Structural Flakeboards and Composites 2995 



Anthony and Moslem! (1969) found that hickory flakeboard bonded with 

 urea-formaldehyde resin (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 linear expansion between 

 50- and 90-percent RH of 0. 146 percent. 



MIXED-SPECIES BOARDS FROM SHAPING-LATHE FLAKES 



By use of mechanical micrometers and measuring between grommeted holes 

 in panels, Price (1978) measured the linear expansion after 24-hour water soak 

 of boards composed of 20 percent each of shaping-lathe-cut 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 linear expansion exceed 0.20 

 percent (table 24-20). 



Through use of microscopes arranged in an optical comparator. Price and 

 Hse^ measured linear expansion of flakeboard comprised of a mixture of shap- 

 ing-lathe flakes of seven southern hardwood species or species groups (table 24- 

 21). These flakeboards, if pressed to a density of 41 pounds/cu ft or more, were 

 most stable linearly if both face flakes and core flakes were 3 inches long — 

 rather than 1.5 inches long, and if face flakes were 0.015 inch thick and core 

 flakes 0.025 inch thick (fig. 24-43). If so fabricated, linear expansion at board 

 density of 42 pounds/cu ft was as follows: 



Test Linear expansion 



Percent 



OD-VPS 0.16 



30- to 90-percent RH .04 



Mechanical properties of these flakeboards are given in figure 24-33. 



Because some parts of the coastal plains of the South and Southeast carry a 

 large component of baldcypress, phenolic-bonded flakeboards comprised of 

 shaping-lathe flakes with the following species mixture were evaluated by Hse 

 and Price^: 35.4 percent baldcypress, 31 .4 percent soft hardwoods, 17.1 percent 

 oak sp., 14.7 percent other hard hardwoods, and 1.4 percent minor species. 

 Both face and core flakes were 3 inches long; face flakes were 0.015 inch thick 

 and core flakes 0.025 inch thick. These boards had linear expansion of 0. 1 16 and 

 0.113 percent, at 40.7 and 42.7 pounds/cu ft panel density, after ovendry- 

 vacuum-pressure-soak treatment (table 24-13). 



24-11 THICKNESS SWELL 



Rainwetting and moisture content increase attributable to increase in relative 

 humidity (fig. 8-18) cause flakeboard to swell in thickness (fig. 24-42). Some of 

 this swelling is irreversible. 



