Comprehensive Notes on Natural Cellulosic Fibers
Natural Cellulosic Fibers
Chapter Objectives
Identify Cellulosic Fibers: Learn to recognize various fibers derived from plants.
Explain Common Characteristics: Understand properties shared by all cellulosic fibers.
Describe Unique Characteristics: Detail processing, properties, and performance unique to commonly used cellulosic fibers.
Articulate Basic Processing Steps: Outline the fundamental stages in preparing natural cellulosic fibers.
Integrate Properties with Market Needs: Connect fiber characteristics to suitable applications in textiles.
Classification of Textile Fibers
Textile fibers are broadly classified into Natural and Manufactured categories, further broken down by chemical composition and origin.
Natural Fibers
Cellulose: Derived from plants.
Seed Hair: Cotton, Kapok.
Bast: Flax, Hemp, Jute, Ramie.
Leaf: Manila, Sisal.
Protein: Derived from animals (e.g., Silk, Alpaca, Camel, Cashmere, Llama, Mohair, Vicuna, Wool).
Mineral: Asbestos.
Manufactured Fibers
(Generic classification based on chemical composition as defined by the Textile Fiber Products Identification Act.)
Organic:
Rayon, Lyocell, Acetate, Triacetate, Acrylic, Anidex, Aramid, Elastoester, Lastrile, Fluoropolymer, Melamine, Modacrylic, Novoloid, Nylon, Nitril, Olefin, Polyester, Rubber (synthetic), Saran, Spandex, Sulfur, Vinal, Vinyon.
Natural Polymer: PLA (Polylactic Acid), Chitosan.
Inorganic: Glass, Metallic.
Natural Cellulosic Fibers Overview
Origin: Derived from plants.
Sub-divisions based on plant part:
Seed Hair Fibers: Attached to the seeds in a pod.
Examples: Cotton, Kapok, Milkweed.
Bast Fibers: Fibrous part of the plant stem, located just under the outer covering or bark.
Examples: Flax, Ramie, Hemp, Jute, Kenaf, Hibiscus, Nettle.
Leaf Fibers: Originate from the fibrous part of the leaf.
Examples: Piña, Abaca, Sisal, Henequen, Seagrass, Raffia.
Fruit Husk Fibers: Cover the hard shell of the fruit.
Example: Coir (from coconuts).
Additional Miscellaneous Fibers
Rush, Maize, Palm fiber.
Bamboo: While traditionally used in agriculture, papermaking, furniture, and architecture as a natural fiber, most bamboo in textiles undergoes extensive chemical processing similar to rayon. The Federal Trade Commission (FTC) requires such products to be described as "rayon from bamboo." However, some bamboo is processed directly from the plant, justifying its inclusion as a natural cellulosic fiber.
Common Cellulosic Fiber Properties (Table 4.2)
Absorbency: High, making them good for moisture absorption.
Heat Conductivity: High, leading to comfort in hot weather.
Resistance to High Temperatures: Generally good, allowing for versatility in care and use.
Low Resiliency: Tendency to wrinkle easily, often requiring ironing.
Lacks Loft: Does not trap air well, resulting in less bulkiness.
Electrical Conductivity: High, meaning they do not generate static electricity.
Heavy Fiber: Density of approximately 1.5
Mildew Susceptibility: Attacked by mildew in damp conditions.
Flammability: Flammable, igniting quickly and smelling like burning paper.
Chemical Reactivity:
Alkali (Base): High resistance.
Acids: Destroy the fibers.
Oxidizing Agents: Bleachable, but control is necessary to prevent damage.
Cellulosic Seed Fibers
1. Cotton
Designation: "King of fibers" due to its widespread use and versatility.
Nature: A staple fiber.
Characteristics: Depend on the seed variety, growing conditions, and processing methods.
History & Economic Significance
Ancient Origins: Spinning and weaving of cotton originated in ancient China, Egypt, and India.
Mechanization: Eli Whitney significantly mechanized cotton production with the cotton gin in 1793
U.S. Export: Cotton became a leading U.S. export.
Globalization Impact: From the 1980s to 1990s, many U.S. mills closed due to intense competition from globalization.
Cotton Production
World Production: Grown primarily in tropical and sub-tropical regions.
Major Producers: Almost 2/3 of the world's cotton is grown in China, the United States, and India. Pakistan and Brazil also produce significant amounts.
Main U.S. Varieties:
Upland: Accounts for 95% of U.S. production.
Pima.
Cotton Production Terms
Boll: The seedpod of the cotton plant.
