The Effects of Elastic Stretch on the Infrared Spectrum of Rubber

Abstract

The absorption spectrum of stretched rubber has been studied in the region between 2μ and 8μ. In the case of unilateral stretch transmission measurements indicate that the absorption bands near 3.3μ and 7μ become broader with increasing stretch while the general background absorption becomes more pronounced. Radial stretch was found to produce similar effects in the 3.3μ and 7μ regions while the bands near 6μ became less intense for both unilateral and radial stretch. In the spectrum of rubber stretched radially to approximately twelve times its original area a band was observed near 4.8μ in a region where there is no intense absorption in the unstretched material. Since both absorption and reflection are involved in transmission measurements, it was necessary to determine reflection and extinction coefficients. The results indicate that the reflection coefficient diminishes and the extinction coefficient increases with increasing stretch. The observed variations in the extinction coefficients are of greater magnitude than those to be expected from the known density changes which accompany stretching.