (sodium-exchanged Ca-montmorillonite), Mineral Colloid BP (pristine Na-montmorillonite), poly(propylene oxide) treated montmorillonite, and a hydroxy-terminated poly (ethylene oxide / propylene oxide) copolymer treated montmorillonite. 72 hours after adding salt solution to the water slurries at a level corresponding to 4% clay in the final nanocomposite the following types remained in suspension: Gelwhites H and L, Mineral Colloid BP and certain of the polyether organoclays. The other slurries were stable for at least one hour. Any clays that would not hydrate in water were also found not go into suspension when nylon salt was added.

Suspensions of the following clays made by the above technique were then polymerized without mixing in test tubes using a Parr reactor: Gelwhites H and L, Mineral Colloid BP, and certain of the polyether organoclays. However, the silicate layer d-spacing measured by WAXS in the resulting nanocomposite was still low (13.9 - 14.3 A), indicating little polymer intercalation of at least a portion of the clay. However, the spacing is larger than found in the as- received Mineral Colloid BP Na-montmorillonite. Addition of carboxymethyl cellulose (CMC) was investigated to hold the clay surfaces apart until a low molecular weight polymer is formed. Nylon 6 examples

By using a modified nylon 6,6 two hour batch polymerization cycle, nylon 6 nanocomposites were prepared in-situ from a water solution of caprolactam containing a range of pristine nanoclays, including Ca-montmorillonite, Na-montmorillonite, laponite RD synthetic hectorite and attapulgite. The laponite appeared to disperse most readily, showing no peaks in the WAXS spectrum of the resulting nanocomposite. The relative viscosity (RV) of the resulting nanocomposite was equal to the neat control and its translucency indicated good clay dispersion. A 4-9°C rise in recrystallization temperature vs. the control indicates that the nanoparticles are altering the crystal structure of the nylon matrix in the manner of nucleating agents.

It is thus seen that the presence of the silicate does not appear to affect the polymerization of the nylon. Tensile data on nylon 6 nanocomposite film samples prepared by hot pressing autoclave extrudate between flat plates show a general increase in stiffness with increasing concentration of Gelwhite H pristine Ca-montmorillonite, while tensile strength and elongation are somewhat reduced. The modulus of composites made from Mineral Colloid BP pristine Na-montmorillonite was found to be significantly (40%) higher than any of the other clays tested.

The above experiment was repeated at 1% and 2.5% mineral with the addition of Laponite B mineral as an additional run. Addition of tetrasodium pyrophosphate (TSPP) peptizer to the Gelwhite H sample during homogenization aided in forming a dispersion. The resulting fiber was delustered in comparison to the other candidates. All 1% nanocomposites demonstrated a 10°C increase in recrystallization temperature.

Experiments were conducted on intercalation of layered silicate with molten nylon of low molecular weight into pristine Ca-montmorillonite.

Nylon 6 nanocomposite fiber spun from the polymerization autoclave and comprising 2.5% laponite RD silicate showed a measure of electrical conductivity under high voltage testing. At 5% and 10% concentrations, the melt viscosity was so high that the nanocomposite melt could not be discharged from the autoclave.

Additional mechanical results were obtained on nylon 6 fiber: Gelwhite L and Laponite RD are preferred over Mineral Colloid BP, Gelwhite H, Laponite B and attapulgite for improving modulus without loss in tenacity and elongation. Both spun and drawn yarns were bright and free of nubs.

All of the clay types did show nucleating activity. The above experiments were repeated in part at the 0.5% and 1.0% clay levels, with the clays predispersed in a 70% caprolactam solution. The fourth cycle of the standard nylon 6,6 polymerization cycle was extended from 30 to 60 minutes.

These nanoclays produce enhanced modulus at the 0.5% and 1.0% levels, along with some increase in tenacity at 0.5%). They were also seen to be efficient nucleating agents for nylon 6. However, they also produced higher gel levels, showing HPLC fluorescence numbers of around 100 ppm vs.0-1 ppm for the nylon control. Nylon 6.6 examples

Nylon 6,6 nanocomposites may be polymerized by standard industrial procedures as described in the "Nylon Plastics Handbook" (Melvin I. Kohan, Hanser Publishers, Munich, 1995, pp. 17-23). Gelwhite L may be made into a concentrate of up to 20%> in nylon 6 via in-situ polymerization (with Tamol 850, a sodium polymethacrylate from Rohm and Haas Company, to aid clay dispersion). These concentrates were extruded at the end of the third cycle of the standard polymerization process and given a water quench. The nanocomposites were pulverized and added back to a nylon 6,6 polymerization, either to the salt solution at the beginning of the process or later after the batch achieved a temperature of 220°C. The latter technique generated gels, and neither resulted in any enhancement to the mechanical properties of spun fiber.

