Hybrid mixed ion clay structures for polymer nanocomposite...

Details Hybrid mixed ion clay structures for polymer nanocomposite... Hybrid mixed ion clay structures for polymer nanocomposite...

2000-03-03

2002-07-02

Cain, Edward J. (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...

C524S186000, C524S431000, C501S148000

Reexamination Certificate

active

06414069

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to novel hybrid layered silicates containing galleries within the layers incorporating both organic and inorganic ions. In particular, the hybrid layered silicates have different inorganic ion and organic ion compositions in different of the galleries.
(2) Description of Related Art
Smectite clays are natural or synthetic layered alumino-silicates such as montmorillonite, bentonite, hectorite, fluorohectorite, saponite, beidellite, nontronite, and related analogs. Smectite clays have layered lattice structures in which the tactoids (crystallites) consist of stacked two dimensional oxyanions separated by layers of hydrated cations. The oxygen atoms define layers approximately 10 Å-thick, containing two sheets of tetrahedral sites and a central sheet of octahedral sites. The 2:1 relation between the tetrahedral and the octahedral sheets in a layer defines 2:1 layered silicates. This same layered structural element is found for the mica minerals; therefore smectite clays and related 2:1 layered silicate minerals such as vermiculite and rectonite are sometimes referred to as mica-type silicates. For a typical 2:1 layered silicate, such as montmorillonite, the layer is made up of a central octahedral sheet, usually occupied by aluminum or magnesium, sandwiched between two sheets of tetrahedral silicon sites. Various isomorphous cation substitutions, e.g., Si
4+
by Al
3+
in the tetrahedral sheet, or Al
3+
by Mg
2+
, or Mg
2+
by Li
+
in the octahedral sheet among others also result in negatively charged nanolayers. These negatively charged layers are separated by hydrated cations such as alkali or alkaline earth metal ions in the gallery (interlayer) regions between the 2:1 layered silicates. The negative charge on the layer is balanced by interlayer or “gallery” cations, normally Ca
2+
and Na
+
. The gallery cations in a natural smectite can be replaced by simple ion exchange process with almost any desired cation, including alkylammonium alkyl phosphonium and other organic cations. Some idealized unit cell compositions and layer charge densities of 2:1 layered are listed in Table 1.
TABLE 1
Ideal Structural Formulas for some 2:1 Layered Silicates
Layer
Charge
Density
per O
20
Mineral Name
Ideal Formula
unit
Hectorite
M
x

