The Chemistry of Wood

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• The Chemistry of Wood
• Value Added Alternatives

Sally Krigstin Faculty of Forestry University
of Toronto
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Presentation Summary

• Structure of Wood
• Structure of wood cell
• Chemistry of wood
• Cellulose
• Hemicellulose
• Lignin
• Extractives
• Value-added products derived from chemical
  components

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Wood Structure
Softwoods
Hardwoods
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Cellular Structure

• Fibre diameter is 25-35 microns
• Cell wall is 5-10 microns thick
• Cell wall is composed of 3 layers
• Layers are made up of microfibrils
• Orientation of the microfibrils is specific for
  each layer

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Structure of a Microfibril
25-30 nm
Elementary Fibrils
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Cellulose

• Linear homopolymer composed of several thousand
  monomer units (ß-D-glucose) units linked end to
  end.
• Absence of branches allows the chains to come in
  close contact and bond to one another.
• 3 hydroxyl groups available on each glucose unit
• Many OH groups make it very hydrophilic
• Forms a very strong, rigid structure through
  lateral bonding of hydroxyl and oxygen.
• Crystalline regions and amorphous regions

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Hemicellulose (Polyoses)

• Group of heteropolymers.
• Softwoods (4 types) Hardwoods (2 types)
• Galactoglucomannan Glucoronoxylan
• Glucomannan Glucomannan
• Arabinoglucuronoxylan
• Arabinogalactan
• Molecule has shorter chain length than cellulose,
  branched.
• 150 to 200 monosaccharides
• Amorphous, strongly hydrophilic.
• Industrially classified as non-cellulosic
  polysaccharide that are soluble in alkaline
  media.

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Hemicellulose (Polyoses)

• Chains are composed of
• 6-C sugars glucose, galactose, mannose
• 5-C sugars xylose and arabinose
• Uronic and aldonic acids
• Hardwood Softwood
• Contain 30-35 25-30
• Types Xylans Galacto-glucomannans

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Lignin

• Lignin is a high molecular weight, amorphous
  polymer
• 3 dimensional structure
• made from several hundred phenyl propane units
  

Softwood Hardwood 25-33 19-28 Guaiacyl
Guaiacyl Syringyl
Benzyl ether Benzyl ester Phenyl glycosidic

• Acts as a binding agent to hold cells together.
• Impart rigidity in cell wall- strongly bonded.
• Very high energy content (26 MJ/kg versus 18
  MJ/kg)

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Extractives

• 2 to 15 of wood's dry weight
• Large variety of different compounds
• Non- structural component of wood
• Soluble in neutral solvents
• Contribute to color odour of wood
• Some substances are toxic or deterrent to
  bacteria, fungi and termites

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Chemical Composition of Wood
W. Birch
J. Pine

• Extractives
• 2-15
• Cellulose
• 40-50
• Polyoses
• 20-25
• Lignin
• 25-30

6 41 40 19
9 41 30 29
Elemental Composition 50 C, 6 H, 44 O and
lt0.1 N
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Historical Value

• Use of non-wood products from forests was
  practiced by indigenous people.

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Historical Value

• Early North American settlers fully utilized
  non-wood components.

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Extractives Conversion Strategies

• Extractives can be found in all parts of the tree
• Foliage
• Taxus important source of taxol
• Ginko bilobaalleviate symptoms associated with
  cognitive disorders such as dementia due to
  Alzheimer disease.

Fengel Wegener, 1984
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Extractives Conversion Strategies
Fengel Wegener, 1984
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Extractives

• Terpenes terpenoids
• Low molecular weight, volatile compounds
• Obtained by steam distillation.
• Hydrophobic
• Turpentine Rosin
• a-pinene, camphene abietic acid (resin acid)
• -clean scent -highly hydrophobic
• Use industrial solvent Use varnish,soap,laquer,
  inks, paper sizing, wax.

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Extractives

• Fats Waxes
• Low molecular weight, hydrophobic compounds
• Tall Oil
• Fatty Acids Oleic linoleic acids
• Use sizing paper, synthetic adhesives, surface
  coatings, paints, varnishes, synthesis of
  chemicals and pharmaceuticals

Weight loss
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Extractives

• Phenols
• By-products of lignin synthesis
• 4 types simple phenols, lignans, stilbenes,
  flavonoids.
• Use Natural tanning agent, pigments, dyes,
  phenol-formaldehydge resins

Catechin (Flavonoid) Anti-oxidant
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Taxol

• Bark of Pacific yew Taxus brevifolia.

• 1960s National Cancer Institute evaluated
  plants.
• Extracted and tested for cancer drug potential
• 1983 clinical studies
• 1988 active against Ovarian cancer
• 1992 FDA approval
• Forest Management strategies needed.
• 1993 Bristol Meyer found alternative source.
• 1.6 billion

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Cellulose Conversion Strategies
Cellulose
Fengel Wegener, 1984
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Cellulose Fibres Derivatives

• Biocomposites
• Cellulose Esters
• Cellulose Nitrate (celluloid)
• Cellulose Acetate
• Cellulose Ethers
• Carboxymethylcellulose (CMC)
• Hydroxyethylcellulose(HEC)
• Regenerated Cellulose
• Cellulose Xanthate (rayon, cellophane)
• Microcrystalline cellulose (MCC)

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Biocomposites Microfibrils

• Matrix and reinforcing material are obtained from
  renewable resources.
• Biodegradable
• Matrix polymer
• Bioplastics
• Example
• PLA (poly lactic acid)
• Starch, cellulose acetate
• Reinforcing agents
• Wood microfibrils
• Enhance strength and stiffness

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Dissolving Pulp

• Preparation
• Acidic sulfite
• Prehydrolysis Kraft
• Can use both hardwood softwoods
• Yield is very low (30-40)
• Composition is 92-96 cellulose.