Gin: A machine used to separate usable fibers from the seeds.
Bale: A standard unit of processed cotton, weighing 480 lbs each.
Lint: The usable cotton fibers removed during the ginning process.
Linters: Short fibers, typically about 1/8" long, that remain on the seeds after ginning.
Physical Structure & Grading of Cotton
Cotton is graded based on:
Length: Longer fibers are considered higher grade.
Color: Whiter cotton generally receives a higher grade, except for naturally colored cotton.
Cleanliness: The absence of "trash" (brown flecks from plant debris) is desirable.
Fineness: Finer fibers are preferred.
Strength: Stronger fibers are indicative of better quality.
Cotton Fiber Length
Cotton is a staple fiber, with lengths ranging from 1/2" to 2" depending on the variety.
Upland: 7/8" – 1 5/16"
Long Staple: 1 5/16" – 1 9/16"
Includes Sea Island, Pima & Supima®, and Egyptian* & American Egyptian varieties.
Note: Not all cotton grown in Egypt is of "Egyptian quality."
Short Staple: Less than 3/4"
Extra Long Staple (ELS): Pima and Egyptian are notable examples, indicating higher quality and often included on product labels.
Distinctive Parts of Cotton Fiber
Cuticle: A waxy film covering the primary (outer) wall.
Secondary Wall: Composed of multiple layers of cellulose.
Lumen: The central canal through which nourishment travels during fiber development.
Convolutions: Ribbon-like twists characteristic of cotton fibers. These develop when the central canal collapses after drying, and reverse spirals in the secondary wall cause the fiber to twist. Convolutions are crucial for yarn spinning as they allow fibers to cling to one another.
Cotton Fiber Fineness
Diameter: Generally 16-20 micrometers.
Cross-section Shape: Varies with the fiber's maturity.
Immature Fibers: U-shaped with a thin cell wall.
Mature Fibers: Nearly circular with a thick cell wall and a small central lumen.
Spinning and Dyeing Issues: Every boll contains some immature fibers, which can cause problems during spinning and dyeing processes.
Contour & Shape of Cotton
Surface Contour (Longitudinal view): Appears like a twisted ribbon under a microscope due to natural twists (convolutions).
Shape (Cross-section): Kidney-shaped with a hollow central core known as a lumen.
Fiber Color of Cotton
Typical Color: Usually off-white, requiring bleaching before dyeing.
Naturally Colored Cotton: Available in limited quantities. It does not require bleaching or dyeing, making it an eco-friendly option. Its quality is generally lower than white cotton fibers, but many colored cottons are organically grown.
Cotton Fiber Class or Grade
Depends on length, quality, and fineness.
"King of Cotton" – Supima: A registered trademark for Pima cotton that meets specific brand criteria, known for its softness, strength, and brilliance of color.
Cotton Properties & Performance
Usage: The most commonly used natural fiber.
Quality Fabrics: Long-staple varieties are used for higher quality fabrics.
Strength: Medium strength. Longer staples are relatively stronger than shorter staples. Heavier weight cotton fabrics are strong enough for rugged applications.
Abrasion Resistance:
Poor flexing abrasion resistance.
Fabrics show wear at edges (e.g., shirt cuffs/collars) or areas of rubbing.
Wrinkle Resistance: Poor wrinkle resistance, often requiring blends (e.g., with polyester) or applied finishes to improve it.
Hydrophilic: Good moisture absorption.
No static buildup in dry weather.
Comfortable and breathable in warm climates.
Slow to dry; may feel clammy when wet.
Does not irritate the skin.
Biodegradability: Biodegradable. When used outdoors, it degrades over time and is susceptible to rot, often requiring functional finishes to prevent degradation.
UV Exposure: Damaged by UV exposure, leading to yellowing and degradation with extended sunlight exposure. Cotton draperies should be lined to prevent fading and degradation.
Summary of Cotton Performance (Table 4.3)
Aesthetics:
Luster: Matte, pleasant.
Drape: Attractive.
Texture: Soft to stiff.
Hand: Smooth to rough.
Durability: Good.
Abrasion Resistance: Good.
Tenacity: Good.
Elongation: Poor.
Comfort: Excellent.
Absorbency: Excellent.
Thermal Retention: Poor.
Appearance Retention: Moderate.
Resiliency: Poor.
Dimensional Stability: Moderate.
Elastic Recovery: Moderate.
Recommended Care:
Apparel: Machine-wash and dry.
