Stabilization of thermoplastic nanocomposites

The instant invention discloses a nanocomposite material comprising (a) a synthetic polymer, (b) a natural or synthetic phyllosilicate or a mixture of such phyllosilicates in nanoparticles, (c) a phenolic antioxidant and/or a processing stabilizer, and (d) a mono or polyfunctional compound selected from the class consisting of the epoxides, oxazolines, oxazolones, oxazines, isocyanates and/or anhydrides.

The present invention relates to a nanocomposite material comprising (a) a synthetic polymer, especially a polyolefin, (b) a natural or synthetic phyllosilicate or a mixture of such phyllosilicates in nanoparticles, (c) a phenolic antioxidant and/or a processing stabilizer, and (d) a mono or polyfunctional compound selected from the class consisting of the epoxides, oxazolines, oxazolones, oxazines, isocyanates and/or anhydrides, and to the use of components (b), (c) and (d) as stabilizers for synthetic polymers against oxidative, thermal or light-induced degradation.

The addition of fillers to organic materials, especially polymers, is known and is described for example in Hans Zweifel (editor), Plastics Additives Handbook, 5th Edition, pages 901-948, Hanser Publishers, Munich 2001. The use of fillers in polymers has the advantage that it is possible to bring about improvement in, for example, the mechanical properties, especially the density, hardness, rigidity (modulus) or reduced shrinkage of the polymer.

Using extremely small filler particles (<200 nm), so-called nano-scaled fillers, mechanical properties, heat distortion temperature stability or flame retardant property of the polymers can be improved at a much lower concentration of 2 to 10% by weight compared to 20 to 50% by weight with the micro-scaled normal filler particles. Polymers containing nano-scaled fillers combine favourable mechanical properties like strength, modulus and impact, and show improved surface qualities like gloss, lower tool wear at processing and better conditions for recycling. Coatings and films comprising nano-scaled fillers show improved stability, flame resistance, gas barrier properties and scratch resistance.

Nano-scaled fillers possess an extremely large surface with high surface energy. The deactivation of the surface energy and the compatibilization of the nano-scaled fillers with a polymeric substrate is, therefore, even more important than with a common micro-scaled filler in order to avoid aggregation during processing or conversion of the filled polymer and to reach an excellent dispersion of the nano-scaled filler in the final article.

There is a substantial recent literature on organic-inorganic nanocomposites based on clays or layered silicates such as montmorillonite and synthetic polymers. Polyolefin nanocomposites have been prepared from organic modified clays. The clays used are generally modified with long chain alkyl or dialkyl ammonium ions or amines or in a few cases other onium ions, like for example phosphonium. The ammonium ion/amine additives are usually incorporated into the clay structure by a separate solution intercalation step.

These conventional organic modified clays have a number of disadvantages when used for the preparation of polyolefin nanocomposites. Ammonium salts are thermally unstable at temperatures used in polyolefin processing or may be otherwise reactive under processing conditions. These instabilities result in poor processing stability, inferior mechanical properties, discoloration, odor formation and reduced long-term stability in addition to the formation of volatile by-products.

In order to improve the polyolefin nanocomposite formation by melt processing the use of an additional compatibilizer has been proposed, most often a maleic anhydride grafted polypropylene, which in working examples is present as major component of the final product.

M. Kawasumi et al., Macromolecules 1997, 30, 6333-6338 or U.S. Pat. No. 5,973,053 disclose that a polypropylene nanocomposite is obtained when a clay, premodified with octadecylammonium salts, is compounded with polypropylene in the presence of polyolefin oligomers containing polar functionality, for example maleic anhydride grafted polypropylene.

Although compatibilizers can improve the stability of nanocomposites mainly with regard to avoiding agglomeration of the filler, the other weaknesses of the nanocomposites are not improved.

It has now been found that improved nanocomposites with a better long term thermostability, with reduced odor and reduced undesired discoloration, which occurs as a result of the decomposition of the modification agents, can be prepared by the additional use of a mixture comprising a phenolic antioxidant and/or a processing stabilizer, and a mono or polyfunctional compound selected from the class consisting of the epoxides, oxazolines, oxazolones, oxazines, isocyanates and/or anhydrides

The present invention therefore provides a nanocomposite material comprisinga) a synthetic polymer,b) a natural or synthetic phyllosilicate or a mixture of such phyllosilicates in nanoparticles,c) a phenolic antioxidant and/or a processing stabilizer, andd) a mono or polyfunctional compound selected from the class consisting of the epoxides, oxazolines, oxazolones, oxazines, isocyanates and/or anhydrides.

The mixtue of components (c) and (d) is suitable for stabilizing synthetic polymers, especially thermoplastic nanocomposites [components (a) and (b)] against oxidative, thermal or light-induced degradation.

Examples of such materials are:1. Polymers of monoolefins and diolefins, for example polypropylene, polyisobutylene, polybut-1-ene, poly-4-methylpent-1-ene, polyvinylcyclohexane, polyisoprene or polybutadiene, as well as polymers of cycloolefins, for instance of cyclopentene or norbornene, polyethylene (which optionally can be crosslinked), for example high density polyethylene (HDPE), high density and high molecular weight polyethylene (HDPE-HMW), high density and ultrahigh molecular weight polyethylene (HDPE-UHMW), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), (VLDPE) and (ULDPE).

