Preparation and characterization of vulcanized silicone rubber/halloysite nanotube nanocomposites: Effect of matrix hardness and HNT content

• Silicone rubber/halloysite nanotube (HNT) vulcanizate nanocomposites of different matrix hardness and HNTs were prepared.
• Cure characteristics, swelling behavior, dynamic mechanical, thermal and tensile properties of nanocomposites were studied.
• Accelerated curing process and higher effective torque was observed for nanocomposites compared with neat matrices.
• A significant increase in transition temperature of compounds was observed with HNT content.
• The elastic modulus, ultimate strength and thermal stability of the nanocomposites improved with HNT content.
• A structure-property correlation was established in rubber nanocomposites.

Halloysite nanotube (HNT) was successfully surface-treated. The grafted HNT was evaluated by TEM, FTIR and TGA. Modified HNT was used to prepare silicone rubber/HNT vulcanizate nanocomposites. The effects of silicone rubber hardness and HNT loading on the cure characteristics, swelling behavior, dynamic mechanical, thermal and mechanical properties of the resulting rubber compounds were systematically studied by rheometry, DMTA, TGA and tensile testing, respectively. The obtained results were correlated with the microstructure of the samples as investigated by XRD and SEM analyses. Vulcanization curves revealed that the HNT had a positive effect on the cure kinetics of the rubber compounds via steady decrease in scorch time and optimum cure time along with a gradual increase in effective torque with HNT content. The incorporation of HNT into the silicone rubbers enhanced the crosslink density of the nanocomposites. DMTA results showed restricted relaxation processes in HNT-reinforced systems compared with the unfilled silicone rubbers, with more pronounced effect for system with silicone rubber matrix of lowest hardness. The tensile data demonstrated a rise in Young's modulus and tensile strength of the filled rubbers with HNT content. The thermal stability of the rubber compounds gradually improved with HNT loading in the material according to TGA results.

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