On the structures and yields of the first peroxyl radicals in .gamma.-irradiated polyolefins

Carlsson, D. J.; Chmela, Štefan; Lacoste, J.

doi:10.1021/ma00225a009

Cited by 69 publications

(26 citation statements)

References 5 publications

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“…From Table 1, the data for g-initiated oxidation of tetradecane, in the presence of vitamin E indicate that free hydroperoxide is produced at a higher initial rate ($ 3Â10 À4 mol/l kGy) than found in pure tetradecane ($ 0.7Â10 À4 mol/l kGy), consistent with peroxyl scavenging by reaction (3). In fact the increased rate of initial, free hydroperoxide production in the presence of vitamin E ($ 2.3Â10 À4 mol/l kGy) is close to the rate of vitamin E loss ( $ 2.6Â10 À4 mol/l kGy), consistent with the reported G values (2-3Â10 À4 ) for peroxyl production in liquid alkanes and in HDPE [28]. As oxidation proceeds, the free hydroperoxide yield drops below that of phenol loss, probably as a result of hydrogen bonding increasing to accumulated oxidation products.…”

Section: Discussionsupporting

confidence: 88%

“…Most alkyl radicals undergo a very fast reaction with dissolved O 2 to give peroxyl radicals (G peroxyl radical formation in HDPE $ 2, i.e. $ 2Â10 À4 mol/l kGy ) [28]. Each initial peroxyl radical may propagate by the abstraction of a hydrogen atom from the alkane to give hydroperoxide, reforming peroxyl radicals [reaction (1)], or undergo cage termination with its geminate radical.…”

Section: Discussionmentioning

confidence: 99%

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Antioxidant effectiveness of vitamin E in HDPE and tetradecane at 32°C

Mallégol

Carlsson

Deschênes

2001

Polymer Degradation and Stability

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Vitamin E was found to be a very effective antioxidant both in a model, liquid alkane, (teradecane) and in HDPE when oxidations at close to room temperature were initiated with g-radiation. FTIR was used to follow changes in vitamin E in oxidising tetradecane and HDPE, even at very low concentrations of the antioxidant. Formation of isolated hydroperoxide groups as a direct result of the vitamin E-peroxyl radical reaction were clearly visible. Quinone products from vitamin E were formed during g-irradiation, but different quinones were formed depending on the vitamin E concentrations. Vitamin E quite effectively retarded the oxidation of HDPE during g-irradiation and so should be useful in polyethylene intended for radiation sterilisation, as packaging materials or medical devices. Crown

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Section: Discussionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Antioxidant effectiveness of vitamin E in HDPE and tetradecane at 32°C

Mallégol

Carlsson

Deschênes

2001

Polymer Degradation and Stability

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“…In irradiated UHMWPE, the carbon free radicals resulting from the breakage of the C-H bonds are prevalent [11]. When oxygen is present in irradiated polyethylene, it reacts with the primary free radicals to form peroxy free radicals [12,38].…”

Section: Introductionmentioning

confidence: 99%

Vitamin E diffused, highly crosslinked UHMWPE: a review

Oral

Muratoglu

2010

International Orthopaedics (SICOT)

