Preparation and investigation of chemically modified porous polyamide ultrafiltration membranes

The asymmetric ultrafiltration membranes for these investigations were made from a fully aliphatic (PA 66), a fully aromatic (polyaramid referred to as PA-L48) and an aliphatic-aromatic polyamide (Trogamid T). The latter were heterogeneously reacted with glycidyl methacrylate yielding an epoxidized polyamide membrane. The reactive epoxy group opened up a spectrum of further modifications. Both positively and negatively charged substituents were introduced. Heterogeneous chemical modification of the cast membrane is needed as homogeneous polymer modification eliminates the polymers film forming properties. The reaction steps reduce the transport cross section as grafting is performed also on the inner pore walls and some reactions needed higher temperatures with shrinking of the membrane as a consequence. The fouling behavior was determined using dilute human serum albumin solutions at different pH values. The original polyamide membranes display the expected performance: the polyaramid membrane is least sensitive to protein adsorption followed by the mixed aliphatic-aromatic and the aliphatic ones. Applying negatively charged membranes at higher pH of the solution the protein is repulsed due to its isoelectric point of 4.8. On the contrary, the positively charged membranes adsorb the oppositely charged protein causing a strong volume flow reduction. The change in surface properties by protein adsorption is demonstrated by means of electrokinetic measurements.