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Hard versus soft

It is common to classify wood as either softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from dicotyledons (usually broad-leaved trees, e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than many hardwoods.

There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it.[citation needed] The density of wood varies with species. The density of a wood correlates with its strength (mechanical properties). For example, mahogany is a medium-dense hardwood that is excellent for fine furniture crafting, whereas balsa is light, making it useful for model building. One of the densest woods is black ironwood.

Chemistry

Chemical structure of lignin, which makes up about 25% of wood dry matter and is responsible for many of its properties.

The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight.[25] Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity.

Aside from water, wood has three main components. Cellulose, a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is hemicellulose, which is around 20% in deciduous trees but near 30% in conifers. It is mainly five-carbon sugars that are linked in an irregular manner, in contrast to the cellulose. Lignin is the third component at around 27% in coniferous wood vs. 23% in deciduous trees. Lignin confers the hydrophobic properties reflecting the fact that it is based on aromatic rings. These three components are interwoven, and direct covalent linkages exist between the lignin and the hemicellulose. A major focus of the paper industry is the separation of the lignin from the cellulose, from which paper is made.

In chemical terms, the difference between hardwood and softwood is reflected in the composition of the constituent lignin. Hardwood lignin is primarily derived from sinapyl alcohol and coniferyl alcohol. Softwood lignin is mainly derived from coniferyl alcohol.[26]

Extractives

Aside from the structural polymers, i.e. cellulose, hemicellulose and lignin (lignocellulose), wood contains a large variety of non-structural constituents, composed of low molecular weight organic compounds, called extractives. These compounds are present in the extracellular space and can be extracted from the wood using different neutral solvents, such as acetone.[27] Analogous content is present in the so-called exudate produced by trees in response to mechanical damage or after being attacked by insects or fungi.[28] Unlike the structural constituents, the composition of extractives varies over wide ranges and depends on many factors.[29] The amount and composition of extractives differs between tree species, various parts of the same tree, and depends on genetic factors and growth conditions, such as climate and geography.[27] For example, slower growing trees and higher parts of trees have higher content of extractives. Generally, the softwood is richer in extractives than the hardwood. Their concentration increases from the cadmium to the pith. Barks and branches also contain extractives. Although extractives represent a small fraction of the wood content, usually less than 10%, they are extraordinarily diverse and thus characterize the chemistry of the wood species.[30] Most extractives are secondary metabolites and some of them serve as precursors to other chemicals. Wood extractives display different activities, some of them are produced in response to wounds, and some of them participate in natural defense against insects and fungi.[31]

Forchem tall oil refinery in Rauma, Finland.

These compounds contribute to various physical and chemical properties of the wood, such as wood color, fragnance, durability, acoustic properties, hygroscopicity, adhesion, and drying.[30] Considering these impacts, wood extractives also affect the properties of pulp and paper, and importantly cause many problems in paper industry. Some extractives are surface-active substances and unavoidably affect the surface properties of paper, such as water adsorption, friction and strength.[27] Lipophilic extractives often give rise to sticky deposits during kraft pulping and may leave spots on paper. Extractives also account for paper smell, which is important when making food contact materials.

Most wood extractives are lipophilic and only a little part is water-soluble.[28] The lipophilic portion of extractives, which is collectively referred as wood resin, contains fats and fatty acids, sterols and steryl esters, terpenes, terpenoids, resin acids, and waxes.[32] The heating of resin, i.e. distillation, vaporizes the volatile terpenes and leaves the solid component – rosin. The concentrated liquid of volatile compounds extracted during steam distillation is called essential oil. Distillation of oleoresin obtained from many pines provides rosin and turpentine.[33]

Most extractives can be categorized into three groups: aliphatic compounds, terpenes and phenolic compounds.[27] The latter are more water-soluble and usually are absent in the resin.

Uses

Fuel

Wood has a long history of being used as fuel,[37] which continues to this day, mostly in rural areas of the world. Hardwood is preferred over softwood because it creates less smoke and burns longer. Adding a woodstove or fireplace to a home is often felt to add ambiance and warmth.

Construction

The Saitta House, Dyker Heights, Brooklyn, New York built in 1899 is made of and decorated in wood.[38]

Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction. Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).

Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.[39] In Medieval Europe oak was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from poplar, small-knotted pine, and Douglas fir.

The churches of Kizhi, Russia are among a handful of World Heritage Sites built entirely of wood, without metal joints. See Kizhi Pogost for more details.

New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials.

In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.

Wood is also commonly used as shuttering material to form the mold into which concrete is poured during reinforced concrete construction.

Flooring

Wood can be cut into straight planks and made into a wood flooring.

A solid wood floor is a floor laid with planks or battens created from a single piece of timber, usually a hardwood. Since wood is hydroscopic (it acquires and loses moisture from the ambient conditions around it) this potential instability effectively limits the length and width of the boards.

Solid hardwood flooring is usually cheaper than engineered timbers and damaged areas can be sanded down and refinished repeatedly, the number of times being limited only by the thickness of wood above the tongue.

Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building (the joists or bearers) and solid construction timber is still often used for sports floors as well as most traditional wood blocks, mosaics and parquetry.

softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from dicotyledons (usually broad-leaved trees, e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than many hardwoods.

There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it.[citation needed] The density of wood varies with species. The density of a wood correlates with its strength (mechanical properties). For example, mahogany is a medium-dense hardwood that is excellent for fine furniture crafting, whereas balsa is light, making it useful for model building. One of the densest woods is black ironwood.

Chemistry

Chemical structure of lignin, which makes up about 25% of wood dry matter and is responsible for many of its properties.

The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight.[25] Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity.

Aside from water, wood has three main components. Cellulose, a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is hemicellulose, which is around 20% in deciduous trees but near 30% in conifers. It is mainly five-carbon sugars that are linked in an irregular manner, in contrast to the cellulose. Lignin is the third component at around 27% in coniferous wood vs. 23% in deciduous trees. Lignin confers the hydrophobic properties reflecting the fact that it is based on aromatic rings. These three components are interwoven, and direct covalent linkages exist between the lignin and the hemicellulose. A major focus of the paper industry is the separation of the lignin from the cellulose, from which paper is made.

In chemical terms, the difference between hardwood and softwood is reflected in the composition of the constituent lignin. Hardwood lignin is primarily derived from sinapyl alcohol and coniferyl alcohol. Softwood lignin is mainly derived from coniferyl alcohol.[26]

Extractives

Aside from the structural polymers, i.e. cellulose, hemicellulose and lignin (lignocellulose), wood contains a large variety of non-structural constituents, composed of low molecular weight organic compounds, called extractives. These compounds are present in the extracellular space and can be extracted from the wood using different neutral solvents, such as acetone.[27] Analogous content is present in the so-called exudate produced by trees in response to mechanical damage or after being attacked by insects or fungi.[28] Unlike the structural constituents, the composition of extractives varies over wide ranges and depends on many factors.[29] The amount and composition of extractives differs between tree species, various parts of the same tree, and depends on genetic factors and growth conditions, such as climate and geography.[27] For example, slower growing trees and higher parts of trees have higher content of extractives. Generally, the softwood is richer in extractives than the hardwood. Their concentration increases from the cadmium to the pith. Barks and branches also contain extractives. Although extractives represent a small fraction of the wood content, usually less than 10%, they are extraordinarily diverse and thus characterize the chemistry of the wood species.[30] Most extractives are secondary metabolites and some of them serve as precursors to other chemicals. Wood extractives display different activities, some of them are produced in response to wounds, and some of them participate in natural defense against insects and fungi.[31]

Forchem tall oil refinery in Rauma, Finland.

These compounds contribute to various physical and chemical properties of the wood, such as wood color, fragnance, durability, acoustic properties, hygroscopicity, adhesion, and drying.[30] Considering these impacts, wood extractives also affect the properties of pulp and paper, and importantly cause many problems in paper industry. Some extractives are surface-active substances and unavoidably affect the surface properties of paper, such as water adsorption, friction and strength.[27] Lipophilic extractives often give rise to sticky deposits during kraft pulping and may leave spots on paper. Extractives also account for paper smell, which is important when making food contact materials.

