Wood Physics & Wood Materials
ETHZ / D-BAUG / FS23
ETHZ / D-BAUG / FS23
Microfibril angle
The microfibril angle (MFA) refers to the angle between the longitudinal axis of a cell and the direction of the cellulose microfibrils in the secondary cell wall of wood fibers and tracheids. Microfibrils are bundles of cellulose molecules that provide strength and flexibility to the cell wall.
The importance of the microfibril angle lies in its strong influence on the mechanical properties of wood:
- Strength: A lower microfibril angle, where the microfibrils are more aligned with the longitudinal axis of the cell, tends to increase the tensile strength of the wood.
- Stiffness: higher MFA leads to lower stiffness (more flexible)
- Shrinkage and Swelling
Resin
Resin is a type of substance produced by many plants, particularly coniferous trees. It's a viscous compound that is secreted in response to injury to the plant, such as a break in the bark, and it's used to seal up wounds and prevent the invasion of insects and pathogens.
Pits
Pits (ger. Tüpfel) refer to small openings in the cell wall that allow for water and nutrients to be transported between cells.
Simple Pits: These are essentially just holes in the cell wall, allowing for direct communication between the adjacent cells. They're typically found in longitudinal cells, like fibers, which are responsible for giving the wood its strength.
Bordered Pits: These are more complex structures, found in tracheids and vessel elements, which are involved in water transport. A bordered pit has a central hole (or aperture) surrounded by a doughnut-shaped border. This structure allows for the movement of water, while also having a safety mechanism to prevent air bubbles (which can block water transport) from spreading throughout the tree.
Vessel distributions
Swelling and shrinkage anisotropy
Longitudinal direction
0.1 - 0.2% per 1% change in moisture content
Radial direction
2 - 4%
Tangential direction
3 - 8%
Factors
- degree of swelling and shrinkage
- density
- chemical composition of the cell wall
(extractives, volume fraction of hemicellulose and lignin)
- swelling and shrinkage anisotropy
- density
- fiber orientation
- microfibril angle (tension/compression/juvenile wood)
Cellulose nanofibers production
a fibrillation process
Examples:
- Grinding (Masuko Grinder)
- Homogenizing (e.g. Microfluidizer, APV Homogenizer)
- Cryocrushing (Liquid N2)
Particle and fiber-based products
particle-based products
- production of the particles --> drying --> gluing
--> sheet formation --> pre-press --> press - typical density profiles:
- homogeneous
- clear differentiation
- little differentiation
fiber-based products
- wet process (high-density fiberboards, insulation boards)
- dry process (MDF, nowadays also for insulation boards)
- typical density profiles:
- medium density, homogeneous
- medium density, distinct density differences
- high-density fiberboard
- smooth side --> highest
- middle --> lowest
- wire side --> higher
- applications:
- roof and wall panels
- insulation panels (low density)
- flooring panels (high density)
- furniture (MDF)
Cell wall polymer distribution
Cellulose - Hemicellulose - Lignin
Spruce
40.4% - 31.1% - 28%
Beech
43.3% - 31.8% - 24.4%
Softwood and Hardwood
Hardwoods are evolutionary younger and have reached a higher level of specialization in their wood structure.
Softwood - tissue structure
- Tracheids (~90%)
- structural parameters of one cell type are varied according to the function
- functions
- water transport (earlywood tracheids)
- mechanical function (latewood tracheids)
- parameters
- cell wall thickness
- lumina size
- parenchyma cells
- mainly in the wood rays
- storage function
- resin production
- production of extractives
- living cells until heartwood formation
Hardwood - tissue structure
- specific cell types for each function
- vessels --> water transport
- fibers/tracheids --> mechanical function
- ray cells more prominent than in softwoods
Density and Hardness
- Softwoods --> generally softer (they grow faster)
- Hardwoods --> generally denser (exceptions e.g. balsa) --> more resilient
Leaves
- most softwoods are coniferous
- most hardwoods are deciduous and broad-leaved (except: spruce)
Reproductive Structures
- softwoods --> cones (gymnosperms)
- hardwoods --> flowers/fruits (angiosperms)
Reaction wood
Reaction wood is a type of wood formed by a tree in response to environmental stress or gravitational pull to restore its vertical orientation or to support branches. It has a different structure, chemical composition, and mechanical properties compared to normal wood.
