CHEM-E2105
Wood and Wood Products
Mark Hughes
12th January 2016
Background to the course
• The aim of the course is to develop expertise in the
materials science of wood, bridging the gap between
fundamental aspects of fibre science and the applications of
wood
• You will learn about the anatomical, physical and mechanical
characteristics of wood that will affect the performance of
wood-based products and structures
• In addition, you will learn about how the key groups of
wood-based products are manufactured
• It is assumed that you have a solid foundation in wood
chemistry and ultrastructure but not specifically about wood
as a material
Learning outcomes
• knows the key anatomical features of wood and is able to differentiate
between softwood and hardwood and is able to identify several key
commercially important species from their microstructures
• is familiar with the anisotropic structure of wood and is able to describe
how the anatomical structure of wood affects its physical and
mechanical properties
• knows the states of water in wood and is able to describe how it affects
the mechanical and physical properties of wood
• is familiar with the relationship between cell wall density, bulk density
and void volume (porosity) and can apply this information to predict how
fluids may behave in wood
• is familiar with the thermal characteristics of wood, especially thermal
conductivity, heat capacity and diffusivity
Learning outcomes
• is familiar with the acoustic properties of wood and how this might
be utilized in non-destructive testing and construction
• is familiar with the electrical properties of wood
• is familiar with the combustion properties of wood and its fire
performance
• knows about the short-term mechanical properties of wood and how
structure/anatomy, density and moisture affect these
• is familiar with the long-term behavior of wood under static and
cyclical loading
• is able to describe the key steps in the manufacture of the major
wood products (solid wood, wood-based composites and engineered
wood)
Content
• Wood anatomy and structure
• Wood-water relationships
• Wood density and density-volume relationships, fluid flow in wood
• Thermal and acoustic properties of wood
• Short-term mechanical properties and structure-property
relationships
• Long-term mechanical properties
• Manufacture of wood products (solid wood, wood-based composites
and engineered wood products)
Structure
• Runs in Periods III & IV
• Two 2 hour sessions per week scheduled (lectures/laboratory work)
– Not all lecture ‘slots’ will necessarily be filled (please see
schedule)
• 5 credit course
• Combination of ‘formal’ lectures, laboratory work and own study
Lectures
#
1
2
3
4
Topic/activity
Content
Introduction
Information about the course and background, wood formation,
environmental factors, wood structure, basic terms and concepts
Wood structure
The anatomy of wood and relationship to properties
Mass-volume relationships
Bulk density, cell-wall density, porosity and fluid flow in wood
Wood-water relationships I
States of water in wood, measuring MC, FSP, sorption, EMC
Wood-water relationships II
Moisture buffering, heat of sorption, dimensional changes, effect
on mechanical and physical properties
Physical properties of wood
Thermal conductivity, heat capacity, diffusivity, electrical
conductivity, combustion and fire properties
Mechanics of wood I: Elastic and
strength properties
The orthotropic nature of wood, elastic properties of the wood cell
wall and wood, tensile, compression and shear, influence of
Mechanics of wood II: Fracture and
failure in wood
Toughness, cracks and crack-like defects, the nature of cracks,
fracture mechanics, interfaces as crack stoppers, energy
absorbing mechanisms
Mechanics of wood III: Creep, stress
relaxation and fatigue
Creep and stress relaxation, fatigue: viscoelasticity, mechanosorption, S-N curves etc.
Manufacture of solid wood products
Scanning, sawing, grading, drying
5
6
7
8
9
10
11
12
Manufacture of wood-based panels
Manufacture of veneer-based wood
products
Structure-property relationships, size reduction, drying , pressing
physics,
Plywood and LVL, soaking, peeling, drying, gluing, pressing and
properties
Schedule: period III
Date
Topic/activity
Content
12.1
Introduction
Information about the course and background, wood
formation, environmental factors, wood structure,
basic terms and concepts
13.1
No lecture
19.1
Wood structure
20.1
No lecture
26.1
Mass-volume relationships
27.1
Wood anatomy lab
2.2
Wood-water relationships I
States of water in wood, measuring MC, FSP, sorption,
EMC
3.2
Wood-water relationships II
Moisture buffering, heat of sorption, dimensional
changes, effect on mechanical and physical properties
9.2
Physical properties of wood
10.2
No lecture
The anatomy of wood and relationship to properties
Bulk density, cell-wall density, porosity and fluid flow in
wood
Thermal conductivity, heat capacity, diffusivity,
electrical conductivity, combustion and fire properties
Schedule: period III (updated 29.1.2016)
Date
12.1
Topic/activity
Introduction
Content
Information about the course and background, wood
formation, environmental factors, wood structure,
basic terms and concepts
13.1
19.1
Wood structure
The anatomy of wood and relationship to properties
20.1
26.1
27.1
2.2
Lecture cancelled
Lab cancelled
Mass-volume relationships
3.2
9.2
Wood anatomy lab
Wood-water relationships I
10.2
Wood-water relationships II
Bulk density, cell-wall density, porosity and fluid flow
in wood
States of water in wood, measuring MC, FSP,
sorption, EMC
Moisture buffering, heat of sorption, dimensional
changes, effect on mechanical and physical
properties
Schedule: period IV
Date
Topic/activity
Content
23.2
Mechanics of wood I: Elastic and
strength properties
The orthotropic nature of wood, elastic properties of the
wood cell wall and wood, tensile, compression and
shear, influence of
1.3
Mechanics of wood II: Fracture
and failure in wood
Toughness, cracks and crack-like defects, the nature of
cracks, fracture mechanics, interfaces as crack
stoppers, energy absorbing mechanisms
2.3
Wood mechanics: fracture
8.3
Mechanics of wood III: Creep,
stress relaxation and fatigue
Manufacture of solid wood
products
Manufacture of wood-based
panels
Creep and stress relaxation, fatigue: viscoelasticity,
mechanosorption, S-N curves etc.
