EP1648957A2 - Nanocomposite compositions and their production - Google Patents

Nanocomposite compositions and their production

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Publication number
EP1648957A2
EP1648957A2 EP04740508A EP04740508A EP1648957A2 EP 1648957 A2 EP1648957 A2 EP 1648957A2 EP 04740508 A EP04740508 A EP 04740508A EP 04740508 A EP04740508 A EP 04740508A EP 1648957 A2 EP1648957 A2 EP 1648957A2
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EP
European Patent Office
Prior art keywords
compositions according
thermoplastic polymer
solid
montmorillonite
nylon
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP04740508A
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German (de)
French (fr)
Inventor
Nicolas Fedullo
Michel Sclavons
Jacques Devaux
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Universite Catholique de Louvain UCL
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Universite Catholique de Louvain UCL
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Publication of EP1648957A2 publication Critical patent/EP1648957A2/en
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
    • C08K5/098—Metal salts of carboxylic acids
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function

Definitions

  • This invention concerns nanocomposite compositions, for example for use in producing structural elements, and processes for their production.
  • EP398551-A describes a process for the preparation of polyamide nanocomposite compositions by pre-swelling a layered silicate with a mixture of water and 12-aminododecanoic acid, separating the pre-swelled silicate and carrying out further swelling of the silicate using a mixture of water and ⁇ -caprolactam, dispersing nylon-6 into the resulting product, and melting and kneading the dispersion before finally extruding the resulting blend to form a nanocomposite composition.
  • JP11310643 describes a method for dispersing an inorganic clay into a hydrophobic thermoplastic polymer using a solvent containing water in which the three components are extruded together at a temperature above the melting temperature of the polymer.
  • Another hitherto proposed method of preparing polyamide nanocomposite compositions consists of forming a slurry of Na-montmorillonite in water, and mixing and extruding the slurry with molten nylon-6 to form an extrudate of the nanocomposite compositions .
  • liquids are used to assist dispersion of the inorganic solid in the molten polyamide. This liquid which is used to assist in the dispersion is then allowed to evaporate, and so no significant amounts of it remain in the final nanocomposite.
  • Nanocomposite compositions which comprise melt blends of a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer.
  • Nanocomposite compositions in accordance with the present invention preferably contain substantially no surfactants.
  • the invention further provides a process for the preparation of polymer-based nanocomposite compositions in accordance with the present invention which comprises mixing in the melt phase a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer.
  • Nanocomposite compositions in accordance with the present invention can in general be prepared without the use of surfactants .
  • Nanocomposite compositions in accordance with the present invention can be in a form of finished articles or in a form suitable for further processing into finished articles, for example in a form for extrusion directly into finished articles, or in the form of a masterbatch.
  • processes in accordance with the present invention will be effected without aqueous pre-treatments of the solid inorganic substance.
  • water or other liquids can be used as processing aids, for example as described in W099/29767 and JP11310643.
  • the solid additive used to increase the polarity of the polymer will, however, be present in the nanocomposite which is produced, becoming part of it.
  • Other additives can also be used as further processing aids, for example compatibilizers for compatibilizing solid additives used to increase the polarity of the polymer and the polymer matrix itself.
  • the compatibilizers will also be present in the nanoco posites which are produced, becoming part of them.
  • thermoplastics polymers Mixing of the nanometric fillers with the thermoplastics polymers is preferably effected with high shear compounding.
  • Use of reactive processing techniques can also be of assistance in effecting processes in accordance with the present invention.
  • nanocomposites formed in accordance with the present invention can be used to produce molded parts having good mechanical properties combined with good other physical properties such as low flammability and low permeability, and surface properties which can be modified compared with the thermoplastic polymer alone.
  • a particular advantage of nanocomposite compositions produced in accordance with the present invention is that they can be used to produce molded products which hitherto have used polymeric materials reinforced with large amounts of fibrous materials, thereby avoiding unacceptable disadvantages which occur with the use of such reinforcements, for example reductions in gloss and abrasion resistance.
  • they can be used to produce molded articles where fibrous reinforcements are unacceptable, for example where the overall dimensions of the articles are too small, for example very small gears.
  • They can also be used to produce molded articles having a modified outer surface which is more compatible with subsequent surface treatments (e.g. painting) compared with the thermoplastic polymer matrix.
  • they can be used to produce molded articles with surfaces which reduce gas diffusion into the interior of articles, thereby enabling a barrier effect to be achieved which can be varied with the process used to make the composites.
  • the additive can be such that it is soluble in or forms a homogeneous mixture with the molten thermoplastic polymer.
  • the solid additive can also be such that it forms a second phase dispersed in the polymer.
  • thermoplastics polymers can be used in accordance with the present invention to produce nanocomposite materials, for example polyamides, polyolefins, acrylonitrile- butadiene-styrene copolymers, polyphenylene oxide, polycarbonates, and polyesters, e.g. poly- ⁇ -caprolactone, polyethylene terephthalate and polybutylene terephthalate, or a mixture of two or more thereof.
