I'm working with mixing polymer blends on both a Farrel K1 and K5 mixer. The K1 produces lab batches, with a mixing chamber 5.5L in volume whereas the K5 makes master batches for production with a 143L capacity.
The issue is that we design certain properties such as durability, tensile strength, etc and make batches on the K1. These batches are tested and the properties come out as expected. For some compounds however, when we scale up to the K5, even though we keep the same 'recipe' and adjust the rotor speed such that the angular speed is equivalent to that in the K1, the properties do not remain the same; sometimes they are drastically different.
Any thoughts on an approach to coordinating this scale up? There doesn't seem to be a single fit equation from what I've found thus far.
A very simple suggestion - as you scale up, the heat transfer might be significantly complicated due to limited thermoconductivity of the polymer bulk, and thus temperature conditions inside K5 chamber may be much different from those in K1, eben under the same stirring conditions...
I had thought of heat transfer being a possible issue, but we're unsure as to how to adjust the temperature in response. It's unlikely that it's a linear relationship relating only to the size of the mixing chamber, but perhaps we should try an increase and note the effects.
I suggest to look carefully at the maximum temperature when using K1 and repeat at the K5.
Agreed with Victor. Direct T-profile modelling is a sophisticated task, however, merely measuring temperature at a defined reactor point (say, center) might indicate the heat problem clearly.
What polymer? What fillers? Have you analyzed DSC profiles (for semi-crystalline polymers to see if you have altered the molecular architecture during processing? Have you run molecular weight studies? Have you looked at activation energy of decomposition???
Matthew, the polymer and filler types vary. That's why I made the question so general; we're looking for a general solution that works most of the time. We can approach special cases differently, but we need an overall solution for production purposes. As to your other questions, we do not have a DSC so that testing isn't a viable option for us. I will certainly take a look at your suggest regarding activation energy; we just started looking into this problem so there are many avenues we will be exploring such as the rotational speed of the rotors, distance between those rotors as it may affect dispersion, and a slew of other factors. Thank you for your insight.
Activation energy may be even not necessary at this stage. Temperature data from working mixers compared with (presumably known) DSC/TGA data for the polymer(s) under question would be enough for the first approximation.
However, the suggested analysis + probably some easily available tests (melt/solution rheometry, DSC, MALDI, whatever easily available) for the materials processed with both mixers (!!! better - taken from different mixer spots) will be valuable for detailed discussion.
There isn't something that you can use as an umbrella. That's why it's research :-)
You are best off taking each on a case by case basis. It will save you the most time. Look at filler dispersion and molecular weight (or FTIR). That will tell you if fundamentals have shifted. Outside of that, you will chase your tail for a LONG time.
I agree, but we're hoping for some kind of general principle to apply. We do think that it has something to do with the thermal degradation of carbon polymers because we haven't experienced the same kinds of issues with our inorganic polymer blends. You're probably right that there is no 'umbrella' but if we can even find ten solutions (hypothetical number I'm throwing out there) depending on the polymer type and filler, then that would mean a lot to us in terms of cutting down production waste etc. Thanks again!
Also remember that under mechanical forces (mixing) some polymer chains may break down, generating radicals; some other polymers may develop a molecular superstructure (hydrogen bonds, etc.) that may also be drastically affected under mechanical forces. The results usually consist in viscosity decreasing, either due to decreasing of molecular weight or due to disrupting the physical interactions.
You want molecular weight. You want DSC. Those two techniques, when comparing apples to apples, will give you carbon chain effects. Without those specific techniques, you will suppose all day.
Have you tried blending under a N2 blanket?
There's no such thing as a general principle on this. Using a DSC as Matthew mentioned or a TGA would help you significantly. Our lab had a similar problem with polymer mixing and we wound up investing in a TA Instruments DSC. It is used all the time now.
FTIR is also a good option (and I noticed Matthew suggested it also) if you are wanting to check distribution of nanoparticles in a solvent prior to mixing into a base polymer.
Your comment about a relationship to thermal degradation of carbon polymers leads me to think you should at least consider a DSC or TGA to test your samples. Even without a DSC, you could likely search for papers on your base polymer that did run DSC and find out the glass transition temperature, as well as melt. You can get similar info from a TGA if that is an option for you. If you are at an academic institution, you might be able to check with another nearby institution's chemistry department to see if they'd let you run a sample there. Also, you could check with the person at a neighboring institution that handles purchases greater than $3k or $5k (depending on the university) to ask if a department has a DSC or TGA. Sometimes an engineering department or even a surprise department could have what you seek. There are tracking systems in place for large ticket equipment .
