The current OSB production has shown a trend toward the utilisation of liquid and powder phenol-formaldehyde (PF) resin combination binder system in order to improve resin efficiency. A new resin application system equipped with two nozzles for liquid resin and one blower for powder resin application has been installed at Forintek. To understand how the resin application system affects resin efficiency as measured by improved resin coverage and physical and mechanical properties, an experiment was conducted to manufacture a series of OSB panels with various powder/liquid resin combination ratios (0/100, 25/75, 50/50, 75/25, 100/0), resin contents (2.0%, 3.5%, 5.0%), and dwell times (1, 2, 3 min) during blending.
Two statistical methods, Duncan’s Multiple Range Test and Response Surface Analysis, were used for the analysis of variance (ANOVA) of resin coverage on the surfaces of strands and mechanical and physical properties of OSB panels made from these strands. The former method was employed to determine the means of panel properties significantly different at the 95 percent confidence level, and the latter to determine the significant model terms at the 95 percent confidence level in Response Surface Quadratic Model and to predict the overall trends of panel properties and/or resin coverage influenced by these model terms.
This study indicated that among the variables investigated resin content was the only attributing factor that significantly affected resin coverage and all panel properties, including internal bond strength (IB), thickness swelling (TS), water absorption (WA), modulus of rupture (MOR) and modulus of elasticity (MOE) at the 95 percent confidence level. An increase in resin content broadened the resin coverage and meanwhile improved panel performance for both blowing and tumbling methods used for powder application. In addition, an overall increase in resin coverage improved IB, TS, WA and MOR, but not MOE. Powder/liquid combination (between 25/75 and 75/25) improved resin efficiency regarding IB and TS properties of panel compared to powder or liquid resin alone. When blowing method was used for powder application in powder PF/liquid PF combo system, a shorter dwell time (1 min) was optimal for resin efficiency compared with a longer dwell time (2 or 3 min). The reverse trend was observed when tumbling method was utilised for powder application in the powder binder system. An overall comparison between the two blending methods for the powder also indicated that the blowing method had an advantage over the tumbling method regarding resin efficiency and bond quality at a short dwell time.