Radiation processing of ethylene-propylene rubber (original) (raw)
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DSC and oxygen uptake studies of γ-irradiated ethylene–propylene elastomers
1999
The speci®c heat capacity of irradiated ethylene±propylene copolymer was examined by dierential scanning calorimetry. Additional measurements on oxidative stability of g-exposed EPR were performed by isothermal and isobaric oxygen uptake. The c p dierences between vacuum ± and air ± radiolysis of polymers are pointed out. The oxidative irradiation environment generates peroxy radicals that are involved in the air-degraded samples. The c p dependencies on temperature determined for the two manners of irradiation are not alike. The assessment of the thermal behavior by DSC and oxygen uptake con®rms the key role of RO 2 . in the radiolytic and thermal degradation of these polymers. #
Post-irradiation oxidation of different polyethylenes
Polymer Degradation and Stability, 2011
The radiation-induced oxidative degradation of polyethylenes (PEs) with different degrees of crystallinity was characterized after electron-beam irradiation and during storage at room temperature.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
The effect of gamma irradiation conditions on the radiation-induced degradation of uncrosslinked, commercial isobutylene-isoprene rubbers has been investigated in this study. Influence of dose rate and irradiation atmosphere on the degradation of butyl rubber has been followed by viscosimetric and chromatographic analyses. Limiting viscosity number of all butyl rubbers decreased sharply up to 100 kGy and leveled off at around the same molecular weight, independent of dose rate. Slightly higher decrease in viscosity was observed for samples irradiated in air than in nitrogen especially at low dose rate irradiation. Cross-linking GðX Þ, and chain scission GðSÞ yields of butyl rubbers were calculated by using weight-and number-average molecular weights of irradiated rubber determined by Size Exclusion Chromatography analyses. G-value results showed that chain scission reactions in isobutylene-isoprene rubber in air atmosphere are more favorable than in nitrogen atmosphere, and that lower dose rate enhances chain scission over cross-linking.
Profile of oxidation in irradiated polyethylene
1998
Following gamma irradiation in air which causes bond scission and yields large concentrations of peroxy radicals, maximum oxidation and an increase in crystallinity occurs on the surface of ultrahigh molecular weight polyethylene. Here, bimolecular reactions of peroxy radicals generate carbonyls, mostly ketones. On the polymer surface, peroxy radicals continue to react over time periods of years to generate carbonyls and chain scission. Peroxy radicals in the interior of the polymer abstract hydrogens and form hydroperoxides, inducing chain reactions and a slow but continue increase of ketone. Within the polymer sample, to a decreasing depth with increasing dose, a reduced concentration of oxygen is available to react with radiolytic radicals, so that more efficient crosslinking and a low level of hydroperoxide chain reaction occur. After long periods of time a surface maximum in carbonyl concentration is produced. Heating polyethylene in high pressures of oxygen accelerates the oxidative process.
Irradiation effects on ethylene-propylene elastomers in an aqueous environment
Polymer Testing, 1996
Ethylene-propylene elastomers (EPR and EPDM), which generate free radicals at considerable rate during gamma irradiation, show the competition between crosslinking and degradation of these materials in the temperature range from 130°C to 150°C. The overall effect of simultaneous processes on the studied polymers is evaluated by the oxygen uptake method. The oxidation rate depends on the pre-existance of peroxyl radicals. If the temperature is not high enough to promote degradation. oxygen consumption will be stopped when the free radical concentration reaches trace level.
Radiation-induced degradation of butyl rubber vulcanized by three different crosslinking systems
Radiation Physics and Chemistry, 2012
Butyl rubber (IIR) is an isobutylene/isoprene copolymer and is provided with good properties including low permeability to gases, good thermal stability and high resistance to oxygen and ozone action, among others. It is well known that the major effect of ionizing radiations on butyl rubber is chain scission accompanied with a significant reduction in molar mass. This work aimed to study the effects of gamma radiation on the properties of butyl rubbers vulcanized by three different curing systems, such as, the ones based on sulfur, sulfur donor and phenolic resin to identify which curing system is the most stable under irradiation. The butyl rubber vulcanized by three different systems was gamma irradiated with doses of 25 kGy, 50 kGy, 100 kGy, 150 kGy and 200 kGy. Irradiated and non-irradiated samples were characterized by the following techniques: tensile, elongation and hardness. It was observed that doses higher than 150 kGy practically destroy the assessed properties for all butyl compounds, irrespective of the vulcanization system used; however compounds cured with phenolic resin showed a decrease in properties proportional to the dose.
