CLAY

Amal kumar CBPST Kochi

CLAY Clay is a fine-grained natural rock or soil material

that combines one or more clay minerals with traces of metal oxides and organic matter.

Clay is one of the oldest building materials on Earth

Clay is a mineral, belonging to phyllosilicate category.

Chemically it consists of aluminium silicate as a principal component along with variety of other metals like magnesium, calcium, potassium and varying level of watermolecules.

Atomic configuration of clays consists of alternating ‘sheets’ of tetrahedral SiO4 and octahedral AlO6 units formed by oxygen sharing

Fig : Silica tetrahedral and alumina octahedral sheets formedthrough oxygen sharing

Combination of such sheets through chemical bonding producesphysically distinct entities called ‘layers’

Facts Exhibit plasticity when mixed with water in certain

proportions. When dry, clay becomes firm and when fired permanent physical and chemical changes occur.

Being relatively impermeable to water

Applications Used for making Bricks, cooking pots, art

objects, dishware, and even musical instruments such as the ocarina can all be shaped from clay before being fired.

Also used in many industrial processes, such as paper making, cement production, and chemical filtering.

Clay is also often used in the manufacture of pipes for smoking tobacco

Used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage

Montmorillonite : properties

Layer charge originates from the substitution of Mg2+ for Al3+ in the octahedral sheet

Unstable (weathers to something else) under low pH and high moisture

Most swelling of all clays “Nutrient rich”

Structure of montmorillonite : it is built of two sheets of silicon tetrahedra and one sheet of aluminum octahedra, linked by shared oxygen atoms.

Structure of Montmorillonite

Al

O

Structure of Montmorillonite

Isomorphous substitution here, in the octahedral sheet

Causes cations to move into the interlayer space, where they can be replaced by other cations

= Mg

OrganoclayOrganoclay is the organically modified pyllosillicate,derived from a naturally occuring clay mineral.

By exchanging the original inter layer cations for organo cations (typically alkylammonium ions) an organophillic surface is generated, consisting of covalently linked organic moieties.

The lamellar structure remains analoguos to the parent phyllosilicate.

Separation of the layers due to ion exchange from the initial interlayer spacing of as little as 3 Å in the case of Na + cations to the distances in the range of 10 - 40 Å as well as the change of chemical character of the clay surface , allows the insitu polymerisation or mixing with certain polymers to obtain what is known as nano composite.

When ordered alluminasilicate sheets are lying parellel to each other ,separated with polymerchains of certain type the system is classified as intercalated nano composite.

If separation of the layers is so significant ,that they are no longer lying opposite to one another , but randomly ordered , then one get the exfoliated nano composite.

Methods for modifications Hydrophobic modification Intercalation Exfoliation

The cations residing between the layers are exchangeable with quaternary ammonium ions like acetyl-trialkyl-ammonium or acetyl-vinyl-dialkyl ammonium. This process converts the hydrophilic surface of the layer into a hydrophobic one thereby improving the compatibility of nanoclay into polymer matrix. Presence of a polymerizable group like vinyl, on the surface, facilitates encapsulation by a polymer by in-situ polymerization.

Hydrophobic modification

Intercalation

This is a physical process by which a macromolecule like a dye or polymer is ‘inserted’ in the gallery.

Such a molecule is flanked by two clay layers and isimmobilized and shielded. Width of the gallery is however not much affected

during intercalation.

Exfoliation

This is a delaminating process where in the gallery is expanded from its normal size of 1 nm to about 20 nm or higher. Thus there is a clear disruption of the layers which get spacially separated apart bringing about nanoscale dispersion in the polymer matrix. Thus exfoliated clays represent true nanomaterials.

Modification of cationic sodium MMT and synthetic fluorinated Mica

A series of poly(oxyalkylene)-polyamine salts (POA-salts) including hydrophobic poly-(oxypropylene)-(POP-) and hydrophilic poly(oxyethylene)- (POE-) amines of molecular weights ranging from 230 to 5,000 g/mol had been used to modify the natural clays.

As a result, high d spacing up to 92 Å was reported in the case of POP-amine salt of 4,000 g/mol Mw for the intercalation of Na+- MMT.

The lamellar interlayer expansion is generally proportional to

molecular lengths of the intercalating agents.

In the gallery of layered structures, the POP organics aggregated into a new hydrophobic phase which ultimately expanded the basal spacing.

The interlayer expansion was reported to occur in a critical concentration manner similar to the so-called Critical Micelle Concentration (CMC) as a surfactant behaves in water.

Modification of anionic Al-Mg LDH

A new approach was reported for interacting with the clays through counter-ion exchange, chelating and hydrogen bonding association mechanism by using POA-derived amindoacids.

In the chelating mechanism involving the POA-amidoacid with Na+-MMT, a seven-member ring cyclic intermediate was proposed.

A similar mechanism with an acid-chelating intermediate was reported for intercalation of alkylcarboxylic acids, CH3(CH2)nCOOH, into the gallery of clay containing divalent metal counter ions.

For comparison, the use of C12−18 carboxylic acids such as lauric acid (n = 10) and stearic acid (n = 16) intercalated into Na+-MMT resulted in only low organic embedment of 10−15 wt % organics and low XRD basal spacing of 15 Å. For the divalent M2+-MMT analog (XRD = 10.1 Å), the same acid species could expand the silicates with a larger d spacing of 30 or 43 Å. The difference between the M2+-MMT and Na+-MMT intercalation was attributed to the formation of thermally stable intermediates for the divalent M2+, but not for Na+ form of MMT.

However, the LDHs are different from MMTs, not only in opposite charges of ionic characteristics but also in charge density. The strong interlayer electrostatic interaction among individual Mg-Al oxide platelets leads to a tight stacking of the lamellae and difficulty for organic incorporation.

Alkyl carboxylates and sulfonates are common species as the intercalating agents, but which could widen the interlayer spacing only up to 30 Å .

In addition to the limitation on interlayer widening, the rate of ionic exchange reaction is considerably slow as compared to the MMT intercalation. In comparing with the alkyl carboxylic acids, the amidoacids are suitable for interacting with the anionic LDH clay.

For example, POA-derived amidoacids of high molecular weight could render LDH wide basal spacing of 92 Å .

Exfoliation of MMT and Mica with multifunctional amine copolymers

Besides the wide expansion of layered silicates through intercalation, random silicate platelets could be obtained by using amphiphilic copolymers, such as Mannich condensates, hydrophobic backboned polyamidoacids and other polyamines .

The subsequent formation of amine-HCl salts was required for such exfoliation agents. Their structures generally consisting of multiple amines enabled to form stable emulsion in water with clays and exchange their counter Na+ ions.

As a result, the layered stack of multiple silicate sheets in the Na+-MMT primary structure was exfoliated and randomized into individual clay platelets.

The process involved the exfoliation of the layered clay through ionic exchange reaction and further NaOH treatment to phase separate and recover the organic amines.

The randomized silicates were shown to have a unique ionic character and suspension in water.

The physical properties of the platelets demonstrated an inherent 120 meq/100 g cation exchange capacity, averaged 720 m2/g surface areas, 20,000 ions, 0.9 nm2 area per ion and 4 × 1016 platelets per gram.

Applications Owing to its large surface area together with hydrophobic

chains emerging from the clay surface, organoclay can be used to remove oil from water also applied as a component in paint formulations as a viscosifier for oil-based drilling fluids can be used in polymer chemistry as a nucleating agent

Thank You Done by,

Amal kumar

layered double hydroxide (LDH) montmorillonite (MMT) clay