**3. Montmorillonite structure**

The physical structure of montmorillonite particle is generally perceivable in sheets and layers. Each layer is composed of two types of structural sheets: octahedral and tetrahedral. The tetrahedral sheet is composed of silicon-oxygen tetrahedra linked to neighboring tetrahedra by sharing three corners resulting in a hexagonal network. The remaining fourth corner of each tetrahedron forms a part to adjacent octahedral sheet. The octahedral sheet is usually composed of aluminum or magnesium in sixfold coordination with oxygen from the tetrahedral sheet and with hydroxyl. The two sheets together form a layer. Several layers may be joined in a clay crystallite by interlayer cations, by Van der Waals force, by electrostatic force, or by hydrogen bonding.

Theoretical formula and structure is indicated in **Figure 1** [13]. The important natural physical properties of montmorillonite are given in **Table 3**. The best field indicators are softness, color, water, soapy feel, and expansion with water absorption.

The major montmorillonite deposits found at five places include Himalayas (China), Urals (Pakistan), Caucasians (Georgia, Russia), Andes (Peru, Ecuador), and Wasatch (UT, USA) [10].

Bentonite is an important rock of clay found in nature. It is an important source of montmorillonite in nature. It is a rock formed of highly colloidal and plastic clays mainly composed of montmorillonite [2]. In addition to montmorillonite, bentonite may contain some amount of

The variety of bentonite applications are the result of its useful and interesting chemical and physical properties. This range of properties include rheology, sorbent effects, plasticity and lubricity, high dry bonding strength, high shear and compressive strength, impermeability,

Natural bentonite particles are indistinguishable from kaolin clay minerals viewed under scanning electron microscope; however, the main difference indicated was thickness. Sodium or potassium salts of bentonite exfoliate into thin plates that could be of 1 nm in thickness

In general, the clay minerals based on bentonite may exhibit the properties of thixotropic gel formation with water, high water absorption, and high cation exchange capacity (CEC). These properties could be varied in clay minerals depending upon the nature of interstitial water

Bentonite, which mainly contained montmorillonite, was discovered in about 1890 in USA, and the name "bentonite" is associated with the name of an American geologist for the one

Montmorillonite derived from bentonite may contain sodium or calcium. Sodium montmorillonite is the main fraction in bentonite found in combination with 10–20% of various minerals

The physical structure of montmorillonite particle is generally perceivable in sheets and layers. Each layer is composed of two types of structural sheets: octahedral and tetrahedral. The tetrahedral sheet is composed of silicon-oxygen tetrahedra linked to neighboring tetrahedra by sharing three corners resulting in a hexagonal network. The remaining fourth corner of each tetrahedron forms a part to adjacent octahedral sheet. The octahedral sheet is usually composed of aluminum or magnesium in sixfold coordination with oxygen from the tetrahedral sheet and with hydroxyl. The two sheets together form a layer. Several layers may be joined in a clay crystallite by interlayer cations, by Van der Waals force, by electrostatic force,

**2. Bentonite**

crystalline quartz, cristobalite, and feldspar.

6 Current Topics in the Utilization of Clay in Industrial and Medical Applications

and exchangeable cations in the interlayer space.

including feldspar, calcite, silica, and gypsum [10].

**3. Montmorillonite structure**

or by hydrogen bonding.

time Fort Benton in the eastern Wyoming Rock Creek area, USA [2].

and low compressibility [11].

theoretically [12].

The variation in the chemical formula of montmorillonite is possible resulting from the modifiable structure. The cation substitution introduces charge imbalance. Therefore, the chemical composition can vary. The exact theoretical formula is never seen in nature [13]. However, the structure in nature in any form consists of water molecules.

The chemical formula for montmorillonite discovered at Montmorillon, France, is (Ca0.14 Na0.02)∑ <sup>=</sup> 0.16 (Al1.66 Mg0.36 Fe0.04) ∑ <sup>=</sup> 2.08 (Si3.90 Al0.10) ∑ <sup>=</sup> 4.00O10 (OH)<sup>2</sup> 1.02H2 O.