Polyolefins, i.e. the polymers of monoolefins exemplified in the preceding paragraph, preferably polyethylene and polypropylene, can be prepared by different, and especially by the following, methods:a) radical polymerisation (normally under high pressure and at elevated temperature).b) catalytic polymerisation using a catalyst that normally contains one or more than one metal of groups IVb, Vb, VIb or VIII of the Periodic Table. These metals usually have one or more than one ligand, typically oxides, halides, alcoholates, esters, ethers, amines, alkyls, alkenyls and/or aryls that may be either π- or σ-coordinated. These metal complexes may be in the free form or fixed on substrates, typically on activated magnesium chloride, titanium(III) chloride, alumina or silicon oxide. These catalysts may be soluble or insoluble in the polymerisation medium. The catalysts can be used by themselves in the polymerisation or further activators may be used, typically metal alkyls, metal hydrides, metal alkyl halides, metal alkyl oxides or metal alkyloxanes, said metals being elements of groups Ia, IIa and/or IIIa of the Periodic Table. The activators may be modified conveniently with further ester, ether, amine or silyl ether groups. These catalyst systems are usually termed Phillips, Standard Oil Indiana, Ziegler (-Natta), TNZ (DuPont), metallocene or single site catalysts (SSC).2. Mixtures of the polymers mentioned under 1), for example mixtures of polypropylene with polyisobutylene, polypropylene with polyethylene (for example PP/HDPE, PP/LDPE) and mixtures of different types of polyethylene (for example LDPE/HDPE).3. Copolymers of monoolefins and diolefins with each other or with other vinyl monomers, for example ethylene/propylene copolymers, linear low density polyethylene (LLDPE) and mixtures thereof with low density polyethylene (LDPE), propylene/but-1-ene copolymers, propylene/isobutylene copolymers, ethylene/but-1-ene copolymers, ethylene/hexene copolymers, ethylene/methylpentene copolymers, ethylene/heptene copolymers, ethylene/octene copolymers, ethylene/vinylcyclohexane copolymers, ethylene/cycloolefin copolymers (e.g. ethylene/norbornene like COC), ethylene/1-olefins copolymers, where the 1-olefin is gene-rated in-situ; propylene/butadiene copolymers, isobutylene/isoprene copolymers, ethylene/vinylcyclohexene copolymers, ethylene/alkyl acrylate copolymers, ethylene/alkyl methacrylate copolymers, ethylene/vinyl acetate copolymers or ethylene/acrylic acid copolymers and their salts (ionomers) as well as terpolymers of ethylene with propylene and a diene such as hexadiene, dicyclopentadiene or ethylidene-norbornene; and mixtures of such copolymers with one another and with polymers mentioned in 1) above, for example polypropylene/ethylene-propylene copolymers, LDPE/ethylene-vinyl acetate copolymers (EVA), LDPE/ethylene-acrylic acid copolymers (EAA), LLDPE/EVA, LLDPE/EAA and alternating or random polyalkylene/carbon monoxide copolymers and mixtures thereof with other polymers, for example polyamides.4. Hydrocarbon resins (for example C5-C9) including hydrogenated modifications thereof (e.g. tackifiers) and mixtures of polyalkylenes and starch.

Homopolymers and copolymers from 1.)-4.) may have any stereostructure including syndiotactic, isotactic, hemi-isotactic or atactic; where atactic polymers are preferred. Stereoblock polymers are also included.5. Polystyrene, poly(p-methylstyrene), poly(α-methylstyrene).6. Aromatic homopolymers and copolymers derived from vinyl aromatic monomers including styrene, α-methylstyrene, all isomers of vinyl toluene, especially p-vinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, and vinyl anthracene, and mixtures thereof. Homopolymers and copolymers may have any stereostructure including syndiotactic, isotactic, hemi-isotactic or atactic; where atactic polymers are preferred. Stereoblock polymers are also included.6a. Copolymers including aforementioned vinyl aromatic monomers and comonomers selected from ethylene, propylene, dienes, nitriles, acids, maleic anhydrides, maleimides, vinyl acetate and vinyl chloride or acrylic derivatives and mixtures thereof, for example styrene/butadiene, styrene/acrylonitrile, styrene/ethylene (interpolymers), styrene/alkyl methacrylate, styrene/butadiene/alkyl acrylate, styrene/butadiene/alkyl methacrylate, styrene/maleic anhydride, styrene/acrylonitrile/methyl acrylate; mixtures of high impact strength of styrene copolymers and another polymer, for example a polyacrylate, a diene polymer or an ethylene/propylene/diene terpolymer; and block copolymers of styrene such as styrene/butadiene/styrene, styrene/isoprene/styrene, styrene/ethylene/butylene/styrene or styrene/ethylene/propylene/styrene.6b. Hydrogenated aromatic polymers derived from hydrogenation of polymers mentioned under 6.), especially including polycyclohexylethylene (PCHE) prepared by hydrogenating atactic polystyrene, often referred to as polyvinylcyclohexane (PVCH).6c. Hydrogenated aromatic polymers derived from hydrogenation of polymers mentioned under 6a.).

