Measurement of high disorder state of high-density polyethylene (HDPE) on irradiation by gamma rays
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ORIGINAL SCIENTIFIC RESEARCH
Measurement of high disorder state of high-density polyethylene (HDPE) on irradiation by gamma rays V Kumar1*, A Tundwal2, N S Raghaw3, U Das1 and S Kumar1 1
Center of Advance Research, Department of Physics, Rajiv Gandhi University, Doimukh, Arunachal Pradesh 791112, India 2
Guru Teg Bahadur Institute of Technology, New Delhi 110064, India
3
Parishkar College of Global Excellence, Mansarovar, Jaipur 302020, India Received: 26 November 2019 / Accepted: 17 March 2020
Abstract: High-density polyethylene (HDPE) is irradiated to moderate gamma doses 10, 20, 30, 40 and 50 kGy to carry out the study of change in its states. It is conducted by measuring resistivity and capacitance due to scissoring of chains; hence, immergence of various functional groups in the bulk of samples is irradiated to three doses 10, 30 and 40 kGy. Enhanced resistivity is found to follow sequential change as q10kGy [ q30kGy [ q40kGy [ qpris. Fractional change of resistivity, (q - q0)/q0, at small frequencies is correlated with fractional change of volume which is measured using the positron annihilation lifetime spectroscopy to estimate index of disorder, X. Disorder index, X, is the highest in the case of sample irradiated to 10 kGy gamma dose. Electrical capacitance, C, measured across the bulk of HDPE is found maximum in the case of 10 kGy dose, while samples irradiated to 30 and 40 kGy show capacitance smaller than the pristine HDPE indicating different dielectric behavior. Similarly, dissipation factor is found to be the smallest in the case of 10 kGy than 30 and 40 kGy doses up to several thousands of frequency in Hz. In all cases, electrical capacitance is found to be sustainable at high frequencies in the pristine as well as samples irradiated to the 10, 30 and 40 kGy doses. Keywords: Polymer; Gamma irradiation; Resistivity; Mean free volume; Highly disorder resistivity
1. Introduction Polyethylene (PE) is a big molecule made of ethylene monomers (CH2). Commercial high-density polyethylene (HDPE) has density varying from 0.93 to 0.97 gm/cm3, and it is highly tensile and possesses high electrical resistance. Soft irradiation by UV and visible light has been vastly applied to produce layering of monomers and small chemical changes for enhancing strength of PE [1–4]. On the other hand, PE when irradiated to high gamma dose * 100 kGy weakening of bonds is observed and it is suggested that it can facilitate colonization of entophytic fungi [5] which helps for degradation of PE. Even hard metal like iron when irradiated to low doses of gamma rays has established that mono vacancies [6] can be produced. In the case of PE material, mono vacancies can be produced by way of scissoring of chain structure and liberation of hydrogen from the CH2 molecule and this is exploited
for developing MEMS sensors by way of hydrogen pressure dosimeter, HPD [7, 8]. These monitors are useful for monitoring the high gamma radioactivity at the high power energy reactors. Scissoring of polymer chains and development of different
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