- Tension wood (hardwood trees/angiosperms)
- pulls the tree back toward its original position
- higher proportion of cellulose
- lower microfibril angle (~ 0°)
- Compression wood (softwood trees/gymnosperms)
- pushes the tree back to its original position
- compression stresses are generated during cell differentiation
- cells are more rounded, have thicker cell walls rich in lignin
higher microfibril angle (~ 30-50°) - lack S3-layer
Juvenile and adult wood
Juvenile wood, also known as core wood or inner wood, is the wood that forms near the center of a tree during its early growth years.
- higher microfibril angle
- lower density
- generally less stiff and lower strength
Mature or adult wood, also known as outer wood, is the wood that a tree produces after the juvenile phase.
Heartwood types
False heartwood, also known as discolored heartwood or incipient heartwood, is a type of wood that forms in some tree species when the living sapwood near the center of the tree begins to darken in color, typically due to fungal infection or other forms of stress (environmental factors). Only the lumina of the cells are impregnated with extractives and there is no increase in durability.
Evergreen vs Deciduous
Deciduous trees lose their leaves during a particular season, typically autumn in temperate climates, to conserve water during the dry or cold season. Evergreen trees, on the other hand, retain their leaves year-round.
Evergreen (generally softwoods)
- Most species of conifers (e.g., pine, hemlock, spruce, and fir), but not all (e.g., larch)
- live oak, holly, and "ancient" gymnosperms such as cycads
- Many woody plants from frost-free climates
- Rainforest trees
- All Eucalypts
- Clubmosses and relatives
- Most Bamboos
Deciduous (generally hardwoods)
- many broadleafs (oak, ash, birch, beech, maple)
Angiosperms vs Gymnosperms
Angiosperms, also known as flowering plants, whose seeds are produced inside a protective structure called a fruit, which develops from the fertilized ovule after flowering.
- typically broad-leaved
- no conifers
- most decidiuous and some evergreens
- oak, maple, birch, beech, ash
Gymnosperms, from the Greek gymnos "naked" and sperma "seed".
The seeds are not enclosed in a fruit. They are often formed in and released from cones, which is why gymnosperms are sometimes referred to as conifers.
- all conifers
- most evergreens
- larch, spruce, pine, fir
Wood types
Water uptake
- wood is a hygroscopic, porous material with interconnected capillaries of a wide range of diameters
- water movements in the microsystem (cell wall) and macrosystem (cell lumina)
- cell walls take up water (vapor) from the air (sorption)
- cell lumina transport liquid water
Free water --> Macrosystem (cell lumina)
Bound water --> Microsystem (cell wall)
Water transport
Combination of:
- capillary transport
- Diffusion (Fick's laws)
Diffusion rate depends on the following:
- density
- temperature
- moisture content
- cutting direction
The pressure in a capillary depends on its diameter
the smaller the diameter --> the higher the pressure
Phases of sorption
Chemisorption
- Formation of a monomolecular layer
- almost no swelling
- heat release
- ~0.6% moisture content, rel. humidity below 20%
Adsorption/Physiosorption
- formation of a molecular multilayer
- less heat release
- ~6-15% moisture content, rel. humidity below 75%
Capillary condensation
- saturation pressure in a micro-capillary is lower than at a plane surface or a macro-capillary
- water vapor is condensing
- ranges of adsorption and capillary condensation are overlapping (transition zone)
- ~15% moisture content to FSP, rel. humidity 75-100%
Impact factors:
- previous history
- chemistry of the cell wall (hemicellulose > lignin)
- mechanical loading (compressive loading --> slower sorption)
- thermal pre-treatment (higher temperature --> higher sorption)
- impregnation (chemical pre-treatment)
salt impregnation --> higher sorption - extractives
Types of density
Bulk density \(\rho_u\)
Oven-dry density \(\rho_{dtr}\)
"Raumdichtezahl" \(R\)
cell wall density \(\rho_r\)
Moisture content measurement
Drying method
moisture content \(u = \frac{m_u - m_{dtr}}{m_{dtr}} \cdot 100 \: [\%]\)
Resistance test
Making use of the correlation between wood moisture content and electrical resistance.
