Vulcanized natural rubber (NR) sheet was epoxidized in performic acid solution (6 moles of 30% H2O2 + 2 moles of formic acid) for 0-120 min under ambient conditions. Degree of epoxidation determined by ATR-IR increased with epoxidation time up to 60 min while at 120 min most of the epoxide rings of epoxidized NR (ENR) were opened up. Atomic Force Microscopy (AFM) was used to characterize surface properties of ENR. It indicated that both relative stiffness and roughness increased gradually as compared to control NR. Peel strength between ENR and chloroprene rubber (CR) increased up to 30 min of epoxidation time and then decreased. It was concluded that optimum peel strength was attributed to the balance between chemical interaction (epoxide groups on ENR with allyl chlorine groups on CR) and physical properties of ENR surface. (C) Koninklijke Brill NV, Leiden, 2012