Homopolymers and copolymers may have any stereostructure including syndiotactic, isotactic, hemi-isotactic or atactic; where atactic polymers are preferred. Stereoblock polymers are also included.7. Graft copolymers of vinyl aromatic monomers such as styrene or α-methylstyrene, for example styrene on polybutadiene, styrene on polybutadiene-styrene or polybutadiene-acrylonitrile copolymers; styrene and acrylonitrile (or methacrylonitrile) on polybutadiene; styrene, acrylonitrile and methyl methacrylate on polybutadiene; styrene and maleic anhydride on polybutadiene; styrene, acrylonitrile and maleic anhydride or maleimide on polybutadiene; styrene and maleimide on polybutadiene; styrene and alkyl acrylates or methacrylates on polybutadiene; styrene and acrylonitrile on ethylenetpropylene/diene terpolymers; styrene and acrylonitrile on polyalkyl acrylates or polyalkyl methacrylates, styrene and acrylonitrile on acrylate/butadiene copolymers, as well as mixtures thereof with the copolymers listed under 6), for example the copolymer mixtures known as ABS, MBS, ASA or AES polymers.8. Halogen-containing polymers such as polychloroprene, chlorinated rubbers, chlorinated and brominated copolymer of isobutylene-isoprene (halobutyl rubber), chlorinated or sulfo-chlorinated polyethylene, copolymers of ethylene and chlorinated ethylene, epichlorohydrin homo- and copolymers, especially polymers of halogen-containing vinyl compounds, for example polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, as well as copolymers thereof such as vinyl chloride/vinylidene chloride, vinyl chloride/vinyl acetate or vinylidene chloride/vinyl acetate copolymers.9. Polymers derived from α,β-unsaturated acids and derivatives thereof such as polyacrylates and polymethacrylates; polymethyl methacrylates, polyacrylamides and polyacrylonitriles, impact-modified with butyl acrylate.10. Copolymers of the monomers mentioned under 9) with each other or with other unsaturated monomers, for example acrylonitrile/ butadiene copolymers, acrylonitrile/alkyl acrylate copolymers, acrylonitrile/alkoxyalkyl acrylate or acrylonitrile/vinyl halide copolymers or acrylonitrile/alkyl methacrylate/butadiene terpolymers.11. Polymers derived from unsaturated alcohols and amines or the acyl derivatives or acetals thereof, for example polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, polyvinyl benzoate, polyvinyl maleate, polyvinyl butyral, polyallyl phthalate or polyallyl melamine; as well as their copolymers with olefins mentioned in 1) above.12. Homopolymers and copolymers of cyclic ethers such as polyalkylene glycols, polyethylene oxide, polypropylene oxide or copolymers thereof with bisglycidyl ethers.13. Polyacetals such as polyoxymethylene and those polyoxymethylenes which contain ethylene oxide as a comonomer; polyacetals modified with thermoplastic polyurethanes, acrylates or MBS.14. Polyphenylene oxides and sulfides, and mixtures of polyphenylene oxides with styrene polymers or polyamides.15. Polyurethanes derived from hydroxyl-terminated polyethers, polyesters or polybutadienes on the one hand and aliphatic or aromatic polylsocyanates on the other, as well as precursors thereof.16. Polyamides and copolyamides derived from diamines and dicarboxylic acids and/or from aminocarboxylic acids or the corresponding lactams, for example polyamide 4, polyamide 6, polyamide 6/6, 6/10, 6/9, 6/12, 4/6, 12/12, polyamide 11, polyamide 12, aromatic polyamides starting from m-xylene diamine and adipic acid; polyamides prepared from hexamethylenediamine and isophthalic or/and terephthalic acid and with or without an elastomer as modifier, for example poly-2,4,4,-trimethylhexamethylene terephthalamide or poly-m-phenylene isophthalamide; and also block copolymers of the aforementioned polyamides with polyolefins, olefin copolymers, ionomers or chemically bonded or grafted elastomers; or with polyethers, e.g. with polyethylene glycol, polypropylene glycol or polytetramethylene glycol; as well as polyamides or copolyamides modified with EPDM or ABS; and polyamides condensed during processing (RIM polyamide systems).17. Polyureas, polyimides, polyamide-imides, polyetherimids, polyesterimids, polyhydantoins and polybenzimidazoles.18. Polyesters derived from dicarboxylic acids and diols and/or from hydroxycarboxylic acids or the corresponding lactones, for example polyethylene terephthalate, polybutylene terephthalate, poly-1,4-dimethylolcyclohexane terephthalate, polyalkylene naphthalate (PAN) and polyhydroxybenzoates, as well as block copolyether esters derived from hydroxyl-terminated polyethers; and also polyesters modified with polycarbonates or MBS.19. Polycarbonates and polyester carbonates.20. Polyketones.21. Polysulfones, polyether sulfones and polyether ketones.22. Crosslinked polymers derived from aldehydes on the one hand and phenols, ureas and melamines on the other hand, such as phenol/formaldehyde resins, urea/formaldehyde resins and melamine/formaldehyde resins.23. Drying and non-drying alkyd resins.24. Unsaturated polyester resins derived from copolyesters of saturated and unsaturated dicarboxylic acids with polyhydric alcohols and vinyl compounds as crosslinking agents, and also halogen-containing modifications thereof of low flammability.25. Crosslinkable acrylic resins derived from substituted acrylates, for example epoxy acrylates, urethane acrylates or polyester acrylates.26. Alkyd resins, polyester resins and acrylate resins crosslinked with melamine resins, urea resins, isocyanates, isocyanurates, polyisocyanates or epoxy resins.27. Crosslinked epoxy resins derived from aliphatic, cycloaliphatic, heterocyclic or aromatic glycidyl compounds, e.g. products of diglycidyl ethers of bisphenol A and bisphenol F, which are crosslinked with customary hardeners such as anhydrides or amines, with or without accelerators.28. Blends of the aforementioned polymers (polyblends), for example PP/EPDM, Polyamide/EPDM or ABS, PVC/EVA, PVC/ABS, PVC/MBS, PC/ABS, PBTP/ABS, PC/ASA, PC/PBT, PVC/CPE, PVC/acrylates, POM/thermoplastic PUR, PC/thermoplastic PUR, PON/acrylate, POM/MBS, PPO/HIPS, PPO/PA 6.6 and copolymers, PA/HDPE, PA/PP, PA/PPO, PBT/PC/ABS or PBT/PET/PC.

The synthetic polymers to be protected are preferably thermoplastic polymers, especially polyolefins, polystyrenes, polyamides, polyesters, polyacrylates, most preferably polyolefins, in particular polyethylene and polypropylene or copolymers thereof with mono- and diolefins.

Preferred natural or synthetic phyllosilicates in nanoparticles are for example layered silicate clays in nanoparticles. Of special interest are nanocomposite materials comprising as component (b) a montmorillonite, bentonite, beidelite, mica, hectorite, saponite, nontronite, sauconite, vermiculite, ledikite, magadite, kenyaite, stevensite, volkonskoite or a mixture thereof in nanoparticles.

Preferably, component (b) is modified or intercalated by a modification agent such as, for example, an ammonium, an amine or a phosphonium compound.

Nanocomposite materials which are of interest include those comprising as component (c) compounds of the formula I

Y is hydrogen or —NH—; and,if n is 1,X is

where Y is attached to R2, and

if n is 2,

where Y is attached to R2, andR2is C2-C12alkylene, C4-C12alkylene interrupted by oxygen or sulfur; or, if Y is —NH—, R2is additionally a direct bond; and,if n is 3,X is methylene or

where the ethylene group is attached toR2, andR2is

andif n is 4,X is

where Y is attached to R2, andR2is C4-C10alkanetetrayl.

C2-C12alkylene is a branched or unbranched radical, for example ethylene, propylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, decamethylene or dodecamethylene. A preferred definition of R2is, for example, C2-C10alkylene, especially C2-C8alkylene. An especially preferred definition of R2is, for example, C4-C8alkylene, especially C4-C6alkylene, for example hexamethylene.

C4-C12alkylene interrupted by oxygen or sulfur can be interrupted one or more times and is, for example, —CH2—O—CH2CH2—O—CH2—, —CH2—(O—CH2CH2—)2O—CH2—, —CH2—(O—CH2CH2—)3O—CH2—, —CH2—(O—CH2CH2—)4O—CH2—, —CH2CH2—O—CH2CH2—O—CH2CH2— or —CH2CH2—S—CH2CH2—. A preferred definition of R2is, for example, C4-C10alkylene interrupted by oxygen or sulfur, especially C4-C8alkylene interrupted by oxygen or sulfur, for example C4-C6alkylene interrupted by oxygen or sulfur. An especially preferred meaning of R2is —CH2CH2—O—CH2CH2—O—CH2CH2— or —CH2CH2—S—CH2CH2—.

