Synthesizing Bioplastic Part 2

In this practical, we synthesized a protein-based bioplastic using milk and ethanoic acid (vinegar). The protein extracted is a common milk protein called casein.

>Add 100 ml of milk and an equal amount of vinegar to a beaker
>Heat to 60 degrees Celsius. The milk should be coagulated. If not, continue heating until clumps are visible.
>Cool and filter
>The residue is the casein plastic. It can be moulded.

 The product synthesized was very soft and would disintegrate when water is added. Usually, plasticisers such as glycerine are also added to the protein to make the plastic harder and more durable.

This is also the method to make homemade cheese! See the recipe here.

Acid makes milk curdle - separate into curds (containing milk solids, fats and proteins) and whey (contains mostly water). To understand why this happens, we need to know about the structure of milk.

Milk is an emulsion of fat, water, lactose (sugar) and a mixture of proteins. Fat globules are surrounded by phospholipids and proteins that keep them apart and suspended in the mixture. If we beat milk, the fat globules clump together and separate from the liquid. This is how butter is made!

The water contains soluble proteins that are hydrophobic on one end and hydrophillic on the other. Because of this, they organise themselves into globes called micelles. These proteins are called caseins. There are 4 different types of caseins and they make up 80% of the weight of proteins in milk.

Casein micelle. The submicelle contains a hydrophobic core and is oriented towards the center.

The outer surface of a casein micelle is made of up of a layer of negatively-charged kappa-casein. Since like charges repel, casein micelles repel one another and are kept in solution.

Acids release H+ ions in solution. When acid is added to milk, H+ ions bind to kappa-casein molecules, causing them to lose their negative charge. Therefore, the casein micelles with bind together and become visible as clumps in the milk.

Heat weakens the interaction forces between casein components within the micelles, causing them to dissociate more readily.

If the milk is heated to 85 degrees Celsius before adding the acid, kappa-casein reacts with a whey protein (protein that is dissolved in the water) called b-lactoglobulin to form a complex that makes the casein micelle surface much coarser. So when acid is added, the casein molecules clump into an open spongy gel that soaks up the water. This produces yogurt!

In commercial cheese making, lactic acid bacteria and rennet are added instead of ethanoic acid. Lactic acid bacteria digest the lactose sugar in milk to form lactic acid needed to discharge kappa-casein. This process is called lactic acid fermentation. Rennet contains an enzyme called rennin that facilitates casein micelle dissociation (curdling) by acting on the casein micelles.

The flavours of cheese are affected by many factors - the type of milk (goat or cow for instance), the type of bacteria used to innoculate it, and the conditions in which the cheese is aged. Ageing allows the cheese to develop complex flavours as the microbes act on it.

Swiss cheese. The holes are formed by bubbles of carbon dioxide gas, produced when propionibacteria consume the lactic acid excreted by other bacteria.

Back to the topic of bioplastics. Protein-based plastic is advantageous over petroleum-based plastic because it is biodegradable. Protein is synthesied naturally, making it a renewable resource unlike petroleum which is a finite resource.

The principle of synthesizing bioplastic from proteins is similar to the principle of synthesizing bioplastic from starch. Like starch, protein is a natural polymer. It is made of many amino acids, forming an amino acid chain known as a polypeptide. A polypeptide folds into complex structures due to its make-up.

Polypeptide folding showing primary, secondary, tertiary and quarternary structures.

This is not good for synthesizing bioplastic, as a linearised form of the amino acid is needed to make a strong homogenous structure. Many steps are taken to denature proteins into a linear form. Watch this video for a more detailed explanation.

http://www.youtube.com/watch?v=N3a9gr6SpZU

Proteins' complex structure makes it challenging for viable protein-based bioplastics to be synthesized. Currently, many researchers are working on this issue, waiting for a breakthrough.

Sources

http://wiki.answers.com/Q/Why_does_milk_curdle_when_acid_is_added

http://science.howstuffworks.com/innovation/edible-innovations/food-preservation7.htm

http://www.sciencedirect.com/science/article/pii/S0022030296764901

http://voices.yahoo.com/why-there-so-many-different-cheeses-if-they-are-8229631.html?cat=22

http://en.wikipedia.org/wiki/Swiss_cheese

Synthesizing Bioplastic

Bioplastics are plastics that are derived from renewable biomass, such as corn. This contrasts with conventional plastics, which are made with petroleum, a non-renewable resource.

Bioplastics are more sustainable because they come from renewable sources. However, using food crops such as corn to produce bioplastics poses a problem - crops require large amounts of water, land, fertiliser and other materials to grow. The production of bioplastics is also energy-intensive. Some bioplastics also produce methane gas when they decompose. Methane gas is a greenhouse gas many times more potent than carbon dioxide.

However, unlike petroleum-based plastics, bioplastics are biodegradable. Although bioplastics may require as much energy to produce as petroleum-based plastics, they will not clog landfills and are more environmentally-friendly in this aspect.

