Beta phase crystallization and ferro/piezoelectric performances of melt-processed PVDF blends with PMMA copolymers containing ionizable moieties

Abstract

[EN] Poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) copolymer containing ionizable moieties is here investigated as a melt processing additive for PVDF to develop high-quality ferro/piezoelectric polymer films by extrusion-calendering. The PVDF/PMMA-co-MAA miscibility and the β-phase crystallization from the melt state at high cooling rates were first explored by Flash DSC. Transposition to the melt-processing of thin films by extrusion-calendering is attempted and a direct production of β-crystals in high amounts is attested at a specific content of 5 wt-% PMMA-co-MAA. Ferro/piezoelectric properties were subsequently investigated and classical ferroelectric-type hysteresis loops clearly appear at room temperature for AC electric fields higher than 900 – 1200 kV/cm. Enhanced remanent polarizations (P) are observed with only 5 wt-% PMMA-based additives and the best ferroelectric performances are identified for PVDF/PMMA-co-MAA blends, in agreement with a higher β-phase content. Stable piezoelectric properties are also highlighted with maximal piezoelectric coefficient (d) of 11 pC/N for these formulations. A linear relationship is found between d and P in accordance with several models and, in this respect, the origin/optimization of the remanent polarization was investigated. Crystal transformations are revealed during high-voltage AC poling and high-quality ferroelectric behaviors with high P values up to 7 µC/cm are obtained at elevated poling temperatures for PVDF/PMMA-co-MAA blends (theoretical d up to 16 pC/N) approaching the theoretical limit value for perfectly-poled β-crystals. This study clearly opens up interesting perspectives in the development of cost-effective electroactive polymer films using industrially-relevant processes and demonstrates that PVDF-based blends with miscible functional PMMA copolymers represent an interesting approach for this purpose.