Review on development of natural rubber/nanoclay nanocomposites

The advantages of nanocomposites containing single silicate layers uniformly dispersed in a polymer matrix were first demonstrated by researchers at Toyota in Japan, who developed nylon-6 nanocomposites and published in 1993. Polymer-nanoclay nanocomposites have attracted the attention of many researchers thereafter due to their outstanding mechanical and barrier properties. This concept is first applied to synthesis of plastics/nanoclay nanocomposites and then expanded to preparation of rubber/nanoclay nanocomposites, since few years later. The various types of synthetic rubbers, such as silicon rubber, nitrile rubber and epoxy rubber, were used to prepare nanocomposites using different techniques, namely, melt intercalation, in situ intercalative polymerization, exfoliation-adsorption and template synthesis, etc. Natural rubber (NR) was also used to prepare nanocomposites using the same techniques but with some modifications in the last decade. Nowaday's nanocomposites are widely developed in NR latex industry to achieve required properties with minimum use of clay content. NR/nanoclay nanocomposites exhibit markedly improved properties when compared to pure NR or their traditional composites. Most notable properties are increased tensile properties, gas barrier properties and heat distortion temperature, resistance to small molecule permeation, increase in atomic oxygen resistance and retention of impact strength. Tensile strength and modulus were recorded in current research as enhanced by more than two times or even ten times. It was noticed that obtaining a fully exfoliated structure is not at the desired level. Nanoclay nanocomposites are considered as fully exfoliated when inter gallery distance is greater than 10 nm but it was not achieved in many research work. Establishment of exfoliated structures in nanocomposites prepared in industrial scale is the major challenge that NR industry faces at present. NR/nanoclay nanocomposites produced with existing techniques develop high property fluctuations. Therefore, it is necessary to develop a technique to minimize property fluctuations and to obtain a reliable NR based product. It is predicted by this review that co-coagulation technique is the most promising and potential technique to fulfill the requirements of developing a NR/nanoclay nanocomposite. Use of modified nanoclays like Organoclays will aid to obtain a reliable NR based product.