Curable fluoroelastomer compositions
Provided herein is a curable fluoroelastomer composition including at least one fluoroelastomer comprising copolymerized units of a nitrile group-containing cure site monomer; a cure system comprising at least two different dihydrazides; and optionally at least one additive. Further provided are pre-forms comprising the curable composition, methods of curing the fluoroelastomer composition, compositions that are the product of curing the curable fluoroelastomer composition, and articles comprising the cured fluoroelastomer composition.
1. A curable fluoroelastomer composition comprising:
A) at least one fluoroelastomer comprising copolymerized units of a nitrile group-containing cure site monomer;
B) a cure system comprising at least two different dihydrazides, wherein the cure system comprises isophthalic dihydrazide and oxalyl dihydrazide; and optionally
C) at least one additive.
2. The curable fluoroelastomer composition of claim 1 , wherein the at least one fluoroelastomer comprises copolymerized units of:
i) at least one fluorinated olefin;
ii) at least one fluorovinyl ether; and
iii) at least one nitrile group-containing cure site monomer selected from the group consisting of nitrile group-containing perfluorinated olefins and nitrile group-containing perfluorinated vinyl ethers.
3. The curable fluoroelastomer composition of claim 2 , wherein the at least one fluorinated olefin is selected from the group consisting of 1,1-difluoroethylene (C 2 H 2 F 2 ); hexafluoropropylene (HFP); tetrafluoroethylene (TFE); 1,2,3,3,3-pentafluoro-propene (1-HPFP); 1,1,3,3,3-pentafluoropropene (2-HPFP); chlorotrifluoro-ethylene (CTFE); 1,1,2-trifluoroethylene; 1-fluoroethylene; and a combination of two or more of 1,1-difluoroethylene; hexafluoropropylene; tetrafluoroethylene; 1,2,3,3,3-pentafluoro-propene; 1,1,3,3,3-pentafluoropropene; chlorotrifluoro-ethylene; 1,1,2-trifluoroethylene; and 1-fluoroethylene.
4. The curable fluoroelastomer composition of claim 2 , wherein the at least one fluorinated olefin is selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and a combination of tetrafluoroethylene and hexafluoropropylene.
5. The curable fluoroelastomer composition of claim 2 , wherein the at least one fluorovinyl ether is selected from the group consisting of perfluoro(methyl vinyl) ether; perfluoro(ethyl vinyl) ether; perfluoro(propyl vinyl) ether; CF 3 O—(CF 2 O) n -CF 2 CF 2 -OCF═CF 2 , where n is 0, 1, 2, 3, 4 or 5; and a combination of two or more of perfluoro(methyl vinyl) ether; perfluoro(ethyl vinyl) ether; perfluoro(propyl vinyl) ether; and CF 3 O-(CF 2 O) n -CF 2 CF 2 -OCF═CF 2 , where n is 0, 1, 2, 3, 4 or 5.
6. The curable fluoroelastomer composition of claim 2 , wherein the at least one nitrile group-containing cure site monomer comprises perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene).
7. The curable fluoroelastomer composition of claim 1 , wherein the at least one additive is present and comprises one or more additives selected from the group consisting of carbon black, lubricants, fillers, fluoropolymer micropowders, stabilizers, plasticizers, and processing aids.
8. The curable fluoroelastomer composition of claim 1 , wherein the at least one additive comprises at least one filler selected from the group consisting of a silica, an alumina, an aluminum silicate, a barium sulfate, a titanium dioxide, and a combination of two or more of a silica, an alumina, an aluminum silicate, a barium sulfate, and a titanium dioxide.
9. The curable fluoroelastomer composition of claim 1 , wherein the weight ratio of isophthalic dihydrazide to oxalyl dihydrazide ranges from about 3:1 to about 1:2.
10. The curable fluoroelastomer composition of claim 1 , in the shape of a blank or a pre-form.
11. A cured fluoroelastomer composition that is the product of curing the curable fluoroelastomer composition of claim 1 .
12. The cured fluoroelastomer composition of claim 11 , that has a volume swell, measured according to ASTM D1414:2015 after exposure to 225° C. water for 70 hours, of less than 10% or 8%; or an elongation at break, measured according to ASTM D412-06a:2013, of at least 43% or 46%.
13. An article comprising the cured fluoroelastomer composition of claim 11 .
14. The article of claim 13 in the form of a gasket, tube, seal, or O-ring.
15. A cured article of claim 13 having a volume swell, measured according to ASTM D1414:2015 after exposure to 225° C. water for 70 hours, of less than 10% or 8%; or an elongation at break, measured according to ASTM D412-06a:2013, of at least 43% or 46%.