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

## Abstract

**:**

^{3}(‘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.

## 1. Introduction

^{®}open cell foams (from ERG Aerospace, Oakland, CA, USA), in the case of non-granular foams [41,42,43,44,45,46].

## 2. Materials and Methods

#### 2.1. Investigated Material

- liquid prepolymer functionalized with isocyanate groups (pre-reacted from a mixture of polyol and polyisocyanate),
- additives (flame retarder and chemical stabilizer of prepolymer),
- physical blowing agents (mixture of dispersed and partially dissolved in prepolymer compressed-liquefied inert gases),
- vapours of gas mixture in an ‘empty’ part of the can (remaining in thermodynamic equilibrium at the gas–liquid interphase, under pressure of 2–4 bars).

#### 2.2. Sample Preparation

^{3}). The measured density resulted somewhat higher than what was declared by the manufacturer—as a result of the constraints imposed on making each PU panel, which grew in the casting mold that was closed with a cover, which caused a slightly increased pressure (relative to atmospheric) during such hindered expansion. Moreover, the breakage of pores occurs at the surface when the cutting and shaping the samples into the cylinder form (caused by using a precise stainless-steel tool). This effect does not change the sample mass but it may slightly reduce the volume, so the density (measured as mass to true sample volume ratio) increases.

#### 2.3. Experimental Setup

#### 2.4. Scanning Procedure

#### 2.5. The 3D Image Reconstruction from the Scans

#### 2.6. Automated 3D Image Analysis

## 3. Results

#### 3.1. The CTAn Output and Statistical Analysis

#### 3.1.1. Parameters and Relations

_{r}= ρ/ρ

_{s}= (m

_{b}/V

_{b})/(m

_{s}/V

_{s}) ≈ V

_{s}/V = Obj.V/TV

_{r}

_{b}and V

_{b}are the sample bulk mass and volume, respectively, m

_{s}and vs. are the solid matrix (no gas) mass and volume, respectively, ρ is the foam bulk (both solid and gas state) density, ρ

_{s}is the matrix density (only solid state), and ρ

_{r}is the foam relative density (contribution of the solid matrix to the sample volume) [31].

_{r}, add up to unity. Moreover, the Obj.V/TV ratio has the physical sense of relative density, ρ

_{r}, which is a measure of the solid matrix contribution to the total sample volume. As seen from Table 8, the ρ

_{r}≈ Obj.V/TV parameter results were higher for W-foam, so, as expected, the more volume content of solid matrix Obj.V, the more volume of the closed pores Po.V(cl), and the higher their surface Po.S(cl).

#### 3.1.2. Pore Distribution

_{total}is the total number of pores in VOI, N(d

_{i}) is a number of pores of a given size d

_{i}, and V(d

_{i}) is the volume of the pore population, indexed by i = I, II, ..., and so on.

_{total}of the pores of a given diameter (d) to the total VOI space, either for the W- or S-foam. The explicit maximum of the fitted solid line (distribution mode) results for both were 0.155 ± 5 mm and reached 3.8% for the W-foam and 2.9% for the S-foam. Its position could be compared with the mean pore size values −0.271 mm and 0.418 mm (‘structure separation’ in Table 8). The distribution spread, standard deviation (SD), is 0.182 mm and 0.398 mm for the W- and S-foam, respectively.

_{i}, d

_{i}, and w

_{i}—denoting the distribution peak area, peak center, and its width, are shown in Figure 4, with their resulted values. For the W-foam, j = III, and for the S-foam, j = IV.

_{total}function slope change in Figure 3, which is due to the existing relation, derived from Equation (8), as follows:

_{total}/6V

_{total})—so that each new apparent gradient on the numerical distribution function indicates on a new possible Gaussian peak in the volumetric distribution at the corresponding pore size interval.

#### 3.1.3. Strut Distribution

_{total}of the struts of a given diameter, d, to the total matrix volume (Obj.V), either for the W- or S-foam. Each distribution is slightly skewed right, with a longer right tail, left-modal, yet, it could be well approximated by standard normal distribution.

