Polymer Particle Size

[chumster]

We manufacture several types of acrylic polymers using suspension polymerization. We have only one reactor so typically we will make 4-10 batches of one type then switch to the next type. With one type only we are experiencing a significant difference in particle size between the first batch in a run and subsequent batches. The polymer is a copolymer of MMA and styrene. We use BPO as the initiator and corn starch as the suspension agent. This happens every time we make this polymer type regardless of what is made before. Any ideas on why this is happening?

 

[patprimmer]

At a wild guess

Temperature.

Rate of addition of a component.

Level of agitation.

Regards
Pat
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[chumster]

Thank you patprimmer. Based on comparison of graphs of heating rate, reaction time, pressure, agitation rate etc. we can see no obvious difference between the first and second batch. This is why we are puzzled.

 

[MacGyverS2000]

Starting temp the same? This is a complete wild guess, not being a plastics guy or knowing the process... but start conditions are almost always the culprit when I run into issues like this. If the reactor is already warmed up from the first batch, compared to changing batch type, which gives things time to cool down.

Just a thought...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[patprimmer]

I agree with Dan.

As I remember for PMMA which I expect is similar, it is an exothermic reaction and done in water with emulsifiers present. The quality of the emulsifier and the heat sink of the cold equipment is my best guess.

Regards
Pat
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[btrueblood]

Is there residue left in the reactor/vessel/pot/whatever from the first batch that helps to provide initiation sites for subsequent batches?

 

[chumster]

Thanks so much for your ideas.
We've tried several things. Doesn't seem to matter whether the reactor is cold or warm. We have run the 1st and 2nd batch on the same day and on a Friday/Monday. The last thing we tried was to powerwash the reactor both before and after the 1st batch thinking residuals from the previous type was causing small particle size of the 1st batch or residuals from the 1st batch was causing larger particle size of the 2nd batch. This also made no difference.

 

[Demon3]

I would suggest adding seed particles. That is how they control PSD in industry. You prepare a batch of seed particles that are very small. Then you add those and they seed the growth of all the other particles. The final particle size depends on monomer amount and the number of particles so using a seed improves control a lot.

Chris DeArmitt PhD FRSC CChem