If you want to continue to gamble though, you could try sonicating, then horn sonicating your nanoparticles/particles/beads/whatever in your solution prior to adding to the mix of the base polymer in your mixer. For sonication times, this depends on your particle but I'd suggest an hour of each and going from there.
If the polymer is crosslinking too early or stiffening too early (your problem statement is really almost too vague here) you could try using the mixer in a cold room to slow heat effects.
Question: In case this is actually a problem with a simple solution, when you scaled for the angular rotation was the new surface area of the mixer taken into consideration?
I think if you want to only look at simple solutions, start with making sure your additive is well mixed into the solvent. Then compare surface areas and temperatures for the K1 vs. the K5 for operations and make sure the K5 isn't creating a heat issue with your carbon based polymers. You could compare this to the temp of the solution in the K5 mixer to determine if you are having too much heat in the process and then decide to use a cold room for the mixer if necessary. If you don't have access to a cold room, you could temporarily try a large fridge or kegorator provided there aren't reaction products that could be harmful and that it isn't a fire marshall violation for you to have an electrical cord going into the fridge. If nothing else, it would give you a direction to pursue if it worked in a cold environment.
Good luck!
Matthew, no we haven't tried a nitrogen blanket. We don't think that the root cause is an unwanted contaminant. SEM data has shown that the composition (in elemental terms) is the same. That's why we think it's a mixing issue. Tabitha, thank you for your detailed response. We have both TGA and FTIR and we're looking into contacting another lab at the moment for DSC. I think those tests are a good place to start from.
Besides of all of the good suggestions already mentioned, a compound rheology would be helpful, the easy way is using a melt rheometer, the hard is using a DMA equipment (nevertheless data is bigger). At the end of the day, it must be remembered this problem is about rheology.
I agree with victor, it all about the melt flow behaviour of your polymer. Try to analyse your sample using polymer melt rheometer and take a look on the rheology properties of your material. Compare the rheology properties between product produce from k1 and k5. In your case, the problem might come from the processing temperature because the different contact area of the k5 and k1 barrel. The heat produce also different and might influence the shear and melt properties of your polymer. Consider the retention time of your polymer in the barrel too. Hopefully this suggestion will help you
You could try using block copolymers instead of mixing homopolymers (or gafting to compatibilize).
scaling up for mixing and compounding of polymers is not only the formula or torque, it consist of many parameters that changes via batch volume for example heat transfer that directly affect heat dissipation and thermal degradation of your polymer. also in balanced rotor speed in larger mixer volume you will have greater shear forces due to larger mixer parts so you must consider these parameters. but simply i suggest to use primary anti-oxidant agents. (exp. IRGANOX 1010 )
No general rule will help one in polymer mixing as there are a lot of controlling factor that effects mixing.
As previously has been stated, I suggest to develop both FTIR and DSC coupled techniques in order to track if the mixing is occurring as expected due to the Tg as well as the IR active bands due to supramolecular interactions. Besides try to increase the angular velocity since the dimensions of the bigger vessel are not behaving linearly and phase segregation or just inefficient mixing could occur, hence enhancement of the mixing should improve the final formulation. Hope this helps.
The two material properties you mention have MW dependencies. If there is a decrease in MW due to shearing, it would be readily evident via GPC measurements. Granted this might not be the best in-line measurement tool, but it should provide process parameter adjustments for the mixer.
The Nitrogen blanket will not prevent contamination - but - will prevent oxidation. That is likely one of the issues you are seeing. Try it.
Matthew, there are no outside vents on either the K1 or K5; any oxygen present in the chamber would only be that that was originally there before the mixing components were added and before the ram was lowered. As such, there is a small amount of oxygen in both and is not likely to be the cause to such widespread issues with our property loss. Also, our equipment is for production, not experimental, so introducing a nitrogren blanket into the equipment isn't really an option for us and would drive up the price of the batches. The idea is to keep the cost of figuring out the problem as low as possible. We also would not incorporate a nitrogen blanket into our process on a long term basis, so there isn't any point in trying it now since it would never be implemented. Also, nitrogen blankets do prevent contamination as well as oxygen and unwanted moisture.
