Electret properties of polylactic acid – Montmorillonite composites

Abstract

The paper describes electret characteristics of polylactic acids and its composites with montomorillonite at different ratios of the components. Electret properties behavior patterns of both pure and composite polylactic acid films showed two regions – the region of the sharp charge drop and the region of its slight decrease. The sharp drop of the film charge results from a release of charge carriers from the small (surface) energy traps. Following this, the total charge value is determined by the number of injected charge carriers captured by the deeper energy traps. Corona electrets based on polylactic acid have poor electret properties due to significant impact of heterocharge. Addition of montmorillonite increased electret properties of the PLA – 2 % montmorillonite in the composition improved electret performances by 5–10 times, 4 % montmorillonite – by 10–18 times. This significant effect of the fine filler on the electret properties of the polylactic acid arises from high specific surface area of montmorillonite that results in large number of macromolecules being adsorbed on the surface of the nanoparticles. Homocharge relaxation rate reduction due to fine filled addition to the polylactic acid was shown not to be the result of changes in specific surface and volume resistivity of the material. ATR-IR spectroscopy revealed no considerable changes in the chemical structure of the surface of polylactic acid filled with nanoparticles. It was concluded that montomorillonite addition to polylactic acid increased electret properties due to generation of new injected charge carrier traps at a polymer-filler interface boundary. The addition of 4 % montmorillonite was the most efficient for enhancing electret properties of polylactic acid.