Recyclability of plastics

Recent figures from the OECD show that plastic pollution is rising relentlessly because of inadequate waste management and recycling. They state that the world produces twice as much plastic waste as it did two decades ago, most of which ends up in landfills, is burned or leaks into the environment. Only 9% (!) is successfully recycled, which is, of course, ridiculously low. Countries like the United States, which is aiming for a 50% recycling rate by 2030, were at 4% in 2019 (see figure below).

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

To understand plastic waste management, we need to look at the different types of plastic and their ability to be recycled.

Types of plastics and their recyclability

Plastic exists in many different shapes and colors, as well as different types. These differences in types are reflected in their reusability due to their chemical composition, as well as their recyclability. In 1988, the Society of the Plastics Industry introduced a new classification system: the Resin Identification Code (RIC). This code, after some modifications, became the worldwide standard classification for plastics. Recycling plastics is done by first sorting them according to their resin type. After that, there are two ways to recycle plastics: mechanical or chemical. Mechanical recycling involves washing, grinding and melting the plastics, while chemical recycling involves breaking down the polymers into monomers. As for resin codes, the general rule of thumb is: the lower the resin code, the more likely the plastic can be recycled. The difference in recyclability of plastics may have to do with how they are made. Thermosetting plastics contain polymers with irreversible chemical bonds and therefore cannot be recycled. Thermoplastics, on the other hand, can be recycled by remelting and remolding them. Figure 2 lists all resin codes with the corresponding plastic type.

Figure 2: Resin codes with their corresponding plastic type. Here is an explanation of the different plastic types:

1 – PET
PET is the abbreviation for polyethylene terephthalate and belongs to resin code number 1. PET is mostly used for food and beverage packaging, but its usefulness is widespread. That’s because it has a strong ability to prevent oxygen from entering the packaging and spoiling a product inside. This type of plastic is the most recycled in the world! Although PET is relatively easy to recycle, many countries still struggle to achieve a decent recycling rate. A significant portion of PET plastics are recycled into fashion items, such as fleece clothing, backpacks and carpets. But PET can also be converted back into PET! This is one of the few polymers that can be recycled into the same material.

2 – HDPE
The technical name of this type of plastic is High-Density polyethylene. It is an incredibly resistant resin used for shopping bags, milk jugs, agricultural tubes, playground equipment, shampoo bottles and so on. Its long polymer chains make it much stronger than PET. It can withstand relatively high temperatures and is one of the easiest polymers to recycle. Recycled HDPE is usually used for the same purposes, but is also often downcycled, meaning it is used for lower-value products such as plastic lumber, tables, benches and other durable plastic products.

3 – PVC
PVC stands for polyvinyl chloride and is the third most widely used polymer in the world. It is available in hard and flexible form. The hard form is used, for example, in the construction industry in window profiles and pipes. The flexible form is obtained by adding plasticizers and is used in plumbing, wiring and flooring. It is durable, lightweight and easy to process. However, PVC is not recyclable through normal collection.

4 – LDPE
Unlike HDPE, LDPE consists of low-density polyethylene and is used for the infamous plastic bags provided by supermarkets. Technically, this type of plastic can be recycled. But unfortunately, this hardly ever happens. This is because the plastic bags can become entangled in the machines, jeopardizing the entire process. And because LDPE is such a cheap and low-grade plastic, recycling doesn’t really pay off financially.

5 – PP
PP stands for polypropylene and is the second most produced plastic, whose market will continue to grow in the coming years. It is a hard and sturdy plastic that can withstand high temperatures and is used in Tupperware, auto parts, thermal vests, etc. It is also used for plastic hinges because it is foldable and highly resistant to fatigue. Although PP can be recycled, it almost never is. Again, this is due to the difficulty and the fact that it does not make financial sense to recycle.

6 – PS
Polystyrene is supplied as a solid or a foamed resin. Because it is very inexpensive, it can be found everywhere: beverage cups, insulation material, packaging material and disposable dinnerware. The plastic is highly flammable and can leak harmful chemicals. PS is very bad for the environment. It is not biodegradable, it floats in the wind and on water, animals do not recognize the material as artificial. PS is unfortunately never recycled!

7 – Andere plastics
Resin number 7 consists of all plastics that cannot be identified with the 6 categories described above. The best-known plastics in this group are polycarbonates (PC), which are used to make strong, tough products. It is found in eye protection and in making lenses for sunglasses, sports glasses and safety glasses. But it is also found in cell phones and CDs. At high temperatures, bisphenol A, an environmentally hazardous chemical, can be released from this resin. On top of that, plastics with number 7 are never recycled.