Structure and Properties of Strain-Induced Crystallization Rubber–Clay Nanocomposites by Co-coagulating the Rubber Latex and Clay Aqueous Suspension Yiqing Wang, 1 Huifeng Zhang, 1 Youping Wu, 1 Jun Yang, 2 Liqun Zhang 1,2 1 Key Laboratory for Nano-materials, Ministry of Educational, Beijing 100029, China 2 Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical Technology, Beijing 100029, China Received 20 May 2003; accepted 13 August 2004 DOI 10.1002/app.21408 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Natural rubber (NR)– clay (clay is montmo- rillonite) and chloroprene rubber (CR)– clay nanocomposites were prepared by co-coagulating the rubber latex and clay aqueous suspension. Transmission electron microscopy showed that the layers of clay were dispersed in the NR matrix at a nano level, and the aspect ratio (width/thick- ness) of the platelet inclusions was reduced and clay layers aligned more orderly during the compounding operation on an open mill. However, X-ray diffraction indicated that there were some nonexfoliated clay layers in the NR matrix. Stress–strain curves showed that the moduli of NR were significantly improved with the increase of the amount of clay. At the same time, the clay layers inhibited the crystal- lization of NR on stretch, especially clay content of more than 10 phr. Compared with the carbon-black-filled NR composites, NR– clay nanocomposites exhibited high hard- ness, high modulus, high tear strength, and excellent anti- aging and gas barrier properties. Similar to NR– clay nano- composites, CR– clay nanocomposites also exhibited high hardness, high modulus, and high tear strength. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 318 –323, 2005 Key words: clay; strain-induced crystallization rubber; nanocomposites; structure; mechanical properties; gas per- meability INTRODUCTION Polymer– clay nanocomposites, especially plastic ma- trices, have attracted much attention recently, and these nanocomposites exhibit outstanding mechanical properties, low gas permeability, and excellent fire retardant properties 1–6 . But there are only a few stud- ies on rubber– clay nanocomposites. Synthesis of rub- ber– clay nanocomposites has typically involved rub- ber melt or solution intercalation of organclay, which has organic ammonium salts, or protonated amino- terminated polybutadiene/poly(butadiene-co-aryloni- trile) in the interlayer space 7–10 . A new approach for rubber matrices introduced in a patent 11 by the au- thors of this article involves mixing the rubber latex and the clay aqueous suspension and cocoagulating by adding electrolyte, which is simpler and cheaper than the methods using organic clay. In our previous work, morphology and mechanical properties of non- crystallizing rubber such as styrene butadiene rub- ber–, carboxylated acrylonitrile butadiene–, and nitrile rubber– clay nanocomposites are investigated 12–15 . Since natural rubber (NR) and chloroprene rubber (CR) are strain-induced crystallization rubbers and possess high strength without reinforcement, it is in- teresting to investigate the properties of NR– clay and CR– clay nanocomposites. In this paper, the effects of the amounts of clay on mechanical properties, gas permeability, and air-oven aging properties of NR– clay or CR– clay nanocomposites are studied in detail. EXPERIMENTAL PROCEDURES Materials The clay (Na-montmorillonite), with a cationic ex- change capacity of 93 meq/100 g, is from Liufangzi Clay Factory (Jilin, China). NR latex is from Beijing Latex Products Factory (China). CR latex is from Shanxi Latex Factory (China). Preparation of rubber-clay nanocomposites The clay aqueous suspension, the rubber latex, and the interfacial agent (C 4 H 9 N + (CH 2 CH 2 OH) 3 Br - , 0.1 mol/ Correspondence to: L-Q. Zhang (zhangliqunghp@yahoo. com). Contract grant sponsor: National Natural Science Foun- dation of China; contract grant number: 05173003; contract grant sponsor: Beijing New Star Plan Project; contract grant number: H010410010112; contract grant sponsor: Key Project of Beijing Natural Science Foundation; contract grant num- ber: 2031001; contract grant sponsor: National Tenth-five Program; contract grant number: 2001BA310A12. Journal of Applied Polymer Science, Vol. 96, 318 –323 (2005) © 2005 Wiley Periodicals, Inc.