Plastics





Plastics 3010
Photo by: Nataliya Zotova

The term plastic can be used as both an adjective and a noun. As an adjective, the term refers to any material that can be shaped or molded, with or without the application of heat. In this respect, objects such as soft waxes, asphalt, and moist clays are said to be plastic.

As a noun, the term describes a natural or synthetic polymer. A polymer is a material whose molecules consist of very long chains of one or two repeating units known as monomers. As an example, the synthetic polymer called polyethylene consists of thousands of ethylene units joined to each other in long chains. If the letter E is taken to represent an ethylene unit (monomer), then the polymer polyethylene can be represented as:

-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-E-

Although the term plastic is strictly defined as either a natural or synthetic material, it is probably understood by most people today to refer

A scanning electron micrograph of the surface of a sheet of biodegradable plastic, plastic that is able to be decomposed (broken into smaller parts) by bacteria. This spherical object is one of many granules of starch embedded in the surface of the plastic. When the plastic is buried in soil, the starch grains take up water and expand. This breaks the material into small fragments, increasing the contact area with the soil bacteria that digest plastic. (Reproduced by permission of Photo Researchers, Inc.)
A scanning electron micrograph of the surface of a sheet of biodegradable plastic, plastic that is able to be decomposed (broken into smaller parts) by bacteria. This spherical object is one of many granules of starch embedded in the surface of the plastic. When the plastic is buried in soil, the starch grains take up water and expand. This breaks the material into small fragments, increasing the contact area with the soil bacteria that digest plastic. (Reproduced by permission of
Photo Researchers, Inc.
)

primarily to artificial materials. Substances such as nylon, Styrofoam™, Plexiglass™, Teflon™, and polyvinyl chloride (PVC) are examples of such materials.

Thermoplastic and thermosetting plastics

Plastics can be subdivided into two large categories: thermoplastic and thermosetting. The former term refers to a material that can be melted and shaped over and over again. Examples of thermoplastics include acetal, acrylic, cellulose acetate, polyethylene, polystyrene, vinyl, and nylon.

A thermosetting plastic, in contrast, can be melted and shaped only once. If it is then heated a second time, it tends to crack or disintegrate. Examples of thermosetting plastics (or just thermosets) include amino, epoxy, and phenolic and unsaturated polyesters.

Words to Know

Composite: A combination of a plastic and one or more additives that has special properties not possessed by the plastic alone.

Monomer: A fundamental unit of which a polymer is composed.

Polymer: A substance composed of very large molecular chains that consist of repeating structural units known as monomers.

Thermoplastic: A polymer that softens when heated and that returns to its original condition when cooled to ordinary temperatures.

Thermosetting plastic (or thermoset): A polymer that solidifies when heated and that cannot be melted a second time.

Additives

Very few plastics are used in their pure state. Many different materials known as additives are added to improve their properties. Products consisting of pure plastics and additives are known as composites. For example, the strength of a plastic can be increased by adding glass, carbon, boron, or metal fibers to it. Materials known as plasticizers make the plastics more pliable and easier to work with. Some typical plasticizers include low-melting solids, organic liquids, camphor, and castor oil. Fillers are materials made of small particles that make a plastic more resistant to fire; attack by heat, light, or chemicals; and abrasion. They also can be used to add color to the plastic.

[ See also Polymer ]



User Contributions:

will
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Dec 1, 2006 @ 10:22 pm
Do you have any other information on the types of plastics that would work best for this "bacteria eating" approach? This is great stuff.

Thanks for any help you can provide.
Tinna Chan
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Dec 16, 2006 @ 8:08 am
I like the information given! Perhaps for me it would be 100% nice. It is very complete. I thought it is not but when I read the information, It was really good! It has also additional notes to let the people learn.Great Job!
israa
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Oct 23, 2007 @ 9:09 am
do you have any information about the differance between the thermo set plastic and the thermo plastic such as chemical compstion ,mechanical properites ,curing process ,polymaraztion process
ADUDE
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Jun 11, 2009 @ 3:03 am
I think this article is nice except I reckon there should be more information shown about the thermoplastic and thermosetting plastics. Otherwise it is very useful and I reckon that it is a good research web site.
chandan halli
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Jul 30, 2009 @ 5:17 pm
Excellent and good,which help differentiate the the thermoset amd thermoplastic
Megan Trollo
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Nov 29, 2009 @ 6:18 pm
Hello I am writng a paper on plastics and I found your website very helpful, but I was wondering if you could give me the name of the author so I can properly cite this page.
-Megan

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