Evaluation of shear piezoelectric coefficients by a bimorph cantilever technique for extruded and oriented poly(l‐lactide) films

Abstract Uniaxially stretched poly( l ‐lactide) (US‐PLA) films display shear piezoelectric properties of interests for smart applications. However, the measurement of these properties is quite challenging and a simple technique based on bimorph cantilevers is here used. This technique is validated with commercial piezoelectric poly(vinylidene fluoride) (PVDF) films. A piezoelectric coefficient d 31 close to 19 pm/V is then obtained with a precision close to 5% and a good accuracy to expected values. For US‐PLA films made by extrusion—machine‐direction orientation, shear piezoelectric coefficients d 14 up to 5.9 pm/V are found. Relevant trends can be captured but a low precision on d 14 , close to 10%, is highlighted. This behavior is probably related to film thickness heterogeneities arising from the extrusion processing at the laboratory scale. Piezoelectric voltage coefficients ( g 14 ) and electromechanical coupling coefficients could be also easily obtained with additional measurements of the dielectric permittivity and mechanical compliance. Outstanding g 14 coefficients up to 320 mV.m/N are confirmed for US‐PLA films with a precision close to 20%. The bimorph cantilever technique consequently represents a simple and reliable technique to evaluate piezoelectric properties of soft materials, in particular shear piezoelectric properties of US‐PLA films for future developments and optimizations at the pilot scale.