bubbles in contact with the membrane. This increases the gas pressure and alters the surface tension so that the bubbles burst. The gas from the burst bubbles is discharged through the pores of the membrane so that there is no overwhelming rise in the internal pressure of the apparatus.

In a test, the heated membrane was sealed to the top of a vessel of water with 1% added surfactant. Air was bubbled into the bottom of the vessel at a pressure of 1.0 kg/cm 2. The foam was broken down satisfactorily and the pressure inside the vessel remained at a constant 0.1 kg/cm 2 above ambient pressure. This confirmed that the gas (in this case, air) was being effectively discharged to the outside atmosphere. Patent number: EP 376634 Date: 4 July 1990 Inventor: Y. Chikamori, Y.

Shibata, Y. Shimizu Applicant: Japan Gore-Tex Inc.

Fabric reinforced composite membrane The mechanical strength and abrasion resistance of thin expanded PTFE membranes are lower than desirable in certain

Example of reinforced composite membranes featured in WO 9006337

perfluoro ion t exchange resin (

bond between fabric and EPTFE /

~ - . - EPTFE layer

synthetic fabric

applications. One way to address this is to encapsulate PTFE fibres within the membrane polymer. The 5-10 mill thickness of membrane resin needed for full coverage of the fabric can be too thick for some potential uses.

This multi-layer material comprises a synthetic fabric bonded at points of contact to one surface of a layer of porous, expanded PTFE. which has a continuous perfluoro ion exchange polymer film laminated to it on the opposite side. The fabric and porous expanded PTFE are coated on at least part of their surfaces with a perfluoro ion exchange resin.

A second composite membrane is configured as a sandwich-like structure with the ion exchange polymer (the 'meat') having a layer of expanded PTFE on each surface. A fabric layer (the 'bread') covers each outer PTFE surface. The manufacturing method for these composites is claimed as novel.

Abrasion tests on these

Example of reinforced composite membranes featured in WO 9006337

fabric layer

fabric layer b o n d between fabric and EPTFE

EPTP laye:

ion exchan~ film EPTFE layer

composites show greatly increased mechanical strength compared to unsupported membranes. Patent number: WO 9006337 Date: 14 June 1990 Inventor: R. Mallouk, P. Branca,

R. Perry Applicant: W L Gore Associates;

E.I. DuPont de Nemours

Ultrafiltration for protein extraction The recovery of inert protein from the ceils of gene-recombinant bacteria can be achieved by homogenising the cells in a buffer solution, then centrifuging the liquid to separate the insoluble fraction.

If this fraction is then denatured by reaction with urea, guanidine hydrochloride or an alkali, it becomes soluble. It can then be fractionated by gel filtration, centrifugal separation or ultrafiltration.

The effect of the denaturant can then be reduced (by dilution in the case of guanidine hydrochloride and urea or by neutralising the alkali) to restore the original properties of the protein. Patent number: JP 2128687 Date: 17 May 1990 Inventor: Y. Nagao Applicant: Tosoh Corporation

Membrane Technology 15