Structural Flakeboards and Composites 297 1 



Table 24-13. — Mechanical and physical properties of 1 12 -inch-thick flakeboard com- 

 prised of one-third baldcypress and two-thirds mixed southern hardwoods from the 

 coastal plains of the southeastern United States (Hse and Price, text footnote^) '•^■^ 



Board density, pounds/cu ft"* 



Property 407 42^7 



Modulus of elasticity, thousand psi 670 720 



Modulus of rupture, psi 5,300 5,630 



Internal bond strength, psi 64 73 



Linear expansion, percent^ 0. 1 16 0.1 13 



Thickness swell, percent^ 28 27 



Internal bond strength after 



OD-VPS treatment, psi 32 37 



'Species mix was: 35.4 percent baldcypress; 31.4 percent soft hardwoods; 17. 1 percent oak sp.; 

 14.7 percent other hard hardwoods; 1.4 percent minor species. 



^The three-layer board had face flakes 0.015-inch thick and core flakes 0.025 inch thick; all flakes 

 were 3 inches long and cut on a shaping-lathe headrig. 



-^Resin content was 5.5 percent of ovendry weight. 



"^Basis of ovendry weight and volume at test moisture content of about 5 percent. 



^ After ovendry- vacuum-pressure-soak treatment. 



Resin content. — Increases in resin content increase modulus of rupture and 

 internal bond strength moderately, but affect MOE of hardwood flakeboards to a 

 lesser degree. In fabricating scarlet oak panels from veneer flakes randomly 

 oriented, Post (1961) found that urea-formaldehyde resin content was a much 

 less potent factor determining MOE than was flake length-to-thickness ratio. 

 Rice and Carey (1978) found that MOE of yellow-poplar and sweetgum flake- 

 boards was less affected by increased content of phenol-formaldehyde resin than 

 were internal bond strength and modulus of rupture (fig. 24-37). 



Optimization of MOE with retention of acceptable internal bond 

 strength. — On the basis of the literature and their prior experiments, Hse and 

 Koch^ fabricated a series of flakeboards as follows: 



• Fixed factors 



Panel thickness, 1/2-inch 



Species mix: 20 percent each of hickory, white oak, southern red 



oak, sweetgum, and southern pine 



Flake type: Shaping-lathe headrig; i.e., lathe flakes 



Flake length: 3 inches 



Flake moisture content: 3 to 4 percent 



Specific pressure on mat: 575 psi 



Press temperature: 335°F 



