Multilayer tubular structure having better resistance to extraction in biofuel and use thereof

1. A multilayer tubular structure (MLT) suitable for the transport of fuels, wherein the MLT comprises, from the outside inwards, at least one first barrier layer, at least one inner layer located below the first barrier layer, and optional layers located below the first barrier layer, wherein:

the first barrier layer comprises EVOH or comprises PPA; and

the inner layer comprises at least two aliphatic polyamides, wherein the aliphatic polyamides are selected from the group consisting of PA610, PA612, and PA1012,

with the proviso that when the inner layer comprises at least three polyamides, at least one of said polyamides PA610, PA612 and PA1012 is excluded,

wherein at least one first outer layer is present and wherein the first outer layer is located further outwards, above the first barrier layer, wherein the at least one first outer layer comprises at least one polyamide of aliphatic type or comprises more than 75% of aliphatic units,

wherein the first outer layer comprises plasticizer in a proportion from 0% to 5% by weight relative to the total weight of the composition of the at least one first outer layer,

wherein at least one second outer layer located above the barrier layer is present, and is located above the at least one first outer layer wherein the at least one second outer layer comprises plasticizer in a proportion from 0% to 5% by weight relative to the total weight of the composition of the at least one second outer layer,

wherein the inner layer and the optional layers located below the first barrier layer do not comprise plasticizer,

wherein at least one first binder layer is present, where the first binder layer contains at most 15% by weight of plasticizer relative to the total weight of the constituents of the first binder layer, where the first binder layer comprises at least one aliphatic polyamide of an aliphatic type or which comprises more than 75% of aliphatic units, wherein the aliphatic polyamide is selected from the group consisting of:

a polyamide denoted A, having a mean number of carbon atoms per nitrogen atom, denoted C A , of from 4 to 8.5;

a polyamide denoted B, having a mean number of carbon atoms per nitrogen atom, denoted C B , of from 7 to 10; and

a polyamide denoted C, having a mean number of carbon atoms per nitrogen atom, denoted C C , of from 9 to 18,

with the proviso that when the first binder layer comprises at least three polyamides, at least one of the polyamides A, B and C is excluded;

wherein the first binder layer is located between the first barrier layer and the inner layer;

wherein the thickness of the first binder layer comprises at most 15% of the total thickness of the MLT.

2. The MLT according to claim 1 , wherein the at least one second outer layer is the outermost layer and wherein the at least one second outer layer is the only layer that comprises plasticizer.

3. The MLT according to claim 1 , wherein a second binder layer is present, and wherein the second binder layer comprises at least one aliphatic polyamide of an aliphatic type or which comprises more than 75% of aliphatic units, wherein the aliphatic polyamide is selected from the group consisting of:

a polyamide denoted A, having a mean number of carbon atoms per nitrogen atom, denoted C A , of from 4 to 8.5;

a polyamide denoted B, having a mean number of carbon atoms per nitrogen atom, denoted C B , of from 7 to 10; and

a polyamide denoted C, having a mean number of carbon atoms per nitrogen atom, denoted C C , of from 9 to 18;

or the second binder layer is comprised of binder, wherein the thickness of the second binder layer represents at most 15% of the MLT, with the proviso that the

at least one aliphatic polyamide of the second binder layer can be identical to or different from the polyamide of the first binder layer;

wherein the second binder layer is located between the first or the second outer layer and the first barrier layer and wherein the first binder layer is located between the first barrier layer and the inner layer.

4. The MLT according to claim 3 , wherein the polyamide of at least one of the first binder layer or the second binder layer is selected from the group consisting of the binary mixtures: PA6 and PA12, PA6 and PA612, PA6 and PA610, PA12 and PA612, PA12 and PA610, PA1010 and PA612, PA1010 and PA610, PA1012 and PA612, PA1012, and PA610; and the ternary mixtures: PA6, PA610, and PA12; PA6, PA612, and PA12; PA6, PA614, and PA12.

5. The MLT according to claim 3 , wherein at least one of the inner layer, the first outer layer, the first binder layer, or the second binder layer comprises at least one of an impact modifier and at least one other additive.

6. The MLT according to claim 3 , wherein the structure comprises six layers in the following order from outside to inside:

a second outer layer, the first outer layer, the second binder layer, the first barrier layer, the first binder layer, the inner layer, wherein the second outer layer comprises from 1.5% to 5% plasticizer by weight relative to the total weight of the composition of the second outer layer, and the thickness of the second outer layer comprises up to 20% of the total thickness of the multilayer tubular structure, and the thickness of the second outer layer is up to 200 μm.

7. The MLT according to claim 1 , wherein the polyamide of the first outer layer is totally aliphatic.

8. The MLT according to claim 1 , further comprising a second barrier layer wherein the second barrier layer may be located adjacent to, or located not adjacent to, the first barrier layer, and wherein the second barrier layer is located below the first barrier layer.

9. The MLT according to claim 8 , wherein the first barrier layer is comprised of EVOH and the second barrier layer comprises PPA or fluoropolymer.

10. The MLT according to claim 8 , wherein the structure comprises five layers in the following order from outside to inside: the second outer layer, the first outer layer, the first barrier layer, the second barrier layer, the inner layer;

wherein the first barrier layer comprises EVOH, the second barrier layer comprises PPA; or

wherein the structure comprises five layers in the following order from outside to inside: second outer layer, first outer layer, first barrier layer, inner layer, second barrier layer;

wherein the first barrier layer comprises EVOH, the second barrier layer comprises PPA; or

wherein the structure comprises five layers in the following order from outside to inside: the second outer layer, the second binder layer, the first barrier layer, the first binder layer, the inner layer;

wherein the first outer layer comprises at least one aliphatic polyamide of aliphatic type or comprises more than 75% of aliphatic units, wherein the aliphatic polyamide has a mean number of carbon atoms per nitrogen atom of from 9.5 to 18.

11. The MLT according to claim 1 , wherein the first barrier layer comprises EVOH, and the EVOH comprises up to 27% of ethylene.

12. The MLT according to claim 1 , wherein the first barrier layer comprises EVOH, and the EVOH further comprises an impact modifier.

13. The MLT according to claim 1 , wherein the polyamide of the first outer layer is selected from the group consisting of PA11, PA12, PA610, PA612, PA1012, the corresponding copolyamides thereof, and mixtures thereof.

14. The MLT according to claim 1 , wherein the polyamide of at least one of the layers is a conductive polyamide.

15. The MLT according to claim 1 , wherein the first outer layer and the second outer layer each contains at most 1.5% by weight of plasticizer relative to the total weight of the composition of each layer.

16. The MLT according to claim 1 , wherein the thickness of the at least one second outer layer comprises up to 20% of the total thickness of the multilayer tubular structure.