Toughening mechanisms of nanoparticle-modified epoxy

1 Polymer, vol. 48, 2007, 530-541 Toughening mechanisms of nanoparticle-modified epoxy B.B. Johnsen, A.J. Kinloch, R.D. Mohammed, A.C. Taylor* Department of Mechanical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. S. Sprenger Nanoresins AG, Charlottenburger Strasse 9, 21502 Geesthacht, Germany ___________________________________________________________________________ Abstract An epoxy resin, cured with an anhydride, has been modified by the addition of silica nanoparticles. The particles were introduced via a sol-gel technique which gave a very well dispersed phase of nanosilica particles which were about 20 nm in diameter. Atomic force and electron microscopy showed that the nanoparticles were well dispersed throughout the epoxy matrix. The glass transition temperature was unchanged by the addition of the nanoparticles, but both the modulus and toughness were increased. The measured modulus was compared to theoretical models, and good agreement was found. The fracture energy increased from 100 J/m 2 for the unmodified epoxy to 460 J/m 2 for the epoxy with 13 vol% of nanosilica. The fracture surfaces were inspected using scanning electron and atomic force microscopy, and the results were compared to various toughening mechanisms proposed in the literature. The toughening mechanisms of crack pinning, crack deflection and immobilised polymer were discounted. The microscopy showed evidence of debonding of the nanoparticles and subsequent plastic void growth. A theoretical model of plastic void growth was used to confirm that this mechanism was indeed most likely to be responsible for the increased toughness that was observed due to the addition of the nanoparticles. * Corresponding author: Tel: +44 20 7594 7149, Fax: +44 20 7594 7017, email: [email protected]

Toughening mechanisms of nanoparticle-modified epoxy

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