Plywood

The material. Plywood is laminated wood, the layers glued together such that the grain in successive layers are at right angles, giving stiffness and strength in both directions. The number of layers varies but is always odd (3, 5, 7 …) to give symmetry about the core ply; if it is asymmetric it warps when wet or hot. Those with few plies (3, 5) are significantly stronger and stiffer in the direction of the outermost layers; with increasing number of plies the properties become more uniform. High-quality plywood is bonded with synthetic resin. The following data describes the in-plane properties of a typical five-ply.

Composition

Cellulose/hemicellulose/lignin/12%H2O/adhesive.

Plywood dominates the market for both wood and steel stud construction. It is widely used, too, for furniture and fittings, boat building, and packaging.

Ecoproperties: material

Embodied energy, primary production CO2 footprint, primary production Water usage Eco-indicator

13

0.73

*500

37

– 17

– 0.77

– 1000 – 41

MJ/kg

kg/kg

l/kg

millipoints/kg

Ecoproperties: processing

Construction energy Construction CO2

*0.455

*0.022

– 0.55

– 0.027

MJ/kg

kg/kg

Recycling

Recycle fraction in current supply

1

– 2

%

Typical uses. Furniture, building and construction, marine and boat build­ing, packaging, transport and vehicles, musical instruments, aircraft, modeling.

The material. Softwoods come from coniferous, mostly evergreen, trees such as spruce, pine, fir, and redwood. Wood must be seasoned before it is used. Seasoning is the process of drying to remove some of the natu­ral moisture to make it dimensionally stable. In air seasoning the wood is dried naturally in covered but open-sided structures. In kiln drying the wood is artificially dried in an oven. Wood has been used for construction and to make products since the earliest times. Timber continues to be used on a massive scale, particularly in housing and commercial buildings.

Composition

Cellulose/hemicellulose/lignin/12%H2O.

General properties

Density

440

– 600

kg/m3

Price

1.04

– 2.07

USD/kg

Mechanical properties

Young’s modulus Yield strength (elastic limit) Tensile strength Compressive strength Elongation Hardness—Vickers Fatigue strength at 107 cycles Fracture toughness

Wood remains one of the world’s major structural materials as well finding application in more delicate objects such as furniture and musical instruments.

Typical uses. Flooring; furniture; containers; cooperage; sleepers (when treated); building construction; boxes; crates and palettes; planing-mill products; subflooring; sheathing; and as the feedstock for plywood, particle­board, and hardboard.

The material. Softwoods come from coniferous, mostly evergreen, trees such as spruce, pine, fir, and redwood. Wood must be seasoned before it is used. Seasoning is the process of drying to remove some of the natu­ral moisture to make it dimensionally stable. In air seasoning the wood is dried naturally in covered but open-sided structures. In kiln drying the wood is artificially dried in an oven. Wood has been used for construction and to make products since the earliest times. Timber continues to be used on a massive scale, particularly in housing and commercial buildings.

Composition

Cellulose/hemicellulose/lignin/12%H2O.

General properties

Density

440

– 600

kg/m3

Price

1.04

– 2.07

USD/kg

Mechanical properties

Young’s modulus

0.6

– 0.9

GPa

Yield strength (elastic limit)

*1.7

– 2.6

MPa

Tensile strength

3.2

– 3.9

MPa

Compressive strength

*3

– 9

MPa

Elongation

1

– 1.5

%

Hardness—Vickers

2.6

– 3.2

HV

Fatigue strength at 107 cycles

*0.96

– 1.2

MPa

Fracture toughness

*0.4

– 0.5

MPa. m1/2

Thermal properties

Glass temperature

77 –

102

°C

Maximum service temperature

120 –

140

°C

Thermal conductor or insulator?

Good insulator

Thermal conductivity

0.08 –

0.14

W/m. K

Specific heat capacity

1660 –

1710

J/kg. K

Thermal expansion coefficient

*26 –

36

p, strain/°C

Electrical properties

Electrical conductor or insulator?

Poor insulator

Electrical resistivity

*2.1 X 1014 –

7 X 1014

pnhm. cm

Dielectric constant

*5 –

6.2

Dissipation factor

*0.03 –

0.07

Dielectric strength

1-

2 106

V/m

Wood remains one of the world’s major structural materials as well finding application in more delicate objects such as furniture and musical instruments.

Typical uses. Flooring; furniture; containers; cooperage; sleepers (when treated); building construction; boxes; crates and palettes; planing-mill products; subflooring; sheathing and as the feedstock for plywood, particle­board, and hardboard.

The material. Hardwoods come from broad-leaved, deciduous trees such as oak, ash, elm, sycamore, and mahogany. Although most hardwoods are harder than softwoods, there are exceptions: balsa, for instance, is a hard­wood. Wood must be seasoned before it is used. Seasoning is the process of drying the natural moisture out of the raw timber to make it dimensionally stable, allowing its use without shrinking or warping. In air seasoning the wood is dried naturally in covered but open-sided structures. In kiln drying the wood is artificially dried in an oven or kiln.

