INTRODUCTION:

Definition - Nanocomposites are composites in which at least one of the phases shows dimensions in the nanometre range (1nm = 10-9m)¹.

Size limits for these effects have been proposed:

<5nm for catalytic activity

<20nm for making a hard magnetic material soft

<50nm for refractive index changes

<100nm for achieving superparamagnetism, mechanical strengthening or restricting matrix dislocation movement².

The nanocomposite is a solid compound made up of several layers where at least one of the layers has one, two, or three dimensions with a nanometer size³ In nanocomposites, the atoms of the materials are arranged in the form of clusters or small grains. A solid multiphase having one of the 1, 2, or 3 phases less than 100 nm is called nanocomposites⁴Nanoparticles, nanoclays, and nanofibers are examples of nanocomposites. Nanocomposites find their applications in the fields of medical and engineering.

HISTORY:

Nanocomposites have been studied for nearly 50 years. Nanocomposites were first referenced as early as 1950, and polyamide nanocomposites were reported as early as 1976. Toyota researchers began a detailed examination of polymer/layered silicate clay mineral composites that nanocomposites became more widely studied in both academic and industrial laboratories. Acquarulo and O’Neil (2002) in their work observed that in the early 1980s that Toyota’s Central Research and Development Laboratories began working with polymer-layered silicate-clay mineral composites and that the period was when the technology began to be studied more widely. nanocomposites history was in 1990 when “Toyota first used clay/nylon-6 nanocomposites for Toyota car in order to produce timing belt covers.” He pointed out that after that other automotive application was implemented.⁵

Fig 01- Nanocomposites

ADVANTAGES:

Fig no - 02 Advantages of Nanocomposites

DISADVANTAGE:

Component stability,

Long-term stability,

Structural integrity,

Mechanical and corrosion properties,

Uncertain cytotoxicity,

High Viscosity

Method of Preparation of Nanocomposites:

A. In situ polymerisation

B. Meit mixing

C. Solution mixing

D. Precipitation

E. Sol gel process

F. Electrospinning

Types of Nanocomposites:

Fig no - 03 Types of Nanocomposites

1. Polymers Based:

A) Polymers - Ceramic Matrix Nanocomposites:

In scientific applications, polymer–ceramic nanocomposites are a novel class of composite materials in which a clay or filler with nanosize dimensions is added to a polymer matrix in a very small ratio. When dispersed in the nanocomposites at less than 5%, clay causes significant enhancement in various properties such as mechanical, optical, magnetic barrier, and specially permeability and flammability resistance. Drug delivery, which is one of the applications of nanotechnology in medicine currently being developed involves employing nanoparticles to deliver drugs, heat, light, or other substances to specific types of cells (such as cancer cells).⁶

B) Polymer Matrix Nanocomposites:

Polymer nanocomposites (PNC) consist of a polymer or copolymer having nanoparticles or nanofillers dispersed in the polymer matrix. These may be of different shape (e.g., platelets, fibers, spheroids), but at least one dimension must be in the range of 1–50nm. Polymer nanocomposites (PNCs) are the combination of polymer continuous phase and nanoparticles as discontinuous phase that show several advantages in mechanical, electric, and optical properties as compared with individual components.⁷

Fig no.04: Polymer matrix nanocomposites

ADVANTAGES:

1. They are lighter than conventional composites because high degrees of stiffness and strength are realized with far less high-density material

2. Their barrier properties are improved compared with the neat polymer

3. Their mechanical and thermal properties are potentially superior and

4. Exhibit excellent flammability properties and increased biodegradability of biodegradable polymers^.8

C) ORGANIC - INORGANIC POLYMER BASED NANOCOMPOSITES:

Polymer nanocomposites are a new class of composite materials containing inorganic nanoparticles dispersed in organic polymer matrix to improve its performance properties. Polymer nanocomposites have two components: polymer and the nano-fillers.⁹

