Plastics

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Plastics

Definition

The term ‘plastics’ refers to synthetic organic materials that contain macromolecules as essential components [1].

All natural materials (rubber, protein, cellulose) and plastics contain molecules as their smallest particles, which in turn consist of a large number of atoms. The term ‘macromolecule’ takes this special feature into account, with a minimum of 1000 atoms per macromolecule being considered the lower limit. A distinction is made between low-molecular compositions, such as water H₂O, and high-molecular compositions.

The macromolecules present in a plastic vary in the number of atoms per macromolecule and thus in their molar mass or molar mass distribution.

Macromolecules are usually consisting of many identical or similar particles and are often referred to in chemical terminology as polymer molecules or, for short, as polymers (see also: polymers & structure).

The importance of plastics processing

Processing, i.e. plastics processing [2], is of particular importance in the plastics industry. It is only through this processing that the polymer as a raw material acquires its final properties as a material. There is therefore a clear difference between a ‘polymer(s)’ and a ‘plastic(s)’. This difference is often ignored in the literature.

The following diagram describes the development of a plastic – starting with a polymer as a raw material for plastics – in the order of the terms polymer (substance), moulding compound (mixture of substances), plastic (moulding compound/material).

Fig.:

Distinction between terms: polymer (substance), moulding compound (mixture of substances), plastic (moulding compound/material) [1]

The word ‘plastic’ is a collective term for an entire class of materials whose final properties are determined not only by the polymeric material, but also decisively by additives such as plasticisers, solvents, colourants (pigments), fillers and reinforcing agents, lubricants, stabilisers and much more.

Classification into material groups

Plastics are classified according to whether they can be plastically deformed using heat and/or pressure into non-cross-linked and cross-linked plastics. When heated, non-cross-linked and cross-linked plastics generally exhibit different behaviour. With uncrosslinked plastics, plastic shaping can be repeated, i.e. it is possible several times. In contrast, crosslinked plastics undergo irreversible hardening, i.e. they do not soften again when reheated.

In plastics practice, a classification based on thermal-mechanical behaviour is used to divide plastics into three different categories:

• Thermoplastics and thermoplastic elastomers
• Elastomers
• Thermosets

Thermoplastics are further classified according to their order state into

• amorphous thermoplastics (unordered)

and

• semi-crystalline thermoplastics (partially ordered).

See also

• Polymers & structure
• Polymer
• Polymer blend
• Barrier plastics
• Layer silicate-reinforced plastics
• Bio-plastics
• Short-fibre reinforced composites
• Smart Materials
• Particle-filled plastics

References

[1]	Kaiser, W.: Kunststoffchemie für Ingenieure. Carl Hanser, Munich Vienna (2006) pp. 30/31 (ISBN 3-446-22069-0; see AMK-Library under N 12)
[2]	Radusch, H.-J.: Bestimmung verarbeitungsrelevanter Eigenschaften. In: Grellmann, W., Seidler, S. (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2024) 4th Edition, pp. 41–73 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23)
[3]	Rätzsch, M., Arnold, M.: Hochpolymere und ihre Herstellung. Fachbuchverlag Leipzig (1973), see AMK-Library under G 13