Fiberboards 2891 



For reasons not entirely clear, all of the eight commercial boards tested 

 exceeded the maximum linear expansion allowed by the standard (table 23-18). 

 Many properties are not included in the standard because they are not easily 

 tested or because they are not important in all applications. Surface smoothness 

 is one such property. Suchsland et al. (1978) found that at redried condition after 

 a 24-hour water soak, all of the medium-density fiberboards tested were signifi- 

 cantly smoother than commercial conventional particleboard. 



COMMERCIAL INSULATION BOARD 



Insulation board standards. — Voluntary Product Standard PS 57-73 (U.S. 

 Department of Commerce 1973b) describes property requirements and test 

 methods for insulation board and defines it as fiberboard in the density range 

 from 10 to 31 pounds/cu ft (specific gravity of 0.16 to 0.50). The standard 

 establishes 1 1 types of insulation board and several classes (table 23- 1 9) . 



Property requirements vary with board type and class; in general, however, 

 insulation board does not have great strength. Minimum values for the most 

 demanding end uses are as follows: 



Minimum 

 Property for most demanding use 



Modulus of rupture, psi 



Dry 500 



Wet 95 



After accelerated aging 50 percent of dry value 



Modulus of elasticity, psi 40,000 



Tensile strength parallel to surface, psi 300 



Tensile strength perpendicular to surface, 



pounds/square foot 1 ,000 



In the most demanding use, linear expansion between 50 and 90 percent relative 

 humidity cannot exceed 0.5 percent. 



Of the properties listed in the standard, the thermal conductivity "k" (Btu/hr/ 

 sq ft/inch thickness/°F temperature differential) is perhaps most important; its 

 minimum specified value varies with board type and use class, but is in the range 

 from 0.38 to 0.40. Insulation board conducts heat at less than half the rate of an 

 equal thickness of solid wood; the "k" value for softwood is about 0.80 and that 

 of hardwood about 1.10. 



Actual properties of commercial insulation board are not available in the 

 literature. 