A never-dried slurry of an ion exchanged Ca-montmorillonite in which the Ca²⁺ ions have all been exchanged for Na⁺, and containing polyacrylate as peptizer was also polymerized into nylon 6,6 fiber at 1%> concentration, but with no improvement in yarn properties. Melt viscosity was high, but spinnable. The resulting yarn appearance was smooth, but delustered. The Ca²⁺ mined ores are attractive for fiber applications because of their whiter color. However, the aspect ratio of their exfoliated platelets is known to be lower than those from mined Na- montmorillonite. If the clay dispersion in nylon 6,6 salt solution is allowed to age for even a few hours, it begins to coagulate. Polymerization of a one-day old dispersion resulted in a lower RV of the nylon 6,6.

Silicate concentrate carrier solutions

An alternative embodiment for the preparation of silicate / polyamide nanocomposites via in-situ polymerization is to pre-disperse the clay at high concentration in a carrier (as a "concentrate") for addition to the polymerization vessel. For example, it was found possible to disperse Gelwhite L at concentrations of 10-30% in an aqueous solution comprising 25% (based on the weight of the clay component) of a solution of 70% epsilon caprolactam in water and 1%- 5% Tamol 850 dispersing agent. These dispersions remained stable for over three weeks at room temperature. Without the dispersing agent, the dispersion of Gelwhite L at concentrations of or above 10% become unpourable gels. An advantage to the use of these clay concentrates is their possible addition to the reaction mixture later in the polymerization cycle after the ionic aqueous environment has largely been dissipated through vaporization, thus reducing the chances for flocculation. In this example, the dispersion was injected into a nylon 6,6 batch polymerization when the temperature was in the range of 220°C-235°C. The resulting fibers contained nubs which fluoresced under UV light, indicating the presence of gel. Fiber properties were consequently not improved over the nylon control.

In another example of the above technique, Laponite RD could be dispersed at a high concentration of 10% in a 70% solution of caprolactam in water by combining 3% Tamol® 850 with 100%) ethylene glycol, both concentrations based on the weight of the clay. Tetrasodium pyrophosphate (TSPP) and carboxymethyl cellulose (CMC) were found to not be effective peptizers to stabilize montmorillonite suspensions after addition to the nylon 6,6 salt solution, according to WAXS data.

Tamol® dispersing agent was effective in polymerizing 1.5-2% nanocomposites of Mineral Colloid BP in nylon blends comprising 20-30% nylon 6 in nylon 6,6 from aqueous mixtures of caprolactam and hexamethylene adipamide. However, the viscosity of the 2% nanocomposite was so high that it could not be extruded from the reactor. The copolymer composition is attractive because the lower salt concentration reduces clay flocculation while the caprolactam component enhances intercalation of the clay structure, leading to more efficient exfoliation. Potassium tripolyphosphate (KTPP) has been found to be an effective peptizer for nanosilicates in nylon 6,6 salt solution. It is also believed to suppress gel formation. Spun and drawn fibers prepared by injecting stabilized Gelwhite slurry later in the nylon 6,6 polymerization cycle were bright and gel-free, unlike the nubs and fluorescent gels routinely obtained with TSPP and Tamol® 850 peptizers. Fiber containing 0.3% nanoclay retained its matrix properties.

Note: A 10% GELWHITE L slurry in 70% aqueous caprolactam solution was prepared with various amounts of KTPP. In 5820350* and 5820351*, however, GELWHITE L/caprolactam solution was kept at 1/1. Fiber comprising 0.6% Mineral Colloid BP, 1%> KTPP based on the clay weight and a small amount of caprolactam also appeared bright with only minor nub generation.

Many quaternary ammonium halide salts, such as those used in the organomontmorillonites lack the thermal stability required to withstand nylon 6,6 polymerization temperatures of 280-300°C. A lauryl-dimethyl-3-sulfopropyl betaine (Ralufon DL from Raschip Corp.) with higher temperature stability successfully intercalated Gelwhite L pristine Ca-montmorillonite at 1%> concentration in 70% caprolactam solution which, when injected late in the nylon 6,6 polymerization cycle, produced a nylon 6,6 fiber at 0.3% mineral concentration with good luster and absence of gel, along with acceptable mechanical properties. 2% nanocomposites of Mineral Colloid BP, aminolauric acid and (2-ethylhexyldimethyl hydrogenated tallow)modified montmorillonite, were made by infiltration of molten hexamethylene adipamide salt and low (9-10) RV nylon 6,6 polymer, in order to avoid exposure to the ionic environment of the salt solution. WAXS data show the latter approach to improve polymer intercalation in opening up the clay structure.

