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
2002-11-01
2004-11-02
Wyrozebski, Katarzyna (Department: 1714)
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...
C524S447000, C501S147000
Reexamination Certificate
active
06812272
ABSTRACT:
The invention relates to a nanocomposite material, to a process for the preparation thereof and to a modified clay.
In the past decades, it has, already often been proposed to improve the properties of polymeric materials by including in these materials a specific amount of a clay. The presence of a clay in a polymeric material particularly contributes to properties such as the mechanical strength and the heat resistance of the polymeric material.
A great difficulty when including a clay in a polymeric matrix resides in the mutually rather different nature of the materials. The polymeric material of the matrix is a usually non-polar organic material, whereas the clay is a much more polar inorganic material. Because of this difference the materials are poorly intermixable; they are intrinsically not mixable.
To circumvent this difficulty, it has been proposed to carry out the synthesis of the polymer that forms the matrix, a polymerization reaction, in the presence of the inorganic material. The idea was that the clay is perhaps more easily intermixable with a monomeric material than with a polymeric material. This method, however, proved to result in an inhomogeneous product which does not have the desired properties. The clay has a layered structure which cannot be broken easily, so that a homogeneous mixing is hard to obtain.
U.S. Pat. Nos. 4,889,885 and 4,810,734 propose to first swell the clay before adding monomeric material and carrying out a polymerization. To this end, the clay is modified with a swelling agent which increases the mutual distance between the layers of the clay structure to such an extent that monomers fit therebetween. After polymerization of the monomers polymeric material is then automatically located between the clay layers.
The swelling agent described in the above patents is so-called onium ions. Within this context an onium ion is a surfactant 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 an onium ion is exchanged for cations between the crystalline layers of the clay. The tails must have a functional group capable of entering into a bonding interaction with the monomeric material, so that the polymers are formed between the layers of the clay.
Nevertheless, swelling with an onium ion also often proved ineffective in obtaining a proper mixing of the clay with a polymeric matrix. European patent application 0 747 322 describes that even when an onium ion with two non-polar tails is used, additional measures are necessary to homogeneously disperse a clay in a polymeric matrix which particularly consists of rubbery materials. Accordingly, the above European patent application proposes to introduce, in addition to an onium ion with two non-polar tails, one or more host molecules, also surfactant-like molecules, between the clay layers. A drawback of this method is that it is very complicated and does not in all polymeric materials enable a homogeneous dispersion of clay in the polymeric matrix.
Another approach is described in U.S. Pat. No. 5,578,672. This approach comprises two steps. In the first step, an aqueous layered clay is swollen with monomers, oligomers or polymers that are compatible with water. This leads to a partly hydrophilic material. This first step is often referred to as the so-called intercalation. The distance between the clay layers is thereby increased. The second step comprises the mixing of the intercalated clay with a second polymer. This step is referred to as the so-called exfoliation and must lead to loose individual clay plates. The resulting product is finally included in the desired polymeric matrix through extrusion. In this procedure it is essential that the clay contains a specific minimum content (usually at least 5%) of water. The method described in this U.S. patent is rather laborious and complicated. Moreover, this method is not applicable to many polymeric matrices, so that a clay cannot be included in every polymeric material.
The international patent application WO-A-93/04118 describes a composite material on the basis of a polymeric matrix and a clay, which clay is modified with a specific compound. This specific compound consists of a silane or an onium group and a group compatible with the polymeric matrix. It has turned out that with this specific compound a substantial dispersion of a clay in a polymeric matrix is only obtainable with nylon as polymeric matrix.
It is an object of the invention to provide a nanocomposite material in which a clay is very homogeneously dispersed in a polymeric matrix, which nanocomposite material is easy to prepare. The invention therefore relates to a nanocomposite material on the basis of a clay having a layered structure and a cation exchange capacity of from 30 to 250 milliequivalents per 100 gram, a polymeric matrix and a block copolymer or graft copolymer, which block copolymer or graft copolymer comprises one or more first structural units (A), which are compatible with the clay, and one or more second structural units (B), which are compatible with the polymeric matrix.
It has been found that by using a block copolymer or graft copolymer of the above-mentioned type a clay can be very homogeneously mixed with a polymeric matrix. Moreover, by suitably selecting the structural units of the block copolymer or the graft copolymer a clay can be included in a polymeric matrix of any desired nature. A nanocomposite material according to the invention has very favorable properties, such as a great heat resistance, a great mechanical strength, in particular a great tensile strength and a good impact resistance, a low electric conductivity, a high glass transition temperature and a very low permeability to gases, such as oxygen or water vapor, and liquids, such as water or solvents.
A nanocomposite material according to the invention is, as stated before, based on a clay having a layered structure. The clay may be of a natural or synthetic nature. Preferably, the clay has a large contact surface.
Very suitable are clay types based on layered silicates, such as layered phyllosilicate composed of magnesium and/or aluminum silicate layers which are each about 7-12 Å in thickness. Especially preferred are smectite-like clay minerals, such as montmorillonite, saponite, hectorite, fluorohectorite, beidellite, nontronite, vermiculite, halloysite and stevensite. These materials impart very favorable mechanical properties and a great heat resistance to a nanocomposite material.
A suitable clay type has a cation exchange capacity of from 30 to 250 milliequivalents per 100 gram. When this capacity exceeds the above upper limit, it proves difficult to finely disperse the clay on a molecular level because of the strong mutual interaction of the clay layers. When the cation exchange capacity is lower than the above lower limit, it turns out that the clay is hard to modify, owing to the fact that the interaction with the block copolymer or graft copolymer is small. There is preferably used a clay having a cation exchange capacity of from 50 to 200 milliequivalents per 100 gram.
The polymeric matrix present in a nanocomposite material according to the invention can be formed by any polymeric material. Both homopolymers and copolymers may serve as polymeric matrix. It is one of the advantages of the invention that by selecting the block copolymer or the graft copolymer any polymeric matrix can be modified with a clay of the above-described nature. Accordingly, by providing the right constituents, e.g. in the form of a kit, the skilled worker is afforded an opportunity to prepare for any desired use a combination of a specific clay and a specific polymeric material, and thus a desired nanocomposite material.
Polymeric materials suitable as polymeric matrix in a nanocomposite material according to the invention are both polyadducts and polycondensates. Examples are polyolefins, such as polyethylene or polypropylene, vinyl polymers, such as polystyrene or polymethyl methacrylate, polyesters,
Muserlian, Lucas & Mercanti, LLP
Nederlandse Organisatie voor toegepast-natuurwetenschappelijk On
Wyrozebski Katarzyna
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