Sugars are not only used to sweeten life. Nature forms multiple sugars (polysaccharides) with an enormous structural variation, which chemists can transform into new products in the laboratory. Many of these polysaccharides have become an integral part of our everyday lives. The best known of these are cellulose, which is obtained from wood and cotton, and starch, which is found in tubers and plant seeds. Starch not only provides energy in our daily diet, it can also be found in chemically modified form as a food additive and a component of pharmaceutical products. We encounter cellulose in the form of cotton and viscose fibers in textiles. It is also processed - chemically modified - into thickening agents for paints and toothpaste, films for flat screens and filters for environmental technology.
You are invited to experiment with polysaccharides yourself in demonstrative experiments.
Tear-resistant films made of cellulose acetate: In contrast to cellulose, cellulose acetate is soluble in acetone ("nail polish remover"). You spread the solution on a glass plate and spread it evenly with a squeegee. After the acetone has evaporated, you can remove the cellulose acetate as a film and convince yourself of its mechanical stability.
Compostable objects made from starch: Vegetable starch is mixed with water and other ingredients to form a dough from which various objects can be baked.
Artificial caviar and other items made from alginate: Alginic acid is also a polysaccharide that is used in food. It contains acid functions which, as a sodium salt, cause the polymer to be soluble in water. When this solution is dripped into a calcium salt solution, the calcium ions are enveloped by the polymers in a similar way to the eggs in the packaging carton. The molecules are thus cross-linked and can no longer move freely - a gel is formed. If dyes are mixed into the alginate solution, they are trapped in the gel.
Cellulose is spun into threads: Cotton is a plant-based fiber material that consists almost exclusively of cellulose. Wood pulp can also be processed into textile fibers. To do this, the polymer must first be dissolved. This can be done with "Schweizer's Reagens", a mixture of water, copper(II) sulphate and ammonia. The deep blue solution flows through a nozzle into the precipitation bath. There, the cellulose becomes insoluble; it is regenerated and can be wound onto a spool.
