Porous hollow fiber membrane
An object of the present invention is to provide a porous hollow-fiber membrane having high strength while maintaining high pure-water permeation performance. A porous hollow-fiber membrane of the present invention is a porous hollow-fiber membrane including a fluororesin-based polymer, in which the porous hollow-fiber membrane has a columnar texture oriented in a longitudinal direction of the porous hollow-fiber membrane, and a molecular chain of the fluororesin-based polymer is oriented in the longitudinal direction of the porous hollow-fiber membrane.
1. A porous hollow-fiber membrane comprising a fluororesin-based polymer,
wherein the porous hollow-fiber membrane has a columnar texture oriented in a longitudinal direction of the porous hollow-fiber membrane,
a molecular chain of the fluororesin-based polymer is oriented in the longitudinal direction of the porous hollow-fiber membrane,
an orientation degree π of the molecular chain calculated based on the following formula (1) is 0.4 or more and less than 1.0:
Orientation degree π=(180°- H )/180° (1)
provided that H is a half-width)(°)of a diffraction intensity distribution in a circumferential direction of a wide-angle X-ray diffraction image, and
the columnar texture has a short-side length of from 0.5 μm to 3 μm, and has an aspect ratio of 3 or more.
2. The porous hollow-fiber membrane according to claim 1 , wherein the columnar texture has a thickness uniformity of 0.60 or more.
3. The porous hollow-fiber membrane according to claim 1 , wherein the half-width H is a half-width of an intensity distribution obtained by circumferentially scanning a crystal peak (2θ=20.4°) derived from a (110) plane of polyvinylidene fluoride in wide-angle X-ray diffraction measurement.
4. The porous hollow-fiber membrane according to claim 1 , wherein, when the wide-angle X-ray diffraction measurement is performed at measurement points at 1 cm intervals in the longitudinal direction of the porous hollow-fiber membrane, the orientation degree π is 0.4 or more and less than 1.0 at 80% or more of the measurement points.
5. The porous hollow-fiber membrane according to claim 1 , wherein the fluororesin-based polymer is polyvinylidene fluoride, and a Raman orientation parameter v of the molecular chain obtained by Raman spectroscopy is 3.0 or more.
6. The porous hollow-fiber membrane according to claim 1 , which has a porosity of from 50 to 80%.
7. The porous hollow-fiber membrane according to claim 1 , which has a pure-water permeation performance at 50 kPa and 25° C. of 0.7 m 3 /m 2 /hr or more and a breaking strength of 25 MPa or more.
8. The porous hollow-fiber membrane according to claim 1 , which is formed by thermally induced phase separation.