Chapter 23 

 Fiberboards^ 



23-1 INTRODUCTION 



Fiberboards comprise one category among numerous reconstituted products 

 (fig. 23-1) made from southern hardwoods, including plywood (sees. 22-9 and 

 22-10) particleboard and flakeboard (ch. 24), and paper (ch. 25). Fiberboards 

 differ from plywood and flakeboard in that they are composed of cellular-size 

 particles bonded together with little or no adhesive. Paper, also made from 

 cellular-size particles, is continuously formed wet into thin sheets and dried 

 continuously over hot rolls (fig 25-19); fiberboard, however, may be formed dry 

 as well as wet (fig. 23-2), is usually 1/10- 3/4-inch thick, and is usually (except 

 for insulation board) platen pressed. 



Fiberboard was first made in this country by the wet process (fig. 23-2 top). 

 Dry-process boards (fig. 23-2 bottom) were developed more recently as an 

 extension of the particleboard industry. 



Fiberboards are also classified by density. Insulation board, wet-formed in 

 thicknesses from ys- to y4-inch, has lowest density. Medium-density fiber- 

 boards (MDF) are made by both wet and dry processes in intermediate densi- 

 ties. MDF-wet, with thickness range from V4- to !/2-inch, is generally used as 

 siding for buildings. MDF-dry, in thickness from ys-inch to 1 inch, competes 

 with particleboard as core material in furniture panels. High-density fiberboard, 

 manufactured in thickness from 1/10- to 5/16-inch, is called hardboard; al- 

 though there are significant differences in hardboard- wet and hardboard-dry, 

 they compete for the same markets. 



The foregoing classification of fiberboards differs from definitions of volun- 

 tary product standard ANSI/AHA A- 135.4 promulgated by the American Hard- 

 board Association (U.S. Department of Commerce 1973a, 1982), which defines 

 hardboard as any fiberboard (wet or dry) pressed to a density of 3 1 pounds per 

 cubic foot (specific gravity 0.50) or greater. Thus this standard does not recog- 

 nize MDF as a separate classification, nor does it include MDF-dry, which is 

 manufactured and traded under a different standard developed under the aus- 

 pices of the National Particleboard Association. In the trade MDF-wet is called 

 hardboard, and the MDF-dry is called medium-density fiberboard. Insulation 

 board is defined as a fiberboard ranging in density from 10 to 31 pounds per 

 cubic foot, corresponding to a specific gravity range from 0.16 to 0.50 (U.S. 

 Department of Commerce 1973b; American Society for Testing and Materials 

 1978). 



^Chapter 23 is greatly condensed from Suchsland and Woodson (1985), readers needing addi- 

 tional information on the subject should consult the source document. 



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