Banana Fiber: Manufacturing, Properties, and Composition

By Eman abdallah Kamel

Eman is a writer and textile engineer. She received a bachelor’s degree in textile sciences from the College of Applied Arts, Egypt.

This article covers the manufacturing of banana fibers, from extraction to weaving, their chemical composition, physical and chemical properties, and uses.

Banana fibre is eco-friendly, similar to cotton, linen, and silk. Image source: sustainme. in

Banana Fiber

Bananas are one of the most important fruit crops cultivated in tropical parts of the world. The principal sources of fiber are the peduncle and pseudostem. Banana fiber is mainly composed of cellulose, hemicellulose, and lignin.

Banana fiber is eco-friendly, like cotton, linen, silk, bamboo, and jute fiber. Banana fiber can be blended with viscose, Tencel™, jute, and hemp fibers to enhance its properties.

In the textile industry, banana fiber was first used and was first developed in India due to its very high yield, using banana fiber mixed with other fibers.

Japan is also at the forefront of the world in textile technology, with Nissin Textiles collaborating with the Nagoya City University Research Institute to successfully commercialize banana fiber.

Swiss luggage brand QWSTION developed the Bananatex® fabric made entirely of banana fibers.

Countries like the United States of America, Malaysia, Korea, the European Union, and the Philippines are currently experiencing high demand for banana fiber.

Banana tree and cross-section of banana trunk. Image source: mdpi.com

Chemical Composition

Banana trees consist of four different sections: the outer layers of banana bark, the middle layers of banana bark, the inner layers of banana bark, and the middle rib of banana leaves.

The main components of banana fiber are cellulose (55–65%), hemicellulose (15–25%), lignin (10–15%), and pectin (3-5%).

Cellulose provides structural integrity for the fiber.

Lignin also plays a crucial role in the mechanical strength of the plant.

The chemical composition of banana fiber can vary depending on species, geographic locations, agro-climatic conditions, soil nutrients, plant age, and extraction conditions.

Did You Know?
The yellow color of banana fiber is mainly due to its lignin content.

Raw banana fiber. Image source: alibaba.com

Banana Fiber Manufacturing Process

The banana fiber industry goes through the following stages:

The extraction
Grouping and Knotting
Spinning
Weaving

1. The extraction

There are many methods for extracting banana fiber, including:

Retting or Manual Process
Mechanical Process
Chemical Process
Steam Explosion Process

1. Retting

Retting is the separation of the fiber bundles from the cortex, which affects the lignin and hemicellulose between the fibers in the bundles. There are two stages in the retting process: the physical stage, in which water is absorbed, swelling then occurs, and some soluble substances are extracted. The second stage is the microbial stage, either aerobic or anaerobic, by fungi or bacteria.

The retting process involves several factors, such as microbiological agents (bacteria or fungi), the nature of the retting water, aeration, and macronutrients. Microbial growth on plant fibers usually results in tenacity loss, odor release, and various types of strains on the fiber substrates. Sometimes, certain microorganisms grow on the stem of a living plant and produce brown spots on the fibers.

Process time reductions of up to 78% are possible. It depends on the temperature, length of retting, added chemicals (magnesium oxide), and pure culture of microorganisms such as pectin-decomposing bacteria in the retting liquid. It was found that the pseudostem retting time of 28 hours was quite adequate, and the process was effective at a controlled pH of 6.8–7.4 with sodium carbonate and room temperature.

The retting process is done to increase the mechanical properties of the banana pseudo-stem fibers. According to an article written on ResearchGate.net, fiber tenacity tests indicated that extractive removal of pectin from pseudostem fibers through retting did not cause any significant change in fiber tenacity except when over-retting.

Then comes the degumming process, where the fibers are manually removed from the pulp matrix shaft and then gently twisted to remove excess moisture. Workers manually remove impurities from the twisted fibers, including broken fibers, dyes, and cellulose coatings. The fibers are then dried and cleaned.

The manual extraction of banana fiber needs experienced personnel, takes a long time, and causes damage to the fiber. Therefore, manual extraction of banana fiber is not suitable for large-scale production.

The banana fiber extraction machine. Image source: mayboommachine.com

2. Mechanical Process

Many companies have developed banana fiber extraction machines to improve the efficiency of the extracted fibers. Banana fiber extraction machines feature high production efficiency, low labor intensity, low production cost, and clean fiber extraction.

In this process,

Raw materials can be automatically or manually fed to the feeding mechanism of a banana fiber extraction machine. Then, the feeding mechanism feeds the raw materials to the knife ball. The intermediate texture of the raw material is broken using a fixed knife and a high-speed rotating knife ball to separate the fibers. The separated fibers fall from the conveyor belt.

The fibers are then cleaned and dried.

After the extraction process, the weaving process is done on looms.

3. Chemical Process

In chemical extraction, hemicellulose, lignin, oil, wax, and other substances are removed from the surface of the fiber. Because lignin, hemicellulose, fats, and waxes are acidic, mild alkalis such as soap or sodium carbonate are used. The process is done by boiling for 30–60 minutes.

(Fiber-OH and NaOH Fiber-ONa + H2O). Researchers have mostly used alkalinization as an effective technique that involves reducing or removing hydrogen from the structure.

Researchers also found that calcium hydroxide, magnesium carbonate, and sodium bicarbonate are effective in removing hemicellulose, lignin, and other impurities present on the surface of fibers.

A combination of hydrogen peroxide and sodium hydroxide may provide better fiber whiteness.

It is preferable to perform a mild acidic treatment after alkali degumming to remove excess alkali content, if any. This process can be done either in an open vessel or an autoclave.

The high temperature and high pressure (HTHP) process in the autoclave causes partial breakdown of the lignocellulose structure. It also causes hydrolysis of the hemicellulose fraction, depolymerization of lignin, defibrillation, and better-quality fiber.

