High toughness hollow fiber membranes based on vinylidene fluoride polymers
Hollow fiber membranes having improved toughness and durability are prepared using a vinylidene fluoride polymer-containing component, such as Kynaro resins, having relatively low crystallinity. One aspect of the invention provides a membrane in the form of a fiber, wherein i) the fiber has a porous wall of a polymeric component enclosing a central hollow space extending the length of the fiber, ii) the polymeric component has a crystallinity as determined by wide angle x-ray diffraction of less than about 35%, iii) the polymeric component is comprised of at least one homopolymer or copolymer of vinylidene fluoride and iv) the membrane has an energy to break of at least about 0.5 J per square mm of membrane cross section.
1. A membrane in the form of a fiber, wherein i) the fiber has a porous wall of a polymeric component enclosing a central hollow space extending the length of the fiber, ii) the polymeric component has a crystallinity as determined by wide angle x-ray diffraction of less than about 35%, iii) the polymeric component is comprised of at least one homopolymer or copolymer of vinylidene fluoride and iv) the membrane has an energy to break of at least about 0.5 J per square mm of membrane cross section.
2. The membrane of claim 1 , wherein the polymeric component is selected from the group consisting of:
a) a polymer which is a copolymer of from about 80% to about 99% by weight of vinylidene fluoride and from about 1% to about 20% by weight of one or more co-monomers;
b) a blend of from about 10% to about 80% by weight vinylidene fluoride homopolymer and from about 20% to about 90% by weight of a copolymer comprising from about 60% to about 99% by weight of vinylidene fluoride and from about 1% to about 40% by weight of one or more co-monomers;
c) a blend of from about 10% to about 80% by weight high crystallinity vinylidene fluoride homopolymer and from about 20% to about 90% by weight low crystallinity vinylidene fluoride homopolymer;
d) a vinylidene fluoride homopolymer or copolymer containing long chain branching; and
e) a vinylidene fluoride copolymer containing a fraction of very high molecular weight vinylidene fluoride homopolymer or copolymer.
3. The membrane of claim 1 , wherein the polymeric component has a crystallinity as determined by wide angle x-ray diffraction of at least about 20%.
4. The membrane of claim 1 , wherein the polymeric component is a polymer which is a copolymer of from about 80% to about 99% by weight of vinylidene fluoride and from about 1% to about 20% by weight of one or more co-monomers selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, trifluoroethylene, vinylacetate, vinylsulfonic acid, vinyltrimethylsilane, tetrafluoropropylene, acrylic acid and methacrylic acid.
5. The membrane of claim 1 , wherein the polymeric component is a blend of from about 10% to about 80% by weight vinylidene fluoride homopolymer and from about 20% to about 90% by weight of a copolymer comprising from about 80% to about 99% by weight of vinylidene fluoride and from about 1% to about 20% by weight of one or more co-monomers selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, trifluoroethylene, vinylacetate, vinylsulfonic acid, vinyltrimethylsilane, tetrafluoropropylene, acrylic acid and methacrylic acid.
6. The membrane of claim 1 , wherein the polymeric component is a blend of from about 10% to about 80% by weight of a first vinylidene fluoride homopolymer having a degree of crystallinity of greater than 35% and from about 20% to about 90% by weight of a second vinylidene fluoride homopolymer having a degree of crystallinity of less than 20%.
7. The membrane of claim 1 , wherein the porous wall is substantially free of macrovoids.
8. The membrane of claim 1 , wherein the membrane is unsupported.
9. A membrane module, wherein i) the membrane module comprises a plurality of hollow porous fibers of a polymeric component, ii) the polymeric component has a crystallinity as determined by wide angle x-ray diffraction of less than about 40%, the polymeric component is comprised of at least one homopolymer or copolymer of vinylidene fluoride and iv) the membrane has an energy to break of at least about 0.5 J per square mm of membrane cross section.
