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Effects of Curie particle induced accelerated curing on thermo mechanical performance of 2K structural adhesives – Part I: Bulk properties

ABSTRACT Adhesive bonding represents a widely established manufacturing process, which offers many advantages such as joining of different materials while resulting in a more advantageous stress distribution when loaded. Compared to other, mainly mechanical, joining techniques, the long curing times of adhesives – sometimes up to days – represent a decisive disadvantage. After adhesive application, contractors have to maintain these times until components can be moved for further processing, or full load can be applied. Different methods are used to circumvent the problem of adhesive cure, and thus accelerate polymerisation, among others, microwave, UV or conventional oven curing. In addition to aforementioned methods, the use of electromagnetic induction represents a promising non-contact method for accelerated curing. With this method, bonded components are exposed to a high frequency (HF) electromagnetic field (EMF), which generates heat that is transmitted to the adhesives to be cured, and in turn speeds up polymerisation. If adherends, like for example wood, glass, or G-FRP, are not sensitive to EMF, so-called susceptors (e.g. meshes, fibres or particles) are introduced into the adhesives, which can be heated inductively. Curie particles (CP) represent a special type of susceptors, which can only be inductively heated up to their material specific Curie temperature (T c) above which heating automatically stops. Thus, a curing process is designed, which is independent from external temperature monitoring techniques and – at the same time – prevents the adhesives from overheating. The present study investigated the influences of inductive curing with CP on the bulk properties of a 2 K epoxy resin and a 2 K polyurethane using standardised specimen types: adhesive bulk (AB) and dynamic mechanical analysis (DMA) specimens. The authors showed with an experimental programme of 92 specimens that resulting thermo-mechanical bulk properties of the two investigated adhesives are fundamentally changed by application of the process.