Aramid nanofiber filaments and related methods
The disclosure relates to a method for forming nanofiber-assembled filaments in which an aromatic polyamide nanofiber suspension is first formed into wet nanofiber-assembled filaments via wet-spinning and protonation in a coagulation medium including at least one proton donor along with a non-solvent for the aromatic polyamide. The wet nanofiber-assembled filaments are then drawn to reduce/remove voids in the nanofiber-assembled filaments and improve the mechanical properties of the assembled filaments. The method can be used as a recycling method for used aromatic polyamide fiber/filament materials in which the recycled filaments have high/good mechanical properties relative to virgin filament materials.
1 . A method for forming nanofiber-assembled filaments, the method comprising:
providing a nanofiber suspension comprising aromatic polyamide nanofibers dispersed therein, wherein (i) the nanofiber suspension comprises a suspension medium comprising water, deprotonated aromatic polyamide nanofibers as the aromatic polyamide nanofibers, a water-miscible solvent for the deprotonated aromatic polyamide nanofibers, and a base, and (ii) the water-miscible solvent comprises at least one of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and methyl ethyl ketone (MEK);
wet-spinning the nanofiber suspension into a coagulation medium comprising at least one non-solvent for the aromatic polyamide nanofibers and at least one proton donor, thereby forming wet nanofiber-assembled filaments in the coagulation medium;
optionally washing the wet nanofiber-assembled filaments;
drawing the wet nanofiber-assembled filaments, thereby reducing or removing voids in the nanofiber-assembled filaments;
optionally drying the wet nanofiber-assembled filaments, thereby forming dry nanofiber-assembled filaments; and
optionally annealing the dry nanofiber-assembled filaments, thereby forming annealed nanofiber-assembled filaments.
2 . The method of claim 1 , wherein the aromatic polyamide of the nanofibers is selected from the group consisting of aromatic polyamide homopolymers, polyamide copolymers, and combinations thereof.
3 . The method of claim 1 , wherein the aromatic polyamide nanofiber comprises aromatic polyamide repeat units selected from —(NH—C 6 H 4 —NHCO—C 6 H 4 —CO) n —, —(NH—C 6 H 4 —CO) n —, and combinations thereof.
4 . The method of claim 1 , wherein:
the aromatic polyamide nanofibers have a diameter in a range of 1 nm to 500 nm; and
the aromatic polyamide nanofibers have a length in a range of 0.5 μm to 250 μm.
5 . The method of claim 1 , wherein:
the nanofiber suspension contains the deprotonated aromatic polyamide nanofibers in an amount of 0.001 wt. % to 5 wt. % based on the nanofiber suspension.
6 . The method of claim 1 , wherein the coagulation medium comprises water as the at least one non-solvent and the at least one proton donor.
7 . The method of claim 1 , wherein the coagulation medium comprises an acid as the at least one proton donor.
8 . The method of claim 1 , wherein the coagulation medium comprises an aprotic solvent as the non-solvent for the aromatic polyamide nanofibers.
9 . The method of claim 1 , wherein the coagulation medium comprises at least one of a crosslinker, a reinforcement material, a binder, and a functional component.
10 . The method of claim 1 , comprising washing the wet nanofiber-assembled filaments.
11 . The method of claim 1 , wherein drawing the wet nanofiber-assembled filaments comprises subjecting the wet nanofiber-assembled filaments to an extensional strain of at least 2%.
12 . The method of claim 1 , comprising drying the wet nanofiber-assembled filaments.
13 . The method of claim 1 , comprising annealing the nanofiber-assembled filaments.
14 . The method of claim 1 , further comprising:
repeating the steps of claim 1 to form a plurality of nanofiber-assembled filaments; and
assembling the plurality of nanofiber-assembled filaments into a composite structure having a predetermined geometry.
15 . The method of claim 1 , wherein the nanofiber-assembled filaments have at least one of the following properties:
a Young's modulus of at least 30 GPa;
a tensile strength of at least 600 MPa;
a toughness of at least 30 MJ/m 3 ; and
an orientation index of at least 0.3.
