A hollow fiber membrane made of a cellulose ester having a membrane thickness of not more than 75 .mu.m, and having void volume (x, % by volume) of the membrane and a rate of ultrafiltration (y, ml/m.sup.2.hr.mmHg) satisfying the following formula: wherein x.gtoreq.60, and further has a .beta.-lipoprotein sieving coefficient (sc) of not less than 0.95, and preferably having further not more than 2% of change ratio in the axial direction and in the radial direction when dipped freely in water at 121.degree. C. for 20 minutes. Said hollow fiber membrane is useful for the medical use, such as the exchange of plasma in patients, collection of plasma from healthy donor, the pre-treatment of plasma for the collection and purification of valuable materials contained in plasma.

A blood-purifying regenerated cellulose membrane, in which the occurrence of the leukopenia phenomenon and the activation of the complement system are moderated, is prepared by applying a solution of a polymeric substance comprising as one component units derived from one or more basic vinyl monomers having an amino group in the side chain in an organic solvent to a regenerated cellulose membrane, removing the excessive solution, and then fixing the polymeric substance to the regenerated cellulose membrane.

In a tensioner, in which a rotary body and an urged body are attached within a casing in a screwed portion and the urged body advances in an axial direction by the rotation of the rotary body with a spring force, a portion where an inner space of the casing and its outside interconnects is isolated with a selective transmission material which prevents oil penetration but allows air transmission.

Disclosed is a porous membrane comprising (1) a hydrophilic copolymer X composed principally of (poly)alkylene glycol mono(meth)acrylate units A and ethylene units B and (2) a polyolefin Y, the (poly)alkylene glycol mono(meth)acrylate units A being of the formula ##STR1## where R.sup.1 and R.sup.2 independently represent hydrogen or methyl, and n has a value in the range of 1 to 9. This porous membrane has permanent hydrophilicy suitable for the treatment of water-based liquids and can be produced by an industrially advantageous process. This process comprises melt-forming a blend of (1) a hydrophilic copolymer X composed principally of (poly)alkylene glycol mono(meth)acrylate units A and ethylene units B and (2) a polyolefin Y; heat-treating the melt-formed product in a vacuum or an inert gas medium at a temperature not higher than the melting point of polyolefin Y for a period of an hour or more; and stretching the heat-treated, melt-formed product to make it porous.

Composite membranes are disclosed having a separation layer comprised of a mixture of poly(methy methacrylate) or a copolymer thereof and at least one cellulosic derivative resulting in enhanced separation and permeating characteristics of the overall composite membrane. Processes for making these composite membranes and the methods of using them are also disclosed. The membranes are particularly useful in gas separation applications and are most suited for the separation of hydrogen from a hydrogen containing stream.