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 m 3  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 m 3  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 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  Primary Wall  Secondary Wall:  S1 Layer:  S2 Layer  S3 Layer  Middle Lamella:

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. 

Chemical structure  Cellulose  Glucose monomers  Primary wall 6000 units  Secondary 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: