Types, Properties and Application of Vegetable Fibers

Vegetable Fibers: Types, Properties and Uses

Nikhil Yogesh Upadhye
Department of Textiles (Textile Chemistry)
DKTE’S Textile and Engineering Institute, Ichalkaranji, India
Intern at Textile Learner
Email: nyupadhye@gmail.com

 

Introduction
The main chemical component of vegetable fibers is cellulose. So vegetables fibers are also called cellulosic fibers. Vegetables fibers are plant origin, so it is also called plant fiber. Cotton, hemp, jute, flax, abaca, pia, ramie, sisal, bagasse, and banana are examples of vegetable fibers based on cellulose arrangements, typically with lignin. Plant fibers are used to make paper and textiles (clothing), and dietary fiber is an important part of human nutrition. Spinning and weaving were accepted daily routines in every home prior to the Industrial Revolution, and the transformation of fibers into textiles remained a household industry. It was a craft, a skilled occupation practiced by working people who passed down their knowledge from generation to generation.

Classification of Vegetable Fibers / Plant Fibers:

Classification of plant fibers
Figure 1: Classification of plant fibers

A. Vegetables Fibers from Seed

1. Cotton fiber:
Cotton fiber is made up of hundreds of thousands of cellulose molecules. Cotton ginning is a mechanical process that removes cotton from seed bolls. The cotton is then ginned and pressed into bales before being sent to factories to be spun into yarns. Cotton is a vegetable fiber that surrounds the cotton plant’s seeds. Cotton has been grown in some form or another for over 5000 years. Cotton is a member of the “GOSSYPIUM” family of plants. Cotton is the world’s most widely used natural fiber and the undisputed “king” of the global textiles industry, consisting almost entirely of cellulose used for many applications.

Physical properties of cotton fiber:

Sr. No Property Values
1. fiber structure Kidney shape
2. Length 10mm-80mm
3. Fineness 12-25µ
4. Tenacity (gpd) Dry 3.0-5.0
5. Tenacity (gpd) wet 3.5-6 (20% higher than dry)
6. Tensile Strength 2800-8400
7. Elongation (%) 5-10
8. Elastic Recovery (at 2- %) 74
9. Elastic recovery (at 5%) 45
10. Density (gm/cc) 1.54
11. Moisture Regain (%) 6-8
12. Effect of age Small loss of strength
13. Effect of sunlight Turns yellow
14. Effect of heat Decomposes markedly at 150°C
15. Crystallinity 63-67
16. Mol. Wt. 30000-40000
17. DP 2000-5000
18. CED (cal/mol/5Å chain length) 6200

Applications of cotton fiber:
It is used in wide range of wearing apparel for example in shirts, dresses, swimwear, suits, jackets, skirts, pants, sweaters, hosiery.

Cotton nonwovens are used as swabs, puffs, wipes, filters, weddings, personal care products like in diaper, for home decoration curtains, draperies, bedspreads, comforters, throws, sheets, towels, tablecloths, table mats, napkins, bedding, and household furnishing.

2. Kapok fiber:
Kapok, also known as capok, is a cellulosic fiber that is found in nature. It’s made from the kapok tree’s seed hairs (Ceiba pentandra). Silk cotton or java cotton are other names for kapok. It has a smooth, light, unicellular, cylindrically shaped, hollow body, is very buoyant, and has a twist-free fiber. However, it quickly degrades. Kapok fibers are not suitable for spinning into yarn on their own. The cause is silky, slick, and brittle. As a result, spinning fiber into yarns is difficult. The kapok fiber is distinguished by its yellowish or light-brown color and silk-like luster. Unlike cotton fiber, kapok fiber is made up of single-celled plant hairs. Because of its hollow air-filled lumen and high void content, this fiber is commonly used as stuffing for sound and heat insulation, bedding, life preservers, and other water safety equipment. Due to its exceptional buoyancy. Kapok fiber-based materials have opened up a world of possibilities in various application fields due to their unique characteristics.

Physical properties of kapok fibers:

Component Characteristics
1. Appearance Lustrous, yellowish brown and made of a mix of lignin and cellulose.
2. Fineness 0.4-0.7 denier.
3. Elongation at break 1.8-4.23.
4. Tenacity 1.4-1.74 gram/denier.
5. Thermal behavior of kapok Static immobile air held in the large lumen region of kapok makes a better heat retention.
6. Absorbency Excellent oil absorbency and retention capacity due to its waxy surface and large percent of lumen.
7. Light weight 8-10 times lighter than cotton by volume.
8. Effect of Acids Damaged by acid.
9. Effect of Alkalis Showed good resistance and doesn’t damaged by alkalis.
10. Moisture content 11.23

Applications of kapok fiber:

  1. Mattress/Pillow stuffing
  2. Clothing
  3. Life-saving equipment
  4. Construction of thermally insulated and soundproof covers and walls,
  5. Technical textiles Yachts and boats furnishing, insulating materials in refrigeration systems
  6. Substitute of cotton in surgery
  7. By products such as Kapok seed oil.

B. Vegetables Fibers from Fruit

1. Coconut / Coir fiber:
Coir, also known as coconut fiber, is a natural fiber derived from the husk of a coconut that is used in products such as floor mats, doormats, brushes, and mattresses. The fibrous material found between a coconut’s hard internal shell and its outer coat is known as coir. Upholstery padding, sacking, and horticulture are some of the other applications for brown coir (made from ripe coconut). Finer brushes, string, rope, and fishing nets are made from white coir, which is harvested from unripe coconuts. It has the advantage of not sinking, allowing it to be used in long lengths in deep water without dragging boats and buoys down.

Physical properties of coir fiber:

Ultimate length 0.6 mm
Diameter/width 16 micron
Single fiber Length 6 to 8 inches
Density 1.4 g/cc
Tenacity 10 g/ tex
Breaking Elongation 30%
Moisture regain at 65% RH 10.5%
Swelling in water 5% in diameter

Applications of coir fiber:
Brushes, doormats, mattresses, and sacking are all made from coir. A small amount is used to make twine. Curled brown coir fiber pads are shaped and cut to fill mattresses and for erosion control on river banks and hillsides using needle-feting (a machine technique that mats the fibers together). Rubber latex is sprayed on a large percentage of coir pads to bond the fibers together (rubberized coir) for use as upholstery padding in automobiles. Insulation and packaging are two other applications for the material. Coir is primarily used in the production of rope. Hand or mechanical looms are used to weave woven coir fiber mats from the finer grades of bristle and white fiber. Rope and twine, brooms and brushes, doormats, rugs, mattresses and other upholstery, often in the form of rubberized coir pads, are all traditional uses for the resilient and durable coir fiber.

C. Vegetables Fibers from Leaves

1. Abaca fiber:
The fibers are usually obtained from the leaves. Manila hemp is another name for abaca. It has a similar appearance to the banana plant, but its properties and uses are completely different. It is a Musasea family plant that is native to Asia and is commonly found in humid areas such as the Philippines and Indonesia’s east coast. Ecuador and Costa Rica also grow it commercially. Ropes, woven fabrics, tea bags, filter paper, and banknotes are all made from abaca fibers. It’s also known as biodegradable and long-lasting fiber. Abaca fiber is three times stronger than sisal fiber and far more resistant to saltwater decomposition than most vegetable fibers. Typically, fibers are obtained through a variety of methods.

abaca fiber
Figure 2: Abaca fiber

Properties of abaca fiber:

Sample fiber thickness Tensile strength Strain Young’s Moduls
( MPa ) (mm/mm) ( MPa )
Abaca 1 72.594 0.0102 7117.09
5 148.9336 0.0199 7484.102
10 188.6538 0.0301 6288.462
15 262.071 0.0398 6584.602
20 308.7 0.0484 6186.373

Applications of abaca fiber:

  1. Cordage products– ropes, twines, marine cordage, binders, cord.
  2. Handmade paper – paper sheets, stationeries, all-purpose cards, lamp shades, balls, dividers, placemats, bags, photo frames and albums, flowers, table cloth
  3. Fiber crafts– handbags, hammocks, placemats, rugs, carpets, purses and wallets, fishnets, door mats, table clock.
  4. Furniture, Others– wire insulator and cable, automobile, automobile components/composites

