Adhesion Improvement of Thermoplastics-Based Composites by Atmospheric Plasma and UV Treatments

Gennaro Scarselli,Alojz Ivankovic,Dong Quan,Brian Deegan,Neal Murphy,Denis Dowling

doi:10.1007/s10443-020-09854-y

Gennaro Scarselli, Alojz Ivankovic + Show 4 more

Open Access

https://doi.org/10.1007/s10443-020-09854-y

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Abstract

The present work is concerned with adhesive bonding of thermoplastic composites used in general aerospace applications, including polyphenylene sulfide (PPS), polyetherimide (PEI) and polyetheretherketone (PEEK) carbon fibre composites. Three different surface treatments have been applied to the PEEK, PPS and PEI-based composites in order to enhance the adhesion: atmospheric plasma, ultraviolet radiation (UV) and isopropanol wiping as a control. Water contact angles and free surface energies were measured following the standard experimental procedure based on the employment of three different liquid droplets. Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) were subsequently performed to characterize the surface chemistry of the samples after treatment. The single lap joints were manufactured and bonded by an Aerospace grade epoxy-based film adhesive originally developed for use on metals but with the ability to bond treated thermoplastics to good strength (supplied by Henkel Ireland). Quasi-static (QS) tests were conducted. The lap shear strength was evaluated, and the failure mechanisms of the different joints were examined for the range of surface treatments considered. It was found that the performances of the PEEK and PPS joints were considerably improved by the plasma and UV treatments resulting in cohesive and delamination failures, while PEI was unaffected by the plasma and UV treatments and performed very well throughout.

Highlights

The increasing use of polymer composites in a wide variety of industrial applications has resulted in a corresponding interest in the most effective ways by which these materials may be joined together
The results indicated a substantial improvement of the lap shear strength for polyphenylene sulfide (PPS) and PEEK while PEI samples were essentially insensitive to the treatment or even somewhat negatively affected
Single lap joints comprised of carbon fibre reinforced PEEK, PPS and PEI composite substrates and an epoxy film adhesive have been tested to evaluate the effect of a variety of surface treatments on the lap shear strength

Summary

Introduction

The increasing use of polymer composites in a wide variety of industrial applications has resulted in a corresponding interest in the most effective ways by which these materials may be joined together. Al-Maliki et al [11] determined that post-treatment there was an increase in oxygen content and a decrease in carbon content forming polar functional groups that increased the wettability of the surface making the surface more hydrophilic. They attributed plasma treatment’s ability to increase surface energy to the combination of two main factors, increased wettability and increased surface roughness. All the above studies had consistent results regardless of how the topography changed This indicates that topography plays a much lesser role in increasing the surface energy than surface chemistry effects. It is vital that bonding occurs as soon as possible post-treatment

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