The Identification of Plastics

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The Identification of Plastics 2016-12-06T05:35:25+00:00

The Identification of Plastics

Clues to get you started.

There will always be something you can glean from an object itself to help you decide what material it is made of or how it was manufactured.

  • When was it made?
  • What does it look like?
  • What does it feel like?
  • Does it smell?
  • What signs of deterioration can you see?
  • What marks are on it?

When was it made?

If you have an idea when the object was made, use the information under the relevant date span to narrow down the probabilities. Bear in mind though what you are getting are probabilities not certainties. Many plastics have had long periods of gestation and, as more and more plastics are invented, some become outmoded but nonetheless stay in production. And, although some materials are used most often with a particular manufacturing process, they may also be used from time to time with another.

Period Materials Manufacturing processes
1840 – 1880 Bois durci
Celluloid (see cellulose nitrate)
Gutta percha
Parkesine (see cellulose nitrate)
Shellac
Vulcanite
Compression moulding
Compression moulding , fabrication
Compression moulding, extrusion
Compression moulding, fabrication
Compression moulding
Compression moulding
1880 -1915 Cellulose nitrate
Shellac
Vulcanised rubber
Blow moulding, fabrication, thermoforming
Compression moulding
Compression moulding, fabrication, turning
1915 -1925

Casein formaldehyde
Cellulose nitrate
Phenol formaldehyde
Shellac
Vulcanite

Fabrication, extrusion
Blow moulding, fabrication, thermoforming
Compression moulding, casting
Compression moulding
Compression moulding, fabrication, turning

1925 -1940

Casein
Cellulose acetate
Cellulose nitrate
Phenol formaldehyde
Urea formaldehyde
Shellac

Extrusion, fabrication, thermoforming
Compression moulding, fabrication, injection moulding
Blow moulding, fabrication, thermoforming
Compression moulding, casting
Compression moulding
Compression moulding

1940 -1950

Cellulose acetate
Phenol formaldehyde
Polyamides
Polymethyl methacrylate
Polythene
Urea formaldehyde

Fabrication, injection moulding
Compression moulding, casting
Casting, extrusion, injection moulding
Casting, extrusion, fabrication, thermoforming
Extrusion, blow moulding, injection moulding
Compression moulding

1950 -1965

Acrylonitrile butadiene styrene
Glass reinforced plastic
Melamine formaldehyde
Phenol formaldehyde
Polyamides
Polymethyl methacrylate
Polypropylene
Polystyrene
Polythene
Polyurethane
Polyvinyl chloride
Silicones

Injection moulding
Compression moulding, fabrication
Compression moulding
Compression moulding
Casting, extrusion, injection moulding
Casting, extrusion, fabrication, injection moulding, thermoforming
Blow moulding, injection moulding, casting
Extrusion, foaming, injection moulding
Extrusion, blow moulding, rotational moulding
Blow moulding, extrusion, injection moulding, foaming
Blow moulding, extrusion, injection moulding, foaming, rotational moulding
Injection moulding

1965 onwards Acrylonitrile butadiene styrene
Glass reinforced plastic
Polyamides
Polycarbonate
Polythene
Polypropylene
Polyethylene terephthalate
Polymethyl methacrylate
Polystyrene
Polyurethane
Polyvinyl chloride
Silicones
Injection moulding
Compression moulding, hand lay-up, fabrication, pultrusion, vacuum laminated
Casting, extrusion, injection moulding
Blow and injection moulding, extrusion, foaming
Blow moulding, extrusion, injection moulding, rotational moulding
Blow and injection moulding, casting (film)
Blow moulding, extrusion, injection moulding
Casting, extrusion, fabrication, injection moulding, thermoforming
Extrusion, foaming, injection moulding
Blow moulding, extrusion, foaming, injection moulding
Blow moulding, extrusion, injection moulding, foaming, rotational moulding
Injection moulding

What does it look like?

Transparent ? Pale or bright coloured? Amber, ivory, tortoiseshell or pearlised? Shiny?

