Information about plastics

A plastic granulate diagram on a grey background with most of the plastics processed at b-plastic

The first four datasheets below give a brief overview of the properties of the main plastics processed at b-plastic.

This is followed by a small glossary of other plastics, additives, compounds and many other interesting points relating to plastics.

This brief summary has been developed in discussions with our raw material suppliers and excludes any warranty or liability.

Mainly processed plastics at b-plastic

PA – polyamide

Physical – mechanical properties

Normal polyamide (1.07-1.14 g/cm³) is a medium-weight, semi-crystalline technical all-round thermoplastic. Polyamide has a relatively high water absorption (hygroscopic), which, depending on the type of polyamide and application, is adapted to the ambient climate in the factory by conditioning (warm water storage) the moulded parts, insofar as diffusion of the air humidity is not sufficient. Only …continue reading

PE – polyethylene

Physical – mechanical properties

0.90-0.96 g/cm³, PE is a very light semi-crystalline thermoplastic from the class of polyolefins, whereby VLD= Very Low Density ~0.90 g/cm³ and HD= High Density ~0.96 g/cm³ limit the density range. PE is water-repellent (hydrophobic) in normal settings like most polyolefins. PE is very tough. The modulus of elasticity, tensile strength and surface hardness give low values, increasing from VLD-PE to HD-PE. Good resistance to expansion cracking is predominantly found in VLD-PE and LLD/MLD-PE. With …continue reading

PP – polypropylene

Physical – mechanical properties

With 0.90-0.91 g/cm³, normal PP is a very light semi-crystalline thermoplastic from the class of polyolefins. PP has good toughness and excellent fatigue bending strength with suitably thin cross-sections. Compared to homopolymer PP, copolymer PP also has particularly good notched impact strength and is therefore also suitable for technical applications. The creep strength decreases sharply with increasing temperature. PP is water-repellent (hydrophobic), like most polyolefins. In terms …continue reading

PVC – polyvinyl chloride

Physical and mechanical properties

At 1.14-1.56 g/cm³, soft PVC is a relatively heavy amorphous thermoplastic, due to its halogen component (Cl). Depending on the plasticiser used, there are soft-rubber-like compounds of 40 Shore A (Shore A = hardness determination for soft plastics) to hard-rubber-like compounds of 98 Shore A. The latter corresponds roughly to the transition range …continue reading

Small glossary

For other thermoplastics, thermosets, thermoplastic elastomers, a brief explanation follows with the most important basic knowledge and properties of the plastics and terms described:

Image of other plastics: A schematic representation of the grid structure of thermoset plastic
thermoplastic
Images of other plastics: A schematic representation of the grid structure of thermosets
thermosets
Image of other plastics: A schematic representation of the grid structure of elastoplastic
elastoplastic

Collective term thermoplastic

Thermoplastics are normally hard or even brittle at room temperature. However, when they are heated in a certain temperature range, they become soft and plastic because the loose, non-toothed molecular filaments can now move against each other more easily. If they are heated further, the molecular filaments flow and the thermoplastic melts. Above the melting temperature, thermoplastics gradually begin to decompose. In the presence of oxygen or open fire, the thermoplastic burns with an open flame or by charring.

Thermoplastics are the largest group of synthetic polymers (= plastics) in terms of volume. The four most important ones are mentioned as examples:

These four bulk plastics account for two-thirds of all plastics production. They surround us every day in the form of packaging, appliance housings and endless other everyday objects.

Collective term thermosets

The collective term thermosets (before processing and cross-linking of single- or multi-component resins or powders) covers hard, no longer thermally plasticisable plastics with three-dimensional, close-meshed cross-linked molecular chains, which can essentially be divided into the following types:

The various thermoset settings are numbered in a standardised manner under the term moulding material (FS), e.g. FS31.