Scanning, sawing, grading, drying
Manufacture of veneer-based
wood products
Wood composites
Plywood and LVL, soaking, peeling, drying, gluing,
pressing and properties
24.2
9.3
15.3
Structure-property relationships, size reduction, drying ,
pressing physics,
16.3
22.3
23.3
29.3
30.3
Schedule: period IV (updated 29.1.2016)
Date
23.2
Topic/activity
Physical properties of wood
24.2
Mechanics of wood I: Elastic
and strength properties
1.3
Mechanics of wood II: Fracture
and failure in wood
2.3
8.3
Wood mechanics: fracture
Mechanics of wood III: Creep,
stress relaxation and fatigue
9.3
Manufacture of solid wood
products
Manufacture of wood-based
panels
Scanning, sawing, grading, drying
Manufacture of veneer-based
wood products
Wood composites
Plywood and LVL, soaking, peeling, drying, gluing,
pressing and properties
15.3
16.3
22.3
23.3
29.3
30.3
Content
Thermal conductivity, heat capacity, diffusivity,
electrical conductivity, combustion and fire
properties
The orthotropic nature of wood, elastic properties of
the wood cell wall and wood, tensile, compression
and shear, influence of
Toughness, cracks and crack-like defects, the nature
of cracks, fracture mechanics, interfaces as crack
stoppers, energy absorbing mechanisms
Creep and stress relaxation, fatigue: viscoelasticity,
mechanosorption, S-N curves etc.
Structure-property relationships, size reduction,
drying , pressing physics,
…a bit more admin!....
• Information about the course, resources and
timetable can be found from MyCourses
• Slides accompanying the lectures will be available in
MyCourses
Some good text books and sources
• J.M. Dinwoodie, “Timber: Its nature and behaviour”
– Provides a good overview of many of the topics covered in this course
– E-version available through the Nelli portal:
http://otalib.aalto.fi/en/instructions/guides/electronic_materials/myilibrary/
(just type in the author’s name!)
• P.O. Kettunen, “Wood structure and properties”
– Materials science approach to wood, very detailed
• R. Bruce Hoadley, “Understanding wood: A craftsman’s guide to wood
technology”
– Good overview of wood
– Available through Google books
• J.E. Gordon, “The New Science of Strong Materials”
– Not specifically about wood, but a very good introduction to materials!
• Wood structure and properties / Wood Handbook: wood as an
engineering material (USDA Forest Products Laboratory)
– Can be downloaded at:
http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_i
d=100&header_id=p
– Good detail about a number of topics
Passing the course!
• 40% Exam
• 30% Labs (‘light’ reporting in pairs)
• 30% Literature-based report (individual):
– How wood anatomy affects mechanical properties
– The effect of moisture on the short-term mechanical
properties of wood
– Creep in timber
– The toughness of wood
– Moisture sorption in wood
– Fatigue in wood and wood-based materials
Wood and Wood Products
Wood throughout history
5000 year old Loch Tay crannog
(http://www.geograph.org.uk/photo/35551)
Merchant shipping in the 19th Century
(http://www.victorianweb.org/technology/ships/3.html)
Dugout canoe
(http://en.wikipedia.org/wiki/Dugout_(boat))
Two wood bow (Insulander 2002)
Contemporary use of wood
• Domestic dwellings
• Commercial buildings and
other structures
• Furniture
• Others….
What is wood (as a material)?
Polymer
• Chemical composition:
– Cellulose
– Hemicelluloses
– Lignin
•
•
•
•
Composite
Complex hierarchy
Macrostructure (mm to m)
– Growth rings
– Grain
– Knots
Microstructure (µm to mm)
– Wood cells
Ultrastructure (nm to µm)
– Cell wall hierarchy (lamellae)
– Microfibrils
Wood is a complex polymer matrix composite material
Wood structure
(Adapted from: Dinwoodie, 2001)
(Source: Society of Wood Science and Technology)
Plants versus materials
• When we speak of a material (especially in the
context of this course), we speak of a set of
properties that we, as humans, find desirable for our
purposes
• These may be not be the same set of properties that
are desirable (have evolved) in the plant!
