3000 Chapter 24 



In the 50 to 90 percent RH test, there was Uttle difference in thickness stability 

 between panel densities of 39.5 and 44.5 Ib/cu ft. Thickness swelling increased 

 slightly as panel density increased to 49.5 Ib/cu ft. 



White oak panels swelled significantly more than those of other species, and 

 they delaminated substantially between particles after the 5-hour boil. Hse 

 (1975c) found no relationship, for any species, between initial IB and thickness 

 stability. 



Post (1961) made scarlet oak flakeboard from veneer flakes and found that 

 thickness swell was least when flakes were very thin (0.006 or 0.012 inch). 

 Jorgensen and Odell (1961), in an extension of Post's work, observed that high 

 resin content favored thickness stability; thickness swell proceeded slowly with 

 an increase in RH to 5 percent at 83 percent RH but increased to about 30 percent 

 at 90 percent RH (see also fig. 24-42). 



Single-species flakeboards made from non-veneer flakes. — Price and Leh- 

 mann (1978) evaluated thickness swell of boards composed of flakes cut on ring, 

 disk, drum, and shaping-lathe flakers. When exposed to the OD-VPS test, 

 southern red oak and mockemut hickory boards made of shaping-lathe flakes 

 had least thickness swell (fig. 24-8). Between 30- and 90-percent RH, oak 

 boards made with shaping-lathe flakes and hickory boards made with ring flakes 

 had least thickness swell. In sweetgum panels, shaping-lathe flakes yielded least 

 thickness swell (14.1, 9.9, and 28.2 percent in the 30-to-90-percent-RH, 24- 

 hour- water-soak, and OD-VPS tests). Price and Lehmann found that, on aver- 

 age, the 30-to-90-percent-RH test caused least thickness swell, the 24-hour 

 water soak caused the same or slightly more, and OD-VPS treatment caused 

 about twice the thickness swell of the 30-to-90-percent-RH cycle. Sweetgum 

 flakeboards, for example, had average thickness swell as follows (pooled data 

 for all four types of flakers): 



Treatment Average thickness swell 



Percent 



30-to-90-percent-RH 15 



24-hour- water-soak 15 



OD-VPS 31 



They also found that increasing resin content from 5 to 8 percent decreased 

 thickness swell by 2.7, 4.0, and 7.6 percentage points for the 30-to-90-percent- 

 RH, 24-hour-water-soak, and OD-VPS tests (fig. 24-9). 



Yellow-poplar flakeboards made similarly were found by Price (1978) to have 

 thickness swell of 9.9 percent after a 24-hour water soak cycle (table 24-20) — 

 about the same as for sweetgum boards of this design. 



Hse (1981) found that thickness swell of phenol-formaldehyde-bonded white 

 oak flakeboard subjected to the OD-VPS cycle was substantially greater (41.4 

 percent) than that of southern red oak flakeboard (26.0 percent), but was signifi- 

 cantly reduced by applying polyisocyanate to the flakes before addition of liquid 

 phenol-formaldehyde resin (table 24-10). 



Heebink and Lehmann (1977) made flakeboards of yellow-poplar, red oak, 

 and hickory from randomly oriented 1 -inch-long flakes 0.015 inch thick cut in 



