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To get optimal results from any type of wipes—especially in controlled environments—engineers need to be savvy about the technology they select and the packaging in which the wipes come.

Everybody uses wipes. Wiping surfaces is such a common, natural, and pervasive cleaning process that we tend to forget the complex technology embedded in these inexpensive and reliable cleaningtools.

In general, there are three broad categories of wipes: wipes made of paper, wipes made of woven or knitted cloth, and wipes made of nonwoven synthetic cloth. Here’s a quick review of the choices and the attributes to consider when investigating the best product for any specific application.

WIPE SPECIFICATIONS
With hundreds of choices and grades, selecting the most cost-effective wipe can be tricky. The most obvious criteria is the absorbency of the wipe. But, it is not well understood that absorbency varies by the contamination. Some wipes will not absorb water; others are better with solvents and lacquers. The general rule is that “like absorbs like.” For example, polyester is petroleum-based, so polyester wipes easily absorb gasoline, fuel oils, and alcohols but are far less effective on water-based contamination. Natural fibers, such as cellulose, are water-based and so are best for water-based contamination. In short, the contamination defines which type of wipe will be best.

The second criteria is cleanliness; that is, contamination caused by the wipe itself. Cleanliness usually is inversely related to absorbency, and balancing the conflicting requirements can be a challenge. The cleanest wipes often are less porous and will not absorb as much contamination, while more absorbent materials may be more fragile and leave fibers or residues.

Engineers also must consider any special requirements of their application. Medical applications may require sterile wipes. Schools, hospitals, and the wood-working industry use wipes impregnated with a“ tackafier” that attracts and retains dust. Wipes that will be usedwith solvents need to be tested to ensure that the solvents will not degradeany glues or binders in the wipe, which would leave residues. So, understanding the application is essential to a successful selection process.

The penultimate criteria concerns the packaging. Many cellulose wipes come in cheap but dirty cardboard. Electronics grade wipes often are packaged in electrically-conductive, static-dissipative packaging that avoids damage to circuit boards and avoids attracting dust while in transit. Most cleanroom environments require “double-packaging.” There are dozens, maybe hundreds of packaging choices, so consider what you need and can afford before setting the specification.

And while we’re on the subject of packaging, check the packaging material and the packaging processes. Semiconductor companies require the packaging to be as contaminatefree as the wipes inside, with no fibers, plasticizers, silicones, or ionics to cross-contaminate the cleanroom. Additionally, the wipes must be cut, counted, and packaged in a cleanroom, or else the wipe becomes expensive, double-packaged dirt.

Lastly, cost must be evaluated. Fabric wipes tend to be more absorptive, stronger, and durable; they may be more expensive to buy but generally are less expensive to use since they can be used several times. Paper wipes often are found in applications where re-contamination cannot be allowed, such as electronics and medical applications.

cleaning with a lint-free polyester wipe

high-purity lint-free wipes

solvents and wipes are not always the best of friends

NONWOVEN WIPES
Synthetic paper is an innovative and versatile technology with hundreds or maybe thousands of permutations. Originally developed for medical applications, such as disposable operating room garments, these materials have the strength, softness, and quality of a woven textile, but are produced at the volumes, speeds, and cost of paper. These materials use high quality synthetic fibers (polyester and rayon are common choices, and sometimes a mix of synthetics and cellulose is preferred for great absorbency) but the manufacturing process binds the fibers together without glues. Because the raw fibers are synthetic, they tend to be stronger than wipes made from natural fibers so they lint less and fewer fibers on substrates.

In the middle price range are nonwovens made from synthetic fibers or sheets of synthetic materials. Some products use glues (also called “binders”) to hold the fibers in place. Made from polyester, polypropylene, or rayon, these are ideal for pharmaceutical companies because they minimize the bioburden trapped in the wipe. They also can be textured and presaturated, adding to the cleaning versatility.

But binders can be a problem. Binders can amount to 30% by weight of some nonwoven products. The most common binder is a water-based latex glue such as polyacrylate. Most binders will dissolve when exposed to solvents, introducing unwanted contaminates, so wipes made with binders are usually unsuitable for cleanroom applications.

At the bottom of the food chain are cheap cellulose wipes. Cellulose is a very absorptive but feeble fiber, with little internal strength. Cellulose wipes will leave adhesives, lint, and fibers on the surfaces being cleaned, especially when wet. Made with binders, one industry wag has described cellulose wipes as “clouds of dust flyingin tight formation.” Most cellulose wipes simply are insufficiently strong,clean, and absorptive to handle anything but the simplest cleaning tasks. Their only positive attribute is theirinexpensive price.

structural differences between paper wipes

FABRIC WIPES
Woven wipes come in a range of materials, qualities, and prices. The least expensive material is simply “reclaimed fabric” and the slightly higher quality “mill ends.” These wipes are cut from cotton shirts, jeans, old uniforms, pajamas, and other materials. Obviously, these are completely unsuited for controlled environments.

Nearing the top of the woven fabric quality range is “ washed diaper fabric.” This material is soft, strong, and highly absorbent. With proper processing, and a thorough washing with the special surfactants and detergents, diaper fabric may qualify for Class 1000 cleanrooms. Synthetic fibers bring cleaning performance to an even higher level. A treated polyesyter/polymide micro-fiber from Asia is sweeping the auto detailing industry. Under amicroscope, you can see grooves and ridges on eachfiber which scrape the contamination away, so microfiberwipes deliver swirl-free results in half the time.

If cleanroom performance is essential, opt for knitted synthetic fabrics of polyester or rayon. Since contamination is most often generated from the edges and ends of fibers, the interlocking weave of the knitting process minimizes loose ends and locks stray fibers into the fabric. Some manufacturers use lasers to cut the wipes, which melts the fiber ends and further minimizes linting. Other companies use special knitting machines which knit tubular wipes, which by definition have no ends or seams and are optimal for very high purity applications. These also can be pre-washed, to further minimize any residual particulate.

Polyester materials can be extremely soft, clean, and absorbent, so polyester is the leading choice for cleaning optical systems and clean rooms, for example. The cleanest wipes are pre-washed, knitted polyester wipes with heat-sealed edges.

WRAP-UP
Whatever special requirements there may be, engineers can be comfortable that today’s wipe manufacturers will have the answer they need.

Mike Jones is Vice President at MicroCare Corp., which specializes in critical cleaning for electronics, telecommunications, aerospace, medical devices, and other industries. He can be contacted at MikeJ@MicroCare.com.

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