Abstract
The dynamic elastic modulus of cellophanes has been measured by use of the resonant frequency of a 2 × 60‐mm. strip of film in longitudinal vibration. The niodulus was computed from the resonant frequency length of specinieii, and the cross‐sectional area determined from its resonant frequency in transverse vibration. The apparatus is described briefly. Unsoftened film and glycerol‐softened films containing 7.3, 13.7, and 21.3% glycerol prepared from the same roll of never‐dried regenerated cellulose were conditioned a t 75°F. and 15, 35, and 81% R. H., and the elastic moduli were measured in both directions. Moisture and softerier contents were determined. The reciprocals of the geometric means of the moduli in the machine and transverse directions were plotted as a function of the volume of film containing 1 g. of cellulose. The displacement of the curve obtained for each softened film from the curve for the unsoftened film measures the effect of the softener, since the curves would coincide if the effect of softener were from swelling only. This permits construction of an empirical equation for the modulus of these glycerol‐softened films as a function of moisture and softener content. It was found further that the logarithms of the corrected compliance (1/EV^2/2^~c~), where E is the geometric mean modulus and V~c~ is the volunie of film containing 1 g. of cellulose, gave a straight line when plotted as a function of the number of moles of water plus twice the number of glycerol present in 100 g. of cellulose. This indicates that the effect of a mole of glycerol in breaking up the hydrogen‐bonded structure of the cellulose is twice as great as that of a mole of water. These results have been compared with similar results obtained on films containing ethylene carbonate and ethylenediamine. With the exception of ethylenediamine‐treated films studied a t high humidities, these fdms gave points falling approvimately on the corrected compliance curve obtained for the glycerol‐softened and unsoftened films. For these films, however, the simple sums of moles of water plus moles of ethylene carbonate or ethylenediamine monohydrate present in 100 g. of cellulose were used rather than the weighted sum used for the glycerolsoftened films.