Ultraviolet Irradiation Studies in a Polyester Using Positron Annihilation Spectroscopy (original) (raw)
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Positron annihilation studies of the effect of gamma irradiation dose in polymers
2003
Positron annihilation lifetime (PAL) technique has been applied to study the effect of gamma irradiation dose on the structure of low-density polyethylene and polystyrene. The positron annihilation lifetime measurements were performed with a conventional fast-fast coincidence system. Gamma irradiation was carried out at room temperature with a 60 Co gamma source up to a dose of 1000 kGy. The delayed lifetime spectra of irradiated and unirradiated samples were decomposed into three lifetime components. The lifetime parameters give indication of the free-volume size and concentration. It was found that the crosslinking efficiency in the polymer increases significantly with increasing irradiation dose. This appears as a decrease in the intensity of the long-lived positron lifetime components attributed to ortho-positronium formation.
Positron annihilation lifetime study of irradiated and deformed low density polyethylene
Polymer Degradation and Stability, 2003
Positron annihilation lifetime spectroscopy has been used to study the free volume hole properties of unirradiated and irradiated low density polyethylene (LDPE) as a function of deformation in the range from 0 to 110%. Deconvolution of the lifetime spectra into three components reflected three different morphologies of the polymer structure. The variation of positron annihilation parameters with deformation shows three stages; the elastic range, strain-softening region, and plastic region. The free volume was probed using ortho-positronium (o-Ps) pick-off annihilation lifetime parameters as a measure of electron density and the mean free volume hole radius. For unirradiated sample, the average of the free volume hole increases with deformation in the elastic region, remains unchanged within the strain softening region, and finally tends to increase in the plastic region. A reduction in the size of the free volume holes and concentrations has been observed in the case of irradiated sample which is due to a structural change. The distribution of the free volume for unirradiated sample shifts from a small to large size as the deformation increases and has very similar Gaussian-like distribution. For irradiated one, the distribution becomes broader and has an asymmetric appearance. The results show that positron lifetime is a sensitive means to probe the microstructural change of polymers during deformation.
Journal of Radioanalytical and Nuclear Chemistry, 2017
Radiation exposure modifies the nano scale free volume of the polymers which has direct correlation to certain properties of polymeric materials. CR-39 (DOP) polycarbonate polymeric films were exposed to gamma radiation at different doses for the study of nano scale free volume as well as structural and optical properties. An overall increase in the number of free volume holes at all doses was observed. UV-visible studies showed an improvement in the optical properties due to decrease in direct band gap energy. X-ray diffraction spectra of the polymer samples showed the increased amorphous nature of the polymer.
Electron Irradiated Effect in Polyurethanes Studied by Positron Annihilation Lifetime Spectroscopy
Khulna University Studies
The intensity variation of positronium as a result of electron irradiation has been studied on polyurethanes (PU) using positron annihilation lifetime spectroscopy (PALS). The PALS measurement was carried out at room temperature with a conventional fast-fast coincidence system. The lifetime spectra were analyzed into four components using melt program to extract the positron parameters such as lifetime and intensity. Due to irradiation a decrease of intensity about 2.7% was observed up to 10kGy. Free volume radius has been calculated for electron irradiated PU. PALS measurement has also been performed to study the effect of temperature variation in the range 30K to 310K. Analysis by melt program on the spectra shows that the fourth lifetime component increases significantly above glass transition temperature.
Dose effect in gamma-irradiated polyethylene studied by positron annihilation lifetime technique
Radiation Physics and Chemistry, 1994
Positron annihilation spectroscopy, thermogravimetric and FT-IR techniques are used to study the effect of low doses of gamma irradiation on microscopic structure of cellulose triacetate films. The irradiation is done at room temperature with doses ranging from 5 to 25 kGy. The ortho-positronium lifetime component associated with the pick-off annihilation of positronium trapped by the free volume is analyzed. Alternation in the ortho-positronium lifetime is observed reaching to a minimum value at10 kGy which is followed by a sharp increase at 15 kGy. Afterward, the ortho-positronium lifetime remains almost constant up to 25 kGy. The intensity of ortho-positronium component, I 3 , revealed an opposite trend with respect to the ortho-positronium lifetime manner. The obtained results are discussed on the basis of free volume model. The thermogravimetric and FT-IR measurements bearded out the findings of positron annihilation spectroscopy and explained the variations on the CTA microstructure due to the effect of the low doses of gamma irradiation.
