Nitrogen-PBII modification of ultra-high molecular weight polyethylene: Composition, structure and nanomechanical properties

Plasma based ion implantation of nitrogen was performed on mechanically polished UHMWPE model samples by applying 27.13 MHz RF energized low pressure N2 plasma with 15–30 kV pulses and fluences up to 5 · 1017 ions/cm2. Surface compositional and structural alterations and nanomechanical property changes were investigated by XPS, Raman and by nano-indentation and nano-scratch techniques. The implanted N amounted up to 13–20 at.% (N/C = 0.18–0.30), while a significant amount of oxygen could also be detected on the surface. Three types of chemical states of the incorporated nitrogen were detected, related to linear sp2 CN–C and to planar and non-planar sp3 type C–N bonds. The applied PBII treatment led to severe dehydrogenation of the polyethylene resulting in conversion of the surface into a nitrogen-containing DLC type structure. Up to four-fold increase of the hardness at 50–100 nm depth was measured compared to the untreated samples. The scratch volume, characterising the wear resistance, decreased also significantly down to 25–35% of the original value.