Polyolefins 7-irradiation

Irradiation of polymer blends containing a polyolefin — Irradiation of polymer blends can be used to crosslink or degrade the desired component polymer, of to fixate the blend morphology [4],... 

Ionizing radiation, see Radiation, ionizing lonomer. see Polyolefines Irradiation 161... 

FIG. 42 Effects of dose rate on electrical dissipation factor (a) and volume resistivity (b) for some polyolefins irradiated in air at 1 MGy. Ethylene-propylene rubber with quinoline as antioxidant ( , ) XLPE free of antioxidant ( , O) XLPE with thiobisalkylphenol as antioxidant (A, A)-(Adapted from Ref. 76.)... 

In most cases of polyolefin irradiation, some volatile products are detected, such as hydrogen, low hydrocarbons (methane to butane), etc. [41, 51]. 

Food packaging (electron-beam-irradiated polyolefins)... 

In addition, there are many surface modification processes that use triplet sensitizers to permit oxidation reactions. In a typical process, polyisocyanate is applied on a polyolefin together with a sensitizer such as benzo-phenone and then irradiated with UV light. As shown in Eq. (15) the sensitizer has an oxidizing effect to produce hydroxyl groups over the polymer surface. These hydroxyl groups finally react with isocyanate to provide a functional polymer [56,57]. 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

In spite of the high polarity of PA6, identification of additives was also feasible in formulations of PA6/additive dissolutions, although with decreased sensitivity. Hostavin N 20, Irganox B 1171, Tinuvin 320 and Tinuvin 350 can be determined in PA6 in technical concentrations, although the sensitivity is less than for nonpolar polymers, such as polyolefins. This was tentatively explained as follows. In a nonpolar polymer matrix, the electronically excited polar additive molecule can easily be desorbed. In the polar polyamide matrix, desorption of the additives is hindered by strong polar interactions (e.g. hydrogen bridges) between the excited analytes and the polymer matrix. This hinders selective desorption of the additives by laser irradiation. However, in a polymer/additive matrix-modified solution, evaporated to dryness, the interactions between the polar... 

The y-initiated oxidation of polyolefins produces a product mix which is less complex than that resulting from photo-or thermally initiated degradation. This results from the mild conditions in the Y-cell, where the major initial oxidation product, the -OOH group, is stable. Although the derivatization methods are applicable to all types of oxidation, for simplicity only the y-irradiated systems will be considered here. 

A material, such as (a) a terpolymer of propylene, ethylene and butene-1, (b) a polyolefin composition, which includes about 31 to 39% of a copolymer of propylene and ethylene and about 58 to 72% of a terpolymer of propylene, ethylene and butene-1 or (c) a polyolefin composition, which includes about 30 to 65% of a copolymer of propylene and butene-1 and about 35 to 70% of a copolymer of propylene and ethylene, is irradiated and extruded through a die in the presence of a physical expanding agent and a cell nucleating agent to produce a structure having a density, which is at least 10 times less than the initial density of the material. The foam articles exhibit improved flexibility and low temperature toughness compared to conventional propylene polymer materials. 

Plastics are by far the largest group of polymeric materials being processed by electron beam irradiation. Cross-linking of polyolefins, PVC, polyesters, polyurethanes, fluoropolymers, and fiber-reinforced composites is a common practice. 

Irradiation of polyolefins, particularly the family of polyethylenes, represents an important segment of the radiation processing. Polyolefins can be... 

As with other polyolefins, upon irradiation the free radicals are formed along with evolution of hydrogen gas. If the radical is formed on the pendant methyl, the resulting reaction is cross-linking. However, if the radical is formed in the main chain, the chain end may react with hydrogen, thus causing an irreversible scission. Although the processes of chain scission and... 

Both processes have advantages and disadvantages. Currently, they have about an equal share of the global market. The initial investment cost in the irradiation equipment is high, but it is considerably more productive than chemical cross-linking, having the additional advantage of uniform product quality and flexibility of feedstock selection. The product from radiation cross-linked polyolefins is thin, with fine cells and smooth white surfaces. The comparison of chemical and radiation processes is in Table 8.8. ... 

As with other polyolefins, the free radicals are formed upon irradiation, along with evolution of hydrogen gas. If the radical is formed on the pendant methyl, the... 

W.R. Grace started to manufacture heat-shrinkable polyolefin packaging films. At about the same time, Goodyear and Firestone initiated an investigation of the modification of rubber compounds by EB irradiation for tire applications.1... 

In addition to ESR spectroscopy, which is a general method for detecting radicals, Dole et al. (9, 10, 11, 12) have developed a method of ultraviolet spectroscopy at low temperatures, which is specific for allylic and polyenylic radicals. Numerous papers have dealt with changes in polymers on irradiation, and all of these conclude that the reactions, in one way or another, arise from the formation of free radicals. Only a few papers describe experiments in which the radicals have been observed directly by ESR or ultraviolet spectroscopy at low temperatures. This article merely summarizes the present knowledge of the nature of radicals formed in polyolefins by irradiation in vacuum (ionizing radiation and ultraviolet light) and discusses some new trends in studying these radicals. 

Chlorination is one of the most interesting processes for polymer modification, and is usually carried out by means of catalysts or by UV irradiation. Since 1960, radiation-induced chlorination of polyethylene and polypropylene has been studied, especially by Soviet workers (1-3). As the polymers used in that work are insoluble in the usual solvents at normal temperature, chlorination was done in the heterogeneous phase— for example, by leading continuously a stream of chlorine over the finely ground polymer or through an aqueous suspension of the polyolefin. It is, therefore, difficult to compare the results obtained under the different conditions used. 

Abstract The oxidation of polymers such as polypropylene and polyethylene is accompanied by weak chemiluminescence. The development of sensitive photon counting systems has made it comparatively easy to measure faint light emissions and polymer chemiluminescence has become an important method to follow the initial stages in the oxidative degradation of polymers. Alternatively, chemiluminescence is used to determine the amount of hydroperoxides accumulated in a pre-oxidised polymer. Chemiluminescence has also been applied to study how irradiation or mechanical stress affects the rate of polymer oxidation. In recent years, imaging chemiluminescence has been established as a most valuable technique offering both spatial and temporal resolution of oxidation in polymers. This technique has disclosed that oxidation in polyolefins is non-uniformly distributed and proceeds by spreading. 

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