Adhesive bonding of pultruded fiber-reinforced plastic to wood

Although glued-laminated timber (glulam) beams were used extensively in construction, their application to large-scale structures is often limited by their relatively low bending stiffness and strength. Glulam beams can be reinforced with synthetic fiber-reinforced plastic (FRP) to significantly increase their mechanical properties. The pultrusion process offers an inexpensive means of mass producing FRP for wood reinforcement. Pultruded composites and wood can be concurrently laminated to produce glulam beams using traditional manufacturing techniques. The pultruded FRP plates can replace the high quality tension or compression laminates that are needed for high strength and stiffness combinations. In this research, combinations of yellow-poplar (Liriodendron tulipifera) and polyester- or vinylester- pultruded composites were bonded with resorcinol-formaldehyde (RF), epoxy, and emulsion polymer isocyanate adhesives. Samples were tested following both ambient and vacuum-pressure soak conditioning using a modified ASTM D 905 shear-block test. While all the adhesives produced adequate strength values under dry conditions, only the RF adhesive produced promising results under the wet conditions. Further testing of the RF adhesive using a multiple-cycle accelerated-aging test did not result in any delaminations of the wood-FRP composite samples.

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