10. The membrane module of claim 9 , wherein the polymeric component is selected from the group consisting of:
a) a polymer Which is a copolymer of from about 80% to about 99% by weight of vinylidene fluoride and from about 1% to about 20% by weight of one or more co-monomers;
b) a blend of from about 10% to about 80% by weight vinylidene fluoride homopolymer and from about 20% to about 90% by weight of a copolymer comprising from about 60% to about 99% by weight of vinylidene fluoride and from about 1% to about 40% by weight of one or more co-monomers;
c) a blend of from about 10% to about 80% by weight high crystallinity vinylidene fluoride homopolymer and from about 20% to about 90% by weight low crystallinity vinylidene fluoride homopolymer;
d) a vinylidene fluoride homopolymer or copolymer containing long chain branching; and
e) a vinylidene fluoride copolymer containing a fraction of very high molecular weight vinylidene fluoride homopolymer or copolymer.
11. The membrane module of claim 10 , wherein the polymeric component has a crystallinity as determined by wide angle x-ray diffraction of at least about 20%.
12. The membrane module of claim 10 , wherein the polymeric component is a polymer which is a copolymer comprising from about 80% to about 99% by weight of vinylidene fluoride and from about 1% to about 20% by weight of one or more co-monomers selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, trifluoroethylene, vinylacetate, vinylsulfonic acid, vinyltrimethylsilane, tetrafluoropropylene, acrylic acid and methacrylic acid.
13. The membrane module of claim 10 , wherein the polymeric component is a blend of from about 10% to about 80% by weight vinylidene fluoride homopolymer and from about 20% to about 90% by weight of a copolymer comprising from about 60% to about 99% by weight of vinylidene fluoride and from about 1% to about 40% by weight of one or more co-monomers selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, trifluoroethylene, vinylacetate, vinylsulfonic acid, vinyltrimethylsilane, tetrafluoropropylene, acrylic acid and methacrylic acid.
14. The membrane module of claim 10 , wherein the polymeric component is a blend of from about 10% to about 80% by weight of a first vinylidene fluoride homopolymer having a degree of crystallinity of greater than 35% and from about 20% to about 90% by weight of a second vinylidene fluoride homopolymer having a degree of crystallinity of less than 20%.
15. The membrane module of claim 10 , wherein the polymeric component is a blend of vinylidene fluoride homopolymer or copolymer and methyl methacrylate homopolymer or copolymer.
16. A method of making a hollow porous fiber useful in manufacturing membrane modules, comprising:
a) extruding a composition comprised of a polymeric component, a pore enhancement agent and a solvent capable of dissolving the polymeric component and the pore enhancement agent to form a hollow fiber; and
b) removing the solvent and pore enhancement agent from the hollow fiber to form the hollow porous fiber;
wherein the polymeric component has a crystallinity as determined by wide angle x-ray diffraction of less than about 35% and the polymeric component is comprised of at least one homopolymer or copolymer of vinylidene fluoride.
17. The method of claim 16 , wherein the polymeric component is selected from the group consisting of:
a) a polymer which is a copolymer of from about 80% to about 99% by weight of vinylidene fluoride and from about 1% to about 20% by weight of one or more co-monomers;
b) a blend of from about 10% to about 80% by weight vinylidene fluoride homopolymer and from about 20% to about 90% by weight of a copolymer comprising from about 60% to about 99% by weight of vinylidene fluoride and from about 1% to about 40% by weight of one or more co-monomers;
c) a blend of from about 10% to about 80% by weight high crystallinity vinylidene fluoride homopolymer and from about 20% to about 90% by weight low crystallinity vinylidene fluoride homopolymer;
d) a vinylidene fluoride homopolymer or copolymer containing long chain branching; and
e) a vinylidene fluoride copolymer containing a fraction of very high molecular weight vinylidene fluoride homopolymer or copolymer.
18. The method of claim 16 , wherein the pore enhancement agent is miscible with or soluble in water.
19. The method of claim 16 , Wherein the solvent and pore enhancement agent are removed from the hollow fiber by soaking the hollow fiber in water.
20. The method of claim 16 , wherein the solvent is selected from the group consisting of amides, ketones, carbonates, ethers, ureas, trialkyl phosphates, esters, dimethylsulfoxide, hexamethylphosphoramide and combinations thereof.
21. A method of making a membrane module, comprising forming a plurality of membranes in accordance with claim 1 into a bundle.