Cross-linking compositions for polymer-modified asphalt compositions

1. A method for preparing bitumen/elastomeric polymer compositions comprising:

a. heating the bitumen in a stirred tank to a temperature of between 220 and 430° F.;

b. adding the elastomeric polymer to the tank in an amount of between 2 and 30 weight percent, to form a mixture of bitumen and elastomeric polymer;

c. adding 0.01 to 5 weight percent of a cross-linking composition to the mixture and continuing stirring while maintaining the temperature of the mixture at between 275 and 430° F. for a time period of between 20 and 120 minutes;

wherein said cross-linking composition comprises:

a. 5 to 50 percent by weight of elemental sulfur:

b. 0.5 to 10 percent by weight of a sulfur-containing derivative selected from the group consisting of compounds having the formula

where R 1 and R 2 are like or different alky radicals having 1 to 4 carbon atoms and wherein M is selected from the group consisting of zinc, barium, copper, cadmium and thallium;

c. 5 to 50 percent by weight of a sulfur activator selected from zinc compounds;

d. 5 to 50 percent by weight of a solubilizing agent selected from fatty acids and fatty acid derivatives; and

e. 10 to 85 percent by weight of a polymeric carrier,

said cross-linking composition having a zinc content of at least 2 weight percent, based on the total weight of the cross-linking composition and a zinc to sulfur content weight ratio of 0.5:1 to 2:1.

2. The method according to claim 1 wherein said bitumen is selected from the group consisting of straight-run bitumens and fluxed bitumens.

3. The method according to claim 2 wherein said elastomeric polymer is selected from the group consisting of butyl rubber, polybutadiene, polyisoprene, ethylene/propylene/diene (EPDM) terpolymers, and styrene/conjugated diene block copolymers.

4. The method according to claim 3 wherein said elastomeric polymer is a styrene/conjugated diene block copolymer having a structure represented by the following general formulae

S—B—S, (S—B) n —-X, (S—B) or a mixture thereof,

wherein each S independently is a poly(vinyl aromatic) block and each B independently is a poly(conjugated diene) block, n is an integer equal to or greater than 2 and X is the residue of a coupling agent.

5. The method according to claim 4 wherein said styrene/conjugated diene block copolymer is a radial styrene/butadiene block copolymer having a diblock content of between 65 and 85 mole percent.

6. The method according to claim 4 wherein said styrene/conjugated diene block copolymer is a styrene-butadiene diblock copolymer.

7. The method according to claim 4 wherein said sulfur-containing derivative is zinc dimethyl dithio carbamate.

8. The method according to claim 7 wherein said sulfur activator is zinc oxide and said solubilizing agent is calcium stearate.

9. The method according to claim 8 wherein said polymeric carrier is selected from the group consisting of ethylene/propylene rubber, and ethylene/vinyl acetate copolymers.

10. The method according to claim 8 wherein the polymeric carrier is a polyethylene having a number average molecular weight of 7700.

11. A method for preparing bitumen/elastomeric polymer compositions comprising:

a. heating the bitumen in a stirred tank to a temperature of between 220 and 430° F.;

b. adding the elastomeric polymer to the tank in an amount of between 2 and 30 weight percent, to form a mixture of bitumen and elastomeric polymer;

c. adding 0.01 to 5 weight percent of a cross-linking composition to the mixture and continuing stirring while maintaining the temperature of the mixture at between 275 and 430° F. for a time period of between 20 and 120 minutes;

wherein said cross-linking composition comprises:

a. 5 to 50 percent by weight of elemental sulfur:

b. 0.5 to 10 percent by weight of a sulfur-containing derivative selected from the group consisting of compounds having the formula

where R 1 and R 2 are like or different alky radicals having 1 to 4 carbon atoms and wherein M is selected from the group consisting of zinc, barium, copper, cadmium and thallium;

c. 5 to 50 percent by weight of a component selected from fatty acid derivatives of zinc; and

d. 10 to 85 percent by weight of a polymeric carrier, said cross-linking composition having a zinc content of at least 2 weight percent, based on the total weight of the cross-linking composition and a zinc to sulfur content weight ratio of 0.5:1 to 2:1.

12. The method according to claim 1 wherein said bitumen is selected from the group consisting of straight-run bitumens and fluxed bitumens.

13. The method according to claim 2 wherein said elastomeric polymer is selected from the group consisting of butyl rubber, polybutadiene, polyisoprene, ethylene/propylene/diene (EPDM) terpolymers, and styrene/conjugated diene block copolymers.

14. The method according to claim 3 wherein said elastomeric polymer is a styrene/conjugated diene block copolymer having a structure represented by the following general formulae

S—B—S, (S—B) n —X, (S—B) or a mixture thereof,

wherein each S independently is a poly(vinyl aromatic) block and each B independently is a poly(conjugated diene) block, n is an integer equal to or greater than 2 and X is the residue of a coupling agent.

15. The method according to claim 4 wherein said styrene/conjugated diene block copolymer is a radial styrene/butadiene block copolymer having a diblock content of between 65 and 85 mole percent.

16. The method according to claim 4 wherein said styrene/conjugated diene block copolymer is a styrene-butadiene diblock copolymer.

17. The method according to claim 8 wherein said polymeric carrier is selected from the group consisting of ethylene/propylene rubber, and ethylene/vinyl acetate copolymers.