Plastics have been playing an increasing role in consumer and industrial products, posing unique challenges to recycling initiatives. Due to these challenges many plastic products are not included in municipal recycling programs. One of the greatest challenges is the large molecular structure that occurs as a result of the polymerization process. Unlike metals, which have a small molecular structure, different forms of plastics do not mix well using only thermal energy (heat). This makes it difficult to use recycled resins to produce a product that is structurally identically to a plastic product made from virgin resin. Plastics produced through different manufacturers, even when it is the same type of plastic, often vary structurally as well. This causes poor mixing and weakens the plastic made from recycled resin, thus limiting the applications of the recycled plastic.
There are 6 main forms of plastic, each characterized by a resin identification code. Plastics that enter a Materials Recycling Facility are sorted based on these numbers. The main plastics that are sorted in municipal programs are #1 PET, #2 HDPE, #4 (Film) and mixed plastics in the form of Tubs & Lids. These can be sorted either manually or automatically through optical sorting. The resin identification codes are described below.
Polyethylene terephthalate (PET): Clear or coloured, bottles have a raised dot on the base. (ex. Single serve water)
High-density polyethylene (HDPE): Translucent, opaque or coloured, does not crack when bent. (ex. Detergent bottles, motor oil, crinkly retail bags)
Polyvinyl chloride (PVC): Clear, colourless, white creases, bottles have a seam on the base. (ex. Liquor bottles, household chemical containers, film wrap on meat packaging)
4. Low-density polyethylene (LDPE): Flexible, smooth, soft to the touch (ex. Grocery bags, garbage bags)
5. Polypropylene (PP): Transparent, clear or opaque, smooth, semi-rigid (ex. Coating on milk cartons, shrink wrap, bottle caps)
6. Polystyrene (PS): Stiff but flexible, snaps when bent (ex. Foam PS - Coffee cups / Crystal PS - clear take out containers)
7. Mix of Plastics: ex.Squeezable bottles for ketchup.
Once the plastics have been sorted they are marketed to different plastics processors that use the scrap plastic in a range of applications. Some plastics are easier to reprocess than others, which leads to large differences in the marketability and market price of each form of scrap plastic. Most often scrap plastics are sold to processors who produce an intermediate product that can then be sold to another company who will use the processed plastic to produce a final good. The plastic is eventually transformed into a range of products from new bottles to fabrics in t-shirts.