Softwood, grading

The updated BS 4978 (BSI, 1986) specification for softwood grades for structural uses replaced the four grades by just two visual stress grades, general structural (GS) and select structural (SS), which have strength ratios of the order of 0.3-0.35 and 0.5-0.6, respeetively. However the strength ratio is no longer derived. 

Hardwood grades 2010,4010,6010,8010,10010,12010,14010-materials ofdifferent particle sizes Softwood grades 2020,4020,6020,8020,10020,12020,14020-materials of differentparticles sizes... 

Aaertcan Wood Plbars Standard Softwood Grades 2020 ... 

Aaerlcan Wood Flbera Standard Softwood Grades tContinued) 10020 ... 

The adhesive used in virtually all softwood plywood has a phenol—formaldehyde (PF) base to provide an exterior-grade, durable, waterproof bond. Thus, most grades of plywood can be used in stmctural appHcations. A very small percentage of softwood plywood is made using interior-grade adhesive systems, and this material is used in interior cabinetry, furniture, and shelving. 

Market prices are extremely volatile and follow cycles of advance and decline related to fluctuations ia global iaventories and world economic forces. For example, for northern bleached softwood kraft, which is considered a global benchmark pulp grade, market price went from 840/t ia 1990 down to 440/t ia 1993 as a result of oversupply and worldwide recession (3). By 1995 virtually all of the price losses had been recovered. 

Plywood is also divided into softwood and hardwood plywood products. The classification depends on the type of wood the face pHes are made from. The principal appHcation for 1 cm and thicker hardwood plywoods are cabinets and furniture. The thinner grades are used to make paneling and doorskins, which represent approximately 56% of the total hardwood plywood products. The total market in 1989 was estimated to be 2.1 biUion. 

Timber is derived from a great number of botanical species, and has a wide range of properties. Variability also occurs within a single species and in order to achieve acceptable levels of uniformity, selection by grading is necessary. The timber trade differentiates between softwoods and hardwoods, and the latter are again separated into temperate and tropical types. Hardwoods are derived from broad-leaved and mainly deciduous trees, which are anatomically more complex and differ in chemical composition... 

The furnish of a paper machine varies widely, depending on the grade of paper being made. Newsprint usually consists of about 80 percent groundwood and 20 percent chemical fiber (sulfite or semibleached kraft). Bag papers and linerboard are usually 100 percent unbleached softwood kraft. Printing papers are made from bleached pulps and contain both hardwoods and softwoods. By selecting the proper pulps and refining conditions, a wide variety of paper qualities can be achieved. 

Phenolysis Reaction Procedure. To explore the concept of phenolation, mixtures of a commercial spray-dried softwood ammonium lignin sulfonate (10 g, Orzan A, 60% ammonium lignin sulfonate (MW0 = 228), 28% sugars, 6.2% sulfur, 2.5% ash, ITT-Rayonier, Shelton, Washington available in bulk at 17 cents a pound (<9) and commercial grade phenol (15 mL, Reichhold Chemicals Inc., Tacoma, Washington) contained in small pressure bombs (30 mL, Parr Instrument Company, Moline, Illinois) were heated by suspension in a hydraulic... 

On the other hand, certain types of wood pulp, prepared by se((uences involving both acidic and alkaline treatments, show a linear relationship between gamma-cellulose and non-cellulosic polyoses. This may be illus-strated from the studies of White, Steinman and Work on acetylation pulps. Acetylation-grade pulps are usually prepared from softwoods by sulfite cooking followed by hot-caustic refining. When the total polyose content of a number of such pulps was compared with their gamma-cellulose content, a linear relationship was obtained (see Fig. 3). In spite of this excellent correlation, it cannot be assumed that all of the non-cellulosic polyoses are contained in the gamma fraction of these pulps (see below). 

The ThermoWood process has been developed in Finland (Finnish ThermoWood Association, 2003) and both hardwoods and softwoods are available in two classes - ThermoWood D (durability) and ThermoWood S (stability), where the ThermoWood D grade is treated at a higher temperature to allow use in exterior applications out of ground contact (hazard class 2). The process uses steam to limit the extent of pyrolysis, and control crack formation. A similar system called... 

Further there is an increased ineidenee of large spike knots when live-sawing, which results in a lower recovery of better grades in softwoods. 

Such kilns are inappropriate for industrial and structural softwood lumber that may be dried at over 100°C in less than a day, but they stand comparison with a two-day 90/60°C schedule for 25 mm appearance grade softwood lumber. Dehumidifiers can dry such wood in 6-7 days at 40-60/35-50°C (dry/wet-bulb temperatures) - but down to only 20%, from 150% MC. Further they are particularly well-suited for slow-to-dry, collapse-prone, check-prone hardwoods that must be dried at low temperatures. These ean be dried in about 15 days to 20% MC. 

As with hardwoods, here softwood lumber is sorted at the sawmill into factory or shop grades on the basis that these boards can be recut to yield a certain proportion of smaller pieces of specific quality and size. This lumber provides the basic raw material for many secondary manufacturing operations. 

Figure 10.2. Typical examples of softwood boards in lower Common grades.

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