Effects of High Temperatures on Silicone Performance
As an established supplier of silicone vacuum blankets to the Aerospace Industry, Mosites Rubber Company is occasionally asked, “How many cycles can I expect from this blanket?” It is a very difficult question to answer because of the number of factors which must be taken into consideration. Among those factors are; the temperature and duration of the cure cycle, the degree of stretch or movement of the blanket during the vacuum process, how well the blanket can be protected from the volatile gasses given off by some of the epoxy or polyester curatives when heated, and the handling and care taken with the blanket during removal from the tool and storage between cure cycles.
Silicone rubber is affected, to varying degrees, by exposure to amine curatives used in epoxy resins, peroxide curatives used in polyester resins, and formaldehyde liberated by some adhesive compositions used in laminating cements. After prolonged exposure, the physical properties will deteriorate and if direct contact occurs between the silicone and resin, adhesion can result. The use of appropriate bleeder systems and barrier films where applicable will minimize this problem. Silicone rubber has excellent resistance to elevated temperature, but as would be expected, exposure to temperatures in excess of 400°F will reduce the service life of a blanket as compared to the same time and temperatures of 350°F or less.
Mosites #1453
Our standard vacuum blanket material, Mosites #1453 has been tested under laboratory conditions of elevated temperature and after exposure to several common aerospace adhesive materials. These properties are not intended as specification standards and actual production applications may not duplicate these effects. The tests conditions and physical properties are shown below.
Resistance of #1453 to high temperature aging | ||||
---|---|---|---|---|
#1453 D | 480 hrs | 288 hrs | 100 hrs | |
Control | @ 350°F | @ 400°F | @ 480°F | |
Hardness (shore A) | 46 | 49 | 51 | 55 |
Tensile (psi) | 1430 | 1260 | 1045 | 1020 |
Elongation (%) | 670% | 510% | 375% | 310% |
Modulus at 300% (psi) | 490 | 680 | 840 | 960 |
Tear Strength (ppi) | 229 | 228 | 164 | 154 |
Resistance to amine volatiles – Type A
A sample of #1453 D silicone sheet was used to seal a fixture containing a 3″ x 3″ square of Hexcel prepreg conforming to BMS-8-79 using di-cyandiamide curative. After each cure cycle of 1 hour at 350°F, new resin prepreg was inserted. Testing was completed after 15 cycles.
Type A | ||
---|---|---|
Control | After 15 cycles | |
Hardness (shore A) | 47 | 51 |
Tensile (psi) | 1440 | 1460 |
Elongation (%) | 540% | 540% |
Modulus at 300% (psi) | 640 | 740 |
Tear Strength (ppi) | 212 | 231 |
Resistance to amine volatiles – Type B
A sample of #1453 D silicone sheet was used to seal a fixture containing a 3″ x 3″ square of Hexcel prepreg conforming to BMS-8-79 using triethylene tetramine curative. After each cure cycle of 1 hour at 350°F, new resin prepreg was inserted. Testing was completed after 25 cycles.
Type B | ||
---|---|---|
Control | After 25 cycles | |
Hardness (shore A) | 45 | 49 |
Tensile (psi) | 1275 | 810 |
Elongation (%) | 600% | 300% |
Modulus at 300% (psi) | 545 | – |
Tear Strength (ppi) | 228 | 146 |
Resistance to direct epoxy contact – Type C
A sample of #1453 D silicone was placed in direct contact (no bleeder system) with FM-53 supported Epoxy Adhesive. The cure cycle consisted of 1 hour at 260°F and 50 psi pressure. Testing was completed after 25 cycles.
Type C | ||
---|---|---|
Control | After 25 cycles | |
Hardness (shore A) | 45 | 46 |
Tensile (psi) | 1320 | 1310 |
Elongation (%) | 560% | 560% |
Modulus at 300% (psi) | 590 | 590 |
Tear Strength (ppi) | 259 | 253 |
Resistance to direct epoxy contact – Type D
A sample of #1453 D silicone was placed in direct contact (no bleeder system) with FM- 1000 supported Epoxy Adhesive. The cure cycle consisted of 1 hour at 350°F and 50 psi pressure. Testing was completed after 25 cycles.
Type D | ||
---|---|---|
Control | After 15 cycles | |
Hardness (shore A) | 47 | 49 |
Tensile (psi) | 1420 | 980 |
Elongation (%) | 600% | 330% |
Modulus at 300% (psi) | 620 | 860 |
Tear Strength (ppi) | 238 | 160 |