A material typically characterized by low density, low stiffness, low electrical and thermal conductivity, high deformation at break, low melting temperature. Plastics can be shaped easily, possess good chemical properties and from the point of view of industrial manufacturing require less machining, coating and thermal treating than other materials, while having lower mechanical properties. Plastics are normally made of polymers with the addition of other substances to improve performance and reduce costs. Polymers are a class of materials having a structure based on long molecules with a strong backbone of carbon (or silicon) atoms but linked to each other by weak bonds, amorphous or semi-crystalline microstructure, strong time and temperature dependence of mechanical properties. Polymers are substantially different from and alternative to metals and ceramics, but can be combined with those to form composites. Most polymers are obtained by synthesis from oil products, and this technology has developed since less than a century ago – nevertheless the number of applications in everyday life has grown immensely and the world production is now in the order of some cubic kilometers per year. Notable examples of natural polymers exist, e.g. cellulose and gum.
Thermoplastics can soften and melt if enough heat is applied, so they can be processed, mixed and shaped again if needed – this is especially good for recycling, although properties need to be monitored. Thermosets undergo more complex and irreversible reactions when processed, so they can be easily shaped only once. However, they typically possess better mechanical and thermal properties and are the most common basis for high-performance composites.
Oil industry and basic industrial chemistry supply the starting ingredients for polymers: simple structural units are later ‘polymerized’ (by means of special chemical reactors and catalysts) forming long chains and acquiring the typical properties of these materials. The length of backbone chains, their composition and internal bonds, plus the occurrence of branching, determine an unlimited variety of properties, further widened by the addition of other chemicals, inert substances, reinforcing phases, coloring agents and so on – giving the world of plastics.
Due to the peculiar range of properties and complexity, plastics require dedicated scientific instrumentation for analysis and characterization, with a focus on each step of their life cycle - from raw materials production to compounding (blending and mixing), processing, manufacturing of finished parts, plus recycling.
Some examples of applications of plastics (classified by basic polymer)
- Polyethylene (PE): Wide range of inexpensive uses including supermarket bags, plastic bottles.
- Ultra-high molecular weight polyethylene (UHMWPE): Parts for prostheses
- Polypropylene (PP): Food containers, appliances, car fenders (bumpers), plastic pressure pipe systems.
- Polystyrene (PS): Packaging foam, food containers, disposable cups, plates, cutlery, CD boxes.
- High impact polystyrene (HIPS): Fridge liners, food packaging, vending cups.
- Acrylonitrile butadiene styrene (ABS): Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.
- Polyethylene terephthalate (PET): Drinking water bottles, jars, plastic film, microwavable packaging.
- Polyester (PES): Fibers, textiles.
- Polyamides (PA): (Nylons) Fibers, toothbrush bristles, fishing line, under-the-hood car engine moldings.
- Polyvinyl chloride (PVC): Plumbing pipes and guttering, shower curtains, window frames, flooring.
- Polyurethanes (PU): Cushioning foams, thermal insulation foams, surface coatings, printing rollers.
- Polycarbonate (PC): Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.
- Polyvinylidene chloride (PVDC): Food packaging.
- Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS): A blend of PC and ABS used in car interior and exterior parts, and mobile phone bodies.
- Polytetrafluoroethylene (PTFE): Frying pan coatings, low-friction and chemical-resistant parts.
- Polyetheretherketone (PEEK): Substitutes light metal alloys or ceramics for specific applications.