The Effects of Mild Chemical Extractions on the Dimensional Stability of uf and pf Bonded Red Oak Flakeboard
Keywords:Phenol formaldehyde, urea formaldehyde, flakeboard, dimensional stability
AbstractRed oak (Quercus rubra L.) flakes were chemically extracted under mild conditions to determine the effects on red oak flakeboard properties, particularly dimensional stability. Flakes were extracted with weak acetic acid solutions or water under selected treatment pressures and treatment times. Weight loss values of extracted flakes ranged from 4 to 25%. Phenol formaldehyde (PF) and urea formaldehyde (UF) bonded flakeboards were manufactured using either red oak or chemically extracted red oak flakes. Physical and mechanical properties evaluated were modulus of elasticity, modulus of rupture, internal bond, water immersion related properties, and linear expansion. Static bending properties of flakeboards using extracted flakes for both resins, even at high levels of flake weight loss, were similar to boards from unextracted flakes. Internal bond average values for the extracted flakes were lower for the PF boards compared to the controls. Internal bond values for the UF boards were similar to the controls. Dimensional stability values for the PF boards were similar for the extracted and control boards. Dimensional stability tests on the UF boards produced the following results: (1) 2-hour dimensional stability values were improved for the extracted versus control boards; (2) 24-hour dimensional stability values for the extracted boards were similar to the control boards; and (3) linear expansion values for the extracted boards were similar to the control values.
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