Role of free radicals in the radiation chemistry of polymers

Turner, D. T.

doi:10.1002/pol.1971.230050104

Cited by 11 publications

(5 citation statements)

References 271 publications

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“…Considering the experimental irradiation procedure adopted here, one plausible alternative is that some of the free radicals produced may not have combined to produce chain linking, thus remaining trapped in the semicrystalline medium. If this is the case, then it is expected that upon exposing the samples to air these free radicals could react with oxygen, producing different oxygenated products in polyethylene 1, 2, 5, 7, 9. In this way, the radicals could have followed alternative reactions to those conducting to chain linking, precluding the formation of higher amounts of gel.…”

Section: Resultsmentioning

confidence: 99%

“…1–6 Radiation causes various chemical reactions, mainly involving free radicals, that alter the molecular structure and, consequently, the properties of the irradiated materials. In the case of the linear polyethylene family, the most important reaction that occurs during irradiation is the combination of free radicals that leads to molecular chain linking 1–10. During the early stage of the irradiation processes, chain linking produces an increase in molecular weight.…”

Section: Introductionmentioning

confidence: 99%

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Effect of initial crystallinity on the response of high-density polyethylene to high-energy radiation

Failla¹,

Vallés²,

Lyons³

1999

J. Appl. Polym. Sci.

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Samples of each of two high-density polyethylenes with various initial degrees of crystallinity, but otherwise identical, were exposed under a vacuum to moderate doses of gamma irradiation. The results indicate that, for otherwise initially identical polymer samples, the dose required to reach the gel point increases with increase of the initial degree of crystallinity. Above the critical dose for gelation, the gel content decreases with higher degrees of crystallinity at equal radiation doses. The mechanical behavior of the polymers changed progressively from ductile to brittle as the crystallinity was increased. The extensibility of originally ductile samples decreases with increasing radiation dose. The irradiation of samples having intermediate behavior produces a change to ductile behavior. Mechanical behavior is not modified substantially when brittle samples are irradiated. The initial modulus is little altered by irradiation, while the yield stress shows a slight increase with irradiation. The mechanical properties, such as draw ratio at break and ultimate tensile stress, decrease with dose in ductile samples.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of initial crystallinity on the response of high-density polyethylene to high-energy radiation

Failla¹,

Vallés²,

Lyons³

1999

J. Appl. Polym. Sci.

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“…Several very good reviews have been written on this subject, most of which cover a wider range of polymers [3][4][5][6][7][8][9]. Articles that deal exclusively with PE include those by Salovey (PE single-crystals) [10], Mandelkern [11] and Dole [12].…”

Section: Introductionmentioning

confidence: 99%

Radiation effects in polyethylene and n-alkanes

Ungar

1981

J Mater Sci

138

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The effect of high-energy radiation on n-alkanes and polyethylene (PE) are reviewed. The article includes a description of (a) primary radiation events, formation, spatial distribution and decay of free radicals and radical migration mechanisms, (b) formation of cross-lin ks and other sta ble products, (c) the effects of crystal linity, crystalline modifications and morphology on radiation cross-linking, and (d) radiation-induced changes in the crystal lattice and the destruction of crystallinity at high irradiation doses.An attempt is made to bring together conflicting views on various unsolved problems of the radiation physics and chemistry of these important and much studied substances. Long-chain paraffins are given considerable attention since their radiation behaviour often provides a link between that of PE and its short-chain analogues.

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“…By contrast, the yield stresses for the IWQ samples irradiated to 200 kGy were only about 20% larger than the corresponding values of the nonirradiated samples. At this level of dosage, the major effect was the introduction of crosslinks and oxygenated species within the noncrystalline phase because it was expected that the irradiation process would not significantly affect the crystal core 10–12. Therefore, the increase in the yield stress with dosage could be associated with the modification introduced into the noncrystalline phase.…”

Section: Resultsmentioning

confidence: 99%

“…The enhancement of these properties is directly related to the intermolecular crosslinks that are produced by irradiation. It has been established that various factors exist that control the amount of crosslinks generated by the radiation process 7, 10–13. When the irradiation is performed at temperatures close to room temperature, that is, 25–30°C, the crystallinity level is one of the factors that affects the efficiency of crosslinking 10, 13.…”

Section: Introductionmentioning

confidence: 99%

Effect of the temperature on the tensile mechanical behavior of irradiated linear polyethylene

Vallés

Failla

2003

J of Applied Polymer Sci

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ABSTRACT:The mechanical behavior of two ␥-irradiated linear polyethylenes was determined at 75 and 105°C under tensile stress. Each polymer was crystallized from the melt after different thermal histories so that samples would be obtained with various degrees of crystallinity. Subsequently, they were irradiated in vacuo and at room temperature to total doses ranging from 20 to 200 kGy. The initial crystallinity, dose level, and test temperature determined whether the samples displayed ductile, brittle, or transitional behavior. The yield stress decreased as the temperature increased. The value of the yield stress at a given temperature showed a tendency to increase with dose; this became more evident as the initial crystallinity increased. The extensibility of ductile samples, estimated from the draw ratio after break, decreased with the gel content. For ductile samples, the temperature affected the values of this property when the gel fraction that developed in the samples was relatively low. The effect of temperature became less noticeable when the gel reached values larger than 60%. The ultimate stress, normalized with the crosslinking density, correlated with the draw ratio after break in a way that resembled the type of relationship observed in other crosslinked systems.

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Role of free radicals in the radiation chemistry of polymers

Cited by 11 publications

References 271 publications

Effect of initial crystallinity on the response of high-density polyethylene to high-energy radiation

Effect of initial crystallinity on the response of high-density polyethylene to high-energy radiation

Radiation effects in polyethylene and n-alkanes

Effect of the temperature on the tensile mechanical behavior of irradiated linear polyethylene

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