2.2 Preparation of epoxidized natural rubber
High ammonia (HA) latex with 60 wt% of dry rubber content was used to prepare ENR via an in situ performic epoxidation reaction [13]. The reaction between Cdouble bond; length as m-dashC of the NR molecule and performic acid, arising from a reaction between formic acid and hydrogen peroxide, was carried out in a continuously stirred reactor at a temperature of 40 °C, where alkylphenol ethoxylate non-ionic surfactant (Teric N30, Huntsman Corp., Australia) was used as a stabilizer [24] and [25]. The ENRs with 10, 38, and 51 mole% of epoxide groups were obtained when the reaction times were varied at 2, 10 and 12 h, respectively. The ENR latex was subsequently coagulated with methanol. The ENR coagulum was sheeted, washed thoroughly with water and dried in an oven at 50 °C for approximately 4 days. The reaction time of epoxidation was set according to the required level of epoxide groups in the ENR product. The 1H NMR spectroscopic technique was used to analyze the molecular structure of the ENR and the mole% of epoxide groups was calculated using Eq. (1):