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MECH 450 – Pulping and Papermaking Topic 2 - Natural Resources

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

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MECH 450 – Pulping and Papermaking Topic 2 - Natural Resources

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  1. MECH 450 – Pulping and Papermaking Topic 2 - Natural Resources James A. Olson, NiciDarychuk Pulp and Paper Centre, Department of Mechanical Engineering, University of British Columbia

  2. 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.

  3. Types of Trees • Two Types: • Gymnosperms (Naked seed) • Conifers • Softwoods • Angiosperms (Vessel – seed) • Deciduous • Hardwoods

  4. 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 Evolution of the two types

  5. Softwoods Douglas-fir Pines Spruces Firs Hemlocks Cedars Hardwoods Poplars Aspen Birches Oaks Maples What species are common in Canada?

  6. Structure of trees Definitions Heartwood: Sapwood: Juvenile Wood: Mature wood:

  7. Tree Cross Section Cambium: Outer Bark: Inner Bark (Phloem):

  8. Growth ring Annual ring: Earlywood: Latewood:

  9. Types of Cells

  10. Cell Types • Tracheids (Fibres): • Vessels: • Parenchyma: • Rays: constructed of parenchyma cells • Pits: Opening in cell walls to support radial movement of water and solutes

  11. Micrographs

  12. Different types of cells

  13. Primary Wall Secondary Wall: S1 Layer: S2 Layer S3 Layer Middle Lamella: Cell Structure

  14. 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 Fibrils

  15. 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 O B A HO HO O OH O OH OH HO O O HO HO E O OH C O OH OH Fiber HO O D O HO HO O OH Cellulose Molecule Chemical structure

  16. 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 Lignin

  17. 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

  18. Relative amounts through cell wall Middle Lamella: Cell Wall:

  19. 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.

  20. Properties of common fibres

  21. Non-Woods • Common papermaking non woods are:

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