  • polyamides which can be used include polymers derived from one or more of - ⁇ -caprolactam, ⁇ -aminocaproic acid, ⁇ -enantholactam, 7-aminoheptanoic acid, 11-aminodecanoic acid, 9-aminononanoic acid, ⁇ -pyrrolidone or ⁇ -piperidione, and condensation polymers obtained by reacting one of more diamines, for example tetramethylene diamine, hexamethylene diamine, nonamethylene diamine, undecamethylene diamine, dodecamethylene diamine or meta-xylene diamine, with one or more dicarboxylic acids, for example terephthalic acid, isophthalic acid, adipic acid or sebacic acid, and mixtures of such polyamides.
  • examples of such polymers include nylon-6, nylon-9, nylon-11, nylon-12, nylon-4,6 and nylon-6, 6.
  • polyolefins which can be used include polypropylenes, polyethylenes, for example low density polyethylenes, medium density polyethylenes and high density polyethylenes, and copolymers containing units derived from one or more of ethylene, propylene, butylene-1 and octene-1, e.g. linear low density polyethylenes.
  • the solid inorganic substance having at least one dimension in the scale is preferably in the form of plates with an average aspect ratio of from 5 to 10,000, and an average thickness of not more than lOnm, and more preferably of not more than 5nm, a preferred average thickness being in the range of from 0.4 to 2.5nm.
  • solid inorganic substances having at least one dimension examples include silica, phyllosilicates, for example smectite clay minerals, vermiculite clay minerals and micas.
  • suitable smectite clay minerals include montmorillonite, nontronite, beidellite, volkonskoite, hectorite, stevensite, pyroysite, saponite, sauconite, magadiite and kenyaite, montmorillonite being preferred.
  • the solid inorganic substances can be used in an unpurified raw state and without any chemical treatment being required before use. However, they can, if desired, be washed with water containing a surfactant in order to reduce aggregation of the solid inorganic substances .
  • the amount of solid inorganic substance mixed with the thermoplastic polymer and the additive which is solid at room temperature and increases the polarity of the polymer can in general be freely chosen, the amount generally being dependent on the desired properties of the nanocomposite composition which is to be produced. Preferred amounts are up to 30% by weight of the resulting nanocomposite.
  • thermoplastic polymers A wide variety of additives can be used to increase the polarity of the thermoplastic polymers, and they will in general be selected according to the thermoplastic polymers which are used, providing they are solid at room temperature.
  • thermoplastic polymers examples include polar polymers other than the matrix thermoplastic polymer, which may or may not form a separate phase dispersed within the thermoplastic polymer, and salts of organic or inorganic acids, for example lithium bromide or sodium benzoate.
  • a compatibilizer When a polar polymer is used to increase the polarity of the thermoplastic polymer, a compatibilizer will usually also be used.
  • the use of a compatibilizer generally serves to improve dispersion of organic additives which are solid at room temperature, for example nylon-6, within the matrix of the thermoplastic polymer, for example polypropylene. It can also reduce the size of nodules of the polar polymer (e.g. nylon-6) containing the inorganic solid in the finished composite, for example from about lO ⁇ m to less than l ⁇ m, and enhance adhesion between nodules of the polar polymer (e.g. nylon-6) containing the inorganic solid and the matrix of the thermoplastic polymer.
  • nylon-6 nodules in a polypropylene matrix can vary with the compatibilizer which is used. More particularly, smaller nodules have been observed using maleic anhydride grafted styrene-based copolymers (Kraton - Trade Mark) compared with maleic anhydride grafted propylene copolymers (Polybond - Trade Mark) , which is believed to be due to the high concentration of grafted maleic anhydride groups in the Kraton.
  • compatibilizers can be used to aid compatibility of solid additives with the thermoplastic polymer matrix.
  • examples of compatibilizers which can be used include block or grafted copolymers having one segment which is miscible or substantially compatible with an apolar matrix, for example polypropylene, and another segment which is miscible or substantially compatible with a polar dispersed phase, for example nylon-6.
  • a preferred compatibilizer can be obtained by the in situ reaction of a maleic anhydride grafted apolar homopolymer or copolymer with nylon-6 as the dispersed phase.
  • the presence or absence of a compatibilizer has not been found to influence exfoliation of the solid inorganic substances having at least one dimension in the nanometer scale.
  • Raw, untreated montmorillonite (2.5kg/hour) was mixed with powdered nylon-6 and the mixture was fed at 50kg/hour into a twin-screw extruder (Megacompounder - Coperion W&P 25mm diameter working at 1200rpm) with simultaneous injection of an aqueous solution or suspension of either sodium benzoate, lithium benzoate or lithium bromide (2.5kg/hour) .
