Kinds Of Plastics?
What do each of the numbers on plastics mean?
Also which mean they are reuseable/heat proof/anything else.. ?
- Anonymous1 decade agoFavorite Answer
Plastic is the general term for a wide range of synthetic or semisynthetic polymerization products. They are composed of organic condensation or addition polymers and may contain other substances to improve performance or reduce costs. There are many natural polymers generally considered to be "plastics". Plastics can be formed into objects or films or fibers. Their name is derived from the malleability, or plasticity, of many of them.
* 1 Overview
* 2 Cellulose-based plastics: celluloid and rayon
* 3 Bakelite (phenolic)
* 4 Polystyrene and PVC
* 5 Nylon
* 6 Synthetic rubber
* 7 Plastics explosion: acrylic, polyethylene, etc.
* 8 Negative health effects
* 9 The environment
o 9.1 Bioplastics and biodegradable plastics
o 9.2 Bioplastics
* 10 Price, environment, and the future
* 11 Common plastics and their uses
* 12 Special-purpose plastics
* 13 See also
* 14 References
* 15 External links
Plastic can be classified in many ways, but most commonly by their polymer backbone (polyvinyl chloride, polyethylene, polymethyl methacrylate, and other acrylics, silicones, polyurethanes, etc.). Other classifications include thermoplastic, thermoset, elastomer, engineering plastic, addition or condensation or polyaddition (depending on polymerization method used), and glass transition temperature or Tg.
Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). So-called semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.
Plastics are polymers: long chains of atoms bonded to one another. Common thermoplastics range from 20,000 to 500,000 in molecular weight, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as "repeat units", derived from "monomers"; each polymer chain will have several 1000's of repeat units. The vast majority of plastics are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone. (Some of commercial interest are silicon based.) The backbone is that part of the chain on the main "path" linking a large number of repeat units together. To vary the properties of plastics, both the repeat unit with different molecular groups "hanging" or "pendant" from the backbone, (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). This customization by repeat unit's molecular structure has allowed plastics to become such an indispensable part of twenty first-century life by fine tuning the properties of the polymer.
Molded plastic food replicas on display outside a restaurant in Japan.
Molded plastic food replicas on display outside a restaurant in Japan.
People experimented with plastics based on natural polymers for centuries. In the nineteenth century a plastic material based on chemically modified natural polymers was discovered: Charles Goodyear discovered vulcanization of rubber (1839) and Alexander Parkes, English inventor (1813—1890) created the earliest form of plastic in 1855. He mixed pyroxylin, a partially nitrated form of cellulose (cellulose is the major component of plant cell walls), with alcohol and camphor. This produced a hard but flexible transparent material, which he called "Parkesine." The first plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented by Leo Hendrik Baekeland in 1909, the product being known as Bakelite. Subsequently poly (vinyl chloride), polystyrene, polyethylene (polyethene), polypropylene (polypropene), polyamides (nylons), polyesters, acrylics, silicones, polyurethanes were amongst the many varieties of plastics developed and have great commercial success.
The development of plastics has come from the use of natural materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., natural rubber, nitrocellulose, collagen) and finally to completely synthetic molecules (e.g., epoxy, polyvinyl chloride, polyethylene).
In 1959, Koppers Company in Pittsburgh, PA had a team that developed the expandable polystyrene (EPS) foam. On this team was Edward J. Stoves who made the first commercial foam cup. The experimental cups were made of puffed rice glued together to form a cup to show how it would feel and look. The chemistry was then developed to make the cups commercial. Today, the cup is used throughout the world in countries desiring fast food, such as the United States, Japan, Australia, and New Zealand. Freon was never used in the cups. As Stoves said, "We didn't know freon was bad for the ozone, but we knew it was not good for people so the cup never used freon to expand the beads."
The foam cup can be buried, and it is as stable as concrete and brick. No plastic film is required to protect the air and underground water. If it is properly incinerated at high temperatures, the only chemicals generated are water, carbon dioxide and carbon ash. If burned without enough oxygen or at lower temperatures (as in a campfire or household fireplace) it can produce carbon black and carbon dioxide. EPS can be recycled to make park benches, flower pots and toys.
