Autohesion of semi-crystalline PEEK near and under the glass transition temperature

Autohesion of semi-crystalline polymers under the glass transition temperature (T _g ) is fundamentally difficult due to severe restriction in molecular chain mobility. We demonstrate that enhanced autohesion of semi-crystalline polyetheretherketone (PEEK) at temperatures close or under T _g can be achieved through plasma immersion ion implantation (PIII) treatment. Autohesive bonding strength of PEEK increased linearly with PIII bias voltage up to tenfold compared to untreated controls at 160 C (T _g +10 C). At 130 C (T _g -20 C), PIII treatment increased bonding strength of PEEK by more than fivefold compared to the untreated control. PIII treated surface exhibited higher surface energy, polar component and oxygen content. A model based on the formation of covalent bonds on the plasma treated PEEK by radicals present at the interface was found to predict the bonding strength above and below T _g . The major mechanism responsible for improved autohesion of PEEK near and under T _g is believed to be free radicals based covalent bonding assisted by an increase of surface wettability and reduction in surface crystal structure as was evidenced by SEM images.