  • the extruder temperature was set to a value varying between 190 and 215°C over the entire length of the cylinder.
  • Injected water was degassed from the extruder and polyamide nanocomposites containing sodium benzoate, lithium benzoate or lithium bromide, respectively, were extruded.
  • Electron micrographs of the nanocomposites indicated exfoliation combined with intercalation of the montmorillonite, plus remaining tactoids.
  • a series of commercially available ionic olefin oligomers in the form of their sodium salts were injected (0.5kg/hour) as aqueous solutions or suspensions or emulsions into the twin-screw extruder used in Example 1 into which a mixture of raw, unpurified montmorillonite (2.5kg/hour) and polypropylene (50kg/hour) was also being fed.
  • Raw, unpurified montmorillonite was mixed with benzoic acid and sodium benzoate at a temperature of about 150°C to produce a gel-like material which looked similar to that obtained by swelling montmorillonite with water at room temperature.
  • Raw, unpurified montmorillonite was extruded under high shear (1200 rpm) with pure isotactic polypropylene homopolymer whilst a lOOg/l solution of n-octadecyl succinic anhydride in dodecane (non-polar solvent) was injected into the molten polymer in the extruder.
  • the first (concentrate 1) contained 60% by weight of nylon-6, 20% by weight of a maleic anhydride grafted propylene copolymer (Polybond - Trade Mark) and 20% by weight of raw, unpurified montmorillonite .
  • the second (concentrate 2) contained 80% by weight of nylon-6, and 20% by weight of raw, unpurified montmorillonite.
  • Both concentrates were dispersed in a mixture of either pure isotactic polypropylene or of isotactic polypropylene blended with a maleic anhydride grafted propylene copolymer (Polybond - Trade Mark) , and then extruded to form a nanocomposite material in which the final amount of montmorillonite was 5% by weight.
  • the resulting materials were in the form of fine dispersions in the polypropylene of the montmorillonite which was itself dispersed in the polar nylon-6. X-Ray diffraction showed that intercalation had occurred, and electron microscopy showed that the montmorillonite remained partly exfoliated, and partly intercalated with a few remaining tactoids.
  • a further improvement in the dispersing of the montmorillonite in the polypropylene was achieved by the use of injected water as a processing aid during the extrusion process. Electron microscopy of the resulting products showed that the dispersed polar phase (mainly nylon-6) had overall dimensions of the order of magnitude of the exfoliated montmorillonite plates included in the polar phase.
  • the presence of the two polymeric phases in these nanocomposite materials can result in synergistic effects with the dispersed clay, for example increased toughness.
  • a first series (concentrates MB-D) was produced from 60% by weight of nylon-6, 20% by weight of a compatibilizer (either a maleic anhydride grafted polypropylene copolymer (Polybond 3002 or 3200) or a styrene based copolymer (Kraton) ) , and 20% by weight of raw, unpurified montmorillonite.
  • a compatibilizer either a maleic anhydride grafted polypropylene copolymer (Polybond 3002 or 3200) or a styrene based copolymer (Kraton)
  • a second series (concentrates MB-H) was produced from 80% by weight of nylon-6 and 20% by weight of raw, unpurified montmorillonite .
  • the concentrates of both series were produced using a process in accordance with the present invention, X-ray diffraction showing that intercalation has occurred. Electron microscopy showed that the montmorillonite in both series of concentrates had become partially exfoliated and partly intercalated with a few remaining tactoids.
  • concentrates MB-D pure isotactic polypropylene
  • concentration MB-D a mixture of isotactic polypropylene blended with a compatibilizer which is either a maleic anhydride grafted propylene copolymer (Polybond 3002 or 3200 - concentrate MB-H) or a styrene based copolymer (Kraton) , and then extruded at 220-240°C with or without the addition of water (50ml/minute, 50 to 120bar) to form nanocomposite materials in which the final amount of montmorillonite was 4.76 or 5% by weight for concentrates MB-H and MB-D, respectively (Table 3) .
  • a compatibilizer which is either a maleic anhydride grafted propylene copolymer (Polybond 3002 or 3200 - concentrate MB-H) or a styrene based copolymer (Kraton)
  • the resulting materials were in the form of fine dispersions in the polypropylene of montmorillonite which was itself dispersed in the polar nylon-6 which in turn was surrounded by the compatibilizer. Electron microscopy showed that the montmorillonite remained partly exfoliated and partly intercalated with a few remaining tactoids.
  • the first of these compositions was produced by first forming a first concentrate (concentrate MB-a) from 75% by weight of nylon-6 and 25% by weight of a maleic anhydride grafted propylene copolymer (Polybond 3200) which had first been oven-dried for 48 hours.
  • a second concentrate (concentrate MB-b) was then produced from 80% by weight of concentrate MB-a and 20% by weight of raw, unpurified montmorillonite in the presence or absence of water.
