Polymer packaging materials for preservation of foodstuffs
One of the most important high-molecular-mass compounds is at present the class of polymers. As compared with common substances, such as, e.g., water (molecular mass, 18), benzene (molecular mass, 78), chalk (molecular mass, 100), the values of polymers’ molecular masses vary within the range of tens of thousands up to millions. In polymers, their giant molecules are built from consecutively bound groups of atoms forming a long chain, which contains sometimes hundreds of thousands repeating structural units: elements, links. The word “polymer” means “many parts” and is derived from the Greek words “polys” meaning “many” and “meros” meaning “parts”. An example of a polymer consisting of atoms linked by chemical forces into a chain is plastic sulfur. As is known, it is produced by pouring molten sulfur into cold water. The structure of polymer sulfur is represented by a chain of atoms linked by chemical bonds: . In this state, the properties of sulfur differ from the properties of common crystalline sulfur. They resemble rubberlike rather than solid bodies. For most polymers, the repeating elements of the structure are usually small groups of atoms. One of the simplest (from the point of view of its chemical structure) and widespread polymers – polyethylene – has the following structure: .