Polyethylene – Its Properties and Uses
Jan 24, · Polyethylene is one of the most commonly used engineering plastics. Its chemical resistance properties and ease of fabrication make it popular in the chemical industries. Its molecular structure provides the key to its versatility. Keywords: HDPE, Author: Mike Sondalini. Uses: sandwich bags, cling wrap, car covers, squeeze bottles, liners for tanks and ponds, moisture barriers in construction: freezer bags, water pipes, wire and cable insulation, extrusion coating.
Polyethylene Polythenfwuat, versatile synthetic resin made from the polymerization of ethylene. Polyethylene is a member of the important family of polyolefin resins.
It od the most what are brazilian bikini bottoms used plastic in the world, being made into products ranging from clear food wrap and shopping bags to detergent bottles and automobile fuel tanks. It can also be slit or qre into synthetic fibres or modified to take on the elastic properties of a rubber.
How to wean a baby from pacifier C 2 H 4 is a gaseous hydrocarbon commonly produced by the cracking of ethanewhich in turn is a major constituent of natural gas or can be distilled from petroleum.
Under the influence of polymerization catalysts, the double bond can be broken and the resultant extra single bond used to link to a carbon atom in another ethylene molecule. Thus, made into the repeating unit of a large, polymeric multiple-unit molecule, ethylene has the following chemical structure:. This simple structure, repeated thousands of times in a single molecule, is the key to the properties of polyethylene. The long, chainlike molecules, in which hydrogen atoms are connected to a carbon backbone, can be produced in linear or branched forms.
The basic polyethylene composition can be modified by the inclusion of other elements or chemical groups, as in the off of chlorinated and chlorosulfonated polyethylene. In addition, ethylene can be copolymerized with other monomers such as vinyl acetate or propylene to produce a number of ethylene copolymers.
All of these variants are described below. ICI during studies of the effects of extremely high pressures on the polymerization of polyethylene. ICI was granted a patent on its process in and began commercial production in It was first used during World War II as an insulator for radar cables. The process was later improved by the Italian chemist Giulio Nattaand the compounds are now known as Ziegler-Natta catalysts.
In part for this innovationZiegler was awarded the Nobel Prize for Chemistry in Since that time, by using different catalysts and polymerization methods, scientists have produced polyethylene with various properties and structures.
These processes yield a polymer structure with both long and short branches. Because the branches prevent the polyethylene molecules from packing closely together in hard, stiff, crystalline arrangements, LDPE is a very flexible material. Principal what are signs of food poisoning are polythdne packaging film, trash and grocery bags, agricultural mulch, wire and cable insulation, squeeze bottles, toys, poljthene housewares.
The plastic recycling code of LDPE is 4. It is made by copolymerizing ethylene with 1-butene and smaller amounts of 1-hexene and 1-octene, using Ziegler-Natta or metallocene catalysts. The resultant structure has a linear backbone, but it has short, uniform branches that, like the longer branches of LDPE, prevent the polymer chains from packing closely together. HDPE is manufactured at low temperatures and pressures, using Ziegler-Natta and metallocene catalysts or activated chromium oxide known as a Phillips catalyst.
The lack of branches in its structure allows the polymer chains to pack closely together, resulting in a dense, highly crystalline material of high strength polythdne moderate stiffness. Products include blow-molded bottles for milk and household cleaners; blow-extruded grocery bags, construction film, and agricultural mulch; and injection-molded pails, caps, appliance housings, and toys.
The plastic recycling code number of HDPE is 2. Linear polyethylene can be produced in ultrahigh-molecular-weight versions, with molecular weights of 3, what are the uses of polythene 6, atomic units, as opposed toatomic units for HDPE. These polymers can be spun into fibres and then drawn, or stretched, into a highly crystalline state, resulting in high stiffness and a tensile strength many times that of steel. Yarns made from these fibres are woven into bulletproof vests.
Ethylene can be copolymerized with a number of other compounds. Ethylene-vinyl acetate copolymer EVAfor instance, is produced by the copolymerization of ethylene and vinyl acetate under pressure, how do i convert percentages to fractions free-radical catalysts.
Many different grades are manufactured, with the vinyl acetate content varying from 5 to 50 percent by weight. EVA copolymers are more permeable to gases and moisture than what are the uses of polythene, but they are less crystalline and more transparent, and they exhibit better oil and grease resistance. Principal uses are in packaging film, adhesives, toys, tubing, gaskets, wire coatings, drum liners, and carpet backing.
Ethylene-acrylic arf and ethylene-methacrylic acid copolymers are prepared by suspension or emulsion polymerization, using free-radical catalysts. The acrylic acid and methacrylic acid repeating units, making up 5 to 20 percent of the copolymers, have the following structures:.
The acidic carboxyl CO 2 H groups in these units are neutralized with bases to form highly polar ionic groups distributed along the polyethylene chains. Ionic polymers of this type are called ionomers. The ethylene-acrylic acid and ethylene-methacrylic acid ionomers are transparent, semicrystalline, and impervious to moisture. They are employed in automotive parts, packaging film, footwear, surface coatings, and carpet backing.
One prominent ethylene-methacrylic acid copolymer is Surlyn, which is made into hard, tough, abrasion-resistant golf-ball covers. Other important ethylene copolymers are the ethylene-propylene copolymers. Polyethylene How many tourists visit the colosseum a day Media Additional Info.
