1. Natural and Synthetic Materials
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6. Natural and Synthetic Materials
Some materials are natural, meaning that they are found in nature
While other materials are synthetic, meaning they are produced by chemical means in a lab

7. Polymers
Polymers have been around as long as life on Earth – plants, animals and other living things produce many natural materials made of large polymer molecules
Polymer: large complex molecule built from smaller molecules joined together in a repeating pattern
Polymers form when chemical bonds link large numbers of monomers in a repeating pattern.
Monomer: smaller molecules from which polymers are built
Natural and synthetic polymers exist

8. Natural Polymers Examples of Natural Polymers:
Starches in pancakes and proteins in meats and eggs are examples of natural polymers
Cellulose in fruits and vegetables are natural polymers
Snake venom is a natural polymer made of approximately 90% proteins
Spider webs are made of a silken polymer which is one of the strongest known materials
Proteins in your body are also made of natural polymers, including your fingernails and muscles

9. Synthetic Polymers
Polyester and nylon clothing and plastics are examples of synthetic or manufactured polymers.
Many synthetic polymers come from coal or oil
the most common being plastics, which are synthetic polymers that can be molded or shaped
Synthetic polymers are often used in place of natural materials that are too expensive or wear out too quickly

10. Too Many Polymers?
Synthetic polymers are inexpensive to make, strong and last a long time – they have replaced many natural materials
It is cheaper to throw away plastics and make new ones instead of reusing them, this increases the volume of trash because plastics are not easily broken down – they are around for a long time
Natural polymers react more easily with other substances and they break down easier and sooner than synthetic polymers
Making synthetic polymers from waste plastics can help to reduce this problem, often you may see bottles, fabrics, cars, benches, or fences that are made from recycled waste products

11. Composites
Every substance has desirable and undesirable properties – what if you could take the best properties of two substances and put them together?
Composites: combines two or more substances in new material with different properties
many composites contain one or more polymers
many synthetic composites are made to imitate a common natural composite – wood
wood is made of long fibers (cellulose), held together by a plant polymer (lignin). Cellulose is flexible but cannot support much weight, lignin is brittle and will crack under the weight of a tree branch
together these two polymers make the tree trunk strong

12. Uses of Composites
The idea of combining the properties of two substances to make a more useful one has led to many new products
Fiberglass composites are one example
strands of fiberglass are woven together and strengthened with a liquid plastic that sets like glue, this combination makes a strong, hard solid that can be molded around a form to give it shape, is lightweight and still strong enough to be used as a boat hull or car body
Many other useful composites are made from strong polymers combined with lightweight polymers
bicycles, cars, and airplanes are all built from composites that make them littler than the same vehicles built form steel or aluminum
fishing rods, tennis rackets, and other sporting equipment are made from composites that are both strong an flexible

13. The Development of Polymers
Celluloid
Made using cellulose, celluloid became a substitute for ivory in billiard balls and combs and tooth brushes. It was later used to make movie film. Because celluloid is very flammable, other materials have since replaced it for almost all purposes.
Synthetic Rubber
Charles Goodyear invented a process that turned natural rubber into a hard, stretchable polymer. It did not get sticky and soft when heated or become brittle when cold, as natural rubber does. Bicycle tires were an early use.
Bakelite
Bakelite was the first commercial polymer made from compounds in coal tar. Bakelite doesn’t get soft when heated, and it doesn’t conduct electricity. these properties made it useful for handles of pots and pans, for telephones, and for parts in electrical outlets.

14. The Development of Polymers
Nylon
A giant breakthrough came with a synthetic fiber that imitates silk. Nylon replaced expensive silk in women’s stockings and fabric for parachutes and clothing. It can also be molded to make objects like buttons, gears, and zippers.
2002 – Light-Emitting Polymers
Discovered accidently in 1990, light-emitting polymers (LEPs) are used commercially in products such as MP3 players and electric shavers with display screens. LEPs give off light when exposed to low-voltage electricity. Newer, more colorful LEPs may be useful as flexible monitors for computers, TB screens, and watch-sized phones.
Kevlar
Kevlar is five times stronger than steel. Kevlar is tough enough to substitute for steel ropes and cables in offshore oil rigs but light enough to use in spacecraft parts. It is also used in protective clothing for firefighters and police officers.