User:Sam ERTH/Pulpwood

Pulpwood can be defined as wood that is ground and processed into a fibrous pulp. This type of timber is commonly used for paper-making, but can also be made into low-grade wood and used for chips, energy, pellets, and engineered products.

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.

Hardwoods are raw material that are preferred for pulp used in printing papers. It has small dimensions in its fibers, which can be useful for small-scale uniformity, opacity, and surface smoothness, all important for printing paper. Hardwood pulp comes from low value and poor quality trees. Some examples include white birch and beech.

Softwoods are the preferred raw material for strong papers, due to the length and slimness of the fibers. Low-density softwoods, such as firs with thin-walled fibers are preferred for papers with high demands for bonding-related strength characteristics. Some of these characteristics include tensile, burst, and surface strength. Softwood has a more regular growth pattern. While hardwoods value comes from the quality of the wood, softwoods value comes from its volume.

Pulpwood is a versatile natural resource that can be used to produce a handful of forest products, such as paper, pellets, chips, firewood, bio-fuels, and more.

A pile of pulpwood to show one of the first steps of producing paper.

Hardwood

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.

Hardwood applications can be sectioned into four areas:

• Solid wood products
• Wood-based materials
• Use after modification
• Supplemental services

Solid wood products

Hardwoods (such as oak) are the preferred raw material for joists, roof structures and timber frames. The use of solid hardwoods has decreased during the last couple centuries, most likely due to the development of wood-based materials that allow for larger constructions not limited to the size of trees.

Additional fields of application include playgrounds, wood-facings, railway sleepers, bridges, and more. Furniture is another application of hardwood. Furniture made of pure solid wood is relatively rare. Most parts of furniture such as table boards, shelves or cabinet doors belong to wood-based materials because of their glued components.

Solid wood can be used for: chairs, tables, beds, upholstery frames, sideboards, cabinets, bathtubs, and more.

Hardwood is also used for interior work, such as parquet flooring, doors, and windows. Hardwood is especially preferred for parquet flooring. Tree species in darker colours are commonly used to give the flooring a "used look," for visual appeal. Solid wood is used for front doors and windows, while internal doors are mainly made of wood-based panels.

Wood-based materials

Wood-based materials can be separated into a few different types. These include solid wood, ply, particle, and fibre materials. Solid wood materials are used as beam or panels. Typical tree species used for solid wood materials include beech, oak, birch, alder and chestnut. Hardwoods are commonly used for nonstructural products such as plywood.

Structural products such as cross laminated timber, are mainly composed of softwoods. Particle materials are ideal to use low-rate timber assortments and saw mill waste. Types pf particle materials include particle board, mineral-bonded wood composites, oriented strand board, laminated strand lumber, and oriented strand lumber.

Fibre materials include fibreboards, insulating fibreboards, wood particle mouldings and wood plastic composites. The quality and processing of fibreboards and insulating fibreboards are influenced by the fibre percentage, the geometrical structural of the fibre, and the specific chemical composition of wood. The fibres of hardwoods are short, smooth and thin, and are suited for the dry production process because they do not mat. Ironically, hardwoods are barely used for fibreboards and insulating fibreboards.

Use after modification

The purposes of wood modification are dimensional stabilization and resistance increase. Wood can be modified in a multitude of ways, including but not limited too; chemical modification, heat treatment, ammonia treatment, electrodialysis, and more.

Chemical modification, heat treatment, and impregnation (with salts, metals, monomers and polymers) are the most used methods.

Supplemental services

Hardwood can be used in other ways outside of physical wood structures and paper. It can be used as a substance, such as through food production. The sawdust of beech and oak is used to make edible mushrooms. Oak, beech and maple are used to cure meat or fish, while oak staves, chips and powder add aroma to wine. The sawdust of oak and robinia can be used to filter elements such as copper, nickel, zinc and cadmium. It can also be added to plastics. 60% of linoleum flooring consists of sawdust.

Wood can also be used as an energy source, with sawmill waste and low-rate timber. Combustion, wood gasification, and production of bioethanol are the three main ways hardwood is used for energy.

Combustion: split billets, chips and wood pellets. High-density wood species burn down slower, and the heat value depends on wood moisture content. Burning rate decreases with increasing density.

