A preliminary study of glue joint parameters and reaction to fire between wood cellular material and magnesium oxide sheet

The increasing demand for lightweight, durable, and fire-resistant construction materials has led to the development of hybrid composites combining wood-based cores with mineral- nonorganic sheets. Currently, birch plywood with aluminum sheets glued into its inner layers is used to improve the fire resistance of wood cellular materials (WCM) when applied on both sides. However, MgO sheets offer the potential to produce WCM composites with even greater fire resistance. Although screws could be used for attachment, each screw may act as a localized heat conductor, effectively creating small internal “furnaces” that promote heat transfer. Therefore, gluing is, in practice, the only viable method for attaching MgO sheets to WCM. Because WCM contains grooves, the effective gluing area is reduced, which may influence adhesion performance. The novelty of this study lies in clarifying these combined effects, as well as examining the influence of pressing methods (vacuum and/or hydraulic) on the MgO-WCM composite system using different types of industrial glues. This study evaluates the performance of glue joints between Dendrolight WCM and magnesium oxide (MgO) sheets under elevated temperature exposure. Four industrial glues: polyvinyl acetate (PVA), melamine-urea-formaldehyde (MUF), emulsion polymer isocyanate (EPI), and polyurethane reactive (PUR) were tested to determine their fire resistance and thermal stability. A custom-built small-scale fire testing chamber, designed to approximate the ISO 834-1 standard time-temperature curve, was used to assess joint integrity and composite panel performance Iqra(15(19):3513, 2025). The results of the preliminary study showed that MUF glue failed within the first 5 min, while PVA glue exhibited highly variable results due to its thermoplastic nature. PUR and EPI glues demonstrated significantly better performance, maintaining structural integrity for up to 18 and 21 min, respectively, under equivalent thermal exposure. Larger-scale composite panel tests confirmed that relocating the MgO-wood glue interface toward the panel centre improved cohesion and delayed delamination, thus achieving sustained integrity for up to 39 min. The findings highlight the importance of glue type, joint placement, and controlled testing environments in optimizing the fire performance of MgO-WCM composites.