Ageing Of Low Density Polyethylene Research Articles

Natural weather aging of low density polyethylene: effect of prodegradant additive

The present paper reports the results of studies on the effect of a prodegradant additive, named commercially as PDQ-H, on the natural weather aging in Saudi Arabia of low density polyethylene (LDPE), with special reference to the stress–strain properties, thermal behaviour, morphology and rheological properties. Incorporation of the additive caused a sharp fall in the elongation at break of LDPE on aging. Results of rheological and Fourier transform infrared spectroscopy (FTIR) spectroscopic studies and scanning electron microscope (SEM) analysis of the blends retrieved after aging showed that addition of the prodegradant enhanced the degradation of LDPE. Results of FTIR and gel permeation chromatography studies show that the degradation occurs due to chain scission, which is presumably followed by crosslinking. These findings are corroborated by the SEM images.

Electrical treeing behavior of DC and thermally aged polyethylenes utilizing wire-plane electrode geometries

This paper presents electrical treeing behavior in low density polyethylene (LDPE) and cross-linked polyethylene (XLPE) after exposure to thermal and DC electro-thermal ageing. Both the ageing and the treeing tests were performed by means of two different types of test objects with wire-plane electrode geometry. One type of the tested objects contained only wire electrode of 10 μm diameter, whereas in the other type the wire electrode was attached through a semiconducting tab. The ageing was performed at 80°C with and without 10 kV DC voltage of both polarities connected to the wire and lasted up to 800 hours. The AC electrical treeing tests were applied afterwards for detecting changes of material properties after the ageing. The results showed that the electrical tree inception voltage consistently decreased with increasing time of thermal exposure, whereas the applied DC electric stress had a negligible effect on the observed behavior. Similar effects were found in both the tested materials (LDPE and XLPE) though the object type also influenced the results. For the objects with semiconducting tab, a higher level of the scale parameter was registered because of shielding effect of the tab on the electric field strength at the wire electrode. It also yielded less number of trees growing in parallel at the electrode. The dominant effect of thermal stress on the ageing of LDPE was elucidated by using various analytical techniques, like differential scanning calorimetry, infrared spectroscopy, inductively coupled plasma optical emission spectrometry and oxidation induction time, and it is believed to mainly affect antioxidant content in the test objects.

Electrical treeing behavior of DC and thermally aged polyethylenes utilizing wire-plane electrode geometries

This paper presents electrical treeing behavior in low density polyethylene (LDPE) and cross-linked polyethylene (XLPE) after exposure to thermal and DC electro-thermal ageing. Both the ageing and the treeing tests were performed by means of two different types of test objects with wire-plane electrode geometry. One type of the tested objects contained only wire electrode of 10 μm diameter, whereas in the other type the wire electrode was attached through a semiconducting tab. The ageing was performed at 80°C with and without 10 kV DC voltage of both polarities connected to the wire and lasted up to 800 hours. The AC electrical treeing tests were applied afterwards for detecting changes of material properties after the ageing. The results showed that the electrical tree inception voltage consistently decreased with increasing time of thermal exposure, whereas the applied DC electric stress had a negligible effect on the observed behavior. Similar effects were found in both the tested materials (LDPE and XLPE) though the object type also influenced the results. For the objects with semiconducting tab, a higher level of the scale parameter was registered because of shielding effect of the tab on the electric field strength at the wire electrode. It also yielded less number of trees growing in parallel at the electrode. The dominant effect of thermal stress on the ageing of LDPE was elucidated by using various analytical techniques, like differential scanning calorimetry, infrared spectroscopy, inductively coupled plasma optical emission spectrometry and oxidation induction time, and it is believed to mainly affect antioxidant content in the test objects.

Transition metal catalyzed oxidative aging of low density polyethylene: effect of manganese (III) acetate

The paper discusses the effect of manganese (ІІІ) acetate in the degradation of low density polyethylene (LDPE). Stearic acid has been used as a dispersion promoter to circumvent non-uniform dispersion of inorganic compound like manganese (ІІІ) acetate in LDPE. A detailed study has been made to investigate the effect of dispersion promoter on degradation of LDPE. The combined effect of dispersion promoter and manganese (ІІІ) acetate has been studied in accelerated aging of LDPE. Masked degradation of LDPE has been noted in presence of natural rubber (NR). The degradation processes of LDPE eventually have been observed to follow different mechanistic pathways in presence of dispersion promoter and transitional metal catalyst. At an optimized condition of time and temperature, LDPE has been found to be degraded into a semi-solid state in combined presence of manganese (ІІІ) acetate and the dispersion promoter. The Arrhenius equation has been adopted to predict the life time of the LDPE having different amount of manganese (III) acetate.