Nylon 6,6 nanocomposites comprising 1%> nanoclay were prepared from never-dried aqueous suspensions, with the exception of dry Gel-White H which had to be re-dispersed in water. The pre-dispersions are further mixed under high shear with an Omni homogenizer for 10 minutes after introduction to the salt solution.

All of the above clays were obtained from SCP. The Ca-montmorillonite slurry was ion exchanged with sodium ions and also contained an acrylic peptizer.

Samples 8515, 8517 and 8520 could not be extruded out of the polymerization autoclave due to their high melt viscosity, suggesting a significant degree of clay exfoliation despite the presence of a residual WAXS peak at 14.4 A. The greater breadth of the peak does indicate that the original lamina stacks in the clay have been reduced somewhat in thickness. A nylon 6,6 nanocomposite comprising 1% nanoclay from Na-montmorillonite never-dried slurry showed high reinforcement efficiency with a 15% increase in tensile modulus. Sample 8522 was injection molded into tensile test bars which showed a 15%> increase in modulus from 435 to 500 kpsi, a highly efficient reinforcement from the small amount of clay present. The presence of clay does not appear to have any significant effect on the molecular weight of the polymer formed, or its distribution. The presence of CMC in Sample No. 8515 reduces molecular weight, as expected.

Five replicate runs of carpet and industrial tire cord fibers modified with 0.5% and 1.0%) Gelwhite L were prepared in a small autoclave from a 10% clay pre-dispersion in 70%> aqueous caprolactam solution containing 1% each of KTPP and Tamol 850 based on the weight of the clay. The clay slurry was injected into a nylon 6,6 polymerization during the second cycle of the process at 235°C. Modulus increased by 10-20%) in the spun fibers at both concentration levels, although this advantage was retained after drawing only in the carpet fiber at the lower concentration level. Tenacity and elongation of both spun and drawn fibers of both types showed small decreases. It was later shown to be preferable to omit the Tamol ingredient in this particular formulation. A significant level of nano-reinforcement was achieved in injection molded nylon 6,6 nanocomposites made by in-situ polymerization in a 250-pound (113 kg) batch with a very low mineral concentration. A tensile modulus enhancement of 90 kpsi (20%) over neat nylon due to incorporation of only 0.072% mineral content by weight of laponite RD synthetic hectorite represents ten times the maximum benefit that could be anticipated from classical reinforcement mechanisms. Very small crystallite size, indicating nucleation, was detected in these nanocomposites by optical microscopy through crossed polarizers.

Pristine sepiolite, a chain-like silicate, has been demonstrated to be equally effective as montmorillonite or hectorite for nylon fiber reinforcement via in-situ polymerization. At 0.1 %> concentration it provides a high draw capability and enhanced mechanical properties. At 6.5 draw ratio the following fiber properties were obtained vs. a neat nylon control fiber: 84 vs. 76 g/d modulus, 10.2 vs. 9.1 g/d tenacity and 12.3 vs. 10.4% elongation to fail. The nylon matrix RV was equivalent to the neat nylon control.

Sepiolite (1%) increased flex modulus by 13%> in nylon 6,6 polymerized in a lab autoclave. In scale-up to the 250-pound autoclave (113 kg), however, the sepiolite nanocomposites did not demonstrate as great an improvement on the nanocomposite as in the smaller scale experiments. Injection moldings containing 0.09%) by weight pristine sepiolite showed lower reinforcement than the corresponding laponite materials. Tensile strength still increased significantly from 11.1 to 12.0 kpsi in comparison to the unreinforced nylon 6,6 control. The increase in modulus was only a modest 6%, while elongation still reached 30% strain. As with laponite, the presence of the sepiolite mineral during the nylon polymerization had no effect on the nylon polymer, which registered an RV of 42 and acid/amine end group concentrations of 72/52.4. An advantage of sepiolite is that it can be effectively dispersed directly into the HMA salt solution without the need for making a predispersion in water.

