Enhanced dielectric properties of nanocomposites with cyanoethyl cellulose and core‐shell structured BaTiO₃@Al₂O₃ fillers

The interface between the polymer matrix and inorganic fillers plays a determinative role in dielectric properties of the composites. In this work, dielectric composites containing core‐shell structured BaTiO 3 @Al 2 O 3 (BT@AO) nanoparticles and cyano functionalized cellulose (cyanoethyl cellulose, CEC) were prepared to achieve enhanced interface and dielectric properties. With the wide bandgap Al 2 O 3 (AO) shell, the carrier motion inspired by elevating electric filed and temperature was significantly impeded in the composites. Meanwhile, the moderate dielectric constant and surface energy of AO shell between CEC and BaTiO 3 (BT) alleviated the inhomogeneous local electric field distribution and improve the interfacial compatibility between inorganic filler and CEC matrix. As a result, enhanced dielectric properties including restrained dielectric loss (0.23 for BT@AO/CEC versus 0.51 for BT/CEC at 100 Hz), suppressed conductivity, increased breakdown strength and improved dielectric constant were accessed in the BT@AO/CEC composites. The excellent thermal conductivity of AO also offered the composites with additional advantage of low electrical conductivity at high temperature of 100°C (1.56 × 10 −10 S/cm) exhibiting two orders of magnitude smaller than that of pure CEC. Highlights Core‐shell structured BaTiO 3 @Al 2 O 3 were prepared and incorporated into cyanoethylated cellulose to yield flexible nanocomposites. Carrier motion was significantly restricted by the wide band gap of Al 2 O 3 shell. Enhanced interfacial compatibility was accessed in the BaTiO 3 @Al 2 O 3 /CEC composite. Improved dielectric properties and thermal conductivity were achieved.