Raman Imaging
Purpose: investigate cell wall polymers with high spatial resolution, while retaining the structure
Sample requirements: for surface scans the surface has to be as flat as possible (microtome cuts or polishing)
Spectral imaging: for every pixel a spectrum covering the entire wave number range is obtained
Fast imaging: intensity only at one specific wave number
Applications:
Visualization of the wood composition (cellulose and lignin)
Information about the orientation of the cellulose microfibrils
Visualization of the chemical modification area
Bulk Densities
in \(\left[ kg/m^3 \right]\)
spruce
470
douglas fir
530
larch
500 - 560
pine
350 - 850
maple
620 - 750
oak
600 -900
birch (european)
670
ash (european)
710
beech
700 - 900
ebony
1100 - 1300
balsa
110 - 140
Relative Moduli of Elasticity
\(E_T < E_R << E_L\)
softwood:
1 : 1.7 : 20
hardwood
1 : 1.7 : 13
Moduli of Elasticity
Impact factors
- moisture content
- microfibril angle
in \(\left[ N/mm^2 \right]\)
\(E_L -- E_T -- E_R\)
Spruce
10'000 -- 450 -- 800
Pine
11'000 -- 500 -- 1000
Oak
13'000 -- 920 -- 1580
Azobe/Bongossi
17'000 -- 2060 -- 3230
Shear Moduli
in \(\left[ N/mm^2 \right]\)
\(G_{LR} -- G_{RT} -- G_{IT}\)
Spruce
600 -- 40 -- 650
Pine
- -- 70 -- 680
Oak
1080 -- 400 -- 800
Extended Hooke's law for orthotropic materials
\(\begin{bmatrix}\varepsilon_1 \\ \varepsilon_2 \\ \varepsilon_3 \\\gamma_{23} \\ \gamma_{13} \\ \gamma_{12} \\\end{bmatrix}=\begin{bmatrix}\frac{1}{E_1} & -\frac{\mu_{21}}{E_2} & -\frac{\mu_{31}}{E_3} & 0 & 0 & 0 \\-\frac{\mu_{12}}{E_1} & \frac{1}{E_2} & -\frac{\mu_{32}}{E_3} & 0 & 0 & 0 \\-\frac{\mu_{13}}{E_1} & -\frac{\mu_{23}}{E_2} & \frac{1}{E_3} & 0 & 0 & 0 \\0 & 0 & 0 & \frac{1}{G_{23}} & 0 & 0 \\0 & 0 & 0 & 0 & \frac{1}{G_{13}} & 0 \\0 & 0 & 0 & 0 & 0 & \frac{1}{G_{12}} \\\end{bmatrix}\cdot\begin{bmatrix}\sigma_1 \\ \sigma_2 \\ \sigma_3 \\\tau_{23} \\ \tau_{13} \\ \tau_{12} \\\end{bmatrix}\)
3 E-Moduli
3 Shear Moduli
6 Poisson's ratios
Tensile and compressive strength
Splitting strength
Brinell hardness
\(H_B = \frac{2 \cdot F}{\pi D \left( D - \sqrt{D^2 - d^2} \right)} \quad \left[ \frac{N}{mm^2} \right]\)
F - Force to indent a polished steel ball into the sample
D - Diameter of the ball
d - Diameter of the indent
Brinell hardness - moisture content
E-Modulus and Strength correlation
is technically used for stress grading
Frequency distribution of strength values
Rheological properties
creep
stress relaxation
creep strength
Creep behavior
a) idealized creep curve
b) creep curves for different stress levels
The asymptote indicates the stress level that an element can take "forever".
Superimposition of deformation
(total) strain = elastic + viscoelastic + mechano-sorptive + plastic
Superimposition of creep and swelling
Strong influence of sample cross-section
Tensile loading and adsorption
Sample length increase due to creep plus increase due to swelling
Compressive loading and adsorption
Sample length decreases due to creep but increases due to swelling
Mechano-sorptive creep
The mechano-sorptive effect refers to the increased creep behavior in wood that occurs under changing moisture conditions.
This swelling or shrinking, combined with mechanical stress, can lead to significantly increased deformation, or creep, over time.
Delignification
Chemical Modification
Remove the matrix component lignin while retaining the inherent cellulose hierarchical architecture.
Cellulose Composites
Enhancing the mechanical properties of wood by chemical modification such as delignification.
