Addition to polyethylene

Ethylene (structure in Figure 13.1) is the most widely used organic chemical. Almost all of it is consumed as a chemical feedstock for the manufacture of other organic chemicals. Polymerization of ethylene to produce polyethylene is illustrated in Figure 13.4. In addition to polyethylene, other polymeric plastics, elastomers, fibers, and resins are manufactured with ethylene as one of the ingredients. Ethylene is also the raw material for the manufacture of ethylene glycol antifreeze, solvents, plasticizers, surfactants, and coatings. 

Simultaneously with Charlesby s findings, work along similar lines was carried out in G. E. s Research laboratories in Schenectady (22) and also in Research Institutes in the Soviet Union, although the latter only became known several years later (23). The results of this research demonstrated that in addition to polyethylene, many other polymers could be cross-linked by radiation. These include silicones, rubber, poly (vinyl chloride), polyacrylates and, to a lesser extent, polystyrene. In contrast, polymers such as polymethacrylates, polyisobutylene, polytetrafluoroethylene and cellulose underwent "degradation" by main-chain scission. These early findings were confirmed and extended to other compounds by numerous studies. 

Group 4 metallocene catalysts are, in addition to polyethylene and polypropylene, able to generate syndiotactic polystyrene, to polymerize cycloolefins (cyclopentene, nor-bomene, and their substituted compounds), and to give access to various copolymers. During the polymerization of cycloolefins, only the double bond is opened and not the ring. 

However, one of our customers (27) found it to be an effective additive to polyethylene terephthalate in order to increase the strength and reduce the striation when the polymer was extruded into polyester film. This certainly was an unexpected commercial success. I would regard this commercial success as pure luck on our part. After all. Dr. Walsh s group designed the compound to be a flame retardant. 

Kuhn model, Equation (1.1). Data for several polymers in addition to polyethylene are given, including a rigid-rod aromatic nylon polymer, poly(p-phenylene terephthalamide) (Kevlar ), as well as the aliphatic nylon polymer poly(hexamethylene adipamide) (nylon-6,6). 

All phosphor organic compounds appeared practically more effective additives to polyethylene in comparison with the industrial stabilizer polyolefin s lrganox-1010. 

In addition to polyethylene and polypropylene, a wide range of olefin comonomers are produced which consist of copolymers of C2 to Cg olefins. A case in point is a copolymer of ethylene and hutane-1 containing up to 10% hutane-1. The preparation of calibration standards presents a difficulty in IR methods for analysing such copolymers. 

The Bakelite Division of Union Carbide received US. Patent 2,462,331 on February 22, 1949, for the use of carboxylic acid esters or metal salts of carboxylic acids as additives to polyethylene, that improved the processing of polyethylene into film and sheets. The addition of 0.2-0.5 wt% of these compormds to polyethylene was reported to cause the ready release of the polyethylene film or sheet from hot milling and calendaring rolls at elevated temperatures (115-150°C) to provide films and sheets with good surface appearance. Examples of these releasing agents were calcium stearate, aluminum laurate and aluminum tristearate. 

The problems assoeiated with the recovery of a high grade reeycled polyethylene product start with the quality of the postconsumer waste stream. In addition to polyethylene, the waste stream inevitably contains polymeric and nonpolymeric contaminants. Small amounts of certain thermoplastics can be accommodated in recycled polyethylene, but the presence of even a few tens of parts per million of others ean cause significant problems [2]. Particles of thermosets, such as polyurethanes and cross-linked polyesters, that survive the sorting and washing processes ean plug screenpacks. Those that make it into the final... 

Lamination Inks. This class of ink is a specialized group. In addition to conforming to the constraints described for flexo and gravure inks, these inks must not interfere with the bond formed when two or more films, eg, polypropylene and polyethylene, are joined with the use of an adhesive in order to obtain a stmcture that provides resistance properties not found in a single film. Laminations are commonly used for food applications such as candy and food wrappers. Resins used to make this type of ink caimot, therefore, exhibit any tendency to retain solvent vapor after the print has dried. Residual solvent would contaminate the packaged product making the product unsalable. 

Addition or chain-growth polymerization involves the opening of a double bond to form new bonds with adjacent monomers, as typified by the polymerization of ethylene to polyethylene ... 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

Chlorinated polyethylene (CPE) has excellent o2one, oil, and heat resistance. In addition chlorinated polyethylene has replaced chloroprene elastomers. CPE has a lower specific gravity than chloroprene compounds and produces compounds that are similar to CR in properties but with lower costs. In addition, due to high levels of chlorine in the polymer, the flame resistance of the compounds of CPE are high. 

In addition to copolymerisation, polyethylenes terrninated as ketones, alcohols, and carboxyHc acids with molecular weights as high as 700 daltons are now available. The products offer the same chemical functionaHty as common fatty alcohols and acids, but are higher melting and harder. Similar to the fatty alcohols and acids, derivatives such as ethoxylates, esters, and amides also are available as higher melting versions of the fatty derivatives. 

Polyethylene is sometimes blended with ethylene-propylene rubber (see Chapter 11). In this application it is most commonly used as an additive to the rubber, which in turn is added to polypropylene to produce rubber-modified... 

The homopolymer finds a variety of uses, as an adhesive component, as a base for chewing gum, in caulking compounds, as a tackifier for greases, in tank linings, as a motor oil additive to provide suitable viscosity characteristics and to improve the environmental stress-cracking resistance of polyethylene. It has been incorporated in quantities of up to 30% in high-density polyethylene to improve the impact strength of heavy duty sacks. 

In addition to acting as impact modifiers a number of polymeric additives may be considered as processing aids. These have similar chemical constitutions to the impact modifiers and include ABS, MBS, chlorinated polyethylene, acrylate-methacrylate copolymers and EVA-PVC grafts. Such materials are more compatible with the PVC and are primarily included to ensure more uniform flow and hence improve surface finish. They may also increase gelation rates. In the case of the compatible MBS polymers they have the special function already mentioned of balancing the refractive indices of the continuous and disperse phases of impact-modified compound. 

The acetal polymer moleeules have a shorter backbone (—C—O)—bond and they pack more closely together than those of polyethylene. The resultant polymer is thus harder and has a higher melting point (175°C for the homopolymer). The position of the glass transition is a subjeet of debate since at least two transitions in addition to the melting point are discernible. The true glass transition is usually associated with the temperature at which movement of segments of about 50-150 baekbone atoms becomes relatively easy, in the... 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

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. 

Ethylene reacts by addition to many inexpensive reagents such as water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. It can be initiated by free radicals or by coordination catalysts to produce polyethylene, the largest-volume thermoplastic polymer. It can also be copolymerized with other olefins producing polymers with improved properties. Eor example, when ethylene is polymerized with propylene, a thermoplastic elastomer is obtained. Eigure 7-1 illustrates the most important chemicals based on ethylene. 

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