Interior Textiles: Hot-water extraction method or dry-clean with caution.
Care of Cotton
Cleaning: Easy to clean with most laundry detergents; not damaged by alkalis.
Wet Strength: Stronger when wet, allowing cotton fabrics to withstand agitation during washing and drying.
Shrinkage: May shrink during the first few washes due to relaxation shrinkage.
Bleaching: Can be bleached with chlorine bleach, but excessive use will weaken fibers.
Dry Cleaning: Not damaged by organic solvents; dry cleanable.
Ironing: Iron at high temperatures. Fabrics with durable press finishes should be ironed at a lower setting; other finishes may also require lower temperatures.
Environmental Properties of Cotton
Resistance to Microorganisms: Mildew grows on cotton.
Resistance to Insects:
Not damaged by clothes moths or carpet beetles.
Damaged by silverfish.
Resistance to Environmental Conditions: Sunlight will fade and eventually degrade cotton.
Eco-Friendly Cotton Initiatives
Goal: Minimize the use of pesticides, fertilizers, or other auxiliary chemicals.
Organic Cotton: Produced using organic farming practices, meeting specific criteria for organic products. The Global Organic Textile Standard (GOTS) certifies organic cotton using international standards.
Green Cotton: Finished without harsh chemicals. Note that this term has not been defined by standards-setting organizations and is subject to interpretation.
End Use of Cotton
Apparel: Casualwear, sleepwear, undergarments, socks, accessories. Cotton and cotton/poly blends dominate the market for jeans, T-shirts, men's dress shirts, casual shirts, and pants. Also used for sweaters, children's clothing, and work clothing.
Textiles for Interiors: Draperies, curtains, upholstery, bedspreads. Often treated with stain repellent finishes and glazes to improve luster. Used for area rugs and mats but rarely as carpeting due to low crush resistance.
Household & Institutional Textiles: Major market share due to absorbency. Includes bed linens, comforters, table linens, shower curtains, dishcloths, and mops.
Industrial & Technical Textiles: Cotton balls, gauze bandages, personal hygiene products. Treated with functional finishes for protective workwear garments (e.g., FR (Flame Retardant) Cotton).
Identification of Cotton
Microscopic: Relatively easy due to readily visible convolutions along the fiber.
Burn Test: Verifies cellulose, but does not allow for precise identification of cotton specifically.
Solubility: Soluble in strong mineral acids, such as sulfuric acid.
2. Kapok
Source: From the silk cotton tree.
Use: Primarily as fiberfill. Used in life jackets because the fiber floats on water.
3. Milkweed
Description: A hollow-floss seed hair fiber.
Use: Used in comforters and personal flotation devices.
4. Coir
Source: Outer shell of the coconut.
Description: A stiff fiber, cinnamon brown in color.
Use: Indoor and outdoor mats, rugs, and floor tiles.
Cellulosic Bast Fibers
Source: Come from the stem of the plant, near the outer edge (epidermis).
Structure: Lie in bundles in the stem, just under the outer covering or bark.
Binding: Sealed together by a substance composed of pectins, waxes, and gums.
Production of Cellulosic Bast Fiber
Rippling: Removes seeds from the plant stalks.
Retting: A process of loosening the fibers by allowing microorganisms or chemical agents to rot away the stem's woody parts. Retting affects the fiber's color and quality.
Breaking: Breaks the outer woody parts of the stem.
Scutching: Removes the outer bark and woody core from the fibers.
Hackling: A combing process that aligns and separates the fibers.
Line Fibers: The long, fine fibers obtained after hackling.
Tow Fibers: The shorter, coarser fibers remaining after hackling.
Cottonizing: A process that reduces long bast fibers to shorter fibers, making them similar to cotton for use on cotton spinning systems.
1. Flax (Linen)
Historical Significance: One of the world's oldest textile fibers. Fabrics made from flax fibers are known as Linen.
Source: Made from long fibers taken from the stem of the flax plant.
Major Producers: France, Belgium, and Ireland are historically known for fine linens. Today, much flax is imported from Russia and China.
Fiber Types:
Line Fibers: Long, finer quality fibers, which are more expensive and limited in quantity.
Tow Fibers: Shorter, coarser fibers.
Structure & Shape of Linen
Surface Contour (Longitudinal view): Straight with characteristic node-like thickenings that resemble bamboo. Fibers are often bundled, which gives linen fabrics an inherently uneven texture (the "Linen Look" is often imitated by other fibers).
