Press time flakeboard

In three-layer flakeboards based on five softwood and hardwood species of 4, 10, and 18% moisture content, with press temperature of 177 °C, 6-min press time, and 3% isocyanate binder, the results showed that moisture content of wood was the most important variable at 18% moisture level, IB and bonding properties were lowest. Species of wood influenced strongly the bonding efficiency. In almost all cases the bending properties were the key characteristic of the panel performance. Southern pine produced the boards with lowest IB (81-116 psi), and red oak gave the highest IB values (98-213 psi) (J95). 

The wood raw material used was red oak flakes. Red oak, an abundant species in the North Central United States, is a relatively dense hardwood, known to be rather difficult to bind. The ultimate goal was the development of a roof decking panel which required a 1-1/8 inch (29mm) board, considerably thicker than typical flakeboard products. An exterior grade binder had to be used but conventional aqueous phenolics are relatively slow curing resins. Polymeric MDI was evaluated in an attempt to achieve the necessary exterior durability without the excessively long press times otherwise needed for curing such thick boards. 

To summarize the mixed hardwood flakeboard study, it can be said that good quality panels were made with Mondur MR at reduced press time, temperature and binder levels and increased flake moisture content vs. the commercial phenolic resin. 

Effect of Press Time on Mixed Hardwood Flakeboard Properties... 

The particleboard copolymer resin was applied at an 8% rate based on oven dry weight as the binder for flakeboards. A commercial phenol formaldehyde resin, catalyzed with resorcinol resin and extra sodium hydroxide was similarly used as the control resin binder for flakeboard evaluation. The density was 48 pounds per cubic foot for oak flakeboards and 43 pounds per cubic foot for pine. The oak flakeboards were pressed at a platen temperature of 350°F, however, the temperature had to be dropped to 335 F for the pine flakeboards due to a deficiency of steam pressure at the time they were to be made. The press times were ranging from 60 seconds to 120 seconds (push button close to push button open). 

One day after the flakeboards were made, the oak flakeboards having a 120 seconds press time were used to laminate with 1/8 southern pine veneers on face and back to form the 1/2 composite panel by the plywood resin. After 20 minutes close assembly time, the panels were hot pressed at a platen temperature of 300 F for 2 or 3 minutes under 200 psi platen pressure. 

The American Plywood Association (APA) 6-cycle test was used to evaluate the properties and durability of the composite panels. The results of the tests along with other physical properties of core flakeboards are listed in Table 8. In Figure 5, the dependence of board thickness (spring back thickness) immediately after hot pressing on the press time is shown separately for each of the two wood species and resins. 

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