Polyethylene, plastic-range

The recommended short-term surface strains that can be used without causing yielding are higher for semi-crystalline plastics (ranging from 4% for polyamides to 8% for polyethylene) than for glassy plastics (1.8% for... 

Those ubiquitous plastics polythene (polyethylene), polystyrene, and PVC (polyvinyl chloride) are made in this way. In the case of polythene the molecule M, which in this context is called a monomer, is ethylene, H2C=CH2. The outcome of the polymerization is a long chain, a polymer, of hundreds of-CH CH - units. Chemists have found that by starting with different versions of ethylene, such as H C=CHX, where X can be a group of atoms, they can form polymers with a wide range of properties. Thus, when X is a benzene ring, the polymer is polystyrene and when X is a chlorine atom the polymer is PVC. To obtain the non-stick Teflon all the hydrogen atoms are replaced by fluorine atoms that is why its more formal name is polytetrafluoroethylene (PTFE). 

The most investigated family of polymeric plasticizers is polyethylene glycols (pegs). These linear polymers can have favourable solubility parameters (Table 5.2), and they are commercially available in a large range of... 

Ethylene is the base for the production of high-volume plastic ranges, including polyvinylchloride (PVC), polyethylene terephthalate (PET), low-density polyethylene, linear low-density polyethylene, polyethyl, and high-density polyethylene. In 200 ethylene production was 109 million tons with an annual growth of 4.5% worldwide. The dehydration of bioethanol or the cracking of bionaphtha processes are actively used to produce ethylene. Bionaphtha can... 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

The separator must be stmcturaHy sound to withstand the rigors of battery manufacturing, and chemically inert to the lead—acid cell environment. Numerous materials have been used for separators ranging from wood, paper, and mbber to glass and plastic. The majority of separators used are either nonwoven—bound glass or microporous plastic such as PVC or polyethylene. 

The properties of elastomeric materials are also greatly iafluenced by the presence of strong interchain, ie, iatermolecular, forces which can result ia the formation of crystalline domains. Thus the elastomeric properties are those of an amorphous material having weak interchain iateractions and hence no crystallisation. At the other extreme of polymer properties are fiber-forming polymers, such as nylon, which when properly oriented lead to the formation of permanent, crystalline fibers. In between these two extremes is a whole range of polymers, from purely amorphous elastomers to partially crystalline plastics, such as polyethylene, polypropylene, polycarbonates, etc. 

Low density polyethylene (LDPE). This is one of the most widely used plastics. It is characterised by a density in the range 918-935 kg/m and is very tough and flexible. Its major application is in packaging him although its outstanding dielectric properties means it is also widely used as an electrical insulator. Other applications include domestic ware, tubing, squeeze bottles and cold water tanks. 

In the field of plastics, the annual production of polyvinylchloride (PVC) is second only to polyethylene. PVC has long been used in various areas, ranging from agriculture and industry to medical equipment and daily life, due to its well-developed production techniques, easy processing, and low price. However, PVC has its own disadvantages, mainly its low stability toward heat and ultraviolet (UV) light. Also, pure PVC is a very hard material that cannot be easily processed and practically used. Common PVC plastics contain various amounts of plasticizers and other additives, including modifiers, stabilizers, and lubricants. 

Chlorinated polyethylene CPEs provide a very wide range of properties from soft/ elastomeric to hard. They have inherent oxygen and ozone resistance, have improved resistance (compared to PEs) to chemical extraction, resist plasticizers, volatility, and weathering. Products do not fog at high temperatures as do PVCs and can be made flame retardant. 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

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