SURFACE ACTIVATION METHODS FOR BONDING TO THERMOPLASTICS: PLASMA AND A NEW TAILORED UV BASED METHOD

摘要

The constant trend to optimize the costs of raw materials and related processing costs has accelerated the use of thermoplastic composites as alternatives to traditional thermoset composites in the Aerospace Industry. While thermoplastics can be easily fused together above their melting temperatures, it is difficult to bond them to dissimilar substrates, including thermosets and aluminum. The high melting temperatures of engineered thermoplastics like Polyarylether Ketone family (350 - 430 °C) limit their process. Therefore, lower temperature bonding systems would be desirable. This paper discusses the development of a new and rapid UV pretreatment method for thermoplastic composites allowing improved bonding to dissimilar substrates. In addition, plasma pretreatment is also investigated as a common method since it can have good proficiency in some cases depending upon the chemistry of adhesives. Contact angle measurement was done for surface analysis of treated substrates where regarding to the new tailored UV method, complementary analysis such as XPS and TOF-SIMS was conducted. To evaluate the bond strength, mechanical tests including fracture toughness (G_1C) and tensile lap shear tests were conducted. Contact angle measurements, XPS, and TOF-SIMS analysis revealed an increase in polarity and wettability of the thermoplastic surface after pretreatments due to the formation of new oxygen-containing functional groups. This rapid UV surface treatment method led to a significant improvement in bonding of PAEK thermoplastic composites with both low and elevated temperature-cure adhesives verified by mechanical test results. This method offers new opportunities for fast and safe bonding to the thermoplastic materials resulting in excellent bond strength comparable with plasma pretreatment.