What is plastic?
Technology – plastics database
Materials comprised of macromolecular organic compounds are known as plastics. Technical terminology refers to them as organic polymers.
Conventional language refers to plastics, while this description– based on history– tends to be associated with poor material properties and lower quality.
Plastics are composed of chains of molecules (polymers) that can be linear as well as branched and cross-linked. Their lengths vary from several thousand molecular polymer units up to over one million. The molecular chains, in turn, always comprise repeating base units (monomers).
The technical properties of plastics can be greatly varied by the selection of the raw material, the manufacturing process and the mixing of various additives (admixtures). In this way, plastics of varying degrees of hardness, breaking strength, temperature resistance, elasticity etc. can be produced. Industrially speaking, this means that plastics can be processed into the most varied products. Among others, typical plastic products are pipes, thermal insulation, seals, textile fibers, floor coverings, coatings, adhesives,
Thermoplastics are plastics that consist of linear molecules. When energy is added these materials become soft and repeatedly moldable (plastic) until they finally melt. They can be brought to a desired form through various molding and remolding processes. After the respective part has been cooled it retains its form. This process is reversible; the behavior relies on thread-shaped, linear macromolecules.
Most plastics used today fall into this group (polyethylene, polypropylene, polystyrene, polyester). They are used for common consumer goods, packaging etc. as frequently as for technical parts in the automobile and electronics industries and, in particular, for roof sheeting, window framing and pipes in the construction industry.
Thermosetting plastics (duromers) are polymers that emerge from a melt or solution of components through a hardening process and cross-linking reactions. This irreversible reaction is usually brought about by heating (and thus the English technical term thermoset), but it can also be initiated and accelerated by oxidizing agents, radiation of sufficient energy or the use of catalysts. Heating thermosetting plastics does not lead to plastic deformability but rather only to decomposition. Cured thermosetting plastics are mostly hard and brittle and can be processed only by mechanical means in a further manufacturing process. This behavior results from the formation of enmeshed macromolecules.
Elastomers can change their form briefly by means of pressure or stretching. After the pressure or stretching is concluded the elastomer can quickly regain its original form again. Elastomers are cross-linked in a wide-mesh and are therefore flexible. They do not become soft when heated and are not soluble in most solutions.
Elastomers include all types of cross-linked rubber. The crosslinking takes place, for example, through vulcanization with sulfur, by means of peroxides, metal oxides or radiation. Sixty-percent of elastomers are used for tires. The remainder is distributed to other rubber items, for example chemical gloves and hygiene goods.
The history of plastics began more than 100 years ago. While this new class of materials was highly underestimated initially and tended to be considered an inexpensive replacement for metal and wood, plastics today are known as one of the most important materials in industry. In the course of the last 50 years the number of different plastics and their quality have increased markedly.