Morphology and Mechanical Properties of Natural Rubber and Styrene-Grafted Natural Rubber Latex Compounds Wanvimon Arayapranee, 1 Garry L. Rempel 2 1 Department of Chemical and Material Engineering, Rangsit University, Phathum Thani 12000, Thailand 2 Department of Chemical Engineering, University of Waterloo, Ontario, Canada N2L 3G1 Received 3 August 2007; accepted 12 February 2008 DOI 10.1002/app.28217 Published online 17 April 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The mechanical properties of natural rubber latex (NRL) modified with styrene-grafted natural rubber (styrene-GNR) latex were investigated. Styrene-GNR was first synthesized via emulsion copolymerization using cumene hydroperoxide/tetraethylene pentamine as an ini- tiator. The styrene-GNR latex produced was mixed with NRL with various latex compounding contents and then prevulcanization was carried out. The mechanical proper- ties and heat, weathering, and ozone resistance of the nat- ural rubber (NR) and styrene-GNR latex compounds were investigated as a function of the grafted NR content. The results indicated that the tensile and tear strength were decreased, whereas Young’s modulus and hardness were increased at high content of styrene-GNR. Addition of sty- rene-GNR improved the resistance of the compounds to heat and weathering ageing. The ozone resistance of the compound containing styrene-GNR is superior to that of the NR-rich compound. The results indicated that NR/sty- rene-GNR latex compounds maintained good antiageing properties required for outdoor applications. The tensile fracture surface examined by scanning electron microscopy confirmed a shift from ductility failure to brittle with an increase of the styrene-GNR content in the com- pounds. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 109: 1395–1402, 2008 Key words: natural rubber; latex; graft copolymer; styrene; compound; ageing resistance INTRODUCTION Graft copolymerization has attracted much attention and is applicable to a new class of specialty poly- mers with an expanded useful range. Graft copoly- mers are produced when a vinyl monomer is poly- merized in the presence of preformed polymer con- taining double bonds to give chemical bonding to that polymer. Natural rubber (NR) obtained from Hevea brasiliensis is classified as one of the most important natural resources used industrially, as it is well-known to be the most excellent rubbery mate- rial, having outstanding mechanical properties while it is weak in oil-resistance, weather-resistance, and ozone-resistance. The chemical modification of NR by grafting with vinyl monomers combines the pro- perties of both NR and the polymer of the monomer grafted. It has gained considerable importance as it leads to polymers with altered and improved pro- perties for the production of new materials. 1 The most promising graft copolymer based on NR, thus far obtained, is that derived from methyl methacry- late (MMA) and styrene (ST). The graft copolymer may be prepared by graft copolymerization of NR in latex form, since the NR, an unsaturated elastomer having the existence of double bonds in its chains, can be readily grafted with a variety of monomers, using the well-established technique of seeded emul- sion polymerization. 2–7 Natural rubber latex (NRL) has a broad size distribution of particles having an average size of about 0.7 lm. 8 Styrene-grafted natural rubber (styrene-GNR) latex is a kind of spe- cialty latex produced by chemical modification of NRL. 1,9,10 ST monomer is graft copolymerized with NRL under the action of a free-radical catalyst to produce graft copolymer. Because the rigid chains of polymer are grafted onto the flexible chains of NR, this characteristic molecular geometry gives grafted NR having high resistance to the outdoor environ- ment. However, grafted NR is poor in film-forming properties and processability. NRL possesses excel- lent film-forming properties and has been widely used in the manufacture of dipping products such as gloves, condoms, and catheters, but the hardness of this film is lower, and the tear strength of this film is comparatively poor. Lu et al. 11 incorporated methyl methacrylate grafted natural rubber latex Correspondence to: W. Arayapranee (wanvimon@rsu.ac.th). Contract grant sponsor: Rangsit Research Institute, Rangsit University. Journal of Applied Polymer Science, Vol. 109, 1395–1402 (2008) V V C 2008 Wiley Periodicals, Inc.