Fraunhofer Institute for Electron Beam
and Plasma Technology FEP
Fraunhofer Institute for Electron Beam
and Plasma Technology FEP

Materials / Analysis

New possibilities for determination of water vapor permeability / transmission rate of coated polymer films

© Fraunhofer FEP
WVTR permeation cell with a coated polymer film

The accurate determination of water vapor permeability is a prerequisite for the development of tailor-made encapsulation films for a wide range of requirements. Fraunhofer FEP has extensive measuring methods and the necessary experience for this.

Barrier layers on polymer films are required to reduce the water vapor transmission rate (WVTR) for food packaging, electronic components, and flexible solar cells to achieve sufficient durability or lifetime. Depending on the application, the requirements for WVTR values vary greatly and range from less than 5 × 10-4 g/m2d for flexible solar cells to 1 g/m2d for food packaging.

When determining the water vapor transmission rate according to ISO 15106-3, the amount of permeated water vapor is registered with an electrolysis cell. The measured electrolysis current is directly proportional to the WVTR, so that a determination is possible without additional calibration. By investing in a new measuring device (Aquatran 3; Mocon), we can now also detect very low WVTR values of 5 × 10-5 g/m2d. The upper measuring limit of the available measuring devices (WDDG, Brugger) is a WVTR value of 10 g/m2d, so that a very wide WVTR measuring range for a broad variety of applications is completely covered. 

Supplementary to the electrolysis method, we also have another measurement device (HiBarSens 2.0 HT, Sempa) in which the WVTR is determined by laser diode spectroscopy of a water vapor absorption band. Depending on the measurement mode used, very low detection limits of 1 × 10-5 g/m2d (diffusion mode) or 1 × 10-4 g/m2d (carrier gas mode) can also be achieved with this method. In addition, the temperature of the permeation cell can be varied in the range from 10°C to 85°C, allowing the investigation of influence of temperature on permeation. Determining the WVTR values at different temperatures allows additionally the evaluation of the activation energy for permeation. The measurement time required for permeation to reach equilibrium can be reduced by increasing temperature, which increases the effectivity of the measurements.

Thanks to our extensive measurement technology and experience, we can effectively and precisely measure the water vapor permeability of coated polymer films for a wide range of requirements. Determining the WVTR values as a function of temperature additionally enables a better understanding of the occurring permeation mechanisms.