Abstract
The single sections of a wood/adhesive bond, namely the adherend wood, the pure adhesive and the interphase are expected to contribute differently to the mechanical behaviour of a joint. Moisture-related changes of the stress/strain states between the adherends tend to result in deformation or even material failure. Therefore, beside the elastic, the moisture-related mechanical properties of the involved components are of significant interest. Adhesively bonded samples of spruce (Picea abies) using adhesives that are common in furniture and flooring production (emulsion polymer isocyanate (EPI), polyvinyl acetate (PVAc), urea formaldehyde (UF) and ultra-low formaldehyde-emitting amino resin (ULEF)) were manufactured under laboratory conditions. Quasi-static nanoindentation was performed on the pure adhesive polymer, the S2 layer of pure wood cells and interphase wood cells, to obtain the reduced elastic modulus, hardness and the indentation creep. To investigate the moisture-related mechanical properties, the testing environment was held under constant temperature and different controlled humidity levels. The pure wood cell walls generally tend to show a more stable behaviour to humidity changes than the investigated adhesives. It can be assumed that the ULEF adhesive penetrated the cell walls, as differences between pure wood cells and those located in the interphase could be identified. EPI, PVAc and UF showed no evidence of modifying the interphase cell walls but revealed different behaviours in relation to pure wood cells.
Highlights
An adhesive layer of a solid wood bond consists, beside the pure adhesive polymer, of multiple sections that are participating differently to the total performance of an adhesive joint (Eckmann 2007; Marra 1992)
The reduced elastic modulus Er of the pure wood cells, the adhesive polymer present in the bond line and the interphase cells surrounded by adhesive are displayed in Fig. 4 for different humidity levels
Mechanical properties of the tested wood cell walls seem to be less affected by moisture changes than the used adhesives
Summary
An adhesive layer of a solid wood bond consists, beside the pure adhesive polymer, of multiple sections that are participating differently to the total performance of an adhesive joint (Eckmann 2007; Marra 1992). The capability of absorbing water vapour (Wimmer et al 2013) and the mechanical response to this have been experimentally demonstrated for cured adhesive polymers present in adhesive joints for different temperatures and relative humidities as reported in the previous studies (Jakes et al 2015; Konnerth and Gindl 2008; Rindler et al 2018; Stöckel et al 2013). For different wood species, moisture- and temperature-related elastic, viscoelastic and plastic micromechanical behaviour is described, and data are available in the literature (Gindl et al 2004; Gindl and Schöberl 2004; Wagner et al 2015; Wimmer et al 1997; Zickler et al 2006), whereas for the interphase region, data are relatively scarce. The interphase is assumed to contribute to the performance of the adhesive joint
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
