Dynamic Measurements of Physical Properties of Pulp and Paper by Audiofrequency Sound

The dynamic Young's moduli of various types of paper were measured by the vibrating reed method. The Young's modulus of paper increases statistically at a rate approximately proportional to the square of its density. The modulus and density of paper increase with the degree of beating. The sulfite and sulfate fibers behave differently during beating. The angular dependence of Young's modulus, tensile strength, and elongation at break was analyzed mathematically; and the results were verified by experiments. According to this theory, the mean value of Young's modulus and tensile strength of machine‐made paper should be expressed by the geometrical mean of the values of the machine and cross directions, whereas the mean value of elongation can be given by the arithmetical mean. The removal of parenchyma cells is very effective in reducing the Young's modulus of dissolving pulp. The viscoelastic properties of paper were observed within the frequency range from 20 to 180 cps. The dynamic modulus and mechanical loss factor of the sheets employed were found to be smaller than one‐tenth of those of cellulose films. The interfiber deformation influences the dynamic properties of paper.