Science – Re-valuing non-recyclable plastic

The global plan to minimise the accumulation of plastics in landfills is called the Circular Economy. This strategy treats plastics waste as a valuable manufactured resource to be reused again and again via recycling. In her column on the following page, Trish Allen has laid out very clearly the requirements of the new Auckland Council waste management system.

The plastics that can be recycled are Type 1 (PET), Type 2 (HDPE) and Type 5 (PP). In future, packaging or other materials made from these recyclable plastics will have to be clearly identified as one of 1,2 or 5 to be included in the mainstream recycling process. As an example, the massive numbers of water and soft drink bottles that litter our landscape are made from fully recyclable Type 1 (PET) so can be readily recycled and reused through several cycles.

What happens, then, to non-recyclable plastic types? Perhaps the most puzzling non-recyclable plastic for consumers are the flexible films and bags commonly used for vegetable and fruit packaging. This is Type 4 (LDPE or low-density polyethylene), which causes flexibility tangles in the mainstream recycling process. In due course, Type 4 is likely to be recycled in NZ. Until this recycling is provided, Kiwis should not include Type 4 plastics in their recyclables bin.

How then does Type 4 get recycled in other countries? After being separated from the three recyclable plastics (Types 1, 2 and 5), LDPE film gets shredded into flakes with grinders. It then gets cleaned to remove contaminants and then dried, melted and turned into pellets for ease of handling. Recycled LDPE is often used in piping, sheeting, films and trash bags for composite lumber, as well as building and agricultural applications.

One current use for Type 4 (LDPE) has been developed by the company, Future Post. In this process, the soft plastic is incorporated in farm fence posts used in agriculture, viticulture, horticulture and equine settings. Also, the fact that these fence posts can last for hundreds of years, make it a much more sustainable proposition than treating LDPE as a single-use plastic.

The short-term challenge for suppliers and consumers of all recyclable plastics is to ensure that every plastic product is clearly identified by its number such as Type 5 (PP or polypropylene). If a plastic object is not identified, it is likely to be consigned to landfills rather than recycled and used again in secondary applications.

Several years ago, the NZ waste management sector reported that only about 60% of plastics were being recycled by New Zealand consumers. The most important task now for the NZ consumer is to raise this recycling figure to close to 100%. That would be a great environmental achievement by Kiwis.