WO2005030850A1 - Process to obtain an intercalated or exfoliated polyester with clay hybrid nanocomposite material - Google Patents

Abstract

Process to obtain an intercalated or exfoliated polyester with clay hybrid nanocomposite material. The present process refers to obtaining nanocomposites (C) containing intercalated and exfoliated lamellar materials, by inserting polyethylene terephthalate (PET) oligomers (B) between the lamellas of a phyllosilicate (A), without using additional reagents and/or solvents, through shearing of the phyllosilicate and oligomer mixture, in solid state. Herein, the phyllosilicate does not need to have been submitted to any previous wetting process. The invention refers to the obtention of a nanocomposite from a melted polymeric matrix (D), wherein a oligomer/clay composite concentrate, prepared through shearing, is diluted, thereby producing a nanocomposite polymer/ lamellar silicate PLSN (E), prepared through the growth of the grafted oligomer chains, a solid post-condensation process of the oligomer in the oligomer/clay composite. These materials are utilized to prepare specific articles for several applications, such as bottles and packaging in general.

Description

"PROCESS TO OBTAIN AN INTERCALATED OR EXFOLIATED POLYESTER WITH CLAY HYBRID NANOCOMPOSITE MATERIAL" . The present invention refers to the preparation and attainment of intercalated and exfoliated layered material containing nanocomposites, obtained by the insertion of polyethylene terephthalate (PET) oligomers, between the layers of a phyllosilicate, by means of the shearing action of mixing the phyllosilicate with the oligomer, in solid state. Wherein the phyllosilicate utilized does not have to have been submitted to any previous swelling process, as those utilized in a number of processes described in patents and articles of literature. This invention also refers to the formation of a nanocomposite from a melted polymeric matrix, in which a concentrate of the oligomer/clay composite, prepared through shearing, is diluted, resulting in the production of a polymer/layered silicate nanocomposite prepared through the growth of grafted oligomer chains, through a process of solid post-condensation of the oligomer in the oligomer/clay composite. The present invention refers yet to the articles produced from the referred nanocomposites as the application thereof and the processes for the production and obtention of these nanocomposites.

Poly (ethylene terephthalate) (PET) is a low production cost and high performance polymer, which has been widely utilized, within other applications, in packaging of certain foodstuff, fruit juices and carbonated beverages. However, due to its limitations regarding its low ability to hinder the passage of gases like oxygen and carbon dioxide, PET flasks and packaging, are not appropriate for packaging products that require a long shelf life as, for example, wine and beer. The diffusion of oxygen from the environment to the inside of the bottles containing these products, promotes the oxidation of the products, changing its properties. In the case of carbonated beverages, the utilization of PET bottles is usual, however it reduces the stocking and storage time, if compared to the time achieved by glass packaging, due to the evasion of carbon dioxide. These limitations to the use of PET stimulate, therefore, several researches directed to the development of PET copolymers and nanocomposites presenting a lower perviousness to gases.

Nanocomposites are multi-phase materials containing two or more different components, mixed in nanometric a scale. In general, one component acts as a continuous matrix where particle (s) of the other phase (s) is (are) dispersed. The particles of the dispersed phase (s) may appear in the three dimensions, in only two or in only one in the nanometer scale. Depending of the nature of the constituting phases, the nanocomposites may be classified as inorganic- inorganic, organic-inorganic (hybrid) , and organic- organic. As a consequence of the dispersion in nanometric scale, the nanocomposites show singular mechanical and physical-chemical properties when compared to the conventional microcomposites, which has made them an object of intense research during the last years .

