TEARING OF UNVULCANIZED NATURAL-RUBBER

The tear behavior of unvulcanized natural rubber has been studied by using established techniques normally adopted for the study of vulcanized rubbers. Unvulcanized rubber has been found to tear in a relatively steady manner, in contrast to the stick-slip tear behavior of the vulcanized rubbber, the tearing energy being dependent on the rate of tearing. Crystallization seems to be an important factor in determining the tear behavior since it has not been found possible to tear unvulcanized SBR under the same conditions. The effect of the pronounced imperfect elastic nature of the material was studied under conditions where the driving force for tearing was solely governed by the rate of release of elastic energy. Under such conditions, it has been found that the tearing energy is determined not by the strain energy required to stretch the material but by the energy which can be recovered on retraction.