Pemulen TR2

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.