Recycling and reuse of plastics is gaining importance as a sustainable method for plastic waste disposal. Unfortunately, plastic is much more difficult to recycle than materials like glass, aluminum or paper. A common problem with recycling plastics is that plastics are often made up of more than one kind of polymer or there may be some sort of fibre added to the plastic (a composite). Plastic polymers require greater processing to be recycled as each type melts at different temperatures and has different properties, so careful separation is necessary. Moreover, most plastics are not highly compatible with one another. Apart from familiar applications like recycling bottles and industrial packaging film, there are also new developments e.g. the Recovinyl initiative of the PVC industry (covering pipes, window frames, roofing membranes and flooring).
Polyethlene terephthalate (PET) and high density polyethylene (HDPE) bottles have proven to have high recyclability and are taken by most curbside and drop-off recycling programs. The growth of bottle recycling has been facilitated by the development of processing technologies that increase product purities and reduce operational costs. Recycled PET and HDPE have many uses and well-established markets.
In contrast, recycling of polyvinyl chloride (PVC) bottles and other materials is limited. A major problem in the recycling of PVC is the high chlorine content in raw PVC (around 56 percent of the polymer’s weight) and the high levels of hazardous additives added to the polymer to achieve the desired material quality. As a result, PVC requires separation from other plastics before mechanical recycling.
Commonly Recyclable Plastics
- High Density Polyethylene (HDPE) used in piping, automotive fuel tanks, bottles, toys,
- Low Density Polyethylene (LDPE) used in plastic bags, cling film, flexible containers;
- Polyethylene Terephthalate (PET) used in bottles, carpets and food packaging;
- Polypropylene (PP) used in food containers, battery cases, bottle crates, automotive parts and fibres;
- Polystyrene (PS) used in dairy product containers, tape cassettes, cups and plates;
- Polyvinyl Chloride (PVC) used in window frames, flooring, bottles, packaging film, cable insulation, credit cards and medical products.
Five Steps in Plastics Recycling
Step 1: Collection
This is done through roadside collections, special recycling bins and directly from industries that use a lot of plastic.
Step 2: Sorting
At this stage nails and stones are removed, and the plastic is sorted into three types: PET, HDPE and ‘other’.
Step 3: Chipping
The sorted plastic is cut into small pieces ready to be melted down.
Step 4: Washing
This stage removes contaminants such as paper labels, dirt and remnants of the product originally contained in the plastic.
Step 5: Pelletization
The plastic is then melted down and extruded into small pellets ready for reuse.