ESR study of irradiated ethylene-propylene rubber
Applied Radiation and Isotopes, 1993
The ESR technique was used to investigate the resonant pammagnetic properties of an ethylene-propylene based material and of its basic components irradiated with a 6oCo source up to 0.1 MGy. A qualitative model for the radical formation in a polymeric material with antioxidant as an additive is proposed.
Dose rate effects on the radiation induced oxidation of polyethylene
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
The yields and spatial distribution of the products arising from the in source oxidation of 50 lm LDPE films induced by 60-Co gamma radiations and by 300 kev electrons have been investigated as a function of the dose rate. The dose rate was found to have a strong influence on the reaction, the hydroperoxides and carbonyls yields at the lowest gamma dose rate of 0.04 kGy/h being decreased by a factor of about three with increasing the gamma dose rate up to 0.69 kGy/h and by a factor of about 30 when operating at the e-beam dose rate of 1.5 kGy/s. The carbonyls depth concentration profiles, the EPR measurements on radicals intermediates and the experiments of post-irradiation oxidation are consistent with the conclusion that, as far as the gamma irradiation is concerned, the observed dose rate effects cannot be imputed to oxygen diffusion control and/or to the chain branching via hydroperoxides decomposition coupled to the longer times between the initiation events. The hypothesis of the dose rate acting on the kinetic chain length of the radioxidation which in turn implies a substantially uniform distribution of radicals in the amorphous phase attained through spur expansion is proposed.
Electron beam irradiation of epoxidized natural rubber
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2000
The eect of irradiation on ENR50 was studied with particular attention to irradiation-induced crosslinking. ENR50 was irradiated by using a 3.0 MeV electron beam machine with doses ranging from 20 to 200 kGy. The in¯uence of several additives such as TMPTA, Irganox1010 and tribasic lead sulfate on irrradiation-induced crosslinking of ENR50 was investigated. The gel fraction, Ts, M100, Eb, hardness and Tg were used to follow the irradiation-induced crosslinking of the rubber. Results revealed that the increase in gel fraction upon irradiation of pure ENR50 could be associated with both irradiation-induced crosslinking as well as ring opening side chain reaction of oxirane group. The observation on the trend shown in the properties studied con®rmed that TMPTA is ecient in enhancing the irradiation-induced crosslinking of ENR50. The addition of Irganox1010 and tribasic lead sulfate found to inhibit irradiation-induced crosslinking of ENR50 to considerable extent. This in¯uence of stabilizing additives in particular, antioxidant, was observed to be more prominent at lower doses. The importance of TMPTA in preventing ring opening side chain reactions as well as the role of the stabilizing additives in introducing free chain ends are also discussed. However studies did not reveal the exact nature of irradiation-induced reactions involved in ENR. Ó
Properties of Selected Polymers after Radiation Cross-linking
2012
Radiation processing involves the use of natural or manmade sources of high energy radiation on an industrial scale. The principle of radiation processing is the ability of high energy radiation to produce reactive cations, anions and free radicals in materials. The industrial applications of the radiation processing of plastics and composites include polymerization, cross-linking, degradation and grafting. Radiation processing mainly involves the use of either electron beams from electron accelerators or gamma radiation from Cobalt-60 sources. The TPE-E thermoplastic elastomer, LDPE low density polyethylene and PA6 polyamide 6 tested showed significant changes of temperature stability and mechanical properties after irradiation. From this point-of-view, new applications could also be seen in areas with service temperatures higher than their former melting point. The comparison of the temperature stability and mechanical properties of irradiated and nonirradiated TPE-E, LDPE and PA6...