INFORMATION SHEETS ABOUT SILICONE PUTTY
by Peter Cobbold

Peter Cobbold (Géosciences-Rennes, France) has compiled and regularly updates information about silicone putty.  The information sheets are posted below.

If you have any information about the commercial availability of silicone putty, or about their properties please send a email to Peter (cobbold@univ-rennes1.fr).



Silicone Putty Information Sheet No. 1, February 2001
 
Silicone Putty Information Sheet No. 2, March 2001



Silicone Putty Information Sheet No. 1, February 2001

Silicone putties: past, present - and future!

Past
Ramberg (1967) may have been the first person to use silicone putties for analogue modelling of tectonic structures. They were Dow Corning products (C-4551, XC-2-0950 and XC-2-0951) and they had non-linear flow laws. They did not flow well under their own weights, but were suitable for use in a centrifuge (Dixon, 1975). A more recent but well-publicized example is Dilatant Compound DC3179 (Dixon and Summers, 1985, 1986).
From 1972 to 1981, Rhône-Poulenc produced a pink silicone (Gomme Spéciale GS1R), which was remarkably Newtonian (Rhône-Poulenc, 1972). We first used it at Rennes for reproducing sheath folds in ductile shear zones (Cobbold and Quinquis, 1980). Because this silicone flowed readily under its own weight, it could be used for tectonic modelling in a normal gravity field (see Faugère and Brun, 1984; Vendeville et al., 1987; Davy and Cobbold, 1988). This avoided the need for an expensive centrifuge. Silicone GS1R was discontinued in 1981, but it was replaced by Silbione Gomme 70009, also Newtonian. More than a hundred publications, describing models at various scales and in various tectonic contexts, refer to these Newtonian silicones.
Weijermars (1986) was the first to undertake a detailed study of silicone fluids and putties. He discovered that opaque silicone putties are mixtures of inert fillers and a transparent base, polyborondimethylsiloxane (PBDMS). Small concentrations of fillers result in Newtonian behaviour, whereas large concentrations result in non-Newtonian behaviour. As well as the varieties made by Dow-Corning and Rhône-Poulenc, filled PBDMSs have been manufactured over the years by General Electric (USA), Bayer (Germany), Wacker (Germany), Midland Silicones (UK) and Imperial Chemical Industries (UK).
Transparent PBDMS has useful properties (including a large viscosity), but apparently it has never been marketed. A more common transparent silicone fluid is polydimethylsiloxane (PDMS). This contains no boron. For many years a variety of PDMS (SG-36) was manufactured and marketed by Dow Corning (Weijermars, 1986). It flowed readily under its own weight and had a suitably large viscosity (about 50000 Pa s). However its specific gravity was rather small (0.97) in comparison with other model materials.

Present
Rumour has it that many varieties of filled silicones, especially the pink ones, have been used for cosmetic surgery and body implants. Rumour also has it that many such products have now been withdrawn from the market, following their possible misuse and consequent legal actions. Whether or not this is true, experimenters are having difficulties in obtaining silicone putties.
Apparently, Newtonian silicones (such as GS1R and 70009) are no longer manufactured by Rhône-Poulenc. The same appears to be true for silicones SGM36 and DC3179, once manufactured by Dow Corning. Fernando Marques for Portugal, Bruno Vendeville for the USA, Patrice Rey for Australia, Jean-Jacques Kermarrec and Olivier Merle for France, all report that small amounts were bought as recently as six months ago, but stocks now appear to be finished.
Wacker GmbH in Germany (http://www.wacker.com) makes two red bouncing putties (M29 and M36), which are filled PBDMSs. We are using them at Rennes. They appear to be nearly Newtonian and have suitable viscosities and densities. However, they are rather tacky and difficult to cut with a knife, which is a problem for experimenters like us, who have limited access to 3D scanners.
Bruno Vendeville reports that transparent PDMS is available from Wacker in the USA. Sandy Cruden reports that an alternative to SGM36 might be Silastic 4-2901 Gum, made by Dow Corning. This transparent PDMS has a viscosity of about 10000 Pa s. I have no information on how easily it can be cut. Cruden also has tested two viscous polybutenes, manufactured by BP: Hyvis 2000 and 150. These he says are “horrible to work with“. Patrice Rey has found another clear PDMS: Rhodorsil Gum FB, priced at 50 FF/kilo. He is currently testing it. Its specific gravity is 0.97. For further information on materials currently used by Patrice Rey, you may visit his website, down under: http://www.es.usyd.edu.au/geology/people/staff/prey/QuAnToM/Intro.html
For information on silicones used at Rennes, now and in the past, see the attached spreadsheet (Excel 5.0 for Power Mac).

