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Pemulen TR2

Page history last edited by Nancie Ravenel 9 years, 8 months ago Saved with comment

Noveon's technical page about Pemulen

 

Pemulen TR2 is a polymeric emulsifier produced by Noveon.  A block copolymer consisting of a poly acrylic acid similar to the Carbopol resins presently used to make aqueous and solvent gels in art conservation (Carbopol 934, Carbopol 940, Carbopol 941) cross-linked with a long-chained methacrylate, this carbomer has a lipohipllic regions (the methacrylate)  as well as hydrophillic regions (the acrylic acid). In the cosmetic industry literature, Pemulen TR-2 is part of a class of copolymers are referred to as acrylate/C10-30 alkyl acrylate cross polymers, having the following structure[1]:

 

 

These regions of differing affinity allow Pemulen TR2 to act as a primary emulsifier, that is, it can be used to make oil in water (O/W) emulsions without the addition of soap or surfactant.

 

Pemulen TR2 does not form emulsions in the same way that traditional surfactants do.  To produce an oil in water emulsion, a traditional surfactant surrounds a droplet of oil to keep it suspended in oil. Nonionic surfactants used for cleaning painted surfaces, as described in Wolbers' Cleaning Painted Surfaces:Aqueous Methods, might be used in concentrations as high as 30% to form a macroemulsion.

 

In contrast, Pemulen TR2 is said to form stable O/W emulsions with as little as 0.4% (Noveon), binding to the oil droplets with the lipophilic portions of the polymer chain that forms the gel.  The emulsions created in the conservation lab at Shelburne use Pemulen TR2 in a 1% concentration in the gel.

 

Gels made with Pemulen TR-2 are most viscous in the pH range of 5-9. A range of alkaline materials are suggested by the manufacturer to formulate aqueous gels using Pemulen TR-2, including sodium hydroxide, ammonium hydroxide, triethanolamine (TEA), and Ethameen C-25.

 

One interesting feature possessed by Pemulen is that this emulsifying agent is designed to break when the gel is in contact with a salt concentration similar to what one would find on human skin. This is a desirable in the cosmetics industry where moisturizers need to be quickly delivered and absorbed into the user's skin, but this may be a less desirable characteristic of an emulsion designed to clean works of art. In practice, this breakage of the emulsion has been observed when attempting to clean very grimy areas and allowing the gel to dwell for an extended period.

 

Richard Wolbers introduced Pemulen TR2 to the conservators at Shelburne Museum in his capacity of consultant to an IMLS-funded project to clean machine-oil infused paintings on canvas from the museum's 1902 Dentzel carousel. Over the two day consultancy, Richard Wolbers tested a number of cleaning methods, including free solvents, solvent mixtures, Carbopol-thickened solvent gels, as well as emulsions of benzyl alcohol in a gel made with Pemulen TR2, triethanolamine (TEA) and deionized water.  He suggested the using a combination of triethanolamine and a 2% solution of Tris(hydroxymethyl)aminomethane (TRIS)  in deionized water as a method of reducing the strength of the Pemulen gel.

 

Since the structure of Pemulen was described as being similar to that of Carbopol, concerns were raised as to the clearance of Pemulen. Wolbers referred to the research into solvent gel research undertaken at the Getty Conservation Institute for analgous results on clearance.  The results of that work were published in Solvent Gels for the Cleaning of Works of Art: the Residue Question.

 

Testing on the environmental toxicology of Pemulen indicates that it will not degrade in a waste water treatment center, but that it would be removed via biomass treatment of waste water. Pemulen was also shown not to inhibit bacteria used in waste water clean up.

 

Shelburne Museum conservators obtain Pemulen TR2 from Protameen

Samples can be requested from the Lubrizol site.

Footnotes

  1. Goddard, Errol Desmond, and James V. Gruber. 1999. Principles of polymer science and technology in cosmetics and personal care. Vol. 22. Cosmetic Science and Technology Series. Informa Healthcare., p.607. http://books.google.com/books?id=56R-6Wyyo6IC&lpg=PA607&dq=pemulen%20tr-2%20goodrich&pg=PA607#v=onepage&q=pemulen%20tr-2%20goodrich&f=false, accessed 6 July, 2010.

Comments (4)

Dale Kronkright said

at 11:49 am on Jun 30, 2009

Hi Nancie. I’m going to use the group ‘we” here in my comments because, like a good WIKI contributor, I want to help take responsibility for some of the work – true read/write technology! SO I’ll try working on some of the following questions and comments: I think we should consider adding a chemical structure diagram of a Pemulen monomer, identifying lipophilic regions and branching structures. We should address why Pemulen is mildly acidic in water and how the use of different common alkalis alter the structure (perhaps all in similar ways? haven't thought about it a lot.) Then, as we discussed early, the gel becomes acidic over time, suggesting additional ionization. We need to speculate how this mechanism might occur and why and how ionic species might impact clearance and cleaning.

Dale Kronkright said

at 11:54 am on Jun 30, 2009

I realize that shameless self-promotion is normally practiced in the Twitter venue, but in the JAIC, vol. 48 (2009), pages 83 -96 I present the first part of a two-part review of both Solvent Gels for the Cleaning of Works of Art: the Residue Question and (coming later) Cleaning Painted Surfaces: Aqueous Methods. I'll be trying to infer some of the chemical structural work we need to do from information done during the writing of those reviews.

Nancie Ravenel said

at 12:32 pm on Jun 30, 2009

Hi Dale. It is probably an understatement to say that I'm *thrilled* that you're interested in thinking through some of these issues. And you bring up some wonderful questions. Your messages prompted me to do a quick search on Google Scholar and I note that there's an article "Thermoanalytical and microscopical investigation of the microstructure of emulsions containing polymeric emulsifier" in the Journal of Thermoanalysis and Colorimetry, Volume 94, Number 1 / October, 2008, pp.271-274. http://resources.metapress.com/pdf-preview.axd?code=c31g621502311j44&size=largest for a maddeningly tantalizing preview. Note that they indicate that they indicate that the authors note that these emulsifiers impart "steric stabilization". I'd bet that different common alkalis would alter the structure. I haven't yet sat down to make a Pemulen gel with ammonium hydroxide to see how that might work on our various projects, but its something that I really want to do in the near future.

Dale Kronkright said

at 6:41 pm on Jun 30, 2009

Perfect. I'll propose a set of formal trial we should set up and develop the chemical theory for, e.g. the funtion of different alkali and pH changes over time, clearance with solvents. I'm going to see if I can Greg Smith at Buffalo State and Carl Dirk, chemist at UT-El Paso to lend an occasional hand. Once I start proposing clinical experiments, we should ask for review from both our networks before getting to work carrying them out and documenting them. Perhaps folks from Mary Striegel's preservation technology blog.

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