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How to make the gel

Page history last edited by Nancie Ravenel 10 years, 3 months ago

    

TDS-237_Neutralizing_Carbopol_Pemulen_in_Aqueous_Hydroalcoholic_Systems--PC.pdf from Noveon includes a chart of indicating the amount of base needed to neutralize 1 part Pemulen to a pH of 7.


The master recipe Shelburne has typically used for the gel, based on Richard Wolber's visit, is

100 mL de-ionized water

10mL  base

1 g. Pemulen TR2


At Shelburne, we have used two alkaline compounds to make up the gel: triethanolamine (TEA) and a solution of 2% Tris(hydroxymethyl)aminomethane (TRIS) in deionized water.  Making the gel up with TEA using this recipe results in a gel with a pH of about 7.5-8, but measure the pH to make sure.

 

When this gel proves to produce an emulsion that is too aggressive for cleaning, the gel recipe is modified replacing some of the TEA with the solution of 2% TRIS, a weaker base than TEA.  This often results in a less aggressive emulsion cleaner even though the pH remains at 7.5-8.

 

The first step in preparing the gel is to mix the water and the base together.  Then Pemulen powder is added slowly with constant stirring.  While we initially had used a magnetic stirrer to create the gel, Laura Brill found that stirring the Pemulen powder into the water by hand using a miniature balloon wisk created a smoother gel from the beginning.  

 

In the course of preparing the gel, we have found that the pH of the gel falls about half a unit over night. This may be a result of the the manual method of preparation not allowing the polymer to quickly unfurl.

 


In a more recent conversation with Richard Wolbers (July, 2010), he indicated that he is currently making gels from 1 g. Pemulen TR-2, 5 mL. TEA, 100 mL. water. He indicates that the pH ends up at about 8 at that weight ratio (1:5). He further explains that at pH 8-8 half of the available TEA is in an alcohol form and the rest acts as a general cation in solution.


 

In light of the neutralization ratios for Pemulen TR-2 expressed in  TDS-237, two other gels have been prepared and tested for use as part of Shelburne Museum's Dentzel carousel project. The documentation indicates that these neutralization ratios were based on those for Carbopol Ultrez, and indicates that because the equivalent weights of Carbopol Ultrez and Pemulen are the same the neutralization ratios should be similar.

 

Gel 1

100 mL. deionized water

1.5 g. triethanolamine

1 g. Pemulen TR-2

 

Water and base were mixed together, then the Pemulen was added with constant stirring using a balloon whisk. It was noted that the gel took longer to reach full viscosity. The pH of the gel after initial mixing was 7.5 but dropped to 7 within an hour and a half. In this gel, there is no free TEA in the gel that could act in a buffering capacity. 

 

Gel 2

100 mL. deionized water

0.7 g. ammonium hydroxide (ACS reagent, 28% ammonium)

1 g. Pemulen TR-2

Water and base were mixed together, then the Pemulen was added with constant stirring using a balloon whisk. Initial pH was 8 but dropped to 7.5 overnight.

This gel was made in order to determine if it was possible to create a neutral gel using an alkaline material that was more volatile than TEA but would still effectively remove darkened linseed oil. There is nothing in this gel which would act as a buffer in the solution.

 

 

 

 

Comments (3)

Suki Fredericks said

at 8:15 pm on Mar 24, 2009

I was wondering just last week about trying out some kind of whisk for stirring. Glad to hear it works! Suki

Dale Kronkright said

at 6:19 pm on May 14, 2009

I am VERY interested which direction, why and by how much the pH is shifting over time. Can you describe in greater detail? Thanks, Nancie

Nancie Ravenel said

at 10:41 am on May 15, 2009

Great question, Dale, and one we really haven't looked at systematically. I'll add it to the Areas to Research Further page. Summer interns start June 1 and that sounds like a great mini-project within the carousel animal project for one of them.

Generally speaking, though, we've noticed that the pH of the gel drops about half a unit overnight, but then levels off. The gels that we have in the cabinet are testing out to be at about 7.5. My guess is that it has to do with the polymer chain unfolding into the gel.

Thanks!

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