X-ray Microscopic Examination of Bathroom Tissue Paper

Micro-CT imaging of toilet tissue allows us to study its structure, which can help manufacturers improve properties such as density and water absorption. Given that it wasn’t until 1930 that splinter-free toilet paper was introduced, toilet tissue has come a long way. This sample was imaged on our high-resolution SkyScan 1272 CMOS Edition micro-CT with an isotropic voxel size of 4 µm. Keeping samples like this completely motionless during imaging is a key consideration for optimal results.

Figure 1: Textured paper imaged in this study (left) and custom mount for flexible sheet samples (right)

X-Ray Microscopic Imaging of a Nonwoven Fiber Composite

This month we imaged a section of textured bathroom tissue using our high-resolution SkyScan 1272 CMOS Edition micro-CT with an isotropic voxel size of 4 µm. With the ability to comfortably operate in low single digit micrometer scale voxel sizes, the SkyScan 1272 is a great match for high resolution imaging of organic structures and composites. Keeping samples completely motionless during imaging is a key consideration for preparing them for micro-CT imaging. One sample type where this is particularly challenging is thin films and sheets such as those commonly encountered in the paper industry.

To address these challenges, Micro Photonics created a custom fixture to hold the sheets upright while the edges are clamped together under tension by plastic frames. During reconstruction, only the data from within the frame center is reconstructed to create our dataset and the sample data between the frame edges or outside of the frame is excluded. While this does discard some of our available imaging area, the increased stability of the sample leads to more reliable imaging with less artifacts and is a tradeoff worth considering.

In your daily work, always feel free to consult with Micro Photonics regarding the development and production of custom fixtures for your samples to better unlock your workflows and improve imaging reliability.

Figure 2: Planar 2D slices through the paper sheet within the custom sample holder ROI

As shown in Figure 2, DataViewer allows us to fine-tune the positioning of the sample in 3D space using a linked set of 2D images through the coordinate planes. This fine-tuning step allows us to orient even thin, high-aspect ratio samples into a desirable position to enable downstream analysis and visualization. It is also especially important to properly orient samples prior to downstream simulation and flow analysis through third party software programs.

Figure 3: CTVox rendered volumetric representation of the paper region of interest showing the perforated cut line added to the sample during the manufacturing process

Using CTVox, we quickly rendered a live volumetric view through our dataset in 3D space as shown in Figure 3. For this sample, we observe the large wavy ridges which provide the macro texture to the product while we also have the necessary resolution to see the fine texture present in the structure on a microscopic level. For this sample, we specifically selected a region between two sheets of the bathroom tissue to allow us to image the perforated tear strip added to the larger roll during the manufacturing process that allows easier separation of sheets. Figure 3 shows this cut line moving from top to bottom through the image and the local brightness of the sample in this region suggests that the cutting blade creates pockets of elevated density along the edges of each cut section.

Figure 4: CTVox rendered representation of the calculated fiber diameters colored by size

Given the detailed microscopic view of the sample produced by the SkyScan 1272, we utilized Bruker CTAnalyzer to calculate the thickness of the various fibers assembled into the larger structure, as shown in Figure 4. Each diameter of thickness was given a slightly different color and since the image is generally uniform in color, this indicates the microscopic fibers used in the product are fairly monodispersed in terms of thickness. The average fiber diameter identified in our analysis was 16.19 ± 5.01 µm.

Figure 5: CTVox rendered representation of the fiber orientations in 3D space

Likewise, in addition to the fiber diameter, we can also take the analysis a step forward and try to determine some trends in fiber orientation with Bruker CTAnalyzer as shown in Figure 5. This view renders the dataset fibers colorized based on their calculated orientation.

Figure 6: Maverick Indie rendered STL model of the paper imaging dataset

While we were able to calculate some useful material characteristics like fiber size and orientation within CTAnalyzer, a key benefit of the data produced on a SkyScan instrument is the portability to move into many downstream analysis programs for more specialized inspection. In this case, we took the sample into Synopsys’ Simpleware ScanIP software with the CAD add-on module (Synopsys, Inc., Mountain View, USA) to create a detailed STL model before 3D rendering using Maverick Render Indie (Random Control, Madrid, Spain), as shown in Figure 6.

Conclusion

Among the SkyScan product line, the SkyScan 1272 is a versatile instrument with the ability to be equipped with an optional 16-position sample changer for semi-automated imaging. As the highest-resolution desktop model available within the SkyScan portfolio, the SkyScan 1272 is a great match for many low to medium density samples where the need for high resolution often outweighs the need for extremely high throughput.

We hope you found this Image of the Month informative and encourage you to subscribe to our newsletter and social media channels in preparation for the continuation of our Image of the Month series next month.

Scan Specifications

Sample Nonwoven Fabric Paper
Voltage (kV) 50
Current (µA) 120
Filter None
Voxel Size (nm) 4
Rotation Step 0.15
Exposure Time (ms) 488
Rotation Extent (deg.) 360
Scan Time (HH:MM:SS) 04:50:10

These scans were completed on our SkyScan 1272 micro-CT system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon 2.0 while visualization and volumetric inspection of the 2D and 3D results were completed using DataViewer and CTVox. The sample was converted to STL volumetric models using Synopsys’ Simpleware ScanIP software with the CAD add-on module (Synopsys, Inc., Mountain View, USA) before 3D rendering using Maverick Render Indie (Random Control, Madrid, Spain).

Would you like your work to be featured in our monthly newsletter? If so, please contact us by calling Seth Hogg at 610-366-7103 or emailing seth.hogg@microphotonics.com.

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