Preparation of Polysulfone Membranes and Their Use in Micellar-Enhanced Ultrafiltration of Coconut Water

Abstract

Ultrafiltration (UF) membranes were prepared containing the mass ratio 18:82 of polysulfone (PS) resin to N,N-dimethylacetamide (DMA); polyvinyl pyrrolidone (PVP) was added to constitute 10% of PS. The pinhole-free membranes were characterized in terms of uniformity of thickness, water flux, molecular weight cut-off, fouling, pore size and pore density. Two sets of membranes designated as a and b were selected with mean thicknesses of 0.110 mm and 0.114 mm, respectively. The mean water flux values for sets a and b, respectively, were 164.7 and 140.1 L/m-h. The corresonding rejection coefficients were 0. 78 and 0.84 for sets a and b, respectively, using bovine serum albumin (66 kD) as molecular weight standard and 0.47 and 0.75 using α-chymotrypsinogen a. Scanning electron microscopy (SEM) showed that for the bottom surface (glass side) of the membranes the average pore diameter as 0.76 mm and the average ratio of total pore surface area to membrane area was 0.27 µm. The membranes were used to concentrate the sugars of coconut water through micellar-enhanced ultrafiltration (MEUF) after adding either sodium dodecylsulfate (SDS) concentration: σ or betaine. The rejection coefficient (σ) for total sugars in coconut water increased from 24.2% at <0.005 M SDS to 49.1% above this SDS concentration: σ value increased tram 18.6% at <0.05 M betaine to 59.2% at >0.05 M betaine. This may be explained by the formation of micelles above the critical micelle concentration which trapped the sugar molecules and kept them in the retentate. The results showed the potential of MEUF for the recovery of sugars from coconut water.