 Cellulose-based plastics: celluloid and rayon
All Goodyear had done with vulcanization was improve the properties of a natural polymer. The next logical step was to use a natural polymer, cellulose, as the basis for a new material.
Inventors were particularly interested in developing synthetic substitutes for those natural materials that were expensive and in short supply, since that meant a profitable market to exploit. Ivory was a particularly attractive target for a synthetic replacement.
An Englishman from Birmingham named Alexander Parkes developed a "synthetic ivory" named "pyroxlin", which he marketed under the trade name "Parkesine", and which won a bronze medal at the 1862 World's fair in London. Parkesine was made from cellulose treated with nitric acid and a solvent. The output of the process hardened into a hard, ivory-like material that could be molded when heated. However, Parkes was not able to scale up the process reliably, and products made from Parkesine quickly warped and cracked after a short period of use.
Englishmen Daniel Spill and the American John Wesley Hyatt both took up where Parkes left off. Parkes had failed for lack of a proper softener, but they independently discovered that camphor would work well. Spill launched his product as Xylonite in 1869, while Hyatt patented his "Celluloid" in 1870, naming it after cellulose. Rivalry between Spill's British Xylonite Company and Hyatt's American Celluloid Company led to an expensive decade-long court battle, with neither company being awarded rights, as ultimately Parkes was credited with the product's invention. As a result, both companies operated in parallel on both sides of the Atlantic.
Celluloid/Xylonite proved extremely versatile in its field of application, providing a cheap and attractive replacement for ivory, tortoiseshell, and bone, and traditional products such as billiard balls and combs were much easier to fabricate with plastics. Some of the items made with cellulose in the nineteenth century were beautifully designed and implemented. For example, celluloid combs made to tie up the long tresses of hair fashionable at the time are now highly-collectable jewel-like museum pieces. Such pretty trinkets were no longer only for the rich.
Hyatt was something of an industrial genius who understood what could be done with such a shapeable, or "plastic", material, and proceeded to design much of the basic industrial machinery needed to produce good-quality plastic materials in quantity. Some of Hyatt's first products were dental pieces, and sets of false teeth built around celluloid proved cheaper than existing rubber dentures. However, celluloid dentures tended to soften when hot, making tea drinking tricky, and the camphor taste tended to be difficult to suppress.
Celluloid's real breakthrough products were waterproof shirt collars, cuffs, and the false shirtfronts known as "dickies", whose unmanageable nature later became a stock joke in silent-movie comedies. They did not wilt and did not stain easily, and Hyatt sold them by trainloads. Corsets made with celluloid stays also proved popular, since perspiration did not rust the stays, as it would if they had been made of metal.
Celluloid could also be used in entirely new applications. Hyatt figured out how to fabricate the material in a strip format for movie film. By the year 1900, movie film was a major market for celluloid.
However, celluloid still tended to yellow and crack over time, and it had another more dangerous defect: it burned very easily and spectacularly, unsurprising given that mixtures of nitric acid and cellulose are also used to synthesize smokeless powder.
Ping-pong balls, one of the few products still made with celluloid, sizzle and burn if set on fire, and Hyatt liked to tell stories about celluloid billiard balls exploding when struck very hard. These stories might have had a basis in fact, sincSource(s): http://en.wikipedia.org/wiki/Plastic
- 6 years ago
Thermosetting plastics can be divided into two kinds with thermoplastic, the former can not be used to re shape, which can be repeated production. The structure of plastic polymers, there are two basic types: the first is the body structure; the second kind is linear structure.
Molecular structure of polymer:
(a) linear structure
(b) the linear structure (with a branch)
(c) network structure (a small amount of crosslinking between molecular chains)
(d) type structure (a lot of crosslinking between molecular chains)
Two different structures, dissolved; shape structure polymer with no independent existence macromolecules, so no elasticity and plasticity, cannot dissolve and melt, only swelling.
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- Anonymous5 years ago
complicated situation. browse onto bing and yahoo. it could help!
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- Anonymous6 years ago