Plastics are an integral part of modern life, even to the point of being deliberately incorporated in our bodies within knee and hip replacements. Plastic cards give us entry to buildings and transport, allow us to pay our way and obtain cash. Plastics form part of popular culture: from vinyl records through to the tape in music cassettes, from CDs to the portable devices on which we now play digital music files. As the UK Government consults on plastic waste recycling, we examine the broad spectrum of issues that affect our relationship with plastic. What is it made of, how long has it been around, why is it such a successful material? How are chemical substances incorporated into plastics regulated and what new steps are proposed to regulate harmful environmental impacts from plastic waste? Such issues are generating a great deal of interest at present from consumers and may affect buying choices. Regulation is being targeted to manufacturers and suppliers of goods incorporating plastics and those wrapped in plastic packaging. In the UK, Government is using the tax system to incentivise the use of recycled plastic, and at the same time proposing to extend existing schemes so as to ensure that it is industry rather than the tax payer who bears the full financial cost of the eventual disposal of plastic waste. These measures will inevitably bring greater compliance costs for the consumer goods sector. Plastics: Have consumers fallen out of love? OF CONSUMER FUTURE THE 02 HERBERT SMITH FREEHILLS Plastics – a love–hate relationship The contemporary uses of plastics in all their forms are almost too numerous to count and not always readily apparent, such as the use of microplastics within inks or the plastic liner inside the tin can, needed to prevent rusting and consequent spoiling of food. Plastics also perform sophisticated functions, for example slow release capsules within modern fertilisers and drugs, helping to feed growing populations and stave off disease and discomfort. The very affordability and ubiquity of plastics is also their Achilles’ heel. Being cheap to produce in mass quantity using injection moulding techniques, they are seen as having little value and are also readily discarded after use. As has been much publicised recently, microplastics in rinse-off products find their way into the marine environment and drinking water and studies now show that a large amount ends up in soil spread with sewage sludge. Single-use plastics such as carrier bags have been pictured entangling or having been swallowed by marine animals. The history of plastics Our love affair with man-made plastics really began in the 19th century with a material derived from cellulose called Parkesine after its British inventor Alexander Parkes. Parkes however ran out of funds and Americans, the Hyatt brothers, added camphor and in 1870 renamed it celluloid, from which cinema film strip was originally made. In 1907 another American, Belgian-born Leo Baekeland, invented Bakelite. This was the first synthetic plastic as it derived not from plant or animal products but from fossil fuels. An explosion of discoveries followed in the 1930s and 1940s: polystyrene in 1929, polyester in 1930, the discovery of polyethylene at ICI’s Winnington facility in Cheshire, polyvinylchloride (PVC) and polythene in 1933 and Carothers and Dupont patenting nylon in 1935. As early as 1936, perspex canopies were used in fighter aircraft. Plastic insulation was used for wiring in radar installations during the Second World War. The first toothbrush with nylon tufts appeared in 1938. PET (used for drinks bottles) was patented in 1941 as well as the first polyester fibre, Terylene. Superglue was discovered in 1942. Following the war, mass consumer goods production began in earnest. Tupperware (made from polyethylene) launched in the US in 1949. The first Airfix kit and Lycra appeared the same year. The plastic carrier bag arrived in 1950 and polystyrene foam in 1954. The plastic hula hoop and and Lego in 1958. The chemistry of plastics All plastics are polymers, but not all polymers are plastic. Polymers are large molecules consisting of chains of linked sub-units, called monomers. Where one type of monomer is used these are known as homopolymers Where a mixture of different monomers units are used to link together, these are known as copolymers. Both types can form either straight or branched chains. However, wool, cotton and silk are also polymer-based materials and cellulose, the main component of wood and paper, is a natural polymer too. The difference with plastics is that although they too are organic (the raw material is usually oil), they are made synthetically. They come in two main varieties: Thermoset plastics These plastics hold their shape once cooled to room temperature and hardened completely. They cannot then return to their original form, even if melted down. Examples are epoxy resins. Thermoset plastic is commonly used in tyres, car parts and composites. Thermoplastics These are more flexible and versatile. They return to their original form when heated and can be made into films, fibres and other forms. Plastic facts • Bakelite was the first completely synthetic plastic, made by Leo Baekeland in 1907. Baekeland invented the term plastics. • The word plastic comes from the Greek word plastikos, meaning able to be shaped or moulded. • Plastics are usually solids