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 strandbo ard resin with and without zinc berate addition were investigated in this s tudy. It was shown that the pH of the hardwood flakes was acidic, with whit e 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 t o the hardwood flakes. The alkali buffer capacity was larger than the corre sponding acid buffer capacity for most species tested. The total buffer cap acity varied from 0.09 for cypress to 0.358 for hackberry. Measured resin g el times with and without wood presence decreased as the amount of zinc ber ate increased. The reduced gel time was partially recovered by using polyet hylene glycol (PEG) in combination with the berate. The effectiveness of PE G varied with wood species and the level of berate used. The gel time had n o direct correlation to flake pH and buffer capacity of the wood species us ed.