• St. Anne-Nackawic Pulp Co. Ltd.
• 30 million investment
• Export to India for processing

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Cellulose Nitrate

• One of the first synthetic polymers
• Reaction product of high purity cellulose and
  nitric acid.
• Properties
• Ignites easily
• Moldable

Cellulose
Nitric Acid
Cellulose nitrate
Camphor
Celluloid
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Cellulose Nitrate

• Uses
• Leather finishes
• Printing ink additives
• Lacquers and varnishes
• Molded products
• Gun cotton
• Dental plates

• Invented in 1862
• Substitute for ivory, tortoiseshell.
• Very small industry today (fire hazard)

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Cellulose Acetate

• Reaction product of high purity cellulose and
  acetic anhydride.
• Forms esters with acetate ions
• Properties
• Lowers the hydrophilic tendency
• Breathable
• Difficult to ignite
• Tough
• Transparent
• Moldable
• High impact resistance

Acetyl groups
Cellulose
Acetic anhydride
Cellulose triacetate (diacetate)
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Cellulose Acetate

• Uses
• Airplane dope
• Used in lacquers and coatings
• Biotechnical applications (filters)
• Spun into fibre for use in textile industry
• Cast into films (protective film on LCDs)
• Molded into products
• Industrial leaders
• Daicel Chemical Industries
• Celanese Corporation

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Cellulose Ethers

• Reaction of alkyl chlorides with alkali cellulose
• Methylcellulose (MC)
• Ethylcellulose (EC)
• Carboxymethylcellulose (CMC)
• Hydroxyethylcellulose (HEC)
• Cyanoethylcellullose

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Carboxymethylcellulose (CMC)

• Reaction of alkali cellulose (swollen)
  chloroacetic acid
• Properties
• Solubility in cold water
• Depends on degree of substitution
• High viscosity
• Not toxic and generally non-allergenic

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CMC

• Uses
• Detergents, soaps
• Food products (especially dietetic foods and ice
  cream)
• Textile manufacturing (sizing)
• Coating additive for paper and paper board
• Drilling muds, water based paints,
• Pharmaceuticals, cosmetics (toothpaste,
  laxatives, lubricant)

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Cellulose Xanthate (Rayon, Cellophane)

• Regenerated cellulose made from dissolving pulp.
• Alkali cellulose
• Carbon disulphide
• Cell-OCS2- Na
• Properties
• Highly absorbent
• Soft and comfortable
• Easy to dye
• Drapes well

Figure 1 Process of manufacture of viscose
rayon fiber
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Cellulose Xanthate (Rayon)

• Uses
• Textile filament
• High performance tire cord
• 1930-40s replaced cotton for undergarments,
  stockings
• Cellophane (sheets, tapes)
• 1960 Dupont produced last rayon textile yarn
• Industry Leaders
• Lenzing Modal
• E. I. du Pont de Nemours and Company

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Microcrystalline Cellulose

• Produced by isolating the crystalline regions of
  cellulose by acid hydrolysis of high purity pulp
• amorphous regions are structural defects
• 250 glucose molecule chain
• Properties
• Physiologically inert
• highly absorptive
• insoluble in water
• Uses
• Pharmaceutical tablets
• Compacts easily and carries the active medicinal
  ingredient

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Cellulose Conversion Strategies
Cellulose

• Hydrolysis
• Mineral acids
• Autohydrolysis
• Micro-organisms (or enzyme systems)
• Difficulties
• Accessibility to cellulose (lignin
  hemicellulose)
• Crystallinity - large enzyme molecules.

Fengel Wegener, 1984
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Pre-treatments
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Cellulose Conversion Strategies
Cellulose
Fengel Wegener, 1984
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Polyose Conversion Strategies
Polyoses
Fengel Wegener, 1984
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Autohydrolysis of Wood Polysaccharides

• Arabinose
• Xylose
• Higher molecular weight xylooligomers
• Acidic oligosaccharides
• Glucose
• Cellobiose
• Furfural
• Hydroxymethylfurfural
• Levulinic acid
• furan

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Lignin Conversion Strategies
Lignin
Fengel Wegener, 1984
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Biomass Conversion Strategies
Wood Biomass
Fengel Wegener, 1984
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Conclusion

• I never knew these things came from wood

Acids
Dyes
Explosives
Gas
Animal Fodder
Fabrics
Plastics
Protein supplement
Glues
Emulsifiers
Vitamins
Resins
Food additives
Pharmaceuticals
Liquid Fuels
Essential Oils
Sugars
Toys
Diapers
Furniture
Dietary fibre
films
Filter tips
membranes
Dust control