Displaying the Past: Museum Studies
Displaying the Past: Museum Studies
UHI Student Exhibition 2023
UHI Student Exhibition 2023
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Shop and Drop
Shop and Drop
Telling the story of changing shopping habits and the environmental impact of single-sheet plastic bags
Telling the story of changing shopping habits and the environmental impact of single-sheet plastic bags
Image: Tesco polyethylene single-sheet carrier bag from 1999 || Photo by the author
The Science of Plastic
The Science of Plastic
Trillions of plastic carrier bags have been produced since the 1960's, when a Swedish inventor discovered a method of creating a bag from a single sheet of thin plastic. The plastic used to make this type of bag is polyethylene. First discovered by accident in the late 19th century, an unstable type of polyethylene was created by German scientists. It was not until the 1930s that a different type of polyethylene was adapted for industrial use.
During World War 2, the science behind the creation of this plastic was kept secret by British inventors and engineers. It was applied to radar technology to help insulate wires.
Research into the production and use of polyethylene continued, and in 1965 the Swedish inventor Sten Gustaf Thulin filed a patent for the design of a “Bag with handle of weldable plastic material”. A patent is an official document that establishes a person or company as the original inventor of a process, idea or object.
Click on the image to read Thulin's original patent, and to view a larger copy of the diagram
Image: Patent image for Thulin's plastic bag from Google Patents
The bags are made from a tube of thin sheet plastic that has been melted from small pellets of solid plastic called nurdles.
The sheet is wound into a roll on a large machine where it is then cut into a piece that forms the shape of the bag. The bottom and top are melted into place to form the bag with handles. This style of bag is also known as a "t-shirt bag"
Click on the video to learn more about how plastic bags are made from polyethylene sheets.
Some single-sheet plastic shopping bags are printed with limit-run graphics for a variety of reasons such as advertising a company's association with a charity, marking a national celebration, or highlighting a customer reward scheme. Because so many of these bags were used once and then discarded, some have become collectable.
Changing Habits
Changing Habits
Self-service supermarkets could be found in the US from the early 1920's. In the UK, the shortage of building materials in the immediate post-World War 2 period meant that many retailers had to use old cinema or warehouse buildings. It wasn't until the 1950's that purpose-built supermarkets began to spread through the country, with self-service being a core part of their design.
Image: Illustration of shopping basket at PublicDomainVectors
Rationing from World War 2 continued in the UK until 1954. During this time, the type and amount of food available was limited. It wasn't just the way people shopped that changed dramatically at the end of rationing though. More households now had kitchen appliances such as refrigerators and freezers, and this reduced the number of trips people had to make to the shops each week. Before, food had to be bought fresh or canned. Now it was possible to buy frozen food, and it could be transported further distances.
However, many supermarkets were built in areas that required people to have a car or use a complicated public transport system. Smaller local convenience stores were - and still are - important for many people. Lightweight plastic carrier bags were ideal for smaller amounts of shopping, and they became a convenient way for people to pick up what they needed without having to plan a journey across town.
Image: Advertisement for the opening of a new self-service Sainsbury shop in 1970 from Sainsbury Archive
By 1980, 80% of shopping bags being sold in Europe were made of plastic. In North America, paper remained more popular, as these bags were designed with flat bases that made them easier to transport by car. Two of the largest supermarket chains in the US changed to plastic in 1982, and by the end of the decade, plastic had almost completely replaced paper and other natural materials around the world.
Image: Person with plastic shopping bag || Pxfuel
Environmental Impact
Environmental Impact
Image: Nurdles washed up on a beach by hockadilly at Flickr
Plastic bag production can negatively affect the environment even before a single bag is made. The nurdles that are melted to make sheet plastic are often released by accident when being transported. Many end up in the sea, where marine life mistake them for fish eggs and once ingested, they can remain inside the digestion system of animals. This can pass up the food chain, so if a fish eats a nurdle, it can end up inside a bird. Nurdles, like most plastics, can take up to one thousand years to break down, and they can release damaging chemicals in the process.
Learn more about nurdle pollution at The Great Nurdle Hunt
The average length of time a plastic shopping bag will be used is just twelve minutes. Often, they are only used once and then discarded. Bags that aren't put into landfill make their way into the environment or are burned. Large marine animals often eat plastic bags, thinking they are jellyfish or seaweed.
Image: Sea turtle eating a discarded plastic bag by Paulo de Rivera at National Geographic
Plastic bags have been linked to devastating floods in parts of the world that experience annual monsoons. In 2002, Bangladesh became the first country in the world to ban plastic bags after it was found that the bags had blocked drainage systems, leading to the increased spread of water-born diseases. Most countries in the world now have some sort of legislation over the sale and use of plastic bags, from outright bans to incentivising the reuse and recycling of bags. Despite this, over one trillion single-use plastic carrier bags are produced world-wide each year, and only 1-3% of these are recycled.
Image: Plastic bag refuse after flooding || Pxfuel
Did you know...?
Did you know...?
A dead pilot whale found in Thailand in 2018 had 80 plastic bags in its stomach
Discarded bags have been found at the top of Chomolungma (Mount Everest) to the bottom of the deepest part of the planet's surface, the Mariana Trench
Plastic bags put into landfill never fully degrade - they only break down into smaller and smaller pieces
Alternative Ways
Alternative Ways
People have found creative ways of reusing plastic shopping bags, from sculpture to clothing.
Click through the gallery to view some projects and objects made from used plastic bags
Different types of plastic are still being invented. These can be synthesied from natural sources such as seaweed, corn, or sugar, and are called bioplastics.
Biodegradable means that bacteria speeds up the breaking-down process in any environment. Some biodegradable plastics are also compostable, but not all are, and to be composted correctly, the plastic must be put into a special environment with the right conditions.
Biodegradable bags still take a long time to break down. A study in 2019 showed that biodegradable bags put into the sea were still strong enough to carry goods after three years.
Image: A biodegradable bag that has been in the sea for three years by Napper and Thompson
Image: A field of raw cotton || Pxfuel
Cotton and other natural fibres have become popular alternatives to plastic. However, the environmental impact of these products can be even more severe than synthetic materials. Cotton in particular uses a lot of water at all stages of production, from growing to processing, and the material is both heavier and denser than plastic, so it takes more trips to deliver the same number of natural bags than it would for plastic ones.
In fact, you would have to use a cotton bag over 130 times for it to mitigate the amount of damage caused by using a plastic bag just once. If you reuse a plastic bag 9 times, you would need to use a cotton one nearly 400 times to offset their global warming potential.
“To my dad, the idea that people would simply throw these away would be bizarre.”
“To my dad, the idea that people would simply throw these away would be bizarre.”
- Raoul Thulin, son of the inventor of the single-sheet plastic bag
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