Thermoplastics ( Singular the thermoplastic , from ancient Greek θερμός thermos , warm ',' hot 'and πλάσσειν plassein form', shapes), also plastomers mentioned are plastics , which in a certain temperature range ( thermo - plastic can deform). This process is reversible , which means that it can be repeated as often as required by cooling and reheating until it reaches the molten state, as long as the so-called thermal decomposition of the material does not set in due to overheating . This is where thermoplastics differ from thermosets and elastomers . Another unique selling point is the weldability of thermoplastics.
Structure and division
Thermoplastics are made up of few or non-branched, i.e. linear carbon chains that are only connected to one another by weak physical bonds . These binding forces are more effective when the chains are aligned in parallel. Such areas are called crystalline , in contrast to amorphous (disordered) areas in which the macromolecules are tangled.
Thermoplastics can be divided into the groups of standard plastics , engineering plastics and high-performance plastics with regard to mechanical, thermal and chemical properties . However, this is not a chemical, but an application-related, engineering division.
Thermoplastics were originally mainly processed by injection molding , which is why they were also known as injection molding compounds (in contrast to thermosets, which were called molding compounds ). Today extrusion is another important processing method. Further processing options are e.g. B. blow molding , film blowing , hot caulking and calendering . In principle, thermoplastics can also be processed mechanically and thermally. Mechanical processing means z. B. sawing, milling, grinding, turning, planing as well as the joining processes gluing and welding. The thermal processing methods include z. B. free deformation using a tool and vacuum deep drawing .
- Thermoplastics are solid before heating and after cooling, which does not mean rigid. Many thermoplastics are flexible even in the solid state and some can also be processed and changed in shape in the solid state.
- In the area in which a thermoplastic becomes thermoelastic, its shape can be changed, but it retains its original shape and can be brought back into it.
- The material becomes soft and is no longer dimensionally stable, so it may not be possible to return it to its original shape (for example with tubes).
- When the thermoplasticity range is exceeded, the material becomes flowable. If the material is heated further, it evaporates and decomposes into its basic components.
The thermoplastics include B. Acrylonitrile-Butadiene-Styrene (ABS), Polyamides (PA), Polylactate (PLA), Polymethylmethacrylate (PMMA), Polycarbonate (PC), Polyethylene Terephthalate (PET), Polyethylene (PE), Polypropylene (PP), Polystyrene (PS) , Polyetheretherketone (PEEK) and polyvinylchloride (PVC). The longest known thermoplastic is celluloid . The most commonly used thermoplastics are polyolefins , such as polyethylene and polypropylene.
Purchase / trade of thermoplastics
In Western Europe, thermoplastic plastics are for the most part traded directly between plastics producers and plastics processors. In the case of specialties, small quantities, in regionally or nationally defined areas, distributors are sometimes interposed.
A commodity index , the so-called Plastixx, provides a comprehensive overview of the price development of thermoplastics in Europe . Since the beginning of 2004, the raw materials polyethylene-LLD and polypropylene have also been traded on the London Metal Exchange (LME) as commodity futures . Since mid-2007 there has also been regionally different pricing (for Asia, Europe, North America) using this system in order to map the market situation even more precisely.
- Jürgen Ruge, Helmut Wohlfahrt: Technology of materials . Production, processing, use, 9th edition, Springer Vieweg, Wiesbaden 2013, ISBN 978-3-658-01880-1 .
- Hubert Gräfen, VDI-Gesellschaft Werkstofftechnik (publisher): Lexicon of materials technology . VDI Verlag, Düsseldorf 1993, ISBN 978-3-642-51733-4 .