Polytetrafluoroethylene Films in Rigid Polyurethane Foams' Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor.

Ilze Beverte,Ugis Cabulis,Sergejs Gaidukovs

doi:10.3390/polym13071173

Ilze Beverte, Ugis Cabulis + Show 1 more

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https://doi.org/10.3390/polym13071173

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Abstract

As a non-metallic composite material, widely applied in industry, rigid polyurethane (PUR) foams require knowledge of their dielectric properties. In experimental determination of PUR foams’ dielectric properties protection of one-side capacitive sensor’s active area from adverse effects caused by the PUR foams’ test objects has to be ensured. In the given study, the impact of polytetrafluoroethylene (PTFE) films, thickness 0.20 mm and 0.04 mm, in covering or simulated coating the active area of one-side access capacitive sensor’ electrodes on the experimentally determined true dielectric permittivity spectra of rigid PUR foams is estimated. Penetration depth of the low frequency excitation field into PTFE and PUR foams is determined experimentally. Experiments are made in order to evaluate the difference between measurements on single PUR foams’ samples and on complex samples “PUR foams + PTFE film” with two calibration modes. A modification factor and a small modification criterion are defined and values of modifications are estimated in numerical calculations. Conclusions about possible practical applications of PTFE films in dielectric permittivity measurements of rigid PUR foams with one-side access capacitive sensor are made.

Highlights

Rigid polyurethane foams (PUR foams) exhibit a low dielectric interference, their permittivity is nearly non-dispersive a good dielectric performance can be ensured in a wide frequency range
It can be concluded that the average modifications caused by the PTFE film of thickness 0.20 mm are quite high in both cases: up to 10–14% and exceed ηlim = 3.5%
The impact of PTFE films, thickness 0.20 mm and 0.04 mm, in covering and simulated coating of the active area of one-side access (OSA) capacitive sensor’ electrodes on the true dielectric permittivity spectra of rigid petrochemical- and bio-origin PUR foams is estimated by means of

Summary

Introduction

Rigid polyurethane foams (PUR foams) exhibit a low dielectric interference, their permittivity is nearly non-dispersive a good dielectric performance can be ensured in a wide frequency range. As a non-metallic composite material, widely applied in industry, PUR foams require knowledge of their dielectric properties. Several values of dielectric permittivity (permittivity) are reported in an experimental investigation of rigid PUR foams with a capacitor at frequencies 100 Hz and 10 MHz according to ASTM D1673 [4]. 0.33 MHz for (1) petrochemically-rigid PUR foams, density 32–539 kg/m3 : 1.059 ≤ ε ≤. 2.067 and for (2) monolithic petrochemical-origin polyurethane, density 1280 kg/m3 : 3.47. To characterise the dielectric dispersion, the dropping factor was introduced and calculated for the investigated PUR foams of densities up to 400–450 kg/m3 as F ≤

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