Problems with Polyacrylamide Production

Feb 17, 2005 7 Replies

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Hypersion 21 years ago

I'm producing LPA (linear Polyacrylamide) for in-house gel production. I'm having problems controlling the viscosity of the produced LPA. I'm assuming that viscosity is affected most by molecular size and cross-linking. What is most likely to affect the molecular size of LPA? I'm using ammonium persulfate and temed to produce LPA from acrylamide. I've tried running the reaction at different temps, varying the degassing time, using different lots of raw materials. Wither or not the LPA passes specifications seams more or less random. Thanks for any ideas.

Donald

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john.spevacek 21 years ago

More questions than answers:

What are the specs that you are trying to meet? Why are they set to the values that they are at? Why are you making it in house when you can purchase it? Are you using a controlled source of water? Have you tried running a "Designed Experiment" to understand all of your results better? (Or you can be really hot stuff and use an artificial neural network).

I get a lot of problems like this at work (granted, my employer does contract R & D as a business so that's the type of work I expect to get). There almost always is a way to work through this, sometimes with the data that is available, sometimes with more data, but always with another set of eyes. Is there someone else in your company that you can consult with? They don't have to be knowledgable in polymerization, they just have to be a good scientist.

John

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Frank Logullo 21 years ago

What about iron level in water and chain transfer agent? Frank

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Hypersion 21 years ago

52k + or - 6k * [3% (w/v) in buffer using spindle #4 and 10 rpm @ 25C] It is used to make gel for Capillary Electrophoresis in order to read @ 700 bases. The LPA we buy from outside vendors also fails our specs, they are usually too low in viscosity while the one we make are usually too high. Yes we are using double DI water. We havn't run only experiments yet but we need to if this keeps up. We still label and cap our vials by hand I don't think I could convince my boss to get an artificial neural network. :)

Thanks,

D> More questions than answers:

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Hypersion 21 years ago

I'm using double DI water so iron level should be trace at most I'm assuming. A chain transfer agent might just be the thing I need. I did a google search for one and it looks like sodium formate could be used to control MW of LPA.

Donald

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Ernie 21 years ago

Since persulfate decomposition is susceptible to catalysis by many things, radical generation in persulfate initiated systems can be difficult to control. But, it your problem is too high MW, a chain transfer agent should provide the desired results.

If the sodium is not a problem, as you suggest, sodium formate could control MW. Since acrylamide is a very "hot" radical, many compounds can act as chain transfer agents; methanol, ethanol, mercaptans, etc

Regards,

Ernie

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Frank Logullo 21 years ago

My experience, a very long time ago, was with polyacrylonitrile made by suspension polymerization using persulfate/bisulfite/ferrous ion catalyst which is why impurities in water need be know. In the PAN polym., ferrous ion was added. Frank

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john.spevacek 21 years ago

So the problem is that the viscosity is too high? It seemed from your first post that it was uncontrolled.

John

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