Waferboards

The manufacture of waferboard and OSB has many of the same process steps as particleboard, but adapted to the special needs of producing an exterior quaHty panel with large wafers or strands. This discussion focuses on OSB, because waferboard has been almost entirely replaced by OSB and most of the early waferboard mills have now been converted to production of OSB. The OSB process is outlined in Figure 8. 

Wood Bonding. This appHcation requires large volumes of phenoHc resins (5—25% by weight) for plywood, particle board, waferboard, and fiberboard. Initially, phenoHc resins were used mainly for exterior appHcations, whereas urea—formaldehyde (UF) was used for interiors. However, the concern over formaldehyde emission has caused the replacement of UF by phenol-formaldehyde adhesives. 

Waferboard, a more recent wood constmction product, competes more with plywood than particle board. Waferboard and strand board are bonded with soHd, rather than Hquid, phenoHc resins. Both pulverized and spray-dried, rapid-curing resins have been successfully appHed. Wafers are dried, dusted with powdered resin and wax, and formed on a caul plate. A top caul plate is added and the wafers are bonded in a press at ca 180°C for 5—10 min. Physical properties such as flexural strength, modulus, and internal bond are similar to those of a plywood of equivalent thickness. 

Wood FIa.ke Boards. This category covers a range of products depending on the size and orientation of the wood flakes used. The earliest product was made in the 1950s using low density wood species, such as aspen and pine, with the flakes bonded together with phenoHc resins. Today there are two types of flake board, waferboard and oriented strand board (OSB). 

Waferboard is made almost exclusively from aspen wood and the flakes are roughly square in shape, up to 2 in. (5 cm) on a side. They are used for low end stmctural sheathing appHcations. 

The 1989 OSB/waferboard sales ia the United States were about 669 million and iacreased to 451 x 10 (4.85 biUion ft on a 3/8-ia. basis)... 

In 1932, the first plywood hot press was installed in the United States. This marked the advent of the large market for phenolic wood adhesives [51]. By 1962, the volume of phenolic wood adhesives had reached about 33 kt (solids) in the U.S. Growth was accelerated in 1962 with the development of Southern pine plywood. By 1979, the consumption of phenolic plywood adhesives exceeded 220 kt or about 25% of phenolic resin production [51]. Phenolic adhesive demand for wood products took another jump in 1964 with the commencement of waferboard production. The first oriented strandboard (OSB) plants were built in 1981 [52]. OSB soon replaced most of the waferboard production and began a period of... 

Waelz zinc oxide process, 26 612 Waferboard bonding, phenolic resins in,... 

Eormaldehyde vapour treatment has been applied to improve the dimensional stability of medium-density fibreboard (MDF) (Minato elal, 1992) and albizzia waferboard (Yusuf elal, 1995c). 

Schmidt, E.L. (1983). Effects of a formaldehyde and sulphur dioxide treatment on decay and mechanical properties of aspen waferboard. International Research Group on Wood Preservation, Doc. No. IRGAVP 3242. 

Yusuf, S., Imamura, Y., Takahashi, M. and Minato, K. (1995c). Property enhancement of albizzia waferboard by formaldehyde treatment. Mokuzai Gakkaishi, 41(2), 223-228. 

Recent work has concentrated on the use of ALCELL lignin as a substitute for phenol-formaldehyde resins in wood adhesives, particularly wafer-board. Some of the results obtained when a PF resin (Bakelite 9111) was replaced with different levels of hardwood ALCELL lignin in waferboard manufacture will be briefly discussed below. Table III shows the conditions used for waferboard manufacture. 

Initially three ALCELL lignin samples were evaluated acid (pH 3.95), neutral (pH 7.51), and alkaline (pH 8.96). The moisture content of lignin-PF bonded boards ranged from 4.1 to 4.8%, which is well within the 8% allowable limit of commercial grade waferboard. 

The lignins were separately mixed with PF resin (dry blending) at 30% and 50% levels prior to application as a binder. The formation and testing (9) of the waferboards (30 cm x 30 cm) were done by the Alberta Research Council Panel Testing Laboratory. 

In order to evaluate the method, the three lignins were methylolated, formulated with R-PF resin and waferboards made. The boards were tested for dry MOR, MOE, wet MOR and IB, but only the last term was the pa rameter chosen for quality determinations by the authors. Limited number of testing results are given in Table III. The data are not corrected for board density. The pass level for Canadian requirements is IB = 0.345 MPa, so all of the boards prepared passed, even those containing binder with 50% of the PF resin replaced with methylolated lignin. 

Oriented strand board (OSB) is obtained from wood chips. The orientation is designed to simulate the characteristics of a wood panel, with limited swelling and higher resistance in the fibre direction. Chips are orientated by air with a blowing machine. These panels are commonly used on building sites, and they often make part of the walls in houses, especially in the United States. If no orientation is given, the panel is called waferboard. 

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