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Terahertz Dielectric Spectroscopic Analysis of Polypropylene Aging Caused by Exposure to Ultraviolet Radiation

1
Institute of Automation, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250014, China
2
College of Instrumentation and Electrical Engineering, Jilin University, Changchun 130061, China
3
Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
*
Author to whom correspondence should be addressed.
Polymers 2019, 11(12), 2001; https://doi.org/10.3390/polym11122001
Received: 5 November 2019 / Revised: 28 November 2019 / Accepted: 1 December 2019 / Published: 3 December 2019
Terahertz dielectric spectroscopy is shown to be an effective tool for bench-marking ultraviolet aging of polypropylene. In this, thin-film polypropylene samples exposed to standard artificial ultraviolet radiation in accelerated aging from 1 day to 30 days are closely monitored by a terahertz time-domain spectroscopy system and analyzed using an effective data processing method. It is found that the terahertz absorption of the polypropylene samples is generally weak and the terahertz dielectric constant varies slightly though discernibly during the aging process, with the refractive index decreasing slightly with increasing length of ultraviolet exposure. Nonetheless, the rate of variation of the polypropylene refractive index with increasing terahertz frequency exhibits a drastic inflection around the 15-days aging point and the rate changes suddenly from positive value to negative value. Based on this prominent and consistent THz dielectric spectroscopic feature of the aging process, an efficient judging criterion is established to distinguish the early-term, mid-term, and late-term phases as well as the degree of polypropylene ultraviolet aging, corresponding to the fundamental transformation of the polymer material from a nonpolar to a polar substance at a critical level of oxidation induced by ultraviolet radiation.
Keywords: polypropylene; ultraviolet aging; THz dielectric spectroscopy polypropylene; ultraviolet aging; THz dielectric spectroscopy
MDPI and ACS Style

Chang, T.; Zhang, X.; Cui, H.-L. Terahertz Dielectric Spectroscopic Analysis of Polypropylene Aging Caused by Exposure to Ultraviolet Radiation. Polymers 2019, 11, 2001.

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