Influence of calcium copper titanate filled rubber ceramic composite

The devoted research of flexible dielectric polymer-ceramic composite has relied on the development and advancement of their applications which are notably related to the type of materials used. To achieve the flexible and good dielectric properties, rubber elastomer is mixed with ceramic materials to miniaturing an electronic device that are twistable, stretchable, and deformable. Significantly, calcium copper titanate (CCTO) was chosen as filler and the solid-state reaction method was used to synthesis CCTO (48 hours milling time). Meanwhile, natural elastomers such as natural rubber (NR), 25 mol % of epoxidized natural rubber (ENR-25/ E25), and 50 mol % of epoxidized natural rubber (ENR-50/ E50) were chosen as elastomer matrix because of their green materials and reliable flexibility properties. Thus, the fabrication of the six composites (NR, NR-C, E25, E25-C, E50 and E50-C) was prepared by melt-mixing method in an internal mixer at 60℃ and pressed using compression moulding at 160℃. The reason of remarkable compatibility, faster-curing response, and excellent properties (dielectric, mechanical and thermal properties) in ENR matrix was due to the presence of the polar group in the rubber chain. Even though E50-C recorded the highest dielectric constant, 357 at 0.1 Hz but E25 rubber showed the most stable dielectric constant over the broad frequency tested from 0.1 Hz to 20 MHz. In comparison, the addition of CCTO filler resulted in similar tensile strength in all rubber matrix. Still, the E25-C composite excellently showed a better tensile strength, 5.58 MPa, due to the homogenous distribution of CCTO powder in the rubber matrix as observed in the SEM image. The presence of CCTO also improved the thermal stability of the rubber matrix, notably E50. Above all, the elastomer material life cycle was determined by oxidation, and the oxidation rate could be controlled by the processing method and elastomer type. Therefore, the effects of the vulcanization system (conventional vulcanization: CV, semi-efficient vulcanization: SEV and efficient vulcanization: EV) were tested on the CCTO filled with ENR-50 rubber composite. In addition, the composite of the CV system showed better compatibility with CCTO filler, high dielectric constant (844 at 0.1 Hz) and elasticity up to 591% due to the polysulfidic bond that promotes the rubber network. However, the SEV system had the highest tensile strength (5.47 MPa) and hardness value (47.7) compared to the CV and EV system. The EV system network mainly built of monosulfidic crosslink, which slowed down the decomposition process. Still, the addition of CCTO filler has improved the thermal stability of SEV (375℃) instead promote the EV system (364℃). Therefore, considering all the related properties, the E25 rubber matrix and SEV system showed the most optimum properties. As a result, it can resolve the high temperature processing and brittleness of ceramic and low dielectric performance of elastomer.