2982 Chapter 24 



Flake length/thickness ratio. — McMillin and Koch^, in a study of 1/2-inch- 

 thick boards made from 3-inch-long mixed lathe flakes of sweetgum, hickory, 

 and southern red oak showed that IB was maximum with 0.025-inch thick 

 flakes. In boards of these single species, and of loblolly pine, the same relation- 

 ship prevailed. This observation provided strong evidence for using flakes 

 0.025-inch-thick in core layers. 



Price and Hse^ found that when lathe flakes 0.025-inch-thick were used in 

 core layers, and 0.015-inch-thick in face layers, 3-inch-long flakes in both face 

 and core yielded boards with as high or higher IB strength than core flakes 1.5 

 inches long combined with 3-inch-long face flakes (fig. 24-33 bottom). 



Flake width. — As noted earlier, McMillin and Koch^ found that IB is signifi- 

 cantly improved if lathe flakes of certain species, e.g., sweetgum, hickory, and 

 loblolly pine are reduced in width after they are formed on the shaping-lathe 

 headrig. This improvement results from eliminating very wide flakes that fold 

 (sweetgum and pine) or roll (hickory) in such a manner that resin distribution is 

 poor. 



Moisture content of mat. — The McMillin-Koch experiment^ and ancillary 

 work in connection with it showed that flake moisture content before addition of 

 liquid phenol-formaldehyde resin binder should be near 4 percent to maximize 

 IB; this corresponds to a mat moisture content of about 11 percent. 



Hse (1978) found that higher mat moisture contents (e.g. , 7 percent) could be 

 tolerated if polyisocyanate resin was applied before addition of liquid formalde- 

 hyde resin (table 24-10). 



Inclusion of southern pine in the furnish. — McMillin and Koch^ included 

 observations of flakeboards made of southern pine, and they found that addition 

 of a small proportion of southern pine to the furnish would substantially increase 

 IB at panel densities below 50 Ib/cu ft. 



Inclusion of baldcypress in the furnish. — Flakeboards comprised of one- 

 third baldcypress and two-thirds mixed southern hardwoods had IB strength of 

 64 to 73 psi when bonded with 5.5 percent resin (liquid) at panel densities of 41 

 to 43 pounds/cu ft (table 24-13). 



Seven-species mix of bottomland hardwoods. — Mixtures of flakes from 

 hardwood species typical of south-central Louisiana yielded boards with IB 

 strengths from 62 to 1 13 psi depending on procedures and species (table 24-14). 



Resin content. — Price and Lehmann (1978) found that regardless of type of 

 flake used, flakeboards made with 8 percent phenol-formaldehyde resin solids 

 (applied as a liquid) had higher IB strength initially and after accelerated aging 

 than those made with 5-percent resin content (fig. 24-7). Other researchers in the 

 field agree that IB values are correlated with resin content within the range of 

 resin contents normally used (see fig. 24-37 top). 



Optimization of IB. — IB optimization is limited by economic constraints on 

 permissible resin content, and by the need to maintain MOE and MOR at 

 acceptable levels. Text related to figure 24-38 in the previous subsections on 

 MOE and MOR described a near optimum fabrication procedure for flakeboard 

 comprised of 20 percent each of hickory, white oak, southern red oak, sweet- 

 gum, and southern pine. Small flakeboards of this design had IB of 82 psi when 



