Superabsorbent fabric keeps feet dry in all weathers

07 Oct '08

5 min read

Come rain or sunshine, children prefer to run around outdoors. But the fun is soon over if they get wet feet while hopping through the puddles. Rain boots may keep the moisture out, but they quickly turn into miniature foot saunas.

How can a shoe keep out the rain and still allow sufficient air to reach children's delicate feet? The answer is Luquafleece, a superabsorbent polyester nonwoven material produced by BASF in a unique process.

A small piece of this special, moisture-absorbing fleece is the heart of IQ .TEX, the novel ventilation element launched by the Hamburg company IQTEX: "Compared to conventional functional clothing, shoes made with this technology are not only breathable but, depending on the weather, can also be as air-permeable as cotton socks or as watertight as rain boots," says Michael Dehn, managing director of IQTEX.

When exposed to water, the tiny polymer granules of the superabsorber, which are permanently bound to the nonwoven fibers by a special BASF process, absorb up to 400 times their own weight of liquid and expand accordingly.

Superabsorbers owe this enormous suction power to their molecular structure consisting of the basic component acrylic acid. BASF chemists have joined together countless numbers of these tiny molecules into long chains that are linked together at large intervals. The result is a loose bundle of molecules that absorbs water like a molecular sponge. But the key factor producing the great absorption is the material's high ion charge. It generates an osmotic pressure that draws surrounding water into the polymer network.

Water is absorbed until the elastic restoring force of the polymer network compensates the osmotic forces. The ventilation element utilizes the small particles' thirst to seal the inside of the child's shoe against water from outside: two honeycombed lattices limit the upward and downward expansion of the small Luquafleece sections. The swelling superabsorbent particles can then only expand sideways where they soon meet up again and seal all the cavities in the nonwoven material.

On contact with water, the Luquafleece – although it was highly permeable just a few moments ago – very quickly becomes absolutely watertight. Back in dry surroundings, the water absorbed by Luquafleece evaporates and the pores reopen within a short time depending on the temperature and atmospheric humidity - allowing the air to circulate freely again.

"The superabsorber permanently surrounds the fibers of the fleece like droplets and with its high loading density provides absolute protection against the wet shoe," explains Dr. Peter Rudolf, superabsorber specialist at BASF. "The fleece can saturate itself with water any number of times and then release it again through evaporation. It's exactly this reversible moisture uptake that makes the fleece interesting for a multitude of applications."

A single square meter of the fleece, which is only a few millimeters thick when dry, can absorb up to 26 liters of water. An absolute innovation is the principle of IQ .TEX , in which a small piece of Luquafleece completely self-seals the system when exposed to wet conditions. "The idea of utilizing the mechanical barrier function of our Luquafleece came from the development experts at IQTEX, who in partnership with us then developed it into a marketable product," says Dr. Peter Rudolf.

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