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
2002-06-13
2004-12-28
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
Reexamination Certificate
active
06835766
ABSTRACT:
The present invention relates to nanocomposite materials (hereinafter nanocomposites), to methods of producing nanocomposites and in particular to methods of producing nanocomposites in powder form, or in a form which can easily be processed into a powder form. The invention further relates to methods of producing nanocomposites which, when the nanocomposites are added to a main polymer in a subsequent processing step, providing a product having improved properties as compared to the main polymer alone or the main polymer when simply filled with a clay or other conventional filler. The production of nanocomposites in powder form renders the method of the invention especially suitable for producing master batches of nanocomposite material for use in such subsequent processing steps.
Nanocomposites per se have been known since 1960 or before, but some of the earliest examples to receive widespread attention were described by workers at Toyota in, for example,
Mater. Res. Soc Pnc
171 (1990) 45. These nanocomposites comprised layered silicates in nylon 6, in which the polymer penetrated between expanded layers of the clay. The method employed by the Toyota workers involved in situ polymerisation by inserting the nylon 6 precursor, &egr;-caprolactam between the layers of the clay, and then further expanding and dispersing the clay layers by polymerisation of the &egr;-caprolactam.
A review of nanocomposite materials can be found in
Materials Science and Engineering,
28 (2000) 1-63, the contents of which are incorporated herein by reference. This review article describes the basic types of nanocomposite, that is, intercalated nanocomposites where the polymer chains are sandwiched between layers of the clay, and exfoliated (or delaminated) nanocomposites where the separated, individual, layers of the clay are more or less uniformly dispersed in the polymer matrix. The principal synthetic routes for producing nanocomposites are also described, namely, exfoliation adsorption, in situ intercalative polymerisation, melt intercalation and template synthesis.
In the exfoliation adsorption technique, the layered silicate clay is exfoliated into single layers using a suitable solvent in which the polymer (or a prepolymer) is soluble. The polymer adsorbs onto the delaminated sheet of the clay when the solvent is evaporated and the sheets re-assemble sandwiching the polymer.
In situ intercalative polymerisation requires the layered silicate clay initially to be swollen in a liquid monomer or monomer solution so that polymerisation, when initiated, occurs between the clay layers.
Melt intercalation involves mixing of the layered silicate clay with the polymer in the molten state. The polymer may then “crawl” into the interlayer space of the clay and form either an intercalated or exfoliated nanocomposite.
In template synthesis the layered silicate clays are formed in situ in an aqueous solution containing the polymer and silicate building blocks for the clay.
Thus, although various techniques are known for producing nanocomposites, each is relatively complex to a degree which limits its commercial utility, despite the markedly advantageous properties obtainable by use of the nanocomposites in subsequent polymer processing steps. It is also noted that the modified (organo-) clays which are mainly used in the formation of nanocomposites usually incorporate ammonium salts (acting as surfactants) as the modifying agent. These ammonium salt surfactant components tend to be thermally unstable and may degrade at temperatures as low as 170° C. Therefore any nanocomposite preparation methods using such modified clays which employ higher processing temperatures (such as melt intercalation) are likely to cause significant degradation of the modified clay. However, once intercalation of the polymer in the clay has occurred on formation of the nanocomposite, much better thermal stability is achieved. Therefore, it is advantageous and desirable to employ a method of nanocomposite formation which avoids elevated temperatures, and more preferably to employ a method which can be carried out at or near ambient (room) temperature, such as less than 25° C.
Accordingly, the present invention seeks to provide improved and relatively simple methods of producing polymer-clay nanocomposite materials and in particular to such methods which can be carried out at or near ambient temperature and, preferably, which provide nanocomposite materials in powder form or in a form which may be easily processed into powder form. In particular, the present invention employs compression of polymer-clay mixtures in order to achieve desired nanocomposite materials. The method of the invention can reduce the number of subsequently required processing steps and/or subsequently required processing complexity when preparing a masterbatch by producing the nanocomposite directly in powder form or in a generally solid form such as a cake which requires only simple grinding to form a powder.
The improved properties of polymer materials incorporating the nanocomposites produced by the method of the invention (as compared with the polymers alone or polymers simply filled with clay or other conventional fillers) can be one or more of mechanical, thermal and processing properties of the material and in particular, the improvements can be in one or more of stiffness (Young's modulus), toughness (stress at break) and elasticity (flexural modulus/strain at break). Other possible improvements include wear resistance, heat distortion temperature, flame retardancy, thermal stability, gas permeability and weight reduction.
Accordingly the present invention provides a method of producing polymer-clay nanocomposite materials including the steps of:
intimately mixing the polymer and the clay in powder form, and
compressing the mixture to form a nanocomposite material.
The present invention is based on the surprising finding that, in appropriate mixtures and under the appropriate conditions, penetration of the polymer between the layers of the clay can be achieved simply by compression of a mixture of polymer and clay powders. The compression can be successfully carried out at ambient temperatures (eg at about 25° and below) so that heating of the polymer to a temperature above its glass transition temperature (for melting point, as appropriate) is not necessary. Also, there is no requirement to dissolve or dispense the clay, polymer, prepolymer or monomer in any sort of solvent in order to achieve the desired nanocomposite materials. Thus, the process according to the present invention is inherently simpler than prior art techniques.
In the process of the invention, the polymer and the clay are initially ground by conventional means to provide polymer and clay powders of appropriate particle size and size distribution. Typically, the powders will have a particle size of 200 mesh or less, or, for the clays 10 &mgr;m or less (eg 2 &mgr;m to 5 &mgr;m) and for the polymers, 20 &mgr;m or less. In broad terms, the clay and polymer are ground until free flowing powders are obtained. After grinding, the clay and polymer powders are mixed until an intimate clay-polymer mixture is obtained. Conventional mixing means such as a conventional blender may be used.
After mixing, a quantity of the polymer-powder mixture is placed in a suitable press and compressed until the desired nanocomposite material is obtained. The nature of the press is not crucial to the invention, and the size and type of press will be selected by the person skilled in the art in accordance with, for example, the quantity of nanocomposite which is to be produced and the pressure which is required. It is, however, important that the press provides an even pressure distribution over the entire sample. An applied pressure of as little as 5 Mpa may be sufficient to form nanocomposites from some clay-polymer mixtures. Typically, however, the polymer-clay powder mixture will be subjected to a pressure of 100 MPa or more, for example 200 MPa or more or preferably about 350 MPa. There is no theor
Gao Fengge
Hull Barry
Myers Bigel Sibley & Sajovec P.A.
The Nottingham Trent University
Wyrozebski Katarzyna
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