• When we speak of wood, we must remember that
we use it in an environment it is not ‘designed’ for
• This change in environment leads to some of the
‘adverse’ phenomena associated with the
application of wood in many situations
http://wattsupwiththat.com/2008/04/08/seeing-the-woodfor-trees/
(Source: Society of Wood Science & Technology)
Wood products
Primary e.g.
• Round wood
• Sawnwood
• Wood-based panels
• Plywood
• Laminated Veneer Lumber (LVL)
• Particleboard (chipboard)
• Medium density fibreboard
(MDF)
• Oriented Strand Board (OSB)
• Softboard/hardboard
Secondary processed e.g.
• Laminated panel board
• Glue Laminated Timber (glulam)
• Composite “I” beams
• Coated wood and panels
• Pressure (preservative) treated
• Modified wood (chemical,
physical modification)
(©Katja Vahtikari)
Hösmärinpuisto koulu (©Jonna Silvo)
Hösmärinpuisto koulu (©Jonna Silvo)
Kuokkalan Kirkko (©Jonna Silvo)
Kärsämäen paanukirkko (©Jonna Silvo)
Construction in Vancouver (©Jonna Silvo)
Sneek bridge – the Netherlands (courtesy Accsys Technologies)
But where do wood products
come from?
• Wood is from trees!
• Where do trees come from?
• Trees are composed of a
range of organic compounds
that are ultimately
synthesized from
atmospheric carbon dioxide
and water using sunlight as
an energy source. This
process is known as
photosynthesis
• Carbon dioxide + water + light
energy → carbohydrate +
oxygen
Photosynthesis
• Photosynthesis is the process whereby light energy
is converted into chemical energy that can then be
used by the plant to fuel its metabolism
• The energy is stored in carbohydrates (molecules
containing C, H and O) such as glucose that form
the building blocks of plants and all organic matter
• Light energy is absorbed by proteins called,
reaction centres, that contain the green pigment
chlorophyll. These reaction centres are contained
in organelles that are most abundant in leaves
• Light (photons) is used in reactions to produce
NADPH (nicotinamide adenine dinucleotide
phosphate) and ATP (adenosine triphosphate),
which are subsequently converted in light
independent reactions (the Calvin cycle) into
carbohydrates, by incorporating atmospheric CO2
Tree growth
• Growth occurs in the vascular cambium which in which
living cells divide and differentiate outwards to form the
bark and inwards to form the wood. The cambium is a
lateral meristem – responsible for the increase in girth
• The apical meristem is responsible for increasing the
height
• Meristems are the tissues found in regions of the plant
where growth can take place
Tree types & characteristics
Basic characteristics of the tree:
• Gymnosperms (softwoods; conifers)
– Bear needles, which are usually evergreen
• Angiosperms (hardwoods; broadleaves; deciduous)
– Bear leaves (which are lost in the autumn in
temperate climates)
Tree structure
• The growth of a tree is a combination of genetics and
environmental factors
• Genes dictate species etc.
• Ecological factors influence growth. These include,
for example:
–
–
–
–
Climatic factors (temperature, rain, snow)
Soil
Location (stand / clearing)
External stresses (wind loading, frost)
The tree and timber from it
• A tree consists of:
– Roots
– Trunk
– Branches including needles/leaves
• We are mainly interested in the stem (trunk):
–
–
–
–
Support
Mechanical function
Optimised for its own purposes not ours!
This can present a conflict
Orientation
• The stem is pseudo-cylindrical (slightly tapered)
• Three directions:
– Longitudinal
– Radial
– Tangential
• Properties differ significantly in different directions – wood
can be regarded as an orthotropic material
The effect of orientation
(Source: Society of Wood Science & Technology)
Timber: Nature’s cellular
composite material
Structural levels
•
Gross structure of wood:
– Visible to the naked eye
– Heartwood/sapwood, growth rings, grain, knots
•
Microstructure of wood
– Visible under a light microscope
– Different cell types, morphology of cells
Macro- &
microstructure
THE FIBRE (CELL)
•
The cell wall
– Visible by electron microscopy (some features by optical
microscopy)
•
Chemical composition
– Spectroscopic & chemical techniques
•
Providing background to:
– Appearance
– Properties
– Behaviour
Ultrastructure &
chemistry
Literature and further reading
• Society of Wood Science and Technology:
http://www.swst.org/teach/set2/struct1.html
• Dinwoodie, J.M. (2001): Timber: Its Nature and Behaviour
• Insulander, R. (2002) The Two-Wood Bow, Acta Borealia, 19:1, 49-73,DOI:
10.1080/08003830215543
• Wilson, K. and White, D.J.B. (1986): The Anatomy of Wood: Its Diversity
and Variability