What are plastics?
Plastics are a group of materials, either synthetic or naturally occurring, that may be shaped when soft and then hardened to retain the given shape. They are made from oil or petroleum and produced through a polymerization process. As a result, they contain long chains of molecules, which are combined to create polymers.
Main types of plastics
PET
Polyethylene Terephthalate
Used for bottles for soft drinks and other beverages
HDPE
High-Density Polyethylene
Used for containers for milk and other beverages, squeeze bottles
PVC
Polyvinyl Chloride
Used in bottles for cleaning materials, some shampoo bottles
PET is produced by the polymerization of ethylene glycol and terephthalic acid. When heated together under the influence of chemical catalysts, ethylene glycol and terephthalic acid produce PET in the form of a molten, viscous mass that can be spun directly to fibres or solidified for later processing as a plastic.
HDPE involves the cracking of petroleum, which creates ethylene gas. The gas molecules will attach to form polymers, producing polyethylene.
The electrolysis of salt water produces chlorine, which is combined with ethylene (obtained from oil) to form vinyl chloride monomer (VCM). Molecules of VCM are polymerised to form PVC resin, to which appropriate additives are incorporated to make a customised PVC compound.
LDPE
Low-Density Polyethylene
Used in plastic bags, some plastic wraps
PP
Polypropylene
Used in heavy-duty microwavable containers
PS
Polystyrene
Used in beverage/foam cups, toys, window in envelopes
LDPE is produced by compressing monomer ethylene gas in an autoclave or tubular reactor to facilitate polymerization—i.e., the linking of monomers into polymer chains.
Production of polypropylene takes place by slurry, solution or gas phase process, in which the propylene monomer is subjected to heat and pressure in the presence of a catalyst system. Polymerisation is achieved at relatively low temperature and pressure and the product yielded is translucent, but readily coloured.
Polystyrene is an addition polymer formed when styrene monomers polymerise.
Commercial polystyrene is mostly synthesized by bulk, suspension or solution polymerization of ethylbenzene (styrene). The most common method is free radical polymerization, using benzoyl peroxide as initiator. However, other initiators such as redox systems and azo compounds can be used as well to start the polymerization. The reaction is exothermic, and thus the monomer-polymer mixture has to be cooled.
Why should we recycle plastics?
This is a pie chart showing the types and amounts of waste picked up from various locations in Singapore from September to October 2016. As you can see, plastic materials take up over 36% of the waste in Singapore.
In 2022, plastics had the second lowest recycling rate, 6%, out of all the waste types.
National Environment Agency (NEA)
Singapore’s only landfill, Pulau Semakau, has already seen its lifespan shortening from the initial 2045 to 2035, and possibly even less thanks to the COVID-19 pandemic. In order to reduce the need for incinerating plastics and to extend Pulau Semakau’s lifespan, it is thus very important that Singaporeans minimise the amount of waste produced, especially plastics.
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Most plastics are chemically inert, which is the main reason why they are so useful. However, this means that they take an extremely long time to decompose in the natural environment (20–500 years). In addition, burning plastics releases dioxins (highly toxic and persistent organic pollutants in the environment), acid gases, and heavy metals, which are harmful to both human health and the environment.
Plastics can also end up in seas and oceans, physically breaking down into microscopic pieces known as microplastics. Animals may mistake them for food, or get tangled up in bigger plastics, leading to death. Singapore’s waters provide a habitat for marine life such as corals, anemone, as well as many types of fish, invertebrates, and crustaceans. Plastic can thus harm Singapore’s rich marine ecosystem.
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The circuit breaker in 2020 due to the COVID-19 pandemic resulted in Singaporeans relying heavily on plastics, especially single-use plastics such as plastic packaging from takeaway food and delivery of items bought online. This resulted in Semakau landfill filling up faster than initially anticipated.
Recycling plastics conserves the finite natural resource of petroleum, and in resource-scarce Singapore, recycling plastics can also reduce waste produced in transporting imported plastics.
DID YOU KNOW?
A Singapore study found that the number of meal deliveries shot up by 73% during the circuit breaker
period. For every 100 households, there were 487 food delivery orders before the circuit breaker. This increased to 841 during the period. This resulted in an extra 1334 tonnes of plastic waste, equivalent to the weight of 92 double-decker buses being generated.