2776 Chapter 23 



Myers and Holmes (1975, 1977) have, on an experimental basis at the U.S. 

 Forest Products Laboratory, achieved class B protection of dry-formed fiber- 

 board with 20 percent retention of various chemicals, based on dry fiber weight. 



In the United States, the only fire-retardant treatment of fiberboard in com- 

 mercial use is one patented by the Masonite Corporation (Short and Rayfield 

 1978). The patent described the process, which achieved class A rating, as two- 

 step. In the first step alumina trihydrate is added to the furnish to comprise 45 to 

 60 percent of panel weight. After forming and pressing several coats of borate 

 ester resin, preheated to about 100°C, are applied to panel surfaces with flow and 

 roller coaters, with time for penetration allowed between coats. Treated panels 

 are then heated 1.5 to 2 hours at 150-160°C and finally humidified to about 5 

 percent moisture content. 



Preservative treatments.^ — Fiberboards, like other wood products, may be 

 attacked by termites and may decay if wetted intermittently or placed in ground 

 contact. A sodium salt of pentachlorophenol (e.g., Dowicide G), a common 

 wood preservative soluble in water, can be added to fiberboard furnish to protect 

 against termintes (chemical retention of 0.75 percent of ovendry fiber weight) or 

 rot and mildew (0.5 percent). 



When preservative is added, the furnish should have pH of about 8.5; it is 

 precipitated and fixed on the fibers as insoluble sodium pentachlorophenate, 

 together with size and other additives, by addition of alum or acid. Pentachloro- 

 phenol is a poisonous substance and requires special consideration during water 

 treatment. It also interferes with sizing of fiberboard (U.S. Department of 

 Agriculture, Forest Service 1974). Contamination of board to be used in pro- 

 ducts which may be handled by children or chewed by pets must be avoided. 



PROCESS COMPARISONS AND INDUSTRIAL PRACTICE 



Wet processes, general. — Figure 23-25 illustrates pH level, pulp consis- 

 tency, and introduction of chemicals in a wet-process fiberboard plant from 

 primary refiner to Fourdrinier sheet forming machine. This figure applies equal- 

 ly to the manufacture of insulation board, and SIS and S2S wet-formed hard- 

 board and MDF. Following primary breakdown the stock is diluted to make it 

 pumpable and less acid. Caustic soda is added to further raise its pH from below 

 4,0 to 5.0 -I- , to reduce corrosion and make it easier to wash out dissolved 

 sugars. Caustic soda addition does, however, reduce fibers' affinity for water. 

 Much of the water added is removed in the washer, from whence it carries 

 biodegradable materials which can be recirculated, but which must be removed 

 before the water can be discharged. 



This text reports research involving fungicides and pesticides. It does not contain recommenda- 

 tions for their use, nor does it imply that the uses discussed here have been registered. All uses of 

 fungicides and pesticides must be registered by appropriate State and/or Federal agencies before they 

 can be recommended. CAUTION: Fungicides and pesticides can be injurious to humans, domestic 

 animals, desirable plants, and fish or other wildlife — if they are not handled or applied properly. Use 

 all fungicides and pesticides selectively and carefully. Follow recommended practices for the 

 disposal of surplus fungicides, pesticides, and their containers. 



