EN
Before moving on to the definition and classifications of plastics, we have to understand the building blocks of plastics. Those are called polymers. In short polymers are large molecules made of repetitive units called monomers. They could have linear, branched or cross-linked structure. Linear polymers are often thermoplastic, that is to say they "are fusible in certain temperatures and also soluble in some solvents. Cross-linked polymers are infusible and insoluble. Polymers are widespread in nature. They are building material for plant and animal organisms. Starch, cellulose, proteins and chitin are all polymers. Other large group of polymers are synthetically made from petrochemical sources, natural gas and coal. All polymer groups are used in many industrial branches.