Relaxation Behavior and Crystallization Kinetics of Amorphous Acetaminophen

Relaxation behavior and crystallization kinetics of amorphous acetaminophen are studied by dielectric spectroscopy and standard DSC. Isothermal crystallization experiments at temperatures from 2K below to 35K above the thermal glass transition of amorphous acetaminophen (Tg = 24°C) have been performed. We demonstrate that dielectric on-line measurements provide detailed information about the crystallization kinetics. Dielectric and calorimetric results consistently show that the crystallization slows rapidly down if the crystallization temperature Tc approaches Tg since the mobility is significantly reduced. Polarization microscopy images show that a few large spherulites grow in ultra-viscous acetaminophen. It is discussed why solid-like acetaminophen can also crystallize on time scales of days and weeks in the glassy state below Tg.