NOVEL WAYS OF COVALENT ATTACHMENT OF PEO ONTO POLYETHYLENE - SURFACE MODIFICATION AND CHARACTERIZATION BY XPS AND CONTACT-ANGLE MEASUREMENTS

Procedures involving the surface halogenation of polyethylene (PE) by wet chemical reactions or RF plasma treatments, followed by covalent b onding of poly(ethylene)oxide (PEG) have been developed. The two-step wet chemical halogenation comprised the chlorination of PE by SO2Cl2 a nd the transhalogenation by AlBr3 or NaI. The single-step direct bromi nation of PE was performed by either exposing the PE substrate to a gl ow discharge plasma obtained from CHBr3 vapour, or Ar-plasma activated PE was reacted with bromoform. The Br or I functional groups were rea cted with PEG solution or with PEO melt. XPS and contact angle studies were used to characterize the surfaces during the different stages of the procedures. Wettabilities as well as surface free energies compar ed for various PEO covered surfaces show that the higher the surface a mount of PEO the lower the contact angle (corresponding to higher surf ace free energy). It was established that a relatively small amount of PEO was sufficient to render the PE substrate hydrophilic when it had already been hydrated. Both contact angle studies and analysis of sur face composition suggest that a more homogeneous surface could be obta ined by treatment involving plasma bromination in contrast to those pr oduced by wet chemistry. The relative amount of ether type carbon - de rived from XPS - was proposed as a general parameter for comparison of surface energetics of various PEO grafted surfaces, irrespective of t he nature of the substrate.