#### 3.2. The Structural 3D Visualization

## 4. Discussion

#### 4.1. Pore Distribution

- The K foam cell topology bases on the 6-0-8 14-hedron, including six quadrilaterals (no pentagons) and eight hexagons, which often might rearrange into the Williams cell—2-8-4 14-hedron (W). The energetic ‘cost’ [71] of constructing a single K cell, related to its surface free energy, is lower than W (S·V
^{−2/3}= 5.336 dimensionless), yet, at least equals 5.315 or more (depending on cell anisotropy and surface tension). - The M foam unit cell topology bases on the most abundant 1-10-2 13-hedron or on the much less frequent 1-10-3 or 3-7-3-1 14-hedra, including at least one quadrilateral and even one heptagonal face. The ‘cost’ of the M cells starts from 5.314 (1-10-2), which is better than the K cell.
- The W–P foam duplex unit cell is combined from the eight building blocks of the two topologies, the irregular 0-12-0 dodecahedron and the 0-12-2 tetrakaidecahedron, including 12 penta- and 2 hexagonal faces. The ‘cost’ of constructing the W–P duplex space tiling is ca. 5.288, which is much better than the others, yet, the ‘cost’ may still drop down to the minimum of 5.256 for 0-12-0.

- The first two Gaussian peaks (I and II) extracted from the volumetric distribution (Figure 4) could be interpreted as originating from the pore population of the irregular pentagonal 12-hedra and of the W-P 14-hedra, respectively. The modal values of the two dominating effective fitted distributions are the same (0.155 mm), which indicates on the smallest pore populations formation as dependent on the material features (polymer chains structure and interaction, prepolymer viscosity and surface tension in cells) rather than the blowing gas physical properties.
- The third Gaussian peak (III) extracted from the volumetric distribution could be interpreted as originating from the disordered clustered combinations of the M type pore cells. As seen from Table 8 (structure separation), the W-foam reveals effectively smaller mean pore size (0.27 mm) than that of the S-foam (0.42 mm). This effect is due to relative expansion of the third and appearance of the fourth pore distribution component (Figure 4).
- While the third pore population formation seems to be still dependent on the PU material features, the fourth pore (IV) population depends rather on the blowing gas properties. The highest impact on the effect may have the saturated vapour pressure (SVP), which, according to the Antoine equation, is correlated with boiling point temperature (BP). As seen from Table 2, the lower the BP (at constant pressure), the higher the SVP (at constant temperature), and the higher the fugacity of the volatile gas. As can be seen, the only qualitative difference between the S- and W-foam is presence of the fourth component in the blowing gas mixture. The SVP (840 kPa) of propane is considerably higher than that of the 1,1-difluoroethane (516 kPa). Due to the highest fugacity, propane is the most volatile gas in the mixture. By replacing the 1,1-difluoroethane with propane, the effective pressure in expanding bubbles of the S-foam could considerably increase. In order to estimate the maximum difference between the S- and W-foam initial pressures in bubbles, one may assume the extreme compositions in the range given by the manufacturer (1–10%)—as shown in Table 9. The pressure, which initializes a single bubble growth, can be assessed by assuming equal chance diffusing and vaporing of the uniformly dispersed gas molecules into the bubble. So, the quantitative composition of the gas mixture in the bubble tends to the same as in the whole can. Thus, the total effective pressure of gas mixture in bubble p
_{total}(maximum after initial rise) could be estimated, as the weighted average of the saturated vapour pressures, from the following:$${p}_{\mathrm{total}}={{\displaystyle \sum}}_{\mathrm{i}=1\text{}}^{\mathrm{j}}\frac{{n}_{\mathrm{i}}}{{n}_{\mathrm{total}}}{P}_{\mathrm{i}}={{\displaystyle \sum}}_{\mathrm{i}=1}^{\mathrm{j}}{x}_{\mathrm{i}}\frac{{M}_{\mathrm{total}}}{{M}_{\mathrm{i}}}\text{}{P}_{\mathrm{i}\text{}}$$_{i}is the number of moles of the ith gas component, n_{total}is the total number of moles of gas mixture, P_{i}is the saturated vapour pressure of the ith component (Table 2), x_{i}is the mass fraction of the ith gas component, M_{i}is the molar mass of the ith gas component (Table 2), M_{total}is the molar mass of the W- or S-foam gas mixture, and j = 3 or 4 for the W- and S-foam, respectively.

