Nanocomposite mixed-matrix membrane

Abstract

The nanocomposite mixed-matrix membrane is a nanocomposite made from a nanofiller of Halloysite nanotubes or polypropylene-grafted maleic anhydride nano-layered silica dispersed or embedded in a hydrophobic polymer matrix. The Halloysite nanotubes are a 1:1 layered alumino-silicate clay having the chemical formula Al 2 O 3 Si 2 O 4 4(H 2 O)) formed into multi-layered hollow cylinders having walls that are formed from alternating layers of alumina and silica. The membrane is formed by extrusion of the nanocomposite with stretching over rollers during the extrusion, followed by annealing, cold stretching at room temperature, and hot stretching. The resulting membrane is macroporous and can be used as a membrane distillation (MD) membrane for seawater and brackish water desalination.

1 - 9 . (canceled) 
     
     
         10 . A process of making a nanocomposite mixed-matrix microporous membrane, comprising the steps of:
 (a) blending a hydrophobic polymer with a nanofiller to form a dry mix, the hydrophobic polymer consists of polypropylene and the nanofiller consisting of Halloysite nanotubes, wherein the nanofiller comprises 15% by weight of the dry mix;   (b) pelletizing the dry mix;   (c) extruding the pelletized dry mix using a twin-screw extruder set at 200-230° C. to give a melt extrusion temperature of about 175° C. to 190° C. to form a nanocomposite;   (d) stretching the nanocomposite while it is exiting from the extruder using a casting roller set at a temperature of 60° C.-80° C. and a downstream pick-up roller or haul-off roller;   (e) annealing the stretched, extruded film at a temperature of about 145° C. for 30 minutes:   (f) cold stretching the stretched, extruded film at room temperature after the annealing step; and   (g) hot stretching the stretched, extruded film between 110° C. and 140° C. after the annealing step,   thereby forming the microporous membrane, wherein the microporous membrane includes micron-sized pores, the pores being configured as elongated slits.   
     
     
         11 - 12 . (canceled) 
     
     
         13 . The process of making a nanocomposite mixed-matrix microporous membrane according to  claim 10 , wherein the extrusion linear speed is between 0.21 cm/min and 0.41 cm/min. 
     
     
         14 . The process of making a nanocomposite mixed-matrix microporous membrane according to  claim 10 , wherein:
 said casting roller has a speed of 4.0 m/min; and   said pick-up roller or haul-off roller has a maximum speed of 4.6 m/min and a draw down rate between 9.76 and 12.96.   
     
     
         15 - 17 . (canceled) 
     
     
         18 . The process of making a nanocomposite mixed-matrix microporous membrane according to  claim 10 , wherein said Halloysite nanotubes comprise hollow cylinders having an outer diameter between 40 nm and 300 nm, a longitudinal length between 1000 nm and 5000 nm, and an inner diameter between 16 nm and 50 nm. 
     
     
         19 . A membrane distillation system comprising a hydrophobic microporous nanocompo site mixed-matrix membrane prepared according to the process of  claim 10 .