Method for fusing aramid/aramid fibers

1. A method for welding aramid fibers comprising:

a) treating at least one area of an aramid fiber with an ionic liquid so that the aramid is partially dissolved,

wherein the aramid fiber is a meta-aramid fiber or a para-aramid copolymer fiber,

wherein the ionic liquid meets at least one of the following two criteria:

i) α value <0.6 and β value >0.8;

ii) difference of β value minus α value ≥0.45,

wherein the α value and β value are Kamlet-Taft solvent parameters,

b) contacting the aramid fiber via the dissolved area with another aramid fiber area, and subsequently

c) causing or allowing the partially dissolved area of the aramid to become re-coagulated, wherein the ionic liquid is not 1-ethyl-3-methylimidazolium acetate.

2. The method according to claim 1 , wherein the ionic liquid comprises a salt,

wherein the salt cation is selected from a quaternary ammonium, phosphonium, guanidinium, pyridinium, pyrimidinium, pyridazinium, pyrazinium, piperidinium, morpholinium, piperazinium, pyrrolium, pyrrolidinium, oxazolium, thiazolium, triazinium, imidazolium, triazolium, protonated guanidinium,

and the salt anion is selected from

halide, selected from the group comprising F—, Cl—, Br—

carboxylate of the general formula

[R n —COO]—  (Vd)

wherein Rn represents hydrogen, (C 1-10 )alkyl, (C 3-10 )cycloalkyl, (C 2-10 )alkenyl, (C 3-10 )cycloalkenyl, aryl, or heteroaryl, preferably (C 1-8 )alkyl, (C 3-8 )cycloalkyl, (C 2-_8 )alkenyl, (C 3-8 )cycloalkenyl, 5- to 6-membered aryl, or 5- to 6-membered heteroaryl,

carbonate,

alkylcarbonate of the general formula

[R s —OCOO] −   (Vf)

wherein Rs is (C1-4)alkyl, in particular methyl carbonate and ethyl carbonate

hydroxide,

alkoxide or aryloxide of the general formula

[R m —O] −   (Ve)

wherein R m represents (C 1-10 )alkyl, (C 3-10 )cycloalkyl, (C 2-10 )alkenyl, (C 3-10 )cycloalkenyl, aryl, or heteroaryl, preferably (C 1-8 )alkyl, (C 3-8 )cycloalkyl, (C 2-8 )alkenyl, (C 3-8 )cycloalkenyl, 5- to 6-membered aryl, or 5- to 6-membered heteroaryl,

phosphate PO 4 3− ,

alkyl or dialkyl phosphate, or alkyl- and dialkyl phosphonate of the general formulas

[R u —OPO 3 ] 2−   (Vi)

[R u O—PO 2 —OR v ] −   (Vj)

[R u —PO 3 ] 2−   (Vk) or

[R u —PO 2 —OR v ]—  (VI),

wherein R u and R v independently represent (C 1-10 )alkyl, (C 3-10 )cycloalkyl, (C 2-10 )alkenyl, (C 3-10 )cycloalkenyl, aryl, or heteroaryl, preferably (C 1-8 )alkyl, (C 3-8 )cycloalkyl, (C 2-8 )alkenyl, (C 3-8 )cycloalkenyl, 5- to 6-membered aryl, or 5- to 6-membered heteroaryl.

3. The method according to claim 1 , wherein the partially dissolved area of the aramid is re-coagulated by:

i) precipitating the aramid by adding an anti-solvent, or

ii) removing the ionic liquid by heating to a temperature above the thermal decomposition point of the ionic liquid, but below the thermal decomposition point of the aramid, wherein the ionic liquid is removed in the form of gaseous decomposition products; or below its thermal decomposition point, as long as the coordinating ionic liquid has a vapor pressure sufficiently high to allow distilling it off optionally in vacuum, or

iii) polymerizing the ionic liquid, or

iv) a combination thereof.

4. The method according to claim 1 , wherein contacting the aramid fiber via the dissolved area with another aramid fiber area is performed while applying pressure to the contact area.

5. The method according to claim 1 , further comprising partially dissolving the further aramid fiber area with the ionic liquid.

6. A method for welding aramid fibers comprising:

a) treating at least one area of an aramid polymer fiber with an ionic liquid so that the aramid polymer is partially dissolved,

wherein the aramid polymer fiber is a para-aramid fiber and not a para-aramid copolymer fiber,

wherein the ionic liquid meets at least one of the following two criteria:

i) α value <0.6 and β value >0.8;

ii) difference of value minus a value >0.45,

wherein the α value and β value are Kamlet-Taft solvent parameters, and the ionic liquid comprises a salt,

wherein the salt cation is selected from a quarternary ammonium, phosphonium, guanidinium, pyridinium, pyrimidinium, pyridazinium, pyrazinium, piperidinium, morpholinium, piperazinium, pyrrolium, pyrrolidinium, oxazolium, thiazolium, triazinium, imidazolium, triazolium, protonated guanidinium,

and the salt anion is selected from

fluoride,

hydroxide,

alkoxide or aryloxide of the general formula [R m —O] − . . . (Ve)

wherein Rm represents (C 1-10 )alkyl, (C 3-10 )cycloalkyl, (C 2-10 )alkenyl, (C 3-10 )cycloalkenyl, aryl, or heteroaryl, preferably (C 1-8 )alkyl, (C 3-8 )cycloalkyl, (C 2-8 )alkenyl, (C 3-8 )cycloalkenyl, 5- to 6-membered aryl, or 5- to 6-membered heteroaryl,

b) contacting the aramid fiber via the dissolved area with another aramid fiber area, and subsequently

c) causing or allowing the partially dissolved area of the aramid to become re-coagulated, wherein the ionic liquid is not 1-ethyl-3-methylimidazolium acetate.

7. The method of claim 6 , wherein the partially dissolved area of the aramid is re-coagulated by:

i) precipitating the aramid by adding an anti-solvent, or

ii) removing the ionic liquid by heating to a temperature above the thermal decomposition point of the ionic liquid, but below the thermal decomposition point of the aramid, wherein the ionic liquid is removed in the form of gaseous decomposition products; or below its thermal decomposition point, as long as the coordinating ionic liquid has a vapor pressure sufficiently high to allow distilling it off optionally in vacuum, or

iii) polymerizing the ionic liquid, or

iv) a combination thereof.

8. The method of claim 6 , wherein contacting the aramid fiber via the dissolved area with another aramid fiber area is performed while applying pressure to the contact area.

9. The method of claim 6 , further comprising partially dissolving the aramid fiber area with the ionic liquid.

10. The method of claim 1 , wherein the aramid fiber is a meta-aramid fiber.