Oxygen Polyethylene

In the presence of oxygen polyethylene will exhibit chain lengthening and crosslinking as well as chain cleavage, depending on the particular ambient conditions. Thermal-oxidative degradation is essentially easier than strictly thermal degradation. 

R. K. Shah, L. Cui, K. L. Williams, B. Bauman, and D. R. Paul. Nanocomposites from fluoro-oxygenated polyethylene a novel route to organoclay exfoliation. Journal of Applied Polymer Science, 102 (2006), 2980-2989. 

Poly(ethylene oxide). Although AH j is more than double that of polyethylene, the effect is offset by an even greater increase for AS j. The latter may be due to increased chain flexibility in the liquid caused by the regular insertion of ether oxygens along the chain backbone. 

In some cases, particularly with iaactive metals, electrolytic cells are the primary method of manufacture of the fluoroborate solution. The manufacture of Sn, Pb, Cu, and Ni fluoroborates by electrolytic dissolution (87,88) is patented. A typical cell for continous production consists of a polyethylene-lined tank with tin anodes at the bottom and a mercury pool (ia a porous basket) cathode near the top (88). Pluoroboric acid is added to the cell and electrolysis is begun. As tin fluoroborate is generated, differences ia specific gravity cause the product to layer at the bottom of the cell. When the desired concentration is reached ia this layer, the heavy solution is drawn from the bottom and fresh HBP is added to the top of the cell continuously. The direct reaction of tin with HBP is slow but can be accelerated by passiag air or oxygen through the solution (89). The stannic fluoroborate is reduced by reaction with mossy tin under an iaert atmosphere. In earlier procedures, HBP reacted with hydrated stannous oxide. 

The limiting oxygen index of Tefzel as measured by the candle test (ASTM D2863) is 30%. Tefzel is rated 94 V-0 by Underwriters Laboratories, Inc., in their burning test classification for polymeric materials. As a fuel, it has a comparatively low rating. Its heat of combustion is 13.7 MJ/kg (32,500 kcal/kg) compared to 14.9 MJ /kg (35,000 kcal/kg) for poly(vinyHdene fluoride) and 46.5 MJ /kg (110,000 kcal/kg) for polyethylene. 

Poultry, susceptible to microbiological deterioration, is an excellent substrate for Salmonella. Therefore, the temperature is reduced as rapidly as possible after slaughter. Packagiag at factory level is in soft film, ie, low density polyethylene or plastici2ed PVC, which retards water-vapor loss and permits oxygen entry. 

LDPE, also known as high pressure polyethylene, is produced at pressures ranging from 82—276 MPa (800—2725 atm). Operating at 132—332°C, it may be produced by either a tubular or a stirred autoclave reactor. Reaction is sustained by continuously injecting free-radical initiators, such as peroxides, oxygen, or a combination of both, to the reactor feed. 

Increasingly, plastics are being used as parenteral packaging (qv) materials. Plastics such as poly(vinyl chloride), polyethylene, and polypropylene are employed. However, plastics may contain various additives that could leach into the product, such as plasticizers (qv) and antioxidants. PermeabiUty of plastics to oxygen, carbon dioxide, and water vapor must be tested in the selection of plastic containers. Furthermore, the plastic should withstand sterilization. Flaking of plastic particles should not occur and clarity necessary for inspection should be present. 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

A primary use of vinyhdene chloride copolymer lacquers is the coating of films made from regenerated ceUulose or of board or paper coated with polyamide, polyester, polypropylene, poly(vinyl chloride), and polyethylene. The lacquer imparts resistance to fats, oils, oxygen, and water vapor (165). 

Table 12. Effect of Calcium Carbonate Fillers on Oxygen Permeability of Low Density Polyethylene...

Fig. 15. Oxygen permeability versus 1/specific free volume at 25 °C (30). 1. Polybutadiene 2. polyethylene (density 0.922) 3. polycarbonate 4. polystyrene 5. styrene-acrylonitrile 6. poly(ethylene terephthalate) 7. acrylonitrile barrier polymer 8. poly(methyl methacrylate) 9. poly(vinyl chloride) 10. acrylonitrile barrier polymer 11. vinyUdene chloride copolymer 12. polymethacrylonitrile and 13. polyacrylonitrile. See Table 1 for unit conversions.

High pressure (60—350 MPa) free-radical polymerization using oxygen, peroxide, or other strong oxidizers as initiators at temperatures of up to 350°C to produce low density polyethylene (LDPE), a highly branched polymer, with densities from 0.91 to 0.94 g/cm. ... 

E] Based on oxygen transfer from water to air 77 F. Liquid film resistance controls. (Dwnei- 77 F = 2.4 X 10 ). Equation is dimensional. Data was for thin-waUed polyethylene Raschig rings. Correlation also fit data for spheres. Fit 25%. See Reiss for graph. 

The demands on insulating materials in soil and fresh water are relatively low. Anodically evolved oxygen makes the use of aging-resistant insulating materials necessary. These consist of special types of rubber (neoprene) and stabilized plastics of polyethylene, and polyvinylchloride, as well as cast resins such as acrylate, epoxy, polyester resin and many others. 

Table 10.8 Comparison oE antioxidants in polyethylene in both the absence and presence of copper powder and carbon black (data based on ICI literature). Induction time assessed from oxygen uptake measurements using a Barcroft manometer...

Polypropylene differs from polyethylene in its chemical reactivity because of the presence of tertiary carbon atoms occurring alternately on the chain backbone. Of particular significance is the susceptibility of the polymer to oxidation at elevated temperatures. Some estimate of the difference between the two polymers can be obtained from Figure 1J.7, which compares- the rates of oxygen uptake of eaeh polymer at 93°C. Substantial improvements can be made by the inclusion of antioxidants and such additives are used in all commercial compounds. Whereas polyethylene cross-links on oxidation, polypropylene degrades to form lower molecular weight products. Similar effects are noted... 

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