Light Microscopy of Medium-Density Rigid Polyurethane Foams Filled with Nanoclay

Abstract

Practical applications and mathematical modelling of the physical and mechanical properties of medium-density rigid polyurethane foams require knowledge of their structure. It is necessary to determine structural characteristics without destroying the foams and measuring each element. A methodology is described for the use of light microscopy on environmentally sustainable, medium-density rigid polyurethane foams (in the density region of ≈210–230 kg/m3), by the analysis of two types of light microscopy images: (1) Cutting surface images; and (2) Through-cutting surface images. The dimensions of structural elements of polyurethane foams, filled with the nanoclay Cloisite-30B at concentrations of 0.0, 0.25, 0.50, 1.0, 2.0, 3.0, and 5.0% from the mass of the filled reacting mixture, are estimated. Probability density functions of projections of bubbles’ diameters and struts’ length are determined using images in three mutually perpendicular planes. A mathematical model is developed for the restoration of the actual dimensions of bubbles’ diameters using data of cutting circles’ diameters. Intercalation and exfoliation of the filler’s Cloisite-30B mono-layers is evaluated via the basal spacing by X-ray diffraction at a 5 wt.% concentration of nanoclay.

Characteristics of Components and Density of Rigid Nanoclay-Filled Medium-Density Polyurethane Foams Produced in a Sealed Mould

“…Volume reduction of the polymeric network can lead to reduced dimensions of the network elements (polymeric struts, nodes, walls, and un-foamed volumes). In addition, the nanoclay platelets act as nucleation sites of the gaseous bubbles, increasing the number of cells per unit volume and reducing size of structural elements [ 3 , 26 , 29 ], which can reduce PU foam stiffness and strength. The impact of the filling is determined by: (1) stiffening of the polymeric network due to being filled with nanoclay platelets; and (2) a reduction in the dimensions of the load-carrying elements.…”

“…Intercalation and exfoliation of the nanoclay Cloisite-30B monolayers was evaluated via the basal spacing by X-ray diffraction (XRD), at a 5 wt.% concentration of nanoclay (from the mass of NEOpolyol-380) in “Cloisite-30B/NEOpolyol-380” dispersions. The methodology of the XRD analysis is described in [ 25 , 26 ], which deal with the same nanoclay-filled NEOpolyol-380 PU foams.…”

“…The technological target was to keep the mass of the filled reacting mixture constant for all concentrations at m 0 = 250 g = const [ 25 , 26 ]. The mass m 0 was calculated to produce PU foams of a density exceeding the corresponding free-rise density by approximately 1.75 times.…”

“…When producing a filled PU foam block, the clay filler is dispersed and exfoliated in polyol, and the dispersion is then mixed with the other components of the formulation ( Table 1 ). The acquired liquid reacting mixture (LRM) of the polyurethane forming-substances (PFS) and the nanoclay filler is poured into a steel mould for foaming and the mould is sealed [ 3 , 25 , 26 , 27 ]. Let us estimate how the mass and volume of the monolithic polymer, and the gas in the cells and the filler change with an increase in the filler concentration.…”

“…In a sealed mould, at a high overpressure, nearly isotropic PU foams can be produced [ 3 , 25 , 26 ]. In [ 6 ], the mixed liquid composition of PU foams was poured into cylindrical moulds to produce foams with densities of 100 kg/m 3 … 400 kg/m 3 .…”