Základy polymerů

The word Polymer comes from the Greek ”poly” meaning many, and ”meros”, parts or units. A polymer is a group of many units. You combine many monomers (one unit) to create a polymer.

Polymer is often used as a synonym for ”plastic”, but many biological and inorganic molecules are also polymeric. All plastics are polymers, but not all polymers are plastics. Plastic actually refers to the way a material melts and flows.

Commercial polymers are formed through chemical reactions in large vessels under heat and pressure. Other ingredients are added to control how the polymer is formed and to produce the proper molecular length and desired properties. This chemical process is called ”polymerization”.

A homopolymer results from polymerizing only one kind of monomer. A copolymer results from using different monomers. Homopolymers have the same repeating unit while copolymers (which can be random, block or graft) can very have different numbers of repeating units. A terpolymer results from using three different monomers.

Thermoplastic materials can be repeatedly softened by elevated heating and hardened by cooling. They are either linear polymers or slightly branched. They consist of long molecules and each may have side chains or molecular groups not attached (not cross-linked). There are now newly developed thermoplastics that process as usual, but, at the end of the process are cross-linked with special techniques (e.g., nucleating agent, hot mold above forming temperature, etc.) Materials can also be across- linked by radiation. This cross-linking turns them into either an undeveloped or full thermoset and can greatly improve the physicals properties of the part.

Thermoplastics make up approximately 88-90% of all plastics processed today.

Any thermoplastic resin that can be extruded can be thermoformed. However, those with low hot strenght at forming temperature may be very difficult to form. Sheet and film is produced by extrusion, co extrusion, continuos casting, extrusion casting, calendring, compression molded, autoclave and press laminating, etc.

Basics

Elastomers are plastic material which can be expanded considerably by little force and which will return quickly to their original shape without force. There will be no plastic flow if temperature is increased as occurs with thermoplastics. Thermosettings plastics are hard, solid and remain in this state up to the decomposition temperature. Thermoplastics soften with increasing temperature after the softening point has been exceeded and harden again when cooled down. This procedure, which can be repeated as often as requested, is used for thermoforming of semi-finished products.

Thermosettings plastics are hard, solid and remain in this state up to the decomposition temperature.

Thermoplastics soften with increasing temperature after the softening point has been exceeded and harden again when cooled down. This procedure, which can be repeated as often as requested, is used for thermoforming of semi-finished products.