The aim of this study was to develop high dielectric constant flexible polymers with a highly efficient and cost-effective approach using acrylonitrile butadiene rubber (NBR) as the polymer matrix and barium titanate (BT) as the high dielectric constant filler. The BT powder was synthesized with a solid-state reaction and was characterized using a particle size analyzer, XRD, SEM and Fourier transform infrared spectroscopy. NBR/BT composites were fabricated using an internal mixer with various BT loadings up to 160 phr. The influence of BT loading on the cure characteristics and mechanical, dynamic mechanical, thermal, dielectric and morphological properties was determined. The incorporation of BT in the NBR matrix shortened scorch time and increased delta torque. The mechanical properties, thermal stability and dielectric constant were greatly improved and increased with BT loading. The results suggest that the reinforcement effect was achieved due to strong hydrogen bonding or polar-polar interactions between NBR matrix and BT filler. This is further corroborated by the good dispersion of BT filler in the NBR matrix observed with SEM imaging. These findings can be applied to produce high-performance dielectric elastomers.
A novel in situ rubber cure monitoring system (RCMS) has been developed for monitoring the progress of vulcanization based on the measurement of electrical properties. The sensors connected to an LCR meter were embedded in the compression mold and measured changes in the electrical properties of rubber during vulcanization. Frequencies ranging from 0.75 to 100 kHz were probed for capacitance and conductance, and 5 kHz frequency was found suitable for monitoring natural rubber vulcanization. The results show that capacitance during curing correlated with the time profile of torque from a moving die rheometer (MDR). The scorch time and optimum cure time obtained from MDR and RCMS were reported. The degree of cure and the cure rate from two methods were compared. Good correlations between the alternative methods were observed, supporting the potential of in situ RCMS during the vulcanization of natural rubber.
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