Open Access

ARTICLE

Dielectric Permittivity of Rigid Rapeseed Oil Polyol Polyurethane Biofoams and Petrochemical Foams at Low Frequencies

Ilze Beverte^1,*, Vairis Shtrauss¹, Aldis Kalpinsh¹, Uldis Lomanovskis¹, Ugis Cabulis², Irina Sevastyanova², Sergejs Gaidukovs³

1 Institute for Mechanics of Materials, University of Latvia, Riga, LV-1006, Latvia
2 Latvian State Institute of Wood Chemistry, Riga, LV-1006, Latvia
3 Faculty of Materials Science and Applied Chemistry, Institute of Polymer Materials, Institute of Applied Chemistry, Riga Technical University, Riga, LV-048, Latvia

* Corresponding Author: Ilze Beverte. Email:

(This article belongs to this Special Issue: The 10th Conference on Green Chemistry and Nanotechnologies in Polymeric Materials (GCNPM 2019))

Journal of Renewable Materials 2020, 8(9), 1151-1170. https://doi.org/10.32604/jrm.2020.010215

Received 16 February 2020; Accepted 20 May 2020; Issue published 03 August 2020

Abstract

Early investigations of dielectric permittivity of rigid polyurethane foams at low frequencies were made on petrochemical-origin foams, mainly by means of parallel plate capacitors. In the present investigation biopolyol was synthesized from Latvia-grown rapeseeds’ oil by the transesterification method with triethanolamine, in an environmentally friendly process, without emission of harmful substances, at temperatures 175°C ± 5°C. Rigid, closed-cell rapeseed oil polyol polyurethane biofoams and petrochemical foams were made ensuring content of the renewable rapeseed oil polyol in ready foams 27 wt.%–29 wt.%. Dielectric permittivity of the polyurethane foams and the underlying monolithic petrochemical-origin polyurethane and biopolyurethane was measured with a non-destructive dielectric spectrometer equipped with a capacitive sensor of one-side access type at 16 discrete frequencies distributed geometrically over the band 10 Hz, … , 330 kHz. Permittivity value of the gaseous phase in the closed-cells was estimated to be ε_g ≈ 1.001 that corresponds to the values, characteristic for the most of gases. Dielectric permittivity of petrochemical polyurethane foams and the mentioned biofoams was compared with permittivity of polyurethane foams from industrial producers Sika JSC and General Plastics Manufacturing Co. Polyurethane foams of the developed formulation exhibit competitive, low dielectric permittivity, not exceeding that of the foams from industrial producers: petrochemical foams up to 550 kg/m³ and the mentioned biofoams, comprising the renewable rapeseed oil polyol, up to densities 230–250 kg/m³ . Considering petrochemical-origin polyurethane foams as a heterogeneous media “Polymer—gaseous phase”, the applicability of the rule of mixture and Maxwell–Garnett equation to model mathematically the dependence of effective dielectric permittivity on the volume fraction of phases was showed.

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