Synthetic materials were first used on an industrial scale in the latter half of the 19th century. Today, the impact on the environment far exceeds the possibilities in place for handling the waste they produce. Where is the impact the greatest and what are the trends in recycling plastic?
The term 'plastic' is ambiguous. Literally, it means a material that is malleable (can be shaped without breaking), and can be engineered and molded by flow (the raw material is liquid during manufacture). However, 'plastic surgery' does not refer to the use of materials, but rather emphasises the malleable aspect of plastic, in the reshaping of flesh.
The general use of the word 'plastic' is for a broad range of materials. These consist of large, long-chain molecules, which are organic polymers, and are usually synthetic, with high molecular mass. The large range of plastics have different properties, such as hardness, malleability, elasticity, resistance to temperature and chemicals, which can be controlled by the manufacturing process, and the additives. There are three main sub-groups of plastics: thermoplasts, duroplasts, and elastomers. The raw substance from which plastic is made is typically petrochemical in origin, although biosynthetic plastics can be derived from non-fossil sources, such as natural plant oils.
In 1856, the metallurgist Alexander Parkes produced Parkesine. He had treated cellulose with nitric acid to produce cellulose nitrate (pyroxilin), which, when dissolved in alcohol, hardened into a transparent elastic material. It was pigmented so that it would resemble ivory.
However, it was not until 1907 that the first fully synthetic plastic was commercially produced. Leo Baekeland invented the term 'plastics' for his new 'bakelite'. Once the advantages of plastics over traditional materials, such as wood, stone, leather, metal, glass and ceramics, for household and other goods, had been realised, the plastics industry leapt upon every new polymer the chemists could produce.
Development in the 1920s and 1930s led to synthetics with enormous commercial potential, not only as a cheaper alternative to traditional materials, but materials, such as nylon, which made entirely new products possible. World War Two provided a stimulus for the mass-production of plastics, such as acrylic glass as an alternative to silicate glass for airplane windscreens.
By the 1950s, mass production of products made from plastics like polystyrene (PS) and polyvinyl chloride (PVC) transformed the consumer manufacturing industries. By the 1980s, the world was producing trillions of plastic bags for throw-away shopping conveniences, and packaging still accounts for as much as 40% of plastic use.
As a result, the love affair with the new materials grew into a nightmare, as millions of tonnes of discarded plastic waste entered the biosphere. Its characteristic of durability and non-degradability, so treasured by the manufacturing industry, was a cause of enormous concern for the environment. The natural world does not know what to do with unnatural products.
A thermoplastic is a high-molecular weight synthetic polymer, with the characteristic of malleability when hot. They are used in plastics manufacturing, for injection and compression molding, calendering and extrusion.
An elastomer is a polymer which has rubber-like qualities.
It is unlikely that plastic will ever be 100% recycled or reclaimed, at least not in the foreseeable short-term. Therefore, degradability of plastic is the next best option, ensuring that if the plastic ends up in a landfill, or worse, in the environment, it will degrade on a timescale which reduces the danger to wildlife, and nuisance to humans, considerably.
Many retailers now use degradable plastic carrier bags. Bio-degradable plastics contain a small percentage of non oil-based substance, such as corn starch, which will allow bacteria and ageing to break up the polymers. Fastfood cutlery made of this degradable polymer can now be composted without segregation.
Photodegradable plastics are sensitive to sunlight, and will break up when exposed for a predetermined and controllable time period. An example of a needed application is the deadly beer 'six-pack' carriers, which are strong enough for the purpose they are designed for, but which will photodegrade after 6 weeks, safeguarding wildlife, particularly marine creatures, which easily get trapped in the circular rings.
Genetically engineered bacteria can synthesis a biodegradable plastic, and additives aid the rate of biodegradation.
There are three problems with degradable plastic: 1. the plastic needs particular conditions to successfully degrade. If photodegradable plastics are dumped in a landfill, away from light, they will not decompose. 2. Biodegradable waste will produce emissions of CO2, or worse, methane, if it degrades anaerobically (without sufficient oxygen). 3. Consumers may reverse the better trend of waste minimisation if they believe the waste is no longer an environmental hazard.
Bio-plastics are synthetic polymers made from plants, sugars, or plastic which is grown within genetically modified plants and micro-organisms. The use of bio-plastic avoids the use of non-renewable fossil fuel as feedstock, and also reduces risks from chemical additives in standard plastics. Toy manufacturers have begun to switch over to bio-plastics for health and safety reasons.
Many biodegradable plastics decompose under conditions available only industrial composting facilities. Under normal household conditions (humidity, temperature), plastics need significantly longer periods of time to decompose. In addition, there are no useful soil nutrients from the decomposition of plastic, only chiefly carbon dioxide and water.
In life cycle analysis (LCA), bioplastics have advantages: compared to standard plastics, they save on fossil oil and CO2 emissions during manufacture. On the other hand, they have disadvantages of new problems. The cultivation of raw material, such as corn, potatoes and cane sugar, can have a negative impact on the environment: diesel and fertiliser consume fossil oil, and over-fertilisation and pesticides contaminate watercourses.
