Recyclability of plastics

Recent figures from the OECD show that plastic pollution is growing relentlessly, since waste management and recycling is falling short. They state that the world is producing twice as much plastic waste as two decades ago, whereof the bulk is ending up in landfills, getting incinerated or leaks into the environment. Only 9% (!) is successfully recycled, which of course, is ridiculously low. Countries like the United States, who tend to reach a recycling rate of 50% by 2030, were at 4% in 2019 (see the figure below).

Figure 1: Plastic waste management worldwide in 2019. Source: OECD Global Plastics Outlook Database.

In order to understand the plastic waste management, we need to look further into the different types of plastic and their ability to be recycled or not.

Types of plastic and their recyclability

Plastic exists in a variety of different shapes and colors, but also different types. These differences in types are reflected in their reusability due to their chemicals, but also their recyclability. In 1988, the Society of the Plastics Industry introduced a new division system: the Resin Identification Code (RIC). This code became, after a few adjustments, the worldwide standard plastic classification. Recycling of the plastics is done by first sorting them based on their resin type. Thereafter, there are two ways of recycling plastics, either mechanically or chemically. Mechanical recycling entails the washing, grounding and melting of the plastics, whereas chemical recycling entails the breaking down of the polymers into monomers.

With respect to the resin codes, there is a general rule of thumb: the lower the resin code, the more likely the plastic can be recycled. The difference in the recyclability of the plastic types can be down to how they are made. Thermoset plastics contain polymers with irreversible chemical bonds and therefore can not be recycled. Thermoplastics however, can be recycled via re-melting and re-molding.

Figure 2 lists all the resin codes with the corresponding plastic type.

Figure 2: Resin codes with their plastic types.

Here is an explanation for each plastic type:

1 – PET

PET is short for polyethylene terephthalate and belongs to resin code number one. PET is mostly used for food and drink packaging, but its utility is widespread. This is because it has the strong ability to prevent oxygen from penetrating the package and spoiling a product inside. This type of plastic is the most widely recycled in the world! Although PET is relatively easy to recycle, lots of countries still struggle to reach decent recycling rates. A substantial part of PET plastic is actually recycled into fashion items, such as fleece clothes, backpacks and carpets. But also, PET can be transformed into PET again! This is one of the few polymers that can be recycled into itself.

2 – HDPE

The technical name of this type of plastic is High-Density Polyethylene. It is an incredible resistant resin which is used for grocery bags, milk jugs, agricultural pipes, playground equipment, shampoo bottles and etcetera. The long polymer chains make it much stronger and thicker than PET. It can withstand relatively high temperatures and is one of the easiest polymers to recycle. The recycled HDPE is mostly used for the same purposes but oftentimes it is downcycled as well, which means that it is used for lower-value products like plastic lumber, tables, benches and other durable plastic products.

3 – PVC

PVC stands for polyvinyl chloride and it is the world’s third-most widely used polymer. It comes in a rigid or flexible form. The rigid form is for example used in the building industry in window profiles and pipes. The flexible form is obtained by adding other substances and is used in plumbing, wiring and flooring. It is durable, light and ease to process. However, PVC is not recyclable in normal collections.

4 – LDPE

In contrast to HDPE, LDPE consists of low-density polyethylene and is used for the infamous plastic bags provided by grocery stores. Technically, this plastic type can be recycled. But unfortunately, it hardly happens. This is because the plastic bags can get entangled in the machinery risking the entire process. Also, since LDPE is such a cheap and low-quality plastic recycling it is not really financially worthwhile.

5 – PP

PP stands for polypropylene and is the second-most widely produced plastic, which market is set to grow in the following years. The plastic type is hard and sturdy, able to withstand high temperatures and found in Tupperware, car parts, thermal vests and etc. It is also used for plastic hinges, since it is foldable and very resistant to fatigue. Although PP can be recycled, it hardly isn’t. This is again due to the fact that it is not financially sensible to recycle and it is rather difficult.

6 – PS

Polystyrene can be solid or foamed. Due to it being very inexpensive, it can be found everywhere: beverage cups, insulation, packing materials and disposable dinnerware. The plastic is highly inflammable and can leak harmful chemicals. For the environment, PS is the worst. It is not biodegradable, it floats in the wind and on water, animals do not recognize the materials as artificial. Thereby, PS is never recycled!

7 – Other Plastic

Resin number 7 consists of all the plastic types which can not be identified as the six before. The best known plastics of this group are polycarbonates (PC), used to build strong, tough products. It is found in eye protection in the creation of lenses for sunglasses, sport and safety goggles. But they are also found on mobile phones and CDs.

At high temperatures, this resin may release bisphenol A, which is an environmentally hazardous chemical. On top of this, plastics number 7 are never recycled.