Collective term elastomers (also synthetic rubbers and elastoplastics)

The collective term elastomers covers soft-elastic, no longer thermally plasticisable plastics with three-dimensional, wide-meshed cross-linked molecular chains, which can essentially be divided into the following types:

Rubbers in liquid form are designated with an “L” in front of the abbreviation e.g. LBR. Mixtures of certain rubbers with each other in certain mixing ratios and with the addition of homogenisers or compatibilisers are possible to a very limited extent and sometimes with considerable effort and are usually offered by the raw material manufacturers of the chemical industry or by chemical specialists.

Collective term thermal elastomers – TPE (also elastoplastics)

Thermal elastomers is a collective term for thermoplastics with elastic properties similar to those of real elastomers (with cross-linked molecular chains: synthetic rubber, artificial rubber). These are then subdivided according to their similarity to the corresponding thermoplastics:

These in turn differ from plastomers (with density < 0.9 g/cm³, very light elastomer-like thermoplastics with very short molecular chains – e.g. polyolefin plastomers [POP’s]).

ABS – Acrylonitrile Butadiene Styrene

ABS (1.04-1.05 g/cm³) is a relatively light, amorphous engineering thermoplastic. ABS is relatively hard and rigid. It has a significantly higher toughness than the related impact-resistant polystyrene (SB). ABS is characterised by high thermal shock resistance and low water absorption (weakly hygroscopic). It is resistant to weathering to a limited extent. ABS is mainly used for glossy housings in the visible area, for multi-component injection moulded parts, for chrome-plated parts and for laser-marked components. The inherent colour of the standard types is a highly opaque beige to yellow-brown. Glass-clear is possible for special types. ABS is processed at approx. 240-260 °C and ignites at approx. 400 °C with a bright, sooty flame and a sweet smell.

NBR – Nitrile rubber

Nitrile rubber is a synthetic rubber. The abbreviation NBR is derived from Nitrile Butadiene Rubber. Nitrile rubber is obtained by copolymerising acrylonitrile (ACN) and 1,3-butadiene. Vulcanisates made from nitrile rubber have high resistance to oils, greases and hydrocarbons, favourable ageing behaviour and low abrasion. The thermal application range is between -30 °C and +100 °C, depending on the compound structure, and up to 130 °C for short periods. The material hardens at higher temperatures. Depending on the article, the material has a hardness between 60 and 80 Shore.

PC – Polycarbonate

PC (1.2 g/cm³) is a medium-weight, amorphous engineering thermoplastic. PC is very hard and has a particularly high fracture toughness. PC is characterised by high heat resistance, low temperature dependence and low water absorption (weakly hygroscopic). PC is mainly used indoors for highly transparent housings and covers, for highly fracture-resistant components, and for optical components (CDs, DVDs, lamp components, lenses). The inherent colour is crystal clear-transparent. PC is processed at about 320-350 °C and burns in the flame (extinguishes outside).

POM – Polyoxymethylene (also acetal resin, para- and polyformaldehyde or polyacetal)

POM (1.42 g/cm³) is a relatively heavy, semi-crystalline engineering thermoplastic with the structure -(CH2-O-)n- for the homopolymer. In the range of non-reinforced thermoplastics, POM has very high strength and stiffness (even at high continuous loads and low temperatures) as well as high dimensional stability and excellent fatigue resistance. Wear resistance is almost as good as PA. POM is preferred for technical applications such as snap connections, bearings (also in combination with silicone or PTFE additives), rollers and gearing components. The inherent colour of the standard grades is opaque-white. POM is processed at approx. 180-190 °C and ignites at approx. 375 °C and burns at 323 °C with a slightly bluish flame and pungent formaldehyde odour.

PTFE – Polytetrafluoroethylene (trade names: Teflon – Dupont, Hostaflon, Dyneon, GoreTex)

PTFE (2.16 g/cm³) is a very heavy, semi-crystalline engineering thermoplastic with a Shore D hardness of 55-60. It has the structure CnF2n and belongs to the class of polyhaloolefins. Although PTFE is classified as a thermoplastic, it can generally only be processed by sintering or pressure sintering due to its very close melting and decomposition temperatures and is therefore not subject to the moulding degrees of freedom of most other thermoplastics.