#### 4.2. Strut Distribution

#### 4.3. Other Structural Traits

## 5. Conclusions

- The foams’ microstructure at the microscopic level of cell in terms of the following:
- ○
- the mean pore size (measured with 6.25 µm resolution).
- ○
- the way of cell-to-cell linking (by a given type of interfacing window, pentagonal, hexagonal, etc.).
- ○
- the pore morphology (manifested through various cell forms and window shapes)

- The foams’ structure at the macroscopic level of foam in terms of the following:
- ○
- open and closed porosity.
- ○
- matrix volume and relative density.
- ○
- matrix surface and total closed pore area.
- ○
- tighter pore size distribution (yet, the effect of the blowing gas could not be visualized by comparing strut size distributions, since the broken struts might be immediately absorbed by their closest nodes during foam expansion).

- Detecting the inter-cell macro-pores, as follows:
- ○
- the ‘real’ (only above ca. 6 µm), due to adaptive geometry and resolution limits of X-ray microtomographic system used.
- ○
- the ‘over capillary’ (up to ca. 2000 µm).
- ○
- mostly open pores (open porosity ca. 90% in both the W- and S-foam),
- ○
- some closed pores (ca. 5000 and 2400).

- Assessing the homogeneity of the pore and strut distributions, with the following conclusions:
- ○
- Both the W- and S-foam appeared heterogeneously porous, in terms of the diversity found in the cell and window morphology.
- ○
- Several different 3D forms (basic building blocks topologies) could be assigned to the polydisperse cells—irregular dodecahedra (0-12-0), Weaire–Phelan duplex (with two 0-12-0 and six 0-12-2 tetrakaidecahedra per unit cell), Matzke cells (mostly 1-10-2 and negligibly 1-10-3 and 3-7-3-1 14-hedra), and large anisotropic blisters.
- ○
- The strut population also resulted in being polydisperse, but seemingly of a homogeneous morphology (no reason was found to reject the independence of the strut 3D form from any blowing gas).

- Finding the processing-to-structure relationship for the PU expanding foam, as follows:
- ○
- The relation was found through detecting the morphometric differences between the W- and S-foam, which appeared on macro- and micro-scopic levels.
- ○
- The effect of processing on the structure could be explained by highlighting the impact of the interior vapour pressure of the blowing gas mixture (diffused into the growing bubbles) on the initial foam formation. The higher the pressure, the larger sized and the more topologically diversified the cells.
- ○
- The environment surrounding the expanding cells (prepolymer) impact is related to viscosity change dynamics and the foam hardening rate. This effect is to be further examined.

- Visualizing the apparent difference in the 3D structures.

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**(

**a**) Preparation of the sample for X-ray computed microtomography (µ-CT) measurement from the polyurethane (PU) panel: foam growth along the x-axis, cutting a cuboidal, and further forming the cylindrical sample. The sample rotation in the µ-CT scanner is shown around the z-axis—parallel to vector q and perpendicular to the scanner holder in xy-plane. In this figure, the sample to panel size ratio is kept the same as the original; (

**b**) The enlarged WINTER (W)/SUMMER (S) foam samples are shown over the xz-plane.

**Figure 2.**The example of horizontal (xy-plane) two-dimensional (2D) cross-sectional quarters of the reconstructed 3D cross-sectional image stacks, representing the PU W- and S-foam (BMP not resized, image pixel size 6.25 µm). The 2D cross-sections are the last 3D stack sections, numbers 2100 and 5420, respectively. The white pixels in the reign of interest (ROI) represent the PU foam struts, the dark grey pixels—void space and the black—background. The symbol ‘IV’ denotes the population of largest pores, visible examples (cross-section) even with the naked eye in this image.

