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

Abstract

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.

Effect of residence time in the reactor on the reinforcement of biochar in rubber compounds

“…The specimens with biochar showed a decrease in tensile strength of about 3.0, 56.9 and 53.8% for the NR/BIO30min, NR/BIO60min and NR/BIO240min compounds respectively when compared to the unfilled specimen reinforcement (NR). This decrease in tensile strength is due to the change in the extension of the stretch crystallization process of natural rubber, 43 as the crystalline properties of the biochar, which change with increasing residence time in the reactor, reduce the flexibility of the chains. The higher the crystallinity (longer residence time) of the biochar, the lower is the tensile strength.…”

“…The higher the crystallinity (longer residence time) of the biochar, the lower is the tensile strength. 43 Fillers with different properties, such as crystal structure and texture, affect the interaction with the rubber by modifying crystallization through stretching; usually the addition of fillers slows down this process. 43 For fillers with high structure, such as carbon black and BIO30min, which have a turbostratic structure, the crystallites tend to have the same size, making the tensile strength close to these compounds, provided that the particle size is the same.…”

“…43 Fillers with different properties, such as crystal structure and texture, affect the interaction with the rubber by modifying crystallization through stretching; usually the addition of fillers slows down this process. 43 For fillers with high structure, such as carbon black and BIO30min, which have a turbostratic structure, the crystallites tend to have the same size, making the tensile strength close to these compounds, provided that the particle size is the same. [44][45][46] Since the particle size is different between carbon black and BI-O30min, BIO30min has a larger particle size relative to the specific surface area, and the tensile strength of the mixture NR/BIO30min was lower.…”

Viable Properties of Natural Rubber/Halloysite Nanotubes Composites Affected by Various Silanes

“…One of the methods has been the addition of a compatibilizer or coupling agent. There have been many types of compatibilizers and/or coupling agents used for NR/HNT composites [ 13 , 14 , 15 ]. Over the years, silane coupling agents have been extensively used and studied.…”

“…Many types of silane have been grafted onto HNT when preparing polymer composites. Masa and Hayeemasae [ 14 ] used various types of silane in the ENR/HNT composites. It was reported that sulfur-based silane had given optimum properties.…”