Silane, particularly aminopropyltriethoxysilane, may be incorporated into polyamides such as nylon 6,6 by addition to the salt solution along with the nanoclay prior to polymerization. At low levels (0.12-0.25%>), it provided no significant benefit to the properties of the resulting nanocomposite fibers also comprising low (0.1 %>) levels of nanoclay. However, at the higher concentrations of both silane (up to 0.5%>) and nanoclay (up to 2%o) used for injection molding, it does serve to enhance the nanocomposite ductility. Apparently the interfacial strengthening usually attributed to silanes in melt compounded systems can also be effective via in-situ polymerization. On the other hand, in the absence of the silicate the silane alone showed some reinforcing potential of its own in drawn fiber.

The higher aspect ratio reinforcements in general produce higher properties in fiber drawn from in-situ polymerized nylon 6,6 nanocomposites. Thus, montmorillonite and hectorite are more effective than laponite B, which in turn is more effective than laponite RD. Crystallinity is increased slightly and recrystallization temperatures generally increased

(by up to 8°C) through the incorporation of nanoclay during polymerization. Sepiolite, saponite and, to a lesser extent, hectorite are the most efficient nanosilicate nucleators.

Further examples of fibers spun and drawn from in-situ polymerized nylon 6,6 nanocomposites at the pilot plant scale comprise montmorillonite, hectorite and laponite B, both pristine and ion exchanged with ammonium cations. Increases of 15% in modulus and tenacity were achieved along with a 30% increase in creep resistance at a low mineral concentration of only 0.1% by weight that would be significant for tire cord applications. Higher increases of up to 30% in modulus with 10% in tenacity were observed at the bench scale.

Of particular note, the 2% secant modulus of 0.1 %> pristine hectorite nanocomposite drawn carpet yam of 16.6 g/denier was 44% higher than the 11.7 g/denier control yam produced in the same test and drawn to the same denier. Elongation to fail was equivalent to the control, while tenacity was enhanced slightly. The good performance of this nanocomposite may be attributed to pre-dispersion of the silicate in a minor caprolactam component of the formulation. Dihydroxyethyl octadecylammonium is the preferred cation exchanged onto the phyllosilicate minerals for in-situ polymerization in nylon 6,6. A nanocomposite in-situ polymerized with either 0.2 and 0.4% of montmorillonite previously treated with this cation showed improved appearance retention in carpet walk testing. Due to their less hydrophilic nature, organoclays are pre-dispersed at up to 5% concentration directly in nylon salt solution rather than in pure water, as is preferred for the pristine minerals. A slight inhibition of nylon 6,6 polymerization that may occur at higher silicate concentrations (e.g., 2%) may be overcome by increasing reactor residence time in the finishing cycle by about 30%).

Enhanced modulus along with a slightly reduced ductility indicate a better nanoparticle dispersion resulting from the application of ultrasonic energy to the initial clay slurry.

The ideal mineral concentration for fiber spinning appears to be below about 1%, preferably from about 0.1% to about 0.2% by weight. For injection molding applications, high injection molded properties were found for 1.5% silicate content: tensile strength of 91 MPa, modulus of 3.4 GPa and ultimate elongation of 47%, whereas a typical near nylon 6,6 homopolymer would display 80 MPa, 3.0 GPa, and 60%>, respectively. Fiber applications

Fiber applications via the in-situ polymerization approach benefit from the lower modulus targets vs. plastic molding applications, such that lower clay concentration levels may be used where nanoscale interactions play a greater role. Higher orientation levels can be generated in the fiber spinning and drawing processes than in injection molding. The use of higher draw temperature further improves nanocomposite yam performance by controlling molecular deformation. Luster, smoothness (absence of nubbs) and opacity are indicators of the residual particle size of the clay inclusions in spun and drawn fibers.

Solid State Polymerization of in-situ polymerized nanocomposites Solid statepolymerization was performed for 1.5 hours at 200°C using nylon 6,6 which had been in-situ polymerized with four different silicates. Molecular weights were determined before and after solid state polymerization. The nanocomposite samples were found to increase in molecular weight similarly to neat nylon 6.6.

Comparison of compositions from in-situ polymerization vs. melt compounding. A well hydrated, never-dried slurry of Mineral Colloid BP (Na-montmorillonite) was added to a 50% nylon 6,6 salt solution, homogenized and polymerized to produce a nanocomposites of 1.0% and 1.25% silicate by weight. The nanocomposites were injection molded and tensile tested according to ASTM method D-638. Comparative nanocomposites were compounded on a twin screw extruder from similar montmorillonites that were pre-treated with ammonium compounds to allow their intercalation and exfoliation by a nylon melt, as taught in our earlier patent application. The two treatments, which produced nearly identical results, were dimethyldihydrogenated tallow ammonium and dimethyl(ethylhexyl)hydrogenated tallow ammonium cations. Tensile modulus data plotted as a function of the mineral content of the nanocomposite show the in-situ polymerized compositions to have higher performance at the same loading as the comparative materials made by melt compounding (Figure). Both are superior to traditional composites filled with kaolin clay that is not exfoliated into nanoparticles. All of the compositions, processes, and apparatus disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and processes of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions, processes, and apparatus and in the steps or in the sequence of steps of the processes described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are chemically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention.