**Figure 3.**The number distribution of the pore size for both the W- and S-foam. The number contribution N(d)/N

_{total}of the pores of a given size to the total pore number in volume of interest (VOI) (BMP not resized, image pixel size 6.25 µm), shown as a function of the pore diameter, d, and plotted in the half-logarithmic scale. The inset plotted in the linear scale is to enlarge the highlighted 0–200 microns range. The solid lines, numbers I, II, III, and IV are guiding the eye along the apparent straight intervals of a gradually variable slope. The shapes of the cell faces in the growing pores (5-, 6-, 4-, and 7-sided, with the last n-sided polygon, where 7 < n < 20) are assigned to the corresponding intervals (I–IV), also given their frequency of appearance in the expanding PU foams (see discussion).

**Figure 4.**The volumetric pore size distribution for both the W- and S-foam. The volume contribution V(d)/V

_{total}of the pores of a given size to the VOI (BMP not resized, image pixel size 6.25 µm). Each bar graph shows the apparent pore size distribution, the overlaid thick solid line represents the sum of the overlapped peak-components (I–IV), and the dashed lines represent the distributions separated by Gaussian analysis.

**Figure 5.**The volumetric strut (thickness) distribution for both the W- and S-foam (BMP not resized, image pixel size 6.25 µm).

**Figure 6.**The S- and W-foams 3D realistic visualization screens (image pixel size 25 µm)—mapping the pore system (left) and matrix skeletal frame (right). The scales assign colors to the given pore size and strut thickness. The red arrows point corresponding regions on the pore map and the strut map; they are also to show visible difference in pore size comparing the W- with S-foam (SUMMER/WINTER).

**Figure 7.**The PU foam microstructure, a cutout from the reconstructed W-foam sample (µ-CT resolution 6.25 µm). The cell faces are labeled with numbers of their edges. The greyscale corresponds to strut thickness.

**Table 1.**Classification of pores or cells in solids and examples of detection techniques that can resolve given pore size range or topological state.

Pore Type | Detection Techniques |
---|---|

1. Based on size (by IUPAC) | |

● Micro-pores (d < 2.0 nm): | Scanning tunneling microscopy (STM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), gas adsorption (GA)-α_{s}-plot |

○ Ultra-micro-pore (d < 0.7 nm) | |

○ Super-micro-pore (d > 0.7 nm) | |

● Meso-pore (d < 50 nm) | Atomic force microscopy (AFM), GA-Barrett-Joyner-Halenda method (GA-BJH), nano-CT |

● Macro-pores (d > 50 nm): | Scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), GA-Density-Functional-Theory method (GA-DFT), polarizing optical microscopy (POM), magnetic resonance imaging (MRI), X-ray computed microtomography (µ-CT) |

○ Sub-macro-pore (d < 1 µm) | |

○ Real macro-pore (d < 100 µm) | |

○ Over capillary (d >1 00 µm) | |

2. Based on topology | |

● Three-dimensional (3D) geometry | |

○ Oval (spherical, anisotropic, channeled) | µ-CT |

○ Irregular polyhedron (with polygonal faces) | SEM, TEM |

○ Cellular blister (unshaped) | Confocal Microscopy particularly laser confocal scanning microscopy (LCSM) |

○ Blowhole (at exterior surface) | |

● Openness/closedness | |

○ Open pore (transitive) | Gas Pycnometry |

○ Mixed pore (dead-ended) | Gas Adsorption |

○ Closed pore (latent) | SAXS |

3. Based on the foam cells strength | |

○ Rigid (hard) | Stress–strain tensometry |

○ Flexible (soft) | |

4. Based on the origin of formation | |

● Intra-particle pores | |

○ Intrinsic intra-particle pores | |

○ Extrinsic intra-particle pores | |

● Inter-particle pores | |

● Intra-/inter-grain pores | |

● Intra-/inter-cell pores |

**Table 2.**Gas mixture chemical composition and physical properties of the components. S—SUMMER; W—WINTER.

i | W-Foam | S-Foam | Percent Mass x_{i} (%) | Molar Mass M_{i} (g/mol) | Boiling Point (BP) at 1 atm T_{i} (°C) | Saturated Vapor Pressure (SVP) at 20 °C P_{i} (kPa) |
---|---|---|---|---|---|---|