A recently developed class of hybrid nanocomposites, which has attracted much attention of several new materials research and development groups is the class of nanocomposite polymers formed from layered silicates, the Polymer Layered Silicate Nanocomposites (PLSNs) . These nanocomposites present several advantages compared to pure polymers or conventional composites thereof, such as: increase in the tensile and flexural moduluses, decrease in gas perviousness, increase of the resistance to solvents and heat, reduction in flammability. In the specific case of the reduction in gas perviousness, the high aspect ratio of the silicate monolayers and their imperviousness to gases could be the factor responsible for this phenomenon. The reason would be that, being these layers impervious to gases, when totally dispersed into the polymeric matrix, they act as a barrier to the gaseous diffusing molecules, forcing them to travel a longer path from one interface to the other of the polymeric layer, in a bottle or film. In general two types of PLSN hybrid structures are possible, the "intercalated" and the "delaminated" (or " exfoliated" ) , wherein the characteristics of the nanodispersion (intercalated or delaminated) can be controlled through the compatibility of the components, polymer and clay. The terms "intercalated" and "delaminated" are used to describe two general classes of nano-morphology which can be prepared from the polymers and phyllosilicates . The intercalated structures are multilayered structures, in which the polymer chains are inserted or extended within the spaces existing between the individual silicate layers. Delaminated (or exfoliated) structures result from the more complete separation of the silicate individual layers, which separate from each other sufficiently to interrupt interaction between adjacent layers. In this case, the interlayer spacing may be of the same order as the spinning radius of the polymer, and the silicate layers become well dispersed in the organic polymer. Associating these nano-morphologies with the miscibility of the components, it may be said that intercalated hybrids are systems exhibiting more limited miscibility than the delaminated hybrids, which present practically unlimited miscibility. The most commonly used layered silicates (or clays) in PLSN pertain to the structural family 2:1, and are known as phyllosilicates, such as, for example, montmorillonite, hectorite, saponite, mica, and others. Phyllosilicate space lattices consist of two- dimensional lamellas formed from two external sheets of tetrahedral silica, bonded to one octahedral internal sheet of alumina or magnesia, in such a way that the oxygen atoms of the octahedrons can also belong to the tetrahedrons. The thickness of one layer (lamella) is about 1 nm, whilst the side dimensions may be between 300 A and several microns, depending on the silicate, which results in a very high aspect ratio in the order of 1:1000 to 1:10000. These lamellas agglomerate forming piles, maintaining between them, a Van der Waals regular space, called inter-lamellar or gallery space. The isomorphic substitution phenomenon inside the layers, as for example Al³⁺ substituted by Mg²⁺, generates an excess of negative charges in one lamella. These charges are neutralized by metallic cations located in the inter- lamellar space, the called interchangeable cations. The forces that keep the lamellas piled up are relatively low and therefore it is possible to insert of other species into the inter-lamellar gallery, being by means of ionic interchange, replacing the interchangeable cations, or by covalent linking, or other electrostatic interactions.

The two main ways to obtain PLSN are : the intercalative polymerization in si tu and the melt intercalation. In the first case, the intercalative polymerization, the phyllosilicate is wetted with the liquid monomer (or in solution) in a way that the polymer formation occurs lately between the lamellas. The second method, the melt intercalation, involves the addition of the clay to the melted polymeric matrix, and the application of a shearing force to the mixture; if there is compatibility between the components, the polymer spreads in the inter-lamellar space, expanding the clay.

The obtention of a PLSN passes in general by the step of modification of one or both components thereof, the organic and the inorganic, in a such a way that they become compatible, since clay presents a hidrophobic character and the polymer in general is of hydrophobic nature . Various methods for modifying lamellar silicates with organic cations are known. In general a derivation of the silicate with a surfactant of the alkyl-ammonium type is carried out, via ionic interchange. This substitution increases the inter-lamellar space, reducing thereby the attractive forces, and also making the clay more hydrophobic and thus more liable to be dispersed into the polymer.

Several patents refer to the intercalation of alkyl- ammonium in clays, such as for example: US 4 810 734, US 6 156 835 and EP 1055706, among others. One disadvantage of quaternary ammonium salt-modified clays is that these clays, in general, are stable up to a maximum of 250 °C although the great majority already present a certain degree of decomposition as from 200 °C. Therefore they are not adequate for the polymers having processing temperatures above this value, as is the case of PET that is processed above 260°C.