  • a final nanocomposite MB-c was produced from 30% by weight of concentrate MB-b and 70% by weight of pure isotactic PP.
  • the second of these compositions was produced by forming an initial concentrate (concentrate MB-a' ) from 80% by weight of nylon-6 and 20% by weight of raw, unpurified montmorillonite in the presence of water.
  • a second concentrate was then produced from80% by weight of concentrate MB-a' and 20% by weight of a maleic anhydride grafted propylene copolymer (Polybond 3200) which had first been oven-dried for 48 hours.
  • a maleic anhydride grafted propylene copolymer Polybond 3200
  • a final nanocomposite MB-c' was then produced from 30% by weight of this second concentrate (concentrate MB-b' ) and 70% by weight of pure isotactic polypropylene.
  • the resulting nanocomposite materials (MB-c and MB-c' ) were in the form of fine dispersions of montmorillonite in polypropylene, the montmorillonite itself being dispersed in the nylon-6 which in turn was surrounded by the compatibilizer.
  • Optical microscopy at lOOx magnification of cut surfaces of composites produced in the Examples using an immersed objective in phase contrast showed nylon-6 nodules near to the surface of the composites. These nodules were elongate and aligned in the direction of flow. The elongation of the nodules was observed to be less pronounced when they included the clay. The nodules were also larger in the absence of a compatibilizer.
  • Raman spectroscopy was used to provide a qualitative estimate of the proportion of nylon-6 and polypropylene at the surfaces of composites produced in the Examples, the composites differing by the presence or absence of clay and/or a compatibilizer.
  • the depth of the analysis was about lO ⁇ m over an area of 21x21 ⁇ m 2 with a spectrum recorded every 3 ⁇ m.
  • Both polypropylene and nylon-6 were detected whatever the sample or processing method (DC or MB) , which means that nylon-6 coexists with polypropylene at the surface of the samples.
  • Raman spectroscopy does not allow the shape of the nylon-6 phase to be predicted.
  • X-ray photoelectron spectroscopy of some samples of polypropylene matrices containing nylon-6 showed different results for polypropylene matrices resulting from either the presence or absence or absence of compatibilizer, the presence or absence of water, the nature of the compatibilizer or the process (DC or MB) .
  • This form of spectroscopy enables the atomic composition of the first 5nm of the surface to be investigated, and they showed the presence of both clay (Si 2p peak) and nylon-6 (N Is peak) at the surfaces of each sample. Samples produced using water had more intense N Is peaks indicating a larger amount of nylon-6 at the surface compared with those produced without using water.

Abstract

Polymer-based nanocomposite compositions consisting of a melt blend of a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer. They can be used to produce molded parts having good mechanical properties without the use of fibrous reinforcements, combined with good physical properties such as low flammability and low permeability.

Description

Nanocomposite Compositions and their Production
This invention concerns nanocomposite compositions, for example for use in producing structural elements, and processes for their production.
EP398551-A describes a process for the preparation of polyamide nanocomposite compositions by pre-swelling a layered silicate with a mixture of water and 12-aminododecanoic acid, separating the pre-swelled silicate and carrying out further swelling of the silicate using a mixture of water and ε-caprolactam, dispersing nylon-6 into the resulting product, and melting and kneading the dispersion before finally extruding the resulting blend to form a nanocomposite composition. 099/29767 describes an alternative method for preparing polyamide nanocomposite compositions in which a molten polyamide, a solid substance composed of anisotropic particles with a high aspect ratio, and a liquid, preferably water, are mixed and extruded to produce the compositions. JP11310643 describes a method for dispersing an inorganic clay into a hydrophobic thermoplastic polymer using a solvent containing water in which the three components are extruded together at a temperature above the melting temperature of the polymer.
Another hitherto proposed method of preparing polyamide nanocomposite compositions consists of forming a slurry of Na-montmorillonite in water, and mixing and extruding the slurry with molten nylon-6 to form an extrudate of the nanocomposite compositions .
With the exception of the process described in 099/29767 and JP11310643, hitherto proposed processes generally involve a chemical modification of the inorganic solid substance used to form the composites in which it is subjected to reaction with surfactants • such as ammonium salts under aqueous conditions. A particular problem with the use of ammonium-type surfactants is their often limited temperature resistance, which in turn limits the polymers which can be blended with ammonium treated solid substances, for example montmorillonite, to those which are processable at temperatures of less than 250°C.
Furthermore, even if a pre-treatment of the inorganic solid is not specified in the processes proposed in W099/29767 and
JP11310643, liquids, particularly water, are used to assist dispersion of the inorganic solid in the molten polyamide. This liquid which is used to assist in the dispersion is then allowed to evaporate, and so no significant amounts of it remain in the final nanocomposite.
According to the present invention there are provided polymer-based nanocomposite compositions which comprise melt blends of a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer. Nanocomposite compositions in accordance with the present invention preferably contain substantially no surfactants.
