FR2871805A1 - Preparation of nanocomposite materials comprises preparation of a composition (comprising polyethylene, maleic anhydride grafted polyethylene and a mineral charge) to exfoliate and dispersion of mineral charge in the composition - Google Patents

Abstract

Preparation of nanocomposite materials (I) formed by a polyethylene matrix and mineral nanocharges dispersed in the matrix, comprises preparing a composition (II) to exfoliate (where (II) comprises polyethylene (A) to form the matrix polymer, maleic anhydride grafted polyethylene (B) and a mineral charge (C) constituted by lamellate mineral stacks), and dispersing (C) in (II) by heating to the melting point of (A) and (B). Preparation of nanocomposite materials (I) formed by a polyethylene matrix and mineral nanocharges dispersed in the matrix, comprises preparing a composition (II) to exfoliate (comprising polyethylene (A) to form the matrix polymer, maleic anhydride grafted polyethylene (B) and a mineral charge (C) constituted by lamellate mineral stacks (which is previously treated by means of an organo-ionic agent to make the organophilic lamellate mineral charge)), and dispersing (C) in the composition by heating to the melting point of (A) and (B), where the quantity of (B) is 5-25 wt.%, its rate of grafting is 1-2.5% and the mass ratio (R) of the real mass of mineral particles to the mass of polar groups of (II) is lower than 41 (preferably lower than 14). INDEPENDENT CLAIM are also included for: (1) main mixture with two compounds comprising (C) (10-50 (preferably 15-33 wt.%) (which is previously treated by means of an organo-ionic agent to make the lamellate mineral charge organophilic) dispersed in (B) (50-90 (preferably 67-85) wt.%, where the rate of grafting of (B) is 1-2.5% (preferably 1.2-2.5%) and the ratio (R) is lower than 41 (preferably lower than 14); and (2) useful of (A) for the manufacture of (I).

Description

The present invention relates to the preparation of nanocomposite materials

in a polyethylene matrix.

  The purpose of this invention is to disperse the finest possible nanoscale clay sheets in polyethylene.

  The patent application WO 2004/012917 describes a process for obtaining nanocomposite thermoplastic materials by dispersing lamellar mineral particles in a polymer matrix. According to this document, in order to obtain good dispersion of the mineral filler, it is necessary for the process to contain a low-shear soft mechanical stirring relaxation step after the step of compressing and significantly shearing the mixture at the same time. viscoelastic condition.

  Surprisingly, the inventors of the present application have found that for the manufacture of nanocomposite materials having a polyethylene matrix, the type of process used was not important to achieve good dispersion and even exfoliation. On the contrary, the simple addition of the previously treated feedstock in the polyethylene, even by an efficient compounding process, alone can not allow the total dispersion of the mineral filler (nanofiller) in the matrix. The only necessary conditions discovered by the inventors concern the need for the presence of a maleic anhydride grafted polyethylene-type dispersant having a precise degree of grafting and a precise mass ratio R between the amount of mineral filler present in the composition and the amount of maleic anhydride present in the composition.

  The invention relates to the ratio R equivalent to the mass ratio of the amount of actual nanofiller contained in the mixture over the amount of maleic anhydride.

  It is known to those skilled in the art that the introduction of a maleic anhydride grafted product modifies the basic properties of the host matrix, particularly if it is a high density polyethylene (HDPE) with added d Linear low density polyethylene (LLDPE) grafted maleic anhydride. LLDPE by its properties, relaxes the HDPE and cancels the effects of reinforcements possibly obtained by nanofillers. The interest is therefore to minimize the amount of polyethylene (PE) grafted maleic anhydride in the mixture, so as to preserve the natural properties of the host matrix.

  Moreover, the resulting properties of the nanocomposites are related to the level of dispersion of the nanofillers contained in the mixture. Therefore it is important to be able to control the dispersion of the slats.

  The inventors have surprisingly discovered that the R makes it possible to control the level of dispersion of the nanofillers. For an R less than 14, the mixture is perfectly exfoliated, that is to say that the periodic organization of the lamella stack of the nanocharge is lost.

  For a R between 14 and 40, the mixture is partially exfoliated and there are still some clusters of lamellae.

  Beyond 40, the dispersion of the nanofillers is in an interposed state, that is to say that the polymer has entered between the lamellae, but there still remains a certain level of arrangement between the lamellae.

  Moreover, in order to maintain the level of graft polymer in the mixture at a sufficiently low level so as not to degrade the intrinsic properties of the host polymer (maximum 25% of the composition), while maintaining the ratio R less than 14, it is necessary to have a PE grafted maleic anhydride whose grafting rate is between 1% and 2.5%.