In an attempt to overcome the inconvenience of the low thermal stability of clays intercalated with alkyl- ammoniums, organo-phosphonium cations have also been utilized intercalated with clay. As disclosed in patent WO 98/10012, where the author indicates that intercalated clays are stable up to 350 °C. Nevertheless one disadvantage of these clays is the potential toxicity of the phosphorus compounds, in case it is intended to use the nanocomposite for food or beverage packaging.

A recent patent (WO 00/34393) refers to the obtention of PLSN from the functionalization of polymers or oligomers, in order to make them compatible with the non-modified phyllosilicate. This patent describes the functionalization with amines (dimethylethanolamine and dimethylaminopropylamine) of several polymers, as for example; PETG 6763 (polyethylene-co-1, 4- cyclohexanedimethylene) , AQ55 (a water dispersible polymer) , and polystyrene, and of several oligomers, among which worthy to mention oligo-caprolactone and oligo-ethylene adipate. Although this methodology allows for polymer processing at higher temperatures, it is more difficult and expensive than the modification of clay, because it requires reactions under controlled atmosphere and temperatures above 200°C. Another patent (WO 00/34377) describes the obtention of PLSN of PET from the dispersion, via melt intercalation, of organo-functionalized lamellar silicates in an oligomer compatible with the polymeric matrix, and a subsequent incorporation of this dispersion in the melted polymeric matrix. According to the authors, it is also possible to obtain PLSN through mixture of all the components (modified clay, oligomer compatible with the polymeric matrix and the polymeric matrix) under polymer melting conditions . The patent also describes the obtention of PSLN from the growth of the oligomer chain in the clay/oligomer dispersion. Although the authors confirm that both treated and non treated silicates ca be used, in all the presented examples (16 examples for PET and 7 examples for polyamides) only organo-clays are used. There is also another patent referring to the intercalation of oligomers in clays (WO 01/40369) , with a subsequent formation of nanocomposites with a polymeric matrix. Although the authors generalize the process for oligomers of several polymers, the examples refer only to polyamide oligomers, specifically to poly (m-xylylene adipamide) , produced by Mitsubishi Chemical Co., known under code MXD6- 6007. The nanocomposite obtained from this process, through dispersion in the MXD6-6007 matrix could be used as an internal layer in the composition of multi- layered bottles, with low perviousness to gases. This patent mentions that both modified and non-modified clays or mixtures thereof may be utilized, but in the examples presented, only the modified clays are utilized.

Patent EP 0 909 787 Al refers to the production of nanocomposites through the combination of a host material, such as an organic solvent or a polymeric matrix, with an intercalate, formed from phyllosilicate and one intercalatant selected from one of the following groups: 1) an N-alkenyl monomer and an allyl monomer; 2) an oligomer or a polymer formed from the co-polymerization of the said monomers; and 3) mixtures thereof. According to the authors, the "intercalate" presents an expansion of the silicate lamellas in the range of 3 to 4 nm, and can be easily exfoliated, when mixed to an organic solvent or a molten polymer. In the first case, a material results that can be used as a drug "carrier", in the second case a nanocomposite of the PLSN type is formed. Although the phyllosilicate does not require any modification, the intercalation is carried out with the aid of a "carrier", for example, water and/or an organic solvent for the intercalatant . This patent does not refer specifically to the production of PET nanocomposites .

