Cellulose.doc

Cellulose (纤维素)Uses:wood, fibers (cotton, rayon, flax, hemp), component of shampoo thickenersMonomer:glucoseMorphology:crystallineCellulose is one of many polymers found in nature. Wood, paper, and cotton all contain cellulose. Cellulose is an excellent fiber. Wood, cotton, and hemp rope are all made of fibrous cellulose. Cellulose is made of repeat units of the monomer glucose. This is the same glucose which your body metabolizes in order to live, but you cant digest it in the form of cellulose. Because cellulose is built out of a sugar monomer, it is called a polysaccharide. glucose (葡萄糖)Cellulose has an important place in the story of polymers because it was used to make some of the first synthetic polymers, like cellulose nitrate, cellulose acetate, and rayon. Cellulose NitrateThe very first derivative of cellulose came about when a scientist reacted cellulose, in the form of cotton, with nitric acid. The result was cellulose nitrate. Often times, as soon as something is invented, the first thing we do is figure out a way to use it to kill people. Such is the case with 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. It worked so well that in the First World War, we were capable of killing ten million people in only four short years. In all fairness to cellulose nitrate, it was also used for peaceful purposes. You see, even back then, there was concern that Africas elephant herds were disappearing far too quickly, and a replacement needed to be found for ivory in billiard balls. Cellulose nitrate is also a thermoplastic, and was quickly used to make the balls for the worlds pool halls. The only problem was every once in awhile one of these would explode during the break. 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, sure enough, 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. Cellulose AcetateIf reacting cellulose with nitric acid gives cellulose nitrate, then I suppose its not too much of a stretch to imagine what happens when you react cellulose with acetic acid. Yes, folks, we get cellulose acetate. This is used as a fiber. Cellulose acetate fiber is used to make acetate graduation gowns. As a thermoplastic its 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. Ever hear about how old movies deteriorate because they are on flammable nitrate stock? These movies are on cellulose nitrate film. Cellulose acetate saved the day, by keeping theaters from burning down, and keeping old movies around longer. Of course, some movies we wish would deteriorate faster. But alas, today newer polyester films are replacing good old celluloid. And of course, if cellulose nitrate wasnt already having a hard enough time of it, cellulose acetate replaced it for use in safety glass, too. Rayon （人造纤维）Lets clear something up right at the start. The name rayon has been used for a lot of different polymers, but today when we talk about rayon, were usually talking about cellulose xanthate. Its used as a fiber to make the rayon clothes you may be familiar with, like Hawaiian shirts. The original rayon was actually our old friend 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. Nothing wrong with that, especially. 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. Clean hairAnother cellulose derivative is hydroxyethylcellulose. It differs from plain ol regular cellulose in that some or all of the hydroxyl groups (shown in red) of the glucose repeat unit have been replaced with hydroxyethyl ether groups (shown in blue). These hydroxyethyl groups get in the way when the polymer tries to crystallize. Because it cant crystallize, hydroxyethylcellulose is soluble in water. In addition to being a great laxative, its used to thicken shampoos as well. It also make the soap in the shampoo less foamy, and it helps the shampoo clean better by forming colloids around dirt particles. Normally, particles of dirt are insoluble in water. But a chain of hydroxyethylcellulose (shown in blue) can wrap itself around a dirt particle (shown in red). This mass can be thought of as a snack cake, with the polymer chain as