Positron Annihilation for Characterizing Polymeric Materials
2002
Positron annihilation spectroscopy (PAS) is reviewed as a powerful technique for characterizing a number of materials, emphasizing the case of polymers. The basic physics of positronium, positron and their interactions with matter are discussed, as well as the equipment required for a PAS experiment. A specific example, namely the grafting of low density polyethylene (LDPE) with acrylic acid (AA) and metacrylic acid monomers is used to illustrate the use of PAS for characterizing complex polymeric systems.
Positron Annihilation Lifetime (PAL) technique has been employed to investigate the effect of low doses of -irradiation (in air and vacuum) on the type of polymers namely: polystyrene (PS). A conventional fast-slow coincidence system was used for measuring the positron lifetime spectra. The time resolution of the system was 422±20 ps (the full width at half maximum (FWHM)) at 22 Na energy window. The lifetime spectra were resolved into three components by using PFPOSFIT program. The irradiation performed in air (in the presence of oxygen) and under vacuum with -rays by using (90 Sr/ 90 Y) source at room temperature for ten different total dose, ranging from (0.3-12.3) Gy . The o-Ps lifetime parameters were used to determine the microstructure properties, namely: free volume hole size (V h) and free volume hole fraction (F h). The parameters were measured as a function of -irradiation dose. The results of -irradiation show that, the influence of -irradiation on o-Ps lifetime, he...
Dose effect in gamma irradiated polyethylene studied by the positron annihilation lifetime technique
Polymer Degradation and Stability, 1993
Commercial high-density polyethylene (HDPE) samples were irradiated by y-rays with doses ranging from 10 to 200 kGy. Positron annihilation lifetime measurements were performed to study the effect of y-radiation on the structure of polyethylene. The lifetime r). associated with the pick-off process, in which the positron in o-Ps annihilates an electron from the surrounding material, and its intensity I, are measured as a function of y-dose. It can be concluded that the effect of y-irradiation on polyethylene results in intensive formation of new bonds or crosslinking at doses ranging from 10 to 100 kGy. Saturation of f, for the irradiated HDPE at doses ranging from 100 to 200 kGy may indicate the achievement of a structural stability
Positron Interaction in Polymers
International Journal of Modern Physics A, 2004
A series of dense copolyimide membranes was characterized using positron annihilation spectroscopy. The positron annihilation lifetime spectroscopy performed on film with a classical positron source gives informations on the positronium fraction formed and also on the hole size within the film. The Doppler broadening spectra (DBS) of the gamma annihilation rays coupled with a variable energy positron beam allow the microstructural analyses as a function of the film depth. Experimental data were also linked to the chemical structure of the polyimides. It was found that the presence of the fluorine atoms strongly affects the positron annihilitation process and especially the DBS responses.
Gamma irradiation of polyester films
Radiation Physics and Chemistry, 2007
Irradiation in air of several thermoplastic aromatic polyesters was carried out in order to investigate changes in characteristic properties. Polymers are irradiated at high doses, until 1 MGy, and no drastic changes seem to emerge. Dielectric and resistance measurements are carried out in order to evaluate changes in electrical insulation property; moreover, nanoholes dimensions, analyzed by positron spectroscopy, are measured in pristine and irradiated polyesters. The study shows good durability of this kind of polyesters, due to the aromatic rings able to stabilize the polymeric chains towards ionizing radiations and able to preserve the original structural, electrical and permeability properties. r