In-situ non-contact monitoring algorithm for PET crystallinity and moisture content using Terahertz time-domain spectroscopy

A terahertz time-domain spectroscopy (THz-TDS) system was used to monitor the crystallinity and moisture content of polyethylene terephthalate (PET) specimens. The crystallinity and moisture content were varied by controlling cooling rate and immersion time. Crystallinity, crystallite size, and moisture content of the PET specimens were measured through differential scanning calorimetry (DSC), x-ray diffraction (XRD), and gravimetric methods, respectively. The THz signal with regard to crystallinity and moisture content was subsequently analyzed within the time and frequency-domain. In addition, optical properties of refractive index and absorption coefficient were derived. Consequently, the crystallinity and moisture content could be simultaneously measured by analyzing the THz signals. •The THz amplitude ratio and the moisture content have a negative correlation.•The Low/high amplitude ratio and the degree of crystallinity have a negative correlation.•Degree of crystallinity and moisture content affect electro-magnetic properties.•Degree of crystallinity and moisture content of PET can be monitored in an in-situ condition using a terahertz system.