天然ゴムの応力緩和と赤外二色性変化の同時測定

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A new method of simultaneous measurements of the changes in stress and infrared dichroism on elongation of polymer films was devised by using a double beam infrared spectrometer. The film was installed in a stretching apparatus and was placed in front of the entrance slit of the spectrometer where both the sample and the reference beams came together. Two polarizers were used : one was placed in the sample beam and the other in the reference beam. Thus the sample and the reference beams were polarized to have the electric vectors in parallel and perpendicular to the stretching direction of the film, respectively. With this arrangement the spectrometer responded only to a difference in the transmittance of the two beams. Then, by setting the spectrometer at one of the wave numbers of the absorption maxima one could record the change in its dichroism continuously during the mechanical treatment of the film. The stress generated by the mechanical treatment was transformed to the electric signal by means of a strain gage pasted on the stretching apparatus and was recorded after having been amplified. According to the theoretical considerations of this method, it is concluded that for the sample of unilateral orientation the quantity T recorded by the spectrometer is related to the orientation function F of the transition moment with respect to the stretching direction by the equation, [numerical formula], where A_0 is the absorbance of the unstretched film and d_0 and d_n are the thicknesses of the unstretched and n% stretched films, respectively. The method was applied to the stress relaxation phenomena of vulcanized natural rubber. The simultaneous measurements of stress and infrared dichroism were made at constant elongations less than 600% at room temperature. The absorption bands examined were those observed at 1664, 1380, 1361, 1129, and 844 cm^<-1>, where the last one was a crystallization-sensitive band of natural rubber. When the film was elogated, all the bands gave rise to the instantaneous dichroism to some extent, which was followed by the gradual increase except for the band at 844 cm^<-1>. These results show that there is some correspondence between the dichroic change and the stress relaxation. It is concluded that the stress relaxation observed is attributable to the molecular orientation in a amorphous region rather than the crystal orientation which is completed almost immediately after the elongation.
1965-04-15

天然ゴムの応力緩和と赤外二色性変化の同時測定

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