Method for producing defect free composite membranes

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 physical adhesion and chemical 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 much 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.

1 . A method for strengthening a multi-layer defect free composite membrane, wherein said method comprising impregnation of a support with a binding agent while leaving the membrane surface free of said binding agent, followed by curing said binding agent either at ambient or at elevated temperature with or without the presence of ultraviolet light depending on desired membrane performance.  
   
   
       2 . The method according to  claim 1 , wherein said binding agent is selected from the group consisting of epoxy, polyurethane, silicone, any other adhesive and any other organic or inorganic material which has excellent compatibility between said support and said membrane to chemically or physically bond them together to prevent said membrane from delaminating from said support.  
   
   
       3 . The method according to  claim 1 , wherein said method includes an optional post treatment of said membrane with ozone or a solution containing 100-150,000 ppm free chlorine at ambient or elevated temperature to increase membrane liquid or gas permeability by 2 to 10 folds compared to a virgin membrane never exposed to any post treatment.  
   
   
       4 . The membrane products produced according to the method of  claim 1.