Z. Xia

Charge storage and transport in high density polyethylene and low density polyethylene

High density polyethylene (HDPE) and low density polyethylene (LDPE) are widely used as dielectrics and insulating materials. In this paper, the influence of heat treatment during and after corona charging on charge storage stability and the transportation of detrapping charges in the bulk of HDPE and LDPE were investigated by isothermal surface potential decay and open-circuit TSD analysis. The shifts of mean charge depth for the two kinds of PE at different charging temperature and environmental humidity were measured by heat pulse technique. Comparison of electret behaviors for the two kinds of PE was studied. The experimental results indicated that: (1) with increasing charging temperature and environment humidity, the mean charge depth for the two kinds of materials shifts toward the bulk from the free surface of the sample, especially in high temperature and humidity. (2) the charge storage stability can be improved significantly by heat treatment.

Study on healing effect of PTFE electrets on pig wound

Forty-eight second-degree wounds on the backs of three pigs, which were divided into 3 groups, were covered with vaseline-oiled gauze or /spl plusmn/700 V PTFE electret substrates. The effect on accelerating the wound healing was investigated by determining the content of DNA from an epithelial cell on the wound, observing the the growth of an epithelial cell with the microscope and calculating the reduction rate of wound area by using a computer. The results showed that electret treatment can enhance the growth of an epithelial cell and raise the content of DNA. An electret can accelerate the wound healing. The optimal equivalent surface potential for the PTFE electret film is about -700 V.

Preparation of porous PTFE/PE/PP composite electret and study of its charge storage stability

In this paper we introduced the preparing process and corona charging method of the porous PTFE/PE/PP composite electret film, and furthermore, studied its charge storage stability by using the method of isothermal surface potential decay measurement, open-circuit thermally stimulated discharge current spectra. It was shown that 1) charge storage stability for negative porous PTFE/PE/PP composite electret corona charged at high temperature was almost the same as that of porous PTFE electret charged at room temperature. 2) The charge storage stability of porous PTFE/PE/PP electret was closely related to the structure of porous PTFE and charging condition. 3) Porous PTFE/PE/PP electret exhibited higher charge storage stability than porous PTFE electret under high humidity.

Effect of electret on surface charge of red blood cell in scalded rats

The electrophoretic mobility (EPM) and contents of sialic acid (SA) on the red blood cell (RBC) were determined by means of cell electrophoresis and SA micro-chemical calorimetry to explore the mechanism of effect electret on surface charge of RBC in scalded rats. The results indicated that (1) EPM and SA contents of RBC in each period after rat scalded were decreased significantly as compared with those of in control group. (2) In negative electret group, EPM and SA contents were increased markedly with time. (3) Positive electret showed no notable effect on EPM and SA contents of RBC after rats were scalded. Negative electret can improve the microcirculation and hematological rheology index of scalded rats by stabilizing the SA contents of RBC to repair the electret state of RBC in scalded rats.

Piezoelectric activity in cross-linked polypropylene films stretched at elevated temperature

The charging capability and Youngs modulus of XPP films can be modified by a hot-stretching process. The results show that the onset of piezoelectricity occurs at an elongation ratio of 70% and enhances with the increase of this ratio. A quasistatic piezoelectric d33-coefficient of 308pC/N is achieved for samples with an elongation ratio of 200% and a Youngs modulus of 0.54MPa. An improved piezoelectric d33-coefficient is obtained for samples with a rough surface exposed to the corona during charging.

Investigation into polarization and piezoelectricity in polymer films with artificial void structure

Fluorocarbon polymer films with regular void structure are prepared by using a patterning-fusion bonding process. The critical voltage necessary for the build-up of the “macro-dipoles” in the inner voids observed in the experiments agrees well with the calculated value. The fabricated films show improved thermal stability of the d 33 coefficients.

Piezoelectric polytetrafluoroethylene films with void structure

Polytetrafluoroethylene (PTFE) films with a void structure are prepared by the sintering process. Such void PTFE films are piezoelectric after proper corona charging. The quasi-static piezoelectric d33 coefficients up to 250 pC/N are obtained. Pre-ageing treatment is an effective method to further improve the thermal stability. For the samples with pre-ageing treatment, the the d33 coefficients are very stable when exposed to 120°C. The values of d33 are slightly applied pressure dependent in the range of 50kPa.

Piezoelectric activity of irradiation cross-linked polypropylene films with cellular structure

So far, linear polypropylene (PP) foam is the most extensively investigated ferroelectret. In the present studies, cross-linked PP (XPP) foam sheets are modified by a hot-press process, and then corona charged to be piezoelectric. Thereafter their piezoelectric activities are investigated.

Preparation and piezoelectret properties of laminated fluoropolymer films made of porous polytetrafluoroethylene and non-porous fluoroethylenepropylene

In the present study, an improved process for preparing thermally stable laminated sandwiches of non-porous fluoroethylenepropylene (FEP) and porous polytetrafluoroethylene (PTFE) films is described. Also, the thermal stability of the d33-coefficients for such fluorocarbon films is discussed.

In vivo study of percutaneous absorption of lidocaine using electret in the rat

The present work was undertaken to study the effect of electret on transdermal drug delivery in vivo. The experiment was carried out in depilated abdominal rat skin using lidocaine hydrochloride as a model compound. Rats were divided into control and electret group. The electrets were applied on the drug in a vial and the blood samples were taken from jugular vein at predetermined time intervals. The concentration of lidocaine in plasma was measured by high proficiency liquid chromatograph (HPLC) after extraction. The plasma lidocaine concentration was significantly increased in electret group. The results suggested that electret could promote the permeability of drug by its effect on the structure of epidermis and blood flow change.