The Seven SPIs of Plastic

A good place to start when it comes to knowing your plastics, is understanding that there are seven different kinds of plastic. Being able to differentiate between the seven plastic compounds is also key in being able to utilise them responsibly so that you know which kinds can be recycled and how. This is imperative given that plastic is used daily in most items including water bottles, take-away coffee cups, stationery, food containers and more. The plastic family comprises of the following: Polyethylene Terephthalate (PETE or PET), High-Density Polyethylene (HDPE), Polyvinyl Chloride (PVC), Low-Density Polyethylene (LDPE), Polypropylene (PP), Polystyrene or Styrofoam (PS) and last but not least – the miscellaneous plastic category which includes polycarbonate, polylactide, acrylic, acrylonitrile butadiene, styrene, fiberglass, and nylon. Each of these seven kinds of plastic polymers are assigned as specific SPI (Society of the Plastics Industry) code which help denote their resin content and therefore assist in determining how they can be sorted and recycled (if possible). Some plastics may not be able to be strictly recycled – but rather repurposed.

It is also important to understand the difference between the following terms that are thrown around with regard to the breaking down of plastic polymers through various methods. The term ‘bio-plastics’ has become more commonplace in recent years, however it can be rather ambiguous. Bio-plastics generally refer to plastic polymers that are degradable in some form or another. The most common and wide-spread form of bio-plastics can be found in shopping bags. These can be categorised further by the process used to break down the plastic particles. Plastic bags that are compostable are in essence biodegradable and can be broken down using industrial compositing systems as well as the occasional home compositing system. Biodegradable plastic bags for instance can be broken down using microorganisms such as fungi. They also may require the assistance of UV light and warm temperatures in order to assist the decomposition process. Lastly, one of the biggest misconceptions is the term ‘degradable’. All that the term degradable means is that while the plastic item can be broken down into its base polymers, those polymers will exist for centuries to come. There is no recycling process inherent in degradable plastics.

So, of the seven plastic polymers mentioned, which of them can be easily recycled? Polyethylene Terephthalate (PETE/PET) and High-Density Polyethylene (HDPE) are the most commonly and easily recyclable, however Low-Density Polyethylene (LDPE) and Polyvinyl Chloride (PVC) are also recyclable but more process specific. Polypropylene (PP), polystyrene/Styrofoam (PS) and the miscellaneous plastics (N/A) are not recyclable though there is the possibility of them being repurposed. Next time you see a number encapsulated by a triangle on a plastic container, label or packaging sleeve – you will have a better understanding of what it means to you, and the environment.