Megan,
It is true that it is difficult to comment the interaction part of any two matter with out knowing the activation energy of both to have a nice mixture.The best method to study the activation energy is XPS.
Why not to try to create the same rate of shear deformation in larger mixer? Usage of the same angular velocity is good idea, but if the distance between moving surfaces in K1 and K5 scales differently than rotor radius, there can be different shear deformation at the same angular velocity, isn't it?
Anatoly, thanks for your suggestion. We've decided to take a look at the thermodynamics going on in each mixer as our first trial; if that fails, we'd like to take a look at the shear forces and see if that's what's killing our properties. We know what the rotor diameters are of both machines and the clearance from the edge of the rotor to the mixer body so we'd definitely have the data we need to calculate the shear if need be.
sorry that I am joining this discussion quite late. (I have extensive practical experience with such Farrel equipment of all size from small lab size up to big mass production), and I have done lots of basic research about how heterogeneous polymer systems behave, and why so).
General comment:
Any heterogeneous (multiphase) system is a non-equilibrium system, and such systems do not behave in a linear way, therefore it is hard to predict what the properties of your product will be if your parameters are only slightly different from your lab scale parameters
("weather" and "soccer games" are classical examples of non-equilibrium systems and unpredictability upon small statring parameter changes)
Your properties will be crucially dependant upon the size of the dispersed phase. This is dependant upon the shear rate. It is possible that you can not create the same (identical) shear rate in the big machine as you do in your lab scale mixer.
Please have a look at the below mentioned publications which might help you to understand the background. (although most of the references are dealing with conductive systems, the first one shows you that the principles apply to any heterogeneous polymer system)
https://www.researchgate.net/publication/229762491_Nonequilibrium_thermodynamical_description_of_heterogeneous_polymer_systems_(viii)_New_concept_for_understanding_brittletotough_transition_in_polymer_blends?ev=srch_pub
https://www.researchgate.net/publication/202290104_Critical_Shear_Rate_-_the_Instability_Reason_for_the_Creation_of_Dissipative_Structures_in_Polymers?ev=srch_pub (part 2 of the non-equilibrium thermodynamical theory of heterogeneous polymer systems)
https://www.researchgate.net/publication/233979584_Dispersion_hypothesis_and_non-equilibrium_thermodynamics_key_elements_for_a_material_science_of_conductive_polymers._A_key_to_understanding_polymer_blends_or_other_multiphase_polymer_systems?ev=srch_pub (part 1 of the theory)
https://www.researchgate.net/publication/229816762_Electrical_conductivity_in_heterogeneous_polymer_systems._V_(1)_Further_experimental_evidence_for_a_phase_transition_at_the_critical_volume_concentration?ev=srch_pub
https://www.researchgate.net/publication/240984956_Electrical_conductivity_in_heterogeneous_polymer_systems_(V)_(2)_Further_experimental_evidence_for_a_phase_transition_at_the_critical_volume_concentration?ev=srch_pub
Have fun while reading, and let me know about any comment or question you may have!
Article Non‐equilibrium thermodynamical description of heterogeneous...
Article Critical Shear Rate - the Instability Reason for the Creatio...
Article Dispersion hypothesis and non-equilibrium thermodynamics: ke...
Article Electrical conductivity in heterogeneous polymer systems. V ...
Article Electrical conductivity in heterogenous polymer systems (V) ...
to compare the results from your 2 different mixer size, you may want to use SEM; for this, I suggest you take 2 different approaches:
a) press your product under high pressure (not after injection molding!), and break it after freezing in liquid nitrogen, then investigate the break surface
b) take a useful solvent (or solvent mixture) which is able to only partially and slightly dissolve the matrix polymer, so to remove the surface layer of the matrix polymer, then you will be able to look at the dispersed phase.
(I did both very often, and got very useful information as you can see in the a.m. publications)
another hint (thought): you may be able to achieve similar results in the big mixer as in the small one by adjusting rotor speed, chamber cooling (or heating!), additives addition sequence, residence time. Before doing all kinds of experimetns, I would check what is the difference in the inner morphology, as I suggested above.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry