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Effect of seawater wetting on the weathering of wood

Klüppel, André, Mai, Carsten
European journal of wood and wood products 2018 v.76 no.3 pp. 1029-1035
Fourier transform infrared spectroscopy, Pinus sylvestris, cell walls, crystals, delignification, drying, lignin, nanopores, photolysis, seawater, tensile strength, ultraviolet radiation, weathering, wood
This study examines individual and interactive effects of seawater wetting and UV irradiation on the tensile strength of Scots pine (Pinus sylvestris) micro-veneers. In a first experiment, veneers were cyclically wetted with demineralized water or synthetic seawater and dried at 40 °C. In a second experiment, veneers were exposed to artificial weathering including UV irradiation and spray of seawater or of demineralized water. Cyclic wetting with seawater severely decreased finite-span tensile strength (f-strength) but did not affect zero-span tensile strength (z-strength). Cyclic wetting with demineralized water decreased neither f-strength nor z-strength. During artificial weathering, type of water had no significant effect on f-strength loss. However, FTIR measurements showed that seawater-weathered veneers contained more lignin than those weathered with demineralized water. Repeated wetting with seawater is assumed to damage the cell wall matrix, because salt crystals, which grow inside the cell wall nanopores during drying, exert stress on the adjacent material. At the same time, seawater inhibits delignification resulting from photodegradation. Therefore, seawater wetting changes nature and mode of weathering but not necessarily the degradation rate measured as f-strength loss of micro-veneers.