Nanocomposite material

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...

Reexamination Certificate

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C524S449000, C524S450000, C524S451000, C524S534000, C524S789000, C524S791000, C524S856000, C523S209000, C523S216000, C523S521000

Reexamination Certificate

active

06372837

ABSTRACT:

The invention invention relates to a nanocomposite material, a method for the preparation of a nanocomposite material and to a shaped article of a nanocomposite material.
Over the past decades, it hag already been frequently proposed to improve the properties of polymeric materials by incorporating a certain amount of a clay in those materials. The presence of a clay in a polymeric material is beneficial particularly to properties such as the mechanical strength and the heat resistance of the polymeric material.
To thus obtain a nanocomposite material that has the desired properties, it is important that the clay be dispersed in the polymeric material sufficiently homogeneously. This is not easy because the clay and the polymeric material are of a highly different nature. Polymers constitute a normally non-polar, organic material, whereas the clay is a much more polar, inorganic material. Due to this difference, the materials exhibit poor miscibility with respect to each other; they are intrinsically non-miscible. In the literature, it has been proposed first to modify the clay in different ways before it is mixed with a polymeric material. It has also been proposed to modify the clay and then to mix it with a monomeric material, which is thereupon polymerized in the presence of the clay.
In U.S. Pat. Nos. 4,889,885 and 4,810,734, it is described how a cationic clay is first modified with a swelling agent, which increases the interlayer distance of the clay structure. Used as swelling agents are surfactants, with a head group formed by an ammonium, pyridinium, sulfonium or phosphonium group, and one or more non-polar tails. The cationic head group of the surfactant is exchanged with cations between the crystalline layers of the clay and the tails should be compatible with the polymeric material. Then the modified clay is mixed with monomeric material, which can enter into a bonding interaction with the tails-of the swelling agent. When, finally, the monomeric material is then polymerized, the polymers are formed between the layers of the clay and a nanocomposite material is obtained.
A disadvantage of these known nanocomposite materials is that the quality of the end product is very highly dependent on the quality of the clay used. Cationic clay is virtually always a natural product, which is not homogeneous in composition. This inhomogeneity of the clay leads to inhomogeneities in the composition of the nanocomposite material, which means that the desired properties are not always achieved in a sufficient quality. It is therefore desirable to make it possible to incorporate into polymeric material a kind of clay that has a better controllable quality and composition.
U.S. Pat. No. 5,658,653 describes a polymer composite comprising a polymeric matrix in which a filler is incorporated. The polymeric matrix can be a polyolefin, polystyrene, polyurethane, epoxy resin, polyimide, polyacetal, polyester, polyvinyl, polyether or polyacryl. The filler is a mixed metal hydroxide that satisfies a specific formula.
In order to enhance the compatibility of the polymeric material and the filler, the surface of the filler has been modified in that particular groups have been provided thereon. These groups can be, for instance, organic acids, salts of sulfonic acids or phosphonic acids. It is also possible that anions of the filler have been exchanged with groups that form hydrogen bridges with the polymeric matrix.
A disadvantage of the material described in the above U.S. patent specification is that the filler is not homogeneously dispersed in the polymeric matrix. This inhomogeneity is presumably due to the fact that only the surface of the filler is modified.
The object of the present invention is to provide a method for preparing a nanocomposite material comprising a polymeric matrix in which a clay is incorporated, which nanocomposite material is very homogeneous in composition. It is further contemplated for the clay to be of a kind that has a properly controllable quality and composition.
According to the invention, these objects are achieved by mixing a layered double hydroxide with monomeric material and polymerizing this in the presence of the layered double hydroxide. Layered double hydroxides are anionic clays, which, surprisingly, have presently been found to be modifiable so as to allow of homogeneous dispersion in a polymeric material.
Accordingly, the invention relates to a method for preparing a nanocomposite material based on a polymeric matrix and a layered double hydroxide, comprising the steps of
a) providing a layered double hydroxide which contains an amount of anions of at least 20%, based on the total number of anions of the layered double hydroxide, which anions are compatible and/or reactive with the polymeric matrix;
b) mixing the layered double hydroxide with a monomeric material for forming the polymeric matrix, in an amount such that the polymeric matrix is present in the nanocomposite material in an amount of at least 50% by weight, based on the nanocomposite material;
c) polymerizing the monomeric material for forming the polymeric matrix.
It will be clear that the invention further relates to a nanocomposite material obtainable by the above method.
It has been found that a nanocomposite material prepared according to the present method has highly favorable properties. Thus, the heat resistance, the mechanical strength and the impact resistance of a polymeric material in which a layered double hydroxide is incorporated in accordance with the invention are strongly improved compared with the same properties of the polymeric material in which no layered double hydroxide is incorporated. It has further been found that the electrical conductivity and the permeability to gases and liquids, such as oxygen, water vapor and hydrocarbons, have been reduced to a considerable extent. Since layered double hydroxides can be prepared synthetically, it is possible, according to the invention, to prepare a nanocomposite material of a constant, controllable quality. It has furthermore been found that the in situ polymerization to form the polymeric matrix results in a very homogeneous product.
For that matter, it is known from U.S. Pat. No. 4,558,102 that a particular kind of layered double hydroxide, a hydrotalcite, can be incorporated into a halogen-containing rubber composition as an acid-acceptor to improve the water resistance of the rubber composition. Optionally, the hydrotalcite aggregates used can be modified with at most 10% by weight of a surfactant. What is involved here, however, is only a modification of the surface of the aggregates, whereby the clay is not sufficiently modified to allow of homogeneous dispersion in the rubber composition.
Further, it is known to improve the properties of a hydrotalcite by incorporating a small amount of a polymeric material. Challier et al., in J. Mater. Chem., 1994, 4, 367-371, have proposed to incorporate in a hydrotalcite a monolayer or bilayer of a polymeric material between each two layers of hydrotalcite to render the hydrotalcite electrically conductive.
A nanocomposite material according to the invention consists for the most part of the material of the polymeric matrix, comprising at least 50% and preferably at least 70% by weight of such material. Both homopolymers and copolymers can serve as polymeric matrix. It is one of the advantages of the invention that through the choice of the anions of the layered double hydroxide, any polymeric matrix can be modified with a layered double hydroxide. Thus, by providing the appropriate ingredients, for instance in the form of a kit, those skilled in the art are enabled to prepare, for any desired application, a combination of a particular layered double hydroxide and a particular polymeric material, and thereby a desired nanocomposite material.
Polymeric materials suitable to serve as polymeric matrix in a nanocomposite material according to the invention are both poly-adducts and polycondensates. Preferably, the polymeric matrix has a degree of polymerization of at least

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