LECTURE 5 - WOOD AND WOOD PRODUCTS

Hardwoods

- Wood from angiosperms, broad-leaved and deciduous trees.
- water-conducting vessels

Softwoods

- Wood from gymnosperms, cone-bearing trees like conifers.
- use trachied

Hardwood and Softwood

don't directly
relate to the wood's hardness, as some hardwoods are softer than
softwoods and vice versa.

3 Major polymeric materials of wood

cellulose, hemicelluloses, lignin

Cellulose

- Main structural component, 42% of dry wood weight.
- high degree of polymerization (approximately 14,000).

Hemicelluloses

- Polysaccharides acting as matrix material in wood.
- lower degree of polymerization (100 to 200).

Lignin

Phenolic polymer providing mechanical strength in wood.

micelles or microcrystallites

form longer threadlike structures called microfibrils, which

exhibit a crystalline-amorphous character.

Final fiber cell wall

consists of layers of microfibrils
aligned in various directions.

Middle Lamella

primarily composed of
lignin, holds the fibers together.

Longer fibers from softwoods

used for tear-resistant products

Shorter hardwood fibers

enhance opacity and printability in paper

Microfibrils

Threadlike structures formed by cellulose polymers.

Pulp and Paper Industry

Major global economy sector since mid-19th century.

T'sai Lun

- Inventor of paper from lignocellulosic fibers in 105 AD.
- used materials like hemp rags and bamboo
- Europe and US

US pulp and paper industry

shown cconstant growth with new uses continually being found for paper

Per Capita Consumption of Paper

Increased with rising living standards.

In 1988, the US produced 69.5 million tons of paper and
paperboard

primarily from wood pulp (55.5 million tons) and
recycled wastepaper (15 million tons).

Georgia and Washington

Top US states for pulp production.

Raw Materials

Over 95% of raw materials for pulp and paper come from wood,
with small amounts from rags and agricultural residues.

Wood Preparation

involves the removal of bark, which contains
little fiber and poor-quality material, to ensure a clean finished
paper product.

Mechanical Pulping

involves grinding and abrading wood to

produce pulp, primarily used for newsprint, utilizing methods

like stone groundwood pulping (SGW) and refiner mechanical

pulping (RMP).

Chemical Pulping

process to dissolve and remove lignin
from wood, minimizing the need for mechanical treatment to
separate fibers, with the kraft process accounting for over 90%
of chemical pulp production in the U.S.

Sulfite Process

uses calcium, magnesium, sodium or ammonium
bisulfite in acidic conditions to break down lignin and produce pulp,
yielding 40-50% of the original wood weight.

Kraft Process

uses sodium hydroxide and sodium sulfide to dissolve
lignin and separate wood fibers for pulp production, accounting for over
90% of chemical pulp made in the U.S.

Semichemical Pulping

Mild chemical treatment followed by mechanical refining to partially

remove lignin and produce pulp with 70-85% yield, such as

the neutral sulfite semichemical (NSSC)

Solvent Pulping

Uses organic solvents like alcohols,

ketones or esters, sometimes with acid catalysts, to

dissolve and remove lignin from wood chips to produce

pulp, with processes like the alkali-based soda-

anthraquinone (SAq) pulping.

Recycling of Wastepaper

Expected to increase, especially in New York and Michigan.

Fiber Mat

Formed by separating cellulose from lignin and hemicelluloses.

Wood Fiber Types

Longer fibers for tear-resistance, shorter for opacity.

Pulp Yield

Varies by method, mechanical or chemical treatments.

Glucan

Type of polysaccharide that forms cellulose.

Xylan

Predominant hemicellulose in hardwoods.

Glucomannan

Predominant hemicellulose in softwoods.

Strength-to-Mass Ratio

Key advantage of wood in construction.

Thermal Properties

Wood's ability to insulate against heat.

Workability

Ease of processing wood for various applications.

Soda-Anthraquinone Pulping

An alkali-based process for producing pulp.

Screening and Cleaning of Wood Pulp

Removes uncooked chips and fiber bundles from pulp.

Centrifugal Cleaners

Removes heavy and light contaminants from pulp.

Bleaching of Wood Pulp

Increases pulp brightness by removing residual lignin.

Chemical Bleaching Agents

Includes chlorine, peroxide, and ozone for bleaching.

Biopulping

Uses fungi to degrade lignin before pulping.

Biobleaching

Uses enzymes to improve bleaching efficiency.

Recycling

Repulping waste paper reduces landfill disposal.

Stock Preparation

Mixes pulp with chemicals to create paper stock.

Refining

Fibrillates fibers to enhance bonding in paper stock.