Claims

CLAIMS:

1. A process to prepare a polyamide nanocomposite composition, the process comprising: forming an aqueous mixture of a silicate material and a polyamide monomer; treating the mixture to polymerize the polyamide monomer; and subjecting the mixture to solid state polymerization conditions forming the polymer nanocomposite composition.

2. The process of claim 1, wherein the monomer is hexamethylene adipamide, ╬╡- caprolactam, lauryllactam, ╬╡-caprolactone, or lauryllactone.

3. The process of claim 1, wherein the monomer is hexamethylene adipamide

4. The process of claim 1 , wherein the monomer is a mixture of hexamethylene adipamide and ╬╡-caprolactam.

5. The process of claim 1, wherein the polyamide is nylon 6, nylon 6,6, nylon 4,6, nylon

6,9, nylon 6,10, nylon 6,12, nylon 11, nylon 12, amorphous nylons, aromatic nylons, or copolymers thereof. 6. The process of claim 1, wherein the polyamide is a copolymer of nylon 6 and nylon 6,6.

7. The process of claim 1, wherein the silicate material is laponite, hectorite, sepiolite, saponite, attapulgite, or montmorillonite.

8. The process of claim 1, wherein the silicate material is added in fully hydrated form, in the form of a never-dried slurry, in the form of an aqueous slurry, or in the form of an aqueous suspension.

9. The process of claim 1, wherein the silicate material is an organically treated silicate.

10. The process of claim 1 , wherein the mixture further comprises a dispersing agent.

11. The process of claim 10, wherein the dispersing agent is a sodium polymethacrylate.

12. The process of claim 1 , wherein the mixture further comprises a silane.

13. The process of claim 12, wherein the silane is aminopropyltriethoxysilane.

14. The process of claim 1, wherein the concentration of silicate material in the polyamide nanocomposite composition is less than about 2 weight percent.

15. The process of claim 1 , wherein the concentration of silicate material in the polyamide nanocomposite composition is less than about 1 weight percent.

16. The process of claim 1 , wherein the concentration of silicate material in the polyamide nanocomposite composition is between about 0.05 weight percent and about 0.2 weight percent.

17. The process of claim 1, wherein the solid state polymerization comprises heating the mixture after the polymerization step to a temperature in the range of about 200┬░C to about 240┬░C for a period of about 2 to about 5 hours.

18. The process of claim 1 , wherein the solid state polymerization comprises: adding a catalyst; and heating the mixture after the polymerization step to a temperature at least 20┬░C below the melting or softening point of the polyamide for a period of about 0.5 to about 5 hours; wherein: the molecular weight of the nanocomposite composition formed in the presence of the catalyst is greater than the molecular weight of the nanocomposite composition formed in the absence of the catalyst.

19. The process of claim 1, further comprising heat treating the nanocomposite composition to a temperature in the range of about 200┬░C to about 240┬░C for a period of about 2 to about 5 hours.

20. The process of claim 1 , wherein the mixture has a higher molar concentration of hexamethylene diamine than adipic acid.

21. The process of claim 1, further comprising dissociating at least about 50% of the silicate material prior to solid state polymerization.

22. The process of claim 21, wherein the silicate material is dissociated by a mechanical unit, pressure alteration, ultrasonics, a stirrer, or a high shear homogenizer.

23. The process of claim 1 , wherein the mixture further comprises an oligomer of the polyamide monomer or a low molecular weight polymer of the polyamide monomer prior to the polymerization step.

24. A polyamide nanocomposite composition prepared by the method of claim 1.

25. A polyamide nanocomposite composition comprising a polyamide and a silicate material, wherein: the tensile modulus of the composition is higher than the tensile modulus of a composition prepared from the identical starting materials and concentration of starting materials, when prepared by melt intercalation; and the molecular weight of the polyamide nanocomposite composition is higher than the molecular weight of a composition prepared from the identical starting materials and concentration of starting materials, when prepared by in situ polymerization without solid state polymerization.