Preparation of zinc oxide/poly-ether-ether-ketone (PEEK) composites via the cold sintering process

Appropriate preparation routes allow designing and improving the performances of ceramic-based functional composites. In this work, two powder-preparation methods enabled by the cold sintering process are utilized to fabricate unique ZnO-based varistor composites. The thermoplastic polymer, poly-ether-ether-ketone (PEEK), has been successfully integrated with ZnO to form dense ZnO-PEEK composites. With a dissolution method, PEEK particles can be homogeneously dissolved by the mixed solution of tetrahydrofuran and toluene and then form nanoscale thin grain boundaries after cold sintering process. In the direct mixing method, large PEEK particles are observed in the cold sintered samples. A Finite Element Method (FEM) analysis indicates that von-mises stresses concentrate at the grain boundaries of ZnO and at the interfaces of ZnO and PEEK, and these can be increased with the increase of PEEK particle sizes. The electrical properties have been improved with the addition of PEEK, and the cold sintered 95ZnO-5PEEK shows a high breakdown electric field (0.1 mA/mm) of 3070 V/mm, and a nonlinear coefficient of 5. In addition, the conduction mechanism of the composites has been investigated using impedance spectroscopy. Overall, our work provides a strategy for the development of high-performance ceramic-polymer composites via cold sintering process.