An investigation of polymer dope and heating effects on hollow fiber membranes

Hollow fiber membranes were made from two different dope solutions by using a dry-jet wet spinning process. One dope solution contains cellulose acetate (CA)/N-methyl-2-pyrrolidone (NMP) with a mass ratio of 20/80 and the other contains polysulfone (PS)/NMP with a mass ratio of 15/85. The hollow fiber membranes were heated in a water bath to investigate the effect of heat treatment. It was found that for the CA membranes, the pore size shrank due to the heat treatment as there was a decrease in permeation and an increase in protein rejection. The most dramatic change for the CA membranes occurred after being heated to 95°C, which resulted in an increase in bovine serum albumin (BSA) rejection to 99% while the permeation decreased to 39 L h^-1 m^-2 bar^-1. This is due to heating above the glass transition temperature (67-68°C) for CA. For the PS membranes, the pore size remained unchanged throughout the two heat treatments as the glass transition temperature is 185°C. The PS membranes did however have a smaller pore size to begin with as is evident by the >99% rejection of BSA. The permeation declined more rapidly for the PS membranes compared to the CA membranes due to the more hydrophobic nature of the polymer.