In short, what has been published and patented up to present moment, regardin the intercalation of oligomeric species in clays, compatible with a determined polymeric matrix, always involves chemical modification, either of the clay or of the oligomer, or the presence of any other agent, solvents for example, that assist the intercalation process. The chemical modifications and the use of solvents contribute to increase process costs, and in certain cases they limit the processing temperature of the hybrids due to the low thermal stability of the modifying agents. In view of the above, it is desired to develop a process which eliminates any additional modification step, either of the silicate, or of the compatible oligomer, or the addition of any solvent to assist in the oligomer intercalation/exfoliation in silicate process. Besides turning the process economically more viable, such a development would not present the inconvenience related to the thermal instability of the intercalation based on the quaternary ammonium salt, the toxicity of the phosphonium salts, or the need to remove solvents after the intercalation. The present invention refers to a process to obtain and form an intercalated and/or exfoliated material (C) , obtained when a lamellar silicate (A) , non- modified through ionic interchange or intercalation, is placed in contact, dry and under shearing action, with an intercalating oligomer (B) , whereby to obtain a nanocomposite (C) when the separation of the lamellas of (A) occurs, remaining dispersed in oligomer (B) . This process can be also successfully carried out using previously modified lamellar silicates through ionic interchange or intercalation. In this process the inter-lamellar space of (A) is expanded by at least 3 angstroms, when measured by X- ray difractometry, which is desirable for the subsequent obtention of the nanocomposite material (C) and PLSN (E) . In a preferred embodiment, the intercalated and/or exfoliated nanocomposite material (C) is formed from about 50% to 99.5% of an oligomer (B) and 50% to 0.5% of lamellar silicate (A), exfoliated or intercalated by (B) . This invention also refers to a process to prepare and obtain a nanocomposite consisting of lamellar particles of silicate dispersed in a molten processable polymer matrix (D) , from the dispersion under shearing of the previously obtained intercalated and/or exfoliated composite material (C) , in a molten polymeric matrix of PET or of PET copolymers (D) . Oligomer (B) used in this invention, also defined as a prepolymer, is chemically compatible with polymeric matrix (D) , and preferably, but not exclusively, formed from the same monomeric units as (D) , and further having between 2 to 30 of these repeating units. The amount of lamellar material included in the nanocomposite can widely vary, but in general it will comprise at least 0,001% by weight of composite, preferably between 0,5% and about 20% by weight of composite, more preferably between 0,5% and 10% by weight of composite. This amount will be determined by the use and/or application that is desired for the composite. This invention also refers to the obtention of a nanocomposite material comprising a polyester matrix containing evenly dispersed lamellar particles, which were previously intercalated or exfoliated with another high molecular weight material (oligomer) , compatible with the polyester matrix. The preferred polyester used is polyethylene terephthalate, or copolymers thereof .

Also encompassed by this invention is a process comprising the production steps of a material characterized as intercalated and/or exfoliated (C) , consisting of an oligomer (pre-polymer) (B) , and a phyllosilicate (A) , followed by the enlargement of the polymeric chains of (C) , in a fashion to obtain a nanocomposite of the PLSN type (E) . The molecular weight of the polymer in E may be increased by any known process in the state of the art, or by the combination of these processes, as for example: the extension of the chain, the reactive extrusion, the cure under vacuum, etc. The resulting nanocomposites of this invention present a higher capacity of barrier to gases, when manufactured in the form of films, bottles or any other type of packaging, if compared to the similar structures obtained from the non modified polymer. The oligomer or pre-polymer (B) utilized in this process may be in the crystalline or amorphous form, but preferably in the form of amorphous oligomer. Any oligomeric species that promote intercalation or exfoliation of the phyllosilicate (A) , by shearing, may be utilized in this process, since it is compatible with the PET polymeric matrix or PET copolymers. Preferably the oligomer utilized in this process will be a PET pre-polymer or PET co-polymers. The intercalating oligomer (B) , as above determined, has enough affinity to the lamellar silicate (A) , in a fashion to promote an enlargement of the inter- lamellar space that results in the intercalation in

(A) or in the exfoliation of (A) . The evidence of intercalation in the lamellar silicate or exfoliation of the lamellar silicate (both cases resulting in the formation of nanocomposites) , is a deviation to lower angles, or the absence of a predominant basal spacing in the X-ray difactogram of the sample of the obtained composite. It is believed that the low molecular weight of the oligomer, when compared to the molecular weight of the polymeric matrix, is a factor that favors its diffusion/insertion process into the lamellar material. The masses relation between (A) and

(B) may vary between 0,01 and 1, preferably between 0,03 and 0,25 e more preferably between 0,15 and 0,25.

The present process preferentially utilizes non- modified clays, preferably lamellar silicates (phyllosilicates) of the 2:1 type, wetting liable. These clays are: smectites, particularly montmorillonite, hectorite, mica, vermiculite, saponite, preferably montmorillonite, and more preferably sodic montmorillonite. Previous to the incorporation into the oligomer (B) , the size of the clay particles must be reduced by the known methods, including but not limited to grinding, dusting, the crushing in hammer mills, the milling in ball mills, and/or combination thereof.

