**4. Montmorillonite in nanoclay**

Montmorillonite is the basic raw material used in producing nanoclay. Chemically, it can be described as hydrated sodium calcium aluminum magnesium silicate hydroxide, (Na, Ca)0.33 (Al Mg)<sup>2</sup> (Si<sup>4</sup> O10) (OH)<sup>2</sup> nH2 O [8]. The interaction between nanoclay particles and polymer matrix significantly depends upon the hydroxyl groups and charges present in the nanoclays particle.

In clay-polymer system, the clay nanoparticle can be intercalated or exfoliated. Where clay crystal is used as nanoparticle, it can be referred as intercalated clay (in this case, the polymer chains are between the clay platelets), and when the single particle of clay is the constituent unit, it is referred as exfoliated (i.e., clay platelets are isotropically dispersed in polymer). The important required characteristics include are particle size, surface area, and aspect ratio.

The length and breadth of the particles can range from 1.5μm down to few tenths of a micron [14]. The third dimension of particle, in the study, is described as thickness, width, or diameter; however, diameter may be used. The diameter of the particle is exceptionally smaller relative to its length, measuring to only one-billionth part of a meter (=1 nm). Therefore, an extremely high average length-to-diameter ratio (called aspect ratio) of 200–500 is achievable.

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 area in excess of 750 m2 [15]: that is an equivalent area to nine soccer fields [16].

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

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 utilizations.

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

8. Color White, buff, yellow, green, rarely pale pink to red (presence of high valance Mn produces

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

Montmorillonite is the basic raw material used in producing nanoclay. Chemically, it can be described as hydrated sodium calcium aluminum magnesium silicate hydroxide, (Na, Ca)0.33

matrix significantly depends upon the hydroxyl groups and charges present in the nanoclays

In clay-polymer system, the clay nanoparticle can be intercalated or exfoliated. Where clay crystal is used as nanoparticle, it can be referred as intercalated clay (in this case, the polymer chains are between the clay platelets), and when the single particle of clay is the constituent unit, it is referred as exfoliated (i.e., clay platelets are isotropically dispersed in polymer). The important required characteristics include are particle size, surface area, and aspect ratio.

The length and breadth of the particles can range from 1.5μm down to few tenths of a micron [14]. The third dimension of particle, in the study, is described as thickness, width, or diameter; however, diameter may be used. The diameter of the particle is exceptionally smaller relative

O [8]. The interaction between nanoclay particles and polymer

and replacement of Al3+ is possible by Mg2+, Fe2+, Fe3+ in octahedral coordination.

(measured)

3. Hardness 1–2 on Mohs scale, soft, possess fine-grained occurrence

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

pink to red coloration)

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

was used for nomenclature.

(Al Mg)<sup>2</sup>

**S. no** **Property name Description**

4. Fracture Irregular, uneven

1. Density 2–3 g/cm3

2. Crystal system Monoclinic

5. Cleavage Perfect 6. Luster Earthy, dull 7. Transparency Translucent

particle.

(Si<sup>4</sup>

**4. Montmorillonite in nanoclay**

O10) (OH)<sup>2</sup>

nH2

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 targeted drug release are reviewed [18].

This review discussed various aspects of montmorillonite nanoclay such as structure, properties, multifarious applications, and the results of biocompatibility studies.

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 properties.

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 from natural resources or biopolymers [19].

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 montmorillonite are described.
