Free radicals generated by ion bombardment of a semi-crystalline PEEK surface

Thin films of polyetheretherketone (PEEK) were ion bombarded using a plasma immersion ion implantation (PIII) process in Ar and CH ₄/O ₂ plasmas. Free radicals generated by the treatment were detected using electron spin resonance (ESR) spectroscopy. Several types of radicals were observed after the Ar and CH ₄/O ₂ PIII treatment, including carbon-centred (alkyl) and oxygen-centred radicals. A higher density of radicals was found after CH ₄/O ₂ treatment than after Ar treatment, largely because of an increase in oxygen radicals. The increase in radical intensity was attributed partly to additional radicals contained in a nano-layer deposited by the CH ₄/O ₂ PIII treatment. Ar PIII treatment is believed to generate oxygen-containing radicals as a result of reactions with oxygen in the environment. A strong correlation was observed between the free radical density and the autohesive bonding strength developed between two treated PEEK surfaces. It was possible to identify two types of free radicals, carbon centred and oxygen centred, that are generated as a result of PIII plasma treatment of PEEK. A significant increase in the free radical density was observed as a result of the PIII plasma treatment of PEEK films. The increase in free radicals led to a significant increase in the bonding strength of PEEK films.