“Perfect holes for perfect fibers”

© Photo | Universität Stuttgart

Microfibers are small, but supermicrofibers are miniscule. Anne Feuer used an ultra-short pulsed laser to pave the way for the longest and finest cellulose fibers in the world.

I already have a microfiber cloth and a microfiber running shirt at home, Ms. Feuer. So what extra benefits do supermicrofibers offer?

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Anne Feuer presents the thinnest cellulose-based fiber bundle in the world: ten kilometers of fiber weigh 0.3 grams – about the same as a paperclip. (Photo | Viola Schütz / Baden-Württemberg-Stiftung)

A supermicrofiber cloth would be able to capture more dust and absorb more moisture than your microfiber dust cloth thanks to its significantly larger surface area. And supermicrofibers would do a better job of soaking up perspiration! Supermicrofibers are also a good choice for air filters in motor vehicles and for sanitary products such as tampons.

But if supermicrofibers are so much better, why did they make my running shirt from microfibers?

Because until recently we didn’t have a suitable method for producing long, well-arranged, cellulose-based fibers. At present, the fibers in the resulting weave point wildly in all different directions. To make long, fine fibers, we need spinnerets that are impossible to produce by conventional means.

Why is that?

The direct spinning method involves pressing the raw material — a warm cellulose solution — through a sieve, a bit like pushing spaghetti dough through the holes in a pasta making machine. To get perfectly aligned fibers, you need perfect holes that are round, smooth, vertical and, above all, long. In other words, holes with a diameter of just 25 microns, but a length of 300 microns, and something like 2,000 holes in just half a square centimeter. You can imagine how hard that is to punch!

So a laser was the only realistic option. Was an ultra-short pulsed laser the sole choice?

Effectively, yes. We need two things to produce our micro-holes. First, ultra-short laser pulses that have as little effect as possible on the material around the hole, so you get smooth walls without any burrs or indentations. The only way of achieving that is with “cold machining”. Secondly, we use a method called helical drilling. In other words, we focus the beam on slightly more than half the hole diameter and move it in circles. The laser spirals its way through the workpiece, removing and vaporizing the material as it goes.

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2,000 cellulose-based supermicrofibers are extruded into a spinning bath to harden. (Photo | ITCF Denkendorf)

So when will I be able to replace my running shirt with one that’s more absorbent?

It’s going to take a few years before this new technique commercially viable. A couple of companies have already experimented with a few products as part of the project, but a full-fledged industrial application is still a long way off.

More about the “Top Spin” research project:

Anne Feuer took charge of the “Top Spin” research project following the departure of Martin Kraus, the engineer who initiated the project at the Institute for Beam Tools (IFSW). Together with the Institute of Textile Chemistry and Chemical Fibers (ITCF) in Denkendorf, the team came up with a method able to manufacture cellulose-based supermicrofibers. Their work was sponsored by the Baden-Württemberg Foundation.

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