Future
We are thinking of lobbying Rhône-Poulenc and Dow Corning, to try to persuade them to manufacture some silicone putties, according to our specifications. This may take some time or it may  not work. Meanwhile, I urge you to send me further information, as and when you get it. I undertake to make it available to all users who are on the list.
Another plan is to include a section on model materials in our own website (which has gallic flavour):
http://www.geosciences.univ-rennes1.fr/www/ateliers/analog/analog.html

References
Cobbold, P.R.and Quinquis, H. 1980. Development of sheath folds in shear régimes. Journal of Structural Geology, 2: 119-126.
Davy, P. and Cobbold, P.R. 1988. Indentation tectonics in nature and experiment. 1. Experiments scaled for gravity. Bull. Geol. Inst. Uppsala, New Series, 14: 129-141.
Dixon, J.M. 1975. Finite strain and progressive deformation in models of diapiric structures. Tectonophysics, 28: 89-124.
Dixon, J.M. and Summers, J.M. 1985. Recent developments in centrifuge modelling of tectonic processes: equipment, model construction techniques and rheology of model materials. Journal of Structural Geology, 7: 83-102.
Dixon, J.M. and Summers, J.M. 1986. Anorther word on the rheology of silicone putty: Bingham. Journal of Structural Geology, 8: 593-595.
Faugère, E. and Brun, J.P. 1984. Modélisation expérimentale de la distension continentale. C. R. Acad. Sci. Paris, t. 299, Sér. II: 365-369.
Nalpas, T. and Brun, J.P. 1993. Salt flow and diapirism related to extension at crustal scale. In: New insights into salt tectonics (edited by P.R. Cobbold), Tectonophysics, 228: 349-362.
Ramberg, H. 1967. Gravity, deformation and the Earth’s crust. Academic Press, London, 214 pp.
Rhône-Poulenc. 1972. Rhodorsil Gomme Spéciale GS 1 R. Rhodorsil informations, 26: 6 pp. (unpublished report, in French).
Vendeville, B., Cobbold, P.R., Davy, P., Brun, J.P. and Choukroune, P. 1987. Physical models of extensional tectonics at various scales. In: Continental extensional tectonics (edited by M.P. Coward, J.F. Dewey and P.L. Hancock), Geol. Soc. London Sp. Publ., 28: 95-107.
Weijermars, R. 1986. Flow behaviour and physical chemistry of bouncing putties and related polymers in view of tectonic laboratory applications. Tectonophysics, 124: 325-358.

 
 
SILICONE PUTTIES USED IN PHYSICAL MODELLING LABORATORY, GEOSCIENCES-RENNES, 1978-2000
Data compiled by P.R. Cobbold and J.J. Kermarrec, February 2001
Manufacturer Rhône-Poulenc, France Rhône-Poulenc, France Wacker GmbH, Germany Wacker GmbH, Germany Dow Corning, USA Dow Corning, USA
Product name Rhodorsil Gomme Spéciale Rhodorsil Gomme Silbione Bouncing putty Bouncing putty Dilatant compound PDMS
Code GS 1 R 70007 or 70009 M36 M29 DC3179 SGM36
Colour flesh salmon red red coral none
Composition PBDMS + filler PBDMS + filler PBDMS + filler PBDMS + filler PBDMS + filler PDMS
Supplier Etabl. Robert, Puteaux Etabl. Robert, Puteaux CRC Industries, Argenteuil CRC Industries, Argenteuil Dow Corning STI, France Dow Corning STI, France
Container blue metal drum blue or pink metal drum plastic bags in cardboard box plastic bags in cardboard box cardboard drum
Weight in container (kg) 25 25 30 30 100
Approximate price (FF/kg) 120 159 390 390 82
First produced (year) 1972 1980 1998 1998 before 1985 before 1985
Last produced (year) 1981 1998
First bought at Rennes (year) 1978 1983 1999 2000 1993
Last bought at Rennes (year) 1983 1998 2000
Specific gravity 1.12 1.23 1.16 1.14 1.14 0.97
Stress exponent (n) 1 1 1 1 1 to 9 1
Viscosity at 20°C (Pa s) 20000 - 30000  15000 - 20000 27000 19000 variable 50000
Activation enthalpy (J/mol) 48000 40000
Elasticity negligible negligible negligible negligible some
Adherence to other materials good good tacky tacky good good
Can be cut with a knife readily readily with difficulty with difficulty readily readily
References Rhône-Poulenc, 1972 Davy and Cobbold, 1988 Dixon and Summers, 1985 Weijermars, 1986
Cobbold & Quinquis, 1980 Nalpas & Brun, 1993 Dixon and Summers, 1986
Weijermars, 1986 Weijermars, 1986
Vendeville et al., 1987