but can be crystalline or semi-crystalline solids (crystallites). • They are usually poor conductors of heat and electricity. Most are insulators. • Approximately a third of plastic that is produced is used to make packaging. • Pure plastics are usually insoluble in water and non-toxic. But some additives used in the manufacture of plastics are toxic and may leach into the environment, eg phthalates. • 4% of oil production worldwide is used to produce plastics. There are around 45 unique types of plastics, each with dozens of variations (see text box – Common types of plastics). Manufacturers are able to vary the physical structure to tailor it to the particular application required. By modifying the molecular weight distribution, the density or the melt indices, they can alter the properties of the resulting plastic. Plastic additives Additives are used to make plastic safer, cleaner, tougher and to add colour. They can also reduce production costs and increase durability (see text box – Additives). Manufacturing goods with plastic usually involves melting polymer powder or granules inside a heated tube. This ‘melt’ is forced through a shaped die, injected into a mould, or rolled or blown into flat film (see Text Box – Injection moulding). How easy the plastic is to work with depends on its physical and chemical properties, and this can be improved through the use of certain additives known as process aids. For example, some of these form a liquid around colour particles so that they mix better. Others make the polymer particles melt quicker, saving energy and minimising heat damage. Some additives, however, deliver important properties for the end user rather than just facilitating the manufacturing process. They may filter out light to protect the contents of a package, for example in medicine bottles. Consumer goods such as vacuum cleaners need additives to make the plastic parts impact resistant. Plastics, being organic, are combustible. For electrical goods, flame retardant additives may be used to reduce the risk of the plastic catching fire from an electrical spark. Specialist additives do however significantly increase the cost of PLASTICS: HAVE CONSUMERS FALLEN OUT OF LOVE? 03 Common types of plastic Plastic Use Polyethylene terephthalate (PET) Can be drawn out to make fibres or films. Used for food storage containers and bags and water bottles. Does not leach into food. Polyvinyl Chloride (PVC) Requires stabilizers to make it soft and easy to mould. Used in plumbing applications because of its durability and being non-corrosive, as well as affordability. Plasticisers may leach out of it over a long period of time, leaving it brittle. Polystyrene Very lightweight, easy to mould and can be used an insulator. Used in packaging, furniture and where impact-resistance is required. Can form a harder, impact-resistant plastic for cabinets, computer monitors, TVs, utensils, and glasses. Turns into EPS (Expanded Polystyrene) when heated and air added. Polyvinylidine Chloride (PVC) Durable, non-corrosive, as well as affordable. Used as cling film also for pipes and plumbing. Requires addition of a plasticiser to make it soft and mouldable and this may leach out over a long period making it brittle. Polytetrafluoroethylene (Teflon) Heat resistant and used in bakeware and saucepans but also in tubing, plumbing tapes and waterproof coatings. First manufactured by DuPont in 1938. Stable, strong and resistant to damage by chemicals. Creates an almost frictionless surface. Polypropylene (PP) Applications include tubes, car trims and bags. Polyethylene (HDPE or LDPE) Used to coat electrical wires and as piping but also in several disposable products, including sandwich bags, gloves and garbage bags as well as wraps and bottles and most household plastic packaging. Almost 1,000 different grades. Injection moulding Injection moulding is a manufacturing process allowing manufacturers to produce high volumes of identical plastic goods at minimal cost per unit. Three main units make up an injection moulding machine • feed hopper, • heater barrel; and • ram. Plastic granules or powder in the hopper are heated until liquid. The ram forces the liquid into every crevice and corner of the tightly clamped mould and the liquid plastic sets. More viscous molten plastics require higher pressures (and higher press loadings). The plastic cools as the metal mould conducts heat away and then the press is cycled to remove the moulded item. For thermoset plastics the mould has to be heated to make the plastic set. Advantages • Enables complex shapes to be manufactured, some of which might be near impossible to produce economically by any other means. • Can use a wide variety of materials to deliver the physical properties required by the article, and multiple layers of moulding can be used to deliver specific mechanical properties and visual appearance even in small items. • It is a low-cost process with low environmental impact and leaves little by-product; any scrap that is produced can be re-ground and re-used. Disadvantages • The expensive tooling requires high volume production in order to recover the investment. • It takes time to develop the tooling and not all objects can be moulded easily. • Cheap injection moulding has allowed disposability – for example of razors and ballpoint pens (although this is also an advantage for example in medical devices). •
