They are polymers made from natural gas or refined petroleum.
Polymers are large molecules made up of several units called monomers that are repeated many times along chains like beads on a necklace.
Monomers are small molecules that are linked to other monomers in long chains formed by the union of up to thousands of elements. These chains can be linear, have branches or in the form of a network.
They are generally compounds based on carbon bonds, called organic compounds.
- Mechanical properties of plastics
In general, plastics are soft and have medium mechanical resistance. The toughness depends on the plastic. There are plastics that are very resistant to shocks, such as polycarbonate, and others that are very fragile.
Some special high-performance plastics withstand high temperatures better than others and have good mechanical resistance. This is the case of Kevlar that is used in bulletproof vests.
Plastics are light, with a density similar to that of water (1 kg/litre)
Some plastics are manufactured with gas bubbles inside to achieve very low density and good thermal insulation. For example, polyurethane foam or expanded polystyrene (white cork) have this structure.
- Response to light
Some plastics such as polycarbonate or methacrylate are very transparent and are used to make windows, DVDs, headlights, etc.
Plastics discarded in the environment degrade in sunlight, breaking into polluting microplastics and producing toxic substances.
- Manufacturing properties of plastics
- Plastics are very malleable, extremely ductile, and meltable. All this makes it much easier to carry out welding or the manufacture of thin sheets, wires, or molded parts.
- Conductivity of plastics
- Plastics have low thermal and electrical conductivity, which is why they are used as electrical and thermal insulators.
- Chemical properties of plastics
- They resist oxidation, acids and caustics very well. For this reason, many chemical containers are made of plastic.
- Ecological properties of plastics
Most plastics are not biodegradable, they are toxic in their manufacture and in the environment.
Microplastics currently represent a major environmental problem because they are incorporated into the trophic chain as food for animals, which humans later end up eating. It is estimated that we currently ingest the equivalent in weight of a credit card each year in microplastics. Microplastics emit hormone-like substances that negatively affect the health of all animals.
Plastics can be recycled a small number of times because when they are recycled they degrade, losing their original properties and are not used to manufacture the same product.
It is estimated that only 14% of plastic is collected for recycling.
They can be melted or melted at not very high temperatures and harden again when cooled.
- Polyethylene terephthalate (PET)
- Widely used in beverage containers and textiles.
- Polyethylene (PE)
It is one of the most common plastics due to its low price. It is used in bags, transparent film, pipes, containers, etc.
There are two large types of polyethylene, the high density PEAD and the low density PEBD.
- Polyvinyl Chloride (PVC)
Rigid PVC: used in containers, windows, pipes.
Flexible PVC: used in cables, toys, footwear, floors, and coatings.
- Polypropylene (PP)
It is the most used plastic after Polyethylene.
It is used for food packaging, transparent sheets, fabrics, etc.
- Polystyrene (PS)
This plastic melts at relatively low temperatures (100ºC).
It is used in yogurt containers, razors, expanded polystyrene ("white cork" or polystyrene) for insulation and protection.
- Recycling symbols
Thermoplastics are usually identified with a symbol indicating their composition, to facilitate their recycling.
High performance thermoplastics¶
They are thermoplastics with better mechanical performance and heat resistance than the usual thermoplastics.
- It is used to make very resistant threads such as those for stockings, parachutes, the inside of tires, etc. Also to manufacture mechanisms such as gears and bearings, zippers, etc.
It is practically inert so it does not react with other substances. It has very low friction, is non-stick and resists temperatures up to 270ºC.
It is used as a coating for frying pans, tape to prevent water leaks in tap threads, mechanisms that do not need lubrication, etc.
- It is very transparent and very resistant to impacts, which is why it is used as a substitute for glass. CDs, DVDs, windows, bulletproof glass, riot shields, motorcyclist helmet visors, COVID separation panels, etc. are made with it.
It is even more transparent than polycarbonate. From 10 to 20 times more resistant to impact than glass, it is resistant to weathering and ultraviolet radiation.
It is used to make fiber optics, signs, displays, aquariums, works of art, etc.
They don't melt. If the temperature rises a lot, they degrade without melting, just like wood.
It was the first synthetic plastic, created in 1907. It can be molded as it hardens as it solidifies.
It is still used today to make frying pan handles and handles for kitchen utensils, electrical terminals, etc.
- Its best known use is to cover chipboard together with colored paper or imitation wood. Furniture that uses this technique is also called melamine furniture.
- Epoxy resin
It is used to make very strong two-component adhesives used to make airplanes, automobiles, sports equipment, etc.
Another very frequent use is the production of fiberglass or carbon fiber panels, used to make boats, racing car fairings, glass containers, printed circuit boards, etc.
- Its best-known use is the manufacture of adhesive foams that serve as thermal insulation for walls or to glue door and window frames with a great capacity to fill gaps.
They are highly elastic polymers.
It is of natural origin, a resin that is extracted from the syringa tree (Hevea brasiliensis).
It is used in gloves, condoms, mattresses, clothing, balls, tires, chewing gum, etc.
Its best known use is the manufacture of clothing and water boots that are thermal insulators (diving suits).
It is also used to make adhesive tape, protective covers, sleeping bags, etc.
Most polymers are organic compounds because they are based on long carbon chains. On the contrary, silicones are based on long silicon chains, forming inorganic polymers.
Its use as an adhesive for window panes and joints, kitchen molds for ovens or ice, medical prostheses, etc. can be highlighted.
Multiple choice questionnaire on plastic materials.