Sunday, 27 November 2016

Polymers and Viscosity Demystified

What is a Polymer?
A polymer is essentially the result of organic building blocks called monomers linked together by means of a solvent. Depending on the mix and proportions of crude materials and diverse response conditions, numerous sorts of polymers can be created, for example, polystyrene, polycarbonate, polyethylene and PMMA. Composition of principle crude materials and added substances also result in polymers of different grades. SMM (Polymer) is presently producing 6 distinctive PMMA grades: MH, EX, EXN, MG, LG and LG2.

What is Viscosity?
Viscosity is a property of a fluid that offers resistance to its flow. Viscosity is due to the internal friction of molecules and mainly depends on the nature & temperature of the liquid.
The polymerisation reaction is conducted within specific conditions and boundaries. The quality of the PMMA polymer thus developed can be evaluated by viscosity, which is a significant characteristic for all materials, especially polymers. For liquids, viscosity determines flow characteristics, heat transfer and mass transfer. For polymers, viscosity is often a measuring stick. Viscosity data is crucial as it helps in predicting behavioural properties of the polymer. Also, measurement of viscosity is very important in monitoring the SMM (Polymer) process.

Determining Viscosity
How do you determine the viscosity of a solid cube of polymer?
Polymer viscosities can range from 103 to 107 Poise so one testing method cannot cover them all. So, two common testing methods are used: melt and solution.
Melt Viscosity
The melt index is a common testing technique that studies parameters like compression weight and testing temperature, predominantly in higher viscosity polymers. Of course, the results depend on the type of polymer. For instance, for the melt viscosity test of polyethylene, the study parameters include a temperature of 190˚ C and weight of 10 kg. After a certain time (say 10 minutes), the extruded polymer is weighed. The melt index is then expressed as grams of polymer/10 minutes and this value corresponds to the average molecular weight of the polymer. Polyethylene has an average molecular weight of 150,000 g/mole and a melt index close to 0.3 / 10 minutes.
For processes or final products where ease of processing is required, melt indices above 15 g/ 10 minutes are desirable. Where mechanical properties are needed, melt indices below 1 g/10 minutes are preferred.  
Solution Viscosity
Solution viscosity testing involves dissolving the polymer in a solvent, usually accompanied by gentle heat. The solution is then allowed to travel through an apparatus like a pipette and the travel is timed. The time for the pure solvent to flow through the same apparatus is also calculated. These two values are then compared, resulting in a relative viscosity – which is essentially the ratio of the polymer viscosity to the solvent viscosity.
While melt viscosity technique is carried out by SMM(P) in regular frequency to ensure the polymer formed is well under control, solution viscosity is executed by SCASS during product certification stage as a final confirmation.

Sumitomo Chemical Singapore is one of leading producers of the polymer - PMMA (Polymethyl Methacrylate), a polymer of MMA (Methyl Metacrylate Monomer). Visit us to learn more about polymers, PMMA and MMA.

For more information kindly visit pmma thermoplastic 

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