Most wood extractives are lipophilic and only a little part is water-soluble.[28] The lipophilic portion of extractives, which is collectively referred as wood resin, contains fats and fatty acids, sterols and steryl esters, terpenes, terpenoids, resin acids, and waxes.[32] The heating of resin, i.e. distillation, vaporizes the volatile terpenes and leaves the solid component – rosin. The concentrated liquid of volatile compounds extracted during steam distillation is called essential oil. Distillation of oleoresin obtained from many pines provides rosin and turpentine.[33]

Most extractives can be categorized into three groups: aliphatic compounds, terpenes and phenolic compounds.[27] The latter are more water-soluble and usually are absent in the resin.

  • Aliphatic compounds include fatty acids, fatty alcohols and their esters with glycerol, fatty alcohols (waxes) and sterols (steryl esters). Hydrocarbons, such as alkanes, are also present in the wood. Suberin is a polyester, made of suberin acids and glycerol, mainly found in barks. Fats serve as a source of energy for the wood cells.[28] The most common wood sterol is sitosterol. However, sitostanol, citrostadienol, campesterol and <

    There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it.[citation needed] The density of wood varies with species. The density of a wood correlates with its strength (mechanical properties). For example, mahogany is a medium-dense hardwood that is excellent for fine furniture crafting, whereas balsa is light, making it useful for model building. One of the densest woods is black ironwood.

    The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight.[25] Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity.

    Aside from water, wood has three main components. Cellulose, a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is hemicellulose, which is around 20% in deciduous trees but near 30% in conifers. It is mainly five-carbon sugars that are linked in an irregular manner, in contrast to the cellulose. Lignin is the third component at around 27% in coniferous wood vs. 23% in deciduous trees. Lignin confers the hydrophobic properties reflecting the fact that it is based on aromatic rings. These three components are interwoven, and direct covalent linkages exist between the

    Aside from water, wood has three main components. Cellulose, a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is hemicellulose, which is around 20% in deciduous trees but near 30% in conifers. It is mainly five-carbon sugars that are linked in an irregular manner, in contrast to the cellulose. Lignin is the third component at around 27% in coniferous wood vs. 23% in deciduous trees. Lignin confers the hydrophobic properties reflecting the fact that it is based on aromatic rings. These three components are interwoven, and direct covalent linkages exist between the lignin and the hemicellulose. A major focus of the paper industry is the separation of the lignin from the cellulose, from which paper is made.

    In chemical terms, the difference between hardwood and softwood is reflected in the composition of the constituent lignin. Hardwood lignin is primarily derived from sinapyl alcohol and coniferyl alcohol. Softwood lignin is mainly derived from coniferyl alcohol.[26]

    Aside from the structural polymers, i.e. cellulose, hemicellulose and lignin (lignocellulose), wood contains a large variety of non-structural constituents, composed of low molecular weight organic compounds, called extractives. These compounds are present in the extracellular space and can be extracted from the wood using different neutral solvents, such as acetone.[27] Analogous content is present in the so-called exudate produced by trees in response to mechanical damage or after being attacked by insects or fungi.[28] Unlike the structural constituents, the composition of extractives varies over wide ranges and depends on many factors.[29] The amount and composition of extractives differs between tree species, various parts of the same tree, and depends on genetic factors and growth conditions, such as climate and geography.[27] For example, slower growing trees and higher parts of trees have higher content of extractives. Generally, the softwood is richer in extractives than the hardwood. Their concentration increases from the cadmium to the pith. Barks and branches also contain extractives. Although extractives represent a small fraction of the wood content, usually less than 10%, they are extraordinarily diverse and thus characterize the chemistry of the wood species.[30] Most extractives are secondary metabolites and some of them serve as precursors to other chemicals. Wood extractives display different activities, some of them are produced in response to wounds, and some of them participate in natural defense against insects and fungi.[31]

    These compounds contribute to various physical and chemical properties of the wood, such as wood color, fragnance, durability, acoustic properties, hygroscopicity, adhesion, and drying.[30] Considering these impacts, wood extractives also affect the properties of pulp and paper, and importantly cause many problems in paper industry. Some extractives are surface-active substances and unavoidably affect the surface properties of paper, such as water adsorption, friction and strength.[27] Lipophilic extractives often give rise to sticky deposits during kraft pulping and may leave spots on paper. Extractives also account for paper smell, which is important when making food contact materials.

