What is Green Chemistry?
Green Chemistry encompasses three sectors: environment, economy and social equity.
Firstly, protecting our environment involves producing products that are reusable and recyclable.
Next, increasing efficiency of the chemical reaction is economical , saving costs for companies and individuals.
Most importantly, Green Chemistry ultimately aims to address mankind's concerns, welfare and to benefit people. I believe in Science for Humanity. There are many real-life applications of sustainable chemistry, which benefits people.
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| The solar bottle, made only using a bottle, water and bleach, lights up people's homes in Philippines. |
Green chemists are guided by principles that aim to minimize harmful waste products, increase efficiency and safety, etc. We did a group activity to match examples to the corresponding principles. I was surprised that even simple things, like monitoring chemical reactions (at home too!), will make a great difference in reducing waste products and achieving the optimum reaction efficiency.
Explore the 12 principles here:
http://www.beyondbenign.org/greenchemistry/12principles.html
What are plastics?
Organic, mouldable polymers with high molecular mass.
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| Highly versatile and relatively cheap, used to make a range of products such as bottles, fabrics, food containers, etc. |
Analysing problems with conventional plastic
- Petroleum is used: a finite, non-renewable natural resource, it will eventually be depleted quickly at the rate it is being used to synthesize conventional plastics
- High environmental footprint: releases large amounts of greenhouse gases, such as carbon dioxide
- Releases toxic wastes: contaminates the food chain, whereby toxic substances accumulate in larger predators (bioaccumulation) and eventually ends up in the human body.
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| Many polycarbonate water bottles contain BPA, an estrogen-like endocrine disruptor, which could cause hormone disorders and thus harm the body. Both molecules contain two terminal hydroxyl groups and benzene ring. |
- Difficult to decompose: ends up in landfills (land pollution), forests and oceans
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| Strong C-O bonds within the ester linkage are difficult to break, making conventional plastic difficult to decompose. Furthermore, polymer chains are entangled in a complex manner. |
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| Marine life is endangered by plastic. Turtles mistake plastic bags for jellyfish (food), seals get caught in plastic, seabirds choke on bottle caps... |
Plastic that are compostable and made from renewable resources (eg. plant material).
Analysing pros and cons of bioplastic
+ Lowers environmental footprint: lowers greenhouse gas emission
+ Potential to be used as biofuel
+ Compostable, biodegradable by microbes to produce water, carbon dioxide and humus (nutrients for the soil, thus playing a key role in returning nutrients to the soil in the carbon cycle)
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| Cornware, bioplastic utensils made from corn, is biodegradable |
- As costly as producing conventional plastic
- Bioplastic technology is not advanced yet
- Petroleum is used to generate electricity to power the production of bioplastic: petroleum still used :(
- Methane is released: 20 times more potent greenhouse gas than carbon dioxide, contributing to global warming
- Pesticides used to grow crops: lead to eutrophication, disruption of ecosystem and loss of biodiversity
- Plants are a source of food: people in less-developed countries suffer from hunger and malnutrition. Crops that can be used to feed starving people are used instead to produce bioplastic. This presents a moral controversy and dilemma
Corn starch/ potato starch plastics
Method
1. Mix corn oil, corn starch/ potato starch and a little water in a zip-loc bag
2. Microwave, leaving the zip seal open, for 25s
3. When the mixture has cooled, bioplastic is formed!
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| Potato starch plastic is smooth, more oily and flexible. This could be due to the higher amounts of corn oil added. Corn starch plastic is less oily, brittle and hard. |
The Chemistry behind. starch bioplastics..
Starch contains two chains of polymers: amylose and amylopectin.
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| Amylose is a linear molecule, giving the plastic its firmness. When starch is dried from an aqueous solution, it forms a film due to strong hydrogen bonds between the polymer chains. Amylopectin is highly branched, giving the plastic undesirable softness and inhibiting the formation of film. |
Acid hydrolysis:
By adding corn oil, fatty acids in the oil break down amylopectin. Unbranched amylose chains line up to form a stronger film. Vinegar can also be added, because the acetic acid present helps to break down amylopectin.
However, as the amylose chains are arranged too systematically, the film forms crystals and the starch bioplastic becomes brittle :( This is why the bioplastic formed was easily broken, unlike conventional plastic.
Improvements
Propane-1,2,3-triol/ glycerin acts as a plasticiser and can be added to prevent the brittleness of bioplastic. Because the plasticiser is hydroscopic, water molecules are attracted to it. Water prevents the film from becoming crystalline by entering the regions between the amylose chains. The bioplastic formed will be less strong, but more flexible and moldable. Plastic is more useful when flexible, as it can be molded into different shapes.
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| Plasticiser keeps the polymer chains further apart, disrupting the arrangement and weakening the forces of attraction between the chains. |
References
http://www.philnews.ph/wp-content/uploads/2011/04/solar-bottle-light-bulb.jpg
http://www.phenoxy.com/images/plastics-composite.jpg
http://origin-ars.els-cdn.com/content/image/1-s2.0-S0018506X10002540-gr1.jpg
http://cool.conservation-us.org/jaic/img/jaic39-03-005-ch5fg2.jpg
http://cdn.coastalcare.org/wp-content/uploads/2009/11/plastic-pollution-seal-trapped.jpg
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgt4zSGWnt69Q8pAxu6Y5dSchvNpz9dg_9P7OGCISU6hyreIjMQitB7hQS9DAl4gxWtvISOAFVTFdX3D9E69iAWY46pID-dWnAKfnfa1-Yd26IaOfg-hwnkvvPlWD7hsvFyw-kj4IsY0ilW/s200/bioplastic+fork+decomposing.jpg
http://thegreenmomreview.com/wp/wp-content/uploads/2009/06/5460_web.jpg
http://www.nuffieldfoundation.org/sites/default/files/images/potato-plastic-117.jpg
http://www.gcsescience.com/o59.htm
