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
2001-11-13
2004-07-27
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, C501S148000
Reexamination Certificate
active
06767952
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to layered materials such as clay, which are intercalated by one or more block copolymer(s).
BACKGROUND OF THE INVENTION
Over the last decade or so, the utility of inorganic nanoparticles as additives to enhance polymer performance has been well established. Ever since the seminal work conducted at Toyota Central Research Laboratories, polymer-clay nanocomposites have generated a lot of interest across industry. The unique physical properties of these nanocomposites have been explored by such varied industrial sectors as the automotive industry, the packaging industry, and plastics manufactures. These properties include improved mechanical properties, such as elastic modulus and tensile strength, thermal properties such as coefficient of linear thermal expansion and heat distortion temperature, barrier properties, such as oxygen and water vapor transmission rate, flammability resistance, ablation performance, solvent uptake, etc. Some of the related prior art is illustrated in U.S. Pat. Nos. 4,739,007; 4,810,734; 4,894,411; 5,102,948; 5,164,440; 5,16,460 5,248,720; 5,854,326; and 6,034,163.
In general, the physical property enhancements for these nanocomposites are achieved with less than 20 vol. % addition, and usually less than 10 vol. % addition of the inorganic phase, which is typically clay or organically modified clay. Although these enhancements appear to be a general phenomenon related to the nanoscale dispersion of the inorganic phase, the degree of property enhancement is not universal for all polymers. It has been postulated that the property enhancement is very much dependent on the morphology and degree of dispersion of the inorganic phase in the polymeric matrix.
The clays in the polymer-clay nanocomposites are ideally thought to have three structures (1) clay tactoids wherein the clay particles are in face-to-face aggregation with no organics inserted within the clay lattice, (2) intercalated clay wherein the clay lattice has been expanded to a thermodynamically defined equilibrium spacing due to the insertion of individual polymer chains, yet maintaining a long range order in the lattice; and (3) exfoliated clay wherein singular clay platelets are randomly suspended in the polymer, resulting from extensive penetration of the polymer into the clay lattice and its subsequent delamination. The greatest property enhancements of the polymer-clay nanocomposites are expected with the latter two structures mentioned herein above.
There has been considerable effort towards developing materials and methods for intercalation and/or exfoliation of clays and other layered inorganic materials. In addition to intercalation and/or exfoliation, the clay phase should also be rendered compatible with the polymer matrix in which they are distributed. The challenge in achieving these objectives arises from the fact that unmodified clay surfaces are hydrophilic, whereas vast number of thermoplastic polymers of technological importance are hydrophobic in nature. Although intercalation of clay with organic molecules can be obtained by various means, compatibilizing these intercalated clays in a polymer matrix for uniform distribution still poses considerable difficulty. In the industry, the clay suppliers normally provide just the intercalated clays and the end-users arc challenged to select materials and processes for compatibilizing these clays in the thermoplastics of their choice. This selection process involves trial and error at a considerable development cost to the end-users. Since clay intercalation and compatibilization in the matrix polymer usually involve at least two distinct materials, processes and sites, the overall cost of the product comprising the polymer-clay nanocomposite suffers.
A vast majority of intercalated clays are produced by interacting anionic clays with cationic surfactants including onium species such as ammonium (primary, secondary, tertiary, and quaternary), phosphonium, or sulfonium derivatives of aliphatic, aromatic or arylaliphatic amines, phosphines and sulfides. These onium ions can cause intercalation in the clay through ion exchange with the metal cations present in the clay lattice for charge balance. However, these surfactant molecules may degrade during subsequent melt-processing, placing severe limitation on the processing temperature and the choice of the matrix polymer. Moreover, the surfactant intercalation is usually carried out in the presence of water, which needs to be removed by a subsequent drying step.
Intercalation of clay with a polymer, as opposed to a low molecular weight surfactant, is also known in the art. There are two major intercalation approaches that are generally used—intercalation of a suitable monomer followed by polymerization (known as in-situ polymerization, see A. Okada et Al.,
Polym Prep
., Vol. 28, 447, 1987) or monomer/polymer intercalation from solution. Polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and polyethylene oxide (PEO) have been used to intercalate the clay platelets with marginal success. As described by Levy et. al, in “Interlayer adsorption of polyvinylpyrrolidone on montmorillonite”,
Journal of Colloid and Interface Science
, Vol 50 (3), 442, 1975, attempts were made to sorb PVP between the monoionic montmorillonite clay platelets by successive washes with absolute ethanol, and then attempting to sorb the PVP by contacting it with 1% PVP/ethanol/water solutions, with varying amounts of water. Only the Na-montmorillonite expanded beyond 20 Å basal spacing, after contacting with PVP/ethanol/water solution. The work by Greenland, “Adsorption of polyvinyl alcohol by montmorrilonite”,
Journal of Colloid Science
, Vol. 18, 647-664 (1963) discloses that sorption of PVA on the montmorrilonite was dependent on the concentration of PVA in the solution. It was found that sorption was effective only at polymer concentrations of the order of 1% by weight of the polymer. No further effort was made towards commercialization since it would be limited by the drying of the dilute intercalated layered materials. In a recent work by Richard Vaia et.al., “New Polymer Electrolyte Nanocomposites: Melt intercalation of polyethyleneoxide in mica type silicates”,
Adv. Materials
, 7(2), 154-156, 1995, PEO was intercalated into Na-montmorillonite and Li- montmorillonite by heating to 80° C. for 2-6 hours to achieve a d-spacing of 17.7°Å. The extent of intercalation observed was identical to that obtained from solution (V. Mehrotra, E. P. Giannelis,
Solid State Commun
., 77, 155, 1991). Other, recent work (U.S. Pat. No. 5,804,613) has dealt with sorption of monomeric organic compound having at least one carbonyl functionality selected from a group consisting of carboxylic acids and salts thereof, polycarboxylic acids and salts thereof, aldehydes, ketones and mixtures thereof. Similarly U.S. Pat. No. 5,880,197 discusses the use of an intercalating monomer that contains an amine or amide functionality or mixtures thereof. In both these patents, and other patents issued to the same group, the intercalation is performed at very dilute clay concentrations in a medium such as water, leading to a necessary and costly drying step, prior to melt-processing.
In order to further facilitate delamination and prevent reaggregation of the clay particles, these intercalated clays are required to be compatible with the matrix polymer in which they are to be incorporated. This can be achieved through the careful selection and incorporation of compatibilizing or coupling agents, which consist of a portion which bonds to the surface of the clay and another portion which bonds or interacts favorably with the matrix polymer. Compatibility between the matrix polymer and the clay particles ensures a favorable interaction which promotes the dispersion of the intercalated clay in the matrix polymer. Effective compatibilzation leads to a homogenous dispersion of the clay particles in the typically hydrophobic matrix polymer and/or an improved percentage of exfoliated or delaminate
Blanton Thomas N.
Dontula Narasimharao
Majumdar Debasis
Massa Dennis J.
Nair Mridula
Blank Lynne M.
Eastman Kodak Company
Wyrozebski Katarzyna
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