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

Spruces

Firs

Hemlocks

Cedars

Hardwoods Poplars

• Aspen

Birches

Oaks

Maples

Structure of trees

DefinitionsHeartwood: 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

Primary Wall

Secondary Wall:

S1 Layer:

S2 Layer

S3 Layer

Middle Lamella:

MicrofibrilAngle

SecondaryWall

PrimaryWall

S3S2S1

MiddleLamella

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

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

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: