Durable elastomeric compositions employing cyclododecasulfur as a vulcanizing agent
Vulcanizable elastomeric formulation are disclosed. The formulations comprise at least one elastomer; a vulcanizing agent comprising cyclododecasulfur; and a prevulcanization inhibitor, present in an amount, for example, from about 0.01 phr to about 10 phr. The formulations, when vulcanized, provide articles that exhibit improved durability.
1. A vulcanizable elastomeric formulation comprising:
at least one elastomer;
a vulcanizing agent comprising cyclododecasulfur; and
a prevulcanization inhibitor, present in an amount from about 0.01 phr to about 10.0 phr.
2. The vulcanizable elastomeric formulation of claim 1 , wherein the prevulcanization inhibitor comprises one or more of: a sulfenamide, a sulfonamide, a sulfamide, a bis-thioimide, a thiocycloamide, a thioamide, a poly(thioamide), an N-hydrocarbylthio(amide), or a polysulfide.
3. The vulcanizable elastomeric formulation of claim 1 , wherein the prevulcanization inhibitor comprises N-(cyclohexylthiol) phthalimide.
4. The vulcanizable elastomeric formulation of claim 1 , wherein the prevulcanization inhibitor is present in an amount from 0.02 phr to 8 phr.
5. The vulcanizable elastomeric formulation of claim 1 , wherein the prevulcanization inhibitor is present in an amount from 0.05 phr to 5 phr.
6. The vulcanizable elastomeric formulation of claim 1 , wherein the vulcanizable elastomeric formulation further comprises a reinforcing resin, formed of a methylene acceptor and a methylene donor, present in an amount of no more than 2 phr.
7. The vulcanizable elastomeric formulation of claim 1 , wherein the amount of cyclododecasulfur in the formulation is from 1 to 25 phr.
8. The vulcanizable elastomeric formulation of claim 1 , wherein the amount of cyclododecasulfur in the formulation is from 1.5 phr to 20 phr.
9. The vulcanizable elastomeric formulation of claim 1 , wherein the amount of cyclododecasulfur in the formulation is from 2 phr to 15 phr.
10. A vulcanized elastomeric article formed from the vulcanizable elastomeric formulation of claim 1 .
11. A process for forming a vulcanized elastomeric article, comprising:
a) mixing an elastomer with a vulcanizing agent and a prevulcanization inhibitor, present in an amount from about 0.01 phr to about 10.0 phr, to form a vulcanizable elastomeric formulation that includes the vulcanizing agent dispersed in the elastomer; (b) forming the vulcanizable elastomeric formulation into a formed shape; and (c) vulcanizing the formed shape to form the vulcanized elastomeric article; wherein the vulcanizing agent comprises cyclododecasulfur, and wherein at least one of the mixing and forming steps comprises increasing the bulk average processing temperature of said vulcanizable elastomeric formulation to greater than 125° C. for at least a portion of said step.
12. The process of claim 11 , wherein at least one of the mixing and forming steps comprises increasing the bulk average processing temperature of said vulcanizable elastomeric formulation to greater than 128° C. for at least a portion of said step.
13. The process of claim 11 , wherein at least one of the mixing and forming steps comprises increasing the bulk average processing temperature of said vulcanizable elastomeric formulation to greater than 130° C. for at least a portion of said step.
14. The process of claim 11 , wherein said vulcanizable elastomeric formulation further comprises an antireversion agent.
15. The process of claim 14 , wherein said antireversion agent comprises one or more of: hexamethylene-1,6-bis(thiosulfate), disodium salt, dihydrate and 1,3-bis(citraconamidomethyl)benzene.
16. The process of claim 11 , wherein the prevulcanization inhibitor comprises N-(cyclohexylthio) phthalimide.
17. The process of claim 16 , wherein the vulcanized elastomeric article is in the form of a tire.