An adhesive bond undergoes aging due to exposure to UV radiation, mechanical loads, relative humidity, and temperature cycles. These factors influence its behaviour, appearance, and mechanical performance, and their effects vary depending on the species, the type of adhesive used, and the specific weathering conditions. Over time, the cumulative impact of these environmental and mechanical stresses can significantly alter the bond’s properties, leading to potential degradation in performance and changes in its physical characteristics. Understanding these interactions is crucial for predicting the longevity and reliability of adhesive bonds in various applications.
But how can we study these factors, how they impact our bondline, surface and performance of our composites? We are using the component of “time” or “duration” and expose our adhesives and composites to outdoor natural weathering. Besides in parallel we are looking into the effect of “accelerated aging” to see if we can observe some results even faster. Within the project “Diagnostics and mechanical tests of aged adhesive layers used in joints of wooden structures” we are working with European beech (Fagus sylvatica L.). A well-known dimensionally unstable wood species in combination with different flexible adhesives which in comparison to more rigid like, have lower elastic modulus but higher extension at failure and better stress distribution. These benefits can deal positive on shrinking and swelling of bonded beech wood when we exposed then to different climate conditions and improve their service life. At this time, different adhesives and composites are being exposed to outdoor environment, but for some of them, time has passed, and we are about to test fracture properties of adhesive bondline for commercial polyurethane adhesives, shear strength for different thick bondline flexible adhesives, surface degradation of wood, and also adhesive polymers itself. We are interested in this topic, because we are working with very flexible adhesives, and we would like to know how well they perform when used on wood. Many previous studies have been conducted on the strengthening of cracked masonry infills while with more recent studies also for bonding wood and wooden joints. Why are we doing this? We’re driven by curiosity and a passion for finding solutions that improve the durability of wooden structures. We believe that by understanding how these adhesives behave in real-world conditions, we can make better, longer-lasting wood products. Plus, it’s fascinating to see how something as simple as glue can be so crucial in construction!
Keywords: flexible polyurethane adhesives, adhesive bondline properties, natural ageing, accelerated weathering
Authors
Jaka Gašper Pečnik
InnoRenew CoE and University of Primorska, Slovenia
Andreja Pondelak
Slovenian National Building and Civil Engineering Institute
Martin Capuder
Slovenian National Building and Civil Engineering Institute
Boris Azinović
Slovenian National Building and Civil Engineering Institute
Klaudia Śliwa-Wieczorek
Chair of Bridge, Metal and Timber Structures, Faculty of Civil Engineering, Cracow University of Technology, Cracow, Poland
Arkadiusz Kwiecień
Chair of Structural Mechanics and Material Mechanics, Faculty of Civil Engineering, Cracow University of Technology, Cracow, Poland
Matthew Schwarzkopf
InnoRenew CoE and University of Primorska, Slovenia
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