2. Sisal fiber:
During its productive period, the sisal plant produces approximately 200-250 leaves. The sisal plant has a lifespan of 7-10 years. Sisal leaves have a sword-like shape and grow to be 1.5 to 2 meters tall. Young leaves may have a few small teeth along their edges, but as they mature, they lose them. A good sisal plant produces about 200 commercially used leaves, with a mass composition of 4% fiber, 0.75 percent cuticle, 8% other dry matter, and 87.25 percent moisture in each leaf. A typical sisal leaf weighing 600g yields about 3% by weight of fiber, with each leaf containing about 1000 fibers. Retting, scraping, or retting followed by scraping are all methods for extracting the fiber from the leaf. The fiber is extracted from the leaf using retting, scraping, or retting followed by scraping, as well as mechanical means such as decorticators. The fiber diameter ranges from 100mm to 300mm.

Physical properties of sisal fibers:

  • Length = 2.88 mm
  • Width = 22.6 μm
  • Tenacity = 57.2 cN/Tex
  • Elongation = 3.02%
  • Moisture regain = 13%

Uses of sisal fiber:

  1. Short sisal fiber is an excellent material for high-quality sofas and wadding mats because of its softness, high flexibility, high friction resistance, acid resistance, and alkali resistance. Pulp materials for construction.
  2. The plants’ extensive root system also helps to reduce soil erosion in arid areas, and they can be used as an effective hedge to protect crops and land from predators.
  3. Rope sisal core for steel wire rope, yarn and twine, sisal cloth polishing, buff carpet pulp, constructing materials, and doormats are some of the other sisal materials.

3. Pineapple leaf fiber (PLF):
Because it produces both fruit and textile fiber, pineapple is one of the most important commercially grown fiber crops. The pineapple is a common tropical plant that belongs to the Bromeliaceae family. The pineapple is a ground fruit, unlike most Bromeliads, which grow on trees. This plant is native to Brazil and Paraguay’s southern regions. The quality of the pineapple used for fiber extraction differs from that which is grown as a fruit. The leaves of a fruit-bearing plant also produce fiber, but it is not of high quality. Pineapple plants with long leaves that have been specifically cultivated for their fiber produce the highest quality pineapple leaf fiber. Each leaf on a mature plant is 1-3 inches wide and 2-5 feet long, with a total of about 40 leaves on a mature plant. The average number of plants per hectare is around 53,000, yielding 96 tonnes of fresh leaves. On average, one tonne of fresh leaves yields 25 kg of fibers, implying that total fiber extraction per hectare is around 2 tonnes.

Physical properties of pineapple leaf fibers:

Properties PALF
Density (g/cm3) 1.07
Tensile strength (MPa) 126.60
Elongation at break (%) 2.2
Young’s Modulus (MPa) 4405

Applications of pineapple leaf fibers:
Pineapple silk is the queen of Philippine fabrics, and it is the fabric of choice for the country’s upper crust. Pineapple leaf fiber is sometimes combined with silk or polyester to create a textile fabric that is lightweight, elegant, and easy to care for, similar to linen. Pineapple threads have long been used in India and China for lines and threads, as well as as a silk adulterant. Pineapple leaf fiber is also used to make table linens, bags, mats, and other clothing items that require a lightweight, stiff fabric. The properties of pineapple fiber fabric make it ideal for high-end suits, shirts, divided skirts, and decorative fabrics.

4. Date palm fiber:
No one has ever imagined that date palm fiber could be used to make high-quality yarn. Egyptian researchers at the Consortium have developed high-performance sustainable textile fibers from date palm byproducts such as fronds, leaves, leaflets, and rachis for the first time in the world. The goal of this study was to identify physiochemical, morphological, and mechanical properties of high-performance fiber extracted from date palm byproducts using a combined alkaline-mechanical process.