delignification --> cellulose scaffolds (shapeable and high cell wall porosity at wet state)
--> eases functionalization and densification to high fibre volume fractions
Bio-based cellulose composites
Densified cellulose scaffolds possess excellent mechanical properties in dry state
but exposure to water or high humidity drastically diminishes the mechanical performance
--> Cellulose scaffolds need to be impregnated with a matrix system
for example via impregnation of epoxy resin and a subsequent densification
currently testing different bio-based matrix systems
Cellulose Composites - mechanical properties
DW = delignified wood
DWRP = delignified wood-reinforced polymer (epoxy)
GFRP = glass fiber-reinforced polymer (epoxy)
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Flashcards
Optical properties
wood color changes due to aging
- light exposure (UV light)
- heat and oxygen exposure
most wood species get darker
some get yellower (maple, birch)
some get lighter (teak, thermowood)
UV protection
Application of coating systems with:
- organic UV absorbers and organic radical scavengers
- metal oxides (nanoparticle-based systems)
new systems:
- growth of nanorods on wood surfaces
Fire triangle
Flashing point, Auto-ignition and Pyrolysis
Flashing Point: The temperature at which wood when exposed to a flame starts to burn due to thermal decomposition
--> above 225°C for wood of medium density
Auto-ignition: Temperature at which wood spontaniously ignites in a normal atmosphere without an external source of ignition
--> above 280°C
Pyrolysis: Decomposition of wood with formation of char and flammable gases.
Burning rate
Depth of char layer as a function of fire duration. Helps to estimate how long a certain piece of wood could hold a certain weight while burning.
\(\beta (t) = \frac{d_{char}}{t}\) for example spruce ≈ 0.7 [mm/min]
depends on:
- exposure to fire
- pressure
- temperature
- wood species
Brandverhaltensgruppen
In Switzerland, building materials are classified according to their reaction to fire:
RF1 = no contribution to fire
RF2 = little contribution to fire
RF3 = admissible contribution to fire
RF4 = inadmissible contribution to fire
Wood fire behavior - EN
Building material class B
Influence of wood density:
- Density < 300 kg/m^3 high flammability
- Density 300-1000 kg/m^3 moderate flammability
- Density > 1000 kg/m^3 low flammability
(relates to air accessibility in wood!)
Intumescent coating systems
They offer passive fire protection by swelling in response to high temperatures, increasing in volume and decreasing in density. --> creates an insulating barrier layer
Intumescent materials:
- Binding agent
- polymers like polyamides, polyuretane acrylates
- Blowing agent
- urea, melamine, polyamides
- Inorganic acid source
- ammonium salts, phosphates, sulfates
- Polyhydric compounds (carbon source)
- starch, pentaerythirol, char former polymers
Cone calorimetry
Measures a material's flammability using the technique of oxygen consumption calorimetry (OCC).
Determines the HRR of a fire by measuring the amount of oxygen the fire consumes.
Wood-mineral hybrids with improved fire resistance
- surface coatings
- bulk treatments
- bulk mineralization (CaCO3)
- via decomposition of dimethyl carbonate (DMC)
- or via mineralisation by alternating salt solutions
Fire resistance of wood
Intrinsic wood factors:
- wood species
- density (higher density --> higher resistance)
- thickness of element
treatments:
- surface coatings and treatments (e.g. intumescent)
- bulk treatments and impregnation (e.g. mineralization)
important parameters:
- Heat release rate
- Burning rate
- Smoke release rate
Wood - mechanical summary
Wood is a inhomogeneous, anisotropic and porous solid, whose properties are affected mainly by its structure, moisture and temperature.
Transparent wood for solar cells
Transparent wood layer for:
- mechanical properties
- insulation (low thermal conductivity)
- light scattering (haze)
- sustainability
Conductivity of different materials
Conductor, Insulator and Dielectric
Conductor
A material that allows the flow of electric charge. It conducts electric current very efficiently due to the presence of free electrons that can move easily throughout the material.
Insulator
A material that resists the flow of electric charge. It has few free electrons, so it does not allow electric current to pass through it easily.
Dielectric
A type of insulator that can be polarized when an electric field is applied. This property makes dielectrics useful in various applications, such as in capacitors where they can store energy in an electric field.
Graphitization of wood
To increase its eletric conductivity
via:
- bulk graphitization (by impregnation)
- laser-induced graphitization
Piezoelectricity of wood
Piezoelectricity is the property of certain materials to generate an electric charge in response to applied mechanical stress.
in wood:
- compression in one direction increases the polarization (or charge seperation) between O and the electropositive Si atoms
- when a positive potential is applied to the surface, Si atoms are forced away, producing a mechanical deformation (reverse piezoelectric effect)
Triboelectricity of wood
The triboelectric effect refers to the electric charge that is generated when two different materials come into contact and are then separated.
Thermal conductivity in wood
Thermal conductivity of wood (with a moisture content of 12%) perpendicular and parallel to fibre grain:
\(\lambda_{\perp} = 0.026 + 0.195 \cdot \rho \cdot 10^{-3} \quad [W/mk] \)
\(\lambda_{\parallel} = 0.026 + 0.46 \cdot \rho \cdot 10^{-3} \quad [W/mk] \)
is a function of bulk density!
