Nanocomposites with controlled electrical properties

1. A field grading material comprising:

a polymer matrix, said polymer matrix having two or more polymer phases; and

a field grading effective amount of a semiconducting nanoparticle filler, wherein said filler is heterogeneously distributed in said polymer matrix such that said semiconducting nanoparticle filler is well dispersed in at least part of one of said polymer phases; and wherein said semiconducting nanoparticle filler comprises less than 40% by volume of said field grading material.

2. A field grading material according to claim 1 , wherein said nanoparticle filler is selected from semiconducting materials having an energy bandgap ranging from 0 eV to 5 eV and dielectric materials having a bulk dielectric constant at infinitely high frequencies of at least 5.

3. A field grading material according to claim 1 , wherein said nanoparticle filler comprises a semiconducting material.

4. A field grading material according to claim 1 , wherein said nanoparticle filler is selected from ZnO, SnO, InO, CeO, TiO 2 , SiC, BaTiO 3 , Al 2 O 3 , SiO 2 and mixtures thereof.

5. A field grading material according to claim 1 , wherein said polymeric matrix comprises a rubber, a thermoplastic polymer, a thermosetting polymer, or thermoplastic elastomer.

6. A field grading material according to claim 5 , wherein said polymeric matrix comprises at least one of a polyolefin rubber, a thermoplastic polyolefin elastomer, a silicone rubber, and a crystalline thermoplastic polymer.

7. A field grading material according to claim 5 , wherein said polymeric matrix comprises a polymer selected from EPDM and polyethylene.

8. A field grading material according to claim 1 , wherein said polymeric matrix comprises a polymer blend of immiscible polymers.

9. A field grading material according to claim 8 , wherein said polymer blend is selected from polyethylene/EPDM, LDPE/HDPE, and maleic anhydride-modified EPDM/EPDM.

10. A field grading material according to claim 1 , wherein said nanoparticles have a particle size from 2 to 80 nm.

11. A field grading material according to claim 1 , wherein said nanoparticle filler comprises less than 30% by volume of the field grading material.

12. A field grading material according to claim 1 , wherein a surface of said nanoparticle filler is modified by treatment with an organosilane or organotitanate compound and the organosilane compound comprises an organic group selected from alkyl, alkylamino, amino and carboxy.

13. A field grading material according to claim 12 , wherein said organic group is selected from methyl, decyl, octyl, vinyl, aminopropyl and acetoxy.

14. A field grading material comprising a semiconducting nanoparticle filler heterogeneously distributed in a polymeric matrix, wherein a surface of said semiconducting nanoparticle filler is modified by treatment with an organosilane or organotitanate compound and said organosilane compound comprises an organic group selected from alkyl, alkylamino, amino and carboxy.

15. A field grading material according to claim 14 , wherein said organic group is selected from methyl, decyl, octyl, vinyl, aminopropyl, and acetoxy.

16. A method for reducing electric field stress at a joint or termination of an electric cable, said method comprising introducing in said joint or termination a field grading material according to claim 1 .