The Variation with Temperature of the Dynamic Properties of Rubber and Synthetic Rubberlike Materials. II. Compounded Rubbers

Abstract

The whole of the dynamic modulus results may be summarized as follows. (1) A general sensitivity to temperature over the range studied is shown by all rubbers, natural and synthetic. (2) Natural rubber is least sensitive, followed by Neoprene-GN and GR-S. Next in order come Neoprene-YD and butadiene-acrylonitrile copolymers with low acrylonitrile contents. In general, the higher the acrylonitrile content, the more sensitive to temperature is the polymer. Neoprene-Z is only slightly less sensitive than Hycar OR-15 (45–55). (3) Broadly speaking, the effect of compounding with P-33 black and gas black is to increase the sensitivity to temperature. Notable exceptions are Neoprene-GN and GR-S containing extender, which appear almost unchanged, and Neoprene-YD, which shows a decreased sensitivity with loading. (4) It is evident from the results that any specification for dynamic modulus should be accompanied by a specified temperature of test; in design, account must be taken of the variations which it has been shown can be quite considerable for synthetic rubbers now coming into commercial use, even under normal seasonal variation of temperature. (5) Static methods of determining freeze points, e.g., torsion and bending tests, in general place materials in a similar order with respect to their low-temperature behavior as the present dynamic experiments, although no appreciable temperature effects are noted in the temperature range of the experiments discussed here. The results of resilience measurement are not easy to summarize. Suffice it to say that, over the limited range of temperatures investigated, very great differences in resilience are observed between different polymers. The superiority of natural rubber is again evident, although it is somewhat less marked in loaded stocks. In the case of Thiokol-RD and Hycar OR-15, minima in the resilience curves are indicated at 23° C and about 10° C, respectively. This has been reported by previous workers. In all polymers the resilience-temperature curve is in two parts, with a more or less sharply defined transition point, the temperature of which seems to depend largely on the chemical structure of the polymer. Again this is confirmed to some extent by reference to the literature.