Crosslinking of polyethylene

Stearamide is one of many electron donors which donate an electron to the cationic moiety in excited MAH or in propagating -MAH chains. This results in the inhibition of the homopolymerization of MAH and decreases the crosslinking of polyethylene and the degradation of polypropylene which accompany the peroxide-catalyzed reaction of MAH with these polyolefins (8,9). ... 

Figure 18,8 Peroxide crosslinking of polyethylene a) decomposition of dlcumyl peroxide, b abstraction of hydrogen from polyethylene chain, and c) formation of covalent C-C crosslink...

From industry s viewpoint, the action of nitrous oxide should be useful to cut down the dose required for the crosslinking of polyethylene or polypropylene and to keep polyisobutylene from degradation. However, it is a question whether the complexity of processing caused by using nitrous oxide would pay economically. 

F.-W. Shen, H.A. McKellop, and R. Salovey, Crosslinking of polyethylene for low wear using radiation and thermal treatments, US Patent 6800670, assigned to Orthopaedic Hospital (Los Angeles, CA) and University of Southern California (Los Angeles, CA), October 5,2004. 

The formation of oxygen anion radicals and molecules of ozone also should be counted with at the ionization initiation of oxidation [26]. Initiation reaction caused by oxygen anion radicals may play an important role within the polymer bulk while the effect of ozone forming in the surrounding air atmosphere will include only the formation of radicals on the polymer surface. The latent effect of ionization initiation on polymer oxidation which is very distinct may be documented on a relatively fast increase of concentration of carbonyl groups, observed over 1 year after irradiation crosslinking of polyethylene [27]. 

For example, with only 1% of the carbonyl group, the G value for crosslinking of polyethylene was doubled. Furthermore, as shown in Table TV there was a concurrent reduction in the... 

Meola, C. Nele, L. Giuliani, M. Suriano, P. Chemical and irradiation crosslinking of polyethylene. Technological performance over costs. Polym. Plast. Technol. Eng. 2004, 43 (3), 629-646. 

Crosslinking of polyethylen and its copolymers EPM, EPDM, and EVA is mainly carried out by radicals generated from organic peroxides. Other crosslinking methods like electron-beam radiation and grafting of vinylsUanes assume a smaller role in this process. 

Scheme 1.45. The reaction sequence for radical crosslinking of polyethylene.

This reaction was reported for the benzophenone photosensitized degradation of polypropylene (92),polystyrene (95), poly(vinyl alcohol) (94),polyisoprene (95,96),polyurethane (97) and polyadenylic acid (98) In solid state benzophenone also produce an extensive crosslinking of polyethylene (99-105) It has also been found that benzophenone and its derivatives caused an initial rapid oxidation,increasing with ketone concentration (70) Currently the relative importance of singlet oxygen formation in energy transfer reaction between excited benzophenone and molecular oxygen is discussed (92,104) ... 

Figure 12. Relationship Between % Gel Formation and Peroxide Concentration [ROOR] In the Crosslinking of Polyethylene Materials.

M. Hudis and L.E. Prescott, "Surface crosslinking of polyethylene produced by the ultraviolet radiation from a hydrogen glow discharge," Polym. Letters 10, 179 (1972)... 

The crosslinking of polyethylene resulting from its reaction with peroxides is more profound if maleic anhydride is present in the system [113]. The crosslinked fraction contains a higher proportion of carbonyl groups from grafted maleic anhydride than... 

Zamotaev PV (1988) Photoinitiated Crosslinking of Polyethylene, Proceedings of the 7th Bratislava Conference on Modified Polymers, Bratidava 1988, wiO also be puUished in Makromol. Chem., Supplement C... 

Chvatova TP et al (1980) Crosslinking of polyethylene through organosilanes (in russian), Khimyia... 

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