Dispersion spinning core-shell fluoropolymers
View Patent ↗A process is disclosed for dispersion spinning non-melt-processible fluoropolymer fiber in which a mixture of an aqueous dispersion of non-melt-processible fluoropolymer particles and an aqueous solution of a matrix polymer is formed. The non-melt-processible fluoropolymer particles have an SSG of less than about 2.40 and comprise a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene. The mixture is extruded into a coagulation bath containing a concentration of ions which coagulate the matrix polymer to form an intermediate fiber structure. The intermediate fiber structure is sintered to decompose the matrix polymer and coalesce the non-melt-processible fluoropolymer particles to form the fiber. The present invention also provides a spinning composition useful for the dispersion spinning of non-melt-processible fluoropolymer fiber.
1. A spinning composition useful for the dispersion spinning of non-melt-processible fluoropolymer fiber comprising:
a mixture of an aqueous dispersion of non-melt-processible fluoropolymer particles having an SSG of less than about 2.40, said fluoropolymer particles comprising a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene, and an aqueous solution of a matrix polymer.
2. The spinning composition of claim 1 wherein the SSG of said non-melt-processible fluoropolymer particles is from about 2.14 to about 2.40.
3. The spinning composition of claim 1 wherein the molecular weight of the polytetrafluoroethylene or modified polytetrafluoroethylene in the shell of said non-melt-processible fluoropolymer particles is sufficiently low that an aqueous dispersion at about 45 weight % fluoropolymer and at about 6 weight % surfactant has a gel time greater than about 400 seconds.
4. The spinning composition of claim 1 wherein the molecular weight of the polytetrafluoroethylene or modified polytetrafluoroethylene in the shell of said non-melt-processible fluoropolymer particles is sufficiently low that an aqueous dispersion at about 45 weight % fluoropolymer and at about 6 weight % surfactant has a gel time greater than about 450 seconds.
5. The spinning composition of claim 1 wherein said aqueous dispersion of non-melt-processible fluoropolymer particles comprises about 3 to about 11 weight % of a surfactant based on the weight of said fluoropolymer.
6. The spinning composition of claim 1 wherein said aqueous dispersion of non-melt-processible fluoropolymer particles comprises about 45 to about 65 weight % non-melt processible fluoropolymer.
7. The spinning composition of claim 1 wherein said melt-processible fluoropolymer particles in said aqueous dispersion have an average melt creep viscosity of the polytetrafluoroethylene of said core greater than about 4×10 9 Pa·s.
8. The spinning composition of claim 1 wherein said melt-processible fluoropolymer particles in said aqueous dispersion have an average melt creep viscosity of the polytetrafluoroethylene or modified polytetrafluoroethylene of said shell greater than about 3×10 9 Pa·s and less than the average melt creep viscosity of polytetrafluoroethylene of said core.
9. The spinning composition of claim 1 wherein said melt-processible fluoropolymer particles in said aqueous dispersion have an average melt creep viscosity of the polytetrafluoroethylene or modified polytetrafluoroethylene of said shell of about 3×10 9 Pa·s to about 1.3×10 10 Pa·s.
10. The spinning composition of claim 1 wherein said shell of said melt-processible fluoropolymer particles in said aqueous dispersion comprises about 5 to about 30% by weight of said fluoropolymer particles.
11. The spinning composition of claim 1 wherein the matrix polymer is a cellulosic ether polymer.
12. The spinning composition of claim 1 wherein the matrix polymer is selected from the group consisting of methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose and carboxymethylcellulose.