Method for obtaining nanocomposite thermoplastic materials by exfoliating laminar mineral particles in a polymer matrix and nanocomposite materials obtained thereby

A method of obtaining nanocomposite materials formed of a thermoplastic polymer matrix and mineral nanofillers dispersed in said matrix, these nanofillers resulting from the exfoliation of agglomerates formed of stacked laminar mineral particles in the polymer matrix placed in a thermoviscous state, method consisting in:

(a) using a composition to be exfoliated, comprising at least one thermoplastic polymer compound to form the polymer matrix, mineral particles made of laminar mineral stacks to be exfoliated, previously treated by means of an organo-ionic agent to make these laminar mineral particles organophilic, potentially at least one compatibility agent to make the polymer matrix and the treated laminar mineral particles to be exfoliated compatible with one another;

(b) forming a visco-elastic mixture by kneading and heating the composition to be exfoliated by putting into a viscous state the polymer compounds present in said composition at a temperature at least equal to the use temperature of the most viscous polymer compound, and simultaneously by kneading the polymer compounds with the treated laminar mineral particles to be exfoliated;

(c) the submission of the visco-elastic mixture containing the treated stacked laminar mineral particles to be exfoliated to thermomechanical working in the viscous state comprising compression and significant shearing;

(e) the elimination of the volatile compounds generated by the thermomechanical working of the visco-elastic mixture;

(f) the transformation of the degassed visco-elastic mixture into an industrially useable material;characterised in that, to obtain a complete exfoliation of the treated laminar mineral particles, and a controlled dispersion of the nanometric elementary laminar mineral particles resulting from the exfoliation in the visco-elastic mixture, (d) the visco-elastic mixture coming from the compression and shearing thermomechanical working of step (c) is subjected to a relaxation under gentle mechanical kneading, at low shearing rate, before being transformed into an industrially useable material.

The method according to claim 1, characterised in that the thermoplastic polymer compounds constituting the polymer matrix are thermoplastic homopolymers and/or copolymers selected from the group constituted by polyolefins, polystyrenes, polyamides, polyesters, polyvinyl alcohols, polyurethanes, polysiloxanes, grafted or ungrafted, and thermoplastic elastomers, grafted or ungrafted, selected from the group constituted by olefin elastomers, styrene elastomers, polyester elastomers, polyurethane elastomers, polysiloxane elastomers.

The method according to one or other of claims 1 and 2, characterised in that the polymer compounds forming the matrix are preferentially selected from the group constituted by grafted or ungrafted polyolefins and grafted or ungrafted elastomers.

The method according to any one of claims 1 to 3, characterised in that the polymer compounds forming the matrix are preferentially selected from the group constituted by low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, high-density polyethylene, high-density and high-molecular-weight polyethylene, high-density and ultra-high-molecular-weight polyethylene, medium-density polyethylene, metallocene polyethylene, polyisobutylene, polybutene, polymethylpentene, polyisoprene, polybutadiene, the cycloolefins, in particular cyclopentene or norbornene, polypropylene, ethylene-propylene copolymers, ethylene and C₄ to C₁₀ α-olefin copolymers, propylene and C₄ to C₁₀ α-olefin copolymers, ethylene-propylene-diene copolymers (EPDM), ethylene-propylene copolymers (EPR), ethylene vinyl acetate copolymer (EVA), mixtures of copolymers with a polymer, more particularly polypropylene/ethylene-propylene copolymer, low-density polyethylene, vinyl acetate copolymer, copolymers of ethylene and of acrylic and methacrylic esters, of styrenebutadiene-styrene, of styrene-ethylene-butadiene-styrene, of styrene-propylene-styrene, of styrene-isoprene-styrene, polysiloxane elastomers.

The method according to any one of claims 1 to 4, characterised in that the polymer compounds of the matrix are grafted by means of at least one functional monomer, selected from the group constituted by maleic anhydride, itaconic anhydride, citraconic anhydride, acrylic and methacrylic acids, acrylic and methacrylic esters.

The method according to any one of claims 1 to 5, characterised in that the laminar mineral particles to be exfoliated are of natural or synthetic origin.