1 | propane | propane | 1–10 | 44.10 | −42.1 | 840 |

2 | dimethyl ether | dimethyl ether | 1–10 | 46.07 | −23.6 | 510 |

3 | isobutane | isobutane | 1–10 | 58.12 | −12.0 | 304 |

4 | 1,1-difluoroethane | - | 1–10 | 66.05 | −24.7 | 516 |

Parameter (Unit) | Value | |
---|---|---|

W-Foam | S-Foam | |

Panel form in thermal conductivity measurement | cuboid | cuboid |

Physical panel dimensions (width; length; height) (mm) | 600; 600; 20 | 600; 600; 20 |

Sample form in X-ray µ-CT measurement | cylinder | cylinder |

Physical sample dimensions (diameter; height) (mm) | 20; 20 | 20; 20 |

Bulk density of the hardened foam (declared by the manufacturer)—ρ_{D} (kg/m^{3}) | 24 ± 1 | 22 ± 1 |

Bulk density of the hardened foam (measured for the sample)—ρ (kg/m^{3}) | 28 ± 2 | 26 ± 2 |

Scanner Name | SkyScan 1172 |
---|---|

Source: | |

- Micro Focus X-ray tube type | L7902-20, sealed, air-cooled, Hamamatsu Photonics K.K., Hamamatsu, Japan |

- tube current range (µA) | 0–250 |

- tube voltage operational range (kV) | 20–100 |

- X-ray focal spot size (µm) | <5 |

Detector: | |

- X-ray super high transmission (SHT) tube window type | MH110XC-KK-FA, Ximea, Münster, Germany |

- detector filters (Al or Al/Cu) (mm) | 1 or 0.5/0.040 |

- camera | 12-bit CCD cooled |

- scintillator | fiber-optically coupled |

- matrix | 11Mp (4000 × 2664 pixels) |

- detectability (µm) | 0.45 (at max resolution) |

- image pixel range (µm) | 1–25 |

Sample max size (mm): | |

- standard scan | 25 |

- camera offset on | 50 |

- oversized mode on | taller than 25 |

Parameter (Unit) | Value |
---|---|

W-Foam/S-Foam | |

X-ray source voltage applied (kV) | 33 |

X-ray source resulting current (µA) | 204 |

X-ray detector binning | 1 × 1 |

Number of rows on camera matrix | 2664 |

Number of columns on camera matrix | 4000 |

Number of lines on camera matrix (random movement amplitude) | 40 |

Detector filter | not activated |

Flat field correction | activated |

Geometrical correction | activated |

Median filtering | activated |

Camera offset mode | not activated |

Number of connected scans per step (oversized scanning mode) | 3 |

Rotation range (deg) | 0–195 |

Rotational step (deg) | 0.2 |

Rotation sections count (total number of scans) | 2925 |

Number of frames averaged per step | 4 |

Exposure time (ms) | 1680 |

Scanned sample image pixel (square) size (µm) | 6.25 |

Output files type | 16-bit TIFF |

Parameter (Unit) | Value |
---|---|

W-Foam/S-Foam | |

Smoothing | 0 |

Misalignment compensation (post-alignment) | −2.0 |

Ring artifact reduction | 1 |

Beam-hardening correction (%) | 10 |

First section nr (above glue layer) | 330/3650 |

Last section nr (about sample mid-height) | 2100/5420 |

Sections count (number of 2D cross-sectional images) | 1771 |

Region of interest (ROI) (square) size (pixel) | 3572 |

Image pixel (square) size (µm) | 6.25 |

Reconstruction from ROI | activated |

Reconstruction angular range (deg) | 0–180 |

2D cross-sectional image size (pixel) | 3572 × 3572 |

3D image voxel dimensions (µm) | 6.25 × 6.25 × 6.25 |

3D cross-sectional image layer dimensions (width; length; thickness) (mm) | 22.3; 22.3; 0.00625 |