It was discovered by Roy Plunkett in 1938 and patented by Dupont in 1941. PTFE tends to creep under pressure and may need to be stabilised with glass fibres or other strength-enhancing additives. It is very inert. Even aggressive acids such as aqua regia cannot attack PTFE.

PTFE has one of the lowest coefficients of friction among solids. It slides on PTFE as well as wet ice on wet ice. Moreover, the static friction is just as great as the sliding friction, so that the transition from standstill to movement takes place without jerking (non-stick-slip effect).

An impressive example of this was the displacement of the new 12,500-ton Oberkassel Bridge in Düsseldorf by 47.5 m on PTFE plain bearings on 7 and 8 April 1976 (Link – in german). There are almost no materials that adhere to PTFE because the surface tension is extremely low.

PTFE is extremely resistant to all acids and bases, alcohols, ketones, benzines, oils, etc. and not resistant to sodium. In addition, PTFE is frost-resistant to -200 °C, can only be bonded after pre-treatment, physiologically harmless, non-flammable.

The inherent colour of the standard types is opaque white. The application temperature ranges up to about 260 °C. PTFE melts at 327 °C and also decomposes into highly aggressive hydrofluoric acid and highly toxic pyrolysis products.

For several years PTFE has already been used in the field of furniture glides. Here, the unique combination of rubber and PTFE should be mentioned, which brings both excellent noise damping and optimal floor protection or minimal adhesive and sliding friction forces when moving furniture.

The construction usually consists of a 2-3 mm flat, one-sided spherical rubber earth (also square and rectangular mouldings), to which a PTFE film several 1/10 mm thick is applied under high pressure and temperature. These universal glide inserts (UG) can be provided with a nail for wooden chair legs or other wooden furniture, glued on or inserted into furniture glides.

PTFE glide inserts are recommended for easy moving of furniture on most floor coverings. It makes moving furniture on carpeted floors much easier. PTFE is not suitable for seating furniture on smooth floors, as they slip unintentionally during use.

PU (PUR) – Polyurethane

PU is one of the most versatile plastics. Depending on the formulation and manufacturing process, PU can be produced as a thermoplastic (TPU thermoplastic elastomer), elastomer or thermoset. We encounter PU products in all areas of daily life (mattresses, shoe soles, tyres for rollers and wheels, insulation panels, soundproofing elements, paints, adhesives, insulating foam and much more).

Look in our range under the heading “Divers small parts” for the article series UEP, EP, GUR, UKP/OV

SB – Styrene Butadiene (also impact polystyrene, PS-I)

SB (1.04-1.05 g/cm³) is a relatively light, amorphous thermoplastic. It is tough and has a significantly higher toughness than polystyrene (PS). It is not weather-resistant. SB is mainly used (also foamed -> TSG) for low-cost housings and housing parts in the interior. The inherent colour is a strongly muted white (opaque-white). SB is processed at about 180-280 °C, is highly flammable, burns brightly and strongly sooty with a sweetish odour and smells slightly of burnt rubber.

Additives

Additives are substances that are added to the pure plastic in order to expand or improve its property profile and optimise its cost-benefit ratio. As a rule, every plastic offered to processors on the market already contains several additives. In addition, there are additives that processors can add themselves or that experienced compounders can incorporate into their compounds. Additives are essentially divided into the following groups according to their function:

Flame retardant

Slip and processing aids

Conductivity mediator

Impact resistance modifier

Finishing agents and brighteners

Stabilisers

*) = HALS ((Englisch –hindered amine light stabilizer) – do not absorb UV radiation, but inhibit polymer degradation by continuous and cyclic removal of radicals generated by photooxidation of the polymer

Compounds (composite material)

Compounds are ready-to-use material formulations in granulate or powder form. One or more plastics and, depending on the requirement profile, additives, colourants, fillers and reinforcing materials are used. Compounds for thermoplastics and thermoplastic elastomers are usually produced on adapted mixing extruders with subsequent granulation. This leads to a very material-friendly production with high homogeneity. Highly filled, highly viscous compounds, e.g. for the production of ceramic or metal powder moulding compounds, where the plastics only have a binder function, are produced in mixing kneaders.