Physical properties of date palm fiber:

  1. Length: 20-250 mm
  2. Diameter: 100-1000 μm
  3. Density: 0.9-1.2 g/cm3
  4. Specific Modulus: 7 approx.
  5. Thermal Conductivity: 0.083 W/m K
  6. Tensile Strength: 58-203 MPa
  7. Elongation at Break: 5-10%

Applications of date palm fiber:
The researchers first extracted long textile fiber from date palm byproducts, then converted it into fiber tow, chopped fibers, yarn, non-woven mats, woven fabric, and other products. Date palm fibers mix well with other long fibers such as sisal, flax, and abaca fiber. Yarn can also be made by combining it with hemp or jute. These date palm fibers are not only long-lasting, but also cost-effective to produce and process in textiles and composites. These fibers, in particular, have the properties required for future lightweight cars, sports goods, construction plaster reinforcement, packaging sacks, rope, yarn, and other products.

D. Vegetables Fibers from Stem

1. Jute fiber:
Plants in the genus Corchorus, family Malvaceae, produce jute fiber. Jute is a lignocellulosic fiber that is both a textile fiber and a wood fiber. It’s classified as a bast fiber (fiber collected from bast or skin of the plant). The chemical composition of jute fiber includes cellulose (64.4%), hemicellulose (12%), pectin (0.2%), lignin (11.8%), water soluble (1.1%), wax (0.5%), and water (10%). Jute fiber is made up of multiple cells. These cells are made up of cellulose-based crystalline micro fibrils that are connected to a complete layer by amorphous lignin and hemicellulose. A multiple layer composite is formed when multiple cellulose and lignin/hemicellulose layers in one primary and three secondary cell walls stick together. The composition (ratio of cellulose to lignin/hemicellulose) and orientation of the cellulose micro fibrils differ in these cell walls.

Physical properties of jute fiber:

1 Ultimate length 1.5-4 mm
2 Ultimate diameter .015-.020 mm
3 No. of ultimate in X-section 6-10
4 fiber length 5-12 feet
5 Strength 3-4 gm/den
6 Elongation 1.7% at the break
7 Specific Gravity 1.5
8 Moisture Regain 13.75%

Uses of jute fiber:

  1. Packaging: Bags, sacks, wrapping material i.e. cotton packs and wool packs.
  2. Geotextiles – landfill covering, embankment reinforcement.
  3. Braids and webbing
  4. Cable filler
  5. Rope
  6. Furniture
  7. Camp beds
  8. Filter cloths
  9. Hand bags
  10. Covering fabrics

2. Hemp fiber:
The hemp filaments are notable for their solidity and toughness. Hemp is derived from the Cannabis sativa plant. Hemp strands are profoundly earthy colored to yellowish dark in their raw state. Around 10,000 years ago, hemp was one of the first and most common plants to be turned into texture. It originated in Central Asia and is now grown in the United States, Italy, Canada, Germany, France, the Philippines, and India.

hemp fiber
Figure 3: Hemp fiber

Physical properties of hemp fiber:

  1. Color: The color of hemp fiber is yellowish grey to deep brown.
  2. Length: 4 to 6.5% feet.
  3. Tensile Strength: Hemp is a very strong fiber.
  4. Elongation at break: Hemp fibers stress easily.
  5. Elastic Recovery: Elastic recovery is very poor. It is less than linen fiber.
  6. Moisture Regain (MR %): Standard moisture regain is 12%. It is more than cotton and linen.
  7. Effect of Heat: Hemp fiber has an excellent resistance to degradation by heat.

Applications of hemp fiber:
Rope, textiles, clothing, shoes, food, paper, bioplastics, insulation, and biofuel are just a few of the commercial and industrial products made from hemp. The bast fibers can be used to make 100% hemp textiles, but they’re more commonly mixed with other fibers like flax, cotton, or silk, as well as virgin and recycled polyester, to create woven fabrics for apparel and furnishings.

3. Flax fiber:
Flax (Linum usitatissimum) is a flowering plant in the Linaceae family that is also known as common flax or linseed. In temperate climates around the world, it is grown as a food and fiber crop. Linen is a term for flax-based textiles that have traditionally been used for bed sheets, underclothing, and table linen in Western countries. Linseed oil is the name for the oil that it produces. The term “flax” can also refer to the flax plant’s unspun fibers, in addition to the plant itself. The plant is only known as a cultivated species, and it appears to have been domesticated only once from the wild species Linum bienne, also known as pale flax.

