Effect Postcure of a Rubber Sheet

Early works [24,25] concerned with the study of the profiles of temperature and state of cure developed through the rubber mass, after it was extracted from the mold and allowed to cool down in motionless air at room tanperature, already showed that an increase in the state of cure could be expected during the cooling period. Moreover, an improvement in physical properties such as the swelling in toluene and mechanic properties measured either under static or dynamic conditions [16] has been found. 

Some other studies were made with the objective to determine the increase in the state of cure associated with the conditions of the post cure as well as the value of the state of cure of the material when removed from the mold [24-26]. 

two parameters were especially considered, such as the value of the cure enthalpy [25] and the value of the temperature of the motionless air in which the post cure is achieved [26]. Thus the increase in the state of cure obtained at the mid-plane of the rubber sheet was found to vary linearly with the value of the cure enthalpy. Obviously the lowest value of the coefficient of surface heat transfer at the rubber surface during the period of postcure is desirable 

The increase in the state of cure in vulcanizates after removal from the mold is evaluated when the rubber sheet thickness is rather large, this thickness being of 4 cm. The other characteristics are as follows Temperature of the mold = 170°C 

FIGURE 4.28 Cooling of a rubber sheet of thickness (2L) = 4 cm and postcure in stirred water at 20°C. Cure at 170°C in such a way that the SOC = 80% at the mid-plane. Heating system on the rubber surface. Surface thermal coefhcient h = 276W/(m deg). Profiles of SOC (left) and temperature (right) during the postcure. 

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