Effect of Moisture on GR-S Rate of Cure and Physical Properties
Abstract Moisture has been discussed as a factor which may give rise to variable rates of cure of GR-S. This moisture may be present in GR-S itself or in the compounding ingredients used. Accordingly, a program was initiated in the spring of 1944 to establish the influence of moisture, not only on the rate of cure of GR-S, but also on its physical properties. Since that time two papers have been published on this subject by other investigators. The results reported here verify some of the conclusions drawn by these investigators but seem to be at variance with others. In this study various proportions of water were added in the following ways : by premixing with carbon black, by adding directly on the mill rolls at the completion of normal milling, and by soaking GR-S crumb in water. Curing curves were obtained for each batch, and were used to evaluate the rate of cure. To eliminate day-to-day variations in physical properties due to error in testing methods, three batches of different moisture contents were mixed and tested on the same day. This same group was then remixed and tested on successive days until at least three batches had been tested for each moisture content and each method of addition. The averages of the individual results (stress-strain data and percentage moisture retained) on batches to which the same percentage of water was added, were then considered free from day-to-day variations.