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
2001-09-17
2004-07-06
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...
C524S446000, C524S186000, C524S447000, C524S451000
Reexamination Certificate
active
06759463
ABSTRACT:
The present invention relates generally to polymer clay aqueous nanocomposite dispersions and methods for making and using the same. More particularly, the present invention relates to methods of making polymer clay nanocomposites using lightly hydrophobically modified clays in aqueous systems. This invention also relates to the use of these nanocomposite compositions as, for example, thermoplastic resins, capstock, coatings, sealants, caulks, adhesives, and as plastics additives.
One way of improving polymer properties is by adding a clay material to polymers to form composite materials. However, incorporating clays into polymers may not provide a desirable improvement in the physical properties, particularly mechanical properties, of the polymer. This may be due, for example, to the lack of affinity between the clay and the polymer at the interface, or the boundary, between the clay and polymer within the material. In this connection, affinity between the clay and the polymer may improve the physical properties of the resulting nanocomposite by allowing the clay material to uniformly disperse throughout the polymer. The relatively large surface area of the clay, if uniformly dispersed, may provide more interfaces between the clay and polymer, and may subsequently improve the physical properties, by reducing the mobility of the polymer chains at these interfaces. By contrast, a lack of affinity between the clay and polymer may adversely affect the strength of the composition by having pockets of clay concentrated, rather than uniformly dispersed, throughout the polymer. Affinity between clays and the polymers is related to the fact that clays, by nature, are generally hydrophilic whereas polymers, such as the polymers used in the aforementioned applications, are generally hydrophobic.
Clay minerals are typically comprised of hydrated aluminum silicates that are fine-grained and have a platy habit. The crystalline structure of a typical clay mineral is, a multi-layered structure comprised of combinations of layers of SiO
4
tetrahedra that are joined to layers of AlO(OH)
2
octahedra. The term “gallery”, as used herein, describes the interlayer spaces of the layered clay minerals. The terms “d-spacing” or “basal spacing”, as used herein, define the sum of the single layer thickness and the thickness of the interlayer or gallery, which is the repeat unit of the multi-layer mineral. Depending upon the clay mineral, the gallery may contain water and/or other constituents such as potassium, sodium, or calcium cations. Clay minerals vary based upon the combination of their constituent layers and cations. Isomorphic substitution of the cations of clay mineral, such as Al
3+
or Fe
3+
substituting for the Si
4+
ions in the tetrahedral network, or Al
3+
, Mg
2+
or Fe
2+
substituting for other cations in the octahedral network, typically occurs and may impart a net negative charge on the clay structure. Naturally occurring elements within the gallery of the clay, such as water molecules or sodium or potassium cations, are attracted to the surface of the clay layers due to this net negative charge.
Nanocomposites are compositions in which at least one of its constituents has one or more dimensions, such as length, width or thickness, in the nanometer size range. The term “nanocomposite”, as used herein, denotes the state of matter wherein polymer molecules exist among at least partially exfoliated clay layers. Recently, nanocomposites that contain layered clay materials such as montmorillonite having silicate layers of a thickness of 1 nanometer dispersed within a polymeric matrix, have been developed as a means to improve the physical properties of polymers. In order to effectively improve the physical or mechanical properties, the clay is typically uniformly dispersed throughout the polymer in order to promote more interfaces between the clay and polymer and enhance the affinity of the clay to the polymer at these interfaces. Further, if the clay is uniformly dispersed throughout the polymer, less clay material may be added to the nanocomposite composition while maintaining the physical properties of the nanocomposite.
Polymer-clay nanocomposites can be characterized as being one of several general types: intercalated nanocomposite, exfoliated nanocomposite, or combinations thereof. The term “intercalated nanocomposite”, as used herein, describes a nanocomposite that consists of a regular insertion of the polymer in between the clay layers. The term “exfoliated nanocomposite”, as used herein, describes a nanocomposite wherein the 1 nm-thick layers of clay are dispersed in the matrix forming a composite structure on the microscale. The latter type of composite, or exfoliated nanocomposite, maximizes the polymer-clay interactions thereby making the entire surface of the clay layers available for the polymer. This modification may lead to the most dramatic changes in mechanical and physical properties of the resultant polymer. By contrast, the term “conventional composite”, as used herein, describes a composite where the clay acts as a conventional filler and is not dispersed on a nano-scale. These composites generally do not enjoy the improvement in mechanical and physical properties seen with exfoliated nanocomposites. In certain embodiments of the present invention, some portion of the clay in the polymer clay nanocomposites may exist as structures larger than exfoliated or intercalated composites.
In order to promote more affinity between the clay and the polymer at the interface and provide a uniform dispersion of the clay within the polymer, the interlayer surface chemistry of the clay may be modified to render the silicate layers less hydrophilic. Previous methods of altering the interlayer surface chemistry of the clay include the use of modifying agents, such as surfactants or silanes, to prepare a clay dispersion prior to its incorporation into a polymer. For example, surfactants may typically comprise a molecule having a hydrophilic functions (which has an affinity to polar media such as water or clay) and an organophilic function (which has an affinity to organic molecules such as oil or polymer). The use of surfactants allows one to disperse clay within a polymer. As used herein, the term “hydrophobically modified clays” denotes clays that may have its surface chemistry modified through the use of an agent such as a surfactant, silane, or other modifier.
Typical agents used to render a clay less hydrophilic may include, but are not limited to, amino acids, alkylammonium ions, silanes, aminomethylstyrene, or living free radical polymerization initiator (“LFRP”). Further non-limiting examples of other suitable agents for the synthesis of nanocomposites are provided in the reference, M. Ogawa et al., “Preparation of inorganic-organic nanocomposites through intercalation of organoammonium ions into layered silicates”, Bull. Chem. Soc. Jpn., 70, 2593-2619 (1997).
Amino acid surfactants are molecules that may consist of a basic amino group (—NH
2
) and an acidic carboxyl group (—COOH). When introduced into an acidic medium, a proton may be transferred from the —COOH group to the intramolecular —NH
2
group. It is believed that a cation exchange occurs between the —NH
3
+
functional group that is formed and the naturally occurring cations (i.e., Na
+
, K
+
, etc.) present between the clay layers. This results in an intercalated state wherein the —NH
3
+
functional groups are “sandwiched” between the individual layers replacing the naturally occurring cation. The term “intercalate”, as used herein, refers to incorporating foreign molecules, atoms, or ions in between the layers of the clay material. As a result of this intercalated state, the clay becomes organophilic. Amino acid surfactants are commonly used in the preparation of polyamide 6-clay hybrids because their acid functional group may polymerize with &egr;-caprolactam that is intercalated between the layers. As a result, the intragallery polymerization delaminates the
Lorah Dennis Paul
Slone Robert Victor
Rohm and Haas Company
Wyrozebski Katarzyna
LandOfFree
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