COMPOSITION AND METHOD FOR MAKING ULTRA-FINE, HIGH TENACITY AND HIGH TOUGHNESS POLYMERIC MULTIFILAMENTS
The present invention provides a composition and method for forming polymeric multifilaments having a filament diameter of no more than 10 μm with a high tensile strength and toughness. The composition includes at least one semi-crystalline thermoplastic polymer and a nucleating agent to stabilize the multifilaments during melt-spinning and facilitate phase transformation of the thermoplastic polymer in subsequent drawing and annealing cycles. The method includes a quenching step for the melt-spun filaments immediately after the melt-spinning and collection of the quenched filaments with a specific winding speed to decrease the filament diameter. The subsequent drawing and annealing cycles further enhance the mechanical properties of the filaments after the quenching.
1 . A melt-spinnable or melt-extrudable polymeric composition for forming polymeric multifilaments with a small average filament diameter, high tensile strength and tensile toughness, the composition comprising:
at least one semi-crystalline thermoplastic polymer;
a nucleating agent; and
one or more anti-oxidants.
2 . The polymeric composition of claim 1 , wherein the at least one semi-crystalline thermoplastic polymer comprises polypropylene, polyethylene, polyethylene terephthalate, and polyamide 6.
3 . The polymeric composition of claim 2 , wherein the polypropylene is one or both of isotactic polypropylene having a molecular weight of about 341 kDa and a polypropylene having a melt flow index (MFI) of 1500.
4 . The polymeric composition of claim 3 , wherein the isotactic polypropylene has a melt index of 4 g/10 minutes at about 230° C. under 2.16 kg load.
5 . The polymeric composition of claim 3 , wherein the isotactic polypropylene and the polypropylene with the MFI of 1500 are in a weight ratio of 10:0 to 7:3.
6 . The polymeric composition of claim 1 , wherein the nucleating agent is a sorbitol-based nucleating agent.
7 . The polymeric composition of claim 6 , wherein the sorbitol-based nucleating agent is selected from 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol or 1,3:2,4-dibenzylidene-D-sorbitol.
8 . The polymeric composition of claim 1 , wherein the one or more antioxidants is a blend of two different anti-oxidants.
9 . The polymeric composition of claim 8 , wherein the two different anti-oxidants are selected from a phenolic antioxidant and a hydrolytically stable phosphite processing stabilizer in a weight ratio of 1:2.
10 . The polymeric composition of claim 9 , wherein the phenolic antioxidant is selected from pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate); the hydrolytically stable phosphite processing stabilizer is selected from tris(2,4-di-tert-butylphenyl) phosphite.
11 . The polymeric composition of claim 1 , wherein the at least one semi-crystalline thermoplastic polymer, the nucleating agent, and the one or more anti-oxidants in the composition are in a weight ratio of 993:4:3.
12 . A polymeric multifilament formed from the polymeric composition of claim 1 , having an average filament diameter of 4 to 10 μm, tensile strength of greater than 1 GPa, tensile toughness of greater than 100 MJ/m 3 , and an elongation at break of at least 15%.
13 . A method for forming a polymeric multifilament comprising:
providing the composition of claim 11 ;
melt-spinning said composition under an inert gas environment on a multiple orifice die to generate a plurality of filaments;
quenching the plurality of the filaments at a first temperature within a range higher or lower than a glass transition temperature of the at least one semi-crystalline thermoplastic polymer in the composition to obtain a plurality of quenched filaments;
collecting the quenched filaments with a winder at a winding speed to obtain a plurality of as-spun filaments;
drawing the plurality of as-spun filaments on a multiple furnace platform at a second temperature and with a second winding ratio;
repeating said drawing for at least five times to obtain a plurality of drawn filaments;
annealing the plurality of drawn filaments at a third temperature on a multiple furnace platform as in said drawing and with a third winding ratio; and
repeating said annealing for at least twice to obtain a plurality of annealed filaments.
14 . The method of claim 13 , wherein the inert gas environment is provided by supplying an inert gas comprising nitrogen and argon at a pressure from 1,000 to 2,000 kPa.
15 . The method of claim 13 , wherein the multiple orifice die for said melt-spinning has an orifice number between 10 and 20.
16 . The method of claim 15 , wherein each of the orifices of the multiple orifice die for said melt-spinning has an average size of about 0.15 mm.
17 . The method of claim 13 , wherein the first temperature for said quenching is about 15 to 25° C. higher or lower than the glass transition temperature of the at least one semi-crystalline thermoplastic polymer in the composition.
18 . The method of claim 17 , wherein the at least one semi-crystalline thermoplastic polymer is one or both of isotactic polypropylene with the other polypropylene having an MFI of 1500 such that the first temperature is about 0° C. to 8° C. for said quenching.
19 . The method of claim 18 , wherein a melt extrusion temperature of about 205 to 250° C. is used in said melt-spinning.
20 . The method of claim 13 , wherein the first winding speed of the winder used for said collecting the quenched filaments is up to 200 m/min and not below 100 m/min.
21 . The method of claim 13 , wherein the second temperature for said drawing is lower than the third temperature for said annealing.
22 . The method of claim 13 , wherein the second temperature for said drawing is about 140° C. to 155° C.
23 . The method of claim 13 , wherein the second winding ratio for said drawing is higher than the third winding ratio for said annealing.
24 . The method of claim 13 , wherein the second winding ratio for said drawing is up to 6.
25 . The method of claim 13 , wherein the multiple furnace platform comprises at least three furnaces each having an equal length and spacing to the other furnace.
26 . The method of claim 25 , wherein each of the at least three furnaces has the length of about 40.5 cm and the spacing of about 6.5 cm between two of the furnaces.
27 . The method of claim 13 , wherein said drawing is repeated for at least five times before said annealing.
28 . The method of claim 13 , wherein the third temperature for said annealing is about 160° C. to 170° C.
29 . The method of claim 13 , wherein the third winding ratio is up to 1.2.
30 . The method of claim 13 , wherein said annealing is repeated for at least twice before obtaining said plurality of annealed filaments.
31 . The method of claim 13 , wherein said annealing is performed on the same multiple furnace platform as that for said drawing.
32 . The method of claim 13 , wherein said plurality of annealed filaments are the polymeric multifilaments with an average diameter of 4 to 10 μm, tensile toughness of at least 100 MJ/m 3 , tensile strength of greater than 1 GPa, an elongation at break of at least 15%, and a filament count of at least 10 per batch.