D) POLYMERS /LAYERED SILICATE NANOCOMPOSITES:

Polymer/layered silicate (PLS) nanocomposites have received a great deal of attention during the past decade. They often exhibit attractive improvement of material properties. when compared with pure polymer or conventional composites (both micro- and macro-composites). These improvements can include, high moduli, increased strength and heat resistance, decreased gas permeability and flammability and increased biodegradability of biodegradable polymers. On the other hand, these materials have also been proved unique model systems to study the structure and dynamics of polymers in confined environments. The main reason for these improved properties is interfacial interaction between the polymer matrix and organically modified layered silicate (OMLS) as opposed to conventional composites. Layered silicates (LSS) have layer thickness in the order of 1 nm and very high aspect ratios (e.g., 10-1000). A few weight percent of OMLS that is properly dispersed throughout the matrix thus creates a much higher surface area for polymer-filler interfacial interactions than in conventional composites.¹⁰

2. Nonpolymer Based Nanocomposites:

A. Metal Nanocomposites:

Fig - 06 Metal matrix nanocomposites

Metal matrix composites (MMCs) or nanocomposites (MMNCs) are a class of advanced materials and structures wherein a light-weight metal such as aluminum or magnesium alloy is reinforced by high-strength reinforcing particles in order to produce light-weight high-strength composite materials. They are advanced engineered structures with potential of providing enhanced static and fatigue strength, excellent wear and improved creep resistance, superior damping and thermal properties making them suitable candidate for innumerable applications in transportation, automotive, marine, electronics, cutting tools, medical implants, defense, aerospace, and also packaging to name a few.¹¹

B. Ceramic Matrix Composites:

Fig - 07 Ceramic Matrix nanocomposites

Ceramic matrix composites (CMCs) consist of ceramic fibers embedded in a ceramic matrix. The matrix and fibers can consist of any ceramic material, including carbon and carbon fibers. The ceramic occupying most of the volume is often from the group of oxides, such as nitrides, borides, silicides, whereas the second component is often a metal. Ideally both components are finely dispersed in each other in order to elicit particular optical, electrical and magnetic properties as well as tribological, corrosion-resistance and other protective properties. The binary phase diagram of the mixture should be considered in designing ceramic-metal nanocomposites and measures have to be taken to avoid a chemical reaction between both components. The last point mainly is of importance for the metallic component that may easily react with the ceramic and thereby lose its metallic character. This is not an easily obeyed constraint because the preparation of the ceramic component generally requires high process temperatures. The safest measure thus is to carefully choose immiscible metal and ceramic phases. A good example of such a combination is represented by the ceramic-metal composite of TiO2 and Cu, the mixtures of which were found immiscible over large areas in the Gibbs’ triangle of ' Cu-O-Ti.^12,13,14

Method of Preparation of Nanocomposites:

A. In-Situ Polymerization:

Fig 08 - In - situ polymerization

In polymer chemistry, in situ polymerization is a preparation method that occurs "in the polymerization mixture" and is used to develop polymer nanocomposites from nanoparticles. There are numerous unstable oligomers (molecules) which must be synthesized in situ (i.e. in the reaction mixture but cannot be isolated on their own) for use in various processes. The in situ polymerization process consists of an initiation step followed by a series of polymerization steps, which results in the formation of a hybrid between polymer molecules and nanoparticles. Nanoparticles are initially spread out in a liquid monomer or a precursor of relatively low molecular weight. Upon the formation of a homogeneous mixture, initiation of the polymerization reaction is carried out by addition of an adequate initiator, which is exposed to a source of heat, radiation, etc. After the polymerization mechanism is completed, a nanocomposite is produced, which consists of polymer molecules bound to nanoparticles.¹⁵

