(402g) Grafted Islands-in-the-Sea Nonwoven Fabrics for Enhanced Ion Exchange Binding Capacity

Polybutylene terephthalate (PBT) nonwovens with poly(glycidyl methacrylate) (pGMA) grafts exhibit high protein binding capacities by ion exchanger. The three dimensional structure of the pGMA grafts allow capture of proteins at capacities many times that of monolayer coverage on the fiber surface.  However, at large graft densities, protein diffusion into the grafted layer is slow resulting in long binding times to reach equilibrium and reduced binding capacities under flow conditions.  To reduce these diffusional limitations, high surface area islands-in-the-sea PBT nonwovens were tested as base matrices for anion exchange capture of proteins. Islands-in-the-sea nonwovens are made of bicomponent fibers containing a removable polymer, “the sea”, that encapsulates discreet fiber entities of a permanent polymer, “the islands”, that are substantially smaller in diameter. These materials can be processed using traditional spunbonding techniques.  This study used 50% polylactic acid/50% PBT islands-in-the-sea nonwovens consisting of 108 islands of PBT fibers. Once the polylactic acid sea was removed PBT fibers remained with diameters less than 1µm.  Both commercially available PBT nonwoven fabrics with 3 µm fiber diameter, and islands-in-the-sea PBT were grafted with pGMA and derivatized with a tertiary amine to form weak anion exchangers.  These materials were compared in terms of equilibrium protein binding capacity, and dynamic binding capacity for BSA.  Islands-in-the-sea nonwovens require a minimum degree of grafting that is five times higher than the commercially available PBT due to the larger membrane intrinsic surface area. Additionally, the grafting rate is much faster for the islands-in-the-sea nonwoven due to the increased number of graft initiation sites on the material.  The grafted islands in the sea matrix achieved equilibrium protein binding in approximately 5 min compared to the grafted commercially available PBT with a similar degree of grafting that required 24 hours to achieve equilibrium. In a dynamic format the grafted islands-in-the-sea nonwoven was capable of achieving higher overall binding capacities (420 mg/g at 5 cm/h) than the commercially available PBT (330 mg/g at 5 cm/h) for the same degree of grafting. At very high superficial velocities (300 cm/h) the islands-in-the-sea PBT maintained 80% of its binding capacity compared to the commercial PBT that maintained only 50% of its initial binding capacity.