Study of natural aging of industrial low density polyethylene by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to study the natural outside aging of industrial low density polyethylene (LDPE) under the influence of one year round weather. Two types of LDPE were studied. The first type was LDPE without additives and the second type was doped with 4% of hindered amine light stabilisers (HALS). Unstabilised and 4% HALS stabilised LDPE samples underwent an oxidation of the polymeric matrix, by the production of C–O, C=O and O=C–O groups. These chemical functions were observed in high resolution XPS spectra around C1s and O1s peaks. From these results, it was then possible to propose mechanisms of natural aging of LDPE in such conditions. On the other hand, there is no clear evidence that HALS could be effective in natural aging for the polymer surfaces with exposure to the elements.

The effects of tensile stress and the agrochemical Vapam on the ageing of low density polyethylene (LDPE) agricultural films. Part I. Mechanical behaviour

The effect of tensile stress and of a drastic agrochemical (Vapam) on the ageing of low density polyethylene (LDPE) greenhouse films is presented. The synergistic effect of these two critical ageing factors with UV radiation and temperature on the ageing of selected LDPE films was investigated under artificial ageing conditions. The LDPE used in the present work was non-stabilised in order to investigate the basic characteristics of ageing in a very short period. The ageing was monitored through the changes of selected mechanical properties of the polyethylene film before and after ageing. A modified artificial ageing procedure is proposed, considered to simulate in a more realistic way the weathering of LDPE greenhouse films.

Natural weathering, artificial photo‐oxidation, and thermal aging of low density polyethylene: Grafting of acrylic acid onto aged polyethylene films

AbstractThe photo‐oxidation and thermal initiation changes of commercial low density polyethylene (LDPE) films used in greenhouse covering, in the presence or absence of ultraviolet (UV) stabilizer, were monitored by infrared (IR) spectroscopy, by mechanical tests and by applying the grafting of acrylic acid onto the aged films. It was found that the resistance of PE films to UV irradiation and heat initiation as proved by tensile strength and elongation at break % was better for stabilized PE films compared with the unstabilized ones. A simple correlation was not observed between the fall in mechanical properties and the rate of film oxidation. On the other hand, an almost linear relation was obviously noticed between the degree of PE oxidation (CO) measured by IR spectroscopy and the grafting level. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2365–2371, 2003

Dielectric behavior of aged polyethylene under UV radiation

The present paper reports the results of a study of dielectric aging of low-density polyethylene (LDPE) by UV radiation. The extruded polymer contained carbon black particles, approximately 3% in weight. The aging studies were made for polymer without and with carbon black. LDPE flat specimens were aged under UV radiation for up to 300 h, resorting to dielectric spectroscopy measurements in the frequency range from 10/sup -5/ Hz to 10/sup 5/ Hz. The dielectric susceptibility behaviors indicate the presence of relaxation peaks obeying the asymptotic forms of Dissado and Hill susceptibility functions. As the aging progresses, quasi-DC and flat loss processes may be observed in the low frequency range, for the LDPE specimens without and with carbon black, respectively. In addition, dielectric spectroscopy results have been compared with other results obtained with additional techniques such as Fourier transform infrared spectroscopy and scanning electron microscopy.

Suppression of electrical treeing by addition of lithium carbonate to low-density polyethylene

Low-density polyethylene (LDPE) is used widely as an electric insulating material in electric power cables. The generation of electrical treeing due to aging of LDPE may lose the reliability of its insulating capability. Therefore it is important to suppress its treeing and to improve its electrical properties so that the reliability of cables can be improved. For this purpose, the authors prepared LDPE to which various inorganic materials were added. This investigation focuses particularly on lithium carbonate and quartz which were effective in suppressing the treeing when added to LDPE. Lithium carbonate-added (0.25 phr) LDPE in two hours of discharge showed the tree length 150 μm shorter than that (560 μm) of nonadded LDPE, exhibiting an obvious suppressing effect on treeing generation. It was found that this effect was more significant than quartz-added LDPE and even at elevated temperatures lithium carbonate-added LDPE exhibited suppression of treeing. The thermal decomposition temperature at which lithium carbonate-added (1 phr) LDPE loses 50 percent of its weight rose 100°C more than nonadded LDPE and 60°C more than that of quartz-added LDPE, which showed improvement in heat resistance of LDPE.

Photooxidative ageing of low density polyethylene. Kinetics determined by an electrical method

AbstractThe efficiency of light stabilizers is investigated by electric methods in the initial stage of photooxidative ageing of low density polyethylene (LDPE). Three types of UV light stabilizers are tried to improve the UV stability of LDPE: a phosphite type (3,9‐bis‐[(2,4‐di‐tert‐butyl)phenoxy]‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro[5.5]undecane) a benzophenone type [2‐hydroxy‐4‐octyloxy‐benzophenone] and a stabilizer based on chelate salt [2,2′‐thiobis(4‐tert‐octyl phenolato) (n‐butylamine) nickel (II)]. LDPE is very susceptible to ultraviolet light. UV light stabilizers improve the stability of low density polyethylene for electrical applications, especially the UV stabilizer based on chelate salt.