Research Article Hydrophilicity Enhancement of High-Density Polyethylene Film by Ozonation High-density polyethylene (HDPE) films were ozonated in the gas phase and in distilled water, respectively, to improve their surface hydrophilicity. The efficiency of ozonation conducted in the gaseous and aqueous phases was compared. The results indicated that the aqueous ozonation was more effective than its gaseous counterpart in terms of peroxide generation. The results also showed that the concentration of peroxides generated on the film surfaces increased with the applied ozone dose and ozonation time in both phases. It was found that the per- oxides generated by aqueous ozonation were accessible to monomers for graft polymerization. The hydrophilicity of the HDPE films was significantly improved by graft polymerization of acrylamide (AAm) initiated by the peroxides. The con- tact angle reduction from 74.9° to 38.6° indicated the successful graft polymeriza- tion. The successful graft polymerization of AAm was further confirmed by the formation of new peaks corresponding to amide groups in FTIR spectra and by scanning electron microscope images. Keywords: Graft polymerization, Hydrophilicity, Ozonation, Peroxide, Polyethylene film Received: September 1, 2008; accepted: January 16, 2009 DOI: 10.1002/ceat.200800433 1 Introduction Polymers play important roles in a wide range of applications such as membranes, biomaterials, sensors, etc. For polymers used in medical fields, surface hydrophilicity is one of the most important properties [1–5]. However, most of the polymers are naturally hydrophobic; the improvement of the hydrophi- licity of polymer surfaces is thus an important research task. Among the surface modification techniques, ozonation is widely applied [6–11]. When polymers are exposed to ozone, active peroxide groups can be introduced onto the surface. The active peroxide groups are capable of initiating graft poly- merization of vinyl monomers with hydrophilic groups. Con- sequently, the hydrophilicity of the polymer surfaces can be improved [6–11]. In comparison with other surface modifica- tion techniques such as plasma treatment, irradiation with gamma-rays, corona discharge, ion beam treatment, UV radia- tion, etc., ozonation has the advantage of introducing peroxide groups uniformly even with complicated shapes [6, 11, 12]. To date, most ozone surface modifications have been con- ducted in the gas phase, i.e. the polymers are exposed to ozone-containing gas. Considering the fact that ozone self-de- composes rapidly in water to form free radicals and the free radicals are stronger oxidants than the molecular ozone itself [13], and that for aqueous-phase ozonation catalysts could easily be added to the system to enhance the ozonation effi- ciency no matter whether the catalysts are in the liquid phase, solid phase or in the gas phase, aqueous-phase ozonation of polymers appears attractive. So far, data for aqueous ozonation of polymer films are scarce, especially for the efficacy of ozona- tion under various operating conditions. In this study, high-density polyethylene (HDPE) film, a widely used synthetic polymer, was ozonated in the gaseous phase and in the aqueous phase, respectively. The objectives were to compare the efficacy of ozonation in the two reaction media in terms of peroxide generation and to investigate the effects of some process parameters on surface peroxide genera- tion. In the meantime, a hydrophilic monomer, acrylamide (AAm), was graft-polymerized onto the HDPE film following surface ozonation, to examine whether the peroxides generated are accessible to monomers. In addition, the functional groups of the film surfaces were characterized by Fourier transform infrared (FTIR) spectroscopy, the surface morphology was ob- served by scanning electron microscopy (SEM), and the hydro- philicity of the modified film was examined by water contact angle measurements. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Hongbin Gu 1 Jiangning Wu 1 Huu Doan 1 1 Department of Chemical Engineering, Ryerson University, Toronto, Canada. – Correspondence: Dr. J. Wu (j3wu@ryerson.ca), Department of Chemical Engineering, Ryerson University, 350 Victoria St., Toronto, Ontario M5B 2K3, Canada. 726 Chem. Eng. Technol. 2009, 32, No. 5, 726–731