Key Concept: Sustainability
What is sustainability?
– items that can be recycled/reused
– items that have minimal impact on the environment (i.e. compostable)
– at the same time can benefit as many people as possible
– seeks to reduce and prevent pollution at its source
– minimize use and generation of hazardous substances
eg. biofuels
Practical: Making Bioplastics from Cornstach
Materials:
– constarch/starch/potato starch
– ethanoic acid
– distilled water
– food colouring
– corn oil
– zip lock bag
– microwave oven
Procedure:
1. place the constarch in the plastic bag. Add corn oil and water
2. seal the bag, then mix the ingredients by rubbing outside the bag with fingers
3. Add food colouring
4. Open zip seal a bit and put place bag in a microwave oven
5. Microwave on high 25 seconds
Concept behind manufacturing of bioplastic:
Explanation 1: Heating up the cornstarch makes lactic acid. Lactic acid molecules the combine into long chains of polylactic acid, or PLA. Polymers, with their long interwoven chains, give all plastics, including PLA, their special properties.
Explanation 2: After starch is dried from an aqueous solution, it forms a film due to hydrogen bonding between the chains of polymers. Amylopectin inhibits the formation of film but the addition of strong acid breaks down amylopectin and allows the chains to be formed.
Advantages:
PLA is easier to compost. Under the right conditions it will break down into regular lactic acid in a matter of weeks. That could take pressure off the nation’s mounting landfills, since plastics already take up 25 percent of dumps by volume. Moreover, corn-based plastics are starting to be the cheaper alternative, seeing that oil prices are rising.
Disadvantages:
PLA has a melting point of 46 degrees Celsius, so it melts easily. It is also made from corn; a foodsource which can potentially feed many starving people.
Sources:
http://www.scienceoffcenter.org/science/310-corn-starch-plastic
http://www.smithsonianmag.com/science-nature/plastic.html
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