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Micro-CT of a Wax-coated Paper Cup

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Figure 1. Micro-CT of a section of a wax-coated paper cup

Click here see a 3-D video of a wax-coated paper cup

Why Scan a Cup?

Years ago, communal glass cups were used at public drinking fountains, causing deadly diseases to spread more easily. To prevent the sharing of germs, a lawyer by the name of Lawrence Luellen thought of creating a single-use paper cup. In 1907 Luellen developed an ice-cooled water vending machine with disposable cups called Health Kups, the forerunners of today’s Dixie® Cups.   Paper cups became a bigger necessity at the close of World War I when the 1918 influenza epidemic killed an estimated 50 million people. This catastrophe made the public aware of the need for collective action against infectious diseases. Bolstered by advertising to educate the public, Luellen’s business expanded and moved in 1921 to Easton, PA, (near to our corporate office), producing the Dixie cups that we are familiar with today1.

Now obviously, paper by itself absorbs water and disintegrates over time. The solution was to spray a fine wax or polyethylene coating to seal the paper and prevent leaks. The wax was great for cold beverages but hot beverages required the polyethylene coating, which has a higher melting temperature. We at Micro Photonics use similar wax-coated cups for our drinking water and decided to scan one to show the wax sealing.

The wax-coated cup micro-CT scan

A section of a cup was cut out for scanning purposes to ensure the wax and paper would be clearly visible. Using the SkyScan 1272 micro-CT scanner at 3 microns, we were able to capture an image of the paper with the seal that occurs from the wax. The wax that is normally sprayed on to the cup adheres between the fibers but also forms a nice moisture barrier on the outside (Figure 2).

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Figure 2. Section of cup showing the paper with the wax seal

This wax seal, with its lower density compared to the paper, allows for clear distinction between the layers. The difference in layering is visible based on the atomic number of the materials. The higher the atomic number is, the higher the object appears on the grayscale range from 0 to 255 (Figure 3). In this case, the paper is higher in atomic number than the wax.

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Figure 3. Grayscale range based on material’s atomic number

Conclusion

This demonstrates just one of many applications where the quality of layered samples can be inspected with micro-CT imaging. We hope this image of the month taught you something new about paper cups, and if you have an image of the month sample with layers, we would be glad to scan it for you. Please feel free to call Brandon Walters at 610-366-7103 or e-mail brandon@microphotonics.com to learn more about what micro-CT can offer you.

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