B. MELT MIXING:

Melt blending is the preferred method for preparing clay/polymer nanocomposites of a thermoplastics and elastomeric polymeric matrix. Typically, the polymer is melted and combined with the desired mount of the intercalated clay using banbury or an extruder. Melt blending is carried out in the presence of an inert gas, such as argon, nitrogen, or neon. Alternatively, the polymer may be dry mixed with the intercalant, then heated in a mixer and subject to shear sufficient to form the desired clay polymer nanocomposites. Melt blending has great advantages over in situ intercalative polymerization or polymer solution intercalation. Melt blending is environmentally benign due to the absence of organic solvents. Melt blending is compatible with current industrial processes, such as extrusion and injection molding. Due to its potential in industrial applications, the melt blending process has become popular¹⁶

Fig - 09 Melt mixing

Polymer and nanofiller in solution are mixed, the polymer chains intercalate and displace the solvent within the interlayer of the silicate. Upon solvent removal, the intercalated/exfoliated structure remains, resulting in polymer nanocomposites. Solution mixing of polymer composites involves the dispersion of nanofiller in a polymer solution by energetic agitation, controlled evaporation of solvent, and finally composite film casting. Agitation can be achieved by magnetic stirring, shear mixing, reflux, or the most commonly used method of sonication.¹⁷

C. CO- PRECIPITATION/PRECIPITATION:

Fig - 11 co-precipitation and precipitation

D. SOL- GEL PROCESS:

Sol–gel processing is a versatile technique for the preparation of inorganic and hybrid organic–inorganic materials. Its mild conditions and capability for controlling composition, multiple levels of structure, porosity, mechanical properties, chemical functionality, optical properties, and ultimate form make sol–gel processing a powerful tool. Many questions remain unanswered regarding aspects of reaction mechanisms, molecular level control over properties, physics of gelation and postgelation processing and creation of nanostructures. Yet, based on what is known, sol–gel processing is finding applications ranging from new catalysts and separations media to composites of inorganic and biological systems and complex hierarchical structures that mimic life itself.¹⁸

E. ELECTROSPINING:

Fig - 12 Electrospinning techniques

NANOCOMPOSITES USES and APPLICATIONS:

1. Producing batteries with greater power output:

Researchers have developed a method to make anodes for lithium ion batteries from a composite formed with silicon nanospheres and carbon nanoparticles. The anodes made of the silicon-carbon nanocomposite make closer contact with the lithium electrolyte, which allows faster charging or discharging of power.

2. Speeding up the healing process for broken bones:

Researchers have shown that growth of replacement bone is speeded up when a nanotube-polymer nanocomposite is placed as a kind of scaffold which guides growth of replacement bone. The researchers are conducting studies to better understand how this nanocomposite increases bone growth.

3. Producing structural component with a high strength to weight ratio:

For example an epoxy containing carbon nanotubes can be used to produce nanotube-polymer composite windmill blades. This results in a strong but lightweight blade, which makes longer windmill blades practical. These longer blades increase the amount of electricity generated by each windmill.

4. Using graphene to make composites with even higher strength-to-weight ratio:

Researchers have found that adding graphene to epoxy composites may result in stronger/stiffer components than epoxy composites using a similar weight of carbon nanotubes.

5. Making lightweight sensors with nanocomposites:

A polymer-nanotube nanocomposite conducts electricity; how well it conducts depends upon the spacing of the nanotubes. This property allows patches of polymer-nanotube nanocomposite to act as stress sensors on windmill blades.

CONCLUSION:

Taking everything into account, new innovations require materials showing novel properties and additionally further developed execution contrasted with expectedly handled parts. In this review article we will concluded, nanocomposites are reasonable materials to satisfy the arising needs emerging from logical and technologic progresses. Handling techniques for various kinds of nanocomposites (CMNC, MMNC and PMNC) are accessible, however a portion of these posture provokes subsequently giving open doors for scientists to defeat the issues being encluntered with nanosize materials.

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Received on 22.09.2023 Modified on 16.10.2023

Asian J. Pharm. Res. 2023; 13(4):281-286.

DOI: 10.52711/2231-5691.2023.00051