Monday, September 20, 2010

Smelly socks???

Nanotechnology and smelly socks

Why do feet smell? How do chemists help to provide a solution to the problem? Why do modern washing practices make the smells worse than they used to be? What have bacteria got to do with it?

In this activity you will find out how chemists are helping to solve an unpleasant problem and investigate for yourself how preventing smells is linked to acids, bases and neutralisation, bonding, reversible reactions and nanotechnology.

The problem

Your clothes are next to your skin. Your skin produces oils and sweat, which end up on your clothes. On its own this mixture does not smell bad (in fact, scientists think that sweat contains chemicals called pheromones which help to attract members of the opposite sex). The smell arises when bacteria are present. Bacteria live on both your skin and your clothes and they thrive in these environments.

1.What are the conditions that allow the bacteria to thrive on your skin and clothes?

My answers is (Moist,warmth,Full Nutritent contents of slough and chronic wound with infection ) Whats yours?

In low numbers these bacteria are not a problem as they are mostly harmless and unnoticable. However, as the bacteria multiply they produce waste products and these can be substances which have an unpleasant smell. A bacterial population above about 105 (100 000) per gram of clothing will produce a noticable smell. A population of 106 bacteria per gram causes a medium smell and above 108 per gram there will be a strong smell.

Look at the picture below of T-shirt fibres.

Image Hosted by

Now look more closely:

Image Hosted by

If you look at the middle of the photograph above, you can see that there seems to be some damage to the fibre. This is not visible to the naked eye.

Look at the fibre in close-up:

Image Hosted by

It is still hard to tell what the damage is caused by. The next photograph should help:

Image Hosted by

A colony of bacteria is living on the t-shirt fibre. The bacteria glue themselves to it and form a ‘biofilm.’ This biofilm is very difficult to remove and can remain even after washing.

Image Hosted by

Modern washing practices have not helped this problem. A few years ago it was common to wash many items on a hot wash (60 °C or above). Now, most clothing is washed on a cool cycle at 40 °C and many new fabrics cannot be washed above this temperature.

Scientists at Arch Chemicals have been working on a solution to this problem for a number of years. They have designed a product that manufacturers can apply to clothing to help prevent bacterial growth. This product is a chemical called PHMB and has been used in swimming pools and contact lens solutions for several years. It kills bacteria by puncturing their cell membranes, causing the contents to leak out. It does not have the same effect on human cells so it is safe to use in contact with the skin.

The fabric

Cotton fibres are made of cellulose, which is a polymer of glucose and is similar to starch. When the fibres are

processed some of the cellulose is oxidised and the product is slightly acidic.

Part of the cotton fibre is an acid. The fibre can lose an H+ ion leaving a negative charge on the remaining fibre:

Image Hosted by

For the Purista® treatment to stick to the cotton fibres it is important that there are several negative charges on each fibre.

The treatment

The substance used to treat the cotton is also a polymer. Its chemical name is PHMB, which stands for poly(hexamethylene biguanide hydrochloride).

Image Hosted by

Each molecule of PHMB contains about 16 of the repeating units shown in the diagram.

The PHMB winds along the cotton like a snake and bonds at several places along its length like velcro®. This helps the PHMB to lie flat on the surface of the cotton. The coating on the surface is no more than a few nanometers thick, which makes this an example of nanotechnology. The bonds are strong enough to hold the PHMB on the cloth even during washing.

Image Hosted by

Thanks for great information of RSC advancing the chemical sciences:Nanotechnology and smelly Socks