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Abstract
The objective of this research was to investigate the heat resistant performance of structural adhesive as compared with wood samples. Phenol-resorcinol-formaldehyde (PRF) and two wood species, southern pine (Pinus palustris) and Douglas-fir (Pseudotsuga menziesii), were investigated. Uniform thin cured resin films and wood samples were carefully prepared. Dynamic mechanical analysis (DMA) was employed to evaluate the fixed frequency oscillation properties of these samples over the temperature range of 60 to 250 °C. Shear storage moduli, shear loss moduli, and tan δ values of the prepared samples were obtained through the DMA temperature scan and isothermal testing. DMA temperature scan tests showed that the storage moduli of the tested materials decreased as the temperature increased. At the same temperature level, PRF resin films had higher storage moduli than that of the wood samples. No obvious difference was found between the two wood species in their dynamic performances. The DMA isothermal tests results indicated that the storage moduli of cured rein films increased with prolonged time at the four different temperature levels (90, 150, 200, and 250 °C), while the loss moduli and tan δ values decreased with prolonged time. The moduli and tan δ values of wood samples decreased dramatically with prolonged time at 250 °C, while changed slightly at temperatures of 90, 150, and 200 °C.
Wood has a long history of use in building construction. Because the availability of large dimension solid timber has been decreasing in the past decades, the forest products industry has developed a new generation of glued engineered wood products (EWPs), including I-joists, glued laminated timber (Glulam), structural composite lumber (SCL), and others. These EWPs are processed using small-diameter trees as raw materials and exterior- type adhesives. The adhesive plays an important role since it bonds the wood components (dimensional lumbers, veneers, strands, fibers, and others.) together, transfers and distributes stresses, and provides the required strength and structural integrity when the EWPs are subjected to moisture conditions, long-term weathering, and long-term loading. In addition, the adhesive bonding should provide adequate structural performance under high-temperature conditions, such as those reached in the early phases of a structure fire.
The failure of EWPs' bondline suffering heating may be caused by two reasons: 1) insufficient heat durability of the adhesive bondline...