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Terahertz Dielectric Spectroscopic Analysis of Polypropylene Aging Caused by Exposure to Ultraviolet Radiation
摘要： 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.
关键词： ultraviolet aging,polypropylene,THz dielectric spectroscopy
更新于2025-09-12 10:27:22
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Application of polybenzimidazole as a panchromatic ultraviolet absorber in poly(vinyl chloride) film
摘要： The exposure of poly(vinyl chloride) (PVC) materials to ultraviolet (UV) light can result in the destruction of the molecular structure and consequently a reduction of their mechanical properties. In this study, polybenzimidazole (OPBI) with panchromatic UV absorption was prepared by solution polycondensation and then used as a light stabilizer to improve the UV-resistance properties of PVC. PVC/OPBI composite films with different compositions were prepared by solution casting method, and the effects of OPBI content and UV irradiation time on the properties of these films were investigated by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, dynamic mechanical analysis and tensile test. The results show that OPBI has excellent UV absorption properties in the region of 220–420 nm and high thermal stability with a 3.0% weight loss at 550 °C in nitrogen atmosphere. The PVC/OPBI composite films also show excellent mechanical properties with a yield strength of 46.1–53.4 MPa, which can be attributed to the strong interactions among benzene rings, heterocyclic imidazole and chlorine atoms between OPBI and PVC. The special conjugated structure of OPBI allows the PVC/OPBI composite films to have high UV absorption and excellent mechanical properties, thus making it a promising light stabilizer.
关键词： Ultraviolet resistance,Polybenzimidazole,Light stabilizer,Poly(vinyl chloride),Accelerated ultraviolet aging
更新于2025-09-10 09:29:36