How do velcro strips work ?

What is the mystery in coarse Velcro strip used for fastening the straps of sports shoes, briefcases, wallets, belts, jerkins etc.?

To start with read about an interesting incident: It was the year of 1948. On one early afternoon a researcher named George Dimistral was strolling with his dog in the countryside of Switzerland. He unleashed the dog to let it roam about in the countryside while he strolled. When they returned home Dimistral found strands of some wild flowers stuck all over the dog's furry body. He tried to pull the strands out of the dog's hair but did not find it easy. They held fast in the hair and required some force to pull them out. George Dimistral being a researcher to the core got interested in this mystery and examined some strands under a microscope. He found that the ends of those strands were like hooks. Once the dog's hairs were hooked they remained hooked fast.

Wheels in Dimistral's brain started spinning: What if such hooked artificial fibre is made? No more need of liquid adhesive or nails to hold tast two items! The number of uses to which such fibre could be put was really mind boggling because it had limitless scope for attaching and detaching things repeatedly which was simply absent when using sticking gum or nails.

After relentless research spread over eight years he finally succeeded in developing a textile of nylon—the name of which is Velcro! Today this commercial name is very wellknown. If the name is still strange then it will be interesting to know that it is derived by combining first syllables 'veľ from velvet and 'cro' from crochet. (Crochet means knit work by means of a hooked needle.) The technical name of this thick textile is 'hook-and-loop'. Loop means a coil which is shown on the bottom part of the microscopic photograph of Velcro. On pressing opposite strips of Velcro, hooks get pressed and inserted in the loops as if knitted.

There are a number of interesting aspects of Velcro. As they are unknown to the people at large let us describe them in some detail: (1) The adhesion force of Velcro that Strongly grips any two things is equal to its surface area. E.g. the adhesion force of 6 square centimetres Velcro is three times greater than the force of 2 square centimetres Velcro. (2) For temporary 'fixing' of heavy industrial objects Velcro band of thin steel wire is used whereas in case of items of everyday use Velcro band is made of nylon or polyester. (3) Velcro band of nylon does not work satisfactorily in the environment of excessive rain or sunshine. Ultraviolet rays of the Sun damage the nylon in the long run, whereas rainwater softens its fibre. Gripping power of nylon Velcro band reduces by about 50% if kept immersed in water for an hour or so. However, it regains its earlier gripping strength on drying. (4) The grip of polyester Velcro band remains unaffected by rain or sun rays but it is not as durable as nylon. Velcro made of nylon can be fastened and unfastened 10,000 times whereas polyester loses effectiveness after about 3,500 uses. In any case this comparison it not very

material. Most of the articles are fastened and unfastened not more than 3,000 times. At this rate of 3,000 uses even if Reebok sports shoes are worn daily Velcro bands would last about eight years, but can one say the same for the useful life of the shoes? Or, shall we not replace them with a new pair of the latest fashion long before that?