Physical characteristics of flax fiber:

  • Density- 1.4 gm/cc
  • Standard Moisture regain- 10 to 12%
  • Diameter of stem – 2 to 3 mm
  • Tenacity- 6 to 8.5 gm/ den

Uses of flax fiber:
Uses in the End Demand when extra strength and resistance to moisture required. Because of the production method, it is more expensive than cotton. Sailcloth is one of the most common uses for this material. Tent Threads for shoes Threads for sewing Tablecloths, handkerchiefs, towels, and sheets, garments.

4. Kenaf fiber:
Natural fibers are in high demand around the world because they are renewable and biodegradable. A wide range of fibers are used as raw materials in the textile industry. Kenaf fiber was one of these fibers that was known and used in the pre-civilization era as well as in the modern era. Kenaf fiber is a well-known natural fiber that is used to reinforce polymer matrix composites. Kenaf is derived from the Hibiscus cannabinus plant, which has traditionally been used to make cordage and coarse fabrics. It’s primarily used as a jute substitute. The bast and core of kenaf contain the fibers.

kenaf fiber plant
Figure 4: Kenaf fiber plant

Physical properties of kenaf:

Density (g/cm3) 1.2
Breaking Strength (MPa) 100.64
Elastic Modulus (GPa) 23
Yarn Breaking load (N) 79
Tensile Strength (MPa) 283-800
Elongation (%) 17.3
Moisture Absorption (%) 8.3

Uses of kenaf fiber:

  1. Ropes.
  2. Twine.
  3. Sackcloth.
  4. Newsprint paper
  5. Garments that do not require lining.
  6. Sacking.
  7. Cordage.
  8. Hessian.
  9. Upholstery

5. Raffia fiber:
Raffia is a naturally occurring fiber. Jute, bamboo, and hemp fibers all have similar properties. Raffia fiber is obtained by peeling the leaves of the raffia palm. Raffia is an excellent material for weaving baskets, hats, mats, and rugs because it is soft, pliable, strong, durable, and biodegradable. It’s also commonly used in agriculture to tie vegetables, vineyard plants, flowers, and floral arrangements. Natural pigments are usually used to dye it. Following the growth in a particular geographical region, certain textile fibers become rare in nature. While the rarity of such fibers distinguishes them, there are a few drawbacks associated with their rarity. The sale and global use of such fibers are determined by factors such as international trade, popularity of the fiber in the fashion world, various uses associated with the fiber, economic viability, and so on. Bark, raffia, cotton, wool, and silk fibers are some of the raw materials for textile fabrics in some African regions. Raffia, bark, and silk, for example, are not abundant due to the limited production area.

Properties of raffia fiber:

Months / Physical 3 6 9
Diameter (ym) 10-100 80.120 90-150
Density (p’cm3) 1.332 1.419 1.421
Moisture content (%) 5.8 4.9 3.7
Water absorption (%) 320 306 2B9

Uses of raffia fiber:
Raffia fibers have many uses, such type of uses are given below:

  1. Textiles industry: Hats, shoes clothes, rugs.
  2. Building construction: The leaf stems and axis of a compound leaf or compound inflorescence are utilized in construction materials for houses and furniture, Ropes, sticks and supporting beam, roof covering, decorative mats, garden ties,
  3. Agricultural uses: Tie vegetables, plantain vineyards, flowers and floral arrangements.
  4. Crafting: Doll hair, ribbons, Hawaiian skirts (hula skirts), and table skirts.
  5. Basket weaving: The leaf stems’ skin is used for making baskets after being torn into thin pieces or after collecting the fibers, the skins are dried and used as the core materials of basket weaving.
  6. Packaging: Filler, trying oil, jam, vinegar, wine bottles, soaps, candles and boxes.
  7. The unprocessed or unrefined raffia used for tying raffia shanks or sticks and is processed as strings. The twisted fibers are used exclusively as strings by twisting them into a two-fold yarn with the palms and thighs.

