Knotty tearing temperature

Figure 5.12 The effect of degree of crystallinity and glass transition temperature on development of knotty tearing energy as a function of tear rate at 23 °C. (Reproduced from ref. 8).

The effect of strain crystallization on the development of knotty tearing is clearly noticeable when all the tear measurements are done at relatively the same molecular mobility as NR. The legends in Figure 5.12 show the glass transition temperature and the degree of crystallinity of each rubber. The legends in Figure 5.13 show the required temperature of tear measurements for each rubber in order to get about the same molecular mobility as NR. It is... 

The tear properties of rubber depend on tear rate and temperature. At low rates, tear has a knotty appearance, whereas tearing at high speeds proceeds steadily, and the torn surfaces are much smoother. In the absence of reinforcement or crystallization, tear behavior is dominated by hysteretic properties in the viscous phase of the rubber. It is related directly to the relaxation of stress that occurs at the tip of the growing tear. 

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