Preferably the silicate is found dispersed in the oligomer or in the polymer in the form of individual lamellas, small tactoids, and small agglomerates of tactoids . Nonetheless the nanocomposites with high concentration of individual lamellas are preferable, being that the majority of the present tactoids and tactoids agglomerates shall have, in its minor dimension, a thickness less than 20 nm. Any melting processable, crystalline, semi-crystalline or amorphous polymeric matrix (D) , that is compatible with the intercalating oligomer (B) utilized, jointly with the silicate (A) , in the exfoliate and/or intercalate (C) formation, may be utilized in this process. Illustrative examples of melting processable resins are: polyesters, polyamides, polyuretanes, epoxy resins, polyolefins, polystyrenes, polyacrilates, and similar others or its combinations and blends. As preferred polymeric matrices to utilize in this process are the polyesters, and the preferred polyester is the polyethylene terephthalate (PET) or co-polymers thereof. Any known method may be utilized for applying the necessary shearing for the formation of the intercalate and/or exfoliate (C) , from the oligomer (B) and the silicate (A) , or for the formation of the nanocomposite, obtained through the dilution of (C) in a PET melted polymeric matrix or PET co-polymers (D) . This shearing action may be supplied by any appropriate mechanical equipment, as for an example the internal mixers, the extruders, the disc mills, the mixers , the Banbury^® or Brabender^® type mixers . In the case of the attainment of the oligomer-clay composite (C) , one intercalation and/or exfoliation preferred method, is to intimately mix, for example by extrusion, the intercalating oligomer (B) with the silicate (A) , at a temperature close to the Tg of the oligomer. One advantage of the intercalate and/or exfoliate (C) formation process, obtained by the present process, is that no reagent and/or additional solvent is necessary, avoiding so the toxicity risks, besides the extra expenditure in the later processing steps, as for example drying for the solvent removal. Another further advantage of the present invention, is that the intercalation and/or exfoliation process of the silicate (A) by the intercalating oligomer (B) occurs at temperatures much lower than the melting temperature of the oligomer.

The assessment of the separation grade of the lamellas of the silicate (A) after the insertion of the intercalating oligomer (B) , will be done based on the peak intensity and on the basal spacing value, or in the absence of a predominant basal spacing, attained from the X-ray difactogram of the analyzed sample. The same will be done to assess the intercalation and/or exfoliation grade of the silicate in the nanocomposites obtained by any of the described processes, being it from the dilution under shearing of the intercalate and/or exfoliate (C) (oligomer/silicate) in the melted polymer, being it by the enlargement of the polymeric chain of the intercalate and/or exfoliate (C) (oligomer/silicate) . The X-ray diffraction is the standard technique that has been applied for this analysis. Although this technique alone, does not allow knowing in univocal form if the lamellar particles are individually dispersed into the oligomer or polymer, it allows a good estimate of the level and of the type of dispersion achieved. This technique must be complemented by images obtained by transmission electron microscopy, that is a more adequate tool for a more precise assessment, because it allows for a visualization of the lamellas, dispersed in the obtained material.

The following specific examples are presented to illustrate in more particular form the present process and the materials obtained by thereof, but the same are not exclusive. EXAMPLE 1

Preparation of an intercalate formed by oligoPET and sodic-montmorillonite

200 grams (about 0,2 ol) of MON05 oligoPET, with an average molecular weight of about 1000, produced by

Rhodia-Ster, and 50 g (47,5 eq of interchangeable sodium) of refined sodic montmorillonite (Cloisite-

Na) , produced by Southern Clay Products, were extruded at 60°C and 100 rp . The resulting concentrate presented a basal spacing of

2,07 nm, obtained from the analysis of high angle X- ray diffraction.

EXAMPLE 2

The procedure of Example 1 was repeated, substituting the MON05 by other oligoPET produced by Rhodia-Ster, nominated as PET 900. It occurred a sharp decreasing on the diffraction peak corresponding to the spacing of 1,0 nm, indicating that clay exfoliation occurred.

