Viscosity rise during cure

Viscosity Rise during Cure of Neat Unsaturated Polyester... 

Figure 14.22 Prediction of viscosity rise during cure of OC-E701 with 1.0 wt % TBPB as initiator at various temperatures (°C) (O) 30, (A) 40, ( ) 45, (V) 50, (O) 55, and (O) 60. The prediction is made from the numerical solution of Eqs. (14.16)-(14.19) together with Eqs. (14.20), (14.22), and (14.23), using the values of the parameters given in Table 14.4, and then from Eq. (14.13).

Castro (1980) has shown that use of reduced viscosity, suppress the temperature dependence, where is the viscosity before cure begins. Figure 14.41 gives plots of log versus a for the same urethane system, showing indeed almost temperature independence. Figure 14.41 suggests that the viscosity rise during isothermal cure of the... 

The thickness of the adhesive layer is of importance in most adhesive joints and shonld be measnred and controlled in Tests of adhesion. Adhesive layer thickness is often determined by a nnmber of factors, some intentional in the design process and some resnlting from a variety of items related to the adhesive properties and the processing steps. Factors affecting the final bond thickness inclnde adhesive viscosity (which may fall dramatically and then rise during elevated temperature cure), clamping pressure and... 

Figure 1 illustrates the curing process as measured by a rheometer. The rheometer follows the development of cure state as a function of time. Vulcanization characteristics such as minimum torque Ml (a measure of compound green viscosity), onset of cure (T1 pt rise), Mh (a measure of maximum cure state reached), and T90% cme (time required to reach 90% cure state) are valuable properties defining cure behavior. Likewise the rheometer cure profile can be broken into three regions of interest, an estimate of scorch safety, an idea of what the cure state development looks like during the cross-linking phase, and how the cross-linked vulcanizate network matures with additional heat. 

Fig. 50. Schematic representation of ion and dipole behavior at various stages of thermoset cure (a) beginning of cure in liquid state, (b) during cure as viscosity begins to increase, and (c) after sharp rise in viscosity severely restricts dipole mobility (75).

Mooney viscosity—measure of the resistance of raw or unvulcanized rubber to deformation, as measured in a Mooney viscometer. A steel disc is embedded in a heated rubber specimen and slowly rotated. The resistance to the shearing action of the disc is measured and expressed as a Mooney viscosity value. Viscosity increases with continued rotation, and the time required to produce a specified rise in Mooney viscosity is known as the Mooney scorch value, which is an indication of the tendency of a rubber mixture to cure, or vulcanize, prematurely during processing. 

---