Effects of Nd: YAG LASER irradiation and O₂ plasma on the adhesive performance of poly-ether-ether-ketone (PEEK).

Abstract

To evaluate the effects of neodymium-doped yttrium aluminum garnet (Nd: YAG) LASER irradiation and oxygen (O₂) plasma on the adhesive performance of polyether ether ketone (PEEK) and resin adhesive. Nd: YAG LASERs of varying powers and O₂ plasma for different durations were used to modify PEEK. A total of 168 PEEK specimens were randomly divided into seven groups (n = 24/group): (A) Control group: untreated PEEK, (B) L_0.75 group: PEEK modified with 0.75 W Nd: YAG LASER, (C) L₁ group: PEEK modified with 1.0 W Nd: YAG LASER, (D) L_1.25 group: PEEK modified with 1.25 W Nd: YAG LASER, (E) P₁₅ group: PEEK modified with 15 min of O₂ plasma, (F) P₂₅ group: PEEK modified with 25 min of O₂ plasma, and (G) P₃₅ group: PEEK modified with 35 min of O₂ plasma. The surface characteristics of the materials were comprehensively analyzed using a scanning electron microscope (SEM), profilometer, energy-dispersive spectrometer (EDS), and contact angle tester. The adhesive specimens were bonded with Variolink N resin adhesive in all groups and each group was further divided into two subgroups (n = 12/group): (a) water storage for 56 h at 37 °C and (b) thermal cycling 5000 times. Shear bond strength (SBS) was tested using a universal testing machine, and the fracture modes were observed using an automated chemiluminescence analysis system to assess the effects of Nd: YAG LASER and O₂ plasma on the bond strength of PEEK to resin adhesive. Both Nd: YAG LASER and O₂ plasma treatments altered the surface characteristics of PEEK and significantly increased the SBS between PEEK and Variolink N resin adhesive. The L_0.75 group (Nd: YAG LASER) and the P₃₅ group (O₂ plasma) achieved the highest SBS, respectively. Furthermore, the SBS of the L_0.75 group was higher than that of the P₃₅ group. Following thermal cycling, SBS values decreased compared to the water storage subgroups. The fracture modes of the specimens in each group were predominantly interfacial and mixed, with no cohesive fractures observed. Nd: YAG LASER irradiation and O₂ plasma treatments can improve the SBS between PEEK and resin adhesive, with the 0.75 W Nd: YAG LASER being the preferred treatment method.