Investigating plastics

Introduction

Many recyclable items, like steel and aluminium cans, have only one type of material that can easily be recycled. Other recyclable items can be separated by colour, such as glass. Plastics, however, are far less easy to sort. Different types of plastic are made differently, have different properties and are recycled differently.

What are plastics?

Plastics are a relatively recent invention. They consist of chains of special molecules called monomers. These chains are also known as polymers. This type of molecule gives plastic its unique properties, such as strength, durability and flexibility. Different types of chains give plastics different properties.

The first plastics were invented at the beginning of the 20th century. They provided inexpensive replacements for materials like ivory and silk that were durable and readily resisted decay. The first plastics were manufactured from cellulose, which is a natural material found in plant matter, such as wood. Later plastics, including many of the plastics we use today, are manufactured using petroleum, which is a non-renewable resource.

See Image one - Celluloid was an early plastic that was used to make everything from toys to false teeth.

Different types of plastic

There are many different types of plastics, each with its own specific properties. Each of these types of plastic is used for different applications. Some of them can be recycled easily and some of them cannot. This makes recycling plastic more difficult.

In order to make identifying plastics less confusing, people who manufacture plastic have developed a code called the resin identification code to advise consumers of the type of plastic from which an item has been made. This code lets people know which products they can recycle and which ones they cannot. The code consists of a number between 1 and 7 in a 'chasing arrows' that is engraved on the surface of a plastic object. Each number corresponds to a different type of plastic.

See Image two - The resin identification code helps people identify plastics that can be recycled.

The number 1 means an item is made of Polyethylene Terephthalate, which is also called PET or PETE. PET is usually clear, although it is sometimes tinted colours like green or blue. It is also resistant to pressure and heat. PET bottles are often used to hold soft drinks and other beverages. Peanut butter and jam jars are also often made of PET.

The number 2 is found on items made of High Density Polyethylene, also called HDPE. This type of plastic is translucent (see-through). It is also very resistant to chemical corrosion. HDPE is used to make milk and juice bottles as well as bottles for household cleaners like bleach. It is also used to make tubs for butter, margarine and yogurt.

The number 3 refers to items made of Polyvinyl Chloride, also called vinyl or PVC. Vinyl is a very versatile plastic that can be either rigid or flexible. It has a number of applications, including packaging, insulation, carpeting, clothing, pipes and window frames.

The number 4 means an item is made of Low Density Polyethylene, also called LDPE. LDPE is tough, flexible and clear. It is used to make films such as plastic bags and cling wrap. It is also used to make squeezable bottles for foods like honey and mustard.

The number 5 is found on items made of Polypropylene, also called PP. This kind of plastic is strong and has a high melting point. This property makes polypropylene ideal for applications where a bottle must be filled with a hot liquid. It is used for making bottles for medicine, tomato sauce and margarine.

The number 6 refers to items made of Polystyrene, also called PS. This type of plastic is also versatile and is either rigid or foamed. Foamed PS is also known as Styrofoam and is often used to protect fragile items in packaging. It is also used to make grocery store meat trays and disposable plates and cutlery.

The number 7 is found on items that are made from a plastic not listed above or a mix of plastics. These items have differing properties because they can be made from a variety of plastics. Some examples of these items include some tomato sauce bottles, re-usable water bottles and some juice bottles.

Can it be recycled?

Each type of plastic is recycled differently. Some plastics are easier to recycle than others. PET and HDPE, for example, are very commonly recycled to make clothing, food and beverage containers and carpet. Other types of plastic are not as easily recycled. Since the molecular chains that make up plastics can be very complex, some of them break apart when being recycled. Many types of recycled plastic can only be used to make low-grade items like plastic lumber. It is used to make things such as inexpensive park benches and shipping pallets.

See Image three - Plastic lumber can be made from recycled plastics.

Since there is such a wide variety of ways plastic is recycled, different communities have facilities to recycle different kinds of plastic. Most roadside recycling programs recycle PET and HDPE, or number 1 and 2 plastic. Plastic bags made of LDPE are often recycled at recycling centres and sometimes even at your local grocery store. Some types of plastic, especially mixed plastics, cannot be recycled in most communities due to a lack of facilities. Most roadside recycling programmes do not recycle all types of plastic. Check with your local council to see what you can recycle and where to take it.

If you can recycle plastic in your area, you should. Plastic production is very harmful to the environment because it produces toxic chemicals. In addition, since plastic is so strong, it is non-biodegradable. If plastic ends up in landfill it could remain there for hundreds of years.

See Image four - Plastic in landfills is likely to remain there for hundreds of years.