  However, we do not find on the market products grafted to more than 1% of maleic anhydride. Only products whose maleic anhydride is polymerized in the molecular chain (Lotader, ATOFINA) have high levels (up to 3.6%). Unfortunately, the chemical activity of maleic anhydride when integrated into the chain is lower than when it is grafted onto a PE.

  The inventors have surprisingly discovered that a maleic anhydride grafted PE having a content of between 1% and 2.5% is required to produce an exfoliated mixture with a low level of grafted PE. As the nature of the grafted PE has little influence on the result of the dispersion, it is possible to adapt the grafted dispersant to both the nature of the matrix PE (density, stiffness, viscosity) and both the desired resultant properties. .

  The present invention thus relates to a process for preparing a nanocomposite material formed of a polyethylene matrix and of mineral nanofillers dispersed in said matrix, characterized in that it comprises the following steps: a) preparation of a composition comprising: A) polyethylene to form the polymer matrix (the matrix), B) a maleic anhydride grafted polyethylene (the dispersant), C) a mineral filler consisting of lamellar mineral stacks, previously treated with an organo-ionic agent to make this organophilic lamellar mineral filler (nanofiller), b) dispersion of compound C in the composition by heating and kneading at a temperature at least equal to the melting temperature of compounds A and B, characterized in that the amount of compound B is included between 5 and 25% by weight, that its degree of grafting is between 1% and 2.5%, advantageously between 1.2% and 2.5%, advantageously the grafting ratio is 1.7%, and the weight ratio R, corresponding to the ratio of the actual mass of the mineral particles to the maleic anhydride mass of the composition, is less than 41, advantageously less than 14.

  For the purposes of the present invention, the term mineral filler consisting of lamellar mineral stacks any inorganic agglomerate, of natural or synthetic origin, formed of a plurality of elementary lamellae of nanometric size (nanofillers), stacked, adjacent and bonded between they have weak van der waals, each having a thickness less than 100 Å, and preferably between 2 Å and 20 Å, the surfaces of the elementary lamellae can be made organophilic by appropriate treatment. These mineral fillers may be clays based on magnesium and aluminum silicates, which may contain other cations such as sodium, in the form of a colamellar structure, with a high form factor, with flexible lamellae , linked together by a cohesive force that must be broken for good dispersion.

  For the purposes of the present invention, the term "dispersion" means the result of the introduction of the polymer chains of the compounds A and B between the sheets which constitute the stacks of the lamellar nanofillers, causing the spacing of these sheets to be up to the rupture of the interactions between these layers and the total loss of the periodic organization of the stacks (exfoliation). Advantageously, the dispersion according to the present invention goes from the intercalated state to the total exfoliation. For the purposes of the present invention, the term "intercalated state" is intended to mean the state by which the lamellae constituting the stacks of the lamellar nanofillers are separated from each other by polymer and may be partially exfoliated. These mineral fillers are chosen, advantageously, for the materials of this invention. naturally occurring, in the groups consisting of: - clays whose constituent lamellae surfaces have the capacity to exchange ions with an organo-ionic compound to which they are exposed, such as the group of smectites, composed of montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sanconite, magadiite, and kenyaite, the group of vermicullite, the group of illites such as lédikite; clays whose lamellae or sheets have a particularly high specific surface area, that is to say at least 200 m 2 / g and advantageously between 300 m 2 / g and 800 m 2 / g; clays having a shape factor defined by the ratio of the largest dimension to the smallest dimension of the agglomerates of lamellar particles to exfoliate between 1 and 1000.

  These inorganic fillers consist of lamellar mineral stacks are subjected to a treatment prior to their implementation in the context of the invention by means of a suitable agent such as an organoionic compound, treatment described in the prior art and well known to those skilled in the art.

  This pre-dispersion treatment of the mineral fillers according to the present invention has the aim of making said mineral fillers organophilic in order to facilitate their dispersion and even the exfoliation in the thermosetting polyethylene matrix; One of the possible agents for treating mineral fillers may be an organo-ionic agent having the ability to exchange cations present on the lamellae of clays in the interlamellar interstices, such as, for example, sodium ions, by ions. provided by means of an organo-ionic agent or organoonium such as an organo-ammonium compound or an organophosphonium compound, this organo-onium compound possibly being of, for example, the following general formula NH 3 + R 1, NH 2 + R 2 R 3 or P + R4R5R6R7, in which the groups R1 to R7 represent hydrocarbon chains. At least one of R1 to R7 has at least 4 carbon atoms.

  These various organo-onium agents, which bind during the exchange of ions, for example sodium replaced by ammonium, on the surfaces of the stacked clay lamellae, make the lamellae organophilic, that is to say these various compounds facilitate the compatibility between the nanofillers and the polyethylene matrix.

  Another possible agent for treating the mineral fillers to be exfoliated may be formed by mixing at least one organo-ionic agent and at least one organosilane agent as described in US Pat. No. 5,747,560. .

