Silk and Nylon

Silk has always been a luxury fabric prized by the wealthy of society; its many properties such as its warmth in cool weather and coolness in warm weather, its caressing feel, its wonderful luster, and its capabilty to be easily dyed, have made it so.  First produced in China circa 2500 BC, silk is obtained by boiling the cocoons of silkworms and then unwinding the silk thread onto reels.  Until around the sixth century AD, the Chinese had a monopoly over silk production, who then sold their products to foreign traders who brought it to various locations around the world via the Silk Road, which stretched from China to eastern Europe.  Once the secrets of silk cultivation, also known as sericulture, became known about three thousand years later, European nations, especially those in Itlay, became major producers.  In the New World however, sericulture was not as successful, but important developments that mechanized the spinning and weaving process were made here, mostly in the United States.

But what is it that makes silk such a desirable fabric?  Silk, being a protein, is a polymer made of a variety of amino acids.  Every amino acid has the basic structure H2N-CH-COOH, with a side group attached to the center, or alpha, carbon.  The side group can range from a simple hydrogen atom to a far more complex molecule, and is what gives the amino acid its own unique properties.  There are 22 amino acids, so a polymer of just four amino acids has 234,256 possible combinations.  The polymer chains are in a zigzag arrangement, and lie parallel with adjacent chains running in opposite directions, held together by cross attractions.  This produces a pleated sheet structure, which gives it the flexibilty it needs without stretching it.  These properties make silk a very versatile fabric, but also makes it difficult to replicate.

None the less, attempts to find a synthetic silk were made.  Such attempts proved fruitless, as the structure of silk was far too difficult to replicate, so the search for different fabrics that could fulfill the same properties of silk began.  Artificial silks based on cellulose, called rayons, had similar properties to silk, but had many weaknesses: Chardonnet silk was flammable, and viscose, though still in production today, absorbs water easily.  However, in 1938, a noncellulose based substitute for silk, known as nylon, went on the market.  Nylon, created by Wallace Carothers at DuPont Fibersilk Company, differs from silk in that instead of being a polymer of amino acids that each have an acid group (COOH) and an amine group (NH2), it consists of two alternating molecules.  These are 1,6 diaminohexane, which has two amine groups, and apidic acid, which has two acid groups.  The polymer units are bonded like they are in silk, through amide links, and is structured in much the same way.  This new artificial silk was a huge success, as it had exceptional strength, durability, and lightness.  During World War II, tire cords, mosquito netting, weather balloons, ropes, parachute shrouds, and other military items were made of nylon.  Both silk and nylon have had a significant impact on human society, having opened worldwide trade routes and promoted various other developments that we rely on today.