Polymers

Types of Polymers

Polymers are materials that mainly consist of macromolecules. Within a macromolecule, many smaller molecular units, the so-called monomers, are combined to form very large molecules, the polymers.
Most polymers are synthetic, but many natural materials also belong to polymers.
Polymers are divided into three groups according to their mechanical and thermal properties.

Thermoplastics

Thermoplastics are polymers that consist of very long linear molecules. Due to energy supply, these materials will become soft and malleable (plastic) at the discretion and will finally melt. By applying various forming processes, they can be put into the desired shape. After the part in question has cooled off, it will keep its shape. This process is reversible (meaning “can be reversed”). The behavior is caused by thread-like linear macromolecules.
Most of the polymers used today belong to this group (polyethylene, polypropylene, polystyrene, polyester). They are often used for manufacturing simple consumer products, packages, etc., and technical parts necessary for the automotive, electrical, and building industry such as roof sheeting, window profiles, and pipes.
Two or more thermoplastics that are compatible with each other may be mixed to achieve new properties that have not existed before (polyblends).

Duroplasts

Duroplasts (Duromers) are polymers that emerge in a curing process that form a melting or a solution of components via a cross-linking reaction. This irreversible reaction is mainly achieved by heating but can be initiated and accelerated by oxidizing agents, energetic emissions, or catalysts. Warming Duromers does not result in plastic workability but only in their decomposition. Cured Duromers are mostly hard and brittle as well as only machinable in the further production process.
This group also comprises polyester resins, polyurethane resins for lacquers and surface coatings and practically all synthetic resins such as epoxy resins.

Elastomers

Elastomers may change their shapes due to pressure or elongation for a short period. When the pressure or elongation has ended, elastomers rapidly recapture their original shapes. Elastomers are wide-meshed and cross-linked and thus flexible. They do not soften when heated and are not insoluble in most solvents.
Elastomers comprise all kinds of cross-linked rubber. This cross-linking happens, e.g., via vulcanization by Sulphur, via peroxides, metal oxides, or radiation.
Natural rubber (NR), acrylonitrile butadiene rubber (NBR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), and ethylene-propylene-diene-rubber (EPDM) are elastomers.