1. Puu-0.3240 Wood Products: Properties & Performance
Wood-based composites: non-structural
(“wood-based panels”)
27th January 2014

2. Contents What is a wood-based composite? Wood-based composite products
Why wood-based composites?
Market size
Drivers
Products & characteristics
Manufacture & structure
Product properties & performance
Value adding
Applications

3. What is a wood-based composite?
A material composed of wood particles, ranging in size from fibres to lamellae (including particles, strands and veneers), bonded together with an adhesive.
Typically panel products
Properties range from “non/semi- structural” to “structural”
Typically used in the construction and furniture industries
Products manufactured in many regions Worldwide
Around 40 million cubic metres produced in European Union annually

4. What is a wood-based composite?
Broadly defined as either structural or non-structural
Structural wood-based composites include products such as:
Glue laminated lumber (glulam)
Laminated veneer lumber (LVL)
Plywood
Oriented Strand Board (OSB)
And others…..
Whereas non-structural wood-based composites include:
Particleboard (“chipboard”)
Medium density fibreboard (MDF)
Soft-board & hardboard

5. LVL
Sawnwood
Gluelam
LOG
Plywood
MDF
OSB
Particleboard

6. Why wood-based composites?

7. Drivers: technical
Wood available only in limited shapes and sizes – panel products can be made to a range of dimensions
Create new properties in the material. Wood is highly anisotropic, wood-based composites can be “engineered” to have tailored properties
Improve dimensional stability (e.g. plywood)
Improve machining properties (e.g. MDF)
Reduce variability in properties by removing or randomising defects
Visual improvement through lamination; a greater range of finishes possible
Good strength/stiffness to weight ratios – good in applications and reduces transportation costs

8. Drivers: commercial
Utilise small dimension wood and poor quality material
Effective use of “waste” resources (sawdust, shavings, the “urban forest”)
Use non-wood lignocellulosic resources
Value added opportunities

9. General issues
Raw material; trends towards poorer quality, fast grown species
Competition for the forest resource from energy and other uses (e.g. recreation)
Good way of utilising recycled or reclaimed wood
Non-wood raw materials being used (cereal straws)
Wheat straw, kenaf etc
Formaldehyde from the binder (adhesive): a big issue
Volatile Organic Compounds (VOCs) in general

10. Consumption of wood-based composites

11. (Source: UNECE Forest Products Statistics: http://www. unece

12. Non-structural wood-based composites

13. Particleboard: characteristics
Largest production volume worldwide
Manufactured from particles of wood (or non-wood resources) that have been “chipped” from larger pieces of wood
Chips typically have dimensions of several millimetres or 10s of millimetres. Core material of coarser material (larger chips)
Usually bonded with Urea Formaldehyde (UF) resins, or resins “fortified” with melamine to make them more moisture resistant (MUF)
Mainly used for furniture, worktops, DIY (Do-it-yourself), flooring, roofing and general construction
Particleboard density typically in the region of kg/m3

14. Particleboard (chipboard)
Particleboard arose due to scarcity of veneer and the desire to utilise waste materials such as sawdust and planer shavings etc
It was first produced in Germany in the 1940s
Rapid growth followed
Switch to virgin wood for the manufacture of chips so as to give better performance
Ironically, there has been a switch back to recovered & waste wood with the desire to reduce waste and improve resource efficiency. Now, a significant amount of raw material is waste, or recovered wood (e.g. Kronospan PB mill in Chrik, N .Wales, U.K. uses a high proportion of recycled wood in its manufacture)
Probably no coincidence that production of PB and other wood-based composites arose at the time when waterproof glues such as urea formaldehyde and phenol formaldehyde became widely available

15. Environmental credentials
“Kronospan chipboard comprises 70% recycled fibre and 30% virgin FSC traceable timber – diverting 300,000 tonnes of waste from landfill per year. The product has also been given a carbon-positive award by The Blue Green Carbon Company. Our chipboard exceeds all the relevant UK and European standards; we manufacture via a quality system accredited to BS EN ISO 9002:2000; all Kronospan chipboard is independently certified as low formaldehyde, meeting the European E1 standard”
Kronospan corporate literature (

16. Chipboard

17. Structure of particleboard
Particles of mm dimensions
Typically 3 layers – surface or face material of fine particles
Density profile developed during manufacture for improved properties in bending and a harder surface

18. Applications for particleboard
Examples include: general building work, joinery, upholstered furniture, furniture carcass, veneering, foiling.
Application brochure

19. MDF (LDF and HDF)
MDF, LDF (Low Density Fibreboard) and HDF (High Density Fibreboard) are dry-formed fibre boards (as distinct from hardboard)
It is a relatively “new” product, with significant growth since the 1980’s
Manufactured from wood fibres that have been produced in a pressurised refining process (TMP of CTMP)
Wood fibres are typically 1-3 mm long and 20 µm in diameter
Usually bonded with UF or MDI (methylene diphenyl diisocyanate) resins
Produces a very “fine-scale” and homogeneous product, suitable for a variety of applications
Can be worked, turned and laminated – used for furniture, fittings, partitions, wall-linings, mouldings, flooring and general construction

