Effect of Accelerated Aging Weathering on Fire and Mechanical Properties of Plywood

This study is focused on the impact of aging on the fire and mechanical behavior of a fire-retarded industrial plywood claimed for outdoor use as cladding. Two sets of okoume-based (Aucoumea klaineana) plywood, with and without flame retardant, were examined: one aged 4 weeks by immersion in hot water (40 ℃), and the second aged with artificial UV light coupled to spraying for 12 weeks. Scanning electron microscopy coupled with EDX analysis were used to investigate changes in the material after aging, and distribution of flame retardant in the material. This study reveals the impact of different aging procedures on the physico-chemical modifications of the composite material. In addition, the mechanical properties of aged plywood were measured by static bending tests and vibration analysis as non-destructive method to assess weekly the aging effect. Thus, the fire behavior of the sets of plywood as a function of aging exposure time was evaluated by cone calorimetry. The results show that, whatever the aging, it occurs a microstructural degradation of wood and a fast leaching of the flame retardant in whole wood plies, especially for immersion aging. The mechanical properties are then reduced and the fire retardancy is quickly ineffective after aging.