Modification of polyethylene by high energy ion or electron beam – structural, micromechanical
and conductivity studies of the surface layer (in English)
Polimery 2007, No 5, 329
Commercial grade polyethylenes: high density (PE-HD) and ultra-high molecular weight one (PE-UHMW) were subjected to the surface modification by electron beam irradiation (0.6-1.5MeV/50-500kGy) and ion beam bombardment (He+ 160keV/2·1013-5·1016 ions/cm2; Ar+ 130keV/1·1013-2·1016 ions/cm2). Effects of modifications were studied by spherical nanoindentation and scratch hardness tests. Contrary to electron beam irradiation, the ion beam bombardment, especially of He+ ions, can significantly increase (up to 3 times) hardness of the surface layer of polyethylene in comparison to the bulk. According to Grazing Incidence X-ray Diffraction (GIXRD) it is associated with an increased degree of crystallinity due to the surface modification. Nuclear Reaction Analysis (NRA) reveals a hydrogen release due to ion bombardment which saturates at the CH atomic composition. It cannot however be associated with cross-polymerization or crosslinking of macromolecules because of some unsaturations being present and a graphite formation. Partially graphitized and/or better organized modified macromolecular chains "rooted” in the polymer substrate explain low friction and wear resistance of ion bombarded polyethylenes. Even high stress crackings are not able to proceed with further delamination of the modified surface layer. Treatment of the material with heavy Ar+ ions of energy 150-300keV was combined with an electrical doping by implantation of polyethylene with I+ ions of energy 150keV. Apart an increase in hardness, the modification results additionally in a significant reduction of the surface resistivity (more than 20 times), facilitating a removal of static charge.
Key words: polyethylene, ion bombardment, surface layer, modification, degree of crystallinity, hardness, surface resistivity
D. M. Bieliński, C. Ślusarczyk, J. Jagielski, P. Lipiński
Modification of polyethylene by high energy ion or electron beam - structural, micromechanical and conductivity studies of the surface layer (in English)