Ki-Yup Kim

Thermally stimulated current study in γ-ray irradiated low density polyethylene

Abstract Thermally stimulated current and relaxation map analysis (RMA) were used to characterize the low temperature transition of low density polyethylene (LDPE). Four current peaks were observed. The peaks at about −125°C, −25°C, and 90°C are indications of the γ-, β-, α-transition, respectively, and a new, formerly unknown peak at about 50°C will be attributed to the space charge relaxation. The RMA data showed that compensation temperature (Tc) and degree of disorder increased with increasing the γ-ray intensity and decreasing antioxidant content, whereas the compensation time (τc) decreased. It can be concluded that the cooperative molecular motion in LDPE system becomes more active as the γ-ray intensity increases and antioxidant content decreases.

Radiation effects on electrical and mechanical properties of LDPE/EVA blends

The radiation effects on electrical and mechanical properties of LDPE/EVA blends with various vinyl acetate contents were investigated. Radiation degradation of LDPE/EVA blends was studied using TGA, volume resistivity, dissipation factor, elongation at break, and E-modulus. As vinyl acetate contents of LDPE/EVA blends increased, the electrical insulation characteristics were deteriorated but the flexibility was improved. As irradiation dose was increased, the electrical insulation characteristics were improved, but the flexibility was deteriorated

Radiation effects on electrical treeing resistance and mechanical characteristics of low density polyethylene containing barbituric acid derivatives

The treeing resistance of low density polyethylene containing barbituric acid derivatives under radiation environments were investigated. Barbituric acid, 4-aminouracil and 4-amino-6-hydroxy-2-mercapto pyrimidine were selected for treeing inhibitors. LDPE with the additives were irradiated by Co/sup 60/ /spl gamma/-rays. The treeing inception voltage and tree propagation was observed for electrical insulation properties, and the elongation at break was observed for the mechanical properties, to clarify the relation between the molecular structure and the electrical tree characteristics. Also thermoluminescence and gel contents were carried out at various dosages. LDPE containing treeing inhibitors showed better electrical insulation characteristics than pure LDPE. From the measurements, barbituric acid among the treeing inhibitors had the best treeing and radiation resistance.

Radiation effects on treeing resistance of low density polyethylene containing treeing inhibitors

The effectiveness of treeing resistance in low density polyethylene containing azocompounds were investigated under radiation environments. 4-(4-nitrophenylazo)-1-naphthol and 4-(4-nitrophenylazo) resorcinol were selected for treeing inhibitors. LDPE containing the additives were crosslinked with dicumyl peroxide, irradiated by /sup 60/Co /spl gamma/-ray in the presence of air at room temperature. Treeing inception voltage, AC breakdown strength measurements were carried out for electrical insulation characteristics, thermoluminescence and gel contents were analyzed as various irradiation doses also. LDPE with treeing inhibitors showed much better insulation characteristics than pure LDPE. It is interpreted that molecular structures, polar groups and the type of radicals connected on the benzene ring of the additives affected electrical characteristics. From the results, 4-(4-nitrophenylazo) resorcinol was the most effective upon the best treeing and radiation resistance.

Degradation of LDPE containing antioxidants by gamma-irradiation

Radiation degradation of low density polyethylene (LDPE) containing 2 types of organophosphate antioxidant and 2 types of hindered phenol antioxidant was evaluated by using thermo-luminescence (TL) characteristics. Each sample was irradiated with 60Co gamma-ray up to 1,000 kGy. The TL emission of LDPE containing antioxidants was showed lower values than that of the pure LDPE. The integrated TL response of the LDPE containing organophosphate type antioxidants showed a linear tendency for an irradiation doses

Electrical and Mechanical Properties of γ-ray Irradiated LDPE/EVA Blends

The radiation effects on electrical and mechanical properties of LDPE/EVA blends with various vinyl acetate contents were investigated. Radiation degradation of LDPE/EVA blends was studied using TGA, gelation, volume resistivity, dissipation factor, elongation at break, and elastic modulus. As vinyl acetate contents of LDPE/EVA blends increased, the electrical insulation characteristics were deteriorated but the flexibility was improved. As irradiation dose was increased, the electrical insulation characteristics were improved, but the flexibility was deteriorated

The Improvements for Fire Retardancy and Radiation Resistance of Chloroprene Rubber

This study has investigated radiation degradation of chloroprene rubber in the presence of some fire retardant. Ammonium polyphosphate, aluminium trihydroxide, magnesium hydroxide, calcium carbonate and antimony trioxide were selected as flame retardant. Samples were irradiated using a Co -ray and ray up to 2000 kGy at a dose rate of 5 kGy/hr in the presence of air atmosphere at room temperature. After irradiation, samples were assessed fire retardancy with electrical properties and mechanical properties. Some considerations concerning the effects of the fire retardants added to chloroprene rubber on the radiation and thermal stability of chloroprene rubber are presented. From fire retardancy with electrical and mechanical property measurements, it was found that addition of magnesium hydroxide resulted in maximum fire retardant effect.

Evaluation of radiation degradation of ethylene propylene rubber

For the evaluation of radiation degradation of ethylene-propylene rubber(EPR) cable insulation, EPR was irradiated with /spl gamma/-ray. Dielectric analysis, thermal gravimetric analysis and mechanical tests were carried out for each irradiated EPR. For dielectric analysis, permittivity and tan/spl delta/ increased with irradiation doses. Elongation at break and temperature at 5% weight loss of EPR showed the same tendency as increasing irradiation doses.

The study on electrical insulation characteristics of Co/sup 60/ /spl gamma/-irradiated low density polyethylene containing anti-treeing additives

The effectiveness of diolcompounds as anti-treeing additives in low density polyethylene under radiation environments is evaluated in this study. 1,2-tetradecandiol, 1,10-decanediol, 1,8-octanediol were selected as anti-treeing additives. LDPE containing the additives was crosslinked with dicumyl peroxide, then these specimens were irradiated by Co/sup 60/ /spl gamma/-rays for 200 kGy under air atmosphere. Treeing inception voltage, propagation, AC breakdown strength and volume resistivity measurements were carried out for analysis of electrical insulation characteristics. The type of radicals on which connected additives gave very important clues to the changes in the results for each material. Also, the quantity of polar groups in molecular weight affected electrical insulation characteristics. As irradiated, the insulating characteristics showed a decreased tendency, because of produced conductive ions and gas by irradiation.