The method according to any one of claims 1 to 6, characterised in that the laminar mineral particles to be exfoliated are clays selected from the groups constituted by the smectite group composed of montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sanconite, magadiite, and kenyaite, the vermiculite group, the illite group, in particular ledikite, the chlorinated clay group, chalcogenides.

The method according to claim 7, characterised in that the clays in lamellae or leaves to be exfoliated have a specific surface area of at least 200 m²/g and preferentially of between 300 m²/g and 800 m²/g.

The method according to claim 7, characterised in that the clays in lamellae or leaves to be exfoliated, being in the form of agglomerates, have a form factor defined by the ratio of the largest dimension over the smallest dimension of the agglomerates of between 1 and 1000.

The method according to any one of claims 1 to 9, characterised in that the laminar mineral particles to be exfoliated are made organophilic by a treatment prior to the exfoliation by means of an organo-ionic compound belonging to the group of the organo-ammonium and organophosphonium compounds, this organo-ionic compound being of one of the NH₃⁺R₁, NH₂⁺R₂R₃, P⁺R₄R₅R₆R₇ types, wherein the R₁ to R₇ radicals are hydrocarbon chains having at least four carbon atoms.

The method according to any one of claims 1 to 10, characterised in that the laminar mineral particles to be exfoliated are made organophilic by a treatment prior to the exfoliation by means of a mixture of organo-ionic and organosilane compounds.

The method according to one or the other of claims 10 and 11, characterised in that the quantity of organo-ionic compounds employed varies between 10 mmoles to 1000 mmoles, preferentially between 20 mmoles and 200 mmoles, and very preferentially between 80 mmoles to 120 mmoles, for 100 g of stacked laminar mineral particles to be treated.

The method according to any one of claims 1 to 10, characterised in that the compatibility agent present in the composition to be exfoliated is selected from the group constituted by oligomers and/or telomers functionalised by polar groups, polymers and/or copolymers and/or thermoplastic elastomers functionalised by polar and/or grafted groups.

The method according to claim 13, characterised in that the oligomers and/or telomers have an acrylic, methacrylic, vinylic, styrenic or diene chemical structure.

The method according to claim 13, characterised in that the polymers and/or copolymers and/or thermoplastic elastomers functionalised by polar groups are selected from the group constituted by the polymer compounds forming the polymer matrix.

The method according to any one of claims 1 to 15, characterised in that the quantity of previously treated stacked laminar mineral particles to be exfoliated entering into the polymer composition is at the most 60% by weight and preferentially between 0.2% by weight and 40% by weight of the total weight of said composition.

The method according to any one of claims 1 to 16, characterised in that the quantity of compatibility agent liable to enter into the polymer composition to be exfoliated is between 0% by weight and 40% by weight and preferentially between 2% by weight and 20% by weight of the mass of the stacked laminar mineral particles to be exfoliated.

The method according to any one of claims 1 to 17, characterised in that a dispersing agent of the laminar mineral particles to be exfoliated is introduced into the composition.

The method according to claim 18, characterised in that the dispersing agent is selected from the group constituted by the compounds whose chemical structure includes at least one acid function supplied by a group of the carboxylic, phosphoric, phosphonic, sulphuric, sulphonic type, this structure also including:

- ethylene oxide and/or propylene oxide of which the cumulative number of structures of one and/or the other is selected from the range from 1 to 300,

- a group R which may be a saturated or unsaturated linear or non-linear alkyl group, an aryl group, a saturated or unsaturated heterocycle, each group having a number of carbon atoms at the most equal to 28C and desirably selected from the range from 8 to 24C, a steroid group, the R group being able to have at least one function of the -OH, -COOH, -COOR, -NH₂, -CO-NH₂, -CN type,

- a group R' which may be hydrogen or a carbon chain having a carbon number at most equal to 28C and is preferentially between 1 and 4C.

The method according to any one of claims 18 and 19, characterised in that the concentration of this dispersing agent is between 0.01 % by weight and 1 % by weight, and preferentially from 0.1 % by weight to 0.6% by weight of the mass of the stacked laminar mineral particles to be exfoliated introduced into the composition.

The method according to any one of claims 1 to 20, characterised in that other agents, which are heat stabilisers, photochemical stabilisers, anti-oxidants, antistatics, lubricants, fire retardants, dyes, flavours, aromas, are introduced into the composition to be exfoliated.

