For more information on how you can help our environment, or to make some suggestions of your own, please go to www.coolaustralia.org

Plastic cheat sheet

to become flexible, soft, hard, heat resistant, thin, clear, translucent etc.

When we talk about plastic we’re generally referring to the stuff that is made from non-renewable fossil fuels. Petroleum and natural gas are the key ingredients of plastic. Plastics are composed of polymers. These are large molecules consisting of repeating units called monomers. In the case of plastic bags, the repeating units are ethylene, or ethene. When ethylene molecules are polymerized to form polyethylene, they form long chains of carbon atoms in which each carbon also is bonded to two hydrogen atoms.

Many kinds of polyethylene can be made from ethylene. Plastic bags typically are made from one of three basic types: • High-density polyethylene (HDPE)• Low-density polyethylene (LDPE)• Linear low-density polyethylene (LLDPE).

Those thick, glossy shopping bags from the shopping centre are LLDPE, while grocery bags are HDPE, and garment bags from the dry cleaner are LDPE. The major difference between these three materials is the degree of branching of the polymer chain. HDPE and LLDPE are composed of linear chains, while LDPE chains are branched. Branching can influence a number of physical properties including tensile strength. The more branched a molecule is, the lower its tensile strength. That’s why garment bags from the dry cleaner are so weak and flimsy. They are made from highly branched LDPE. And plastic bags are pretty much just made of the polymer, plus perhaps different pigments which may be added to produce coloured bags.

Chemists and engineers have learned to process and modify molecules of polyethylene in different ways to manufacture common household products with a variety of characteristics. Polyethylene is used to make plastic rubbish bags, dry cleaning bags, milk jugs and soft drink bottles. In industry, materials made from polyethylene are tested for what are called “stress-strain behaviours.” Stress-strain behaviours include tensile strength, abrasion resistance and puncture resistance.

Plastic is an amazing substance! It has allowed our civilisation to flourish and it is all around us. Plastic is so prevalent in our society that you probably can’t go two minutes without coming in contact with it. Think about it; the chair you’re sitting on, the phone in your pocket, the clothes you’re wearing and even the bubble gum you’re chewing all contain plastic. The beauty of this amazing stuff is that it can be moulded, stretched, and coloured to suit a wide range of purposes. Through the addition of a range of different chemicals we can change the properties of plastic

For more information on how you can help our environment, or to make some suggestions of your own, please go to www.coolaustralia.org

Plastic cheat sheetGlossaryPolymers - large molecules consisting of repeating units called monomers

Monomers - a molecule that can be bonded to other identical molecules to form a polymer

Ethylene, or ethene - Polymer used to make plastic bags

HDPE - high-density polyethylene

LDPE - low-density polyethylene

LLDPE - linear low-density polyethylene

Tensile strength - the amount of pulling force placed upon a material before it breaks

Abrasion resistance - toughness of material against scraping, scuffing or scarring toughness of material against scraping, scuffing or scarring

Puncture resistance - ability of a material to keep moving objects from perforating the surface ability of a material to keep moving objects from perforating the surface