Early Synthetic Polymers
By: James Avery
Polymers have been around longer than we have. In fact, polymers are as old as life itself, as all life on earth is based on three types of polymers, namely DNA, RNA, and proteins. But this report is about some of the earliest synthetic polymers, that is, polymers made by humans, specifically, the cellulose derivatives.
The very first synthetic polymer was of course leather, a modified natural polymer, an artificially crosslinked form of the proteins found in animal skins. Leather tanning was discovered thousands of years ago, but I’m going to talk about some synthetic polymers that came a bit later. These are the cellulose derivatives. They are also derivatives of a natural polymer, cellulose. They hold a special place in polymer
history, because their invention in a lot of ways was the beginning of an explosion in the invention of synthetic polymers which continues to this day. Cellulose derivatives are forms of cellulose, a polymer found in wood, cotton, and paper, which have been chemically altered. Scientists first started to make them in the second half of the nineteenth century, long before we really even knew what a polymer was. The very first came about when a scientist reacted cellulose, in the form of cotton, with nitric acid. The result was cellulose nitrate. Cellulose nitrate, also called gun cotton, turned out to be a powerful explosive. It soon replaced common gunpowder as the explosive charge in the ammunition for rifles and artillery.
Cellulose nitrate was also used to make an early polymer containing composite material, safety glass. This was a sandwich made of a sheet of cellulose nitrate in between two layers of glass. The sheet of cellulose nitrate held the glass together when it was broken. This was great for automobile windshields. The glass would still break, but the broken pieces would stay stuck to the cellulose nitrate sheet, instead of flying into the faces of the passengers of the car during an accident.
When you react Cellulose with Acetic Acid we get cellulose acetate. This is used as a fiber. This fiber is used to make acetate graduation gowns. As a thermoplastic it is also used for photographic film. Cellulose nitrate was once used, but the combination of flammable cellulose nitrate and hot film projector bulbs just caused too many theater fires. So Acetate was sustituted to keep the theaters from burning down. Cellulose Acetate also replaced nitrate for use in safety glass, too.
The name “rayon” has been used for a lot of different polymers, but today when we talk about rayon, we’re usually talking about cellulose xanthate. It is used as a fiber, to make the rayon clothes you may be familiar with, like Hawaiian shirts. The original rayon was actually cellulose nitrate, but it was flammable, and soon came to be replaced in the fiber by cellulose acetate and cellulose xanthate.
Now you may well be asking that, seeing as cellulose makes wonderful fibers as it is, why modify it when you want to make fibers? Well you see, cellulose filaments, which make up cellulose fibers, have a fuzzy texture to them. But silk on the other hand has smooth filaments, which give silk fabric its shiny look. Once it was discovered that cellulose nitrate fibers were also smooth, and could be used to produce cloth with a silk-like sheen, cellulose derivatives were seen as a possible cheap replacement for expensive silk.