  These various organo-onium agents facilitate the dispersion of the agglomerates of the stacked lamellar particles by a steric hindrance effect of their molecule because, since these agents, in particular the organo-onium agents, have the capacity to bind to said lamellae by ion exchange, these agents act in the interstitial space as a blowing agent, which widens the interstitial space by increasing the distance between two contiguous lamellar particles and weakens interlamellar cohesion forces. The widening of the interstitial space can pass, thanks to the presence of this agent, from 12A (for example for a natural Montmorillonite) to 28A (for example for the nanowire 15, treated with a dimethyldisteararylammonium). Therefore, the dispersion of the mineral fillers is facilitated and is considered as performed when the distance between the lamellar mineral particles from the process according to the invention is at least equal, and preferably greater than 60 Å.

  Such treatments are described in the state of the art, for example in US Pat. No. 4,793,007, US Pat. No. 5,747,560, EP 0 846 723, International Application WO 09304117, but also in numerous other documents.

  For the purposes of the present invention, the weight ratio R is defined as follows: R _ actual mass of the mineral filler actual mass of the inorganic filler mass of maleic anhydride mass of the component B * (% MA) The acronym MA stands for maleic anhydride and the% MA corresponds to the degree of grafting of the compound B. For the purposes of the present invention, the actual mass of the inorganic filler is understood to mean the mass of the inorganic residue free of the organic treatment of onium type. Advantageously, it is obtained by thermogravimetric analysis at 600 C, which consists of removing all the organic compounds in the mixture.

  The nanocomposite materials according to the present invention are formed of a polyethylene polymer matrix in which the mineral nanofillers are dispersed.

  Advantageously, the amount of compound C in step (a) of the process according to the present invention is between 5 and 33% by weight.

  Advantageously, the compound A and the polyethylene (PE) of the compound B are chosen independently of one another in the group consisting of low density polyethylene (LDPE), linear low density (LLDPE) and very low density (VLDPE). medium density polyethylene (MDPE), high density polyethylene (HDPE). Advantageously, the polyethylene may be viscous or fluid.

  Advantageously, compound A and polyethylene of compound B are chosen independently of each other from the group consisting of LLDPEs or hdPEs.

  Preferably, the MFI of the PE grafted with maleic anhydride must remain greater than 5 g / 10 min at 190 ° C. under 21.6 kg and preferably greater than 10 g / 10 min at 190 ° C. under 21.6 kg.

  The viscosity of a polymer is characterized by the MFI (Melt Flow Index) which is measured according to ASTM D 1238.

  Advantageously, compound B is a PEhd whose Melt Flow Index (MFI) is greater than 5 g / 10 min under 2.16 kg at 190 C.

  In a particular embodiment of the invention, the method according to the present invention comprises an additional step c) pressurizing and granulation of the obtained nanocomposite material.

  In one embodiment of the invention, the process according to the present invention is carried out in a batch mixer-mixer type Banbury internal mixer, from a mixture consisting of the various compounds A, B (preferably in the form of granules) and C (advantageously in powder form). Advantageously, in this case step b) lasts at least 3 minutes and the compounds A, B and C are introduced into the mixer and brought to a temperature sufficient to melt compounds A and B, and to mix the melt . The material can then be extracted from the mixer to be introduced into a single-screw extruder which ensures the pressurization of the material and its granulation at the outlet.

  In another embodiment of the invention, the process according to the present invention is carried out in a continuous mixer of the twin-screw extruder or Buss co-kneader type, advantageously in a Buss co-kneader.

  Advantageously, in the case of the twin-screw extruder, step b) lasts at least 15s. Advantageously, the compounds A, B and C are metered before being introduced into the hopper by weight or volumetric feeders, according to the desired composition; the temperature of the machine and the mechanical work involved make it possible to bring the compounds A and B to a temperature necessary to obtain the melting and mixing of the polymers and mineral fillers. At the exit of the machine, the molten material is granulated.

  On the other hand, it is possible, for example, to introduce the compounds A and B through the feed hopper, then to the compound C via a second hopper or feed booth situated downstream of the first feed hopper.

  In a particular embodiment of the invention, step (a) of the process according to the present invention consists of two successive stages: (a) preparation of a two-compound masterbatch by mixing and kneading at melting of compound B of from 10 to 50% by weight, advantageously from 15 to 33% by weight, of compound C and from 50 to 90% by weight, advantageously from 67 to 85% by weight of compound B, the degree of grafting of the compound B being between 1 and 2.5%, advantageously between 1.2 and 2.5% and the ratio R being less than 41, advantageously less than 14; a2) dilution of the masterbatch obtained in step (a1) by adding compound A in an amount such that the amount of compound B in the final mixture thus obtained is between 5 and 25% by weight.

