Post-processing Thermo-mechanical Treatment (PTT), using Sc-N2 applied to eye-like non-polar cellular structure polymer can increase the aspect ratio (AR) of the cells, which results in a higher piezoelectric electrotechnical d33 coefficient.
STAR POLY TECH Inc.
Physical foaming process through continuous extrusion!
Piezoelectric properties prediction using Dynamic Mechanical Analysis (DMA)!
Dynamic Mechanical Analysis can be used to predict the piezoelectric behavior of the eye-like cellular structures without the need to perform a complete and time-consuming morphological analysis such as SEM/image analysis. New parameter called AMR (anisotropic modulus ratio) can be used to quantify the film cellular structure.
In this method, new parameters called AMR1 and AMR2 are proposed for the ratios of E'(L)/E'(T) and E″(L)/E″(T), respectively. Samples having uniform cellular structures with higher cell aspect ratio (AR) have higher AMR1 and AMR2 values. The variation of AMR1 with frequency showed a more stable trend over a wide frequency range.
A more stretched eye-like cellular structure shows a higher AMR1. Increasing AMR1 results in a higher piezoelectric electrotechnical d33 coefficient
Corona Discharge parameters!
Corona Discharge is very sensitive process, which mostly depends on charging voltage, needle distance, atmosphere pressure, charging gas type, as well as film thickness. It is very important how to manage the parameters to get the maximum charging efficiency.
Maximum charging voltage increases with increasing needle distance. Furthermore, higher charging voltage can be achieved at higher N2 pressure. Nevertheless, shorter needle distance results in higher N2 pressure sensitivity. The difference between the charging voltage is more important at a needle distance of 2 cm than at 5 cm. Finally, more effective corona charging is possible at higher gas atmosphere pressure.
There is always an optimum Needle distance for any Corona Discharge system to get maximum charging voltage, which is depend on material type, material structure, material thickness.
Post-processing thermo-mechanical treatment to improve piezoelectric behaviour of Ferroelectret foam-PP film!
Change in crystalline areas & free volumes by applying post-processing thermo-mechanical treatment.
Supercritical fluids (SCF), as a result of their low viscosity and negligible surface tension, have very high mass transfer rates into polymers.
The diffusion of SC-N2 molecules into the film and between the polymer chains leads to a decrease in the crystalline areas (smaller areas). The crystalline areas of the original sample before TPT are shown with arrows.
During
stepwise thermo-mechanical treatment, as the two tips of the cells in
comparison with the other parts of the cells have more tendency to
propagate/stretch (because they have lower radius of curvature; stress
concentration points), N2 molecules accumulate more in those tips.
Hence, a higher driving force resulting from the accumulated N2 molecules
in both extremities resulted in more cells expansion/stretching in the
longitudinal (L) direction in comparison with the transverse (T) direction. By
its propagation, the tips radius are more decreased and their tendency to propagation
as well as accumulation of N2 molecules is further increased,
finally leading to a more stretched eye-like shape cell with a higher AR
value in comparison with the initial state.
Future with Ferroelectret Materials!
- Living space can unobtrusively determine where everyone is!
- A poster or projection screen on your wall can play music!
