Morphometric Analysis of One-Component Polyurethane Foams Applicable in the Building Sector via X-ray Computed Microtomography

Abstract

A detailed morphometric analysis of one-component polyurethane (PU) expanding foams, with densities of 26 and 28 kg/m3 (‘SUMMER’ and ‘WINTER’ product versions), was conducted to evaluate the topology of the foam cells and to discover processing-to-structure relationships. The microstructural analysis of the heterogeneously distributed pores revealed tight relationships between the foam morphology and the cell topology, depending on the growth rate and local environmental conditions, governed by the properties of the blowing gas used. The most significant morphometric output included the following: open/closed porosity and (heterogeneous) pore distribution, relative density and (homogeneous) strut distribution, and total solid matrix surface and closed pore surface area—at the macroscopic level of the foam. While, at the microscopic level of the cells, the results embraced the following: the size of every detected strut and pore, identified two-dimensional (2D) shapes of the cell faces, and proposed three-dimensional (3D) topologies modelling the PU foam cells. The foam microstructure could be then related with macroscopic features, significant in building applications. Our protocol outlines the common procedures that are currently used for the sample preparation, X-ray scanning, 3D image reconstruction and dataset analysis in the frame of the X-ray computed microtomography (µ-CT) testing of the one-component PU foams, followed by a statistical (multiple Gaussian) analysis and conceptual considerations of the results in comparison with thematic literature.

Analytic Methods of Foamed Plastic Insulation Deteriorated by Moisture

“…Pore Distribution Measurement by X-ray CT: The pore distribution of the samples is measured by Blazejczyk's method [12] with X-ray CT. The difference from Blazejczyk's setup is that there is one connected scan per step, and the Otsu method is used in threshold processing.…”

X-ray Tomographic Reconstruction for Understanding Lignin-Induced Changes in the Microstructure and Properties of Polyurethane Insulation Foam

“…X-ray computed microtomography (X-ray μCT) imaging is an alternative non-destructive technique used to characterize foams, allowing precise 3D quantification of internal morphology such as the spatial parameters (cell porosity, cell volume, and cell orientationellipticity or anisotropy) and the skeletal parameters (cell strut and wall measurements and the volume of struts). − This technique has enabled monitoring structural changes in terms of cell parameters during mechanical property testing and modeling thermal properties of various types (metallic/non-metallic) of cellular materials. − X-ray μCT generates planar 2D X-ray images that are used to reconstruct 2D cross-sectional images of the entire object and its associated density map. These images can be loaded as a group and analyzed in 3D .…”

“…The use of X-ray μCT for RPUF does have technical challenges that complicate the process. For example, setting a joint resolution and field of view is capable of resolving thin cell walls (few micrometers) and large pores simultaneously . Furthermore, given that the scans are of very high resolution, strong computational demands and significant user expertise are required for post-processing the tomograms (reconstruction and quantification of microstructural parameters). , Nevertheless, X-ray μCT is an effective technique to study the effect of functional additives and polyols on the microstructure of RPUF.…”

“…In these studies, the quantification of the skeletal parameters (such as the volumetric strut fraction or thickness and lengths of cell walls and struts) has been challenging using 3D reconstructed images, given that it may result in inaccuracies or loss of data . In such cases, binary operations (2D) such as thresholding, erosion, and dilation are used to take apart the foam skeleton into struts and walls . Also, it is worth pointing out that it is often difficult to quantify cell walls, particularly when they are very thin due to resolution limitations of the machine, which resulted in a partial volume effect during acquisition. ,, Methodologically, a few studies have reported values for some of these parameters (strut volume and cell wall thickness); however, these values were not experimentally evaluated but theoretically estimated with the help of simple models. ,, Hence, it is worthwhile to use such methodologies for precise quantification of these microstructural parameters experimentally, for understanding the influence of lignin.…”

Characterization of Open-Cell Sponges via Magnetic Resonance and X-ray Tomography

“…Surfactants are often added to promote the nucleation of bubbles and pore cell stabilization, which are essential for the control of pore size and permeability within the foam [ 14 ]. During expansion, CO 2 gas distributes unevenly within the growing bubbles, causing an anisotropic expansion of cells [ 15 ], especially along the axis of expansion. This exothermic reaction leads to variability in pore size, even between sponges produced from the same batch, which results in inconsistent behaviour in these types of foams.…”