Process for preparing bitumen/rubber compositions

Abstract

In methods of preparing asphalt and elastomeric polymer compositions, it has been discovered that for a given crosslinker or vulcanizing agent there is an optimum crosslinking temperature to give a composition that has top and bottom softening points that are close. That is, rubber/asphalt compatibility is improved, where the crosslinking is performed within the optimum temperature range.

I claim:  
     
         1 . A method for preparing asphalt and polymer compositions comprising: 
 (a) heating a mixture of asphalt and an elastomeric polymer to within an optimum crosslinking temperature range; and    (b) adding a crosslinker to the mixture, where the crosslinker is selected from the group consisting of a sulfur-containing derivative and elemental sulfur and mixtures thereof.    where the optimum crosslinking temperature range is that where the resulting asphalt/polymer composition has a difference between the top and bottom softening points of 20° C. or less.    
     
     
         2 . The method of  claim 1  where in heating the mixture, the elastomeric polymer is a vinyl aromatic/conjugated diene elastomer.  
     
     
         3 . The method of  claim 2  where the elastomeric polymer is a styrene-butadiene copolymer.  
     
     
         4 . The method of  claim 1  where in adding the crosslinker, the crosslinker is selected from the group consisting of elemental sulfur, mercaptobenzothiazole (MBT), thiurams, and mixtures thereof.  
     
     
         5 . The method of  claim 4  where in adding the crosslinker, the crosslinker comprises a thiuram polysulfide.  
     
     
         6 . The method of  claim 5  where the thiuram polysulfide has the formula:  
       
         
           
           
               
               
           
         
       
       where R 1  and R 2  are the same or different alkyl substitutents having from 1 to 4 carbon atoms, and wherein M is a metal selected from zinc, barium or copper, and n is 0 or 1, and where the optimum crosslinking temperature range is above 180° C.  
     
     
         7 . The method of  claim 6  where the optimum crosslinking temperature range is between about 185 and about 190° C.  
     
     
         8 . The method of  claim 1  where the elastomeric polymer comprises from about 1 to 20 wt % of the asphalt/polymer mixture and where the asphalt has a penetration of between about 20 and 320 dmm.  
     
     
         9 . The method of  claim 1  where the crosslinker is present in an amount ranging from about 0.01 to 0.1 wt %, based on the weight of the asphalt/polymer mixture.  
     
     
         10 . A method for preparing asphalt and polymer compositions comprising: 
 (a) heating a mixture of asphalt and an elastomeric polymer to within an optimum crosslinking temperature range; and    (b) adding a thiuram polysulfide crosslinker to the mixture, where the crosslinker is selected from the group consisting of a sulfur-containing derivative and elemental sulfur and mixtures thereof.    where the optimum crosslinking temperature range is that where the resulting asphalt/polymer composition has a difference between the top and bottom softening points of 20° C. or less, and where the range is above 180° C.    
     
     
         11 . The method of  claim 10  where in heating the mixture, the elastomeric polymer is a vinyl aromatic/conjugated diene elastomer, and where the crosslinker is present in an amount ranging from about 0.01 to 0.1 wt %, based on the weight of the asphalt/polymer mixture.  
     
     
         12 . An asphalt and polymer composition prepared by the method comprising: 
 (a) heating a mixture of asphalt and an elastomeric polymer to within an optimum crosslinking temperature range; and    (b) adding a crosslinker to the mixture, where the crosslinker is selected from the group consisting of a sulfur-containing derivative and elemental sulfur and mixtures thereof.    where the optimum crosslinking temperature range is that where the resulting asphalt/polymer composition has a difference between the top and bottom softening points of 20° C. or less.    
     
     
         13 . The composition of  claim 12  where in the method, in heating the mixture, the elastomeric polymer is a vinyl aromatic/conjugated diene elastomer.  
     
     
         14 . The composition of  claim 13  where in the method, the elastomeric polymer is a styrene-butadiene copolymer.  
     
     
         15 . The composition of  claim 12  where in the method, in adding the crosslinker, the crosslinker is selected from the group consisting of elemental sulfur, mercaptobenzothiazole (MBT), thiurams, and mixtures thereof.  
     
     
         16 . The composition of  claim 15  where in the method, in adding the crosslinker, the crosslinker comprises a thiuram polysulfide.  
     
     
         17 . The composition of  claim 16  where in the method, the thiuram polysulfide has the formula:  
       
         
           
           
               
               
           
         
       
       where R 1  and R 2  are the same or different alkyl substituents having from 1 to 4 carbon atoms, and wherein M is a metal selected from zinc, barium or copper, and n is 0 or 1, and where the optimum crosslinking temperature range is above 180° C.  
     
     
         18 . The composition of  claim 17  where in the method, the optimum crosslinking temperature range is between about 185 and about 190° C.  
     
     
         19 . The composition of  claim 12  where in the method, the elastomeric polymer comprises from about 1 to 20 wt % of the asphalt/polymer mixture and where the asphalt has a penetration of between about 20 and 320 dmm.  
     
     
         20 . The composition of  claim 12  where in the method, the crosslinker is present in an amount ranging from about 0.01 to 0.1 wt %, based on the weight of the asphalt/polymer mixture.