Below you will find a selection of science projects submitted by students doing the Cosmos online science programme.
Petra Reid, age 15, from Te Puke.
Product life-cycle analysis
Life cycle of a biodegradable polyethylene plastic bag vs a paper bag
|biodegradable polyethylene plastic bag||vs||paper bag|
|1. Sourcing materials||Made from renewable plant sources (corn, sugar cane, sugar beet).||A lot of non-renewable fossil fuels are used to log, cut, process and source paper. Also, the cutting down of forests, even purpose planted forests, has a huge impact on the ecosystem in and around it.|
|2. Manufacture||Uses large amounts of electricity to melt to 400’C.||Uses acids and thousands of litres of clean water.|
|3. Distribution||Uses non-renewable fossil fuels to transport worldwide.||Uses non-renewable fossil fuels to transport to shaping company, where a huge amount of electricity is used to make the retail item.|
|4. Product use||One-use shopping/grocery bag, (2nd use- trash bag).||One-use grocery/shopping bag, (2nd use-trash bag).|
|5. Recycling||Recycling takes 2/3 amount of energy as virgin melt.
Plastic ‘down-cycles’-loses value as it’s recycled.
|Recycling paper uses the same amount of clean water and energy as the manufacturing process, and requires chemical compounds such as hydrogen peroxide, sodium silicate and sodium hydroxide, which bleach and separate the fibres.|
|6. Disposal||47-90 days in the sea (which would still be very bad for sea life), but in landfill, with no oxygen or sunlight to break down, it may take as long as a regular, oil-based plastic bag. It can, however compost very well.||If composted, paper takes 2 weeks to decompose.
In landfill it will take anywhere from 2-6 weeks (or in some cases, much longer). In the ocean in will first break down, then decompose, in about the same time, or less.
I decided to research which is easier on the environment, out of two ‘biodegradable’ or ‘eco’ options we would usually be given as a option to non-renewable fossil fuel based plastic bags.
My conclusion is this
Bio polyethylene Is better in the way that it: 1. Takes up much less space in landfill 2. Uses less fossil fuels in the manufacture and sourcing 3. Does not use huge amounts of clean water in its making
Paper is better in the way that it: 1. Breaks down much faster 2. Does not affect our sea life or food chain when if it ends up in the sea 3. It doesn’t ‘down-cycle’. So we can recycle paper again and again (albeit using up water and some chemicals in the process), meaning that we do not need to keep logging and deforestation as much.
Therefore, I think that a paper bag is still a better way to go, and will not endanger our sea-life, food-chain or ecosystem anywhere near as much as bio polyethylene.
Grace Smith, age 10, from Taupo – year 7 programme. Due to the size of the file I had to paste it here one page at a time.