Bond properties of binderless bonded spruce plywood during immersion

摘要

Instead of using adhesives, it is possible to manufacture adhesive free plywood fromrnveneers by correctly choosing the following three parameters: an appropriate moisturerncontent for the raw material, a high enough press temperature and a high enough pressrnpressure. However, adhesive free bonding has not provided satisfactory results due to poorrnbond stability when exposed to moist conditions. As compressed wood can be dimensionallyrnstabilised with certain thermal treatments, the same method was studied to see if it could alsornstabilise binderless bonded Norway spruce (Picea abies, L.) plywood manufactured byrnseveral methods. Thermally treated, as well as untreated specimens were immersed in waterrnand their bond integrity was observed as functions of both time and MC for the first 150rnhours of immersion. According to the results some of the specimens tolerated moisture betterrnthan the others; for instance, the thermally treated specimens were significantly better thanrnthe untreated ones. Moreover, the MC of the thermally treated specimens increased morernslowly and reached a lower MC than that of the untreated specimens. The tests providedrnpromising evidence that the wet stability of self-bonded Norway spruce plywood could bernenhanced by a post-manufacture thermal treatment. However, not all types of self-bondedrnplywood were successfully enhanced by thermal post treatment; the original manufacturingrnmethod was found to be important. Nevertheless, it is possible that another type of a postmanufacturernthermal treatment could enhance the wet stability of these specimens and furtherrnresearch is ongoing.