Dielectric and mechanical optimization properties of porous poly(ethylene-co-vinyl acetate) copolymer films for pseudo-piezoelectric effect

In this article, the authors present a porous copolymer film with pseudo-piezoelectric effects as a new candidate material for sensing applications. Porous films of poly(ethylene-co-vinyl acetate) (EVA) with a thicknesses ranging from 160 to 310 mu m are fabricated by a coextrusion chemical foaming process and charged using a high-voltage contact charging process. Output performances (piezoelectric constant and relative permittivity) with related thermal/mechanical stability are specifically studied as a function of the film porosity and of the electrical charging process. The piezoelectric constant d(33) increases with the cell porosity and an interesting piezoelectric constant close to 5.1 pC/N is achieved with a porous EVA film containing 65% of porosity. Actual results are then discussed using a theoretical solid-gas multilayer model to describe and predict the pseudo-piezoelectric effect of porous polymer materials. The originality of this work lies in the fact that all the steps leading to optimize pseudo piezoelectric films are included, and also in the use of EVA which is not a standard piezoelectric material. Therefore, this work is a contribution in the development of low-cost piezoelectric materials with potential applications as sensor in different fields such as medical, security, environment, sport, and transport. POLYM. ENG. SCI., 59:1455-1461 2019. (c) 2019 Society of Plastics Engineers