The invention further provides a process for the preparation of polymer-based nanocomposite compositions in accordance with the present invention which comprises mixing in the melt phase a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer.
Nanocomposite compositions in accordance with the present invention can in general be prepared without the use of surfactants .
Nanocomposite compositions in accordance with the present invention can be in a form of finished articles or in a form suitable for further processing into finished articles, for example in a form for extrusion directly into finished articles, or in the form of a masterbatch.
In general, processes in accordance with the present invention will be effected without aqueous pre-treatments of the solid inorganic substance. However, if desired, water or other liquids can be used as processing aids, for example as described in W099/29767 and JP11310643. The solid additive used to increase the polarity of the polymer will, however, be present in the nanocomposite which is produced, becoming part of it. Other additives can also be used as further processing aids, for example compatibilizers for compatibilizing solid additives used to increase the polarity of the polymer and the polymer matrix itself. The compatibilizers will also be present in the nanoco posites which are produced, becoming part of them.
Mixing of the nanometric fillers with the thermoplastics polymers is preferably effected with high shear compounding. Use of reactive processing techniques can also be of assistance in effecting processes in accordance with the present invention.
As with hitherto proposed nanocomposites, nanocomposites formed in accordance with the present invention can be used to produce molded parts having good mechanical properties combined with good other physical properties such as low flammability and low permeability, and surface properties which can be modified compared with the thermoplastic polymer alone. A particular advantage of nanocomposite compositions produced in accordance with the present invention is that they can be used to produce molded products which hitherto have used polymeric materials reinforced with large amounts of fibrous materials, thereby avoiding unacceptable disadvantages which occur with the use of such reinforcements, for example reductions in gloss and abrasion resistance. Furthermore, they can be used to produce molded articles where fibrous reinforcements are unacceptable, for example where the overall dimensions of the articles are too small, for example very small gears. They can also be used to produce molded articles having a modified outer surface which is more compatible with subsequent surface treatments (e.g. painting) compared with the thermoplastic polymer matrix. In addition, they can be used to produce molded articles with surfaces which reduce gas diffusion into the interior of articles, thereby enabling a barrier effect to be achieved which can be varied with the process used to make the composites.
The additive can be such that it is soluble in or forms a homogeneous mixture with the molten thermoplastic polymer. The solid additive can also be such that it forms a second phase dispersed in the polymer.
Any of a variety of thermoplastics polymers can be used in accordance with the present invention to produce nanocomposite materials, for example polyamides, polyolefins, acrylonitrile- butadiene-styrene copolymers, polyphenylene oxide, polycarbonates, and polyesters, e.g. poly-ε-caprolactone, polyethylene terephthalate and polybutylene terephthalate, or a mixture of two or more thereof.
Examples of polyamides which can be used include polymers derived from one or more of -ε-caprolactam, β-aminocaproic acid, ω-enantholactam, 7-aminoheptanoic acid, 11-aminodecanoic acid, 9-aminononanoic acid, α-pyrrolidone or α-piperidione, and condensation polymers obtained by reacting one of more diamines, for example tetramethylene diamine, hexamethylene diamine, nonamethylene diamine, undecamethylene diamine, dodecamethylene diamine or meta-xylene diamine, with one or more dicarboxylic acids, for example terephthalic acid, isophthalic acid, adipic acid or sebacic acid, and mixtures of such polyamides. Examples of such polymers include nylon-6, nylon-9, nylon-11, nylon-12, nylon-4,6 and nylon-6, 6.
Examples of polyolefins which can be used include polypropylenes, polyethylenes, for example low density polyethylenes, medium density polyethylenes and high density polyethylenes, and copolymers containing units derived from one or more of ethylene, propylene, butylene-1 and octene-1, e.g. linear low density polyethylenes.
The solid inorganic substance having at least one dimension in the scale is preferably in the form of plates with an average aspect ratio of from 5 to 10,000, and an average thickness of not more than lOnm, and more preferably of not more than 5nm, a preferred average thickness being in the range of from 0.4 to 2.5nm.
Examples of solid inorganic substances having at least one dimension which can be used in accordance with the present invention include silica, phyllosilicates, for example smectite clay minerals, vermiculite clay minerals and micas. Examples of suitable smectite clay minerals include montmorillonite, nontronite, beidellite, volkonskoite, hectorite, stevensite, pyroysite, saponite, sauconite, magadiite and kenyaite, montmorillonite being preferred. In general, the solid inorganic substances can be used in an unpurified raw state and without any chemical treatment being required before use. However, they can, if desired, be washed with water containing a surfactant in order to reduce aggregation of the solid inorganic substances .
The amount of solid inorganic substance mixed with the thermoplastic polymer and the additive which is solid at room temperature and increases the polarity of the polymer can in general be freely chosen, the amount generally being dependent on the desired properties of the nanocomposite composition which is to be produced. Preferred amounts are up to 30% by weight of the resulting nanocomposite.
