Manufacturing and characterization of blended PVDF/PVDF-TrFE polymers: a study towards future sensor applications
Creators: Zongyu Wang
Publisher: name: University of Alberta Library
Year: 2022

<p>Poly (vinylidene fluoride) (PVDF) and its copolymers received increasing attention due to their electroactive properties and lower processing cost in comparison to the conventional piezoelectric ceramic materials, which are widely used in electronics, energy harvesting, biochemistry, and sensor areas. PVDF-Trifluoroethylene (PVDF-TrFE) is a copolymer of PVDF, and this copolymer presents superior piezoelectric response and good ferroelectric properties, but has considerably higher cost compared to PVDF. For many applications, it is desirable to find a blend of PVDF and PVDF-TrFE that presents an optimal combination of good properties and reasonable cost. This can be done by investigating the effects of using different weight ratios of PVDF/PVDF-TrFE and different thermal and electrical treatments on the mechanical and piezoelectric properties of the blended PVDF/PVDF-TrFE samples. <br>
Consequently, this study reports on manufacturing and characterization of blended PVDF/PVDF-TrFE using extrusion and spin-coating. Prepared specimens are analyzed without any further treatment and with post-manufacturing treatments (annealing, poling, poling heating, annealing poling, annealing poling heating) to study the effect of treatments on the properties. The weight ratio of PVDF-TrFE was set at 0, 10, 20, 30 and 100 wt.% to test the mechanical properties of the extruded PVDF/PVDF-TrFE filaments. As the electrical poling was not applicable for the long filament due to safety concerns, only annealing treatment was applied in the mechanical test. As the PVDF-TrFE content increased, the corresponding elastic modulus and ultimate tensile strength decreased, and the decline in elastic modulus followed the rule of mixtures. The annealing treatment was found to impose a negative effect on the elastic modulus and ultimate tensile strength, which might result from spherulite formation during this thermal treatment. An in-house built pendulum impact test set-up was created to investigate the<br><br>
piezoelectric response of the blended PVDF/PVDF-TrFE polymer using spin-coated samples.  The relationship between the electroactive semi-crystalized β-phase content and the output voltage was carried out studied by FT-IR characterization. The PVDF/PVDF-TrFE ratio of 70/30 and 80/20 rendered the highest and lowest averaged β-phase content, at 33.81% and 29.55 respectively, while the percentage for pure PVDF and PVDF-TrFE was 32.16% and 39.90% respectively. The enhancement of β-phase under treatments was found to be more effective in the pure PVDF and PVDF-TrFE, especially under the annealing and annealing poling heating. After blending with 10 to 30wt.% of PVDF-TrFE, PVDF generally witnessed a rise in the magnitude of the maximum output voltage during pendulum impact test. For a single sample, the highest magnitude of output voltage (1.76 V) was shown in one 90/10 sample under annealing poling, which was even higher than the maximum value (1.43 V) for pure PVDF-TrFE. The lowest electrical output level was found in 80/20, which was consistent with its low β-phase content. A sensitivity analysis identified that the pure PVDF-TrFE samples had the highest magnitude of sensitivity, which was attributed to the superior energy conversion efficiency of this material. 90/10 and pure PVDF samples presented better sensitivity than 70/30 and 80/20. The low chain mobility and presence of interfaces in 70/30 and 80/20 might have decreased the energy conversion. <br>
Overall, this study demonstrates the feasibility of blending PVDF and electroactive PVDF-TrFE as an enhancement towards electrical response to mechanical impact under specific thermal and electrical treatments. Blended PVDF/PVDF-TrFE provides a cost-saving possibility for the piezoelectric polymer applications.</p>