Study On Dielectric Energy Storage And Piezoelectric Actuators Of Polylactic Acid Films

Environment-friendly Polylactic acid(PLA)based materials are widely used in biodegradable packaging,bioengineering,and consumer electronics due to their biocompatibility and full degradability.The theses focus on the experimental analysis of the dielectric energy storage performance and piezoelectric actuator using the study of polylactic acid.High quality Poly-L-lactic acid(PLLA)and Poly-D-lactic acid(PDLA)dielectric films were prepared by solution casting and high temperature stretching process.The films showed good dielectric and piezoelectric properties in a wide temperature range.PLA polymer macromolecules have a 10/3 helical structure with C=O polar group bonds.It is difficult to form a large ferroelectric domain,showing the relaxor behavior of slim ferroelectric hysteresis loops.Covalently bonded with less free electrons,the film has greater dielectric breakdown strength.After stretching,there is only the orientation?phase in the film.The unstretched PDLA films exhibit an energy density of 6.5 J/cm³ and a charge-discharge efficiency of74%at an electric field 450 MV/m.After stretching,the stretched PDLA films show an energy density of 18.5 J/cm³ and a charge-discharge efficiency of 95%at 730 MV/m.In order to verify the thermal stability of the stretched PDLA,the density and efficiency of 11.2 J/cm³ and 76% can still be obtained at 620 MV/m after holding the material for 30 minutes at 100?.The chiral symmetric PLLA and PDLA are semi-crystalline polymers and base-centered orthorhombic lattice.When the force is applied to the film,all atoms are displaced,especially the plane rotation of COC and C=O bonds.The dipole C=O bond changes the polarity of the whole molecular chain,resulting in the piezoelectric properties of PLLA in the shear direction.At room temperature,the piezoelectric constant d₁₄ of PLLA and PDLA films are 10.7 p C/N and 9.6p C/N,respectively.The PLLA films exhibit a maximum piezoelectric constant of12.2 p C/N at 80?.According to the piezoelectricity of shear direction,the rotary actuator was designed,which was driven by high frequency and low voltage.the rotation speed of actuator was 186 rpm at a voltage of 65 V and 4.65 kHz.