Speaker
Description
Polyethylene terephthalate (PET) is one of the most widely used plastics worldwide and is applied, i.a., as packaging material in the food industry.[1] Like many polymers, PET is susceptible to photochemical degradation and absorbs in the ultraviolet (UV) range.[2]
As already known, UV irradiation of PET leads to shorter molecular chains and thus to a higher number of carboxyl end groups,[3,4] which was confirmed here with attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). To clarify whether this pretreatment method also affects the chain dynamics of PET, we used centerband-only detection of exchange (CODEX) and rotating-frame spin-lattice relaxation times for protons (T1ρ(1H)) to investigate PET chain dynamics on various timescales at ambient temperature (30 °C) as well as close to its glass transition temperature (70 °C) before and after UV illumination. CODEX is a one-dimensional exchange experiment which allows for characterization of slow segmental reorientations on the millisecond to second timescale,[5] whereas T1ρ(1H) times provide information about molecular dynamics on the microsecond to millisecond timescale.[6]
Both MAS NMR experiments revealed an increased mobility of the PET chains at 70 °C compared to 30 °C. Furthermore, T1ρ(1H) experiments showed slower motions after UV treatment at both temperatures and CODEX experiments indicated lower mobility for the UV illuminated sample at 70 °C.
References:
[1] World Economic Forum, Ellen MacArthur Foundation, McKinsey & Company. The New Plastics Economy – Rethinking the future of plastics. 2016.
[2] M. Day, D. M. Wiles. J. Appl. Polym. Sci., 16:175–189, 1972.
[3] M. Day, D. M. Wiles. J. Appl. Polym. Sci., 16:203–215, 1972.
[4] M. Day, D. M. Wiles. J. Appl. Polym. Sci., 16:191–202, 1972.
[5] E. R. deAzevedo, W.-G. Hu, T. J. Bonagamba, K. Schmidt-Rohr. J. Am. Chem. Soc., 121:8411–8412, 1999.
[6] K. Schmidt-Rohr, H. W. Spiess. Multidimensional Solid-State NMR and Polymers. Academic Press, London, 1994.