    Most wood extractives are lipophilic and only a little part is water-soluble.[28] The lipophilic portion of extractives, which is collectively referred as wood resin, contains fats and fatty acids, sterols and steryl esters, terpenes, terpenoids, resin acids, and waxes.[32] The heating o

    Most wood extractives are lipophilic and only a little part is water-soluble.[28] The lipophilic portion of extractives, which is collectively referred as wood resin, contains fats and fatty acids, sterols and steryl esters, terpenes, terpenoids, resin acids, and waxes.[32] The heating of resin, i.e. distillation, vaporizes the volatile terpenes and leaves the solid component – rosin. The concentrated liquid of volatile compounds extracted during steam distillation is called essential oil. Distillation of oleoresin obtained from many pines provides rosin and turpentine.[33]

    Most extractives can be categorized into three groups: aliphatic compounds, terpenes and phenolic compounds.[27] The latter are more water-soluble and usually are absent in the resin.

    Wood has a long history of being used as fuel,[37] which continues to this day, mostly in rural areas of the world. Hardwood is preferred over softwood because it creates less smoke and burns longer. Adding a woodstove or fireplace to a home is often felt to add ambiance and warmth.

    Construction

    The Saitta House, Dyker Heights, Brooklyn, New York built in 1899 is made of and decorated in wood.[38]

    Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction. Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).

    Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.[39] In Medieval Europe oak was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from poplar, small-knotted pine, and Douglas fir.

    The churches of Kizhi, Russia are among a handful of World Heritage Sites built entirely of wood, without metal joints. See Kizhi Pogost for more details.

    New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials.

    In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.

    Wood is also commonly used as shuttering material to form the mold into which concrete is poured during reinforced concrete construction.

    Flooring

    Wood can be cut into straight planks and made into a wood flooring.

    A solid wood floor is a floor laid with planks or battens created from a single piece of timber, usually a hardwood. Since wood is hydroscopic (it acquires and loses moisture from the ambient conditions around it) this potential instability effectively limits the length and width of the boards.

    Solid hardwood flooring is usually cheaper than engineered timbers and damaged areas can be sanded down and refinished repeatedly, the number of times being limited only by the thickness of wood above the tongue.

    Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building (the joists or bearers) and solid construction timber is still often used for sports floors as well as most traditional wood blocks, mosaics and parquetry.

    Engineered products

    Engineered wood products, glued building products "engineered" for application-specific performance requirements, are often used in construction and industrial applications. Glued engineered wood products are manufactured by bonding together wood strands, veneers, lumber or other forms of wood fiber with glue to form a larger, more efficient composite structural unit.[40]

    These products include glued laminated timber (glulam), wood structural panels (including plywood, oriented strand board and composite panels), laminated veneer lumber (LVL) and other structural composite lumber (SCL) products, parallel strand lumber, and I-joists.[40] Approximately 100 million cubic meters of wood was consumed for this purpose in 1991.[3] The trends suggest that particle board and fiber board will overtake plywood.

    Wood unsuitable for construction in its native form may be broken down mechanically (into fibers or chips) or chemically (into cellulose) and used as a raw material for other building materials, such as engineered wood, as well as Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).

    Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.[39] In Medieval Europe oak was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from poplar, small-knotted pine, and Douglas fir.

    lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.[39] In Medieval Europe oak was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from poplar, small-knotted pine, and Douglas fir.

    New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials.

    In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.

    Wood is also commonly used as shuttering material to form the mold into which concrete is poured during reinforced concrete construction.

    Flooring

    Wood can be cut into straight planks and made into a wood flooring.

    A solid wood floor is a floor laid with planks or battens created from a single piece of timber, usually a hardwood. Since wood is hydroscopic (it acquires and loses moisture from the ambient conditions around it) this potential instability effectively limits the length and width of the boards.

    Solid hardwood flooring is usually cheaper than engineered timbers and damaged areas can be sanded down and refinished repeatedly, the number of times being limited only by the thickness of wood above the tongue.

    Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building (the joists or bearers) and solid construction timber is still often used for sports floors as well as most traditional wood blocks, mosaics and parquetry.

    Engineered products