Investigation of the water absorption in polyamide and wood plastic composite by terahertz time-domain spectroscopy

We employed terahertz time-domain spectroscopy to study the sorption of water into two different materials: polyamide (PA) and wood plastic composite (WPC). The dielectric properties of the samples were determined for frequencies between 0.2 and 1.0 THz for varying water contents. A model for the dielectric behaviour depending on the water content was developed and experimentally verified. For both materials, we calculated the refractive index and the absorption coefficient of bound water in the respective polymer and correlated our findings with results from gravimetric measurements. The sensitivity of terahertz radiation to water suggests that this technique is an ideal tool for a non-destructive, contactless determination of the water content.