The method according to any one of claims 1 to 21, characterised in that pulverulent fillers, which are of mineral, organic, natural and/or synthetic origin, are introduced into the composition.

The method according to claim 22, characterised in that the fillers are pulverulent mineral materials chosen from salts and/or mineral oxides which have or have not been subjected to a surface treatment belonging to the group constituted by calcium carbonates, magnesium carbonates, zinc carbonates, dolomite, lime, magnesium, aluminium trihydroxide, alumina, clays and other silico-aluminas, in particular talc, kaolin, mica, glass beads.

The method according to claim 22, characterised in that the organic fillers of natural or synthetic origin are selected from the group constituted by the biodegradable natural polymers, in particular carbohydrates, starch, cellulose in the form of wood meal and/or cellulose fibres, dyes, pigments, carbon black, powders of thermosetting and/or thermoplastic synthetic polymers.

The method according to any one of claims 22 to 24, characterised in that the pulverulent fillers have dimensions of between 0.01 and 300 µm and preferentially between 0.1 and 100 µm.

The method according to any one of claims 22 to 24, characterised in that the mineral and/or organic fillers are introduced into the composition at a rate of at most 70% by weight and preferentially 0.1 % by weight to 50% by weight of the composition.

The method according to any one of claims 1 to 26, characterised in that the composition to be exfoliated is transformed into a visco-elastic mixture by kneading and heating to a use temperature of the most viscous polymer compound entering into said composition, then is subjected to thermomechanical working involving compression and shearing, the rate of shearing applied to the visco-elastic mixture during the thermomechanical working being at least equal to 10⁴ second^-1 and preferentially between 10⁴ second^-1 and 10⁷ second^-1.

The method according to any one of claims 1 to 27, characterised in that the time during which the visco-elastic mixture is subjected to the thermomechanical working involving compression and shearing of step (c) is between 5% and 30% of the total time necessary to perform steps (b) to (f) of said method.

The method according to any one of claims 1 to 28, characterised in that the visco-elastic mixture coming from the thermomechanical working involving compression and shearing is subjected to a relaxation under gentle mechanical kneading of which the shearing rate is at most equal to 10⁴ second^-1 and preferentially between 10 seconds^-1 and 10⁴ second^-1.

The method according to any one of claims 1 to 29, characterised in that the temperature of the visco-elastic mixture during the relaxation is at least equal, and preferentially at least 3°C greater, and very preferentially 6°C greater than the temperature used in step (c) of thermomechanical working involving compression and shearing.

The method according to any one of claims 1 to 30, characterised in that the relaxation time necessary to reach a virtually complete exfoliation of the stacked laminar mineral particles is preferentially between 3 and 10 times the time during which the visco-elastic mixture has been subjected to the thermomechanical working of step (c) involving compression and shearing.

The method according to any one of claims 1 to 31, characterised in that it is conducted in a non-continuous kneading machine or in an extruder-type continuous kneading machine.

The method according to any one of claims 1 to 32, characterised in that, when it is performed in a double-screw extruder-type kneading machine, of which the barrel is divided into zones which each possess a heating system and a cooling system, the relaxation of step (d) is effected in at least one relaxation zone placed after the thermomechanical working zone of step (c) comprising compression and shearing, this at least one relaxation zone having a total cumulative length of between 8% and 40%, and preferentially between 8% and 25%, of the total length of the screws.

The method according to any one of claims 1 to 33, characterised in that the start of at least one visco-elastic mixture relaxation area in an extruder-type kneading machine is located at a distance expressed as a percentage relative to the total length of the screws of between 30% and 70% from the upstream end of said screw.

The method according to any one of claims 1 to 34, characterised in that, when it is performed in a continuous extruder-type kneading machine, the speed of rotation of the screws is between 50 and 1200 revolutions per minute.

Nanocomposite thermoplastic materials obtained according to any one of claims 1 to 35.

A use of the nanocomposite thermoplastic materials according to claim 36, in the fields of packaging, of storage of liquids and gases, of coating, and more particularly the medical, paramedical, pharmaceutical, parapharmaceutical, hygiene, cosmetics, oil, electrical construction, household electrical appliance, toy, automobile construction, shipbuilding, air, rail, building and the space field.