MECH 450 – Pulping and Papermaking Topic 2 - Natural Resources
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Transcript of MECH 450 – Pulping and Papermaking Topic 2 - Natural Resources
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MECH 450 – Pulping and Papermaking Topic 2 - Natural Resources
James A. Olson, Nici Darychuk
Pulp and Paper Centre, Department of Mechanical Engineering, University of British Columbia
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Forests - Overview
27% of land mass on Earth is forested
Annual world harvest is 3.5 B m3
50% fuel
33% wood
16% Pulp and Paper
Plantations: 6% of annual harvest
23% of Pulp and Paper
Canada’s annual harvest is 60 M m3 10% of worlds harvest
To support a 1.6% population increase requires forest the size of
BC. Solution is plantations.
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Types of Trees
Two Types:
Gymnosperms (Naked seed) Conifers
Softwoods
Angiosperms (Vessel – seed) Deciduous
Hardwoods
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Evolution of the two types
Softwoods are simpler and older 300 M years ago
Hardwoods are more complex and recent Angiosperm plants 160 M years ago
Hardwood trees widespread 100 M years ago
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What species are common in Canada?
Softwoods Douglas-fir
Pines
Spruces
Firs
Hemlocks
Cedars
Hardwoods Poplars
• Aspen
Birches
Oaks
Maples
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Structure of trees
DefinitionsHeartwood: Sapwood: Juvenile Wood:Mature wood:
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Tree Cross Section
Cambium: Outer Bark: Inner Bark (Phloem):
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Growth ring
Annual ring:
Earlywood:
Latewood:
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Types of Cells
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Cell Types
Tracheids (Fibres):
Vessels:
Parenchyma:
Rays: constructed of parenchyma cells
Pits: Opening in cell walls to support radial
movement of water and solutes
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Micrographs
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Different types of cells
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Cell Structure
Primary Wall
Secondary Wall:
S1 Layer:
S2 Layer
S3 Layer
Middle Lamella:
MicrofibrilAngle
SecondaryWall
PrimaryWall
S3S2S1
MiddleLamella
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Fibrils
Fibrils are crystals of
cellulose. The angle at
which the fibrils make
with respect to the axis
in the secondary wall
significantly affects the
strength of the fibre.
q
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Chemical structure
OH
O
HO
O
O
O
OH
OH
OH
OH
O
O
O
O
O
OH
OH
HOHO
HO
HO
HOHO
HO
E
D
O
Cellulose Molecule
B
C
A
Fiber
Cellulose Glucose monomers Primary wall 6000 units Secondary 16000 units
Hemi-cellulose Poly-saccharides Branched polymers Eg, xylose, arabinose
Micro-fibrils Crystals of cellulose 20 nm ~ 2000 cellulose
molecules
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Lignin
Complex phenylpropanoid polymer which is deposited in plant cell
walls
Thermo plastic polymer
Adds rigidity and strength to cell walls and provides barriers to
diffusion and infection
Exists as a single molecule within trees
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Extractives Miscellaneous components that are soluble in acetone are called
extractives Include sugars, amino acids, simple fats and carboxylic acids Mostly they are intermediate compounds from metabolic processes Found in sapwood and inner bark (live part : Phloem) Dissolve rapidly in alkaline (kraft) pulping. Can break down pulping chemicals requiring a higher concentration May also negatively affect the colour, bleachability and wettability of
pulps
Diminish transport of pulping chemicals into the wood
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Relative amounts through cell wall
Middle Lamella:
Cell Wall:
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Variation of raw material (Fibres)
This is one of the largest challenges facing BC industry
Factors affecting variation: Between species (BC has 27 species / subspecies of pine trees)
Between tree variations• Widespread climate variation: Northern / Southern / Coastal / Interior• Local growing conditions (alpine / valley)• Genetic variation
Between ring variations: Juvenile / mature wood, changing climate Within rings: Early wood / latewood
Compare this against mono-clonal plantations in a uniform, southern growing season.
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Properties of common fibres
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Non-Woods
Common papermaking non woods are: