Polytechnique Montreal, Canada
Nusrat Jahan has completed her MSc from Tuskegee University, USA and currently pursuing PhD in Ecole Polytechnique de Montreal, Canada. She has published 5 papers in journals and in a couple of proceedings.
Polyvinylidene fluoride (PVDF) has relatively high thermal stability (~120 °C) with moderate piezoelectric coefficient (d33~30pC/N) while cellular polymers such as polypropylene (PP) has higher d33 value (120-600 pC/N) with poor thermal stability (up to around 50 °C) which limited their applications in high temperature transduction. Therefore, a three-phase composite has been studied where organoclay has been added to enhance polar β phase and CaCO3 to introduce cellular structure in PVDF to get the advantage from both source of piezoelectricity with thermal stability. The samples were prepared by mixing PVDF, organically modified nanoclay (1-12 wt%) and CaCO3 (30-40 wt%) into a twin screw extruder and subsequent calendaring of films with thickness around 100 μm. FTIR result showed that although the supplied CaCO3 is not surface modified, still it results in around 30% of β phase in PVDF in absence of nanoclay and a gradual increase was observed in β phase with increasing amount of CaCO3 and this increment was further elevated by adding surface modified organoclay. Though various percentage of clay was used, 3 wt% of them seems to contribute maximum β phase (~55%) due to better dispersion and DSC as well as XRD confirmed the results further. Maximum 87% β phase was found in PVDF/40 wt% CaCO3/3 wt% nanoclay sample after stretching at a ratio (R=final length/initial length) of 4.5 at 90 °C. Seemingly, increased stretching ratio not only improved the β phase content but also created harmonious voided structure around CaCO3 particles in the sample. SEM on stretched film showed the presence of such lenses shaped voided structure inside the film.