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PEEK adhesive improvement with laser surface modification

TWI has found a way to improve the surface properties of polyether ether ketone (PEEK) using a laser process. Experiments saw a short pulsed solid-state laser used to modify the surface of PEEK polymer, increasing its surface energy and consequently improving adhesive joint strength. Tests confirmed joint strength improvement via lap shear testing of the laser-processed polymers

Raising medical implant reliability

PEEK is commonly used for a wide range of implants in the medical industry. These implants need to be able to be integrated into the body and as such the surfaces need to be compatible and also allow adhesion. Inadequate surface treatment is one of the most common causes of premature degradation and failure of bonded joints. For non-polar polymers or polymers with low surface energy, it is necessary to introduce chemically reactive surface functional groups in order to improve adhesion. Other techniques exist, such as plasma and mechanical abrasion, but lasers provide an additional level of precision.

Figure 1 - Laser processing setup
Figure 1 - Laser processing setup

Refining the technique

TWI selected a nanosecond pulsed Nd:YAG laser to provide energetic treatment of PEEK surfaces, to investigate its effectiveness in increasing the performance of lap shear adhesive joints.  The laser was used to irradiate the PEEK, by rastering a spot of ~1mm diameter across a large area.

The resulting surfaces were characterised using single-lap shear testing and advanced surface analysis techniques. Single-lap shear testing of PEEK joints showed that the strength of adhesively bonded joints is greatly improved by laser treatment – up to 13 times that of untreated PEEK. The higher laser power intensities (≥107 W mm-2) disrupted the surface of the PEEK more than the lower laser powers intensities (<107 W mm-2).

The derived surface free energy increased alongside laser power intensity. High-resolution surface chemical analysis showed that laser treatment only affects the near-surface at the extremity of the 1–2µm sampling depth. The process creates oxygen-containing functional groups at the surface.

The next step

TWI will conduct further work on laser surface modification of an increased number and type of materials, along with a wider range of laser parameters such as pulse duration, average power, pulse frequency and laser fluence.

For more information, please email contactus@twi.co.uk

Figure 2 - Lap shear testing of laser-treated PEEK specimens
Figure 2 - Lap shear testing of laser-treated PEEK specimens
Avatar Andy J Wilson Principal Project Leader, Laser Surface Engineering and Laser Processing of Polymers

Dr. Andy J Wilson is a Principal Project Leader in the Laser and Sheet Processes Section at TWI Ltd having joined TWI as an EngD research engineer in 2011 and becoming a project leader in 2015.

He has a BEng (Hons) in Automotive Materials from Loughborough University and an Engineering Doctorate (EngD) from the University of Surrey on ‘The Influence Of Laser Parameters on the Surface Processing of Materials’.

Andy has over 10 years of experience in ultrashort pulsed laser processing for ablation, surfacing and microprocessing and has managed a wide range of industry projects. Particular specialisations are in laser surface modification of polymers for enhanced adhesion, inducing superhydrophobicity of metals via laser texturing, and laser ablation of complex geometries on multiple material types using nanosecond and picosecond pulsed lasers.

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