Cured Guayule Rubber Containing Compositions And Method For Preparing Same

Abstract

Provided herein are cured rubber compositions containing guayule natural rubber with 2.5-4 weight % resin and fillers. By the use of a specified cure package that contains increased amounts of sulfur and accelerator, the cured rubber compositions are found to exhibit strain induced crystallization (as can be observed by X-ray diffraction). Also provided are related methods for preparing the rubber compositions.

What is claimed is: 
     
         1 . A cured rubber composition comprising:
 a. 100 phr of guayule natural rubber, where the guayule natural rubber contains 2.5-4 weight % resin or 10-90 phr of guayule natural rubber, where the guayule natural rubber contains 2.5-4 weight % resin, and 90-10 phr of at least one conjugated diene monomer containing polymer or copolymer;   b. 5-100 phr of at least one filler selected from the group consisting of carbon black and silica;   
       wherein the cure package used to prepare the cured rubber composition comprises: (i) 1.2 to 4 phr sulfur, (ii) 0.5 to 5 phr of at least one antioxidant, (iii) 0.5 to 5 phr zinc oxide, (iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3 phr of at least one accelerator 
       and the cured rubber composition exhibits strain induced crystallization (as can be observed by X-ray diffraction). 
     
     
         2 . A cured rubber composition according to  claim 1 , wherein the at least one conjugated diene monomer containing polymer or copolymer contains at least one monomer selected from the group consisting of 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene and 2,4-hexadiene;
 and optionally at least one monomer selected from the group consisting of styrene, α-methyl styrene, p-methylstyrene, o-methylstyrene, p-butylstyrene and vinylnaphthalene.   
     
     
         3 . The rubber composition of  claim 1 , wherein the cured rubber composition has a max stress at break, a 300% MPa and an elongation at break that is no more than +/−15% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         4 . The rubber composition of  claim 1 , wherein the cured rubber composition has a max stress at break, a 300% MPa and an elongation at break that is no more than +/−10% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         5 . The rubber composition of  claim 1 , wherein the cured rubber composition has a max stress at break, a 300% MPa and an elongation at break that is no more than +/−5% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         6 . A tire component made from the rubber composition of  claim 1 . 
     
     
         7 . A tire component made from the rubber composition of  claim 1  where the tire component is selected from the group consisting of treads, sidewalls, and body skim plies. 
     
     
         8 . A method of providing a cured guayule natural rubber containing composition with strain induced crystallization comprising:
 a. utilizing a rubber mixture that comprises (i) either 100 phr of guayule natural rubber that contains 2.5-4 weight % resin, or a combination of 10-90 phr of guayule natural rubber that contains 2.5-4 weight % resin and 90-10 phr of at least one conjugated diene monomer containing polymer or copolymer, and (ii) 5-100 phr of at least one filler selected from the group consisting of carbon black and silica, and   b. utilizing a cure package comprising (i) 1.2 to 4 phr sulfur, (ii) 0.5 to 5 phr of at least one antioxidant, (iii) 0.5 to 5 phr zinc oxide, (iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3 phr of at least one accelerator to produce a cured guayule natural rubber containing composition   
       wherein the cured guayule natural rubber containing composition exhibits strain induced crystallization (as evidenced by X-ray diffraction). 
     
     
         9 . A method according to  claim 8 , wherein the cured guayule rubber composition has a max stress at break, a 300% MPa and an elongation at break that is no more than +/−15% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         10 . A method according to  claim 8 , wherein the cured guayule rubber composition has a max stress at break, a 300% Mpa and an elongation at break that is no more than +/−10% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         11 . A method according to  claim 8 , wherein the cured guayule rubber composition has a max stress at break, a 300% Mpa and an elongation at break that is no more than +/−5% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         12 . A cured rubber composition according to  claim 8 , wherein the at least one conjugated diene monomer containing polymer or copolymer contains at least one monomer selected from the group consisting of 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene and 2,4-hexadiene;
 and optionally at least one monomer selected from the group consisting of styrene, α-methyl styrene, p-methylstyrene, o-methylstyrene, p-butylstyrene and vinylnaphthalene.   
     
     
         13 . A method of providing a cured guayule natural rubber containing composition with strain induced crystallization comprising:
 a. utilizing a rubber mixture comprising (i) either 100 phr of guayule natural rubber that contains 2.5-4 weight % resin, or a combination of 10-90 phr of guayule natural rubber that contains 2.5-4 weight % resin and 90-10 phr of at least one conjugated diene monomer containing polymer or copolymer, and (ii) 5-100 phr of at least one filler selected from the group consisting of carbon black and silica, and   b. curing the rubber mixture by increasing the amount of sulfur in the cure package by 30-300% and increasing the amount of accelerator by 30-200% each as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber   
       wherein the cured guayule natural rubber containing composition and the comparative rubber composition both exhibit strain induced crystallization (as can be observed by X-ray diffraction) and have a max stress at break, a 300% Mpa and an elongation at break that are no more than +/−15% different and 
       a tan delta at 0° C. and 50° C. (obtained from temperature sweep experiments conducted with a frequency of 31.4 rad/sec using 0.5% strain for temperatures ranging from −100° C. to −10° C., and with 2% strain for temperatures ranging from −10° C. to 100° C.) that is no more than 5% different that the tan delta at 0° C. and 50° C. of the comparative rubber composition. 
     
     
         14 . A method according to  claim 13 , wherein the amount of sulfur in the cure package is 1.2 to 4 phr and the amount of accelerator in the cure package is 1.05 to 3 phr. 
     
     
         15 . A method according to  claim 13 , wherein the at least one conjugated diene monomer containing polymer or copolymer contains at least one monomer selected from the group consisting of 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene and 2,4-hexadiene;
 and optionally at least one monomer selected from the group consisting of styrene, α-methyl styrene, p-methylstyrene, o-methylstyrene, p-butylstyrene and vinylnaphthalene.   
     
     
         16 . A method according to  claim 13 , wherein the cured guayule rubber composition has a max stress at break, a 300% Mpa and an elongation at break that is no more than +/−10% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber. 
     
     
         17 . A method according to  claim 13 , wherein the cured guayule rubber composition has a max stress at break, a 300% Mpa and an elongation at break that is no more than +/−5% as compared to a comparative rubber composition that contains Hevea natural rubber instead of guayule natural rubber.