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Absorbing material: cleanroom wipes should arrive clean and leave dirty. But how they achieve that best is a very competitive matter.

The cleanroom wipes industry is huge and competitive, and there is constant innovation by the major manufacturers in terms of the fibres used and the way in which they are woven into a wipe, with or without the addition of solvents or other treatments.

The aim of all developments is to maximise the amount that is picked up and minimise the downside--the minute particles that the wipe sheds and leaves behind.

With some wipe fibres, this is a delicate balance. The immense growth in microfibre wipes made of polyester or polyester/nylon from the late 1980s onwards was built on the ability to collect and hold dirt and dust more effectively than earlier fibres such as cotton, and microfibre has a high sorptive capacity too of around six to eight times its own weight in water.

But there are drawbacks with microfibre wipes too. The fibres are less durable than earlier wipe configurations, and can create high levels of very fine particle contamination, and this contamination can be difficult to clean out. The wipes can also Clear degrade over time, particularly with laundering, but the high lea% cost means that they can be an bi expensive option for a single--wipe use.

So the wipes industry has been looking for the past 20 years or so for a product that could offer the benefits of microfibres without the drawbacks. And the US-owned cleaning products giant Contec claims to have done just that with the introduction of its MicroGenesis wipes.

The gist of the MicroGenesis idea is that it uses a smaller amount of polyester microfibre yarn which is knitted into a thermally bonded polypropylene substrate. Contec says that this means that the user gets the fast and efficient pick-up and retention of particles for which microfibre is known without the cost of a full microfibre wipe.

So MicroGenesis can deliver the maximum amount of microfibre to pick-up and retain particles, dust, grease and oil in cleanrooms and other critical applications, but it is more economic and can therefore be more easily considered for single use.

But it is not the only option. Other developments that can provide wipes with better pick-up and retention of particles do away with microfibre entirely. Anticon, formerly part of the Milliken group but acquired by Contec a few years ago, has come up with a treatment that can be applied to many kinds of wipe that permanently bonds to the fabric and traps many more particles than an untreated wipe and then retains 95% of them.

The work that led to this development led also to the filling of a significant gap in the science behind cleanroom wiping. Anticon engineers Peter Kang and David Hildreth noted that although there was a standard JEST test method for determining how many particles and fibres a wipe released, there was no standard test method to show exactly how many particles the same wipe actually picked up.

They set to rectify the omission with a test method that deliberately uses much of the same equipment as the existing IEST test for retention and release.

They used two types of standard dust, a fine test dust and carbon black particles, and made suspensions of both in de-ionised water, using ultrasonics to break up the particles as much as possible. The particle concentration was then measured and a dry wipe added with the whole suspension, wipe and all agitated for five minutes on a biaxial shaker.

The wipe was then removed and transferred to ajar with clean de-ionised water where the particle count had already been measured. The combined weight was measured and the jar with the wipe was again agitated for five minutes. The wipe was then removed and discarded, and the particle concentration in both jars was then measured.

What this test gives is not just a measure of the particles released by the wipe--the count of those left in the jar that originally contained clean water--but also a measure of the particles actually captured by the wipe: the first jar's original contents, minus its final contents and those transferred to the second jar.

And the results obtained by Kang and Hildreth indicated that the treated wipes significantly outperformed untreated wipes: for the larger particles in the fine test dust, the test showed the treated wipes captured 35 times more particles than traditional wipes, and for smaller particles they picked up three times the amount. Results for carbon black were also impressive.

Wipe technology does not stand still, and different products are always likely to be more suited to some applications than to others. The concept of wiping is that the wipe arrives clean and leaves dirty. But there will remain many ways to achieve that.
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Title Annotation:Cleanrooms
Publication:Environmental Engineering
Date:Feb 1, 2013
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