Structural Flakeboards and Composites 3001 



the 0-90 direction by cross-grain planing. Thickness swell in single-species 

 boards of 40 Ib/cu ft density bonded with phenol-formaldehyde resin (6-percent 

 resin content) were as follows: 



Condition Yellow-poplar Red oak Hickory 



Percent — 



O-to-90-percent RH 11 9 13 



30-to-90-percent RH 10 8 11 



30-day-water-soak 38 31 32 



24-hour-water-soak 24 12 24 



Heebink and Lehmann (1977) also found that American elm flakeboard made 

 with 2-inch-long, 0.020-inch-thick ring flakes to 40-lb/cu ft density had thick- 

 ness swell of 31.2 percent after an OD-VPS cycle. 



Anthony and Moslemi ( 1 969) found that hickory flakeboard bonded with urea 

 formaldehyde (8 percent) from 1 -inch-long, 0.015-inch-thick, disk-cut flakes 

 and pressed to a density of 46.2 Ib/cu ft had thickness swell between 50 and 90 

 percent RH of 7.5 percent. 



Rice and Carey (1978) found that an increase in resin content significantly 

 decreased thickness swell in yellow-poplar and sweetgum flakeboards pressed to 

 densities of 35 to 50 Ib/cu ft, and that thickness swell was least in the lowest 

 density boards (fig. 24-44). 



Mixed-species boards from shaping-lathe flakes. — Price (1978) measured 

 thickness swell after 24-hour water soak of boards composed of 20 percent each 

 of shaping-lathe flakes from white oak, hickory, southern red oak, sweetgum, 

 and southern pine fabricated in 4- by 8-foot panels. Boards were made in 1/2- 

 inch and 5/8-inch thicknesses with flakes aligned and randomly placed. In no 

 case did thickness swell exceed 23 percent; dense boards had less percentage 

 thickness swell than those of lower density (table 24-20). 



In flakeboards made from mixed-species shaping-lathe flakes (face flakes 

 0.015 inch thick and core flakes 0.025 inch thick) of seven southern hardwood 

 species (table 24-21), Price and Hse*^ found that after OD-VPS treatment thick- 

 ness swell averaged about 28 percent and was not greatly affected by varying 

 flake length from 1.5 to 3.0 inches. Between 30 and 90 percent RH, these 

 flakeboards had average thickness swell of 15 percent; thickness swell was 

 unaffected by flake length. If flake thickness in face and core was uniform at 

 0.020 inch, thickness swell after OD-VPS treatment was significantly greater, 

 i.e., about 35 percent. 



Hse and Price^ evaluated thickness swell in flakeboards comprised of about 

 one-third baldcypress and the balance mixed southeastern hardwoods. After 

 ovendry-vacuum-pressure-soak treatment, thickness swell averaged 27 to 28 

 percent (table 24-13). 