A wide variety of additives can be used to increase the polarity of the thermoplastic polymers, and they will in general be selected according to the thermoplastic polymers which are used, providing they are solid at room temperature.
Examples of additives which are solid at ambient temperature and can be used. to increase the polarity of the thermoplastic polymers include polar polymers other than the matrix thermoplastic polymer, which may or may not form a separate phase dispersed within the thermoplastic polymer, and salts of organic or inorganic acids, for example lithium bromide or sodium benzoate.
When a polar polymer is used to increase the polarity of the thermoplastic polymer, a compatibilizer will usually also be used. The use of a compatibilizer generally serves to improve dispersion of organic additives which are solid at room temperature, for example nylon-6, within the matrix of the thermoplastic polymer, for example polypropylene. It can also reduce the size of nodules of the polar polymer (e.g. nylon-6) containing the inorganic solid in the finished composite, for example from about lOμm to less than lμm, and enhance adhesion between nodules of the polar polymer (e.g. nylon-6) containing the inorganic solid and the matrix of the thermoplastic polymer. It has been found that the size of nylon-6 nodules in a polypropylene matrix can vary with the compatibilizer which is used. More particularly, smaller nodules have been observed using maleic anhydride grafted styrene-based copolymers (Kraton - Trade Mark) compared with maleic anhydride grafted propylene copolymers (Polybond - Trade Mark) , which is believed to be due to the high concentration of grafted maleic anhydride groups in the Kraton.
A wide variety of compatibilizers can be used to aid compatibility of solid additives with the thermoplastic polymer matrix. Examples of compatibilizers which can be used include block or grafted copolymers having one segment which is miscible or substantially compatible with an apolar matrix, for example polypropylene, and another segment which is miscible or substantially compatible with a polar dispersed phase, for example nylon-6. A preferred compatibilizer can be obtained by the in situ reaction of a maleic anhydride grafted apolar homopolymer or copolymer with nylon-6 as the dispersed phase.
The presence or absence of a compatibilizer has not been found to influence exfoliation of the solid inorganic substances having at least one dimension in the nanometer scale.
The following Examples are given by way of illustration only.
Example 1
Raw, untreated montmorillonite (2.5kg/hour) was mixed with powdered nylon-6 and the mixture was fed at 50kg/hour into a twin-screw extruder (Megacompounder - Coperion W&P 25mm diameter working at 1200rpm) with simultaneous injection of an aqueous solution or suspension of either sodium benzoate, lithium benzoate or lithium bromide (2.5kg/hour) . The extruder temperature was set to a value varying between 190 and 215°C over the entire length of the cylinder. Injected water was degassed from the extruder and polyamide nanocomposites containing sodium benzoate, lithium benzoate or lithium bromide, respectively, were extruded.
X-ray diffraction analysis of the nanocomposites showed a shift in the position of the main diffraction peak to values lower than the original values of 2θ indicating intercalation. Electron micrographs of the nanocomposites indicated exfoliation combined with intercalation of the montmorillonite, plus remaining tactoids.
Example 2
A series of commercially available ionic olefin oligomers in the form of their sodium salts were injected (0.5kg/hour) as aqueous solutions or suspensions or emulsions into the twin-screw extruder used in Example 1 into which a mixture of raw, unpurified montmorillonite (2.5kg/hour) and polypropylene (50kg/hour) was also being fed.
X-Ray diffraction analysis of the extruded nanocomposite did not show peaks characteristic of montmorillonite gallery thickness.
Example 3
Raw, unpurified montmorillonite was mixed with benzoic acid and sodium benzoate at a temperature of about 150°C to produce a gel-like material which looked similar to that obtained by swelling montmorillonite with water at room temperature.
X-Ray analysis of the gel-like mixture of montmorillonite, benzoic acid and sodium benzoate after cooling it to room temperature showed that the montmorillonite had been at least partially exfoliated.
Dispersion of this material into molten polypropylene led to a satisfactory dispersion of the montmorillonite within the resulting nanocomposite as assessed by X-ray diffraction analysis and electron microscopy.
Example 4
Raw, unpurified montmorillonite was extruded under high shear (1200 rpm) with pure isotactic polypropylene homopolymer whilst a lOOg/l solution of n-octadecyl succinic anhydride in dodecane (non-polar solvent) was injected into the molten polymer in the extruder.
X-Ray diffraction analysis and electron microscopy of the extrudate showed that the montmorillonite had been satisfactorily dispersed in the polypropylene.
Example 5
Using direct compounding, 5% of raw, unpurified montmorillonite was extruded at 220-240°C under high shear (1200rpm) with 75% of pure isotactic polypropylene, 15% of nylon-6 and 5% of a compatibilizer (either a maleic anhydride grafted propylene copolymer - Polybond 3002 or 3200 (Trade Mark) or a styrene based copolymer - Kraton (Trade Mark) ) , with or without added water (50ml/minute, 50 to 120 bar) . Details of these processes are shown in Table 1) .
