CHEM-E2105. Wood and Wood Products

Transcription

1 CHEM-E2105 Wood and Wood Products Mark Hughes 10 th January 2017

2 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

3 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

4 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)

5 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)

6 Structure Runs in Periods III & IV Two 2 hour sessions per week scheduled (lectures/laboratory work), but not all lecture slots will necessarily be filled (please see schedule) 5 credit course Combination of formal lectures, laboratory work and own study

7 Lectures # Topic/activity Content 1 Information about the course and background, wood formation, Introduction environmental factors, wood structure, basic terms and concepts 2 Wood structure The anatomy of wood and relationship to properties Mass-volume relationships Wood-water relationships I Wood-water relationships II Physical properties of wood Mechanics of wood I: Elastic and strength properties Mechanics of wood II: Fracture and failure in wood 9 Mechanics of wood III: Creep, stress relaxation and fatigue Manufacture of solid wood products Manufacture of wood-based panels 12 Manufacture of veneer-based wood products 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 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. Scanning, sawing, grading, drying Structure-property relationships, size reduction, drying, pressing physics, Plywood and LVL, soaking, peeling, drying, gluing, pressing and properties

8 Schedule: period III Date Topic/activity Content 10.1 Lecture: introduction Information about the course and background, wood formation, environmental factors, wood structure, basic terms and concepts 13.1 NO LECTURE 17.1 Lecture: wood structure The anatomy of wood and relationship to properties 20.1 NO LECTURE 24.1 Lecture: mass-volume relationships 27.1 Lab: wood anatomy 31.1 Lecture: wood-water relationships I 3.2 Lecture: wood-water relationships II 7.2 Lecture: mechanics of wood I - elastic and strength properties 10.2 Lecture: mechanics of wood II - fracture and failure in wood Bulk density, cell-wall density, porosity and fluid flow in wood States of water in wood; moisture content; fibre saturation point; sorption; equilibrium moisture content Moisture buffering; heat of sorption; dimensional changes; effect on mechanical and physical properties The orthotropic nature of wood; elastic properties of the wood cell wall and wood; tensile, compressive and shear properties Toughness, cracks and crack-like defects, the nature of cracks, fracture mechanics, interfaces as crack stoppers, energy absorbing mechanisms

9 Schedule: period IV Date Topic/activity Content 21.2 NO LECTURE 22.2 NO LECTURE 28.2 Lecture: mechanics of wood III - creep, stress relaxation and fatigue 1.3 NO LECTURE 7.3 Lab: wood mechanics - fracture Creep and stress relaxation, fatigue: viscoelasticity, mechanosorption, S-N curves etc. 8.3 Lecture: manufacture of solid wood products 14.3 Lecture: manufacture of woodbased panels 15.3 Self-study: manufacture of veneer-based wood products Scanning, sawing, grading, drying Structure-property relationships, size reduction, drying, pressing physics Plywood and LVL, soaking, peeling, drying, gluing, pressing, properties and applications 21.3 NO LECTURE 22.3 NO LECTURE 28.3 NO LECTURE 29.3 Revision and feedback Review of topics covered during the course, exam preparation and feedback

10 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

11 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: (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: d=100&header_id=p Good detail about a number of topics

12 Passing the course! 35% Exam 20% Labs ( light reporting in pairs) 45% Literature-based report (individual). Pick a topic: How wood anatomy affects its mechanical properties The effect of moisture on the short-term mechanical properties of wood Mechanosorptive creep in timber structures The toughness of wood Moisture sorption in wood Moisture transport in wood Fatigue in wood and wood-based materials Drying of sawn timber Stress grading sawn timber The use of wood in low carbon construction How wood can affect the indoor relative humidity of a building The physics of hot-pressing Heat of sorption of wood.other? If you wish to propose another topic, please feel free to do so!

13 Literature-based report Up to around 10 pages of text (quality rather than quantity!) Feel free to use illustrations/images/figures Base your report on the literature Prioritise scientific literature over other sources (this is to be a piece of scientific writing!) Please feel free to consult with me as much as you need to Grading will be on the basis of: Defining the scope and objectives Content and depth of the report Structure and clarity Use of literature (including referencing etc.)