EXAMPLE 3 The concentrated prepared on Example 1, was dry mixed with PET S80 (having average molecular weight of 28000 and intrinsic viscosity of about 0,8 dl/g) , it was dried during 6 hours at 160 °C, in a fashion to present a final composition containing 3% silicate, and then extruded in twin-screw extruder.

In this fashion it is attained materials, nanocomposites and PLSN, for the preparation of artifacts, with low perviousness to gases, presented in the form of films, sheets, fibers, tubes, pre- forms, extruded or molded; adequate for the manufacturing of bottles and packaging in general, preferably for food, cosmetics and/or else pharmaceutical products. Being they obtained by an economically viable, innovator and low cost process, compared to the processes known up to now.

Claims

1. Process to obtain an intercalated or exfoliated polyester with clay hybrid nanocomposite material (C) , characterized in that it is a process without the utilization of reagents and/or additional solvents, wherein the intercalated and/or exfoliated nanocomposite (C) , is obtained through the shearing of mixtures of an oligomer (B) and a lamellar silicate

(A) , exfoliated or intercalated by (B) , dry, where the shearing phenomenon occurs under the mechanical action of any known device for this end, as extruders, disc mills, roll or similar mills, in a fashion that the components are turned compatible under the mechanical action at temperatures a little above the Tg of the oligomer.

2. Process, according to claim 1, characterized in that the intercalated and/or exfoliated nanocomposite material (C) is formed from about 50% to 99.5% of an oligomer (B) and 50% to 0.5% of lamellar silicate (A), exfoliated or intercalated by (B) .

3. Process according to claim 1 and 2, characterized in that the oligomer (B) comprises an oligo-ester; that the oligomer (B) comprises an amorphous, crystalline or semi-crystalline species; and/or that the oligomer (B) comprises one oligo-ethylene terephthalate, or one co-oligomer thereof, or a mixture thereof .

4. Process according to claims 1 and 2, characterized in that the lamellar material (A) comprises chemically non modified clays, of the montmorillonite, hectorite, mica, vermiculite, bentonite, saponite type, or mixtures thereof; and/or in that the lamellar silicate (A) comprises a sodium montmorillonite .

5. Process for the obtention of a PLSN nanocomposite (E) , derived from intercalated and/or exfoliated nanocomposite (C) , characterized in that the PLSN nanocomposite material (E) derived from (C) is obtained diluting (C) in a melt processable polymeric matrix (D) ; submitting (C) to determined conditions that allow for the enlargement of the oligomeric chain, for forming a polymeric matrix containing dispersed lamellar particles; being carried on a melt polymerization reactor in the presence of a diacid and a diol; wherein (C) is carried with the melted polymeric matrix (D) , in a batch or continuous regime, respectively in equipment of the internal mixers or extruders; and where the enlarging step is carried on batch or continuous regime, in a solid post- condensation process.

6. Process according to claim 5, characterized in that the PLSN nanocomposite material (E) derived from (C) is comprised of polymers with lamellar silicates where the concentration of the lamellar material in said composition is at least 0.5% in weight up to 20% in weight, based on the weight of the polymeric matrix (D) ; where at least 50% of the lamellar material is dispersed in the polymeric matrix in the form of individual lamellas and small tactoids.

7. Process according to claims 5 and 6, characterized in that the melting processable polymeric matrix (D) comprises a polyester; and/or that the melting processable polymeric matrix (D) comprises the poly (ethylene terephthalate) or a co-polymer thereof, or a mixture thereof.

8. Process according to claims 5 and 6, characterized in that the oligomer (B) and the melting processable polymeric matrix (D) , present the same monomeric units; and/or in that the oligomer (B) and the melting processable polymeric matrix (D) are miscible and/or present similar monomeric units.

9. Nanocomposite materials (C) and (E) obtainable according to any of the preceding claims, characterized in that they are used for the preparation of artifacts presented in the form of films, sheets, fibers, tubes, pre-forms, extruded or molded; and/or in the form of bottles and packaging in general .