Catalytic Effects of Extractives from Pressure-Refined Fiber on the Gel Time of Urea-Formaldehyde Resin

Pressure-refined fiber of five low-grade southern hardwoods — tupelo, hickory, white oak, red oak and sweetgum — and loblolly pine was extracted nonsequentially with ethanol and with water. The amount of each extractive and the reason for their catalytic effects on the gel time of urea-formaldehyde (UF) resin were investigated. The ethanol-soluble extractive content ranged from 5.7 percent to 9.5 percent, and the water-soluble extractive content ranged from 6.2 percent to 12.5 percent. With the addition of less than 1 percent extractive, the ethanol-soluble extractives of each species caused a greater reduction in gel time of a UF resin than the water-soluble extractives. Data indicate that the cause of these catalytic effects was the PH of the extractive. The gel time of the mixture increased exponentially as its pH increased.

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