Nanocellulose Foam

You have probably held polystyrene cups (styrofoam cups) in your hands. It is a wonderful material for making disposable cups because it is light-weight, holds it shape well, and is an excellent insulator. All this means that you can fill a polystyrene cup with hot tea and drink from it without having it burn your hands. High school chemistry teachers are very fond of using polystyrene cups as "cup calorimeters" in the school laboratory. Unfortunately, polystyrene is not an environmentally friendly polymer, it doesn't break down, it is chemically inert, so persists in the environment.
Plant-based polymers which degrade in time, such as cellulose, could replace polystyrene if we can make a cellulose-based material with same properties as polystyrene.
Cellulose is a polysaccharide. It is composed of many glucose units joined together by ether bonds (glycosidic links). During acid hydrolysis these ether bonds (glycosidic links) are attacked and broken so that the final product of a complete reaction is a lot of glucose molecules. The reaction mechanism for the acid hydrolysis of cellulose is shown below:


If only some of the ether bonds (glycosidic links) within a cellulose polymer chain are attacked, then you could end up with shorter chains of glucose polymer, still enough glucose units in the chain to be considered cellulose. If these chains are only 5-20 nanometres wide (even though they may be several micrometres long) they will be referred to as nanocellulose.
Researchers at Washington State University have added polyvinyl alcohol, shown below:

to nanocellulose. Polyvinyl alcohol binds to the nanocellulose which stabilises the foam that can be  produced. This light-weight material is reported to be a better insulator than polystyrene foam (styrofoam) and "can support up to 200 times its weight without changing shape. It degrades well, and burning it doesn't produce polluting ash."

Suggested Further Reading:
Nanotechnology

Suggested Study Questions:

1. Convert the following measurements to metres (m):
   • 5 nm
   • 20 nm
   • 100 μm
   • 1000 μm
2.  Convert the following measurements to nanometres (nm)
   • 5 × 10^-9 m
   • 2.5 μm
   • 5.2 mm
   • 0.75 cm
3. Draw a section of cellulose polymer containing 6 glucose units. Circle the ether bonds (glycosidic links) in red.
4. Draw the results of acid hydrolysis if all the ether bonds (glycosidic links) in this section of cellulose polymer were broken.
5. Draw the results of acid hydrolysis on the section of cellulose polymer you drew for question 3 if only 2 new "molecules" are produced. Is there only one possible answer? If more than one answer is possible, how many possible answers can you think of?
6. Consider the structure of cellulose and of polyvinyl alcohol. Explain how polyvinyl alcohol can "bind with" cellulose. 
7. Explain why a nanocellulose foam can be stabilised by adding polyvinyl alcohol.
8. Consider the combustion of cellulose. Give the products for
   • complete combustion of cellulose
   • incomplete combustion of cellulose
9. Wood is composed largely of cellulose. When a wood log burns on a camp fire it produces a sooty flame. Explain why.
10. Explain why nanocellulose is unlikely to produce a sooty flame when it burns.

Water-Soluble Plastic

I buy boxes of dishwasher detergent containing plastic bags filled with the detergent. I place these bags straight into the dishwasher. When the dishes are clean and I remove them from the machine there is no trace of either detergent or the plastic bag that held it.

What happened to the plastic bag?

Can plastic dissolve in water?

Find out in the December 2018 edition of AUS-e-NEWS, AUS-e-TUTE's free, quarterly, newsletter for chemistry students and teachers. 

To subscribe to AUS-e-NEWS, go to https://www.ausetute.com.au/ausenews.html

Pthalate in Plastics

Researchers in the USA have found a link between premature births and the exposure of  pregnant women to a group of organic (carbon based) chemicals known as phthalates.

Phthalates have been used for more than 50 years as plasticizers, substances which are added to plastics to increase their flexibility, transparency, durability and longevity. For example, adding phthalates to polyvinyl chloride (PVC) makes the PVC soft and flexible, ideal for flexible plastic tubing. You will find phthalates in many products you come into contact with every day, from vinyl upholstery and floor tiles, to plastic food containers and wrappers, to personal care products like perfumes, moisturizer, and liquid soap.

Phthalates have the general structural formula shown below:

R and R' represent alkyl groups.
If R and R' are both CH₃ (methyl) groups, the molecule is known as dimethyl phthalate (abbreviated as DMP).
If R and R' are both C₂H₅ (ethyl) groups, the molecule is known as diethyl phthalate (abbreviated DEP).
When R and R' are very small alkyl groups, like methyl or ethyl groups, the phthalates are colourless, odourless liquids at room temperature and pressure.
The phthalates are added to molten plastic, allowing the phthalates to mix with with the polymer. The polar C=O groups in the phthalate molecules interact with partial positive charges on atoms in the polymer chain, for example, the C^δ+ of the C-Cl covalent bond in a polyvinyl chloride polymer.
When the plastic is cooled, the interactions between the phthalate and the polymer chains remain, and the alkyl groups of the phthalate screen the polymer chains from interacting with each other so that the polymer chains can slide over each other. This results in a more flexible plastic.


Reference:
http://www.abc.net.au/news/2013-11-19/common-plastics-chemical-linked-to-pre-term-births/5101828

Further reading:
Esters and Esterification
Bond Polarity
Intermolecular Forces


Suggested Study Questions:

1. Draw the structural formula for
   • dimethyl phthalate
   • diethyl phthalate
2. Give the molecular formula for
   • dimethyl phthalate
   • diethyl phthalate
3. On the structural formula for dimethyl phthalate, circle a benzene ring.
4. On the structural formala for diethyl phthalate, circle an ester functional group.
5. Dimethyl phthalate can be prepared in an esterification reaction using phthalic acid and methanol. Draw the most likely structural formula for phthalic acid. 
6. In chemistry, what is meant by a polar bond?
7. On the structural formula of diethyl phthalate,  show the partial charges of the atoms in the polar areas of the molecule.
8. Draw a diagram to show the interaction between dimethyl phthalate and a section of the polyvinyl chloride polymer.