I'm using two different type of emulsifiers for my ABS polymerization process. One emulsifier is based on palm oil fatty acid type and the other is palm KERNEL based. The impact strength of ABS produced by using palm KERNEL fatty acid emulsifier resulted in a lower impact strength compared to the ABS produced from palm oil fatty acid emulsifier. The melt flow index for palm KERNEL ABS was higher than palm oil fatty acid ABS. However the grafting % and AS molecular weight for both ABS were comparable.
What could have affected the ABS impact strength ? Lubricanting effect ? Low MW of the palm kernel fatty acid ?
Hope that someone out there can help me by giving me some information
ABS is a two-phase system (AS matrix, SB inclusions). A two-phase system is roughly 4 times as complicated to accurately characterize as a 1 phase system. Melt flow is a horrible test (the second worst test in the world in my humble opinion) as it is only a single point on a curve, and the point isn't even accurate as the exit die is much too short to allow for the development of the flow pattern.
Are the size of the rubber particles the same in both cases?
John Aspen Research, -
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The Melt Flow Index is a good measure when you apply the correct instrumentation, actually is a very good tool to identify potential problems with different batches.
I would beg to differ. MFI is just plain a bad test. First, the ratio of the die length to diameter is only about 4, even though a L/D of about 20 is needed to establish the fully developed flow profile free from any entrance effects. As a result, you are not simply measuring the "viscosity" at a given shear rate, but are measuring the "viscosity" combined with the entrance flow. Secondly, it is well known and widely established that viscosity depends strongly on shear and that the dependence is nonlinear. As I said above, you are looking at just one point on a curve and making a guess about the rest of the curve.
It doesn't even make a good QC test. Yes, two different MFI values tells you that two lots are different, but two identical MFI values do not mean that the two lots are the same for the two reasons that I mentioned above. First, the combination of entrance effects and "viscosity" may be such that they combine to give the same MFI. Or the lots may have the same MFI values at that same point on their viscosity curves, but may have completely different MFI values at different points (assuming that you could run the MFI at those different points).
The test is easy to run which is why it has such staying power, but it still causes incalculable amounts of pain and suffering.
John Aspen Research, -
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Opinions expressed herein are my own and may not represent those of my employer.
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