Influence of corona charging in cellular polyethylene film

Abstract

Cellular polymers have recently attracted attention for their property of exhibiting a piezoelectric constant when they are electrically charged. The electrostatic charge generated in the voids by the internal discharges creates and internal macrodipole which is responsible for the piezoelectric effect. Charging by corona discharge is the most used method for cellular polymers. Many works has been published on polypropylene and polyethylene films mainly focused on the required expansion process or on the results obtained for raw cellular materials electrically activated. Our work is based on commercial polyethylene cellular films which have been physically characterized and electrically activated. The effect of thermal treatment, physical uniaxial or biaxial stretching and corona charging was investigated. The new method of corona charging improved the piezoelectric constant under other activation conditions.

Cellular Polymer Ferroelectret: A Review on Their Development and Their Piezoelectric Properties

“…38,50,53,61,62 PP has a dielectric nature, so the charges are retained at the cell walls after the discharge. 26 Recently, this knowledge was developed for cellular films made from polyethylene, 63 poly(ethylene terephthalate) (PET), 28 45,46,[68][69][70] as well as some cyclo-olefins polymers and copolymers. 25 It also has good stiffness as well as good charge trapping properties.…”

“…25 Single films are shown to have a good piezoelectric d 33 coefficient up to 1200 pC/N at low frequency. 63 Several models were introduced to predict the piezoelectric behavior of cellular polymers and these models can be found elsewhere. 15,53 Moreover, the response of both single layer and hybrid multilayer cellular PP films exhibits a linear relationship with the applied pressure (in direct piezoelectric mode) and also with the amplitude of the exciting voltage (in inverse piezoelectric mode).…”

Piezoelectric property improvement of polyethylene ferroelectrets using postprocessing thermal‐pressure treatment

“…A value of 935 pC/N was obtained for S2n‐6.4‐TPT1. To the best of our knowledge, this piezoelectric coefficient is very high compared to the literature available on polyethylene ferroelectrets (around 400 pC/N), and better than the best coefficients obtained for PP ferroelectrets (800 pC/N), which are the most developed ferroelectrets. The results are in agreement with the literature stating that the piezoelectric activity is inversely proportional to the cell AR .…”

“…In this technique, the films were charged 2 times by reversing their position (flip‐over) under the corona discharge. So a first corona discharge was applied for 60 seconds under the optimized conditions described in Section 3.1, and the exposed side to the corona discharge was metalized to neutralize surface charges and preserve internal charges . Then, the sample was placed upside down under the corona charging setup and charged again under the same conditions.…”

“…In this case, the internal electric field in the cells is reversed and added to the initial external applied electric field. This results on the modification of the gas breakdown dynamics inside the cells inducing stronger internal discharges and higher surface charge . The newly exposed side is then metalized, and the sample is removed for characterization.…”