Colourings

The colouring of plastics is done by means of organic or inorganic colour or effect pigments, which are added to the plastics during processing or compound production in the processing variants

with usually 0.5-5%. If there are high requirements for colour matching of parts from different materials (plastics, metals, wood), paint manufacturers or compounders are usually responsible. However, the involvement of compounders or colour manufacturers usually leads to a considerable increase in the cost of the parts list components. The technical coordination of the colouring of different parts of the BOM is usually circumvented by choosing different colours for the parts of the BOM.

Filler materials

The fillers (additives) are usually inexpensive, cost-reducing substances that do not deteriorate the properties of the plastic through the addition or only in a controlled manner (wood flour, etc.).

Reinforcements

Reinforcements give stressed plastic components or semi-finished products better stiffness, higher mechanical strength and higher heat resistance. Embedded reinforcements in the form of fibres, fabrics, spheres and grains made of glass, carbon, plastic and minerals are used, some of which, with adhesion promoters and an aligned embedding, enable even additional strength increases. Intrinsic reinforcements by stretching fibres, e.g. of polyamide and polyethylene, are also possible.

Blends

Blends (polymer blends) are generally understood to be mixtures of two or more different thermoplastics. No new chemical bonds of the molecules are formed, but purely physical blends are present. This is only possible with the help of a chemical adaptation, as thermoplastics are usually not compatible with each other (destruction, segregation or delamination) or adhesion is only possible by spraying one thermoplastic onto another in the mould. The properties of the resulting plastics differ greatly from the original plastics. Known blends are PA+ABS, PC+ABS, PC+PET, PC+PBT.

Macromolecules

Macromolecules contain a large number of atoms chemically linked by principal valences and, according to Staudinger, are divided into linear molecules and spherical molecules or plastics depending on the degree of polymerisation (hemicolloids – degree of polymerisation 10 to 100, mesocolloids – degree of polymerisation 100 to 500 and eucolloids – degree of polymerisation > 500).

Monomers

Monomers are low-molecular, reactive single molecules of plastics and have at least one functional group (reactive or bonding group as a prerequisite for bonding in polymers).

Homopolymere und Copolymere

Homopolymers are polymers that consist of only one type of monomer. They have only one repeating unit.

Copolymers (also called heteropolymers) are polymers (chemical substances made of macromolecules) that are built up from two or more different monomer units. In the production process, the product properties can be specifically controlled.

Illustration of the chemical structure of a homopolymer
Illustration of the chemical structure of a Copolymere

Polymers or plastics are produced by polymerisation, polyaddition or polycondensation (is specific to the type of plastic). Depending on the degree of polymerisation, they contain a corresponding number of main valency-bound monomers. Plastics are classified according to their (main) chains in terms of chain length differences between molecularly narrow or widely distributed and according to their molecular weight between low and ultra-high molecular weight.

Amorphous and semi-crystalline

Thermoplastics are divided into amorphous and semi-crystalline.

Schematic representation of the disordered structure of amorphous thermoplastics (plastics)
amorphous thermoplastic
Schematic representation of the structure of semi-crystalline thermoplastics (plastics)
semi-crystalline thermoplastic

Tacticity

The arrangement of the side chains on the main chains of the macromolecules essentially determines the properties of the plastics (amorphous or semi-crystalline and thus crystal-clear-transparent or translucent to opaque inherent colour, chemical resistance, mechanical values, etc.). A distinction is made between:

atactic
isotactic
syndiotactic