Types of Plastic
There are many types of plastic, with very variable properties. Of particlular interest is whether they can be recycled, and at least prevented from entering the environment.
|PE||Polyethylene||(C2H4)n||supermarket bags, plastic bottles, and many other packagings and uses||Not recycled, but PE can be made from renewable feedstock, such as wheat grain and sugar beet|
Not readily biodegradable, a limited amount can be degraded by bacteria, and research into turning PE into oil is underway
|LDPE||Low-density polyethylene||(C2H4)n||supermarket carrier bags, bin liners||Not recycled|
Not easily biodegradable
|HDPE||High-density polyethylene||(C2H4)n||milk and washing-up liquid bottles||SPI resin ID code 2, recyclable|
|PP||Polypropylene||(C3H6)n||yoghurt tubs, drinking straws, bottle caps, many appliance casings, car bumpers, piping, resistant to acids and bases||Recyclable, Resin identification code "5"|
|PVC||Polyvinyl chloride||Food trays, drinks bottles, shampoo dispensers, cling film||PVC is broken into small chips, impurities removed, refined to white PVC. Recycled c. 7 times and has a lifespan of 140 years|
EU regulations for reuse of PVC in construction
|PS||Polystyrene||(C8H8)n||Food foam trays, burger boxes, egg cartons, plastic cutlery||Not recycled or collected, except in Germany (packaging law - Verpackungsverordnung)|
Chemically inert, but bacteria (Pseudomonas putida) can convert styrene oil to a biodegradable form. PS is long-lasting and a big litter problem.
- Types of Plastic
Acrylonitrile butadiene styrene, used for electronic equipment casings, computer monitors, printers, and drainpipes
Polypropylene, yoghurt tubs, drinking straws, bottle caps, many appliance casings, car bumpers, piping
Polyethylene, [(C2H4)n], used for supermarket bags, plastic bottles, and many other packagings and uses
High-density polyethylene, used for milk jugs, detergent bottles, molded containers
Low-density polyethylene, used for shower curtains, floor tiling, skirting boards
Polyvinyl chloride, used for plumbing piping, shower curtains, window frames and flooring
Polyvinylidene chloride, used for food packaging
Polystyrene, used for packaging foam, food containers, plastic tableware, CD cases
Polyamide, used for toothbrush bristles, fishing lines, fibres
Polycarbonate, used for CDs, riot shields, break-resistant windows, traffic lights, lenses
Polyethylene terephthalate, used in carbonated drinks bottles, non-glass jars, plastic film, microwave packaging
Polyurethane, very common plastic, used for cushion foam, insulation, car parts
Polyepoxide, used for adhesives, electronic component pots, and in composite materials, such as with hardeners
Polymethyl methacrylate (acrylic), perspex, plexiglas, hard contact lenses, glazing
Silicon is a heat resistant resin, used as a sealant in bathrooms, cooking utensils, and in paint
Polyester, used in fibers and textiles
Recycling categories: 1: PET; 2: HDPE; 3: PVC; 4: LDPE; 5: PP; 6: PS; 7: Other.
Polyvinyl chloride PVC
Polyvinyl chloride, PVC, is synthetic polymer (plastic), used for plumbing piping, shower curtains, window frames and flooring
PVC, polyvinyl chloride, (C2H3Cl)n, is also used for food trays, drinks bottles, shampoo dispensers, and cling film
For recycling, PVC is broken into small chips, the impurities are removed, and the mass refined to white PVC. It can be recycled up to c. 7 times, and has a lifespan of 140 years
There are EU regulations for reuse of PVC in the construction industry. Incineration and degradation of PVC releases chlorine gas and other toxic compounds.
Polystyrene (PS) is common, commercially synthesised polymer, used for packaging foam, food containers, plastic tableware, and CD cases.
The chemical formula of polystyrene is (C8H8)n. It is currently not recycled or collected, except in Germany (packaging law - Verpackungsverordnung).
PS is chemically inert, but bacteria (Pseudomonas putida) can convert styrene oil to a biodegradable form. PS is long-lasting and a considerable litter problem.
Celluloid is a thermoplastic, made from nitrocellulose and camphor. It was the word's first commercially successful plastic.
In 1856, the metallurgist Alexander Parkes produced Parkesine. Prompted by a competition to find a substitute for ivory for billiard balls, he had treated cellulose with nitric acid to produce cellulose nitrate (pyroxilin), which, when dissolved in alcohol, hardened into a transparent elastic material. It was pigmented so that it would resemble ivory. It was registered as Celluloid in 1870, and, being a thermoplastic, could be moulded to any shape, from dentures to movie camera film.
Bakelite was the world's first commercially successful synthetic polymer (plastic), and was invented in 1907, by Belgian chemist Leo Baekeland, working in the US.
The chemical name of Bakelite is polyoxybenzylmethylenglycolanhydride, with chemical formula C6H6O·CH2O)6. It is a thermosetting phenol formaldehyde resin. It is produced by the condensation reaction of phenol with formaldehyde, and has low conductivity, making it useful as an electrical insulator, and for telephone and radio casings, as well as a range of domestic and commercial goods.
Bakelite has become fashionable, and antique Bakelite products are now collectors' items.