Mooney scorch

Fig. 6. Comparison of secondary accelerators where represents Mooney scorch at 121°C and U, optimum (t90) at 153°C A, the primary accelerator is 0.75 phr MBTS and the secondary accelerator is at 0.25 phr B, 0.45 phr TBBS is the primary accelerator and there is 0.2 phr secondary accelerator.

The name Mooney is often used in referring to the value obtained on the Mooney viscometer. Mooney Scorch Test... 

The determination of the ability of a rubber compound to withstand scorching. See Mooney Scorch Test. 

Reduction of up to 10% of the accelerator content may be permissible without seriously affecting the physical properties of the product. This will increase the mooney scorch time by as much as 4 units which is a safe condition. 

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. 

Figure 24 Typical Mooney scorch curve for a rubber compound with curatives.

A lower cure index represents a faster cure rate. There is a limit, however, to the cure information that a Mooney scorch test can provide as the cure advances beyond rix (for a small rotor) and (for a large rotor). This is because as the specimen cures and builds a cross-linked matrix, it loses flow properties and begins to slip and tear on the rotor [95]. 

As discussed earlier, the Mooney scorch test can measure time to scorch and provide some information regarding the rate of cure. However, because the Mooney rotor rotates continuously. slipping and tearing of the specimen occur well before the ultimate state of cure is reached. It is not possible to observe the entire cure curve with the Mooney viscometer. 

R Radical pkj, of Free Amine Mooney Scorch Cure Rate Index at135°C... 

Mechanical properties of PALF-reinforced natural rubber composites were studied in Bhattacharya et al. (1986) in which PALF addition increased hardness, compression set, tear resistance, and Mooney viscosity. However, elongation at break, mill shrinkage, and Mooney scorch time decreased. The use of resorcinol, hexamethylenetetramine, and silica is essential for PALF-rubber adhesion. PALF-reinforced... 

Mooney scorch time n. For a rubber specimen tested in a Mooney viscometer, the time elapsing after the minimum torque has been reached for torque to increase by five Mooney units . 

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