Plastics are made of polymers – long, repeating chains of atoms that are created by combining together building blocks called monomers. These monomers, which form the polymer’s repeating ‘unit’, are shorter chains of atoms such as hydrogen, carbon and oxygen. During the manufacturing process, chemical additives such as pigments, fire retardants and antioxidants are also added, giving the plastic desirable characteristics like colour, heat resistance or durability.
Most plastic recycling plants shred plastic waste and melt it down before remoulding it. But this process means that the recycled plastic is weaker. This is because, firstly, the process breaks the polymers. And secondly, any impurities or additives in the plastic waste are virtually impossible to separate from the rest of the material.
Recycled plastics are mixed with virgin material to make them usable, but even then, they can only usually be recycled two or three times before their quality becomes too poor for use. Glass and aluminium, on the other hand, don’t degrade during the recycling process, so can be recycled endlessly.
To improve the recycling process, scientists are working on chemical methods that can return waste plastics to their original monomer state (a process called ‘depolymerisation’). Part of the challenge lies in developing environmentally friendly enzymes and chemicals that can tease apart the plastic’s monomers.
Another area of research is looking into new types of plastic polymers that allow additives and other contaminants to be removed from them more easily. In time, these advances could mean that plastics (including some currently unrecyclable types) can be recycled again and again.