Viscoelastic behaviour of stabilized polyethylenes irradiated with gamma rays (original) (raw)
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Mechanical response of high density polyethylene to gamma radiation from a Cobalt-60 irradiator
Polymer Testing, 2016
The response of High Density Polyethylene (HDPE) to gamma irradiation is important for a variety of applications, from the durability of hip replacements after gamma sterilization to the degradation of power cable insulation that guides the licensing and regulation of nuclear power plants. HDPE samples are irradiated with up to 58.8 kiloGray from a Cobalt-60 gamma irradiator, and mechanical properties are examined using models assuming exponential behavior. Increasing the radiation dose led to increases to the ultimate strength and the Rockwell hardness with a corresponding reduction in the maximum elongation at ultimate strength, supporting the hypothesis that the samples increased their strength and brittleness.
Change of Physico-Mechanical Properties of Polyethylene During Radiation-Induced Aging
The changes in the physicomechanical properties of LDPE are considered in the kinetic and diffusion regimes of radiation oxidation. In the kinetic regime fall in the instant modulus and strength at low doses is due to degradation of the macromolecules and at high doses to accumulation of oxygen-containing groups. In the diffusion regime strength is determined both by the size of the absorbed dose and depending on the dose rate by the ratio of the thicknesses of the internal crosslinked and external oxidized layers. In the heterogeneous sample the presence of a crosslinked layer does not lead to rise in the strength of the material as compared with that of the uniformly oxidized film.
Rheological and morphological analysis of irradiated high and low density polyethylene samples
Journal of the Serbian Chemical Society, 2022
The influence of intensity of the γ-irradiation on commercial high and low density polyethylene (LDPE and HDPE) granules (Kazanorgsintez PJSC, Kazan, Tatarstan, Russia) on their rheological and morphological properties at irradiation doses of 5 and 10 kGy was studied. Experiments in the oscillation mode revealed an increase in the dynamic moduli values with increasing radiation dose compared to the initial samples. At the same γ-irradiation doses, the HDPE samples compared to the LDPE ones showed the greatest changes in rheological properties, while the zero shear viscosity of HDPE increased by order of magnitude compared to the initial one at the irradiation dose of 10 kGy. Morphology analysis of supramolecular structures revealed an increase in cobweb-type structures for the irradiated sample in comparison with the initial sample, which may indicate the formation of branched structures under γ-irradiation.
Radiation Physics and Chemistry
The effects on different synthetic polymers of distinct types of radiation, gamma rays and electron beam, under different atmospheres are followed by changes in their viscoelastic behavior. Taking into account the two main radioinduced reactions, crosslinking and scissioning of polymeric chains, liquid polydimethylsiloxane has been used as example of crosslinkable polymer and semi crystalline polypropylene as example of scissionable polymer. Propylene-1-hexene copolymers have been also evaluated, and the effects of both reactions were clearly noticed. Accordingly, samples of those aforementioned polymers have been irradiated with 60 Co gamma irradiation in air and under vacuum, and also with electron beam, at similar doses. Sinusoidal dynamic oscillation experiments showed a significant increase in branching and crosslinking reactions when specimens are irradiated under vacuum, while scissioning reactions were observed for the different polymers when irradiation takes place under air with either gamma irradiation or electron beam.
Radiation Physics and Chemistry, 1999
Eects of high energy radiation on stress relaxation behavior of unoriented (l=1) and oriented (l=9) ultrahigh molecular weight polyethylene (UHMWPE) were investigated. As in a previous study, the stress relaxation is interpreted in terms of a model that consists of two thermally activated processes acting parallel. The ®rst process is related to crystal and the second to the amorphous fraction. Application of the two-process model enabled separate studying of the in¯uence of irradiation on viscoelastic behavior of these two fractions. #
The alterations in high density polyethylene properties with gamma irradiation
Radiation Physics and Chemistry, 2017
In the present investigation, high density polyethylene (HDPE) polymer has been used to study the alterations in its properties under gamma-irradiation. Physico-chemical properties have been investigated with different spectroscopy techniques, Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), biocompatibility properties, as well as, mechanical properties change. The FT-IR analysis shows the formation of new band at 1716 cm-1 that is attributed to the oxidation of irradiated polymer chains, which is due to the formation of carbonyl groups (C=O). XRD patterns show that a decrease in the crystallite size and increase in the Full Width at Half Maximum (FWHM). This means that the crystallinity of irradiated samples is decreased with increase in gamma dose. The contact angle measurements show an increase in the surface free energy as the gamma irradiation increases. The measurements of mechanical properties of irradiated HDPE samples were discussed.
Journal of Applied Polymer Science, 1989
Ultrahigh molecular weight polyethylene has been irradiated using a cobalt 60 source to give received dose between zero and 50 m a d. Irradiated specimens were subjected to tensile characterization, dynamic mechanical analysis, and differential scanning calorimetry. Changes in tensile and dynamic mechanical properties following irradiation arise from both molecular rearrangement and from increased crystallinity following scission of long interlamella tie chains. The effects of post-irradiation aging on mechanical properties are associated with increasing crystallinity resulting from decomposition of metastable groups formed in the amorphous region during irradiation. Irradiated materials have been subject to sinusoidal stressing between 0.275 and 0.55 of yield stress for 100,OOO cycles, and changes in mechanical and physical properties measured. Increased resistance to creep during stressing was observed with the irradiated materials, behavior which is consistent with previously observed changes in crystallinity and crosslink density. Overall property changes measured following stressing were small compared with those induced by the initial irradiation.
Evaluation of the radiation resistance of high-density polyethylene. [Gamma Rays]
DE84 010515 Mechanical tests following gamma Irradiation and creep tests during Irradiation have been conducted on high-density polyethylene (HOPE) to provide data to help assess the adequacy of this material for use 1n high integrity containers (HICs). Two types of HOPE, a highly cross-linked rotationally molded material and * non-cross-1 Inked blow molded material, were used in.these tests. Gamma-ray Irradiations were performed at several dose rates in envrionments of air, BarnweiV and Hanford backfill soils, and ion-exchange resins. The results of tensile and bend tests on these materials following Irradiation are presented along with results on creep during irradiation.
Journal of Applied Polymer Science, 1999
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.