Extrusion produces thin fibers or heavy pipes or films or food bottles. Injection molding can produce very intricate parts or large car body panels. Plastics can be molded into drums or be mixed with solvents to become adhesives or paints. Elastomers and some plastics stretch and are very flexible. Some plastics are stretched in processing to hold their shape, such as soft drink bottles.
Polymers are materials with a seemingly limitless range of characteristics and colors. Polymers have many inherent properties that can be further enhanced by a wide range of additives to broaden their uses and applications. Polymers can be made to mimic cotton, silk, and wool fibers; porcelain and marble; and aluminum and zinc. Polymers can also make possible products that do not readily come from the natural world, such as clear sheets and flexible films.
Polymers are usually made of petroleum, but not always. Many polymers are made of repeat units derived from natural gas or coal or crude oil. But building block repeat units can sometimes be made from renewable materials such as polylactic acid from corn or cellulosics from cotton linters. Some plastics have always been made from renewable materials such as cellulose acetate used for screwdriver handles and gift ribbon.
When the building blocks can be made more economically from renewable materials than from fossil fuels, either old plastics find new raw materials or new plastics are introduced. Polymers can be used to make items that have no alternatives from other materials. Polymers can be made into clear, waterproof films. PVC is used to make medical tubing and blood bags that extend the shelf life of blood and blood products. PVC safely delivers flammable oxygen in non-burning flexible tubing.
And anti-thrombogenic material, such as heparin, can be incorporated into flexible PVC catheters for open heart surgery, dialysis, and blood collection. Many medical devices rely on polymers to permit effective functioning. In addressing all the superior attributes of polymers, it is equally important to discuss some of the challenges associated with the materials. Most plastics deteriorate in full sunlight, but never decompose completely when buried in landfills. However, other materials such as glass, paper, or aluminum do not readily decompose in landfills either.
Some bioplastics do decompose to carbon dioxide and water, however, in specially designed food waste commercial composting facilities ONLY.
Polymer Science: A Comprehensive Reference
They do not biodegrade under other circumstances. For 1 the EPA characterization of municipal solid waste before recycling for the United States showed plastics made up Glass and metals made up And yard trimmings constituted Food waste made up The characteristics that make polymers so attractive and useful, lightweight and almost limitless physical forms of many polymers designed to deliver specific appearance and functionality, make post-consumer recycling challenging.
When enough used plastic items can be gathered together, companies develop technology to recycle those used plastics. The recycling rate for all plastics is not as high as any would want. But, the recycling rate for the 1,,, pounds of polyester bottles, Applications for recycled plastics are growing every day. Recycled plastics can be blended with virgin plastic plastic that has not been processed before without sacrificing properties in many applications.
Recycled plastics are used to make polymeric timbers for use in picnic tables, fences and outdoor playgrounds, thus providing low maintenance, no splinters products and saving natural lumber. Plastic from soft drink and water bottles can be spun into fiber for the production of carpet or made into new food bottles. Closed loop recycling does occur, but sometimes the most valuable use for a recycled plastic is into an application different than the original use.
An option for plastics that are not recycled, especially those that are soiled, such as used food wrap or diapers, can be a waste-to-energy system WTE. In , When localities decide to use waste-to-energy systems to manage solid waste, plastics can be a useful component.
The controlled combustion of polymers produces heat energy. The heat energy produced by the burning plastic municipal waste not only can be converted to electrical energy but also helps burn the wet trash that is present. Paper also produces heat when burned, but not as much as do plastics. On the other hand, glass, aluminum and other metals do not release any energy when burned. To better understand the incineration process, consider the smoke coming off a burning item. If one were to ignite the smoke with a lit propane torch, one would observe that the smoke disappears.
This exercise illustrates that the by-products of incomplete burning are still flammable. Proper incineration burns the material and the by-products of the initial burning and also takes care of air and solid emissions to insure public safety. Some plastics can be composted either because of special additives or because of the construction of the polymers.
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Compostable plastics frequently require more intense conditions to decompose than are available in backyard compost piles. Commercial composters are suggested for compostable plastics. In 1 , composting processed 8. Plastics can also be safely land filled, although the valuable energy resource of the plastics would then be lost for recycling or energy capture.
In 1 , Plastics are used to line landfills so that leachate is captured and groundwater is not polluted. Non-degrading plastics help stabilize the ground so that after the landfill is closed, the land can be stable enough for useful futures. Polymers affect every day of our life. These materials have so many varied characteristics and applications that their usefulness can only be measured by our imagination. Polymers are the materials of past, present and future generations.
View our resource center to find press releases, testimonies, infographics and more. The business of chemistry provides , skilled, good-paying American jobs. The Basics: Polymer Definition and Properties. The Structure of Polymers Many common classes of polymers are composed of hydrocarbons, compounds of carbon and hydrogen.
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Molecular Arrangement of Polymers Think of how spaghetti noodles look on a plate. Characteristics of Polymers The majority of manufactured polymers are thermoplastic, meaning that once the polymer is formed it can be heated and reformed over and over again.
Solid Waste Management In addressing all the superior attributes of polymers, it is equally important to discuss some of the challenges associated with the materials. News View our resource center to find press releases, testimonies, infographics and more. Jobs The business of chemistry provides , skilled, good-paying American jobs.
It has a high melting point and is crystalline and resistant to abrasion and the action of solvents. Acetal resins are more like metal than are any other plastics and are used in the manufacture of machine parts such as gears and bearings. A linear polymer characterized by a repetition of ester groups along the backbone chain is called a polyester. Open-chain polyesters are colourless, crystalline, thermoplastic materials.
Those with high molecular weights 10, to 15, molecules are employed in the manufacture of films, molded objects, and fibres such as Dacron. The polyamides include the naturally occurring proteins casein , found in milk , and zein, found in corn maize , from which plastics, fibres, adhesives, and coatings are made. Among the synthetic polyamides are the urea-formaldehyde resins, which are thermosetting.
They are used to produce molded objects and as adhesives and coatings for textiles and paper. Also important are the polyamide resins known as nylons. They are strong, resistant to heat and abrasion, noncombustible, and nontoxic, and they can be coloured. Their best-known use is as textile fibres, but they have many other applications. Another important family of synthetic organic polymers is formed of linear repetitions of the urethane group.
Polyurethanes are employed in making elastomeric fibres known as spandex and in the production of coating bases and soft and rigid foams. A different class of polymers are the mixed organic-inorganic compounds. The most important representatives of this polymer family are the silicones.ignamant.cl/wp-includes/7/4091-espia-para.php
The Basics: Polymer Definition and Properties
Their backbone consists of alternating silicon and oxygen atoms with organic groups attached to each of the silicon atoms. Silicones with low molecular weight are oils and greases. Higher-molecular-weight species are versatile elastic materials that remain soft and rubbery at very low temperatures. They are also relatively stable at high temperatures. Article Media. Info Print Cite.
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