1. Plant Fibres

2. Explain how the arrangement of cellulose micro-fibrils in plant cell walls and secondary thickening contribute to the physical properties of plant fibres which can be exploited by humans.
Describe how the uses of plant fibres and starch may contribute to sustainability e.g. plant-based products to replace oil-based plastics.

3. The use of plant fibres for man-made products is sustainable and renewable as plants can be grown again. (It sustainable when there are replanting programmes). Also, the use of plants is carbon neutral, as the carbon dioxide released when they are burnt or decomposed is equal to the carbon dioxide originally absorbed for the plant to grow.
The use of oil-based products is not sustainable and non-renewable as oil is a finite resource which is predicted to run out in 40 years if rates of consumption continue.

4. Properties and Extraction
Plant fibres have great tensile strength – they cannot be broken down by pulling. They are also flexible which makes them very useful. They normally occur in bundles of fibres.
Plant fibres need to be extracted from plants before they can be used.
The fibres are normally lots of sclerenchyma cells and xylem tissue that are normally very tough. Cellulose and lignified cellulose are not easily broken down by enzymes or by chemicals. However, the matrix of pectates and other compounds can usually be dissolved or removed.

5. Plants commonly used for their fibres
Hemp is used for building material and fabrics. Also in bioplastics.
Jute – twine, rope and matting.
Manila hemp is from the plant abaca – a relative of the banana. It used to be made for rope making. Now used in pulps for – filter paper, tea bags and bank notes.
Flax – linen, lace, high quality paper, twine and rope.

6. Manila Hemp (similar species as bananas)

7. Hemp Flax

8. How fibres are processed
Paper is normally made from fibres from wood. Wood fibres are not normally easy to extract because the matrix around the cellulose fibres contain a lot of lignin.
Wood is therefore soaked in very strong alkalis to produce a pulp consisting of cellulose and lignified cellulose fibres in water. Thin layers of pulp are then pressed onto frames where they dry to form paper.
Trees used for making paper include softwoods fir, pine, spruce, larch and hardwoods eucalyptus, birch and aspen.

9. Many traditional methods of producing fibres rely on the action of decomposers (fungi and bacteria) aerobically respire to decompose (break down) the soft material around the fibres. This is known as retting.
In developed countries manufacturing processes using chemicals and enzymes do the job more quickly.

10. Cotton
The most widely used natural fibre. It is produced in almost pure cellulose fibres, packed around the seeds so there is no need for retting or other treatment.
The short fibres are spun together to make a continuous thread. The threads are woven together to make a fabric. Similar processes are used with sisal, jute and hemp.

11. Wood
Wood is a composite material made up of secondary cells walls of cellulose fibres embedded in hemicelluloses and lignin.
The cellulose fibres make the wood very resistant to compression so it is good for weight bearing in buildings. The matrix is flexible however, and this prevents the wood from cracking.

12. Synthetic Fibres
Nylon and Polyester have been developed in the 20th century. They are cheap, hard wearing and do not crease. (Their downside was they didn’t breathe.)
They are made from crude oil – a non-sustainable non-renewable resource which is getting increasingly expensive.

13. Uses of Wood
Wood can be used for fencing, boats, furniture, building homes and paper. Wood is also a good insulator and needs less heating in winter and cooling in summer than a brick house.
Wood is a sustainable resource if there are replanting programmes.
Pre-historic and historic clearance of UK woodland led us to a low point at the beginning of the twentieth century when woodland was only 5% of Britain – and falling. It is now nearly 12% - and rising.