Dielectric spectroscopy of low-losses sugar lyophiles: III

This paper presents the results of a dielectric spectroscopy study of freeze-dried lactose with a range of moisture contents. Dielectric properties were measured over a wide range of frequency (10 ⁻¹ to 10 ⁶ Hz) and temperature (−120 °C to 120 °C). Four relaxation processes were analysed with respect to moisture content and corresponding relaxation mechanisms were suggested. Two processes ( γ and β) were observed in the sub- T _g range of temperature and another two processes were observed near to and above the glass transition temperature, T _g. The relatively high-frequency γ -process was ascribed to the mobility of pendant hydroxymethyl groups and exhibited only a weak dependence on moisture content. The most moisture sensitive process was the second sub- T _g (Johari–Goldstein) β -process, whereby the relaxation time changed by 2 orders of magnitude as the moisture was increased by 7%. Also the third process ( α-relaxation, near T _g ) was sensitive to moisture content and was in good agreement with DSC data measured for freeze-dried lactose. The fourth process was a proton percolation process at the micro-crystals formed at the surface of amorphous particles during heating at the temperatures higher than T _g and shows the moisture dependence.