The oxide composition comprises silicon and aluminum oxides; however, it was predominantly calcium montmorillonite discovered at Montmorillon. The dominant fractions were SiO2 and Al2 O3, where SiO2 was slightly more than the 50% of total oxides.

The elementary molecular structure is based on units comprising silica tetrahedron and aluminum octahedral. The cation Si+4 is fourfold and possesses tetrahedral coordination with oxygen, while the cation Al+3 occurs in sixfold or octahedral coordination.

A layered structure is influenced by the presence of charge in tetrahedral and octahedral sheets. Isomorphous substitution in clay mineral mainly produces charge. Isomorphous

**Figure 1.** Theoretical formula and structure of montmorillonite (source: Nanocor Inc., IL (USA) [13]).


to its length, measuring to only one-billionth part of a meter (=1 nm). Therefore, an extremely

An increased aspect ratio produces a higher surface area. A smaller mass of nanoclay shows a high surface area, for example, typically 1 g of a nanoclay product is known to have a surface

Nanoclays are available containing over 98% montmorillonite. The variable colors are the result of substitution of interlayer-cations by iron, titanium, and manganese within the lattice

Montmorillonite is required to be surface modified to become organophilic and easy to disperse in polymers. Organophilic montmorillonite is produced using organic cation substitution.

The progress in the study to modify the structural composition of montmorillonite, its processing, and surface treatment may be indicated by the achievement of 40 patents issued to one commercial organization [17]. Montmorillonite nanoclay has experienced a variety of

Montmorillonite nanoclay is indicated as a drug carrier system and as an additive. Montmorillonite composite for application in drug system can be produced through the utilization of anionic, cationic, and nonionic surfactants to enhance basal spacing resulting in organoclay to be used in drug loading and drug release. Important aspects in a drug carrier system including drug entrapment, molecular level interactions, analysis for a sustained drug release, and

This review discussed various aspects of montmorillonite nanoclay such as structure, proper-

Significantly rich intercalation chemistry at a reduced cost is an important reason in producing montmorillonite-polymer nanocomposites. Such hybrid materials, also termed as polymeric nanocomposites (PNC), received extensive interest in research and industry. PNC materials on the nanoscale level exhibit advantageous effects in mechanical properties, heat distortion temperatures, thermal stability, flame retardancy, and enhanced barrier

Commercially, several desired effects obtained in PNC are resulting in an increasing consumption of montmorillonite. The combination of improved properties, including the weight reduction and low cost in the final product, resulted in important commercial applications in automotive and packaging, and so on. The significant findings in the montmorillonite- polymer nanocomposites are reviewed for material types: elastomers, thermosets, and polymers

The volume of recent research literature clearly indicates the interest and growing consumption of clay minerals particularly montmorillonite. In addition to natural montmorillonite applications, the studies are concentrating in the development of montmorillonite as nanoclay/organophilic clay through modifications in its physical and chemical structures. The utilization of nanoclay is discussed in the following sections where performance effects of

ties, multifarious applications, and the results of biocompatibility studies.

[15]: that is an equivalent area to nine soccer fields [16].

Montmorillonite: An Introduction to Properties and Utilization

http://dx.doi.org/10.5772/intechopen.77987

9

high average length-to-diameter ratio (called aspect ratio) of 200–500 is achievable.

structure and depend upon the level of substitution and valence state of cations [13].

area in excess of 750 m2

utilizations.

properties.

targeted drug release are reviewed [18].

from natural resources or biopolymers [19].

montmorillonite are described.

**Table 3.** Important natural physical properties of montmorillonite [9].

substitution is the replacement of an element with another element in mineral crystal without modifying its chemical structure. For example, Al3+ can replace Si+4 in tetrahedral coordination and replacement of Al3+ is possible by Mg2+, Fe2+, Fe3+ in octahedral coordination.

The sheets present in montmorillonite are composed of 2:1 structure. The sheets in the crystal plane have a negative charge and hydroxyl groups linked to aluminum or magnesium. The electrostatic force is primarily the force of attraction between the sheets; however, it is fragile.

Chemical composition, ionic substitution, layer structure, and particle size of natural clay minerals have important role in creating a variety of minerals with specific characteristics. However, sheet structure was used to classify the clay minerals, and chemical composition was used for nomenclature.