The morphological and mechanical properties (Young's modulus (Eyoung) and tensile strengths (ε) ) of the materials produced are shown in Table 2. Example 6 (masterbatch process)
Two concentrated dispersions of raw, unpurified montmorillonite in nylon-6 were obtained by extrusion in accordance with the present invention.
The first (concentrate 1) contained 60% by weight of nylon-6, 20% by weight of a maleic anhydride grafted propylene copolymer (Polybond - Trade Mark) and 20% by weight of raw, unpurified montmorillonite .
The second (concentrate 2) contained 80% by weight of nylon-6, and 20% by weight of raw, unpurified montmorillonite.
Both concentrates were produced using a process in accordance with the present invention, X-ray diffraction showing that intercalation had occurred. Electron microscopy showed that the montmorillonite in both concentrates was partially exfoliated, partly intercalated with a few remaining tactoids.
Both concentrates were dispersed in a mixture of either pure isotactic polypropylene or of isotactic polypropylene blended with a maleic anhydride grafted propylene copolymer (Polybond - Trade Mark) , and then extruded to form a nanocomposite material in which the final amount of montmorillonite was 5% by weight.
The resulting materials were in the form of fine dispersions in the polypropylene of the montmorillonite which was itself dispersed in the polar nylon-6. X-Ray diffraction showed that intercalation had occurred, and electron microscopy showed that the montmorillonite remained partly exfoliated, and partly intercalated with a few remaining tactoids.
A further improvement in the dispersing of the montmorillonite in the polypropylene was achieved by the use of injected water as a processing aid during the extrusion process. Electron microscopy of the resulting products showed that the dispersed polar phase (mainly nylon-6) had overall dimensions of the order of magnitude of the exfoliated montmorillonite plates included in the polar phase.
The presence of the two polymeric phases in these nanocomposite materials can result in synergistic effects with the dispersed clay, for example increased toughness.
Example 7 (masterbatch process)
Other concentrated dispersions of raw, unpurified montmorillonite in nylon-6 were produced by extrusion in accordance with the present invention.
A first series (concentrates MB-D) was produced from 60% by weight of nylon-6, 20% by weight of a compatibilizer (either a maleic anhydride grafted polypropylene copolymer (Polybond 3002 or 3200) or a styrene based copolymer (Kraton) ) , and 20% by weight of raw, unpurified montmorillonite.
A second series (concentrates MB-H) was produced from 80% by weight of nylon-6 and 20% by weight of raw, unpurified montmorillonite .
The concentrates of both series were produced using a process in accordance with the present invention, X-ray diffraction showing that intercalation has occurred. Electron microscopy showed that the montmorillonite in both series of concentrates had become partially exfoliated and partly intercalated with a few remaining tactoids.
These concentrates were dispersed in either pure isotactic polypropylene (concentrates MB-D) or a mixture of isotactic polypropylene blended with a compatibilizer which is either a maleic anhydride grafted propylene copolymer (Polybond 3002 or 3200 - concentrate MB-H) or a styrene based copolymer (Kraton) , and then extruded at 220-240°C with or without the addition of water (50ml/minute, 50 to 120bar) to form nanocomposite materials in which the final amount of montmorillonite was 4.76 or 5% by weight for concentrates MB-H and MB-D, respectively (Table 3) .
The resulting materials were in the form of fine dispersions in the polypropylene of montmorillonite which was itself dispersed in the polar nylon-6 which in turn was surrounded by the compatibilizer. Electron microscopy showed that the montmorillonite remained partly exfoliated and partly intercalated with a few remaining tactoids.
The morphological characteristics and the mechanical properties (Young's modulus (Eyoung) and tensile strengths (ε) are shown in Table 4.
Table 3
Table 4
Example 8
Two further composite compositions were produced in accordance with the present invention and using the following three stage extrusion processes (Table 5) .
The first of these compositions was produced by first forming a first concentrate (concentrate MB-a) from 75% by weight of nylon-6 and 25% by weight of a maleic anhydride grafted propylene copolymer (Polybond 3200) which had first been oven-dried for 48 hours.
A second concentrate (concentrate MB-b) was then produced from 80% by weight of concentrate MB-a and 20% by weight of raw, unpurified montmorillonite in the presence or absence of water.
A final nanocomposite MB-c was produced from 30% by weight of concentrate MB-b and 70% by weight of pure isotactic PP.
The second of these compositions was produced by forming an initial concentrate (concentrate MB-a' ) from 80% by weight of nylon-6 and 20% by weight of raw, unpurified montmorillonite in the presence of water.