3D cross-sectional image stack dimensions (width; length; height) (mm) | 22.3; 22.3; 11.1 |

3D stack files type | 8-bit BMP |

Parameter (Unit) | Value | |
---|---|---|

W-Foam | S-Foam | |

Resize of the dataset (number of times) | not resized | not resized |

Image pixel (square) size (µm) | 6.25 | 6.25 |

3D image voxel dimensions (µm) | 6.25 × 6.25 × 6.25 | 6.25 × 6.25 × 6.25 |

ROI (circle) diameter (pixel) | 2880 | 2880 |

2D cross-sectional image size (pixel) | 2884 × 2884 | 2884 × 2884 |

First section number | 330 | 3650 |

Last section number | 2100 | 5420 |

Sections count | 1771 | 1771 |

3D cross-sectional image stack dimensions (diameter; height) (mm) | 18.0; 11.1 | 18.0; 11.1 |

3D stack files type | 8-bit BMP | 8-bit BMP |

Thresholding: | ||

- lower grey threshold | 51 | 51 |

- upper grey threshold | 255 | 255 |

Despeckle: | ||

- type of item to remove from 3D space | white speckles | white speckles |

- max speckle volume (voxels) | 38 | 38 |

ROI shrink-wrap: | ||

- space to be shrunk | 2D | 2D |

- stretch over blowholes of a diameter above (pixels) | 44 | 58 |

Parameter (Unit) | Abbreviation | Value | |
---|---|---|---|

W-Foam | S-Foam | ||

Resize of the dataset (number of times) | not resized | not resized | |

3D cross-sectional image stack dimensions (diameter; height) (mm) | 18.0; 11.1 | 18.0; 11.1 | |

Total VOI volume (mm^{3}) | TV | 2825.227 | 2825.227 |

Object volume (matrix only) (mm^{3}) | Obj.V | 326.602 | 275.411 |

Volume of closed pores (mm^{3}) | Po.V(cl) | 0.028 | 0.011 |

Volume of open pore space (mm^{3}) | Po.V(op) | 2498.597 | 2549.805 |

Total volume of pore space (mm^{3}) | Po.V(tot) | 2498.625 | 2549.816 |

Number of closed pores | Po.N(cl) | 5052 | 2408 |

Closed porosity (%) | Po(cl) | 0.009 | 0.004 |

Open porosity (%) | Po(op) | 88.439 | 90.251 |

Total porosity (%) | Po(tot) | 88.440 | 90.252 |

Percent object volume (%) | Obj.V/TV | 11.560 | 9.748 |

Relative density | ρ_{r} | 0.116 | 0.097 |

Total VOI surface (mm^{2}) | TS | 1171.529 | 1171.529 |

Object surface (mm^{2}) | Obj.S | 35,921.379 | 29,513.951 |

Surface of closed pores (mm^{2}) | Po.S(cl) | 6.131 | 2.585 |

Structure separation (mean pore size) (mm) | St.Sp | 0.271 | 0.418 |

Structure thickness (mean strut thickness) (mm) | St.Th | 0.033 | 0.033 |

i | Percent Mass (in Can) x_{i} (%) | |
---|---|---|

W-Foam | S-Foam | |

1 | 1 | 1 |

2 | 1 | 10 |

3 | 1 | 1 |

4 | 10 | - |

© 2018 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Blazejczyk, A.
Morphometric Analysis of One-Component Polyurethane Foams Applicable in the Building Sector via X-ray Computed Microtomography. *Materials* **2018**, *11*, 1717.
https://doi.org/10.3390/ma11091717

**AMA Style**

Blazejczyk A.
Morphometric Analysis of One-Component Polyurethane Foams Applicable in the Building Sector via X-ray Computed Microtomography. *Materials*. 2018; 11(9):1717.
https://doi.org/10.3390/ma11091717

**Chicago/Turabian Style**

Blazejczyk, Aurelia.
2018. "Morphometric Analysis of One-Component Polyurethane Foams Applicable in the Building Sector via X-ray Computed Microtomography" *Materials* 11, no. 9: 1717.
https://doi.org/10.3390/ma11091717