Component (c) may also comprise mixtures of different sterically hindered phenols of the formula I.

Nanocomposite materials which are of interest include those comprising as component (c) at least one compound of the formula I in which, if n is 1, R2is C1-C20alkyl.

Preference is given to nanocomposite materials comprising as component (c) at least one compound of the formula I in which,if n is 2,R2is C2-C8alkylene, C4-C8alkylene interrupted by oxygen or sulfur; or, if Y is —NH—, R2is additionally a direct bond; and,if n is 3,X is methylene,R2is

Preference is likewise given to nanocomposite materials comprising as component (c) at least one compound of the formula I in whichR1is methyl or tert-butyl,n is 1, 2, 3 or 4,X is methylene or

Y is hydrogen or —NH—; and,if n is 1,R2is C14-C18alkyl; and,if n is 2,R2is C4-C6alkylene, or is C4-C6alkylene interrupted by oxygen; and,if n is 3,X is methylene,R2is,

Likewise of interest are nanocomposite materials comprising as component (c) at least one compound of the formula I in which the compound of the formula I is a compound of the formula Ia to Ii

Preference is given to nanocomposite materials comprising as component (c) at least one compound of the formula I in which the compound of the formula I is a compound of the formula Ia, Ib, Ic or Id, in particular a compound of the formula Ia, Ib or Ic.

Component (c) of the novel nanocomposite materials, and the compounds of the formula I, are known and in some cases obtainable commercially. Possible preparation processes for the compounds of the formula I can be found, for example, in the U.S. Pat. Nos. 3,330,859 or 3,960,928.

Of interest are nanocomposite materials comprising as component (c) processing stabilizers selected from the group consisting of organic phosphites or phosphonites or benzofuran-2-ones.

Of particular interest are nanocomposite materials comprising as component (c) at least one compound from the group the benzofuran-2-one or of the group of the organic phosphites or phosphonites of the formulae II to VIII

in which the indices are integral andn′ is 2, 3 or 4; p′ is 1 or 2; q′ is 2 or 3; r′ is 4 to 12; y′ is 1, 2 or 3; and z′ is 1 to 6;A′, if n′ is 2, is C2-C18alkylene; C2-C12alkylene interrupted by oxygen, sulfur or —NR′4—; a radical of the formula

or phenylene;A′, if n′ is 3, is a radical of the formula —Cr′H2r′-1—;A′, if n′ is 4, is

A″ has the meaning of A′ if n′ is 2;B′ is a direct bond, —CH2—, —CHR′4—, —CR′1R′4—, sulfur or C5-C7cycloalkylidene, or is cyclohexylidene substituted by from 1 to 4 C1-C4alkyl radicals in position 3, 4 and/or 5;D′, if p′ is 1, is methyl and, if p′ is 2, is —CH2OCH2—;E′, if y′ is 1, is C1-C18alkyl, —OR′1or halogen;E′, if y is 2, is —O-A″-O—,E′, if y is 3, is a radical of the formula R′4C(CH2O—)3or N(CH2CH2O—)3;Q′ is the radical of an at least z′-valent alcohol or phenol, this radical being attached via the oxygen atom to the phosphorus atom;R′1, R′2and R′3independently of one another are unsubstituted or halogen, —COOR4′, —CN— or —CONR4′R4′-substituted C1-C18alkyl; C2-C18alkyl interrupted by oxygen, sulfur or —NR′4—; C7-C9phenylalkyl; C5-C12cycloalkyl, phenyl or naphthyl; naphthyl or phenyl substituted by halogen, 1 to 3 alkyl radicals or alkoxy radicals having in total 1 to 18 carbon atoms or by C7-C9phenylalkyl; or are a radical of the formula

in which m′ is an integer from the range 3 to 6;R′4is hydrogen, C1-C18alkyl, C5-C12cycloalkyl or C7-C9phenylalkyl,R′5and R′6independently of one another are hydrogen, C1-C8alkyl or C5-C6cycloalkyl,R′7and R′8, if q′ is 2, independently of one another are C1-C4alkyl or together are a 2,3-dehydropentamethylene radical; andR′7and R′8, if q′ is 3, are methyl;R′14is hydrogen, C1-C9alkyl or cyclohexyl,R′15is hydrogen or methyl and, if two or more radicals R′14and R′15are present, these radicals are identical or different,X′ and Y′ are each a direct bond or oxygen,Z′ is a direct bond, methylene, —C(R′16)2— or sulfur, andR′16is C1-C8alkyl.

Of particular interest are nanocomposite materials comprising as component (c) a benzofuran-2-one or a phosphite or phosphonite of the formula II, III, IV or V, in whichn′ is the number 2 and y′ is the number 1, 2 or 3;A′ is C2-C18alkylene, p-phenylene or p-biphenylene,E′, if y′ is 1, is C1-C18alkyl, —OR′1or fluorine;E′, if y′ is 2, is p-biphenylene,E′, if y′ is 3, is N(CH2CH2O—)3,R′1, R′2and R′3independently of one another are C1-C18alkyl, C7-C9phenylalkyl, cyclohexyl, phenyl, or phenyl substituted by 1 to 3 alkyl radicals having in total 1 to 18 carbon atoms;R′14is hydrogen or C1-C9alkyl,R′15is hydrogen or methyl;X′ is a direct bond,Y′ is oxygen,Z′ is a direct bond or —CH(R′16)—, andR′16is C1-C4alkyl.

Likewise of interest are nanocomposite materials comprising as component (c) a benzofuran-2-one or a phosphite or phosphonite of the formula II, III, IV or V, in whichn′ is the number 2 and y′ is the number 1 or 3;A′ is p-biphenylene,E′, if y′ is 1, is C1-C18alkoxy or fluorine,E′, if y′ is 3, is N(CH2CH2O—)3,R′1, R′2and R′3independently of one another are C1-C18alkyl, or are phenyl substituted by 2 or 3 alkyl radicals having in total 2 to 12 carbon atoms;R′14is methyl or tert-butyl;R′15is hydrogen;X′ is a direct bond;Y′ is oxygen; andZ′ is a direct bond, methylene or —CH(CH3)—.