Shape (Cross-section): Polygonal with rounded edges and a small lumen (though not visible in all fibers). The shape and diameter can vary considerably along the fiber length.
Flax Properties & Performance
Strength: Very strong, withstanding regular wear and retaining strength over time. Stronger than cotton (by approximately 20%) when wet.
Abrasion Resistance: High flat abrasion resistance due to its high strength. Poor flex and edge abrasion resistance due to high stiffness.
Wrinkle Resistance: Very poor wrinkle resistance, leading to its characteristic creased appearance.
Comfort: Does not irritate the skin.
Hydrophilic: High moisture absorption and wicking properties, making it comfortable in warm weather.
Biodegradability: Biodegradable.
UV Exposure: Damaged by prolonged exposure to sunlight, but more resistant to light than cotton.
Summary of Flax Performance (Table 4.4)
Aesthetics:
Luster: Excellent, high.
Drape: Excellent.
Texture: Thick-and-thin, contributing to its unique aesthetic.
Hand: Stiff.
Durability: Good.
Abrasion Resistance: Good.
Tenacity: Good.
Elongation: Poor.
Comfort: High.
Absorbency: High.
Thermal Retention: Good.
Appearance Retention: Poor.
Resiliency: Poor.
Dimensional Stability: Moderate.
Elastic Recovery: Poor.
Recommended Care:
Apparel: Dry-clean or machine-wash.
Interior Textiles: Hot-water extraction or dry-clean.
Care of Linen
Cleaning: Cleaned with standard laundry detergents.
Bleaching: Can be bleached with chlorine bleach, but excessive use will weaken fibers.
Dry Cleaning: Not damaged by organic solvents; dry cleanable.
Ironing: Iron at high temperatures with a steam setting. Fabrics treated with durable press finishes require a lower setting.
Environmental Properties of Linen
Resistance to Microorganisms: Susceptible to mildew.
Resistance to Insects: Not damaged by moths, carpet beetles, or silverfish unless starched.
Resistance to Environment: Good resistance to deterioration and rot when stored dry.
End Use of Linen
Apparel: Men's and women's clothing. Lightweight linen (handkerchief linen) is used for apparel and high-quality handkerchiefs.
Textiles for Interiors: Draperies, upholstery, wall coverings.
Household & Institutional Textiles: High-quality tablecloths, napkins, bed linens, lint-free glass cloths, dish towels (tea towels), and hand towels.
Identification of Flax
Burn Test: Burns readily, very similar to cotton, indicating cellulose.
Fiber Length: The easiest way to differentiate from cotton. Cotton is seldom more than 2.5 inches long, while flax is almost always longer than cotton.
Solubility: Soluble in strong acids.
Other Bast Fibers
2. Ramie
Properties: High strength, resistance to mold, easily blended with cotton and wool.
Uses: Upholstery fabrics and fashion fabrics.
3. Jute (Burlap)
Properties: Poor elasticity, stretch, and UV resistance/colorfastness. Coarse texture.
Uses: Packaging material (e.g., fruit & vegetable bags), carpet backing.
4. Hemp
Designation: Considered the "ultimate eco-friendly fiber."
Advantages: #1 advantage is its versatility. Offers better colorfastness and breathability than cotton.
5. Kenaf
Description: Soft bast fiber from the kenaf plant. Light yellow to gray in color.
Properties: Harder and more lustrous than jute.
Uses: Twine cordage and other technical applications.
6. Hibiscus
Botanical Family: Same as cotton.
Processing: Retting is required to extract the fiber.
Properties: Stronger than jute.
Uses: Bags, rugs, and some apparel blends.
7. Nettle
Description: Handspun into yarns.
Properties: Similar to flax.
8. Bamboo
Types:
Natural Bamboo Fiber: Removed directly from bamboo culms (stems).
Regenerated Bamboo Fiber: Produced from bamboo pulp through significant chemical treatment (similar to rayon).
Natural Bamboo Fiber Properties: Maintains natural insect and microbial resistance, absorbent, coarse hand. Not typically found in apparel. Primarily processed in China.
Regulation: As per the FTC, if the fiber is created through a chemical process, it must be labeled as "rayon from bamboo" (as discussed in Chapter 7), not simply "bamboo."
Cellulosic Leaf Fibers
Source: Processed from the leaf of a plant.
1. Piña
Source: Processed from the pineapple leaf.
2. Abaca
Source: Processed from the leaf of the abaca plant, a variety of the banana tree.
3. Sisal & Henequen
Source: Leaves of agave plants.
Uses: Traditionally used for rope and twine.