219

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Highly crosslinked UHMWPE has become the bearing surface of choice in total hip arthroplasty. First generation crosslinked UHMWPEs, clinically introduced in the 1990s, show significant improvements compared to gamma sterilised, conventional UHMWPE in decreasing wear and osteolysis. These crosslinked UHMWPEs were thermally treated (annealed or melted) after irradiation to improve their oxidation resistance. While annealing resulted in the retention of some oxidation potential, postirradiation melted UHMWPEs had reduced fatigue strength due to the crystallinity loss during melting. Thus, the stabilisation of radiation crosslinked UHMWPEs by the diffusion of the antioxidant vitamin E was developed to obtain oxidation resistance with improved fatigue strength by avoiding post-irradiation melting. A two-step process was developed to incorporate vitamin E into irradiated UHMWPE by diffusion to obtain a uniform concentration profile. Against accelerated and real-time aging in vitro, this material showed superior oxidation resistance to UHMWPEs with residual free radicals. The fatigue strength was improved compared to irradiated and melted UHMWPEs crosslinked using the same irradiation dose. Several adverse testing schemes simulating impingement showed satisfactory behaviour. Peri-prosthetic tissue reaction to vitamin E was evaluated in rabbits and any effects of vitamin E on device fixation were evaluated in a canine model, both of which showed no detrimental effects of the inclusion of vitamin E in crosslinked UHMWPE. Irradiated, vitamin E-diffused, and gamma sterilised UHMWPEs have been in clinical use in hips since 2007 and in knees since 2008. The clinical outcome of this material will be apparent from the results of prospective, randomised clinical studies. IntroductionOsteolysis triggered mainly by ultrahigh molecular weight polyethylene (UHMWPE) wear particles has been one of the major problems in total hip arthroplasty along with instability/dislocation and infection [7]. Highly crosslinked UHMWPEs were developed using high-dose irradiation (50-100 kGy) to decrease the wear rate of UHMWPE [44,46] and have become the standard-of-care after their first decade of service, especially in North America [61].Irradiation causes crosslinking in the amorphous phase of the UHMWPE [33], but also initiates the formation of free radicals in the crystalline phase [23], unable to recombine due to structural limitations, they become trapped for long periods of time [29]. These residual free radicals are believed to migrate to the crystalline/amorphous interface and cause oxidative degradation in the material [16][17][18]59, 69] through a cascade of reactions with oxygen [32,71].In first generation crosslinked UHMWPEs [34], postirradiation thermal treatment was used to increase the oxidation resistance (Fig. 1). One approach was to annealThe studies discussed here were performed by research funding in part from NIH/NIAMS

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“…In irradiated UHMWPE, the prevalent free radicals are the carbon free radicals resulting from the breakage of the C-H bonds (14) and these radicals are found in three forms: the alkyl, allyl and polyenyl free radicals (15)(16)(17), the latter being formed especially at higher radiation doses ((18) , Fig 1). Most of these free radicals recombine in the amorphous portion of the polymer (19), where the chains are highly mobile.…”

Section: Introductionmentioning

confidence: 99%

“…When oxygen is present in irradiated polyethylene, it reacts with the primary free radicals to form peroxy free radicals ( (14,(24)(25)(26)(27) , Fig 2). These peroxy radicals, in the absence of an antioxidant like a-tocopherol, abstract a hydrogen atom from other polyethylene chains, creating primary free radicals, which can then react with oxygen to further this cascade ((28, 29), Fig 3).…”

Section: Introductionmentioning

confidence: 99%

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

2006

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We developed a radiation cross-linked UHMWPE stabilized with a-tocopherol (Vitamin E) as a bearing material in total joint replacements. The stabilizing effect of a-tocopherol on free radical reactions in UHMWPE is not well understood. We investigated the effect of a-tocopherol on the oxidation and transformation of residual free radicals during real-time aging of a-tocopherol-doped, irradiated UHMWPE (aTPE) and irradiated UHMWPE (control). Samples were aged at 22° C (room temperature) in air, at 40°C in air, and at 40°C in water for seven months. During the first month, aTPE showed some oxidation at the surface, which stayed constant thereafter. Control exhibited substantial oxidation in the subsurface region, which increased with time. The alkyl/allyl free radicals transformed to oxygen centered ones in both materials; this transformation occurred faster in a-TPE. In summary, the real-time oxidation behavior of a-TPE was consistent with that observed using accelerated aging methods. This new UHMWPE is oxidation resistant and is expected to maintain its properties in the long-term.

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On the structures and yields of the first peroxyl radicals in .gamma.-irradiated polyolefins

Cited by 69 publications

References 5 publications

Antioxidant effectiveness of vitamin E in HDPE and tetradecane at 32°C

Antioxidant effectiveness of vitamin E in HDPE and tetradecane at 32°C

Vitamin E diffused, highly crosslinked UHMWPE: a review

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

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