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Viscosity may be simply defined as the resistance to flow of a solid or a liquid. Physicists describe two different modes of flow: Newtonian and non-Newtonian. Newtonian flow is dependent on the amount of applied shear or pressure while non-Newtonian flow is related to the amount of applied force. Epoxy resin compounds, like the great majority of other polymer systems, fall into the non-Newtonian category.

There are many test methods for measuring the viscosity, especially for liquids. They include Brookfield, Cannon Fenske and Gartner Bubble, to list only a few. Viscosity is widely measured in poises or antipoises. One readily available instrument for viscosity tests is the Brookfield viscometer which determines viscosity as a function of shear rates and temperatures.

Master Bond epoxy compounds are available in a very wide range of viscosities from as low as 200 cps to in excess of 1,500,000 cps. The viscosity decreases as the shear rate and temperature are increased.

 
 

The table below lists the viscosities of common fluids and solids at 75°F in cps:

Viscosities of Typical Fluids & Solids
Liquid or Solid Name Viscosity, cps, at 75°F
Water 1
Milk 8-10
Ethylene glycol antifreeze 15
SAE 30 motor oil 250
Castor oil 1,000-1,500
Maple syrup 3,000
Honey 10,000-20,000
Chocolate syrup 20,000-25,000
Ketchup or french mustard 30,000-50,000
Tomato paste 250,000-300,000
Sour cream 250,000-300,000
Caulking compounds 2,000,000-5,000,000
Window putty >5,000,000

An epoxy’s viscosity limits the applications it can be used for, as well as the means by which it can be applied. In general, a low viscosity epoxy formulation is preferred for applications where a very thin gap has to be filled with an adhesive or when space available for a potting compound is limited. Master Bond offers low viscosity polymers for bonding, sealing and casting such as EP30, EP21LV and EP62-1 with service ranges up to 300°F and products including EP121CL and EP112 for thermal stability up to 500°F. Additionally, for applications when a high viscosity (no flow upon application when placed in a vertical position) is desired, compounds such as EP21TCHT-1, EP33ND and Supreme 10HT are available for service over the temperature range of -60°F to +450°F. Viscosities can usually be adjusted by Master Bond to best meet specific requirements.