Melt Crystallization of Nanocomposites of Poly(Vinylidene Fluoride) with OMS
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0949-C03-05
Melt Crystallization of Nanocomposites of Poly(Vinylidene Fluoride) with OMS B. Seyhan Ince-Gunduz, Debeshu Amare, Robert Alpern, Peggy Cebe, Jennifer Crawford, Breanna Dolan, Stacey Jones, Ryan Kobylarz, and Matthew Reveley Tufts University, Medford, MA, 02155
ABSTRACT In our previous work [1] we investigated the impact of cold-crystallization on the structure of nanocomposites of PVDF with Lucentite STNTM OMS and observed the crossover composition in which the crystallographic beta phase dominated over alpha phase. Here, melt crystallization of PVDF/OMS nanocomposites was studied in the range of 0 to 1.0 wt% of OMS. In crystallization from melt, a decrease in crystallinity index occurs as a result of an increase in OMS. While beta phase fraction increased with an increase of OMS content in the range of interest, the amount of alpha crystals was found to be dominant even at high OMS compositions. At 1.0 wt% of OMS, beta crystals had reached at most 30% of the total crystallinity. Polarizing optical microscopy (POM) studies showed smaller, less birefringent spherulites with higher melting temperature compared to alpha spherulites appeared with OMS addition. Growth rate of these weakly birefringent spherulites is smaller than that of the strongly birefringent alpha spherulites. The increase in size and amount of the weakly birefringent spherulites with an increase of OMS and their higher melting point suggests these spherulites may be in the beta crystallographic phase.
INTRODUCTION Crystalline poly(vinylidene fluoride) shows strong piezoelectric properties in its oriented polar beta phase [2]. PVDF can have five different crystalline forms depending on the treatment. The most important polymorphs are alpha (orthorhombic unit cell and TGTG’ chain conformation [3,4]) and beta (pseudo-hexagonal unit cell and TTT chain conformation [5]) phases. The polar beta phase is usually obtained by electric field poling of the non-polar alpha phase PVDF films. Addition of organically modified silicates (OMS) to the PVDF results in beta crystal phase directly [6]. Previous study by our group on the cold crystallized nanocomposites of PVDF in a range 0.01 wt% to 20 wt% OMS showed that alpha and beta phase can co-exist at lower OMS content, but beta phase starts being dominant once the OMS content exceeds 0.025% [1]. The objective of this present work is to investigate the effect of clay on PVDF/OMS nanocomposites that have been melt-crystallized at 150ºC. In neat PVDF this treatment leads to alpha phase crystals. Static and real-time wide angle X-ray scattering (WAXS) and Fourier Transform infrared spectroscopy (FTir) were used to characterize the structure. Morphology information was obtained using POM, and thermal properties were studied using differential scanning calorimetry (DSC).
EXPERIMENTAL SECTION Kynar based PVDF material is obtained from Elf Autochem as grade 740, in pellet form. Lucentite STNTM, an organically modified layered silicate was obtained from Zen-Noh Unico, Americas, as fine powder. Nanocompos
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