Using plant starch & fibres

​People have always exploited plants to provide many of the raw materials of life.

The structure of plants is adapted to their functions, in what areas and how can people use plants?

​1. Plants are central to the human diet

Plants provide the macronutrients of carbohydrates, lipids and proteins and also many micronutrients in the form of vitamins and minerals, contain fibre in the cellulose walls of their cells so it helps the working of the gut

​The properties of plant fibres and wood make them very useful to people

Describe the structure of cellulose fibres and explain where can we use it

​People have used plant fibres such as hemp, jute, manila, flax and sisal for centuries to make ropes, paper and cloth.

​Plant fibres have great tensile strength - the resistance of a material to breaking under tension = means how much can it be stretched before it breaks. This, along with their flexibility, makes them very useful

They usually exist in bundles
of fibres, how does it affect?

​How fibres are processed to make products:

- Retting - natural decomposers break down the material around the fibres

​In many countries,
natural retting has been replaced by manufacturing processes using chemicals and enzymes

- Spinning pulls out the short single fibres and twists them together to form a long thread.

Similar processes are used with other plant fibres such as jute, sisal and hemp.

​In the 20th century, synthetic fibres, for example nylon and polyester, were developed. They were new, quite cheap, very hardwearing and did not crease
Any disadvantages?

​In the 20th century, synthetic fibres, for example nylon and polyester, were developed. They were new, quite cheap, very hardwearing and did not crease

Fabrics made from them do not ‘breathe’ and they do not absorb liquid, so they do not absorb body fluids such as sweat. They are made from chemicals from crude oil, a non-sustainable resource which gets increasingly expensive

​People are realising that natural plant fibres are a much more sustainable alternative for a range of uses, from clothing fabrics to ropes and insulating materials

Sustainability – an increasingly important idea = the quality of not being harmful to the environment or depleting natural resources, and thereby supporting long-term ecological balance

​Sustainability focuses on meeting the needs of the present without compromising the ability of future generations to meet their needs.

​EXAM TASK: Explain why ...something... is a sustainable resource.
- it can be biodegradable = can be easily decomposed
- it can be carbon neutral = taking IN carbon as it grows and releasing it as it is burnt
- it can be available/useful to future generations
- more can be made

​Wood is a composite material, made of lignified cellulose fibres and lignin. The great benefit of a composite is that it has the properties of both materials

​How to make paper from wood?

• ​Wood fibres are not easy to extract because the matrix around the cellulose fibres contains much lignin

• Wood is soaked in very strong alkalis such as caustic soda to produce a pulp which consists of cellulose and lignified cellulose fibres in water

• Thin layers of pulp are then pressed onto frames where they dry to make paper

​Benefits of wood:

- Wood is a good insulator so homes built mainly from wood need less heating in the winter and cooling in the summer than a brick house
- Wood can be carbon neutral – taking in carbon as it grows and releasing it as it is burnt
- Wood is an incredibly versatile material that can be used for a wide range of applications
- Wood is environmentally friendly

​There are so many advantages of using natural materials, BUT during the last century, the use of natural materials in the developed world has declined with the development of new synthetic materials being produced from oil-based chemicals, particularly plastics.

​People are used to make a wide range of products, but environmental problems caused by plastics are becoming increasingly clear and nowadays people are trying to switch back

​https://youtu.be/GD4OuvQXKLw?si=jxdzJ0fClYCGJ4IM

​Bioplastics – plastics based on biological polymers such as starch and cellulose

Bioplastics have two large potential benefits:
- They are a sustainable resource = plants can be grown easily to supply the needs of the bioplastics industry
- Bioplastics are biodegradable. Bacteria and fungi can usually break down bioplastics because they are based on biological molecules

​https://youtu.be/CYlwr-rEu60?si=efGsU-qGkJN_AaI6

​Any disadvantages of using bioplastics rather than oil-based plastics?