The degree of polymerization and the number of molecules in synthetic rubber can be shown by the Mooney viscosity. The Mooney viscosity shows how well rubber can be worked with, how heavy its molecules are, and how wide or narrow its distribution range is. The value of Mooney’s viscosity is closely linked to its plasticity. A high viscosity value mostly affects how well raw rubber and synthetic rubber can be processed. This means that the rubber has a large molecular weight and is not very flexible. Rubber, on the other hand, has a low molecular weight and can bend well.
If the Mooney viscosity is too high, it is hard to work with. If the Mooney viscosity is too low, the tensile strength of vulcanized products will be low, and the performance may not meet the requirements. Controlling the Mooney viscosity of rubber makes it easier to mix, calendar, extrude, inject, and mold, so the vulcanized rubber has good physical and mechanical properties.
What is the Mooney method of viscosity?
Using a Mooney viscometer, the Mooney viscosity method measures how flexible rubber compounds are. The way it works is to measure the sample’s shear resistance when the rotor is turning at a certain temperature, time, and pressure, and then use different torques to show how flexible the rubber compound is.
For the test, the mold cavity is heated to a constant temperature of (100 °C). The sample is then put into the mold cavity, heated for a certain amount of time, and the viscometer starts to work. Watch the scale value of the instrument as its rotor turns. The value shown is the rubber’s Mooney viscosity, which is also called “Mooney viscosity” for short.
The more Mooney viscosity a compound has, the more viscous it is (i.e., the lower the plasticity of the compound). The Mooney viscosity value changes depending on how the test is done, so the method of recording the test should say how the test was done. Most of the time, ML1 + 4100 °C is used to show the Mooney viscosity. Where m is Mooney and L1 + 4100 °C is the torque measured after heating the large (38.1mm) rotor for 1 minute and turning it for 4 minutes (its value is indicated by a dial indicator). The viscosity of Mooney ranges from 0 to 200.
Mooney viscosity is a measure of how thick a substance is under certain conditions and can be used directly as an index to measure its rheological properties. But because this method is slow and has a low shear rate, it can only show the rheological properties of a substance at a low shear rate. If the speed of the test is increased, the result is more like what will happen when the material is processed.
The Mooney viscosity method is a quick and easy way to test how flexible a rubber compound is, and it doesn’t require making samples in standard shapes. Also, the method makes it easy to measure the scorch time of the rubber, which is the time it takes for the Mooney viscosity to drop to its lowest value and then rise by 5 Mooney values after preheating the rubber at 120 °C for 1 minute with a rotor with a diameter of 30.5 mm. This lets you know right away if the rubber is safe to process. So, scientists and manufacturers use the idea of Mooney viscosity a lot in their work.
How does a Mooney viscometer work?
The Mooney viscometer is a standard rotor that uses intelligent digital temperature control technology. It is easy to set and adjust and has a wide temperature control range. The imported chips in the microcomputer are very reliable. All of the data can be automatically drawn, calculated, and printed. Turn the sample at the same speed as in the closed chamber (generally 2 RPM).
The change in the sample’s viscosity during vulcanization is linked to the rotor’s shear resistance as it turns. Through the force measuring tool, it can be shown on the dial with Mooney as the unit. Reading the value at the same time interval lets you make the Mooney vulcanization curve. Mooney scorch time is the time when the Mooney number goes down and then goes up by 5 units from its lowest point. Mooney vulcanization time is the time when the Mooney scorch point goes up by 30 units.
The difference between a rubber vulcanizer and a Mooney viscometer
The Mooney viscometer and the rubber vulcanizer are both used to test rubber. They both look alike. Their jobs and the things they use to test are different. The more Mooney viscosity there is, the more viscosity there is and the less plasticity there is.
The five main differences between the Mooney viscometer and the Rotor-less vulcanizer are:
- The Mooney viscometer and the Rotor less vulcanizer look almost the same. They both look alike. The two different test contents are what make the difference on the inside.
- A vulcanizer is used to find out how well a rubber compound vulcanizes as a whole. The test temperature is the same as the rubber compound’s vulcanization temperature. The vulcanizer obtains a complete vulcanization curve. The hardness and constant elongation strength have something to do with the high torque. The lower cavity of the mold moves back and forth to make the rubber oscillate in a sinusoidal pattern and measure the torque.
