Physico-Chemical nanomaterials science

Effects of molecular structure on dielectric relaxation of substituted cellulose

A. Sobchuk1, M.M. Lazarenko1, K.S. Yablochkova1, R. V. Dinzhos2,3, M.V. Lazarenko4, D. A. Andrusenko1, О.М. Alekseev1 

1 Taras Shevchenko National University of Kyiv, Physical Faculty, Volodymyrs’ka St. 64/13, Kyiv 01601, Ukraine.
E-mail: litrboychik@gmail.com
2 V.O.Sykhomlynsky National University of Mykolayiv, Mykolayiv, Ukraine
3Institute of Engineering Thermophysics of NAS of Ukraine, Kyiv, Ukraine
4National University of Food Technologies, Volodymyrs’ka St. 68, Kyiv-01601, Ukraine.
Cellulose, either plant- or bacteria- derived, is one of the most versatile bio-based materials in existence. The plethora of cellulose applications calls for the close study of its properties. The present research focuses on the investigation of the dielectric properties of hydroxypropyl methylcellulose in which a varying number of hydroxyl groups are substituted by hydroxypropoxy groups. Here we present the results obtained for the microcrystalline cellulose produced by Chemfild Cellulose Pvt. Ltd. (0% substitution degree) and hydroxypropyl methylcellulose samples with different degrees of hydroxypropoxy group substitution: Metolosa 65SH50 ShinEtsu (6%), Pharmacoat 904 ShinEtsu (10%), L-HPC NBD-020 ShinEtsu (15%), HPC AlfaAesar (76%).
We have obtained temperature dependences for the complex dielectric permittivity of the samples at different frequencies. In all samples, a dielectric relaxation was observed between -120 to 40 oC, suggesting the dipole relaxation polarization.
We have previously shown that the dielectric relaxation in MCC is caused by the conformational motion of methylol groups on the surface of nanocrystals. As the degree of substitution of hydroxyl groups increases, the dielectric relaxation occurs at higher temperatures. We have calculated the parameters of the relaxation processes observed. Using these calculations, we show that as the number of hydroxypropoxy groups increases, both the activation energy of the dielectric relaxation and the change in the dipole moment per unit volume also increase. We can thus infer that the conformational motion of the hydroxypropoxy group contributes to the dielectric relaxation at higher temperatures than the conformational motion of the methylol groups, as the conformational motion of the hydroxypropoxy group requires higher thermal energy.