Particular preference is given to nanocomposite materials comprising as component (c) a phosphite or phosphonite of the formula II, III or V.

Special preference is given to nanocomposite materials comprising as component (c) at least one compound of the formula VII

in whichR1and R2independently of one another are hydrogen, C1-C8alkyl, cyclohexyl or phenyl, andR3and R4independently of one another are hydrogen or C1-C4alkyl.

The following compounds are examples of organic phosphites and phosphonites which are particularly suitable as component (c) in the novel compositions.

Particular preference is given to the use of the following phosphites and phosphonites:tris(2,4-di-tert-butylphenyl)phosphite (Irgafos®168, Ciba Specialty Chemicals Inc.), tris(nonyl-phenyl)phosphite,

The above mentioned organic phosphites and phosphonites are known compounds; many of them are available commercially.

Of special interest are nanocomposite materials wherein component (c) is selected from the group consisting of1. Tocopherols for example α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol and mixtures thereof (vitamin E),2. Esters of β-(3,5-di-tert-butyl-4-hydroxyphenyl)progionic acid with mono- or polyhydric alcohols, e.g. with octadecanol, thiodiethylene glycol, pentaerythritol or tris(hydroxyethyl)isocyanurate,3. Benzylphosphonates, for example dimethyl-2,5-di-tert-butyl-4-hydroxybenzylphosphonate, diethyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl-5-tert-butyl-4-hydroxy-3-methylbenzylphosphonate or the calcium salt of the monoethyl ester of 3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid,4. Esters of β-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionic acid with mono- or polyhydric alcohols, e.g. with diethylene glycol,5. Amides of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid e.g. N,N′-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)trimethylenediamide,6. Phosphites and phosphonites, for example tris(2,4-di-tert-butylphenyl)phosphite, tetrakis-(2,4-di-tert-butylphenyl)4,4′-biphenylene diphosphonite, and7. Benzofuran-2-ones, for example 3-(3,4-dimethylphenyl)-5,7-di-tert-butylbenzofuran-2-one, 3-(2,3-dimethylphenyl)-5,7-di-tert-butylbenzofuran-2-one; or mixtures thereof.

Of very special interest are nanocomposite materials wherein component (c) is tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, tetrakis(2,4-di-tert-butylphenyl)4,4′-biphenylenediphosphonite, 3-(3,4-dimethylphenyl)-5,7-di-tert-butylbenzofuran-2-one, 3-(2,3-dimethylphenyl)-5,7-di-tert-butylbenzofuran-2-one, and/or a compound of the formula Ia, Ib, Ic, Id or Ig

Of special interest is a nanocomposite material wherein component (d) is an epoxide.

For the purposes of this invention, epoxides [component (d)] can have an aliphatic, aromatic, cycloaliphatic, araliphatic or heterocyclic structure; they include epoxide groups as side groups, or these groups form part of an alicyclic or heterocyclic ring system. The epoxide groups are preferably attached as glycidyl groups to the remainder of the molecule by way of ether or ester linkages, or the compounds involved are N-glycidyl derivatives of heterocyclic amines, amides or imides. Epoxides of these types are generally known and commercially available.

Preferably, component (d) is a polyfunctional epoxide which comprises epoxide radicals, for example those of the formula E-1

which are attached directly to carbon, oxygen, nitrogen or sulfur atoms, and wherein R11and R13are both hydrogen, R12is hydrogen or methyl and n is 0; or wherein R11and R13together are —CH2CH2— or —CH2CH2CH2—, R12is then hydrogen, and n is 0 or 1.

Examples of epoxides are:1. Diglycidyl and di(β-methylglycidyl)esters obtainable by reacting a compound with two carboxyl groups in the molecule and epichlorohydrin and/or glycerol dichlorohydrin and/or β-methylepichlorohydrin. The reaction is expediently carried out in the presence of bases.

As compounds of two carboxyl groups in the molecule, aliphatic dicarboxylic acids can be used. Examples of these dicarboxylic acids are glutaric acid, adipic acid, pimelic acid, suberic acid, azelic acid, sebacic acid or dimerized or trimerized linoleic acid.

It is however also possible to employ cycloaliphatic dicarboxylic acids such as, for example, tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid.

Furthermore, aromatic dicarboxylic acids, for example phthalic acid or isophthalic acid, can be used.2. Diglycidyl, or di(β-methylglycidyl)ethers obtainable by reacting a compound with two free alcoholic hydroxyl groups and/or phenolic hydroxyl groups and a suitable substituted epichlorohydrin under alkaline conditions, or in the presence of an acidic catalyst with subsequent alkali treatment.

Ethers of this type are derived, for example, from acyclic alcohols, such as ethylene glycol, diethylene glycol and higher poly(oxyethylene)glycols, propane-1,2-diol, or poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene)glycols, pentane-1,5-diol, hexane-1,6-diol, sorbitol, and from polyepichlorohydrins.

However, they are also derived, for example, from cycloaliphatic alcohols such as 1,3- or 1,4-dihydroxycyclohexane, bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane or 1,1-bis(hydroxymethyl)cyclohex-3-ene, or they possess aromatic nuclei, such as N,N-bis(2-hydroxyethyl)aniline or p,p′-bis(2-hydroxyethylamino)diphenylmethane.

The epoxides can also be derived from mononuclear phenols, such as, for example, from resorcinol, pyrocatechol or hydroquinone; or they are based on polynuclear phenols such as, for example, on 4,4′-dihydroxybiphenyl, bis(4-hydroxphenyl)methane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 4,4′-dihydroxydiphenyl sulfone, 9,9′-bis(4-hydroxyphenyl)fluorene, or on condensation products of phenols with formaldehyde, obtained under acidic conditions, such as phenol novolaks.3. Di(N-glycidyl) compounds are obtainable, for example, by dehydrochlorination of the reaction products of epichlorohydrin with amines containing two amino hydrogen atoms. Examples of these amines are aniline, toluidine, n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine or bis(4-methylaminophenyl)methane.

