Confined photo-catalytic oxidation: a fast surface hydrophilic modification method for polymeric materials

When a very thin persulfate salt aqueous solution layer (μm) was sandwiched between two polymer films and strong UV light irradiated the assembly from the side transparent to UV light, a fast surface hydrophilic modification method for most of commercial polymeric materials was developed. For example, irradiating for 90 s and using 30 wt% ammonium persulfate, the static surface water contact angles of polymeric substrates decreased from 100 to 44° for LDPE, from 107 to 34° for HDPE, and from 73 to 15° for PET. The increases in surface hydrophilicity came from the formation of a sulfate salt group (SO4−NH4+)-ionized surface, which was characterized by XPS and ATR-FTIR. The surface topography of the modified polymer substrates were observed by SEM and AFM, and no visible etching effect to original surface were found. A possible reaction model named by ‘confined photo-catalytic oxidation’ was put forward to interpret the above results.