The strength of plant fibresIn this activity you will extract the fibres from nettles and then test their strength. Fibres have been extracted from plant stems for centuries and used in the commercial manufacture of a wide range of textiles and paper. The term fibers does not just refer to the sclerenchyma but is used to describe a range of fibre-like structures. These plant fibres have been used for different purposes, as indicated in the table.

Their use is dependent on their properties.

Fibres can be removed from plant stems by retting. This can be done by either field retting or water retting.

Field Retting:Plant stems are cut or pulled up and left in the field to rot; microbial action breaks down the stalks.

Water Retting:Stems are cut or pulled up and immersed in water to rot; microbial action breaks down the stalks. This process produces more uniform, higher quality fibres, but is more expensive and produces nitrogen rich waste water that must be treated before discharge.

In both kinds of retting, bacteria and fungi breaks down the soft tissues of the stems leaving the cellulose intact. It is them relatively easy to remove the cellulose-rich fibres.

You need to know about the retting process. However, it is time consuming and very smelly. Therefore, for these reasons we are going to do a simpler practical!

Method:

1. Carefully remove a fibrous string from a celery stem.2. Check the string to ensure that it is of constant diameter down its entire length (look for tears and thin sections)3. Tie one end of the string to the clamp 4. Record the length of the hanging string5. Add 20g and record the length of the string6. Repeat step 5 until the string breaks.