Importance

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Abstract

A defect free semipermeable composite membrane having excellent integrity and high water permeability is provided. Said composite membrane comprises an inside support layer to provide sufficient mechanical strength; an outside barrier layer to provide selective separation; and a middle layer to provide both chemical and physical binding between said support and said barrier layer to bond them together. Three different methods for making said defect free composite membrane are discovered. These methods have been successfully utilized to produce high quality coatings and defect free composite membranes, which are independent of chemical composition and physical structure of said support. In the present invention, ultrasonic sonication is discovered to be effective to speed up the phase inversion process of a membrane casting solution, thus allows produce a composite membrane at a speed higher than those disclosed in the prior art. Said defect free composite membranes have broad applications, ranging from filtration of fruit juice, wine and milk to biotech down stream processing and purification of drinking water, municipal and industrial wastewater.

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First Claim