The Absorption of Water by Rubber and Its Relation to the Protein Content

Abstract

Abstract 1. The absorption of water by rubber is dependent upon the degree of division, and comparable results are obtained in a reasonable time only by using shredded samples of rubber. 2. The moisture in rubber appears to be present in two forms, (a) that removed after, say, three days, over sulfuric acid, and (b) what has been termed the residual moisture, which is more difficult to extract from the rubber, but which is evolved by heating the sample for an hour or so at 100° C. In general, the higher the protein content the lower the percentage of residual moisture. 3. Solutions of sulfuric acid provide suitable means of adjusting the humidity of the air. 4. The temperature must be kept constant to avoid deposition of dew upon the rubber. 5. The rate of absorption of moisture decreases rapidly after the first 24 hours of exposure to the prescribed atmosphere. The absorption after 5 days is very slow, and equilibrium was attained in approximately one week. 6. In general the rate of absorption is higher with rubbers containing a large percentage of protein matter. The rate of absorption in an atmosphere of humidity of less than 80 per cent is slow, and for experimental purposes a humidity of approximately 95 per cent is shown to be suitable. 7. It has been found that the ratio of the water absorbed at a constant humidity to the residual moisture is in all cases related to the protein content. 8. In general, the total weight of water absorbed per 100 parts of rubber rises with rising protein content provided the humidity of the air in contact with the rubber is 85 per cent or higher. 9. The proportion of moisture absorbed in atmospheres of less than 70 per cent humidity is small, but increases rapidly with increasing humidity.