The Mooney viscometer is used to measure how well rubber works when it is being worked on. The Mooney viscosity is low, and rubber flows well when it is being made. The Mooney meter can also measure the rubber’s scorch time, which is the time to test if the rubber can be processed safely. The temperature for the test is 100 °C, and the temperature for the scorch test is 120 °C. The torque is measured by the way the rotor keeps cutting through the rubber as it turns.
- It is used to test the rate of vulcanization, the modulus of vulcanization, and the time it takes for a new product to vulcanize. Rubber product makers can use vulcanization instruments to check how repeatable and stable their products are, as well as to design and test the rubber formula. The manufacturer can do an on-site check of the production line to see if the vulcanization characteristics of each batch or even every moment meet the product requirements. It is used to figure out how unvulcanized rubber will change when heated.
The oscillation of the rubber in the mold cavity back and forth and the reaction torque (force) on the mold cavity are used to make a vulcanization curve of torque and time. The time, temperature, and pressure of vulcanization can all be figured out by science. They are the key to figuring out how good a product is in the end, and they can also tell you what a compound’s physical properties are. Quality management of raw materials, processing steps, and finished products can give the manufacturer a good formula and improve the company’s rate and product quality.
- A Mooney viscometeris used to measure how much rubber compounds can be stretched. The way it works is to measure the sample’s shear resistance when the rotor is turning at a certain temperature, time, and pressure, and then use different torques to show how flexible the rubber compound is. A Mooney viscometerhas a standard rotor that spins at a constant speed in a sample in a closed chamber (generally 2 RPM).
The change in the sample’s viscosity during vulcanization is linked to the rotor’s shear resistance as it turns. Through the force measuring device, it can be shown on the software with a Mooney as the unit. Reading the value at the same time interval lets you make the Mooney vulcanization curve. Mooney scorch time is the time when the Mooney number goes down and then goes up by 5 units from the low point. Mooney vulcanization time is the time when the Mooney scorch point goes up by 30 units.
1.The performance of the vulcanizer is to measure the whole vulcanization characteristics of rubber compound, and the test temperature is the same as the vulcanization temperature of rubber compound. The vulcanizer obtains a complete vulcanization curve.
2.A Mooney viscometer is a rotor that rotates continuously to shear the rubber and measure the torque.
3.The rotor less vulcanizer swings the lower mold cavity back and forth to drive the compound to oscillate sinusoidally and measure the torque.
The main factors affecting the Mooney viscosity test
1) Rubber material mixing process and parking time
The sample preparation method has a lot to do with how the molding, mixing, and thin pass processes affect the Mooney viscosity. So, when making comparison samples, the same method and process should be used to prepare all of the samples. The way the rubber was stored and how long it had been there affect the test results. Don’t leave it there for too long. To avoid getting too hot while parking, different parking times should be used for different weather conditions.
2) Temperature test
If the test temperature changes, the viscosity of the rubber will also change. This will cause a change in the torque value and the Mooney curve, which will lead to a test error. So, the test temperature range should be strictly kept within the range given to make sure that the test data is accurate.
3) Glue loading
Since the size of the mold cavity is known, the amount of glue will affect how the rotor turns in the mold cavity. If the sample doesn’t fill the mold’s space, the test results won’t be able to be repeated, and the Mooney value won’t be right.
4) Preheating time
The amount of time spent preheating a compound has a direct effect on its initial Mooney value, so the amount of time spent preheating should be strictly controlled.
5) New and old degree of rotor
After a long time of use, the rotor’s surface will become worn and smooth. This will change the test results, so the rotor should be replaced when it’s time.
Sample preparation method of the Mooney viscometer
The Mooney value is affected by how the Mooney viscometer is set up and how the sample is adjusted before the test. This is why the test should be done exactly as the determination method says.
The sample for the Mooney viscometer must be made according to the rules, and the sample for the compound test must be made according to the rules in the relevant rubber material standards. The Mooney viscometer sample should be made up of two circular films about 50 mm in diameter and 6 mm thick. For the rotor to fit, a hole should be drilled in the middle of one of the films.
The hole should be about 8 mm in diameter. As much as possible, bubbles should be taken out of the film to prevent cavitation on the surface of the rotor and die cavity. The Mooney viscometer sample must be set at the lab temperature for at least 30 minutes, and the sample must be tested within 24 hours.