A second concentrate was then produced from80% by weight of concentrate MB-a' and 20% by weight of a maleic anhydride grafted propylene copolymer (Polybond 3200) which had first been oven-dried for 48 hours.
A final nanocomposite MB-c' was then produced from 30% by weight of this second concentrate (concentrate MB-b' ) and 70% by weight of pure isotactic polypropylene.
The resulting nanocomposite materials (MB-c and MB-c' ) were in the form of fine dispersions of montmorillonite in polypropylene, the montmorillonite itself being dispersed in the nylon-6 which in turn was surrounded by the compatibilizer.
The morphological characteristics and the mechanical properties (Young's modulus (Eyoung) and tensile strengths (ε) are shown in Table 5. Table 5
Contact angles with water and surfaces of composites produced in the Examples were observed to be between 105° (which is typical for hydrophobic surfaces such as polypropylene) and 65° (which is the value for pure nylon-6) . This suggest that the outer surfaces of these composites is heterogenous with hydrophilic "islands" dispersed in hydrophobic polypropylene.
Optical microscopy at lOOx magnification of cut surfaces of composites produced in the Examples using an immersed objective in phase contrast showed nylon-6 nodules near to the surface of the composites. These nodules were elongate and aligned in the direction of flow. The elongation of the nodules was observed to be less pronounced when they included the clay. The nodules were also larger in the absence of a compatibilizer.
Raman spectroscopy was used to provide a qualitative estimate of the proportion of nylon-6 and polypropylene at the surfaces of composites produced in the Examples, the composites differing by the presence or absence of clay and/or a compatibilizer. The depth of the analysis was about lOμm over an area of 21x21μm2 with a spectrum recorded every 3μm. Both polypropylene and nylon-6 were detected whatever the sample or processing method (DC or MB) , which means that nylon-6 coexists with polypropylene at the surface of the samples. Raman spectroscopy does not allow the shape of the nylon-6 phase to be predicted.
X-ray photoelectron spectroscopy of some samples of polypropylene matrices containing nylon-6 showed different results for polypropylene matrices resulting from either the presence or absence or absence of compatibilizer, the presence or absence of water, the nature of the compatibilizer or the process (DC or MB) . This form of spectroscopy enables the atomic composition of the first 5nm of the surface to be investigated, and they showed the presence of both clay (Si 2p peak) and nylon-6 (N Is peak) at the surfaces of each sample. Samples produced using water had more intense N Is peaks indicating a larger amount of nylon-6 at the surface compared with those produced without using water.

Claims

Claims
1. Polymer-based nanocomposite compositions comprising a melt blend of a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer.
2. Compositions according to claim 1, wherein the thermoplastic polymer comprises a polyamide, a polyolefin, acrylonitrile-butadiene-styrene copolymers, polyphenylene oxide, a polycarbonate, a polyester, or a mixture of two or more thereof.
3. Compositions according to either of the preceding claims wherein the thermoplastic polymer comprises a polyamide (nylon) .
4. Compositions according to any of the preceding claims, wherein the thermoplastic polymer comprises polypropylene.
5. Compositions according to either of the preceding claims, wherein the solid inorganic substance having at least one dimension in the nanometer scale comprises a phyllosilicate, a vermiculite clay mineral, a mica or silica.
6. Compositions according to any of the preceding claims, wherein the solid inorganic substance having at least one dimension in the nanometer scale comprises montmorillonite.
7. Compositions according to claim 6, wherein the montmorillonite is used in a raw, unpurified state.
8. Compositions according to claim 7, wherein the montmorillonite is used in a raw, unpurified state without a chemical pretreatment .
9. Compositions according to any of the preceding claims, wherein the additive which is solid at room temperature and increases the polarity of the thermoplastic polymer is present in the mixture in an amount of up to 30% by weight of the mixture.
10. Compositions according ■to any of the preceding claims wherein additive which is solid at room temperature and increases the polarity of the thermoplastic polymer comprises a polar polymer or a salt of an organic or inorganic acid.
11. Compositions according to any of the preceding claims, in the form of molded articles.
12. Compositions according to any of claims 1 to 10, in the form of a masterbatch.
13. A process for the preparation of polymer-based nanocomposite compositions according to any of the preceding claims, which comprises mixing in the melt phase a thermoplastic polymer, a solid inorganic substance having at least one dimension in the nanometer scale, and an additive which is solid at room temperature and increases the polarity of the thermoplastic polymer.
14. A process according to claim 13, in which the melt phase includes water.
15. A process according to claim 13 or claim 14, wherein the mixing is effected with direct compounding of the specified components of the mixture.
16. A process according to claim 13 or claim 14, wherein the mixing is effected in a series of successive extrusion steps in which at least one intermediate masterbatch is produced prior to formation of the nanocomposite.
EP04740508A 2003-07-05 2004-07-01 Nanocomposite compositions and their production Withdrawn EP1648957A2 (en)

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