Method for modifying a natural rubber, and modified natural rubber

1. A process for modifying a natural rubber, comprising at least the following steps:

i. providing at least one natural rubber and epoxidizing said natural rubber to obtain an epoxidized natural rubber, or providing a pre-epoxidized natural rubber,

ii. grafting, to said epoxidized natural rubber or to said pre-epoxidized natural rubber, at least one 1,3-dipolar compound having at least one nitrogen atom.

2. A process according to claim 1 , wherein said epoxidized natural rubber or said pre-epoxidized natural rubber has a degree of epoxidation of less than or equal to 50 mol %.

3. A process according to claim 1 , wherein the step (ii) is carried out in bulk or in solution.

4. A process according to claim 1 , wherein the 1,3-dipolar compound comprises at least one nitrile oxide, nitrilimine or nitrone dipole.

5. A process according to claim 4 , wherein the 1,3-dipolar compound comprises at least one nitrile oxide dipole.

6. A process according to claim 5 , wherein the nitrile oxide dipole belongs to a unit corresponding to the general formula (I)

in which:

R1, R2, R3, R4, R5, which are identical or different, represent a hydrogen atom, a halogen atom, a C 1 -C 5 alkyl, a C 1 -C 5 alkoxyl or a covalent bond enabling attachment to the remainder of the 1,3-dipolar compound;

with the proviso that at least one of R1, R2, R3, R4, R5 represents said covalent bond.

7. A process according to claim 1 , wherein the step (ii) is carried out by heating to a temperature of greater than or equal to 70° C.

8. A process according to claim 1 , wherein the content of said 1,3-dipolar compound ranges from 0.1 to 10 mol %.

9. A process according to claim 1 , wherein the 1,3-dipolar compound bears at least one chemical group intended to be grafted to the epoxidized natural rubber, said chemical group being a hydrocarbon-based chain that may optionally contain a heteroatom.

10. A process according to claim 9 , wherein the chemical group is selected from hydrocarbon-based groups, optionally substituted nitrogenous or sulfur-containing heterocycles, esters, phosphates, dialkylaminos and associative groups comprising at least one nitrogen atom.

11. A process according to claim 10 , wherein the associative group comprising at least one nitrogen atom is selected from the following formulae (IV), (V), (VI), (VII) and (VIII):

in which:

R15 represents a hydrocarbon-based group that may optionally contain heteroatoms,

Q represents an oxygen or sulfur atom or NH,

the symbol * represents an indirect attachment to the dipole of the 1,3-dipolar compound.

12. A process according to claim 10 , wherein the 1,3-dipolar compound is selected from the compounds corresponding to the formulae (IX), (X), (XI), (XII), (XIII), (XIV), (XV), (XVI), (XVII), (XVIII), (XIX) and their mesomeric forms:

13. A process according to claim 1 , wherein said epoxidized natural rubber or said pre-epoxidized natural rubber has a degree of epoxidation of greater than or equal to 0.5 mol %.

14. A process according to claim 1 , wherein the step (ii) is carried out in bulk.

15. A modified natural rubber obtained according to the process defined in claim 1 .

16. A rubber composition based on:

at least one modified natural rubber according to claim 15 ,

at least one reinforcing filler, and

at least one crosslinking system.

17. A process for producing a composition according to claim 16 , the process comprising at least the following steps:

incorporating at least one reinforcing filler into the modified natural rubber, everything being kneaded thermomechanically, once or several times, until a maximum temperature ranging from 130° C. to 200° C., is reached,

cooling the combined mixture to a temperature below 100° C.,

then incorporating at least one chemical crosslinking system,

kneading everything up to a maximum temperature of less than 120° C.,

extruding or calendering the rubber composition thus obtained.

18. A process for producing a composition according to claim 16 , the process comprising at least the following steps:

providing at least one natural rubber and epoxidizing said natural rubber to obtain an epoxidized natural rubber, or providing a pre-epoxidized natural rubber,

incorporating at least one 1,3-dipolar compound having at least one nitrogen atom to the epoxidized natural rubber from the preceding step,

subsequently incorporating at least one reinforcing filler, everything being kneaded thermomechanically, once or several times, until a maximum temperature ranging from 130° C. to 200° C., is reached,

cooling the combined mixture to a temperature below 100° C.,

then incorporating at least one chemical crosslinking system,

kneading everything up to a maximum temperature of less than 120° C.,

extruding or calendering the rubber composition thus obtained.

19. A finished or semi-finished rubber product comprising at least one rubber composition defined according to claim 16 .

20. A tire comprising at least one semi-finished product defined according to claim 19 .