20. MDF: characteristics MDF – Medium Density Fibreboard
Average density: 700 – 800 kgm-3 (typical target 780 kgm-3)
Core density: 600 – 700 kgm-3
Face density: 1000 – 1100 kgm-3
Generic term for a range of dry formed fibreboards all produced in a similar way:
HDF: Above 800 kgm-3
LDF: Below 650 kgm-3
ULDF: Below 550 kgm-3
Produced in a range of thicknesses from “thin” (<2 mm) up to 60 mm

21. Medium Density Fibreboard
(Source: Emeri Enterprise Co.,Ltd.)

22. MDF
First made when fibre produced for wet formed hardboard was processed as particleboard
Good machining and strength properties ensured that MDF rapidly became popular
Technical developments such as “blowline blending” in the 1980’s spurred production
Competition with particleboard manufacture has led to developments in both sectors

23. Other wood-based panels
Other fibre boards
Insulation boards (softboard)
Hardboard
Cement bonded boards

24. Properties & performance of wood-based panels

25. How are wood-based composites typically made?
Wood particles, an adhesive (and additives such as wax) are mixed together and pressed together to consolidate
Wood raw material prepared (e.g. debarking)
Converted (size reduction) into veneers, strands, chips or fibres
Dried
Gluing (typically with Urea Formaldehyde or Phenol Formaldehyde) and application of additives
Forming or lay-up
Hot pressing to compact the particles together and cure the resin
Finishing and value adding

26. Structure, properties & performance
Wood-based composites are heterogeneous materials, in other words they are composites
Their properties are affected by:
Raw material characteristics
Strength, chemical composition, density
Interaction between particles
Particle to particle bonding
Structural organisation of constituents
Size an shape of the particles
Orientation of particles
Packing
Relative proportions of the constituents
Process

27. Basic properties
Particles & resin

28. Ideal properties of a particle
What are the requirements for the particle?
WBCs needs to support mechanical loads. Loads on the board are transferred via the resin bonds to the individual particles (by analogy with synthetic composites: the particle is the “reinforcement” and the resin forms the “matrix”)
Ideally, therefore, the particles should:
Be inherently strong, stiff and free of defects to sustain mechanical loads without breaking
Possess a suitable geometry (size & shape) for good contact with neighbouring particles so as to promote effective load transfer
Have surface characteristics that are compatible with resin binders for a strong glue-line bond or “interface”

29. Particle Inherent properties: Geometry: Surface:
Largely controlled by raw material (e.g. species, tissue), but influenced by processing
Ultimately depends on chemistry and ultrastructure
Geometry:
Controlled by processing and the type of raw material used
High L/W ratio preferable (e.g. promotes multiple numerous bonding opportunities)
Surface:
Largely influenced by raw material and processing

30. Resin
Sufficient cohesive strength to transfer loads from particle to particle
Sufficiently flexible to absorb some movement between particles
Sufficiently compatible with the particle surface to form a good bond - adhesion
Able to wet (“spread”) over the particle for good distribution
Retention of properties under adverse conditions

31. Interaction between constituents
Interface, microstructure & micromechanics

32. Bonding
Stress transfer between resin and particles takes place across the interface (boundary) or interphase (boundary zone) between the two
Model:
Strong enough to transmit stresses
Durable so as not to break down under adverse environmental conditions
Development of interface or interphase depends upon
Surface characteristics of particle
Resin properties

33. Ideal (micro)structure
Resin forms “bridges” between particles
More bonds promote improved stress transfer (particle geometry)
High aspect ratio particles
Low aspect ratio particles
Frequent particle-particle bonding
Fewer particle-particle bonds

34. Factors affecting properties and performance

35. Resin distribution Resin distribution on particle – resin droplet size
Large number of small resin bonds versus small number of large bonds

36. Compaction & bond geometry
Compaction to promote
particle-particle contact
Deformation in particle increases
area for bonding

37. Structure
Alignment, packing arrangement and relative proportions of constituents

38. Particle orientation
Introducing a preferred orientation to the particles alters the elastic & strength properties of the panel

39. Particle packing arrangement and density
Packing arrangement influenced by the size, shape and properties of the particles
Good packing promotes efficient use of material

40. Panel properties
Panel products are frequently used in situations where good flexural or shear properties are needed
Panel flexural stiffness properties are proportional to density
Panel flexural stiffness also affected by board thickness
Make panels thicker or denser…..

41. Through thickness density profile
Average MDF density in the range 500 to 800 kg/m3. Typically around 750 kg/m3
“High” density surface (~1100 kg/m3)
“Low” density core (~700 kg/m3)

42. How does this relate to panel products?
High aspect ratio strands are used in OSB to promote flexural properties
The surface of MDF fibre important in the development of panel properties. Surface properties largely controlled by refining process
Resin distribution on fibre, particles and strands, important for the development of properties
Veneers in plywood and laminated veneer lumber are oriented to maximise certain mechanical properties
Development of the through thickness (vertical) density profile important for panel properties

43. Properties & standards
Main physical tests:
Modulus or elasticity (MOE)/modulus of rigidity (MOR)
Thickness swell (2h and 24 h)
Internal bond strength (IBS)
(Transverse tensile strength)
Main QA test made on panel boards
Formaldehyde emissions
Measures of:
Adhesive bond strength
Panel stiffness and strength
Sensitivity to moisture

44. Resources Manufacturers:
Kronospan
Egger (
Norboard (
European Panels Federation (
Wood-based Panels: An introduction for specialists
Wood-based panels international