Controllable modification of polymer membranes by long-distance and dynamic low-temperature plasma flow: AA grafting penetrated through electrospun PP fibrous membranes

Long-distance and dynamic Ar low-temperature plasma (LDDLTP) flow pretreatment and subsequent acrylic acid (AA) grafting in aqueous solutions were developed to prepare completely hydrophilic electrospun polypropylene fibril (PPF) membranes. The investigation primarily focused on the penetrating grafts and effects of plasma conditions on the grafting. Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy, X-ray photoelectron (XPS) spectroscopy, and scanning electron microscopy (SEM) analyses were employed to characterize the chemical and morphological changes on the surface and cross-sections of the membranes. Improvements in membrane hydrophilicity and anti-fouling were characterized by measuring water contact angle (WCA), bovine serum albumin (BSA) adsorption, and water permeation. FTIR-ATR spectra of two grafted membranes irradiated in a stack showed specific absorbance peaks of carbonyl groups on three of the surfaces, but not on the downstream surface of the second membrane. The XPS and WCA analyses revealed that the active species in the LDDLTP flow can not only penetrate through the top PPF membrane but also irradiate a significant part of the second membrane. The penetration grafting modifications to the PPF membranes by the LDDLTP made the water droplet to penetrate deeply into the bulk and completely wet the whole membrane, increased water flux from 732 to 1763 kg m−2 h−1 at 20 °C and 0.03 MPa, and reduced BSA adsorption fouling by 67% at pH 7.4. These results indicate that the controllable modifications of membranes in a module scale are possible by applying a LDDLTP.