Transcript MECH 450 – Pulping and Papermaking Topic 2

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
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.
Types of Trees
 Two Types:
 Gymnosperms (Naked seed)
 Conifers
 Softwoods
 Angiosperms (Vessel – seed)
 Deciduous
 Hardwoods
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
What species are common in Canada?
 Softwoods
 Douglas-fir
 Pines
 Hardwoods
 Poplars
• Aspen
 Spruces
 Birches
 Firs
 Oaks
 Hemlocks
 Maples
 Cedars
Structure of trees
Definitions
Heartwood:
Sapwood:
Juvenile Wood:
Mature wood:
Tree Cross Section
Cambium:
Outer Bark:
Inner Bark (Phloem):
Growth ring
Annual ring:
Earlywood:
Latewood:
Types of Cells
Cell Types
 Tracheids (Fibres):
 Vessels:
 Parenchyma:
 Rays: constructed of parenchyma cells
 Pits: Opening in cell walls to support radial
movement of water and solutes
Micrographs
Different types of cells
Cell Structure
Secondary
Wall
Microfibril
Angle
S3
S2
S1

Primary Wall

Secondary Wall:

S1 Layer:

S2 Layer

S3 Layer

Middle Lamella:
Middle
Lamella

Primary
Wall
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
Chemical structure


Cellulose

Glucose monomers

Primary wall 6000 units

Secondary 16000 units
O
Hemi-cellulose
A
HO
HO
O

Poly-saccharides

Branched polymers

B
HO
O
O
Eg, xylose, arabinose
E
Micro-fibrils

Crystals of cellulose

20 nm ~ 2000 cellulose
molecules
OH
OH
HO

OH
O
HO
O
C
OH
O
OH
OH
Fiber
HO
O
D
O
HO
HO
O
Cellulose Molecule
OH
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
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
Relative amounts through cell wall
Middle Lamella:
Cell Wall:
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.
Properties of common fibres
Non-Woods
 Common papermaking non woods are: