Water detection and quantification in polymers using a non-destructive microwave technique

A basic aspect of a component´s quality is the water content in the material. Water detection with non-destructivetest methods is a current subject of research in many companies and research institutes. The presence of water in polymer materials like polyamide or epoxy can be an issue in many applications (e.g. adhesive bonding, extrusionprocesses). Only a fast and accurate water measurement technique suitable for on-line or laboratory application ensures a high product quality in combination with low expenditure. In this communication, it is reported how a nondestructiveand portable device based on a microwave resonator technique accurately detects and quantifies water inthe abovementioned polymers. Polyamide-6 and epoxy samples were saturated at 70 °C and 0% rh, 11% rh, 30% rh,50% rh, 62% rh, 75% rh, 95% rh and, 100% rh, respectively. Epoxy samples were produced using Araldit GY250 as resin and isophorone diamine (IPDA) as hardener while commercially available thin polyamide-6 films (0.35 mm thickness) were used. Parameters related to the real and imaginary part of the permittivity were used to quantify the water content in these polymers. Both parameters depend on the specific gravity of the material, their ratio, however, is density independent. A linear correlation has been found between the moisture content in the epoxy samples (from 0.54 wt% to 2.48 wt%). For polyamide-6, a non-linear correlation was found allowing water quantification from 0.56 wt% to 8.14 wt%. Based on these results and due to the importance of the determination of water in composite materials, further research is in progress in order to determine the amount of water in carbon fibre-reinforced polymer (CFRP) and other fibre-reinforced composites using the same technique.