Detailed investigation of the reinforcing effect of halloysite nanotubes-filled epoxidized natural rubber

The properties of rubber composite depend on the compatibility between rubber and filler. This is specifically of concern when preparing composites with very different polarities of the rubber matrix and the filler. Natural rubber (NR) and halloysite nanotubes (HNT) are one of the examples of the incompatible system. Epoxidized natural rubber (ENR) was used as the main matrix, with halloysite nanotubes (HNT) as a filler, in order to obtain composites with improved performance. ENR was prepared in house using performic acid with a controlled reaction time to obtain samples with mole epoxide levels from 10 to 40 mol%. Varying the mole epoxide levels was expected to optimize the formulation for this rubber composite. The compounds obtained were then investigated for the rubber–filler interactions of the ENR and HNT. By increasing the mole percentage of epoxide, the scorch and cure times were decreased while the maximum torque and torque differences increased. The ENR at 40 mol% epoxide exhibited least filler–filler interaction as shown from the Payne effect together with the supporting result from FTIR spectrum. However, this ENR compound did not yield the optimum tensile strength due to the constraint on the rubber–filler interaction. This study revealed that the use of ENR with a suitable mole percent of epoxide can dramatically reduce the filler–filler interaction and hence enhance the dispersion of HNT, which was seen from SEM micrographs, and resulted in enhancement of the mechanical and dynamical properties of the composites.