Mooney scorch time

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. 

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 . 

The Mooney scorch times of ENR mixes can be increased by the use of commercial prevulcanization inhibitors (PVI) once the base has been added. The response of these materials depends on the cure system employed and parallels that observed with NR and other unsaturated polymers. 

Mooney Scorch Time is the total running time to reach a viscosity of five or ten units above the minimum (ts or tio). It is used as a rough measure of the processable life of a compound under normal processing conditions -the greater the scorch time, the longer the processable life. A common test temperature for Mooney Scorch measurements is 121 C (250°F), but some processors may use different temperatures because of particular factory experience. 

Combinations of MgO and PbOa are preferred for maximum heat resistance. Water resistance is also improved with the combination as compared with htharge alone. The best combination is 5 phr MgO with 5 phr Pb02 for optimum retention of elongation and tensile strength. This also gives the better Mooney scorch time. 

An additional experiment was conducted with the medium Mooney and ACN NBR compound given in Table 15.4 in which a comparison was made of Struktols WB 222, WA 48, and HPS 11. The additives had a similar reduction in compound viscosity and spiral flow characteristics, but Struktol HPS 11 provided greater capUlaiy rheometer flow at 125°C as seen in Figure 15.2. There was a very significant improvement in Mooney scorch times when Struktols WB 222 or WA 48 were included in the compound and to a lesser, but still significant extent, with Struktol HPS 11. 

This article describes the performance of a new curative for polychloroprene, a derivative of 2,5-dimercapto-1,3,4-thiadiazole (DMTD). This curative provides long Mooney scorch times, rapid cure rate resulting in short cure times and an exceptionally flat cure plateau. Other performance characteristics are presented, including the effect of other additives in a typical polychloroprene formulation. 5 refs. 

Mooney viscometer is also used to measure the time it takes, from initial exposure of the compound to a particular temperature, to the time of onset of cure at that temperature [2]. This is known as the scorch time. Scorch time is an important parameter to the rubber processor, as a short time may lead to problems of premature vulcanization. As the test is taken past the onset of cure, the rotor tears the cured rubber, and therefore this device cannot be used to investigate rheological properties after the scorch time. 

An early cure instrument which combined in one operation the functions of a Mooney viscometer and of a curometer or vulcameter, i.e., it measures in one quick test the plasticity (viscosity) of the (uncured) mix, its scorch time and cure rate. Now superseded by instruments such as the moving die rheometer. 

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. 

Scorch, Mooney The time to incipient of a rubber compound when tested in the Mooney shearing disc viscometer under specific conditions. 

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. 

Mooney scorch is the time to incipient cure a rubber compound in a test in the Mooney shearing disk viscometer. 

Figure 9.1 Effect of blend ratio on Mooney viscosity (a) and scorch time (is2) along with optimum cure time (tc90) (b) of the compounds.

Mooney viscosities were determined with the large rotor after a one minute warm-up, followed by four minutes at 212°F. Mooney scorch tests were made with the small rotor at 250°F. Time to scorch was three units above the minimum and cure time was taken at eighteen units above the minimum. 

The Mooney Viscometer test is one of the oldest processability tests in the rubber industry. Many processors now prefer the oscillating disk rheometer (ODR) for measming cme time and cme rate, but the Mooney Viscosmeter is usually preferred for viscosity and scorch time measmements. 

Mooney Scorch (MS 121°C) Minimum Viscosity, units Time to Ten Point Rise, Minutes... 

Amount of filler, phr Stock properties Mooney viscosity ML 1 -H 4 at 100°C Mooney scorch, MS at 121°C Minimum viscosity, units Time to 10-unit rise, min... 

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