Plastics are everywhere. Whether used to store leftovers, keep hospital equipment sterile or insulate a home, plastics are unmatched for their adaptability, durability and low cost. Given their seemingly boundless benefits, it is not surprising that plastics have replaced traditional materials in many sectors — for example, steel in cars, paper and glass in packaging, and wood in furniture. As a result, annual plastics consumption worldwide has increased from 5 million tonnes in the 1950s to about 280 million tonnes today.
Roughly half of plastic products, such as packaging, are intended for one-time, short-lifespan (less than six months) applications prior to disposal. Given that most of these items are not biodegradable, and are not recycled, plastics waste is building up — with serious environmental consequences. While governments have begun to implement new (and often quite strict) regulations aimed at managing plastics waste — for example, China banned lightweight plastic shopping bags in 2008 — they are inadequate to address the world’s growing plastics-waste problem.
Moreover, most plastic products are made from so-called “petroleum-based commodity thermoplastics.” Given that a non-renewable resource forms the basis of many plastic products — most of which will not last long — current plastics usage patterns are not sustainable.
Closed-loop recycling, in which plastics waste is used to make another product, therefore carries significant environmental benefits, such as reduced energy and oil consumption.
However, the process of separating the petroleum-based recyclable plastics from other kinds of plastics and solid waste is difficult, costly and labor-intensive, so only a small proportion is recycled.
In 1988, the US Society of Plastics Industry (SPI) developed a coding system in which each kind of resin is labeled with a number, 1 to 7, to facilitate sorting. The system has also been used elsewhere, including in Canada and Switzerland, but has not been adopted worldwide and is still confusing to some consumers. If people knew how to collect and separate household plastics based on their number, when available, the resulting boost to recycling efforts would demonstrate to government and industry the viability of a more sustainable approach, reduce exposure to rising oil prices and support growing global demand for plastics.
There are four categories of plastics recycling: Primary recycling, in which the plastic is reused in the same application; secondary recycling, in which material (mixed or contaminated) is used in less demanding applications; tertiary recycling, in which the plastic is converted into monomers or chemicals; and quaternary recycling, in which only energy is recovered through incineration.
Each of these methods recovers a different amount of the embodied energy of the plastic item. (All of the embodied energy is lost if the plastics are landfilled, a common disposal method worldwide.)
Given the difficulty and expense of separating plastics, the most economically viable option is often secondary recycling of a few commodity thermoplastics — mostly bottles, for which collection infrastructure is already in place. More economical separation methods are crucial to expanding the scope of plastics recycling, as is the identification of new potential markets for the recyclates.