In different applications like tyres, belts, and oil seals, situations where resistance to fatigue with improved life span is desired, and in gaskets, and electronic and electrical equipment, conventional type rubbers are reinforced with filler materials to enhance their physical, electrical, thermal, and mechanical properties. Compared to the conventional rubber/rubber composite-reinforced fillers, the addition of nanomaterials has gained extra attention in recent years, and these are called nanocomposites [40,61]. Nanomaterials have unique properties which are changed due to their size reduction in any one dimension, like chemical (reactivity or catalysis), thermal (melting temperature), electronic (electrical conductivity), optical (scattering or absorption of light), or magnetic (magnetization) properties [40]. Among various types of nanomaterials, CNTs are one of the most attractive reinforcements used in the rubber nanocomposites, due to their high aspect ratio, flexibility, diameter in the nano range, and physical, mechanical, and electrical properties along the axis of the tube. MWCNTs have greater advantages than SWCNTs or DWCNTs in the range of possible industrial applications and low production cost, which can also provide similar composite properties [40,62,63]. In nanocomposites, uniform dispersion of the CNTs plays a very important role in increasing the properties of the developed material. This is because of the bonding between the nanotubes being very high and ending up in a cluster formation [63]. In recent research, MWCNTs/SWCNTs were used as reinforcements and mixed with caoutchouc or natural rubber matrix material to obtain an MWCNT/SWCNT–natural rubber nanocomposite (nanostructures), by adding the CNTs into a polymer solution like acetone, dimethyl formamide, toluene, or tetrahydrofuran and mixing either by high-energy sonication, magnetic agitation, or mechanical mixing. Simultaneously, in addition to the poor solution, the solvent gets evaporated and obtains better dispersion of nanotubes. It is a better method to achieve uniform dispersion and distribution of nanotubes into the matrix material. One major constraint for this method is neglecting the improper solubility of polymer into the solvent to carry out the next process [40]. Also, MWCNTs improved the mechanical and electrical properties of other types of rubbers, such as chloroprene, acrylonitrile–butadiene, styrene butadiene rubber, and ethylene–propylene–diene monomer [62].