Silicone Putty Information Sheet No. 2, March 2001
 

Commercial availability of silicone putties
 

Internet searches
Websites are useful sources of information on silicones and other products that are manufactured by large companies. Try the following.

http://www.rhodia-silicones.com
http://www.wacker.com
http://www.dowcorning.com

Beware of restrictions. Most companies list only those products that are on general sale; whereas many silicones of interest to us are intermediate products, that are used for manufacturing final products. The answer to this problem is to contact sales representatives or technical engineers and plead your case. Be very polite, explain how important this or that product are for your research and ask if they can be supplied in limited quantities, as a special favour.

Rhone-Poulenc, Rhodia, Rhodorsil
Rhone-Poulenc Chimie Fine, the French holding company, no longer exists. It has merged with Hoechst, generating a new holding company that specialises in biochemical products.
The original daughter company, Rhodia Silicones, is now a large independent company. They own the trademarks Rhodorsil and Silbione. However, they no longer manufacture the pink filled PBDMSs (Gomme Spéciale GS1R and Silbione Gomme 70009) that were Newtonian and could so easily be cut with a knife. We have approached Rhodia, to see if they would be willing to manufacture small quantities of pink silicone for us - so far with no success. They would like us to buy at least 50 tons per year ! We are negotiating…

Wacker
Wacker GmbH in Germany makes two red bouncing putties (M29 and M36), which are filled PBDMSs. You will find them listed on their website under the name « bouncing putties ». We are using them at Rennes. They appear to be nearly Newtonian and have suitable viscosities and densities. However, they are rather tacky and difficult to cut with a knife, which is a problem for experimenters like us, who have limited access to 3D scanners.

Dow-Corning
I apologise for misleading you in the previous information sheet. Dow-Corning do indeed still manufacture the transparent PDMS, SGM-36. However, it is not normally on sale, because it is an intermediate product. Marc-André Gutscher (Brest) has recently managed to order some (for himself and for us), by being very polite to a representative in France. We look forward to receiving our quota in due course.
I have no news as to whether or not the pink Dilatant Compound DC3179 is still available. If anyone has bought some very recently, could he or she please advise?

Mix-it-yourself
Sandy Cruden (Toronto) reports that he has been testing mixtures of transparent silicones and mineral fillers (as did Weijermars, 1986). I think that this may be a good way forward. I do not believe that PBDMS can be purchased, which is a shame, as it appears to be rigorously Newtonian (see Weijermars, 1986). In contrast, PDMS (such as SGM-36) is somewhat non-Newtonian for strain rates greater than 3 x 10-3 s-1(the power-law exponent is between 1 and 2).
I have tried mixing SGM-36 (which has a specific gravity of 0.97) with powdered hematite. I chose hematite, because we noticed, in the past, that on adding it to Gomme Spéciale GS1R there was a decrease in viscosity (rather than an increase, as predicted by simple theory ; Weijermars, 1986). Anyway, I hand-mixed 1000 g of SGM-36 with 200 g (16.7% by weight, 3.6% by volume) of finely powdered ferric oxide. The particles of hematite did not appear to settle, even over a period of several days. At 20°C, the mixture had a specific gravity of 1.12. The elastic strain range and fracture strength of the mixture were smaller than those of pure PDMS, meaning that the mixture was even easier to cut. When tested in a thick-walled rotary viscometer (see Cobbold and Jackson, 1992) with a lubricating layer of honey at the base, under applied shear stresses between 300 and 8000 Pa, the best-fit stress exponent was n = 1.22 (R2 = 0.9987, for 7 points) and the average viscosity was 36900 Pa s, which is smaller than that usually quoted for pure SGM-36 (50000 Pa s).

Buy it from us?
Anyone who has hand-mixed large quantities of silicone and fillers will know that it is not to be recommended, if there is anything better to do. Our next step will be to test a large-capacity, slowly-rotating drum, specifically for mixing silicones. Then we aim to test a variety of mixtures.
Should mixing be easy, I will contact you again, to see how many users might be interested in purchasing a ready-mixed product of given properties.
Our objectives will be, not to make money, but to ensure that we are always in stock - and to provide a service to other users.

Keep in touch
For further information, try the following websites (I am sure that others will appear in the near future).

http://www.geosci.usyd.edu.au/users/prey/QuAnToM/Intro.html
http://www.geosciences.univ-rennes1.fr/www/ateliers/analog/analog.html