Also included among the di(N-glycidyl) compounds, however, are N,N′-diglycidyl derivatives of cycloalkyleneureas, such as ethyleneurea or 1,3-propyleneurea, and N,N′-diglycidyl derivatives of hydantoins, such as of 5,5-dimethylhydantoin.4. Di(S-glycidyl) compounds, such as di-S-glycidyl derivatives derived from dithiols, such as, for example, ethane-1,2-dithiol or bis(4-mercaptomethylphenyl)ether.5. Epoxides with a radical of the formula II in which R11and R13together are —CH2CH2— and n is 0 are, for example, bis(2,3-epoxycyclopentyl)ether, 2,3-epoxycyclopentyl glycidyl ether or 1,2-bis(2,3-epoxycyclopentyloxy)ethane; an example of epoxides with a radical of the formula II in which R11and R13together are —CH2CH2— and n is 1 is (3′,4′-epoxy-6′-methylcyclohexyl)methyl 3,4-epoxy-6-methylcyclohexanecarboxylate.

Owing, for example, to their preparation process, the abovementioned difunctional epoxides may include small amounts of mono- or trifunctional fractions.

Predominantly, use is made of diglycidyl compounds having aromatic structures.

If desired, it is also possible to employ a mixture of epoxides of different structures.

Particularly preferred difunctional epoxides are liquid or low-melting diglycidyl ethers based on bisphenols such as, for example, on 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) or mixtures of bis(ortho/para-hydroxyphenyl)methane (bisphenol F).

Very particular preference is given to epoxides of the bisphenol A diglycidyl ether type, for example: Araldite®GT 6071, GT 7071, GT 7072, or epoxides of the bisphenol F type, such as Araldite®GY 281 or PY 306; diglycidyl 1,2-cyclohexanedicarboxylate, e.g. Araldite®PY 284; or phenol novolak epoxy resin, e.g. Araldite®PY EPN 1139.

Mono or polyfunctional, in particular trifunctional, compounds from the oxazoline class in the sense of this invention [component (d)] are known and are described, for example, in EP-A-0 583 807 and are, for example, compounds of the formula OX-1

in which R8, R9, R10and R11, independently of one another, are hydrogen, halogen, C1-C20-alkyl, C4-C15cycloalkyl, unsubstituted or C1-C4alkyl-substituted phenyl, C1-C20alkoxy or C2-C20carboxyalkyl,if t=3,R12is trivalent linear, branched or cyclic aliphatic radical having 1 to 18 carbon atoms, which may be interrupted by oxygen or sulfur, or R12is furthermore an unsubstituted or C1-C4alkyl-substituted benzenetriyl radical,If t=2,R12is a divalent linear, branched or cyclic aliphatic radical having 1 to 18 carbon atoms, which may be interrupted by oxygen or sulfur, or R12is furthermore an unsubstituted or C1-C4alkyl-substituted phenylene radical, andIf t=1,R12is a monovalent linear, branched or cyclic aliphatic radical having 1 to 18 carbon atoms, which may be interrupted by oxygen or sulfur, or R12is furthermore an unsubstituted or C1-C4alkyl-substituted phenyl radical.

A trivalent linear, branched or cyclic aliphatic radical having 1 to 18 carbon atoms, which may be interrupted by oxygen or sulfur, means that the three bonds may be on the same or on different atoms. Examples thereof are methanetriyl, 1,1,1-ethanetriyl, 1,1,1-propanetriyl, 1,1,1-butanetriyl, 1,1,1-pentanetriyl, 1,1,1-hexanetriyl, 1,1,1-heptanetriyl, 1,1,1-octanetriyl, 1,1,1-nonanetriyl, 1,1,1-decanetriyl, 1,1,1-undecanetriyl, 1,1,1-dodecanetriyl, 1,2,3-propanetriyl, 1,2,3-butanetriyl, 1,2,3-pentanetriyl, 1,2,3-hexanetriyl, 1,1,3-cyclopentanetriyl, 1,3,5-cyclohexanetriyl, 3-oxo-1,1,5-pentanetriyl or 3-thio-1,1,5-pentanetriyl.

A divalent linear, branched or cyclic aliphatic radical having 1 to 18 carbon atoms, which may be interrupted by oxygen or sulfur, means that the two bonds may be on the same or on different atoms. Examples thereof are methylene, ethylene, propylene, butylenes, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene or dodecylene.

Unsubstituted or C1-C4alkyl-substituted benzenetriyl, which preferably contains 1 to 3, in particular 1 or 2, alkyl groups, is, for example, 1,2,4-benzenetriyl, 1,3,5-benzenetriyl, 3-methyl-1,2,4-benzenetriyl or 2-methyl-1,3,5-benzenetriyl. Particular preference is given to 1,2,4-benzenetriyl and 1,3,5-benzenetriyl.

Of particular interest are compounds of the formula OX-1 in whichR8, R9, R10and R11, independently of one another, are hydrogen or C1-C4alkyl, andR12is 1,2,4-benzenetriyl or 1,3,5-benzenetriyl.

Of special interest are compounds of the formula OX-1, for example 2,2′,2″-(1,3,5-benzenetriyl)tris-2-oxazoline; 2,2′,2″-(1,2,4-benzenetriyl)tris-4,4-dimethyl-2-oxazoline; 2,2′,2″-(1,3,5-benzenetriyl)tris-4,4-dimethyl-2-oxazoline; 2,2′,2″-(1,2,4-benzenetriyl)tris-5-methyl-2-oxazoline; or 2,2′,2″-(1,3,5-benzenetriyl)tris-5-methyl-2-oxazoline.

Preferred difunctionl compounds from the bisoxazoline class in the sense of this invention have been described by T. Loontjens et al., Makromol. Chem., Macromol. Symp. 75, 211-216 (1993) and are, for example, compound of the formula OX-2, OX-3 and OX-4.

Mono or polyfunctional, in particular difunctional, compounds form the oxazine or oxazolone class in the sense of this invention [component (d)] are known and have been described, for example, by H. Inata et al., J. Applied Polymer Science Vol. 32 4581-4594 (1986) and are, for example, compounds of the formula OX-5 or OX-6

in whichR14is a direct bond or unsubstituted or C1-C4alkyl-substituted phenylene or thiophene, andR15and R16, independently of one another, are hydrogen or C1-C4alkyl; or

Special preference is given to compounds of the formula OX-5 and OX-6 in which R14is a direct bond, in particular 2,2′-bis(4H-3,1-benzoxazin-4-one) or OX-7.