Want to know more about different types of plastics and their pros and cons? Visit the website at this link: http://www.explainthatstuff.com/bioplastics.html


Unlike bioplastics, conventional petroleum-based plastics are non-biodegradable

During this practical, we synthesized bioplastic using corn starch, potato starch and synthesized starch as the biomass material.

Method
> Add one spoon of starch into a ziplock bag. Add corn oil and mix by rubbing the bag. There should be just enough oil to make the flour clump together.
> Add a little water and a few drops of food colouring to colour the plastic. Mix well.
> Microwave the open ziplock bag on high for 25 seconds.
> Remove from microwave and mould with wooden block while still hot.

Before microwaving

After microwaving

The plastic that we synthesized (which was made using potato starch) is soft, bouncy and easily broken apart, very unlike plastic we are used to. The plastic we synthesized also disintegrates when wet, due to its slightly polar nature. Therefore, other additives are needed to give starch-based plastics the desirable properties of plastic. Often, flexibilisers and plasticisers such as sorbitol and glycerine are added. Starch-based plastics are already in the market and are called thermoplastic starch (TPS).

Starch is made of amylose (linear glucose polymer) and amylopectin (highly branched glucose ploymer). The amylose/amylopectin ratio is different for starch from different plant sources.




When heated with water, starch is gelatinised or destructurised: hydrogen bonding sites such as hydroxyl groups bind more water, irreversibly dissolving the starch. Penetration of water increases the randomness of the general starch granule structure and decreases the number and size of crystalline regions. When heated, crystalline regions become diffuse so that the chains begin to separate into an amphorous form.


Crystalline regions are ordered and have characteristic geometry but amorphous regions do not.

During the gelatinisation of starch, 3 main things happen to the starch granule: 1. granule swelling 2. crystal or double helical melting 3. amylose leaching.

Water is first absorbed in the amorphous space of starch, which leads to a swelling phenomenon during heating and then transmitted through connecting molecules to crystalline regions.^[3] Water enters tightly bound amorphous regions of double helical structures to swell amylopectin, thus causing crystalline structures to melt and break free.^[4] Stress caused by this swelling phenomenon eventually interrupts structure organization and allows for leaching of amylose molecules to surrounding water.

The result is a colloidal solution - polymers dispersed in a medium of water - that gels when cooled. This is due to to a process called retrogradation. When cooled, cooked starch molecules will rearrange to form a more ordered crystalline structure and inter-molecular bonding occurs between chains of amylose and amylopectin, with water embedded within the molecule.

Due to strong associations of hydrogen bonding, longer amylose molecules will form a stiff gel.^[6] Amylopectin molecules with longer branched structure, increases the tendency to form strong gels. High amylopectin starches will have a stable gel, but will be softer than high amylose gels.

Molecules that are capable of hydrogen bonding with hydroxyl groups such as water, sorbitol and glycerine act as plasticisers and change the properties of the gel formed.

The corn oil in our practical probably acted similarly to glycerin, making the plastic more pliable by acting as a lubricant at a molecular level. I am not sure about this, because corn oil and glycerin are quite different. But there must be a reason why the plastic was 'bendy'. Classmates that added less oil got a less flexible plastic.

More can be deduced by changing the proportion of reactants and observing the properties of the plastic.

This year, one of the prize-winning projects are the Google Science Fair was about synthesizing bioplastic from banana peels. Check it out here!

Sources:
http://www.sciencehq.com/chemistry/crystalline-and-amorphous-solids.html
http://en.wikipedia.org/wiki/Starch_gelatinization
http://polymerinnovationblog.com/thermoplastic-starch-a-renewable-biodegradable-bioplastic/
http://green-plastics.net/videos/35-howto/52-video-brandon121233

Green Chemistry and Sustainability

Green Chemistry is a philosophy that promotes sustainability. Sustainability is about modifying practices so that they can be maintained long-term. This includes considering impacts on

> the economy: projects should be financially sustainable
> social equity: people involved in production should be treated fairly
> the environment: minimising production of pollutants, increasing yield through optimisation

How does Green Chemistry promote sustainability? By definition,
Green Chemistry encourages the design of products and processes that minimise the use and generation of hazardous substances.

In other words, Green Chemistry encourages us to optimise processes so they generate less waste (including waste harmful to the environment) and more yield.

Companies can use the 12 principles of Green Chemistry as a guide to work towards becoming more sustainable.

Sustainable Companies
Sustainable companies take measures to minimise the impact of their businesses on the environment. One example of a sustainable company is Justin's, a company that sells nut butter.



Justin's modified the design of their jars to use 47% less plastic. This is beneficial to the environment because plastic is non-biodegradable (cannot be broken down by microbes) and comes from petroleum, which is a finite resource.

In addition, Justin's sources their raw materials (like nuts) from as nearby as possible. This saves transport costs and fuel, which reduces carbon emissions. Click on this link to find out more about the nut's journey from soil to jar :)

http://www.justins.com/theDirtOnNuts_CHB.php

Justin's is also working towards a 100% renewable squeeze-pack packaging that can be composted in people's homes. Compostable materials are better than plastic because they can biodegrade.

Justin's sustainable philosophy is inspiring. Do find out more about such companies, and support their sustainable practices! :)