X-ray Microscopic Examination of Organic Polymeric Composites

Figure 1: Photograph of bioplastic and wood fiber composite cutlery imaged with the SkyScan 1273

Bioplastics are polymers produced from plant-based products such as wood or starch, and they can be naturally recycled by biological processes, limiting the use of fossil fuels. Bioplastics are now used in industrial applications such as food packaging, agriculture, composting bags, and hygiene, as well as in biomedical and other consumer products. With global demands for plastic consumption, research exploring green materials and new ways to process them is growing.

Polymers are ubiquitous in our world, and their role is growing. In formulating polymers, composites are often used to enhance the physical properties of a base polymer through the addition of strength or other physical properties, building from the base properties of the polymer used for the product. Micro-CT imaging plays a role in both the formulation and the quality control processes as a non-destructive way to make assessments about the location, loading volume, and orientation of the support fibers within the finished product.

X-Ray Microscopic Imaging of Fiber Reinforced Plastics

We examined a set of bio-plastic cutlery that has been reinforced with wood fibers. For this project we used our versatile SkyScan 1273 desktop micro-CT at an isotropic voxel size of 20µm. For each of the three types of flatware in the set we utilized a different imaging mode within the SkyScan 1273 to acquire the dataset. Of the available SkyScan desktop instruments, only the SkyScan 1273 provides high-speed continuous imaging along with spiral scanning to accompany the traditional step and shoot imaging mode common to all systems.

To maximize resolution within the dataset, the sample was mounted with the longest dimension in the Z plane to minimize our horizontal width, allowing for higher magnification. Using several sequential image acquisitions along the length of each piece of cutlery, the full sample is acquired at high resolution while the individual scans are digitally combined into one dataset within NRecon for downstream analysis and visualization. For the step and shoot and spiral imaging modes, the total acquisition time for these high aspect ratio samples was around ten hours. Switching to continuous imaging allowed us to reduce the acquisition time by over 90% with no change in voxel size for this sample.

Figure 2: Planar 2D views of the knife dataset before (above) and after (below) Heel Effect Correction

As shown in Figure 2, sometimes when producing data from a micro-CT system utilizing a reflection type X-ray source, horizontal banding will appear in the reconstructed datasets near the connections from one segment of imaging to the next. This produces the artificially banded image appearance seen in the top image. With the release of NRecon 2.2, optional automatic Heel Effect Correction has been added to the software. In many cases, simply enabling this new function within your oversize scan reconstruction parameters will be able to detect and minimize the banding effect in your dataset, as shown in the second image.

More information related to Bruker’s new automated Heel Effect Correction is in Method Note 151 announcing the new features in NRecon 2.2. Another more specialized method note is coming soon to provide guidance into the Heel Effect Correction process as well as steps to take when the automatically suggested values fail to correct the banded appearance. The Heel Effect is most seen with the SkyScan 1273 instrument in comparison to the SkyScan 1272 and SkyScan 1275 systems.

 

Figure 3: Clipped 3D CTVox volumetric colorized renderings of the plastic knife (top), spoon (middle) and fork (bottom,) highlighting the polymer in blue and the wood fibers in orange

As shown in Figure 3, CTVox provides us with an interactive view of the dataset, allowing us to artificially color the individual components within the cutlery samples. In these examples, the polymer is rendered in blue while the wood fibers are rendered in orange, allowing us to examine for local density of fibers as well as to qualitatively examine their orientation.

Figure 4: Rendered views through the knife dataset, highlighting the local orientation of the individual fibers (top) as well as the location and size of the identified voids (bottom)

Figure 4: Rendered views through the knife dataset, highlighting the local orientation of the individual fibers (top) as well as the location and size of the identified voids (bottom)

Figure 5: Quantitative assessment of fiber diameter within the knife sample from CTAnalyzer

In addition to local fiber orientation, CTAnalyzer also calculated the average fiber diameter to be 128 ± 69 µm with a loading volume of 22% (Figure 5). Likewise, the average void diameter was 130 ± 73 µm with a total porosity of 0.1%.

Figure 6: Maverick 3D rendering of the bioplastic spoon and wood fibers extracted from the imaging data

After separating the wood fiber components from the bulk polymer into individual volumetric meshes, we’re free to move into any downstream 3D software suite to complete further work. In this case, we imported our mesh into Maverick Render Indie to create high resolution photo realistic renderings and videos of our scan data as shown in Figure 6, highlighting different views of the composite spoon.

Conclusion

Among the SkyScan product line, the SkyScan 1273 stands apart from the field based on its unmatched imaging versatility with three different imaging modes. This combination of speed and a large available sampling volume along with the powerful 130kV X-ray source make the SkyScan 1273 a great workhorse for laboratories and shared facilities where versatility is a key choice in the purchasing decision.

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 Knife Spoon Fork
Imaging Mode Std. Stop and Shoot Continuous Spiral
Voltage (kV) 40 40 40
Current (µA) 200 220 220
Filter None None None
Voxel Size (µm) 20 20 20
Rotation Step 0.3 Continuous 0.3
Exposure Time (ms) 225 225 225
Rotation Extent (deg.) 180 360 Continuous
Scan Time (HH:MM:SS) 10:43:04 00:57:10 10:13:54

 

This scan was completed on our SkyScan 1273 micro-CT system at the Micro Photonics Imaging Laboratory in Allentown, PA using an oversize imaging mode. Reconstructions were completed using NRecon 2.2 while visualization and volumetric inspection of the 2D and 3D results were completed using DataViewer and CTVox. Porosity and fiber orientation were calculated using CTAn 1.23. The individual components of the spoon sample were converted to 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 e-mailing seth.hogg@microphotonics.com.

References

https://www.synopsys.com/simpleware.html

*Simpleware software (Synopsys, Inc., Mountain View, USA) enables you to comprehensively process 3D image data (MRI, CT, micro-CT, FIB-SEM…) and export models suitable for CAD, CAE and 3D printing. Use Simpleware software’s capabilities to visualize, analyze, and quantify your data, and to export models for design and simulation workflows. Simpleware™ is a trademark of Synopsys, Inc. in the U.S. and/or other countries.

 

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