Polymers and Composites

by

Joseph A. Castellano, Ph.D.RESEED Silicon Valley

Adapted from Focus on Physical Science, California Grade 8Glencoe/McGraw-Hill, Columbus, Ohio (2007).

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What Are Polymers and How Are They Made?

Polymers are very large molecules made of a chain of many smaller molecules bonded together. The small molecules that are used to create polymers are called monomers.

Polymers are made of organic compounds that contain the elements carbon and hydrogen, but may also include O, N, P, S, and other elements.

Polymers form when chemical bonds link large numbers of monomers together in a repeating pattern.

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Think of polymers like chains of many paper clips connected together. This is why chemists often call them “polymer chains.” Each paper clip would represent a monomer molecule.

When two different monomers combine, they form a copolymer

Polymer Classes

Monomer

Monomer 1(Green)

Monomer 2(Red)

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Polymer Types - Natural

Polymers that occur in nature are called natural polymers and include:

1. Cellulose formed in trees, plants, fruits and vegetables from small sugar molecules.

2. Silk and wool produced by animals.

3. Proteins created in the human body from small molecules called amino acids such as:

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Polymer Types - Synthetic

Polymers that are man-made are called synthetic polymers and include:

1. Plastics used in bottles, storage bags, toys, automobiles, and many other items.

2. Fibers made into clothing and carpets.

3. Adhesives used in glue and even chewing gum.

Thousands of products made today useone or more synthetic polymers

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Types of Synthetic Polymers - Soft

1. Polyethylene used in squeeze bottles, and toys.

2. Nylon and polyesters used in clothing

3. Polystyrene used in cups and packing material

4. Teflon (Polytetrafluoroethylene) used for cooking pans:

Soft Plastics are called thermoplastic because they can be recycled by melting to a thick liquid and reforming into a new item. Examples include:

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Types of Synthetic Polymers - Hard

Hard Plastics are called thermosetting because they cannot be remolded to form a new item. One example is Bakelite used in electrical equipment.

Sometimes hard plastics are recycled by grinding the material into small particles for use in composites.

Another hard plastic is polyvinyl chloride used for plumbing pipes.

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Comparing Polymers

Synthetic polymers like polyester and nylon are widely used to replace natural polymers like wool, silk, and cotton for clothing.

Some synthetic polymers have made possible the creation of new products such as CDs, DVDs, and cabinets for computer equipment.

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History of Polymer Development

1839 – Charles Goodyear developed a process called “vulcanization.” This converted natural, soft rubber into a hard, stretchable polymer that could be used to make tires for bicycles and later automobiles.

In vulcanization, the long polymer chains are connected together from their sides like a chain-link fence in a process called “cross-linking.”

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History of Polymer Development

1856 – Cellulose nitrate, known as “Celluloid,” was created by Alexander Parkes from naturally occurring cellulose. It was used to make the first movie films.

1909 – Bakelite was the first all-synthetic polymer that became a commercial success. Invented by Leo Baekeland, it was made from phenol and formaldehyde, two compounds derived from oil and coal processing. It was used to make the first telephones.

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History of Polymer Development

1933 – Polyethylene was first synthesized in England by chemists using high pressure.

By the early 1940s, many factories were established in Europe and the United Sates to make polyethylene for various applications during the World War II years.

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Formation of a Synthetic Polymer - Polyethylene

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Formation of Polyethylene

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History of Polymer Development

1934 – Nylon was synthesized at the DuPont Corporation to form fibers that became a substitute for silk. It is widely used today for stockings, clothing, carpets and other products.

Nylon is a copolymer formed by adding one monomerwith two diamino (NH2) groups to a second monomerwith two carboxylic acid (COOH) groups in the presenceof a catalyst:

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Nylon Product Examples

Gloves Jackets

Playhouse Rope

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History of Polymer Development

1937 – First synthesized by Otto Bayer in Germany, polyurethanes are widely used in flexible foam seating, rigid foam insulation panels, seals, gaskets, and adhesives.

Polyurethanes are copolymers formed by reacting one monomer with two isocyanate (NCO) groups and another monomer with two alcohol (OH) groups in the presence of a catalyst.

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Polyurethane Product Examples

Furniture

Insulation

SurfboardsCar Seats

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1946 to 1952

Many of the polymers we use today were synthesized during the years following World War II. Among these are:

History of Polymer Development

Polystyrene

Dacron

Orlon

Polypropylene

Polyvinyl Chloride

Teflon

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History of Polymer Development

1965 - Kevlar was developed by chemists at the DuPont Company. Because it is five times stronger than steel, Kevlar is used in bullet proof vests worn by police officers. It is also used in protective clothing for fire fighters due to its fire resistant properties.

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History of Polymer Development

Today

Scientists are making displays with light emitting diodes based on organic compounds and polymers. This has led to light emitting displays for cell phones and small televisions on flexible film instead of rigid surfaces.

Samsung Flexible Display Sony Television Display

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Composites

A composite combines two or more materials to form a new material that has different and improved properties.

Many composite materials contain one or more polymers.

Wood is a naturally occurring composite – it consists of long fibers of cellulose, held together by another plant polymer called lignin. Together these two polymers form a very strong tree trunk.

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Composites in Today’s Products

Fiberglass composites combine glass fibers woven together and strengthened with a plastic material. The resulting composite is so strong and hard that it is widely used for automobile bumpers and boat hulls.

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Composites that combine synthetic polymers with the graphite form of carbon are so strong and flexible that they are used in golf clubs, fishing rods, and tennis rackets.

Composites in Today’s Products

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This presentation was produced as a public service to help middle school and high school science teachers develop experiments, presentations and demonstrations that can be used in their classes.

More science experiments and demonstrations are available on the RESEED Silicon Valley web site: www.reseed-sv.org.

RESEED (Retirees Enhancing Science Education through Experiments and Demonstrations) is a program aimed at stimulating greater interest in science by middle school students.