Understanding Plastics: Definition, Polymers, and Classification
Understanding Plastics
Today, plastic is used in our daily lives. It has replaced metal parts in the automotive industry and is used in construction, packaging, household appliances (washing machines, blenders, refrigerators, etc.). In the near future, it will be entering other branches of industry, for example, in medicine, such as joint replacement (artificial joints), games of all kinds, and sporting goods. As you can see, the plastic industry is in the process of growth. It is common to see pieces that were previously produced with other materials, e.g., wood or metal, and have already been replaced by plastics.
What is a Plastic?
“Plastic” is the generic name by which this material is known, but chemically, it is part of the family of polymers.
What is a Polymer?
The word “polymer” comes from the Greek poly, meaning “many,” and mere, meaning “part” or “segment.” Therefore, we can say that a polymer is a substance composed of many segments. It can be a natural or synthetic organic compound whose main feature consists of large molecules (macromolecules), and these, in turn, are made up of small molecules that are repeated several times. This small molecule that is repeated is called a monomer.
Monomer
A monomer is a compound of low molecular weight.
- Monomer
- Polymer
In the wider sense of the word, plastics include those organic substances which are produced by the chemical transformation of natural products or through the synthesis of primary products based on the disintegration of coal, oil, and natural gas.
How is Plastic Made?
Most plastics are derived synthetically, and the reaction by which molecules are joined to form a lightweight polymer is called polymerization. There are two basic processes of polymerization:
- Addition polymerization
- Condensation polymerization
How are Plastics Classified?
Plastics can be classified by their chemical structure, since that determines their properties. Classification by chemical structure is according to their heat conduction, crystallinity, and the presence of monomers.
Plastics are generally classified by their behavior in heat: thermoplastics, thermosets, and elastomers.
Thermoplastics
These are materials whose macromolecules are arranged as long chains linked together by secondary bonds. Their arrangement can be compared to a tangle of long, thin wires. The main feature of these materials is that they can be brought to a viscous state and processed several times by warming.
Thermosets
These materials are formed into practically a large molecule-shaped network, with very strong bonds between molecules. This causes these materials not to soften with heat application after they have been processed. Unlike thermoplastics, these materials can no longer be shaped by heat; they are destroyed when subjected to heat.
Elastomers
Elastomers are composed of long chains that are united by very few chemical bonds. This allows a large intermolecular movement, which is reflected in their good flexibility. These are materials that have memory, i.e., they resist efforts to alter their form, recovering when the effort is removed. Because of their chemical bonds between molecules, they cannot be reprocessed, and plastics have an amorphous structure.
While these plastics have been managed independently because their market is channeled as replacements for natural rubber, there are also thermoplastic rubbers, which are a family of advanced elastomers.