Article Contents. Home Science Chemistry Polyethylene chemical compound. Print print Print. Table Of Contents. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Facebook Twitter. Give Feedback External Websites. Let us know if you have suggestions to improve this article requires login. External Websites. Polymer Science Learning Center - Polyethylene.
The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree See Article History. Alternative Titles: PE, polyethene, polythene. Read More on This Topic. Ethylene, commonly produced by the cracking of ethane gas, forms the basis for the largest single class of plastics, the polyethylenes Get a Britannica Premium tje and gain access to exclusive content.
Subscribe Now. The branched form of polyethylene, known as low-density polyethylene LDPE. The linear form of polyethylene, known as high-density polyethylene HDPE.
Learn More in these related Britannica articles:. Ethylene, commonly produced by the cracking of ethane gas, forms the basis for the largest single class of plastics, the polyethylenes. Between andZiegler and Hans-Georg Gellert, one of his former tue from How to call singapore from the united states, found that in the polymerization reaction organolithium compounds, except for lithium aluminum hydride, irreversibly decomposed into lithium hydride and an alkyl.
To establish whether lithium or aluminum was the…. Unless hydrogen bonds are present in which case molecular solids resemble ionic solids in brittlenessmolecular solids are generally soft and have low usses points because the bonds between the molecules are easily overcome.
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Production of LDPE
Uses. Poly (ethene) 'polythene'. Flexible, cheap, can be made into thin films. Carrier bags, shampoo bottles, food wrap. Poly (propene) 'polypropylene'. Flexible, strong, resists shattering. The primary uses of polyethylene are in packaging film, garbage bags, grocery bags, insulation for wires and cables, agricultural mulch, bottles, toys, and houseware. Polythene is also used in trays, fruit juice containers, milk containers, crates, and food packaging products. What is cross-linked polyethylene? Principal uses are in packaging film, trash and grocery bags, agricultural mulch, wire and cable insulation, squeeze bottles, toys, and housewares. The plastic recycling code of LDPE is #4. The branched form of polyethylene, known as low-density polyethylene (LDPE). Encyclop?dia Britannica, Inc.
Polyethylene PE is a plastic. It is made by combining single carbon atoms together to create long chains of carbon atoms. The long chains are called macromolecules. Attached to each carbon atom are usually two hydrogen atoms. Figure 1 shows how the macromolecule of polyethylene is arranged. PE belongs to the family of plastics called thermoplastics. These plastics have weak forces that attract the macromolecules together. The other family of plastics is the thermosets. In these the hydrogen atoms are occasionally replaced with other atoms that attach to neighboring chains, locking them together.
The thermoplastics can be melted and reshaped but the thermosets can only be used once. The process of using solvents and heat to convert from single atoms to a string of thousands of atoms long is called polymerization. During polymerization, many carbon chains are created at the one time. When PE is molten the long chains are mobile but upon cooling, the long chains intertwine and lock together. Much like when spaghetti is boiled and let cool.
The density of PE depends on the process used to make it. The properties of each type of PE depend on the shape and length the carbon chains and how closely they compact. The carbon chain length and extent of branching greatly affect the properties of the plastic. The amount of side-chain branching varies the closeness that molecules can come together. Closely compact chains give more rigid and solid plastics. Occasionally the molecules will lie side by side. This creates a harder clump known as a crystalline alignment.
Plastics with high amounts of crystalline arrangements are harder and stronger but more brittle. This permits the development of many more crystalline areas than the lower density PEs.
Randomly arranged chains without order make an amorphous structure. Examples of each structure are shown in Figure 3. This makes them a useful plastic for molding and extruding in shapes of bottles, tanks, sheets, and pipes.
In its natural form, PE is clear and goes white and translucent as the amount of crystallinity increases.
It is used in stretch films, plastic bags, and plastic bottles. Coloring agents can be added. It degrades from ultraviolet radiation. Life expectancies in outside conditions of over 25 years are attainable. Chemical resistance properties of PE are excellent, covering a wide range of chemicals. Check compatibility with the supplier. A major consideration with the use of PE is its tendency to exhibit environmental stress cracking ESC.
ESC is sudden failure induced by internal stresses from outside loads or fabrication strains. Often involving containment of liquid hydrocarbons and man-made soaps and oils. ESC decreases as carbon chain entanglement increases. ESC tests are available and recommended if using PE to store previously undocumented chemicals.
Since PE is a thermoplastic it can be melted and joined. When welding, the temperature is raised above the melting point — oC to a temperature of about oC using a hot air gun for hand welding or a heated plate for butt- welded pipes.
When hand welding PE a filler rod is pushed into the melt. When butt-welding pipe the two ends are heated and pushed together for 10 to 15 seconds. At the melted surface the carbon chains intertwine and cool. Successful welds need a sufficiently high temperature and pressure at the melted surfaces for a long enough time to let the carbon chains mesh well. A weak failure prone weld results which break away from the parent material. Web: trade-school. Thanks for overview. Wikipedia has some information.
And other free drill down links on this subject? Hi Bernard, yes the world of polymers is pretty broad and versatile. I used to work at Raychem Corp. Your email address will not be published. Is Intelligence One of Them? Never Purchase a Retired Rental Car ». Comments Thanks for overview. Leave a Reply Cancel reply Your email address will not be published.