Composition

Cellulose/hemicellulose/lignin/12%H2O.

General properties

Density

850

– 1030

kg/m3

Price

3.11

– 4.15

USD/kg

Mechanical properties

Young’s modulus

20.6

– 25.2

GPa

Yield strength (elastic limit)

43

– 52

MPa

Tensile strength

132

– 162

MPa

Compressive strength

68

– 83

MPa

Elongation

*1.7

– 2.1

%

Hardness—Vickers

*13

– 15.8

HV

Fatigue strength at 107 cycles

*42

– 52

MPa

Fracture toughness

*9

– 10

MPa. m1′

Thermal properties

Glass temperature

77

– 102

°C

Maximum service temperature

120

– 140

°C

Thermal conductor or insulator?

Good insulator

Thermal conductivity

*0.41

– 0.5

W/m. K

Specific heat capacity

1660

– 1710

J/kg. K

Thermal expansion coefficient

*2.5

– 9

p, strain/°C

Electrical properties

Electrical conductor or insulator? Poor insulator

Electrical resistivity

*6 X 1013

– 2 X 1014

pnhm. cm

Dielectric constant

*5

– 6

Dissipation factor

*0.1

– 0.15

Dielectric strength

*0.4

– 0.6 106

V/m

Wood remains one of the world’s major structural materials as well finding application in more delicate objects such as furniture.

Ecoproperties: material

Embodied energy, primary production

7.4

– 8.2

MJ/kg

CO2 footprint, primary production

0.45

– 0.49

kg/kg

Water usage

*730

– 1.5e3

l/kg

Eco-indicator

6.3

– 6.9

millipoints/kg

Ecoproperties: processing

Construction energy

*0.909

– 1.1

MJ/kg

Construction CO2

*0.045

– 0.05

kg/kg

Recycling

Recycle fraction in current supply

8

– 10

О/

%

Typical uses. Flooring; stairways, furniture; handles; veneer; sculpture; woodenware; sashes; doors; general millwork; framing—but these are just a few. Almost every load-bearing and decorative object has, at one time or another, been made from wood.

The material. Hardwoods come from broad-leaved, deciduous trees such as oak, ash, elm, sycamore, and mahogany. Although most hardwoods are harder than softwoods, there are exceptions: balsa, for instance, is a hard­wood. Wood must be seasoned before it is used. Seasoning is the process of drying the natural moisture out of the raw timber to make it dimensionally stable, allowing its use without shrinking or warping. In air seasoning the wood is dried naturally in covered but open-sided structures. In kiln drying the wood is artificially dried in an oven or kiln.

Composition

Cellulose/hemicellulose/lignin/12%H2O. General properties

Density

850

– 1.13e3 kg/m3

Price

3.11

– 4.15 USD/kg

Mechanical properties

Young’s modulus

4.5

– 5.8

GPa

Yield strength (elastic limit)

*4

– 5.9

MPa

Tensile strength

7.1

– 8.7

MPa

Compressive strength

*12.7

– 15.6

MPa

Elongation

1

– 1.5

%

Hardness—Vickers

10

– 12

HV

Fatigue strength at 107 cycles

*2.1

– 2.6

MPa

Fracture toughness

*0.8

– 1

MPa. m1/2

Thermal properties

Glass temperature

77

– 102

°C

Maximum service temperature

120

– 140

°C

Thermal conductor or insulator? Thermal conductivity

Good insulator 0.16 – 0.2

W/m. K

Specific heat capacity

1660

– 1710

J/kg. K

Thermal expansion coefficient

*37

– 49

p, strain/°C

Electrical properties

Electrical conductor or insulator?

Poor insulator

Electrical resistivity

*2.1 x 1014 – 7 x 1014

pnhm. cm

Dielectric constant

*5 – 6

Dissipation factor

*0.1 – 0.15

Dielectric strength

*0.4 – 0.6 106

V/m

Wood remains one of the world’s major structural materials as well finding application in more delicate objects such as furniture.

Eco properties: material

Embodied energy, primary production

7.4

– 8.2

MJ/kg

CO2 footprint, primary production

0.45

– 0.49

kg/kg

Water usage

*730

– 1.5e3

l/kg

Eco-indicator

6.3

– 6.9

millipoints/kg

Eco properties: processing

Construction energy

*0.909 – 1.1

MJ/kg

Construction CO2

*0.045 – 0.05

kg/kg

Recycling

Recycle fraction in current supply

8 – 10

%

Typical uses. Flooring; stairways, furniture; handles; veneer; sculpture, woodenware; sashes; doors; general millwork; framing—but these are just a few. Almost every load-bearing and decorative object has, at one time or another, been made from wood.

This page intentionally left blank