The mechanical and physical properties of strand boards treated with preservatives at different stages of manufacture

The physical and mechanical properties of boards treated with a preservative at different points during the manufacture process were evaluated to determine the best stage for the application of preservative. A copper boron tebuconazole amine water-based preservative was used in 3% PF-bonded strand boards to achieve five different retentions. Preservative addition was examined at different stages of the manufacture cycle, namely, green strand diffusion, dry strand vacuum treatment, glue-line spray addition, heat and cold quench of manufactured board, and by post-manufacture vacuum treatment. The treatment methods had marked effects on the mechanical properties of some of the boards when the boards with the highest preservative retention were compared with their respective untreated controls. The best results were achieved where the preservative was applied by vacuum treatment of dry strands or by diffusion of green strands before board manufacture. Increasing preservative retention had minimal effects on board properties with these two methods but significant deterioration was noted when the preservative was applied by spraying dry strands or by post-board-manufacture heat and cold quench. An increase of pressing temperature resulted in significant improvements to the mechanical properties of the spray-treated boards. Post-manufacture vacuum treatment of boards caused excessively high losses in internal bond strength.