Mono or polyfunctional, in particular difunctional, compounds form the isocyanate class in the sense of this invention [component (d)] are known and are, for example, compounds of the formula IC-1
O═C═N—R23—N═C═O  (IC-1)
in which R23is C1-C20alkylene or polymethylene, arylene, aralkylene or cycloalkylene.

These diisocyanates are commercially available or can be prepared from commercially available amines.

However, it is also possible to employ diisocyanate generators, such as polymeric urethanes, uretdione dimers and higher oligomers, cyanurate polymers, urethanes and polymeric urethanes of cyanurate polymers and thermally dissociable adducts of Schiff's bases.

Mono or polyfunctional, in particular difunctional, compounds form the anhydride class in the sense of this invention [component (d)] are known and are, for example, compounds of the formula AH-1

in which R24is a radical of the formula AH-1a to AH-1j

in which R25is —CH2—, —CH(CH3)—, —C(CH3)2—, C(CF3)2—, —S—, —O—, —(O)S(O)—, —NHCO—, —CO— or —P(O)(C1-C20alkyl)- and in which the aromatic rings in the formula AH-1a to AH-1e are unsubstituted or substituted by one or more C1-C6alkyl groups, C1-C6alkoxy groups or halogen atoms.

An example of a trifunctional anhydride is mellitic anhydride.

Preference is given to tetracarboxylic dianhydrides containing aromatic rings. These tetracarboxylic anhydrides are commercially available. It is also possible to employ a mixture of tetracarboxylic dianhydrides having different structures.

Preferably, the natural or synthetic phyllosilicate or a mixture of such phyllosilicates in nanoparticles [component (b)] is present in the nanocomposite material in an amount of from 0.01 to 30%, in particular 0.1 to 20%, for example from 0.5 to 10%, based on the weight of the synthetic polymer [component (a)].

The phenolic antioxidant and/or processing stabilizer [component (c)] is preferably added to the nanocomposite material in an amount of from 0.01 to 5%, in particular 0.05 to 5%, for example from 0.1 to 2%, based on the weight of the synthetic polymer [component (a)].

The mono or polyfunctional compound selected from the class consisting of the epoxides, oxazolines, oxazolones, oxazines, isocyanates and/or anhydrides [component (d)] is preferably added to the nanocomposite material in an amount of from 0.01 to 5%, in particular 0.1 to 5%, for example from 0.1 to 2%, based on the weight of the synthetic polymer [component (a)].

The costabilizers are added, for example, in concentrations of 0.01 to 10%, relative to the total weight of the synthetic polymer to be stabilized.

In addition to the nano fillers other fillers may be used as reinforcing agents (item 11 in the list), for example talc, calcium carbonate, mica or kaolin. These are added to the synthetic polymers in concentrations, for example, of from 0.01 to 40%, based on the overall weight of the synthetic polymers to be stabilized.

The fillers and reinforcing agents (item 11 in the list), for example metal hydroxides, especially aluminium hydroxide or magnesium hydroxide, are added to the synthetic polymers in concentrations, for example, of from 0.01 to 60%, based on the overall weight of the synthetic polymers to be stabilized.

Carbon black as filler is added to the synthetic polymers in concentrations, judiciously, of from 0.01 to 5%, based on the overall weight of the synthetic polymers to be stabilized.

Glass fibers as reinforcing agents are added to the synthetic polymers in concentrations, judiciously, of from 0.01 to 20%, based on the overall weight of the synthetic polymers to be stabilized.

Further preferred compositions comprise in addition to components (a), (b), (c) and (d) further additives as well, especially alkaline earth metal salts of higher fatty acids, for example calcium stearate.

Especially preferred further additives are modification agents for nanocomposites as outlined at the beginning of the description, compatibilizers and/or metal passivators.

Compatibilizers are mediators between a hydrophobic and a hydrophyllic phase. Preferably, compatibilizers are polymeric dispersing or solvating agents having amphiphilic properties.

Of interest as compatibilizers are block-graft copolymers like for example maleic anhydride grafted polypropylene (PP-g-MA), ithaconic acid grafted polypropylene, acrylic acid grafted polypropylene or polyethyleneoxide-block-polystyrene (PEO-bl-PS). Preferably, block-graft copolymers have molecular weights of Mn1000 to 100000, and for the maleic anhydride modified polypropylene oligomers (PP-g-MA) the maleic anhydride content is from 0.1 to 10% [for example Epolene® E43, MA content 2.9 weight %, Mn 8800 (Eastman); Hostaprime® HC5, MA content 4.2 weight %, Mn 4000]. A compatibilizer of special interest is maleic anhydride grafted polypropylene (PP-g-MA).

Polymeric dispersing or solvating agents having amphiphilic properties are polymeric dispersing or solvating agents which have polar and nonpolar groups in the same molecule and they are, for example, dispersing or solvating agents based on polyethylene glycols (PEG), polyacrylates, polysiloxanes, polyvinyl acetate or on block copolymers containing at least one block copolymer based on acrylate, acrylic acid or methacrylate.

Polymeric dispersing or solvating agents of interest having amphiphilic properties have at least two different polarities within one polymer molecule. Oligomeric structures are also possible. They are usually copolymers, for example random copolymers, or block copolymers which can be prepared by known polymerisation reactions, for example by radical or anionic polymerisation, by polycondensation reactions, such as by reaction of end-functionalised oligomeric or comb polymers, which polymers may be prepared e.g. by graft reaction. Block copolymers are, for example, diblock copolymers (A-B type) or triblock copolymers (A-B-A or A-B-C type) and so-called tapered structures.

Long-chain block copolymers of particular interest have a chain length of more than 10 carbon atoms, preferably of C12-C18carbon atoms.

The polyalkylene oxides are preferably polyethylene oxide, polypropylene oxide and polybutylene oxide.

Other likewise preferred dispersing or solvating agents based on polyacrylates are described, inter alia, in U.S. Pat. No. 5,133,898.

As a conventional stabilizer combination for processing synthetic polymers, for example polyolefins, to form corresponding mouldings, the combination of a phenolic antioxidant with a secondary antioxidant based on an organic phosphite or phosphonite is recommended.

