Document ID: EPA-HQ-OAR-2004-0008-0519
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2007-02-22T05:00Z

http://www.dowcorning.com/content/rubber/rubberprop/thermal_low.asp

Rubber Physical and Chemical Properties

 

Rubber Home > Physical and Chemical Properties > Temperature Resistance
Properties > Low Temperature Characteristics

Low Temperature Characteristics 

No permanent change occurs in the physical structure of Silastic®
silicone rubber after exposure to extremely low temperatures. Original
mechanical characteristics are regained when the rubber is returned to
room temperature. The most important consideration, however, is that
silicone rubber stays flexible and continues performing at temperatures
which cause most organic elastomers to become brittle and, if flexed, to
crack.

Since the base polymer determines low temperature behaviour, Silastic
silicone rubber is usually classified in accordance with the low
temperature characteristics of three principal polymer types:

1. General purpose rubber (VMQ or MQ)

2. Fluorosilicone (FVMQ)

3. Extreme low temperature service rubber (PVMQ or PMQ)

 

Low temperature capabilities of Silastic silicone rubber and
fluorosilicone rubber* 

Basic type of Silastic rubber	  Brittleness Temperture by Impact ASTM
D2137 	  Stiffening Point Young’s Modulus in Flexure ASTM D797	TR-10
Temperature of Retraction, ASTM D1329

General purpose (VMQ)	-73°C (-100°F)

	-55°C (-67°F)

	      -50°C (-58°F)

High performance (VMQ)

	-78°C (-108°F)

	-60°C (-76°F)

	-50°C (-58°F)

Extreme low temperature (PVMQ)

	-118°C (-180°F)

	-115°C (-175°F)	-116°C (-177°F)

Fluorosilicone (FVMQ)

	-68°C (-90°F)	-59°C (-74°F)

	-57°C (-70°F)

       

* Depends on specimen hardness; values shown are for 50 durometer. 

Low Temperature Testing 

Low temperature testing of Silastic silicone rubber involves a study of
the rubber's behavior at temperatures ranging from room temperature down
to the point where the rubber no longer functions as an elastomer. Four
different tests can be used to determine the low temperature
capabilities of Silastic silicone rubber:

1. Brittleness Temperature by Impact (ASTM D2137) - measures the
temperature at which the rubber becomes so brittle that test specimens
break when hit sharply. Brittleness temperature is reached when 50
percent of the specimens break.

2. Young's Modulus in Flexure (ASTM D797) - measures how much a rubber
specimen, supported by a simple beam, is bent by a measured weight at
increasingly lower temperatures. The temperature at which Young's
modulus reaches 69 MPa is called "Young's Modulus Stiffening
Temperature" for rubber.

3. Gehman Stiffness or Flexure (ASTM D1053) - measures the amount of
twist produced in a specimen that is subjected to constant torque at
various temperatures.

4. Temperature of Retraction (ASTM D1329) - measures the temperature at
which a frozen test specimen becomes flexible enough to contract.

Rubber Physical and Chemical Properties

 

Rubber Home > Physical and Chemical Properties > Chemical Resistance
Properties > Resistance to Chemical Solvents, Fuels, and Oils

Resistance to Chemical Solvents, Fuels, and Oils 

The table below lists typical percent-swell ratings for Silastic®
silicone rubber when exposed to various fluids. The data can be best
interpreted with the following in mind:

1. General purpose rubber is slightly more resistant to most solvents
than low temperature service rubber (those with brittle points of -116
°C).

2. Other factors being the same, high durometer rubber is generally more
solvent resistant than low durometer rubber (The harder materials
usually contain more filler, which does not swell).

3. When immersed in concentrated solutions of strong oxidizing acids,
some rubber materials show a shrink (negative swell). Concentrated
solutions of sulphuric acid have a particularly powerful action, and
dissolve the silicone rubber.

4. The data given in the table are useful only for comparison of the
swell of silicone rubber to that of other elastomers. Swell figures
alone may not always give an accurate picture of the deterioration of a
rubber. The best way to predict the performance of a silicone rubber is
to test it under actual service conditions.

Resistance of Silastic silicone rubber and fluorosilicone rubber to
effects of chemicals, solvents, fuels, and oils 

 

The following guide provides the performance profile of various classes
of silicone rubbers when immersed in different fluids.