Evaluation of natural durability of solid wood and mixed heartwood-sapwood Cypress (Cupressus sempervirens L.) plywood against Basidiomycete fungi
F Faraji, M F Thévenon, N Lemenager, B Thibaut
The aim of this research was to study the response of mixed plywoods composed of durable heartwood and non-durable sapwood to fungal attack. For this purpose, the species of Cupressus sempervirens (cypress) was chosen for its well-known durable heartwood. The evaluation of durability of plywood panels against fungi was done according to ENV 12038 and the fungi used were Coriolus versicolor (CV) and Coniophora puteana (CP). In order to have the basic data on the wooden element of plywood, the natural durability of cypress sapwood and heartwood in the state of solid wood was also determined against fungi according tothe guidelines of EN 350-1. Plywoods
made of pure sapwood and pure heartwood (as controls) allowed a comparison with the mixed ones. 17 different plywoods were laboratory made. The influence of thickness of plies, number of MUF
glue line, percentage of heartwood plies integrated to sapwood plies in the mixed plywood, and finally, the way of integration of durable plies in to non-durable plies has been evaluated.
In case of solid wood, the heartwood of cypress was found “very durable” against both CV and CP while the sapwood was found “slightly durable”. In the case of plywoods, the evaluation of fungal resistance of pure plywood showed a slight diminution in comparison with the solid wood state. This decrease can be explained by a loss of some extractives molecules during the stage of steaming and peeling. In the mixed plywoods, some of the integrations were found more resistant to the fungal attack. These panels were composed of heartwood layers on the surfaces. It was also found that the criteria of vulnerable surfaces or durable surfaces in plywood is more related to its resistance than the criteria of volume of non durable plies or durable plies that is generally recognized