14 Wood and Wood Products

15 Wood throughout history 5000 year old Loch Tay crannog ( Merchant shipping in the 19 th Century ( Dugout canoe ( Two wood bow (Insulander 2002)

16 Contemporary use of wood Domestic dwellings Commercial buildings and other structures Furniture Others.

17 Is wood a hi-tech material? Wood has been used to build aeroplanes! Howard Hughes Spruce Goose

18 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

19 Wood structure (Source: Society of Wood Science and Technology) (Adapted from: Dinwoodie, 2001)

20 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

21 (Source: Society of Wood Science & Technology)

22 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)

23 ? LOG

24 ( Katja Vahtikari)

25 Hösmärinpuisto koulu ( Jonna Silvo)

26 Hösmärinpuisto koulu ( Jonna Silvo)

27 Kuokkalan Kirkko ( Jonna Silvo)

28 Kärsämäen paanukirkko ( Jonna Silvo)

29 Construction in Vancouver ( Jonna Silvo)

30 Bridport House, Hackney, London, UK Multi storey CLT construction

31 Sneek bridge the Netherlands

32 But where do wood products come from?

33 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

34 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 CO 2

35 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

36 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)

37 Softwoods Spruce Pine

38 Hardwoods Birch Oak Maple

39 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)

40 Environmental factors Snow load Wind load

41 Environmental factors Forest stand Clearing

42 Environmental factors Woodland Park

43 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

44 Stem structure

45 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

46 The effect of orientation (Source: Society of Wood Science & Technology)

47 Timber: Nature s cellular composite material

48 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 THE FIBRE (CELL) The cell wall Visible by electron microscopy (some features by optical microscopy) Chemical composition Spectroscopic & chemical techniques Macro- & microstructure Ultrastructure & chemistry Providing background to: Appearance Properties Behaviour

49 Gross structure of wood

50 Gross structure of wood Bark, pith, heartwood, sapwood Growth rings Growth features (defects, usually in wood products): e.g. knots, grain angle

51 Heartwood and sapwood Heartwood usually darker in colour (extractives), generally more durable Also gums and resins Sapwood lighter in colour, often perishable (Source: Society of Wood Science and Technology)

52 Extractives in heartwood Darkening of timber heartwood is caused by extractives. Different compounds (that are extractable by organic solvents). They include: Lipids Terpenoids Phenolic compounds Extractives have an effect on: Colour Durability (e.g. pine heartwood much more durable than sapwood) Can also affect gluing etc.

53 Growth rings

54 Growth rings Width varies according to ring age and external conditions The width of a growth ring in Finland is an average of 1.5 to 2 mm, however: Variation is great: Pine mm Spruce mm Birch mm Composed of earlywood and latewood (springwood/summerwood)

55 Earlywood and latewood Sometimes referred to a springwood and summerwood Earlywood lighter in colour as it is less dense than the darker latewood

56 Earlywood/latewood proportions Wood stronger the more latewood it contains (Strong relationship between density and strength of wood) Strength etc. qualities can be determined according to the relative share of latewood Pine 25% (variation %) Spruce 15% (variation %) latewood

57 Differences between earlywood and latewood Share of latewood depends on a) ecological factors & b) species As growth decelerates latewood percentage grows A warm autumn increases the latewood percentage A drought in the autumn results in a lower proportion of latewood The relative and absolute share of latewood is greatest at the base of the tree Volume weight (pine): Earlywood kg/m 3 Latewood kg/m 3

58 Knots

59 Knots Live (or tight) knot Dead (or lose) knot (Source: Wilson & White, 1986)

60 Grain angle (spiral grain) ( ( rain.jpg)

61 Grain angle (spiral grain) ( ( rain.jpg)

62 Grain angle (spiral grain) ( ( rain.jpg)

63 Grain angle (spiral grain) ( ( rain.jpg)

64 Summary Hierarchical structure at macroscopic and microscopic levels Anatomy differs between softwood and hardwoods Cell types and functions differ between hardwoods and softwoods Many natural defects that affect wood s properties

65 Literature and further reading Society of Wood Science and Technology: Dinwoodie, J.M. (2001): Timber: Its Nature and Behaviour Insulander, R. (2002) The Two-Wood Bow, Acta Borealia, 19:1, 49-73,DOI: / Wilson, K. and White, D.J.B. (1986): The Anatomy of Wood: Its Diversity and Variability