The thermal conductivity of paper was measured using a thermoacoustic method based on the propagation of a periodic temperature wave in the medium. Thermal diffusivity and thermal conductivity can be calculated from the resulting phase shift.
The thermal conductivities of sheets prepared from different pulps were measured under standard conditions and at 70°C and 10% RH.
In paper, heat is conducted through both the solid phase and the gaseous phase. In the case of dense paper and at high moisture contents, heat transfer due to diffusion of water vapour makes a major contribution.
The results were used to construct a qualitative physical model for the conduction of heat in paper. In the normal paper density range of 400 – 900 kg/m³ heat conduction can be explained in terms of layers of air and solid phase connected together in different ways.
At higher densities and higher moisture contents the mechanisms of hear conduction change.
The heat conduction characteristics of paper are better explained using thermal diffusivity calculated in terms of basis weight than by using thermal diffusivity and thermal conductivity.