16 . The method of claim 1 , wherein the nanofiber-assembled filaments have a diameter in a range of 1 μm to 50 μm.
17 . The method of claim 1 , wherein the filaments are formed in the absence of binders and/or crosslinkers.
18 . A method for forming nanofiber-assembled filaments, the method comprising:
providing a nanofiber suspension comprising aromatic polyamide nanofibers dispersed therein, wherein (i) the nanofiber suspension comprises a suspension medium comprises water, deprotonated aromatic polyamide nanofibers as the aromatic polyamide nanofibers, a water-miscible solvent for the deprotonated aromatic polyamide nanofibers, and a base, and (ii) the water-miscible solvent comprises at least one of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and methyl ethyl ketone (MEK); and
wet-spinning the nanofiber suspension into a coagulation medium comprising at least one non-solvent for the aromatic polyamide nanofibers and at least one proton donor, thereby forming wet nanofiber-assembled filaments in the coagulation medium;
wherein:
the coagulation medium comprises at least one of (i) an acid as the at least one proton donor, and (ii) an aprotic solvent as the non-solvent for the aromatic polyamide nanofibers.
19 . The method of claim 18 , wherein the coagulation medium comprises the acid as the at least one proton donor.
20 . The method of claim 18 , wherein the coagulation medium comprises the aprotic solvent as the non-solvent for the aromatic polyamide nanofibers.
21 . The method of claim 18 , further comprising:
washing the wet nanofiber-assembled filaments;
drawing the wet nanofiber-assembled filaments, thereby reducing or removing voids in the nanofiber-assembled filaments;
drying the wet nanofiber-assembled filaments, thereby forming dry nanofiber-assembled filaments; and
annealing the dry nanofiber-assembled filaments, thereby forming annealed nanofiber-assembled filaments.
22 . A method for forming nanofiber-assembled composite filaments, the method comprising:
providing a nanofiber suspension comprising (i) aromatic polyamide nanofibers dispersed therein, and (ii) an additional polymeric material dissolved or dispersed in the suspension, wherein (a) the nanofiber suspension comprises a suspension medium comprising water, deprotonated aromatic polyamide nanofibers as the aromatic polyamide nanofibers, a water-miscible solvent for the deprotonated aromatic polyamide nanofibers, and a base, and (b) the water-miscible solvent comprises at least one of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and methyl ethyl ketone (MEK); and
wet-spinning the nanofiber suspension into a coagulation medium comprising at least one non-solvent for the aromatic polyamide nanofibers and optionally at least one proton donor, thereby forming wet nanofiber-assembled composite filaments in the coagulation medium.
23 . The method of claim 22 , wherein:
the additional polymeric material comprises cellulose nanofibers; and
the coagulation medium further comprises a crosslinker.
24 . The method of claim 22 , wherein the additional polymeric material comprises polyamide-imide (PAI).
25 . A method for recycling aromatic polyamide fibers, the method comprising:
forming a nanofiber suspension from one or more of an aromatic polyamide fiber, fabric, or filament material by converting the aromatic polyamide fiber, fabric, or filament material to aromatic polyamide nanofibers dispersed in a nanofiber suspension, wherein (i) the nanofiber suspension comprises a suspension medium comprising water, deprotonated aromatic polyamide nanofibers as the aromatic polyamide nanofibers, a water-miscible solvent for the deprotonated aromatic polyamide nanofibers, and a base, and (ii) the water-miscible solvent comprises at least one of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and methyl ethyl ketone (MEK);
wet-spinning the nanofiber suspension into a coagulation medium comprising at least one non-solvent for the aromatic polyamide nanofibers and at least one proton donor, thereby forming wet nanofiber-assembled filaments in the coagulation medium;
optionally washing the wet nanofiber-assembled filaments;
drawing the wet nanofiber-assembled filaments, thereby reducing or removing voids in the nanofiber-assembled filaments;
optionally drying the wet nanofiber-assembled filaments, thereby forming dry nanofiber-assembled filaments; and
optionally annealing the dry nanofiber-assembled filaments, thereby forming annealed nanofiber-assembled filaments.