Humidity response of Kraft papers determined by dynamic mechanical analysis

Dynamic mechanical analysis combined with relative humidity (DMA-RH) was used to examine the viscoelastic properties of standard Kraft and extensible Clupak paper in dry and humid atmosphere. Knowledge regarding these viscoelastic properties combined with the natural hygroscopicity of paper is fundamental for the prediction of paper behaviour under stress conditions. Results from DMA-RH under dynamic (frequency/strain experiments) and static measurement modes (creep/recovery experiments) indicated that the change of paper structure during the Clupak process is significant. Marked changes in elongation and stiffness as well as relaxation ability of Clupak paper were found. DMA-RH allows the combining multiple conditions (frequency, temperature, time, load, and humidity) during a single measurement and it can thus simulate similar conditions to those in paper processing and product-use.