pulpwood

Harvesting a stand of eucalyptus pulpwood in Australia.

Pulpwood refers to timber with the principal use of making wood pulp for paper production.

Applications

• Trees raised specifically for pulp production account for 16% of world pulp production, old growth forests 9% and second- and third- and more generation forests account for the balance.^[1] Reforestation is practised in most areas, so trees are a renewable resource.
• Pulpwood is also used as the raw material for some wood products, such as oriented strand board (OSB).
• There is an increasing demand for pulpwood as a source of 'green energy' by the bio-energy sector.

Properties

The fibre length of the cellulose fibres is the most important parameter of the pulpwood and determines what it may be used for. The first separation is into softwood and hardwood, that have long and short fibres respectively. In paper production fibres from softwood gives tensile strength and fibres from hardwood gives opacity.

Sources

Logging

In the logging of mixed forest stands, the better trees are usually used for sawlogs for lumber production, while the inferior trees and components are harvested for pulpwood production. Pulpwood usually derives from four types of woody materials in a mixed logging operation:

• Open-grown trees, that are heavily branched low on the trunk, and so make poor sawlogs.
• Dead or diseased trees.
• Tops cut from trees harvested for sawlogs (branches are rarely used since they contain little usable wood after the bark has been removed).
• Small trees, too small to harvest for sawlogs.

Natural forest stands may also be harvested solely for pulpwood where, for various reasons, the value of the trees as sawlogs is low. This may be due to the predominant species in the forest stand (for example, some aspen forests in northern North America), or to the relative proximity of the nearest sawmill or pulp mill.

Plantations

Pulpwood is also harvested from plantations/tree farms established for the specific purpose of growing pulpwood, with little or minimal sawlog production. Monocultures of species intended specifically for pulpwood include loblolly/slash pine in the southern USA; various species of eucalyptus (most commonly Eucalyptus globulus and Eucalyptus grandis) in Latin America, Iberian Peninsula, Australia, south-east Asia^[2] and southern Africa and acacia (most commonly Acacia mangium) in south-east Asia and southern Africa.

Salvage cuttings

Salvage cuts after forest fires, tornadoes, hurricanes, or other natural disasters are often used for pulpwood. An alternative source of wood for use in kraft pulping is recovered lumber from demolition, industrial processing of wood and wooden pallets.^[3]

Wood residuals

Saw residuals are used as pulp wood. The most important of these are the side cuttings from lumber edgers. This gives wood with almost only sapwood and no hearthwood. The sapwood is easier to pulp.^[4] due to a more open structure and less content of extractives than the hearthwood. The fibre length of sapwood is generally longer than the fibre length of hearthwood. The sapwood is also normally lighter and that is an advantage when producing mechanical pulp as less bleaching is needed.

Earlier sawdust had some limited use in paper production. It gives very short fibres that are suitable as part of the furnish for paper tissue and writing papers. Saw blades have become thinner and with smaller teeth making the sawdust too small as fibre source.^[5]

Pulpwoods

Economical important pulpwoods

• Hardwoods

Acacia

Aspen

Birch

Eucalyptus

Maple

Pacific Albus

• Softwoods

Pine

Spruce

Chemical composition of some pulpwoods

See also

• Paper pulp
• Pulp mill
• Paper machine
• Woodchips

References