Studies on the effect of the foams’ polymeric matrix’ properties on the tension and compression properties of pour rigid polyurethane (PUR) foams, apparent core density 65—70 kg/m³, at 296 and 77 K were carried out. PUR foams were produced by the hand mixing method from polyol systems that comprised polyether, polyester polyols, and chain extenders. To produce PUR foams, crude MDI was used, and Solkane 365 mfc/227 ea was used as a blowing agent. The molecular weight per branching unit (M_c) of the polymeric matrix of PUR foams was varied in the range 300—1150. Cohesion energy densities of the blocks forming the polymeric matrix were calculated. The effect of M_c on the formation of hydrogen bonds between the urethane groups was estimated from FTIR spectroscopy data and ratio NH_bonded /NH_free. It has been found that, with increasing polymeric matrix’ M_c, the tensile strength and elongation at break of PUR foams at 296 and 77 K increases, while Young’s modulus decreases. The increase in the parameter M_c promotes the decrease in the compressive strength and modulus of elasticity of PUR foams at 296 K, while compressive strength indices at 77 K are higher for the foams, whose polymeric matrix has the highest M_c. With increasing polymeric matrix’ M _c, the concentration of the urethane groups bonded with hydrogen bonds increases. Structural and mechanical properties of layered spray polyurethane foams, apparent core density approx. 48 kg/m³, having two layers and polymeric matrix’ M_c = 740 were investigated.

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 εg ≈ 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.

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.

Medium-density rigid polyurethane (PU) foams are often produced in sealed molds; therefore, the processes inside the mold and structure of the produced foam blocks need to be understood. The structural and mechanical anisotropy is shown to be the third variable along with (1) concentration of the nanoclay filler and (2) density, to determine the mechanical properties of the filled PU foam composites produced in a sealed mold. The varying anisotropy of the specimens hinders the accurate evaluation of the filling effect. The methodology for the estimation of the anisotropy characteristics of specimens from different locations within the nanoclay filled PU foam blocks is elaborated. A criterion, based on analysis of Poisson’s ratios, is formulated for the selection of specimens with similar anisotropy characteristics. The shear and bulk moduli are estimated theoretically, dependent on the filler’s concentration, using the experimentally determined constants.