Wood gasification (synthetic natural gas and biomass to liquid): synthesis gas production is done by wood smouldering.

Bioethanol: start off by the splitting of cellulose and hemicelluloses in sugar by enzymes and acids, then the fermentation of the sugar with the aid of microorganisms. Lastly, the distillation and dewatering creates the bioethanol.

Economically important hardwoods

Acacia

Aspen

Birch

Eucalyptus

Maple

Pacific Albus

Softwood

Softwoods come from gymnosperm trees that consists of needles and cones. When a sample of softwood is observed under a microscope, they appear to have no (visible) pores because of the presence of tracheids. 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.

Economically important softwoods

Pine

Spruce

Applications

Trees raised specifically for pulp production account for 15% of world pulp production, while old growth forests account for 9% and second/third plus generation forests account for the balance.

Products

Pulpwood can be used for a multitude of different uses, some of them already mentioned above. Some of the main products it is used for is listed below.

Paper

Old Photograph of the production process of paper with pulpwood.

Paper production is the most common and main use for pulpwood. Paper can be produced by both hardwood and softwood tress, and each species for both types of trees have specific and unique properties that make the type of paper and other products produced differ. The short fibres of hardwoods trees produce smoother and more uniform paper, like printing paper. Softwood trees have longer fibres that produce industrial papers like newsprint.

Wood is broken down mechanically or chemically. After the breakdown process, fibres (composed of two kinds of cellulose) and lignin are leftover. Lignin is the glue or cement that holds the fibers in wood together. Simply putting it, wood pulp is a large amount of individual wood fibres with the lignin removed. Wood pulp is naturally between dark brown to light grey in colour. Dark brown wood pulp is used for paper bags and boxes, and bleaching the pulp produces higher grades of paper (among other products).

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 fibers. With both methods, the pulp is washed and screened before becoming paper.

Pellets

Pulpwood also produces wood pellets, which can be used for heating homes and electricity production. They can be formed by the grinding of biomass (in the form of unused tree tops), sawdust, or even entire trees, then compressed into small pellets to be stored, transported, and fed into boilers and furnaces. Softwood species are preferred to make wood pellets due to the resin content required to bind the particles together.

Firewood

Firewood is the oldest use of pulpwood. Poor quality trees are put to better use and burned as a crude energy source as heat, light and cooking fuels. Coppicing refers to the ancient and traditional woodland management technique that involves cutting trees at their base and creating a stool for new shoots to grow. During the stone age, coppicing was done to manage forests for the production of firewood fuels.

Bio-Fuel

Biofuels refer to fuels derived from plant materials or manure. They are currently under debate whether they are a safe and environmentally friendly alternative to fossil fuels as a source of energy. The carbon in plants is produced by absorbing carbon dioxide from the atmosphere via photosynthesis, and burning biofuels/plant-derived fuels puts the same amount of CO2 back into the atmosphere.

Generating heat and electricity from wood-fuel is a complicated process.

1. It starts off by drying the wood, followed by pyrolysis (which is heating in the absence of oxygen) to produce gasses.
2. Next, the gasses are purified and burnt to generate electricity

The ash created during the pyrolysis process contains nutrients that could provide a plant fertilizer, but it could also contain contaminants from the soils of the trees origin site.

Some of the potential sources of wood-fuel include early thinnings from commercial plantations, the residues from timber harvesting and arboricultural activities, coppicing and sawmills.

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 tree farms established for the specific purpose of growing pulpwood, with little or minimal sawlog production. Monoculture of species intended specifically for pulpwood include loblolly and slash pines in the southern USA; various species of eucalyptus (most commonly Eucalyptus globulus and Eucalyptus grandis) in Latin America, Iberian Peninsula, Australia, south-east Asia and southern Africa and acacia (most commonly Acacia mangium) in south-east Asia and southern Africa. (source??)

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.

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 fiber length of sapwood is generally longer than the fiber 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.

Earlier sawdust had some limited use in paper production. It gives very short fibers 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 fiber source.

Chemical composition of some pulpwoods

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

Alternatives

Sugar cane byproducts and bamboo are used in the commercial production of toilet paper. (reference??)

See also

• Paper pulp
• Pulp mill
• Paper machine
• Woodchips