The seemingly unremarkable plastic bag you use at the grocery store has a journey that begins deep underground. Fossil fuels, either crude oil or natural gas, are the source of the plastic’s main ingredient: polyethylene. These hydrocarbons are extracted and then head to a cracking plant, where they undergo a process called cracking. Here, long-chain molecules in the oil or gas are broken down into smaller, more manageable ones, including ethylene. Ethylene, the real building block for our plastic bag, is then polymerized. Imagine tiny Lego bricks; through polymerization, these ethylene units are linked together to form long, chain-like molecules – the polyethylene we need. This polyethylene does not magically appear in pellet form though. It is further processed and transformed into solid plastic pellets. These tiny beads are the raw material that plastic bag manufacturers work with. The journey now moves to a factory where the magic of transforming these pellets into usable bags happens. The first step is feeding the pellets into a machine called an extruder.

Think of it as a giant pasta maker, but for molten plastic. Inside the extruder how are plastic bags made, the pellets are heated to a very high temperature, causing them to melt into a thick, viscous liquid.  This molten plastic is then forced through a die, which shapes it into a thin, continuous tube of film. The thickness and width of this film can be precisely controlled depending on the desired type of bag – grocery bags will be thicker than, say, bread bags. As the hot plastic film emerges from the die, it is rapidly cooled using air jets. This rapid cooling solidifies the plastic, locking it into its final shape. The film is then winded onto large rolls, ready for the next stage.  Depending on the manufacturer’s needs, the plastic film might be directly cut and sealed into bags at this point. But often, there is more to the story. Printing, for example, is a common step.

Bags can be printed with logos, designs, or even warnings. This is done using a variety of techniques, with flexography being a popular choice. In flexography, a raised printing plate transfers ink onto the film, creating the desired design. After any printing is done, the film is cut into specific shapes. This can be a simple matter of using a blade to create individual bags, or it can involve more complex processes for bags with specific features like handles or gussets the triangular folds at the bottom of some bags that allow for expansion. Finally, the bags are sealed. Heat sealing is a common method, where controlled heat melts specific areas of the plastic film, fusing them together to form the bag’s seal. The finished plastic bags are then inspected, counted, and packaged. They are ready to be shipped to stores and eventually end up in your hands at the checkout counter and view www.ketegroup.com. This is the path of polyethylene – a remarkable transformation from fossil fuels deep underground to the familiar, everyday plastic bag.