EPLEXOR® investigations -
The influence of humidity on the dynamic mechanical properties of paper

Products made by paper Products made by „paper” like fleece tissues for the household, coffee filters etc. are common products used nearly every day in every household. Nevertheless, industrial applications like fuel filters, industrial filters for chemical applications, fleece for sausage guts made by “papers” plays a decisive role, too. Thus, the required mechanic and thermal properties for different applications made by paper/paperboards, are frequently in a contradiction to each other. Fleece tissues in the household For sure a fleece tissue used in the kitchen shall be stabile and tearproof. Important requirements for fleece tissues are well pronounced “sucking” or absorption properties in order to remove undesired “liquids” from any surface (e.g. tables, plates). Unfortunately the stability and tensile strength of the tissues will be reduced drastically due to the absorption of liquids. These characteristics can easily be determined with the DMA/DMTS technology. DMTS investigations on dry and wet fleece tissues For that purpose a commercial available fleece tissue was taken and investigated with DMA. The measurements were carried out on dry and wet test stripes at ambient temperature in tensile mode (test frequency: 10 Hz).

Figure 1: Test results at the dry and wet fleece

For both, the dry and the wet specimen, a static load of 2 N was applied. In addition a dynamic oscillation with an amplitude of ±0.5 N was superimposed. The influence of the humidity causes directly to a reduction of the stiffness (E’) for more than 50 %. The inner damping (tan delta) changes, too. The viscosity increases for more than 40 % by the humidity absorption. The damp fleece paper was humidified with a steam push (approx. 95 % rH) briefly before the measurement. During the measurement the fleece drys up. The large surface area of the fleece paper causes a high vaporisation rate of the absorbed amount of liquid. The fleece drys up. The storage modulus increases, the damping value drops. Both measuring data approach to the dry condition.