Sizing Agents

Control liquid penetration in paper products.

Papermaking Process

Involves draining water to form a wet mat.

Finishing

Winding paper into rolls or cutting into sheets.

Environmental Protection

Investments to reduce emissions in paper mills.

Fiberboard

Engineered wood product bonded with adhesives under heat.

Board Formation

Combines wood fibers with adhesives to form boards.

Drying and Pressing

Removes moisture and ensures uniform thickness.

Conditioning

Adjusts moisture content to stabilize fiberboard.

Special Treatments

Enhances fiberboard properties for specific applications.

Particleboards

Made from wood chips bonded with adhesives under heat.

Paper-Base Laminates

Composite materials layered with paper and resins.

Polymer-Modified Papers

Papers treated with polymers for improved properties.

Modified Wood Composites

Enhanced wood using anhydrides, epoxides, and isocyanates.

Preservative Treatment of Wood

Chemical treatment to protect wood from decay.

Preservative Chemicals

Substances used to extend wood's service life.

Wood Preservation

Process enhancing wood durability by 5-15 times.

Chemical Wood-Processing Industry

Second largest industry after pulp and paper.

Organic Liquids

Low volatility, limited water solubility wood preservatives.

Chlorinated Phenols

Organic solvents used for wood preservation.

Water-Soluble Salts

Preservatives like acid copper chromate and arsenates.

Non-pressure Processes

Surface applications, Soaking process, Thermal process, Vacuum process

Surface Applications

Brushing, spraying, or dipping for limited protection.

Soaking Process

Immersing wood in preservative for hours or days.

Thermal Process

Heats wood with preservatives for better penetration.

Vacuum Process

Removes air before submerging wood in preservative.

Pressure Processes

Full-cell process (Bethell) and Empty-cell processes (Rueping and Lowry)

Full-Cell Process (Bethell)

Maximum preservative retention under pressure (125-200 psi).

Empty-Cell Process (Rueping and Lowry)

Lower retention, deep penetration, excess liquid removed.

Preservative Retention

Amount of preservative remaining in wood post-treatment.

Nonconventional Wood Preservation

Minimize toxic chemicals while preserving wood.

Fire-Retardant Treatment of Wood

Protects wood from fire, dating back to Romans.

Impregnated Treatments

Pressure-treated chemicals deposited within wood.

Surface Coatings

Applied as paints; subject to wear.

Commonly used fire-retardant chemicals for impregnation

• Diammonium Phosphate
• Ammonium Sulfate
• Borax
• Boric Acid
• Zinc Chloride
• Amino-Resin Systems

Diammonium Phosphate

Common fire-retardant chemical for wood.

Amino-Resin Systems

Used in fire-retardant formulations for synergy.

Leach-Resistant Alternatives

Developed to prevent water leaching of retardants.

Fire Retardant Formulations

Most fire retardants for wood today are based on
phosphorus, nitrogen, boron, and aluminum trihydrate, often
used in combination due to their synergistic effects, such as in
amino-resin formulations.

American Wood-Preservers' Association Standards

specified the four types of fire-retardant formulations given
below (A, B, C, D).

Silvi-Chemicals

Wood-derived chemicals, similar to petrochemicals.

4 methods of utilization of wood

1. Direct Combustion
2. Saccharification-Fermentation
3. Thermal
Decomposition
4. Thermochemical Liquefaction.

Direct Combustion

Primary energy source using wood for centuries.

Combustion Technology

optimize fuel use and minimize
emissions, making wood a more sustainable energy source
compared to traditional combustion methods.

Cogeneration Technology

- also known as combined heat and power (CHP)
- captures the heat produced during wood combustion to generate electricity while also providing useful thermal energy.

Saccharification-Fermentation

Method converting wood into sugars and alcohol.

2 methods of Saccharification-Fermentatio

Saccharification and Fermentation

Saccharification

breakdown of complex carbohydrates
(cellulose and hemicellulose) into simpler sugars, primarily
through enzymatic hydrolysis.

Fermentation

The conversion of these sugars into ethanol
or other chemicals by microorganisms.

Bergius-Rheinau Process

method for converting
lignocellulosic materials into liquid fuels.

Madison Process

another method for converting
wood and other biomass into fuels and chemicals.

Enzymatic Hydrolysis

critical step in the saccharification process,
where enzymes are used to break down cellulose and hemicellulose into
fermentable sugars.

Fermentation of Sulfite Waste Liquid

process that utilizes the by-
products of the sulfite pulping process, which is used in paper
manufacturing.

Thermal Decomposition

Breakdown of wood into simpler compounds by heat.