Photoacoustic study of layer thickness and moisture content from varnished packaging materials.

By means of a photoacoustic gas-cell technique we estimated the thickness of varnish layers on base paper. Interpretation of the measurements was supported by a theoretical model which describes the packaging material as a multilayer stack with freely eligible thermal and optical properties. The variable moisture content could be taken into account using mixture formulas for the definition of thermal effusivity and thermal diffusivity at different percentages of water. Satisfying correspondence between photoacoustic phase slope measurements and calculations simulating water migration was able to be achieved. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]