Sort by Number - a project on plastics recycling

“Life is ultimately about choices and so is pollution. We can live with sewage-strewn beaches, dead rivers, and fish that are too poisonous to eat. Or we can work together to keep the environment clean so the plants, animals, and people who depend on it remain healthy.” 1

Objectives of this project

  • Collecting plastics by numbers in different bins and subsequent screening of the result to investigate the consumer’s willingness to participate
  • Producing (mechanical) recycled plastic materials out of UW campus packaging and container waste with and without sorting of equal or higher value than the original packaging
  • Analyzing and improving the collection, sorting and distribution system of packaging for the UW campus with the Wisconsin School of Business, School of Human Ecology and College of Engineering as prototype facilities

How you can help

There is a better way to recycle different plastics — but we need your help.

  1. Find a “Sort by Number” recycling bin
  2. Check the bottom of your plastic item to find its recycling number
  3. Place your plastic item in the matching number bin

We will then take your recyclables, shred the plastics into flakes and investigate the blending of the different packaging materials. Upon success of this project we will develop guidelines on how packaging waste can be recycled without sorting. We will further be able to create new, valuable products out of the unsorted materials.


The industrial revolution of the last century was followed by the material revolution due to the invention and fast development of plastics. Today’s plastics are one of the most used materials on a volume basis in U.S. and worldwide industrial and commercial life. Plastics are broadly integrated into today’s lifestyle and make a major, irreplaceable contribution to virtually all product areas. Due to their highly versatile properties and applications, the consumption is still expected to increase as more and more new products are developed. Unfortunately, the properties that make plastics so valuable for technical applications such as its lightweight and durability generate several environmental problems, especially in disposable plastic products.

While reduction and reuse of waste are important goals, plastics’ recycling is beneficial not only from the environmental point of view by reducing the large amount of plastic waste going to landfills, reduce carbon dioxide emissions and conserving non-renewable fossil fuels used for its production, but also from the production point of view, by reducing waste requiring disposal and raw material costs. For example, the recycling of one ton of plastic bottles saves about 3.8 barrels of oil.

According to EPA, in 1960, the US generated 390,000 tons of plastic in the municipal stream, but this number has sharply increased to 31,750,000 tons in 2012 and is increasing every day. The main source of plastic waste is packaging (27,820,000 tons) made from polyethylenes (#2 and #4), polypropylene (#5) and their blends as well as PET (#1). PET is mostly used for plastic bottles, which makes it easier to sort. Thus, they can be recycled by grinding them down and re-manufacturing the shreds into new plastic parts. This mechanical recycling is the most desirable approach in plastic recovery because the macromolecular structure of the material is basically kept intact for subsequent use while at the same time the energy input is smaller than for e.g. chemical recycling.

The following video shows how Pellitteri Waste Systems in Madison, WI, separates recyclables in a state-of-the-art single stream sorting facility. Plastics #1 and #2 can be sorted:

However, the density of the residual packaging plastics, PEs and PPs, is almost identical and therefore they cannot be fully separated during the sorting process. Thus, they are either landfilled or a mix of these materials is recycled in products of significantly lower value. Since all these packaging materials can be identified by the number printed or embossed on the product – mostly on the bottom – the consumer would be able to sort the different plastics, if the necessary bins were available.

1Water Pollution: An Introduction