n+
.yH
2
O[Al
6.0−x
Mg
x
](Si
8.0
)O
20
(OH)
4
0.4-1.0
Fluorohectorite
M
x

n+
.yH
2
O[Al
6.0−x
Mg
x
](Si
8.0
)O
20
(OH,F)
4
0.4-1.2
Montmorillonite
M
x

n+
.yH
2
O[Mg
6.0−x
Li
x
](Si
8.0
)O
20
(OH)
4
0.6-1.2
Nontronite
M
x

n+
.yH
2
O[Fe
4.0
](Si
8.0−x
Al
x
)O
20
(OH)
4
0.6-1.2
Beidellite
M
x

n+
.yH
2
O(Al
4.0
](Si
8.0−x
Al
x
)O
20
(OH)
4
0.8-1.2
Saponite
M
x

n+
.yH
2
O[Mg
6.0
](Si
8.0−x
Al
x
)O
20
(OH)
4
0.6-1.4
Vermiculite
Mg
(x−z)2
2+
[Mg
6−x
Fe
z
III
](Si
8−x
Al
x
)O
20
(OH)
4
1.4-1.8
Muscovite mica
K
2
[Al
4.0
](Si
6.0
Al
2.0
)O
20
(OH)
4
2.0
Biotite mica
K
2
[Al
y
Mg
6+(x/z)−(3y−2)
](Si
6.0−x
2.0
Al
2.0+x
)O
20
(OH)
4
(x < 1,y < 2)
Phlogopite mica
K
2
[Mg
6.0
](Si
6.0
Al
2.0
)O
20
(OH)
4
2.0
Included in Table 1 for comparison purposes are the idealized compositions of 2:1 layered silicates, smectite clays, vermiculite, muscovite mica, biotite mica, and phlogopite mica. Vermiculite has a layer charge density higher than a smectite but lower than a mica. Micas usually have layer charge of 2.0. The gallery cations in a vermiculite or a mica can also be replaced by ion exchange, but the exchange processes are generally slower than for smectite clays. Also, vermiculites and micas exist commonly as single crystals that range in size from 10 &mgr;m to 10 cm or larger. In contrast, smectite clays have sub-micron particle sizes. The particle size of vermiculite and mica can be reduced to the micron size range by mechanical grinding. Other ion exchangeable 2:1 layered silicate including illite, rectorite and synthetic derivative such as tetrasilicic mica and synthetic mica montmorillonite (SMM).
Most important among the properties of smectite clays and related 2:1 layered silicates with cation exchange properties is the ability to replace the gallery cations in the pristine clay with almost any desired cations by ion exchange reactions. The exchange cations are very important in determining the ability of the gallery regions to imbibe (intercalate) neutral molecules. Inorganic cations (M
n+
) such as (Na
+
, Ca
2+
and the like) prefer to be solvated by polar molecules such as water and certain polar organic molecules. Thus, these exchange forms are readily swollen by polar molecules, especially by water. Organic cations (alkylammonium, phosphonium ions and the like) are less hydrophilic, even hydrophobic, and prefer to intercalate organic molecules into the gallery regions. Inorganic cations such as K
+
and Mg
2+
in mica are anhydrous and strongly bound to the intergallery surfaces. Therefore, these silicates are difficult for gallery swelling and ion exchange reaction. However, the exchange of gallery cations in micas can be facilitated by reducing the particle size of the particles, preferably to average values of 2 &mgr;m or less.
Clay-organic intercalates are intercalation compounds in which organic molecules enter the clay galleries and form definite compositions with specific clay basal spacings. The organic compounds that have been reported to form clay intercalates include uncharged polar organic compounds and positively charged organic ions, and ion-paired organic salts. These classes of guest species are intercalated by ion exchange, physical adsorption, or other mechanisms. Intercalation of organic polymers in clay minerals has been recognized to occur as natural processes in soils. Polymer adsorption and desorption also occurs under synthetic conditions (Theng, B. K. G. “The Chemistry of Clay-Organic Reactions”. John Wiley & Sons, pages 136 to 206 (1974)). Interaction between clays and polymeric species has been discussed as natural or synthetic polymer adsorption and desorption (Theng, B. K. G. “Formation and Properties of Clay-Polymer Complexes”, Elsevier pages 63 to 133 (1979)).
Mixed organic/inorganic ion exchanged forms of 2:1 layered silicates can potentially adopt one of several possible structures depending on the distribution of the distinguishable cations in the interlayer galleries. Organo cations, particularly alkylammonium ions such as (CH
3
)
3
NH
+
and (CH
3
)
4
N
+
among others, are known to form interstratified structures when mixed with Na
+
among others, are known to form interstratified structures when mixed with Na
+
ions in the galleries of montmorillonite (Barrer, R. M. and K. Brummer, Trans. Faraday Soc. 59:959-968 (1963); and Theng, B. K. G., et al., Clay Miner. 7:1-17 (1967)). In these interstratified phases the galleries are occupied by “onium-rich” and “sodium-rich” compositions of exchange cations. That is, the organic and inorganic exchange cations are “demixed” or largely segregated into separate galleries. Also, the stacking sequence of “onium-rich” and “sodium-rich” galleries is random in an interstratified mixed ion system. Interstratified onium ion/alkali metal ion smectite clays typically exhibit XRD spacings that increase with the amount of the larger onium ion occupying exchange positions in the galleries. The observed XRD basal spacings for demixed interstratified compositions is equal to the weighted average of the d spacings expected for the homoionic end member inorganic and organic exchanged forms of the layered silicate.
The segregation of organic onium ions and inorganic cations also has been recently observed for mixed ion exchange form of fluorohectorite containing equal molar amounts of a quaternary phosphonium ion, namely (C
18
H
37
)P(C
4
H
9
)
3
+
, and an alkali metal ion, namely, Li
+

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