New Method for the Synthesis of Clay/Epoxy Nanocomposites H. Wang, S. V. Hoa, P. M. Wood-Adams Concordia Center for Composites, Department of Mechanical and Industrial Engineering, Concordia University, Montreal, Quebec H3G 1M8, Canada Received 24 March 2005; accepted 29 September 2005 DOI 10.1002/app.23859 Published online 8 March 2006 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A new liquid–liquid method for the synthe- sis of epoxy nanocomposites was developed. This new method improved the dispersion and exfoliation of the or- ganoclay in the polymer matrix, thus improving the end-use properties. The microstructure and physical properties of the clay/epoxy nanocomposite synthesized by the new method were studied. Rheological tests of the uncured ep- oxy– organoclay system demonstrated that this method re- sulted in a great increase in viscosity, much more than the most commonly used direct-mixing method. The Krieger– Dougherty model successfully described the dispersion of the clay layers in the uncured epoxy. In the 5 wt % organo- clay nanocomposite, compressive tests on the cured samples showed that there was a 45% increase in the maximum strength, a 10% increase in the yield strength, and a 26% increase in the modulus over the pure epoxy–amine cured system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4286 – 4296, 2006 Key words: nanocomposites; epoxy; organoclay; clay exfo- liation; clay dispersion INTRODUCTION The science and technology of nanocomposites has created great excitement and expectations in the last decade. Research in this area has been focused on the nanoscale second phase embedded in the polymeric matrix that gives physical and chemical properties that cannot be achieved by ordinary material synthesis methods. With new methods of synthesis and tools for characterization and manipulation, nanocomposite science and technology is now experiencing explosive growth. 1,2 In 1993, researchers from the Toyota research group in Japan successfully synthesized organoclay/poly- amide 6 nanocomposites 3 that showed great improve- ments in the mechanical properties and thermal sta- bility when only 4 wt % clay was introduced into the polymer matrix. Many researchers then expanded the use of organo- clay to different polymer matrix nanocomposites, in- cluding epoxy, polypropylene, polystyrene, polyim- ide, polyurethane, and dendritic polymers. Their re- sults have shown that the mechanical properties, physical/chemical properties, and fire resistance of the composites have been improved at very low clay contents. Many aspects of clay/epoxy nanocomposites, which are regarded as one of the most promising new materials for industrial applications, have been stud- ied. Areas such as the effect of curing processes, 4 promoters (catalysts), 4,5 choice of clays, 6 choice of cur- ing agents, 7 choice of intercalating agents with alky- lammonium ion with different alkyl chain lengths and different head groups (primary, secondary, tertiary and quaternary alkylammonium), 8 and corresponding morphological, mechanical, chemical, thermal, and rheological properties have been researched. After nearly 10 years of the extensive study of clay/ epoxy nanocomposites, there are still many problems that need to be solved. The dispersion and exfoliation of clay layers in an epoxy matrix are not sufficient for improving the mechanical and physical properties of nanocomposites to a reasonable degree. There are many ways to improve the final mechan- ical, physical, and chemical properties of clay/epoxy nanocomposites. One of the most important ways is to disperse the clay into the matrix evenly to reach the maximum of clay exfoliation. The method of mixing clay with an epoxy resin was considered in this study. The direct mixing (DM) method, in which organo- clay is mechanically mixed with epoxy with or with- out solvents, 5–7,9,10 is the most common method in the synthesis of clay/epoxy nanocomposites (Fig. 1). Commercial clay, such as organoclays from Nanocor and Southern Clay Product, is usually used. The sol- vents (e.g., acetone, ethanol, isopropyl alcohol) needs to have a low boiling point. 9 A common laboratory- Correspondence to: S. V. Hoa (hoasuon@vax2.concordia.ca). Journal of Applied Polymer Science, Vol. 100, 4286 – 4296 (2006) © 2006 Wiley Periodicals, Inc.