Enhanced Autohesive Bonding of Polyetheretherketone (PEEK) for biomedical applications using a methane/oxygen plasma treatment

High performance polymers such as PEEK are currently considered unsuitable for the encapsulation of biomedical implants, partly because of a lack of a strong and durable bonding technology. Strong autohesive bonds were achieved between semi-crystalline PEEK surfaces using a treatment in RF plasma with a mixture of methane and oxygen (CH₄/O₂) gases. The surfaces were bonded under pressure above the glass transition temperature (T _g) and below the melting point (T_m). The treatment with CH₄/O₂ gases produced significantly higher bond strength than untreated samples and samples treated with CH₄ only. The CH ₄/O₂ plasma treatments generated a higher polar component of surface energy than observed for the untreated surfaces and also higher than that observed for surfaces plasma treated in CH₄ alone. XPS analysis of surfaces treated with CH₄/O₂ plasma for more than 3min showed that oxygenated nano-films were deposited that contained CO groups and these showed the highest bonding strength. Free radical induced cross-linking of the deposited nano-film is proposed as a mechanism to explain the high bond strength achieved.