Transparent
Relatively few plastics are transparent like glass. All transparent plastics can be made translucent or opaque by the addition of pigments or fillers. Some plastics are only transparent in sheet form. If it is moulded and transparent it is probably made of one of the following:

  • Phenol formaldehyde as liquid resin not with filler
  • Polycarbonate
  • Polylactide
  • Polyethylene terephthalate
  • Polymethyl methacrylate
  • Polyurethane

The following plastics can also be clear in sheet or film form but are translucent or opaque when injection-moulded:

  • Cellulose acetate
  • PVC
  • Polypropylene

Is it translucent?  If so, it can be any of the above and also:

  • Polythene
  • Silicones

Pale or bright coloured
If so it is unlikely to be made of one of the following as they usually come in dark colours. However plastics that can be light or bright in colour also come in dark colours.

  • Bois durci
  • Gutta percha
  • Vulcanised rubber
  • Horn
  • Phenol formaldehyde as liquid resin not with filler Shellac

Amber, ivory, tortoiseshell, or pearlised
If it imitates one of these it is likely to be made of one of the following:

  • Casein formaldehyde
  • Cellulose acetate
  • Cellulose nitrate
  • Phenol formaldehyde as liquid resin not with filler

Shiny
If it has a hard glossy surface it is likely to be one of the following but bear in mind that nowadays almost any plastic can be made glossy:

  • Acrylonitrile butadiene styrene (ABS)
  • Casein formaldehyde
  • Melamine formaldehyde
  • Phenol formaldehyde
  • Polycarbonate
  • Polymethyl methacrylate
  • Polystyrene

What does it feel like?

Soft? Flexible or rigid? Sticky?

Soft
Some plastics have such a soft surface that they can be indented with a finger nail. If the object feels as if that is likely it is probably made from one of the following:

  • Polythene
  • Polyurethane
  • Polyvinyl chloride (when in flexible form)
  • Silicones

Flexible or rigid
Many plastics can be rigid or flexible however a few are always rigid. These are:

  • Acrylonitrile butadiene styrene (ABS)
  • Bois durci
  • Gutta percha
  • Phenol formaldehyde
  • Vulcanite

Sticky
Stickiness is a sign of degradation. The following can go sticky:

  • Cellulose acetate
  • Cellulose nitrate
  • Polyvinyl chloride
  • Polyurethane foam

Does it smell?

The following smells are sometimes given off by the plastics listed:

Carbolic acid:

phenol formaldehyde

Formaldehyde:

casein formaldehyde

Milky, if rubbed

casein formaldehyde

Mothballs (camphor):

cellulose nitrate

Plasticky (new car smell)

polyvinyl chloride

Sweet:

polyvinyl chloride but only when degrading

Sulphurous:

hard rubber

Vinegar:

cellulose acetate

Vomit /rancid butter:

cellulose butyrate, cellulose acetate butyrate

Waxy:

polythene

What marks are on it?

A small bird’s wing was used to indicate the use of the material bois durci. An infinity sign is the logo of Bakelite and thus frequently indicates the material phenol formaldehyde but the company made many other plastic materials. It only appears on Bakelite promotional mouldings. Bakelite did not make mouldings for the general market. Recycling triangles were introduced in 1988 so any object with these on must date from that year or later. Smooth circular marks are a sign of the use of ejector pins to push the moulding from the mould and thus of injection moulding.

An imperfection on an otherwise smooth surface may be a residue left at the spot the material has been forced into the mould and thus indicate the use of injection moulding. Such marks can be extremely hard to detect and they may not be where you might expect to find them, for example centrally placed on the base or on the edge. They can be polished off so their absence does not tell you anything.

The following are trade names that frequently appear on mouldings. They are associated with the materials indicated:

Bandalasta

Thiourea-urea formaldehyde

Beetleware

Urea formaldehyde

Carvacraft

Phenol formaldehyde

Gaydon

Melamine formaldehyde

Linga Longa

Urea formaldehyde

Melaware

Melamine formaldehyde

Melmex

Melamine formaldehyde

Xylonite

Cellulose nitrate