The Influence of Flake Chemical Properties and Zinc Borate on Gel Time of Phenolic Resin for Oriented Strandboard

The pH and buffer capacity of dry wood flakes from eleven southern species and their effects on gel time of phenol formaldehyde (PF) oriented strandboard resin with and without zinc borate addition were investigated in this study. It was shown that the pH of the hardwood flakes was acidic, with white oak being the most acidic (pH = 4.60) and elm nearly neutral (pH = 6.93). Southern pine flakes had a relatively low pH value (pH = 4.98), compared to the hardwood flakes. The alkali buffer capacity was larger than the corresponding acid buffer capacity for most species tested. The total buffer capacity varied from 0.09 for cypress to 0.358 for hackberry. Measured resin gel times with and without wood presence decreased as the amount of zinc borate increased. The reduced gel time was partially recovered by using polyethylene glycol (PEG) in combination with the borate. The effectiveness of PEG varied with wood species and the level of borate used. The gel time had no direct correlation to flake pH and buffer capacity of the wood species used