| + | Sunday, 29 September 2013 |
Sustainability and Making Bioplastic from Casein
We started off our Green Chemistry options module with learning about what exactly is Green Chemistry. Green Chemistry, also known as Sustainable Chemistry, is in essence about using environmentally friendly methods to reduce pollution and minimise our impact on the environment.Our first group activity was to present on a company's sustainability agenda and what have they done/what are they doing to reduce environmental impact. For our group, we chose Justin's, which is a company based in Boulder, Colorado that manufactures nut butters. They're a very environmentally conscious brand, always seeking ways to reduce the amount of plastic and paper they use, sourcing for local ingredients to minimise carbon emissions from transport etc.
Our practical session involved making bioplastic from carbohydrates. By mixing corn flour or potato starch with some corn oil, water and food colouring and then microwaving it, we could produce a plastic that, while was not strong and would dissolve in water, was environmentally friendly and fully biodegradable. By mixing the correct amounts of oil with starch, we could convert the amylopectin (which is branched) to amylose (which is not branch), thus conferring a proper structure to our plastic. My own products were not very well-formed because I didn't use the proper amounts of corn oil, water and food colouring; I added too much water, resulting in a very sad-looking plastic.
The next practical session focused on making bioplastic from protein. This time, we mixed milk with ethanoic acid (vinegar) and heated it up to 50 degrees C.
As we heated up the mixture, the milk started to smell very sour and unappealing, and solid curds began rising to the surface.
Fig 1. The solid curds rising!
Once that happened, we filtered the mixture to obtain the residue, which we then molded into our desired shape. (A ball.)
Fig 2. Our masterpiece.
We did a little research and found out that this was actually the same method many people use to make cheese! The combination of vinegar and milk is also used by many people in baking as a substitute for buttermilk.
Basically, this bioplastic that we produced is from casein, which is a kind of protein found in milk. It is a protein suspended in collodial solution, meaning that they repel each other. When vinegar was added, the pH is lowered, the negative charges of casein are neturalised and these casein molecules attract instead of repelling each other. The casein molecules then unfold and reorganise into a long chain, hence 'curdling' the milk.
This 'curdling' is possible as protein has various levels of structure - primary, secondary, tertiary and quarternary. In the primary structure, peptide bonds within the protein molecules are visible; in the secondary structure, hydrogen bonds between protein molecules are visible; in the tertiary structure, disulfide bonds between chains of protein molecules are visible; and in the quarternary structure, the overall shape of the protein is visible.