And increases linearly with moisture content
Specific heat capacity
Heat quantity that is needed to increase the temperature of 1 kg of a material by 1 K.
oven-dry wood -- \(\approx 1300 \left[ \frac{J}{kg \cdot K}\right]\)
- minor density influence
- distinct humidity influence
water -- \(4181 \left[ \frac{J}{kg \cdot K}\right]\)
Thermal diffusivity
Thermal diffusivity is the rate at which heat spreads ("diffuses") through a material, from its hot end to its cold end.
\(a = \frac{\lambda}{c \cdot \rho} \cdot 10^{-3} \left[ \frac{m^2}{s} \right]\)
\(c \quad \text{Specific heat capacity in} \left[ \frac{kJ}{kg \cdot K} \right]\)
\(\rho \quad \text{Bulk density in} \left[ \frac{kg}{m^3} \right]\)
\(\lambda \quad \text{Thermal conductivity in} \left[ \frac{W}{m \cdot K} \right]\)
decreases with increasing moisture content
Washboard effect
Due to different thermal expansion of plywood layers.
Heartwood and Sapwood
Heartwood (Kernholz)
Heartwood, also called duramen, is dead, central wood of trees. Its cells usually contain tannins or other substances that make it dark in color and sometimes aromatic. Heartwood is mechanically strong, resistant to decay, and less easily penetrated by wood-preservative chemicals than other types of wood. One or more layers of living and functional sapwood cells are periodically converted to heartwood.
Sapwood (Splintholz)
You can typically identify the sapwood in a tree as it is lighter in color. This is new wood and is used to move water throughout the tree up to the leaves. Excess nutrients are often stored here as well. All wood in a tree is first formed as sapwood.
Phloem and Xylem
Phloem and xylem are two types of transport tissue in vascular plants, and they serve different functions.
Phloem
The main function of phloem is to transport organic nutrients, especially sucrose, a sugar produced by photosynthesis in the leaves, to all parts of the plant where needed. This process is known as translocation.
Phloem tissue is composed of several different kinds of cells, including sieve tube elements and companion cells. Unlike xylem, the cells in phloem are alive at maturity.
Xylem
The primary function of xylem is to transport water and dissolved minerals from the roots to the rest of the plant, including the stems and leaves.
Xylem tissue is composed of elongated cells that are usually dead and empty of cell contents at maturity. This structure allows them to act like tiny tubes for transporting water and nutrients. The walls of xylem cells are thickened with lignin, a compound that gives the cells strength and prevents them from collapsing.
In trees, the bulk of the wood is made up of xylem tissue, which also provides structural support.
Sap
Sap is a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant.
Saps may be broadly divided into two types:
- phloem sap
- watery solution of hormones, minerals and other nutrients
- movement from roots towards the leaves
- xylem sap
- watery solution of sugars, hormones and minerals
- movement from leaves to where sugars are used or stored (sugar sinks)
Cambium
Cambium is a thin layer of plant tissue inbetween the xylem and phloem.
Its primary role is to facilitate plant growth. It produces new phloem towards the outside and new xylem to the inside.
Tracheid
A tracheid is a long and tapered lignified cell in the xylem of vascular plants.
The main functions of tracheid cells are to transport water and inorganic salts, and to provide structural support for trees.
Tracheids are dead at functional maturity and do not have a protoplast.
Transpiration
Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers.
Transpiration occurs through the stomatal apertures, and can be thought of as a necessary "cost" associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots.
The rate of transpiration is regulated by the plant's stomata, tiny pores on the leaf surface that open and close to allow the exchange of gases and water vapor between the plant and the atmosphere.
Mass flow of liquid water from the roots to the leaves is driven in part by capillary action, but primarily driven by water potential differences.
Cohesion-tension theory
The cohesion-tension theory explains how leaves pull water through the xylem. Water molecules stick together or exhibit cohesion. As a water molecule evaporates from the surface of the leaf, it pulls on the adjacent water molecule, creating a continuous flow of water through the plant.
Primary and secondary growth
In botany, secondary growth (cambial growth) is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate, and gives rise to primary tissue.
Cell wall
Wood cells, also known as tracheids or fibers, have a primary and secondary cell wall.
The primary cell wall is thin and flexible, and it expands as the cell grows. It's mainly composed of cellulose, hemicellulose, pectin, and proteins.
The secondary cell wall forms after the cell has completed its growth and is considerably thicker than the primary wall. It provides rigidity and strength to the cell and is primarily responsible for the mechanical properties of the wood. It's primarily composed of cellulose, hemicellulose, and lignin.