  In another embodiment of the present invention, step (a) of the process according to the present invention consists of two successive steps: a3) preparation of a three-compound masterbatch by mixing and mixing at room temperature melting of compounds A and B of 33% by weight, of compound C and - at most 25% by weight of compound B, the degree of grafting of compound B being between 1 and 2.5%, advantageously between 1 , 2 and 2.5% and the ratio R being less than 41, advantageously less than 14; a4) dilution of the masterbatch obtained in step (a3) by adding compound A in an amount such that the amount of compound B in the final mixture thus obtained is between 5 and 25% by weight.

  The present invention also relates to a two-compound masterbatch comprising 10 to 50% by weight, advantageously 15 to 33% by weight, of a mineral filler consisting of lamellar mineral stacks, previously treated with an organic agent. -ionic to make this inorganic lamellar inorganic filler, (compound C), dispersed in 50 to 90% by weight, advantageously 67 to 85% by weight of maleic anhydride grafted polyethylene (compound B) whose grafting rate is between 1 and 2.5%, advantageously between 1.2 and 2.5%, the ratio R of the masterbatch being less than 41, advantageously less than 14.

  The present invention furthermore relates to the use of the masterbatch according to the present invention for the manufacture of a nanocomposite material formed of a polyethylene or polypropylene matrix and of mineral nanofillers dispersed in said matrix and comprising 5 to 25% by weight of the Thus, according to the two embodiments indicated above, it is possible to produce ready-to-use mixtures or masterbatches rich in nanofillers, intended to be diluted in a second step in a polyethylene or polypropylene matrix. In this case the masterbatch may be according to the intended applications, consisting of the three compounds (matrix, dispersant, nanofillers) or simply consisting of dispersant and nanofiller.

  The quantity of nanofillers is included for the 3-compound masterbatches between 10 and 33% of treated nanocharge C for a maximum amount of dispersant contained in the mixture equal to 25%. For bicomponent mixtures (dispersant + nanofillers), the amount of nanofillers is between 10 and 50% of the mixture and preferably between 15 and 33%.

  The nanocomposite material produced by the process according to the present invention is therefore used either directly in the state or as a component of a complex composition requiring a second compounding by hot mixing. In this case, a two or three nanocharged rich masterbatch is used which allows the easy introduction of nanofillers into the material. The masterbatch becomes an additive of the composition thus produced during a second kneading operation.

  In this case the formulation can be carried out using a continuous mixer of extruder type double screw or Buss co-kneader or discontinuous such as an internal mixer type Banbury. Advantageously, it is the Buss comalaxer or an internal mixer Banbury type.

  In another embodiment of the process according to the present invention, the process comprises a preliminary step (aa) for preparing compound B by mixing the polyethylene to be grafted with maleic anhydride and peroxide at the polyethylene operating temperature. to be grafted for at least 10s.

  The manufacture of grafted PE is known. It consists of kneading the PE with a mixture of maleic anhydride + peroxide whose proportions are for example 6/1. The proportion of peroxide required for grafting is variable and well known to those skilled in the art. The grafting is carried out hot at a temperature sufficient to ensure both the melting of the PE and the activation of the initiator (peroxide), in a continuous compounding machine of the twin-screw extruder or Buss co-kneader type, or discontinuous like an internal mixer.

  In general, the grafting operation on the PE generates a viscosity increase directly related to the degree of grafting of maleic anhydride. Regarding the dispersion of the nanofillers in the mixture, the viscosity has an effect on the effectiveness of the dispersant.

  Viscosity is characterized by MFI (Melt Flow Index) which is measured according to ASTM D 1238.

  Preferably, the MFI of the PE grafted with maleic anhydride must remain greater than 5 g / 10 min at 190 ° C. under 21.6 kg and preferably greater than 10 g / 10 min at 190 ° C. under 21.6 kg.

  Advantageously, steps (aa), (a) and (b) of the process according to the present invention are carried out in one pass on a continuous mixer type machine such as a twin-screw extruder or Buss co-kneader.

  In particular, in the first hopper, the PE to be grafted with maleic anhydride and peroxide, the graft being made very rapidly, the grafted PE (compound B) is thus generated before the addition of the nanofiller (compound C) and optionally matrix PE (compound A) which are introduced into a feed hopper or downstream booster well, after degassing to remove the anhydride and the residual peroxide. At the exit of the machine is obtained a dispersed nanocomposite, a master mixture with 3 compounds or bi compounds, concentrated in nanofillers, or ready for use.

  According to the invention, it is also possible to introduce into the composition according to the present invention other agents well known in the state of the art. These various agents may be thermal stabilizers, photochemicals, antioxidants, antistats, anti-copper, lubricants, flame retardants, dyes, or other known agents, introduced in amounts well known in the state of the art. technical.

  It is also possible to introduce into the composition according to the present invention pulverulent fillers of mineral or organic origin, natural and / or synthetic.

  When these fillers are powdery mineral materials, they may be chosen from salts and / or inorganic oxides which have or have not undergone a surface treatment, such as carbonates of calcium, magnesium, zinc, dolomite, lime, magnesia, alumina trihydrate, magnesium hydroxide, alumina, talc, calcined or hydrated kaolin, mica, or synthetic powdery mineral materials such as glass beads for example. When these fillers are organic powdery materials of natural or synthetic origin, they may be chosen from the group consisting of natural biodegradable polymers, in particular carbohydrates such as polysaccharides and, among them, starch, cellulose in form. sawdust or wood flour and / or cellulose fibers, natural fibers such as flax or hemp, dyes, pigments, carbon black, synthetic polymer powders, in particular thermoset polymer powders and / or thermoplastics.

  All these pulverulent materials of mineral or organic origin can be used alone or in combination.

  The dimensions of these inorganic or organic materials are generally between 0.01 and 300 gm and preferably between 0.1 and 50 m. These inorganic and / or organic fillers may be introduced into the composition according to the invention in a proportion of at most 70% by weight and preferably from 0.1% by weight to 60% by weight of the composition to be exfoliated.

  In this case the formulation can be carried out using a continuous mixer of twin screw extruder type or Buss co-kneader. Complementary elements of the formulations are introduced into the machine through inputs (hopper or feeding well) located downstream of the polymer introduction hopper and nanofiller.

  The composition may contain other polymers such as polyolefins from the group consisting of polyethylene, copolymers of ethylene and vinyl acetate (EVA) or copolymers of ethylene and alkyl acrylate (methyl, ethyl, butyl), or the group consisting of polypropylene copolymers.

  The present invention also relates to the use of 5 to 25% by weight of maleic anhydride grafted polyethylene (compound B) having a degree of grafting of between 1 and 2.5%, advantageously between 1.2 and 2.5%, as a dispersant of a mineral filler (compound C) consisting of lamellar mineral stacks, previously treated with an organo-ionic agent to make this inorganic lamellar inorganic filler, in a polyethylene matrix (compound A), the ratio R being less than 41, advantageously less than 14.

  The present invention further relates to a nanocomposite material obtainable by the process according to the present invention.

  The present invention further relates to the use of the nanocomposite material according to the present invention as flame retardant, reinforcing or barrier materials, preferably to oils and O2, an article comprising a material nanocomposite according to the present invention.

  Advantageously, it is sheaths of copper or optical telecommunications cables, insulators for automotive wires, or tubes for hydraulic distribution, advantageously for underfloor heating, sanitary, air conditioning or compressed air.

  The invention will be better understood and other objects, advantages and characteristics thereof will appear more clearly from the description which follows and which is made with reference to the accompanying drawings showing non-limiting embodiments of the invention and on which Fig. 1 shows a small-angle X-ray diffraction spectrum for coarse dispersion, i.e. microdispersion, of nanofillers in a polyethylene matrix. (The dispersant used is the Lotader 3210 marketed by Atofina, whose content of maleic anhydride content is 3%). Figure 2 shows a small angle x-ray diffraction spectrum 2871805 for total exfoliation, i.e. a dispersion of the nanocharging unit particles in a polyethylene matrix.

  FIG. 3 represents a small-angle X-ray diffraction spectrum for the intercalated state of the nanofillers in a polyethylene matrix, ie where the particles are separated from each other by polyethylene and can be partially exfoliated .

  FIG. 4 represents a small angle X-ray diffraction spectrum for a composition according to the present invention made on an internal mixer with R = 14.

  FIG. 5 represents a small-angle X-ray diffraction spectrum of two compositions according to the present invention made with a twin-screw extruder for which R is equal to 14 and 66 and the quantity of nanofiller is equal to 5% and 20% respectively. in weight.

  FIG. 6 shows a small angle x-ray diffraction spectrum for a composition according to the present invention made with a twin screw extruder and R = 14.

  FIG. 7 represents a small angle X-ray diffraction spectrum for a composition according to the present invention made with Buss co-ordinator and R = 14.

  FIG. 8 represents a smallangle X-ray diffraction spectrum for compositions according to the present invention comprising a high density polyethylene compound B grafted to 1.7% by fluid maleic anhydride, that is to say R = 14 and comprising 5% mineral filler as a function of different polyethylene matrices.

  Figure 9 shows a small angle x-ray spectrum for compositions according to the present invention comprising maleic anhydride-grafted compound B LLDPE, for R = 14 and 5% nanofillers with different polyethylene matrices.

  FIG. 10 shows a small angle x-ray diffraction spectrum for compositions according to the present invention comprising a high density polyethylene compound grafted with maleic anhydride, R = 30 and comprising 10% mineral filler based on different polyethylene matrices.

  Figure 11 shows a small angle x-ray spectrum for compositions according to the present invention comprising maleic anhydride grafted compound B LLDPE, for R = 30 and 10% nanofillers with different polyethylene matrices.

  The detail of each composition according to the present invention for each figure is collated in Table 1 below.

Table 1:

  Figures Matrix- Dispersant- (Nanofil Type R Composite A Compound B 15) Compound Mixing

VS

  1 80% PE SR572 15% Lotader 5% Extruder 7 3210 Double Screws 2 80% PE SR572 15% PE 5% Extruder 14 GC7260 Grafted Double Screw MA 1.7% 3 80% PE SR572 15% LLDPE 5% Extruder 233 grafted MA double screw 0.1% 4 80% PE SR572 15% PE 5% Mixer 14 GC7260 internal grafted MA 1.7% 80% PE SR572 15% PE 5% Extruder 14 65% PE SR572 GC7260 Grafted 20% Double Screw 66 MA 1 , 7% 15% PE GC7260 grafted MA 1.7% 6 80% PE SR572 15% PE 5% Extruder 14 GC7260 grafted double screw MA 1.7% 7 80% PE SR 572 15% PE 5% Co- 14 GC7260 grafted mixer MA 1.7% Buss 8 80% PE SR572 15% PE 5% Extruder 14 80% LLDPE GC7260 grafted double screw 80% PEGC7260 MA 1.7% 9 80% PE SR572 15% LLDPE 5% Extruder 14 80% LLDPE grafted MA double screw 80% PEGC7260 1.7% 75% PE SR572 15% PE 10% Extruder 30 75% LLDPE GC7260 grafted double screw 75% PEGC7260 MA 1.7% 11 75% PE SR572 15% LLDPE 10% Extruder 30 75% MA double screw grafted LLDPE 75% PEGC7260 1.7% The evaluation of the dispersion of the nanofillers in the matrix is carried out by diffraction by Yons X at small angles. This technique makes it possible to establish the level of dispersion of the nanocharge in the material. Several dispersion levels can be distinguished, ranging from coarse dispersion (Figure 1: micro-dispersion: nanofillers packets, no penetration of the polymer between the layers) to total exfoliation (Figure 2: dispersion of unit particles). by the intercalated state (Figure 3) for which the particles are spaced apart by polymer and can be partially exfoliated: the height of the peaks directly related to the number of diffracting objects is lower than in Figure 1. The width of the peaks, inversely proportional to the size of the diffracting packets is larger in Figure 3 than in Figure 1. Figure 3 therefore describes smaller and fewer packets.

  The following examples are given as a non-limiting indication.

  EXAMPLE 1 Grafting of Polyethylene with Maleic Anhydride The following process is used: Werner Pfleiderer twin-screw twin extruder ZSK 25 - temperature profile used: 170-180-180-190-190-190-190 C 20 speed of the extruder: 700 rpm - proportion: 97.55% PE GC 7260 (marketed by the company Basell, MFI = 8g / l 0min 190 C / 2.16kg), density 0.960kg, 2.1% maleic anhydride, 0 , 35% dicumyl peroxide.

  - Extruder flow rate: 35 Kg / h - The maleic anhydride actually grafted is 1.7%. The grafting rate is measured by pHmetry or infra-red spectrometry.

  EXAMPLE 2 Method According to the Present Invention with Corotative Twin-Screw Extruder The formulas are all composed as follows: Compound A: high density polyethylene sold by the company Atofina (PEhd SR 572): MFI = 0.2 g / 10 min C / 2,16kg), density: 0.957 kg / dm3 Compound B: Dispersant: maleic anhydride grafted polyethylene, whose grafting rate can be variable - Compound C: Treated montmorillonite: Nanofil 15: 70% Montmorillonite, 30% dimethyldisteararylammonium marketed by the company Süd-Chemie.

  The formulas are carried out in a Werner Pfleiderer ZSK 25 twin-screw extruder equipped with a profile consisting of a conventional melting zone followed by a mixing zone of medium intensity but at the end of which, elements of the type have been placed. not on the left which increases both the mechanical work of the mixing zone and the residence time of the material in the machine.

  The temperature profile used is as follows: 170-180-180-190-190-190190 C. 15 - speed: 360 rpm - flow rate: 15 Kg / h Example 3: Influence of the polar function rate (R) All the results presented in FIGS. 5 and 6 were carried out with the method of example 2, the compound B consisting of a PE grafted fluid (GC 7260, marketed by Basell) (MFI before grafting: 8 g / 10 min, 190 C / 2.16 kg, density 0.960 kg / dm3). The level of maleic anhydride grafted is 1.7%, MFI obtained after grafting: 15 g / 10 min under 21.6 kg at 190 C. Figure 5 shows clearly that there is a strong influence of the ratio R on the pace diffraction curves. For R = 66, 20% nanofillers for 15% grafted PE, the diffractogram has a net diffraction peak at 2.5. The intensity of the diffraction peak decreases sharply as the value of R decreases. The diffractograms are flat for materials having a value of R = 14 (5% nanofiller for 15% grafted PE) (FIG. 6).

  EXAMPLE 4 Influence of Mixing Systems In order to dissociate from the process the impact of the R value, we have made the formulations indicated in Examples 2 and 3 above on tools different from the corotative twin screw extruder: Haake type internal mixer with counter-rotating rotors, for which the shear generated is small compared to a twin-screw extruder. On the other hand, the intermittent nature of this apparatus makes it possible to modify the hot residence time of the material.

  - The Buss co-kneader (batch mixer) which generates less shear than the double-screw corotative extruder. (Buss is more advantageous) Results obtained on the internal mixer 15 Internal mixer conditions: - 170 C - speed: 80 rpm - t = 10 min These X-ray diffraction results (FIG. 4, R = 14) show that the dispersion of nanofillers is also possible with an internal mixer, and that it follows the same law defined on the twin-screw extruder, according to which it is governed by the ratio R. Results on the co-kneader Buss (diameter 140 mm) Operating conditions: - temperature profile: 170-175-180-200-200-200 C - main screw speed: 140 rpm - speed of the final pressurization screw: 30 rpm 30 - flow rate: 450 kg / h On the spectra FIGS. 7 and 6 show the same formulation: (85% compound A: PE SR 572, 15% compound B: PE grafted with 1.7% maleic anhydride, 5% compound C: nanowire 15, R = 14 ) performed respectively on the Buss and the double-screw extruder.

  So we see that the tool has no impact on the dispersion of nanofillers.

  It is more the formulation which in this case makes it possible to obtain a dispersed mixture that is almost exfoliated.

  EXAMPLE 5 Other polymer systems Another type of PE was used for the grafting step (aa) and as dispersant (compound B) to ensure the dispersion of the nanofillers: a LLDPE (MFI = lg / 10 min at 190 ° C. 2.16 kg, density 0.919 kg / dm3, Lupolex 18 KFA marketed by Basell).

  It was used with 3 other PEs as matrix (compound A): a fluid PEhd (GC 7260, MFI = 8 g / 10 min 190 C under 2.16 kg), a viscous PEhd (SR 572, MFI = 0.2 g / 10 min 190 C under 2.16 kg), a LLDPE (Lupolex 18 KFA) The LLDPE was grafted with maleic anhydride (1.7%) (MFI PE grafted: 2.3 g / 10 min, 190 C / 21.6 kg ) to disperse nanofillers in a PE matrix. As for the grafted HDPE (example 1 to 4), we find the influence of R, which determines the level of dispersion of nanofillers in the medium.

  FIGS. 8 and 10 show the dispersion results obtained with the 1.7% grafted HDPE as compound B, in various PE matrices (compound A), for A / B / C: 80/15/5 mixtures ( R = 14) and 75/15/10 (R = 30) using the method according to Example 2.

  Whatever the nature of PE, we have exfoliated mixtures.

  FIGS. 9 and 11 show the dispersion results obtained with the 1.7% grafted LLDPE (MFI of grafted PE: 2.3 g / 10 min, 190 C / 21.6 kg), as compound B, in different matrices PE (compound A), for A / B / C mixtures: 80/15/5 (R = 14) and 75/15/10 (R = 30).

  Whatever the nature of PE, there are indeed exfoliated mixtures for R = 14. For R = 30, the dispersion results are satisfactory, but the mixtures are not completely exfoliated.

  Here we have the influence of the high viscosity of the dispersant (grafted LLDPE) on the dispersion, whatever the nature of the matrix PE. Advantageously, the MFI (Melt Flow Index) of the dispersant must be greater than 5 g / 100 min at 190 ° C. under 21.6 kg, and preferably greater than 10 g / 10 min at 190 ° C. under 21.6 kg.

  The rule of R therefore applies for all pairs of PE + dispersant (compound A and compound B), namely that a ratio of quantity of nanofillers to amount of maleic anhydride contained in the mixture of less than 41 is required. To obtain this ratio and to benefit from a good dispersion, it is necessary to maintain the quantity of dispersant between 5 and 25%, to benefit from the properties of the matrix. Consequently, and to obtain a low R, the degree of maleic anhydride grafting of the dispersant must be between 1% and 2.5%, advantageously between 1.2 and 2.5%.

  Thus, to obtain a good controlled dispersion, it must be ensured that the ratio R is less than 41, or even less than 14 if a total exfoliation is sought for all the pairs of PE. For this, it acts on the grafting rate of maleic anhydride and on the amounts of compound B and compound C present in the mixture.

