Polymer Blends of Epoxy Resin and Epoxidized Natural Rubber S. Chuayjuljit, N. Soatthiyanon, P. Potiyaraj Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Received 3 August 2005; accepted 21 January 2006 DOI 10.1002/app.24193 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The aim of this research was to investigate the behaviors of epoxy resin blended with epoxidized nat- ural rubber (ENR). ENRs were prepared via in situ epoxida- tion method so that the obtained ENRs contained epoxide groups 25, 40, 50, 60, 70, and 80 mol %. The amounts of ENRs in the blends were 2, 5, 7, and 10 parts per hundred of epoxy resin (phr). From the results, it was found that the impact strength of epoxy resin can be improved by blending with ENRs. Tensile strength and Young’s modulus were found to be decreased with an increasing amount of epoxide groups in ENR and also with an increasing amount of ENR in the blends. Meanwhile, percent elongation at break slightly increased when ENR content was not over 5 phr. In addition, flexural strength and flexural modulus of the blends were mostly lower than the epoxy resin. Scanning electron microscope micrograph of fracture surface sug- gested that the toughening of epoxy resin was induced by the presence of ENR globular nodules attached to the epoxy matrix. TGA and DSC analysis revealed that thermal decom- position temperature and glass transition temperature of the samples were slightly different. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 452– 459, 2006 Key words: rubber; blends; resins; mechanical properties; thermal properties INTRODUCTION Epoxy resins are nowadays used extensively because of their excellent properties such as high modulus, low creep, and reasonable elevated temperature perfor- mance. However, they easily fail under impact be- cause of highly crosslinked structure. 1,2 As pure ma- terials, epoxies are brittle and have low fracture en- ergy, ranging from 80 to 200 J/m 2 . 3,4 Materials that have been added to epoxy solids to improve tough- ness include hard particulate materials such as inor- ganic glass particles, 4,5 as well as elastomers and ther- moplastics 6 such as hydroxyl terminated polybuta- diene, 7 carboxyl terminated butadiene acrylonitrile rubbers, 7–9 and PVC plastisols. 10 Numerous investi- gations have shown that the addition of such mate- rials can, if used correctly, result in substantial toughness improvements without significantly af- fecting any other important properties. As epoxies are viscous liquids, their handling and conforming is relatively easy. Therefore, the best combination would be the addition of a liquid rubber to the epoxy resin. Bussi and Ishida studied the mechanical properties of blends of diglycidyl ether of bisphenol-A based epoxy resin and hydroxyl terminated, internally ep- oxidized polybutadiene rubber. The epoxidized rub- ber was prereacted with an excess diepoxide to achieve better bonding between the rubber particles and the epoxy matrix phase. They observed that without rubber prereaction, almost no improvement in fracture tough- ness was achieved. From dynamic mechanical analysis studies, it was also found that the sample containing prereacted rubber exhibited even lower T g than did the sample containing the unmodified rubber. 11 Blends of unsaturated polyesters and functional rubbers such as hydroxy terminated polybutadiene, epoxidized natural rubber (ENR), hydroxy terminated natural rubber (NR), and maleated nitrile rubber were studied. It was reported that the elastomers bearing reactive functional groups show better compatibility with the resin and improve the toughness and impact resistance of the cured resin substantially, compared with unmodified elastomers. 12,13 The aim of this research was to improve tough- ness of the epoxy matrix resin by blending with ENR. ENRs used in this research were prepared from high ammonia concentrated NR latex via in situ epoxidization method with various amounts of hydrogen peroxide, formic acid, and a surfactant, as described by Chuayjuljit et al. 14 The effects of the ENRs on the mechanical and thermal properties were studied by using different rubber concentra- tions in the blends. Correspondence to: P. Potiyaraj (pranut.P@chula.ac.th). Journal of Applied Polymer Science, Vol. 102, 452– 459 (2006) © 2006 Wiley Periodicals, Inc.