Insight into Mechanical Properties and Strain-induced Crystallisation of Epoxidized Natural Rubber Filled with Various Silanized Halloysite Nanotubes

Natural rubber (NR) and halloysite nanotube (HNT) composites are known to perform poorly due to polarity differences between the two components. As such, many extant studies have attempted to increase their compatibility. Therefore, this study introduced epoxidized natural rubber (ENR) together with silane coupling agents into the composite to ensure rubber-filler interactions. Four different silanes namely bis-[(triethoxysilyl)propyl] disulphide (TESPD), bis[(triethoxysilyl)propyl] tetrasulfide (TESPT), triethoxyvinylsilane (VTEO), and 3-mercaptopropyl-di(tridecan-1-oxy-13-penta(ethyleneoxide)) ethoxysilane (VPSi-363) were used. Fourier-transform infrared (FTIR) spectroscopy of the composite confirmed the formation of hydrogen bonds between the silane as the peak of Si-O shifted to higher wavenumbers; i.e., 1080 cm^-1 to 1042 cm^-1. Silane was also found to improve the tensile strength, modulus and tear strength regardless of functionality. This was further supported by the findings of the Payne effect. As for strain-induced crystallisation (SIC), the stress-strain curves agreed well with the development of crystallinity observed during synchrotron wide-angle X-ray scattering analysis.

Keywords:
Epoxidized natural rubber; Halloysite nanotubes; Silane coupling agent; Mechanical properties; Wide-angle X-ray scattering