Cellulose
Composed of long chains of glucose molecules. These chains bundle together to form microfibrils. Cellulose microfibrils provide the main structural support in the cell wall.
Hemicellulose
Made up of various different sugar monomers. Acts like a filler between cellulose microfibrils, helping to bind them together.
Pectin
Complex polysaccharides rich in galacturonic acid. Pectin is the principal component of the middle lamella and is responsible for the jelly-like matrix in which the cellulose and hemicellulose are embedded.
Lignin
A complex, highly branched polymer often associated with the secondary cell walls of woody plants. Being rather hydrophobic, it waterproofs the cell walls of the water-conducting cells in xylem, which helps plants transport water more efficiently.
Proteins
There are many different proteins in the cell wall with a variety of functions. Some are structural proteins that contribute to the strength and elasticity of the cell wall, while others play roles in cell growth and expansion, defense against pathogens, or communication between cells.
Cell types
Parenchyma Cells: These cells have thin and flexible primary cell walls. They are involved in metabolic functions, storage, and tissue regeneration.
Collenchyma Cells: These cells have thickened primary cell walls that provide support for the plant, particularly in regions of active growth.
Sclerenchyma Cells: These cells have thick secondary cell walls often reinforced with lignin, a complex organic polymer that provides rigidity. These cells provide the main structural support to the plant.
Xylem Cells: Tracheids and vessel elements, the main types of xylem cells, have thick secondary cell walls fortified with lignin. These cells, dead at maturity, form hollow tubes for water and nutrient transport.
Phloem Cells: The cell walls of sieve-tube elements in the phloem have sieve plates (areas with many small holes) that allow for the transport of sugars and other organic compounds.
Epidermal Cells: These cells form a protective layer on the plant surface and have a variety of cell wall adaptations, such as a waxy cuticle layer that prevents water loss
Wood and wood-based products
Wood-based products
Made of raw wood or solid wood by processing it to structures, particles, or fibers and subsequent assembly.
- glued laminated timber
- veneer laminates
- particleboards
- fibreboards
- composite panels
Solid wood
Made of raw wood by longitudinal or cross-sectional cut.
- round timber
- sawn timber
- veneer
Wood-based products
solid-wood products
- solid wood boards
- glued laminated timber
- cross-laminated timber
veneer-based products
- laminated veneer lumber (LVL)
- plywood
- parallel strand lumber (Parallam)
particle-based products
- particle board
- oriented strand board (OSB)
- laminated strand lumber LSL (extremely long chips compared to OSB)
- waferboard (weaker and less-stiff cousin of OSB, larger chips)
fibre-based products
- medium density fiberboard (MDF)
- porous fibreboard
- hard fiberboard
composite materials
- composite boards
- wood flooring panels
Solid wood and veneer-based products
veneer-based products
- veneer production by rotary cut
- control of the properties via the fiber direction in the layers
- Parallam --> gluing and compression to beam elements
- ski and snowboard cores
Wood utilization of wood-based products
sawn timber (40 - 50 %)
plywood (50 - 60 %)
OSB (80 - 85 %)
LSL (80 - 85 %)
MDF (87 - 90 %)
particle board (88 - 93 %)
Distinctions of fiber-based products
bulk density
- soft
- medium
- hard
- extra hard
cross-section structure
- single-layered
- multi-layered
- continuous
adhesive
- urea resin
- phenolic resin
- bitumen
- lignin
surface
- sanded
- coated
resistance
- moisture protected
- fungi-protected
- fire-resistant
formaldehyde emission
- very low
- low
- medium
- high
Distinctions of particle-based products
particle type/orientation
- top layer particles
- middle layer particles
- wafers
- flakes
cross-section structure
- single-shift
- three-layered
- multilayered
- continuous
- homogeneous cross section structure
bulk density
- low
- medium
- high
adhesive/binder
- urea resin
- phenolic resin
- melamine resin
- isocyanates
- cement
- gypsum
- tannins
formaldehyde emission
- very low
- low
- medium
- high
production process
- different press processes
surface
- sanded
- coated
resistance
- moisture-protected
- fungi-protected
- fire-resistant
Swelling of particle boards
swelling increases with density
thickness swelling of particle boards is significantly higher than that of solid wood
(spring back effect)
thickness swelling of wood-based products is largely irreversible
swelling of solid wood is reversible
Wood-based composite products
middle layer:
- solid wood
- with cavities
- particle boards
- foams
