Pulpwood can be defined as timber that is ground and processed into a fibrous pulp. It is a versatile natural resource commonly used for paper-making but also made into low-grade wood and used for chips, energy, pellets, and engineered products.thumb|239x239px|Harvesting a stand of eucalyptus pulpwood in Australia.
Pulpwood can be derived from most types of trees. Categorizing trees into hardwood and softwood is the easiest way to characterize types of paper produced from pulpwood.
Softwoods are the preferred raw material for strong papers, due to the length and slimness of the fibres. Low-density softwoods, such as firs with thin-walled fibres are preferred for papers with high demands for bonding-related strength characteristics. Some of these characteristics include tensile, burst, and surface strength.
Hardwood applications
Hardwood has anatomical structural differences to softwood, which influences physical properties, durability, workability, and bonding. Different types of cells complete the three main tasks in hardwoods compared to softwoods. The main tasks include stabilization, water conduit, and storage.
thumb|288x288px|A pile of pulpwood to show one of the first steps of producing paper
Hardwood applications can be sectioned into four areas:
- Solid wood products
- Wood-based materials
- Use after modification
- Supplemental services
Additional fields of application include playgrounds, wood-facings, railway sleepers, bridges, and more. Tracheids are a primitive element of xylem (fluid-conducting tissues). They consist of a single elongated cell and a secondary cellulosic wall containing a thick layer of lignin. Medullary rays and tracheids transport water and produce sap. Approximately 80% of timber comes from softwood, such as cedar trees, Douglas fir, juniper, pine, and many more.
Softwoods are used in wood manufacturing as well, and are sometimes preferred over hardwoods depending on the product being constructed. An important characteristic that softwoods have that make them a suitable pulpwood to build with, is that they can easily absorb any kind of finish. They can become very resistant and last for a long time (centuries). Softwoods tend to be cheaper than hardwood due to their growth rate and development being faster. They are versatile, strong, and can be managed easily. Some of the biggest softwood forests can be found in Canada, Scandinavia, and Russia.
Chemical Wood Pulp
The chemical method of breaking down wood pulp to make paper is more commonly used and energy efficient compared to the mechanical method. In the chemical method, the wood chips are 'cooked' in large tanks. The tanks are called digesters, and are like pressure cookers. Chemicals, referred to as 'cooking liquor' help break down wood chips into a mass of fibres.
Mechanical Pulp
With mechanical pulping, machines are used to grind wood chips into pulp, creating a pulp that retains most of its lignin. Due to the short fibres created by this process, the resulting paper is mostly used for newspapers, phone books, and other low-strength paper. During the Stone Age, coppicing was done to manage forests for the production of firewood fuels.
Generating heat and electricity from wood-fuel is a multi step process.
- It starts off by drying the wood, followed by pyrolysis to produce gasses.
- Next, the gasses are purified and burnt to generate electricity
The ash created during the pyrolysis process contains nutrients that are used as plant fertilizer, but it could also contain contaminants from the soils of the trees origin site.
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
To help feed pulp and paper mills, vast monocultures of conifers eucalyptus, acacia, and other species are being established both in the North and South, where fast tree growth, inexpensive land and labour, and lavish subsidies combine to make wood cheaper. As exotic trees invade native woodlands, grasslands, farmlands and pastures, consequences in most countries include impoverishment, environmental degradation, and rural strife.
Plantations are full of trees similar to forests, but they differ greatly. A forest is a complex, self-regenerating system, consisting of soil, water, microclimates, energy, a diverse ecosystem with a wide variety of plants and animals in mutual relation. In contrast, a commercial plantation is a cultivated area whose species and structure have been simplified dramatically to produce only a few goods, such as lumber, fuel, resin, oil or fruit. The trees in a plantation have a small range of species and ages, and require extensive and consistent human intervention.
Plantations normally replace crops, grasslands, or scrub forests. Since they are used for commercial necessities, they are established on healthy soil, with their objective being short cycles of rapid growth that requires a certain level of fertility and water supply. Therefore, they tend to occupy areas already being used by local people.
Salvage cutting is the removal of trees that have been killed or damaged by insects, disease, wind, ice, snow, volcanic activity, or wildfire. The purpose of salvage cutting is to recover the economic value of trees before they decay. Dead trees decay quickly, and the timing of salvage cutting is crucial to capture as much economic value as possible. Post-fire salvage cutting helps manage fuels and future fire behaviour, as long as logging slash is treated after the harvest.
Wood residuals
Saw residuals are used as pulpwood. The most important of these are the side cuttings from lumber edger. This gives wood with almost only sapwood and no heartwood. The sapwood is easier to pulp. due to a more open structure and less content of extractive than the heartwood. The fibre length of sapwood is generally longer than the fibre length of heartwood. The sapwood is also normally lighter and that is an advantage when producing mechanical pulp as less bleaching of wood pulp is needed.
Sawdust 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.
Chemical composition of some pulpwoods
{| class="wikitable" border="1"
! colspan=6 | Chemical composition of pulpwood (%)
|-
! Wood
! Cellulose
! Lignin
! Mannan
! Araban
! Xylan
|-
| Aspen || 56.5 || 16.3 || 2.3 || 0.4 || 16.0
|-
| Paper Birch || 44.5 || 18.9 || 1.5 || 0.5 || 24.6
|-
| Red maple || 44.8 || 24 || 3.5 || 0.5 || 17.3
|-
| Balsam fir || 47.7 || 29.4 || 12.4 || 0.5 || 4.8
|-
| Jack pine || 45.0 || 28.6 || 10.8 || 1.4 || 7.1
|-
| White spruce || 48.5 || 27.1 || 11.6 || 1.6 || 6.8
|}
Alternative uses
Sugar cane byproducts and bamboo are used in the commercial production of toilet paper.
Wood pulp has many modern-day uses other than paper-making and the other applications mentioned in the "Softwood Applications," and "Hardwood Applications" sections. Their uses can range from hygiene products to innovative medical products.
Wood can also be used as raw material for new bio-products, such as environmentally friendly textile manufacturing technologies. There are a few ways pulpwood is being used to develop technologies that consume less energy and fewer chemicals.