Hardwood grading

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... 

Aaarican Mnnrt Fibers standard Hardwood Grades fContinued1 ... 

Chemical charge, Hquor composition, time of heatup, and time at temperature of reaction are all functions of the wood species or species mix being digested and the intended use of the pulp. A typical set of conditions for southern pine chips in the production of bleachable-grade pulp for fine papers is active alkaH, 18% sulfidity, 25% and Hquor-to-wood ratio, 4 1. Time of heatup is 90 min to 170°C time at temperature of reaction, 90 min at 170°C. Hardwoods require less vigorous conditions primarily because of the lower initial lignin content. 

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... 

Lower formaldehyde emissions were found for the plywoods (all exterior grades) than for particleboard and MDF, but organic acid emissions still occurred, especially for the hardwood-based plywood (black butt) since such woods are... 

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. 

Materials and Regents. Paper samples employed in this study were 8- X 10-in. sheets cut from a continuous portion of a single roll or JCPA-60 bleached kraft paper. This paper had been manufactured from a pulp mixture consisting of 70 bleached southern kraft and 30 bleached hardwood kraft. The paper contained 13 clay materials, which are composed mainly of titanium dioxide. It also contained 212 ppm of iron and 66 ppm of copper and had a pH of 5.4. All chemicals employed were analytical reagent grade. Water used for the washing of paper samples and the preparation of solutions had a minimum resistivity of 15 Mil. 

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... 

Table 6.3. A broad indication of grade recovery for Pinus radiata as compared with those from traditional forest practices in Canada and Sweden (van Wyk, 1990) unimproved pine has generated a disproportionate amount of low grade wood, with upgrading that material being the immediate challenge. Anticipated prospects for hardwoods have been included.

Hardwoods are used for plywood, for structural applications including pallets, in furniture and in the remanufaeturing sector. It is important not to discount the lower grade pallet and eontainer market as this sector absorbs about half of all US... 

Table 7.7. Standing timber sawlog volume and grade recovery of select hardwoods in the Eastern United States (Araman, 1987a). MiU grade outturn should be somewhat better as lumber grades were derived from log grade inventory and many of the small low-grade logs would never be milled.

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. 

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