Plastics & Their Disposal (Cambridge (CIE) O Level Chemistry): Revision Note

Plastics & their Disposal

• Synthetic polymers are ones made in a factory, for example nylon, terylene and lycra 

• Nylon is a polyamide used to produce clothing, fabrics, nets and ropes

• PET, also known as Terylene, is a polyester made from monomers which are joined together by ester links

• PET is used extensively in the textile industry and is often mixed with cotton to produce clothing

Table showing Uses of Plastics

Non-biodegradable plastics

• These are plastics which do not degrade over time or take a very long time to degrade, and cause significant pollution problems

• In particular plastic waste has been spilling over into the seas and oceans and is causing huge disruptions to marine life

• In landfills waste polymers take up valuable space as they are non-biodegradable so microorganisms cannot break them down. This causes the landfill sites to quickly fill up

• Polymers release a lot of heat energy when incinerated and produce carbon dioxide which is a greenhouse gas that contributes to climate change

• If incinerated by incomplete combustion, carbon monoxide will be produced which is a toxic gas that reduces the capacity of the blood to carry oxygen

• Polymers can be recycled but different polymers must be separated from each other which is a difficult and expensive process

PET Re-polymerisation

• PET stands for polyethylene terephthalate, a common polymer used to make things like plastic bottles

• It is a condensation polymer consisting of repeating ester units, so it is a type of polyester

• One of the problems with recycling polymers is that the conditions needed to break them down, which are usually high temperatures and pressures, can degrade the monomers making them unusable for re-polymerisation

• PET is relatively easy to convert back into the monomers

• It can be depolymerised either using enzymes or by chemical methods

• Enzymes present in microbes breakdown the PET into the original monomers

• The same can be achieved using solvents a catalyst and mild heating

The breakdown of PET into its two monomers takes place using enzymes or chemical catalysts and mild conditions

• The monomers are recovered and polymerised into new PET

• This saves on resources and energy, reducing the carbon footprint of the production process