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Epoxidized natural rubbers (ENRs) were prepared. ENRs with different concentrations of up to 20 wt % were used as modifiers for epoxy resin. The epoxy monomer was cured with nadic methyl anhydride as a hardener in the presence of N,Ndimethyl benzyl amine as an accelerator. The addition of ENR to an anhydride hardener/epoxy monomer mixture gave rise to the formation of a phase-separated structure consisting of rubber domains dispersed in the epoxy-rich phase. The particle size increased with increasing ENR content. The phase separation was investigated by scanning electron microscopy and dynamic mechanical analysis. The viscoelastic behavior of the liquid-rubber-modified epoxy resin was also evaluated with dynamic mechanical analysis. The storage moduli, loss moduli, and tan d values were determined for the blends of the epoxy resin with ENR. The effect of the addition of rubber on the glass-transition temperature of the epoxy matrix was followed. The thermal stability of the ENR-modified epoxy resin was studied with thermogravimetric analysis. Parameters such as the onset of degradation, maximum degradation temperature, and final degradation were not affected by the addition of ENR. The mechanical properties of the liquid-natural-rubber-modified epoxy resin were measured in terms of the fracture toughness and impact strength. The maximum impact strength and fracture toughness were observed with 10 wt % ENR modified epoxy blends. Various toughening mechanisms responsible for the enhancement in toughness of the diglycidyl ether of the bisphenol A/ENR blends were investigated. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39906.

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An attempt was made to toughen diglycidyl ether of bisphenol A (DGEBA) type epoxy resin with liquid natural rubber possessing hydroxyl functionality (HTLNR). Epon 250 epoxy monomer is cured using nadic methyl anhydride as hardener in presence of N, N dimethyl benzyl amine as accelerator. HTLNR of different concentrations up to 20 wt % is used as modifier for epoxy resin. The addition HTLNR to an anhydride hardener/epoxy monomer mixture has given rise to the formation of phase‐separated structure, consisting of small spherical liquid natural rubber particles bonded to the surrounding epoxy matrix. The particle size increased with increase in rubber content. The viscoelastic properties of the blends were analyzed using dynamic mechanical thermal analysis. The Tg corresponding to epoxy rich phase was evident from the dynamic mechanical spectrum, while the Tg of the rubber phase was overlapped by the β relaxation of epoxy phase. Glass transition of the epoxy phase decreased linearly as a function of the amount of rubber. The mechanical properties such as impact and fracture toughness were also carefully examined. The impact and fracture toughness increase with HTLNR content. A threefold increase in impact strength was observed with 15 wt % HTLNR/epoxy blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012