Parametric study of hot-melt adhesive under accelerated ageing for automotive applications

The mechanical properties of commercially available hot-melt adhesive, HMA, which is mostly used in automotive applications, have been studied under different environmental and loading conditions, paying particular attention to the ageing effects. Three laboratory accelerated ageing processes were applied to single lap joints (SLJs) of two polypropylene substrates in order to replicate the least favourable environmental conditions in automotive usage. Experimental parametric studies were performed on virgin and aged specimens, investigating the influence of two design factors, the overlap length and adhesive layer thickness, on the load carrying capacity and mode of failure of the SLJ. FT-IR was used to perform qualitative HMA polymer composition analyses. The DSC test was also performed to obtain the thermal behaviour, and the phase transition temperatures of the HMA. In addition, the sliding temperature test was performed in an electronically controlled climatic chamber to understand, by means of tests on SLJs, the temperature resistance of the HMA/polypropylene bonded systems. Results clearly show that depending on the type of ageing process, the strength of SLJ based on HMAs varies, this enhances a relevant difference with respect to the strength of SLJ based on conventional thermosetting adhesive. Furthermore, the parametric study performed revealed the correlation between the strength of the SLJ and its geometry, which might be taken as a design guideline for this kind of flexible adhesive joints.