6. Banana fiber:
Banana fiber, also known as musa fiber, is one of the strongest natural fibers in the world. The natural fiber is biodegradable and made from the stem of the banana tree. The fiber is mainly made up of cellulose, hemicelluloses, and lignin, and is made up of thick-walled cell tissue bonded together by natural gums. Banana fiber is similar to natural bamboo fiber, but it is said to have superior spin ability, fineness, and tensile strength. Depending on which part of the banana stem the fiber was extracted from, banana fiber can be used to make a variety of textiles with varying weights and thicknesses. The outer sheaths of banana trees produce thicker, sturdier fibers, whereas the inner sheaths produce softer fibers.

Properties of banana fiber:

Tenacity 29.98 g/denier
Fineness 17.15
Moisture Regain 13.00%
Elongation 6.54

Uses of banana fiber:
Banana fibers had a very limited application in the past, and were primarily used to make ropes, mats, and some other composite materials. Banana fiber has been recognized for all of its good qualities as environmental awareness and the importance of eco-friendly fabrics has grown, and its use is now expanding in other fields such as apparel garments and home furnishings. Since the Edo period, it has been used in Japan to make traditional dresses such as kimono and kamishimo. People there still prefer it as summer wear because it is lightweight and comfortable to wear.

References:

  1. Handbook of Natural fibers, Volume 1: Types, Properties and Factors Affecting Breeding and Cultivation Edited by Ryszard M. Kozłowski
  2. The Chemistry of Textile fibers by R. H. Wardman and R. R. Mather
  3. Handbook of Textile fibers: Natural fibers by J. Gordon Cook
  4. Introduction to Textile fibers by V. Sreenivasa Murthy
  5. https://textilelearner.net/date-palm-fiber-properties-chemical-treatments-applications/
  6. https://textilelearner.net/banana-fiber-properties-manufacturing/
  7. https://textilelearner.net/abaca-fiber-properties-manufacturing/
  8. https://textilelearner.net/application-of-pineapple-leaf-fiber-in-automotive-industry/
  9. https://textilelearner.net/kenaf-fiber-properties/
  10. https://www.textileblog.com/properties-extraction-and-uses-of-pineapple-leaf-fiber/
  11. https://www.textileblog.com/properties-processing-and-uses-of-kenaf-fiber/
  12. https://www.textileblog.com/kapok-fiber-properties-processing-and-applications/
  13. https://www.slideshare.net/Farhanullahbaig/kapok-fiber
  14. https://en.wikipedia.org/wiki/Coir
  15. http://coirboard.gov.in/?page_id=62
  16. https://www.fiber2fashion.com/industry-article/2394/sisal-fiber-an-overview
  17. https://www.textileschool.com/amp/252/alpaca-fibers/
  18. https://www.slideshare.net/Pachamamadc/alpaca-clothing
  19. https://www.slideshare.net/SyedSamamAli/-141119160
  20. https://www.britannica.com/topic/cashmere
  21. https://polymerdatabase.com/Fibers/Azlon.html
  22. https://www.worlds-finest-wool.com/angora-wool/
  23. https://www.textileschool.com/amp/252/alpaca-fibers/
  24. https://en.wikipedia.org/wiki/Fiber
  25. https://www.slideshare.net/santudutta777/coir-48427034
  26. https://textilevaluechain.in/in-depth-analysis/hemp/
  27. https://en.wikipedia.org/wiki/Hemp#Uses
  28. https://aip.scitation.org/doi/abs/10.1063/1.5082463
  29. https://www.fiber2fashion.com/industry-article/2394/sisal-fiber-an-overview
  30. https://www.textilesphere.com/2020/03/sisal-fiber-properties-applications.html
  31. https://www.sciencedirect.com/science/article/abs/pii/S0261306904002973
  32. https://textilestudycenter.com/jute-fiber-properties-and-end-uses/
  33. https://textilevaluechain.in/news-insights/raffia-fiber-the-heart-of-high-fashion/
  34. https://bioresources.cnr.ncsu.edu/resources/a-study-on-chemical-composition-physical-tensile-morphological-and-thermal-property-of-roselle-fiber-effect-of-fiber-maturity/

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