Incorporation of components (b), (c) and (d) and, if desired, further additives into the synthetic polymers is carried out by known methods, for example before or during moulding or else by applying the dissolved or dispersed compounds to the synthetic polymer, if appropriate with subsequent slow evaporation of the solvent. Components (b), (c) and (d) can also be added to the synthetic polymers to be stabilized in the form of a masterbatch or concentrate containing them, for example, in a concentration of 2.5 to 25% by weight.

The present invention also relates to a nanocomposite material in the form of a masterbatch comprising component (b) in an amount of from 0.03 to 90%, based on the weight of component (a), component (c) in an amount of from 0.03 to 15%, based on the weight of component (a), and component (d) in amount of from 0.03 to 15%, based on the weight of component (a).

Components (b), (c) and (d) and, if desired, further additives, can also be added before or during polymerisation or before crosslinking.

Components (b), (c) and (d), with or without further additives, can be incorporated in pure form or encapsulated in waxes, oils or polymers into the synthetic polymer that is to be stabilized.

Components (b), (c) and (d), with or without further additives, can also be sprayed onto the synthetic polymer that is to be stabilized. It is able to dilute other additives (for example the conventional additives indicated above) or their melts so that they too can be sprayed together with these additives onto the polymer that is to be stabilized. Addition by spraying on during the deactivation of the polymerization catalysts is particularly advantageous, it being possible to carry out spraying using, for example, the steam used for deactivation.

In the case of spherically polymerized polyolefins it may, for example, be advantageous to apply components (b), (c) and (d), with or without other additives, by spraying.

The nanocomposite materials stabilized in this way can be employed in a wide variety of forms, for example as foams, films, fibres, tapes, moulding compositions, as profiles or as binders for coating materials, especially powder coatings, adhesives or putties.

The synthetic polymers stabilized in this way can likewise be employed in a wide variety of forms, especially as thick-layer polyolefin mouldings which are in long-term contact with extractive media, such as, for example, pipes for liquids or gases, films, fibres, geomembranes, tapes, profiles or tanks.

The preferred thick-layer polyolefin mouldings have a layer thickness of from 1 to 50 mm, in particular from 1 to 30 mm, for example from 2 to 10 mm.

Thus, a further embodiment of the present invention relates to a shaped article, in particular a film, pipe, profile, bottle, tank or container, fiber containing a nanocomposite material as described above.

A further embodiment of the present invention relates to a molded article containing a nano-composite material as described above. The molding is in particular effected by injection, blow, compression, roto-molding or slush-molding or extrusion.

The present invention also relates to a process for stabilizing a synthetic polymer against oxidative, thermal or light-induced degradation, which comprises incorporating in or applying to said material at least one each of components (b), (c) and (d), with or without further additives.

A preferred embodiment of the present invention is therefore the use of a mixture of components (b), (c) and (d), with or without further additives, as stabilizers for synthetic polymers against oxidative, thermal or light-induced degradation.

The preferred components (b), (c) and (d) in the process for stabilizing a synthetic polymer and the use thereof as stabilizers for synthetic polymers against oxidative, thermal or light-induced degradation are the same as those described for the nanocomposite material.

The following examples illustrate the invention further. Parts or percentages relate to weight.

Stabilization of Polypropylene

1.5 kg of polypropylene powder (Profax®PH 350, Basell Polyolefins, Germany) are mixed to homogeneity in a high-speed mixer with 5% of Nanofil®N15 (distearyldimethylammonium chloride modified nanodispersed layered silicate clay, Süd-Chemie AG, Germany), 15% of Polybond®3200 (maleic anhydride grafted polypropylene, Crompton Europe Ltd., UK), 0.1% of calciumstearate and with the additives listed in Table 1. This blend is then extruded in a twin-screw extruder, of Berstorff, at a temperature of at most 200° C. After drawing the extrudate through a waterbath to cool, it is granulated. 80×90 mm and 2 mm thick test panels are then moulded from these granules by means of an injection moulding machine (Arburg 320 S) at a temperature of at most 235° C. The oven aging of the test panels is carried out in a Memmert convection oven at 135° C. for 5 days. The ΔYellowness Index (YI) [YI after 5 days minus YI at the beginning of the test] of these test panels is determined in accordance with ASTM D 1925-70. Low YI values signify little discoloration, high YI values strong discoloration of the samples. The less discoloration, the more effective the stabilizer or stabilizer blend. The results are compiled in Table 1.

An other group of test panels are subjected to artificial ageing at 135° C. in a fan-assisted oven until they become brittle. The results are summarized in Table 1. The longer it takes, the better the stabilization.

OIT Measurements of Polypropylene Nanocomposites

43.45 g Moplen HF 500 N (Basell Polyolefins, Germany), 15% Polybond®3000 (maleic anhydride grafted polypropylene, Crompton Europe Ltd., UK), 5% organic modified clay (Somasif®MTE (UNICOOPJAPAN LTD. (Duesseldorf), Germany) respectively Cloisite 20A (Southern Clay Products, Inc.)) and the appropriate amount of additives listed in table 2 are blended in a small vessel. The blends are mixed for 10 minutes at 200° C. in a brabender mixer (Plasticorder PL 2000-3 from brabender), pre-pressed with a hydraulic press from Fontijne and finally pressed at 200° C. into 60×60×1 mm plates. Ca. 25 mg of these plates are analysed by OIT (Oxidative-induction time, according to ASTM D 3895-80 at 190° C.) by aid of a Perkin Elmer DSC 7/3.5 Pyris. The measured OITs are listed in Table 2. A higher value for an OIT is related to a better stabilization of the sample.

OIT Measurements of Polyethylene Nanocomposites

52.20 g Hostalen GM 8255 (Hoechst AG, Frankfurt, Germany), 5% organic modified clay (Cloisite 20A (RTM) (natural montmorillonite modified with a quaternary ammonium salt from Southern Clay Products, Inc.)) and the appropriate amount of additives listed in Table 3 are premixed in a small vessel. The blends are mixed at 200° C. for 10 minutes in a brabender mixer (Plasticorder PL 2000-3 from brabender), pre-pressed with a hydraulic press from Fontijne and finally pressed at 200° C. into 60×60×1 mm plates. Ca. 25 mg of this plates have been analysed by OIT (Oxidative-induction time, according to ASTM D 3895-80 at 190° C.) by aid of a Perkin Elmer DSC 7/3.5 Pyris. The measured OITs are listed in Table 3. A higher value for an OIT is related to a better stabilization of the sample.