  The good dispersion and even the exfoliation of nanofillers, in particular Montmorillonite has been demonstrated in a polyethylene matrix. This dispersion is strongly influenced by the formulation.

  In this study we have shown that for a system whose matrix (compound A) and nanofiller (compound C) are fixed, the ratio of the amount of maleic anhydride to the quantity of nanofillers (R-value) is a major criterion which allows to achieve a good level of dispersion on different types of kneaders, they are very shearing like the twin screw extruder corotative or little shear like the internal mixer or intermediate like the Buss comalaxer.

Claims (11)

  A process for preparing nanocomposite materials formed of a polyethylene matrix and mineral nanofillers dispersed in said matrix comprising the following steps: a) preparing an exfoliating composition comprising: A) polyethylene to form the polymer matrix, B) maleic anhydride grafted polyethylene, C) a mineral filler consisting of lamellar mineral stacks, previously treated with an organo-ionic agent to make this inorganic lamellar inorganic filler, b) dispersion of the compound C in the composition by heating at room temperature. a temperature at least equal to the melting temperature of compounds A and B, characterized in that the amount of compound B is between 5 and 25% by weight, its grafting rate is between 1% and 2.5% and that the mass ratio R, corresponding to the ratio of the actual mass of the mineral particles to the mass of polar functions of the composition, is 41, advantageously less than 14.   2. Method according to claim 1, characterized in that the lamellar inorganic filler of the compound C is a clay selected from the group consisting of smectites, advantageously chosen from montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sanconite, magadiite, or kenyaite, vermiculites and illites, in particular lédikite.   3. Method according to any one of the preceding claims, characterized in that the compound C is a montmorillonite treated with a dimethyldistearylammonium.   4. Method according to any one of the preceding claims, characterized in that it is carried out in a Banbury type internal mixer, a Buss co-kneader or a corotative twin screw extruder.   5. Process according to any one of the preceding claims, characterized in that it comprises a preliminary step (aa) for preparing compound B by mixing the polyethylene to be grafted with maleic anhydride and peroxide at the processing temperature. polyethylene graft for at least 10s.   6. Process according to any one of the preceding claims, characterized in that compound A and polyethylene of compound B are chosen independently of one another in the group consisting of linear low density polyethylene (LDPE) ( LLDPE) and very low density (VLDPE), medium density polyethylene (MDPE) or high density polyethylene (HDPE).   7. Method according to any one of the preceding claims, characterized in that step (a) consists of two successive steps: a) preparation of a two-compound masterbatch by mixing and kneading at the melting temperature of compound B of from 10 to 50% by weight, advantageously from 15 to 33% by weight, of compound C and from 50 to 90% by weight, advantageously from 67 to 85% by weight of compound B, the degree of grafting of compound B being between 1 and 2.5%, advantageously between 1.2 and 2.5% and the ratio R being less than 41, advantageously less than 14; a2) dilution of the masterbatch obtained in step (a1) by adding compound A in an amount such that the amount of compound B in the final mixture thus obtained is between 5 and 25% by weight.   8. Process according to any one of claims 1 to 6, characterized in that step (a) consists of two successive steps: a3) preparation of a three-compound masterbatch by mixing and mixing at room temperature for melting compounds A and B of from 10 to 33% by weight, of compound C and not more than 25% by weight of compound B, the degree of grafting of compound B being between 1 and 2.5%, advantageously between 1.2 and 2.5% and the ratio R being less than 41, advantageously less than 14; a4) dilution of the masterbatch obtained in step (a3) by adding compound A in an amount such that the amount of compound B in the final mixture thus obtained is between 5 and 25% by weight.   9. Two-compound masterbatch comprising 10 to 50% by weight, advantageously 15 to 33% by weight, of a mineral filler consisting of lamellar mineral stacks, previously treated with an organo-ionic agent to make this organophilic lamellar inorganic filler (compound C), dispersed in 50 to 90% by weight, advantageously 67 to 85% by weight of maleic anhydride grafted polyethylene (compound B), the degree of grafting of which is between 1 and 2.5%, advantageously between 1.2 and 2.5%, the ratio R of the masterbatch being less than 41, advantageously less than 14.   10. Use of 5 to 25% by weight of maleic anhydride grafted polyethylene having a degree of grafting of between 1 and 2.5%, advantageously between 1.2 and 2.5%, as a dispersant of a mineral filler constituted lamellar mineral stacks, previously treated with an organo-ionic agent to make this inorganic lamellar inorganic filler, in a polyethylene matrix, the ratio R being less than 41, advantageously less than 14.   11. Use of the masterbatch according to claim 9 for the manufacture of a nanocomposite material formed of a polyethylene or polypropylene matrix and mineral nanofillers dispersed in said matrix and comprising 5 to 25% by weight of compound B.