Hollow fiber technology materials

In dialysis, size exclusion is the main separation mechanism, while osmotic pressure and concentration difference drive the transport across two typically aqueous phases. While dialysis is used in some analytical separations, dialysis for the removal of toxins from blood (hemodialysis) is the most prominent application for hollow fiber technology in the biomedical field. The hemodialyzers are used to treat over one million people a year and have become a mass produced, disposable medical commodity. While the first hemodialyzers were developed from cellulosic material (Cuprophane, RC, etc.), synthetic polymers such as polyacrylonitrile, poly(ether) sulfone, and polyvinyl pyrrolidone are increasingly used to improve blood compatibility and flux. Hemodialyzer modules consist of thousands of extremely fine hollow fibers... 

The history of the membrane developments for reverse osmosis and gas permeation shows that because of inherent differences, it is not possible to simply apply the techniques and materials from one separation technology to the other. The success of the resistance-model hollow-fiber technology which is based on the glassy-fiber technology invented for reverse osmosis, demonstrates the necessity to search for advanced techniques to prepare more selective membranes free of imperfections, rather than to look for new, unavailable materials. 

Pabby, A.K. and Sastre, A.M. (2006) Hollow-fiber membrane based separation technology performance and design perspectives, in Solvent Extraction and Liquid Membranes Fundamental and Application in New Materials (eds Cortina and Aguilar), Marcel Dekker, New York. 

Polymeric materials are still the most widely used membranes for gas separation, and for specific apphcations the separation technology is well established (see Section 4.6). Producing the membranes either as composites with a selective skin layer on flat sheets or as asymmetric hollow fibers are well-known techniques. Figure 4.5 shows an SEM picture of a typical composite polymeric membrane with a selective, thin skin layer of poly(dimethyl)siloxane (PDMS) on a support structure of polypropylene (PP). The polymeric membrane development today is clearly into more carefully tailored membranes for specific... 

Recently, microporous polypropylene (PP) materials (sheets, films and hollow fibers) have gained acceptance in various fields of separation technology. Usually, these microporous materials are prepared by using uniaxial or biaxial stretching of adequate preforms. Some examples of processing routes are ... 

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