Bull. Mater. Sci., Vol. 29, No. 2, April 2006, pp. 133–145. © Indian Academy of Sciences. 133 Nanoclays for polymer nanocomposites, paints, inks, greases and cosmetics formulations, drug delivery vehicle and waste water treatment HASMUKH A PATEL, RAJESH S SOMANI, HARI C BAJAJ* and RAKSH V JASRA Silicates and Catalysis Division, Central Salt and Marine Chemicals Research Institute, G.B. Marg, Bhavnagar 364 002, India MS received 25 October 2005 Abstract. An overview of nanoclays or organically modified layered silicates (organoclays) is presented with emphasis placed on the use of nanoclays as the reinforcement phase in polymer matrices for preparation of polymer/layered silicates nanocomposites, rheological modifier for paints, inks and greases, drug delivery vehicle for controlled release of therapeutic agents, and nanoclays for industrial waste water as well as potable water treatment to make further step into green environment. A little amount of nanoclay can alter the entire pro- perties of polymers, paints, inks and greases to a great extent by dispersing 1nm thick layered silicate throughout the matrices. The flexibility of interlayer spacing of layered silicates accommodates therapeutic agents which can later on be released to damaged cell. Because the release of drugs in drug-intercalated layered materials is controllable, these new materials have a great potential as a delivery host in the pharmaceutical field. The problem of clean water can be solved by treating industrial and municipal waste water with organo- clays in combination with other sorbents like activated carbon and alum. Organoclays have proven to be su- perior to any other water treatment technology in applications where the water to be treated contains substantial amounts of oil and grease or humic acid. Keywords. Layered silicates; nanocomposites; rheological modifier; drug delivery; waste water. 1. Introduction Organically modified layered-silicates or nanoclays have become an attractive class of organic–inorganic hybrid materials because of their potential use in wide range of applications such as in polymer nanocomposites, rheological modifier in paints, inks, greases and cosmetics, adsorbent for toxic gases, effluent treatment and drug delivery carrier. The generic term, layered silicates, refers to natural clays as well as synthesized layered silicates such as mont- morillonite, laponite and hectorite. The most commonly used clay in the synthesis of poly- mer nanocomposites is montmorillonite (MMT) which is the major constituent of bentonite. It is well known that filler anisotropy, i.e. large length to diameter ratio (aspect ratio), is especially favourable in matrix reinforcement. Due to unique structure of montmorillonite, the mineral platelet thickness is only one nanometer, although its dimensions in length and width can be measured in hundreds of nanometers, with a majority of platelets in 200–400 nm range after purification. Due to very small size and thickness of the platelets, a single gram of clay contains over a million individual platelets. The term polymer layered silicate nanocomposites describes a class where the rein- forcing phase, in the shape of platelets, has only nano- level dimensions. There is substantial improvement in mechanical and physical properties of nanocomposites and this too at a very low silicate content (3–6 wt%). Im- proved mechanical and thermal properties are of interest for under-the-hood applications in the automotive industry (Fukushima and Inagaki 1987). Excellent barrier proper- ties combined with good transparency make these materi- als ideal for packaging applications (Okada et al 1990, Okada and Usuki 1995; Giannelis 1996; Giannelis et al 1999; LeBaron et al 1999; Vaia et al 1999; Biswas and Sinha Ray 2001). The era of polymer nanocomposites received an impetus after the work of a researcher from Toyota in 1987 (Fukushima and Inagaki 1987). Toyota discovered the possibility of synthesizing polymer nano- composites based on nylon-6/organophilic montmorillonite clay that showed dramatic improvements in mechanical and physical properties and heat distortion temperature at very low content of layered silicate. The intercalation chemistry of polymers when mixed with appropriately modified layered silicate and synthetic layered silicates has long been known (Theng 1979). The field of polymer/ *Author for correspondence (hcbajaj@csmcri.org)