Nanofiltration membrane prepared from polyacrylonitrile ultrafiltration membrane by low-temperature plasma: I. Graft of acrylic acid in gas

Low temperature plasma-induced grafting modifications of polyacrylonitrile (PAN) ultrafiltration membrane were studied to prepare hydrophilic nanofiltration membranes. By argon (Ar) treating and subsequent grafting reaction, a hydrophilic monomer, acrylic acid, was introduced onto PAN membrane. Fourier transform infrared attenuated total reflection (FTIR-ATR) spectrum, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and differential scanning calorimetry (DSC) were employed to characterize the chemical and physical changes of modified membranes. FTIR-ATR spectra suggested that the C≡N bonds were not broke during Ar plasma irradiation. One can infer Ar plasma irradiation caused the scission of C-H bonds for subsequent graft reaction on PAN membrane surface. Results from DSC measurement demonstrated that the pores in the modified membranes became smaller and the distribution of pores narrowed. But prolonged irradiation time caused surface etching from plasma, which resulted in increase of pore size. For a surface hydrophilization with an improved permeability change, short graft reaction time (∼10 min) is recommended. Longer graft time (e.g., 20 min, 36 W) caused saccharose solution flux of QH2 PAN membrane to decrease from 82 to 18 kg/(m² h) at 2 MPa. Saccharose retention of this nanofiltration membrane is of 76%.