Fiberboards 



2757 



100 200 300 400 500 

 STEAM PRESSURE (PSIG) 



600 



Figure 23-1 0. — Hot-water extractability of wood chips (percent of ovendry weight) as a 

 function of saturated steam pressure (gage) used in the preheat segment of the 

 Masonite cycle. (Drawing after Spalt 1977.) 



Yield. — Yields by the Masonite process decrease with increasing temperature 

 or heating time (fig. 23-1 1) and have been reported as low as 65 to 70 percent, 

 but more recently between 80 and 90 percent. 



Pulp characteristics. — Koran (1970) found that Masonite-process jack pine 

 (Pinus banksiana Lamb.) fibers were dark, stiff, little collapsed, with smooth 

 surfaces enveloped by a continuous network of primary wall heavily encrusted 

 with lignin, and in many areas covered by thick layers of middle lamella 

 substance. They are not fibrillated and further refining does not produce the 

 fibrillation necessary for hydrogen bonding in paper manufacture; they are 

 therefore unsuited for paper. For the same reason, however, these fibers make a 

 very free pulp well suited for wet-formed hardboard. The low yield of Masonite 

 mechanical pulp and its rather high energy requirement may cause its gradual 

 replacement with disk-refined pulp. 