4. Steam Explosion Process

This process uses high-temperature and high-pressure water steam to deal with fibrous raw materials, separation, and structural change through the instantaneous release component to achieve the pressing process of raw materials. The main purpose is to penetrate the compressed gas of the paroxysmal part released in an extremely short time (0.00875 seconds) into the plant tissue and make the plant tissue temperature and pressure normal by the sudden release of high temperature and high pressure, thus achieving the purpose of decomposing cellulose and lignin.

The process can be summarized as follows:

Fast frying steam extraction: Get a 20 kg fresh banana stalk, put it into the steam blasting vessel after splitting, press for 100 seconds at a steam blasting pressure force of 1.40 MPa, and suddenly release after washing and drying to get 660 g of raw banana fiber. The yield is 3.3%.

Pre-alkali treatment: Raw banana fibers are soaked in a 12 g/L NaOH solution, soaked at room temperature for 30 hours, then washed until neutral and dried.

Vapor-exploding degumming: The fiber after the pre-alkali treatment is put into a steam-explosion jar once more. The dimension pressure time is 120s under the condition of pressure 1.40 MPa. The fiber moisture is controlled at 30%. Abrupt release after washing and drying.

Bleach: Adopt twice-bleaching for handling. For the first time, the temperature is 58 degrees Celsius, the solid-to-liquid ratio is 1:16, and the bleaching liquid contains 1.3% Na₂SiO₃, 2.5% NaOH, and 2.9%. H₂O₂ and treated for two hours, and then washed to neutrality. The second time: the temperature is 65 degrees Celsius, and the ratio of solids to liquids is 1:17. The bleaching liquid contains 2% Na₂SiO₃, 1% NaOH, and 1.3% H₂O₂. Handle for 2 hours, and be washed to neutrality.

Post-processing stage: Banana fibers are processed after bleaching by supplying oil, drying, cutting, carding, and obtaining pure white banana fibers. The length of the obtained banana fiber is 140 mm, the fiber count is 530 Nm, the breaking strength of the bundle fiber is 3.2 g/D, and the residual gum content is 3.9%.

Did You Know?
Although banana fiber has the features of hemp fiber, the spinning rate is relatively low compared with hemp fiber. To solve this problem, the researchers combined hemp fiber with low-cost bananas to obtain a mixture that is easy to color and has a high spinning rate.

2. Grouping and Knotting

The dried fibers are separated according to their size and grouped. These fibers are then knotted to the ends of other fibers by hand. The knotting continues until a long, continuous strand is obtained.

3. Spinning

These yarns are spun on a hand-spinning machine to introduce the required twist and strengthen the yarn for weaving.

4. Weaving

The spun yarns are woven on handlooms.

Banana Fiber Properties

1. Physical Properties

Banana fiber is a strong fiber with a lower strain at break.
Its appearance is quite shiny, which depends on the extraction and spinning processes.
The average fineness of banana fiber is 2400 nm.
It has a low density.
Its absorbance and release of moisture are quite fast.

Did You Know?

Research conducted at the Center for Studies of Natural Fibers and Natural Dyes (CSNFD) at the Department of Chemical Engineering, Textile Engineering Concentration, Universitas Islam Indonesia (UII), has shown that the durability of banana pseudo-stem fibers can last up to 3 months of storage. However, if the storage period of the fiber is longer than 3 months, the strength of the fiber decreases significantly.

2. Chemical Properties

The banana fibers consist of the following components:

Cellulose is the main component of fiber.

Hemicelluloses are amorphous short-chain polysaccharides and polyuronides. Polysaccharide hemicelluloses are partially chemically linked or intermingled with molecules of cellulose.

Lignin is a short-chain, non-crystalline, isotropic polymer composed of phenylpropane-derived units.

Pectin exists in water-soluble form as calcium and magnesium from galacturonic acid. These substances are transformed into butyric and acetic acids through biological retting.

Fats and waxes found on the surface of plants can be extracted using gasoline.

The chemical reaction of cellulose (banana fiber) with different chemicals. Image source: Journal of Natural Fibers.

Heat Effect: According to research, the thermal decomposition of banana fibers begins at a temperature between 25 and 700 °C in an N2 environment with a constant heating rate of 10 °C/min. The thermal decomposition of banana pseudo-trunk fibers occurs in three stages.
Alkali Effect: NaOH treatment at high temperatures improves the whiteness of fibers by removing lignin and also increases dye absorption due to the formation of soda cellulose. Treating banana fibers with hot alkali removes surface impurities and enhances the mechanical strength of the fibers. Alkali treatment also improves thermal stability, thermal conductivity, and fiber spreading.
Silane Treatment: Silane coupling is performed to replace the OH group of the natural fiber with an organosilane group. As a result, the fibers become hydrophobic. The most common silane coupling agents are tetraethyl orthosilicate, 3-aminopropyltriethoxysilane, and vinyltriethoxysilane. The coupling agents hydrolyze into silanol. An effective ester bond is formed with the carboxylic fiber groups. Silane treatment increases the surface energy and reduces the surface wettability.
Enzyme Effect: This process is environmentally friendly and results in a smooth fiber surface. Enzymes are used in the de-dying, drying, and bio-finishing processes. Enzymes are biological molecules and have a specific activity. The most commonly used enzymes in textiles are cellulase, laccase, transglutaminase, protease, xylanase, lipase, amylase, and peroxidase. The main goal of the enzymatic treatment of natural fibers is to remove surface impurities such as fats and waxes. High concentrations of processing enzymes may negatively affect the mechanical strength of the tissue.
Acetylation Process: The fiber’s hydroxyl (OH) group is replaced with an acetyl group during this process. This treatment improves the hydrophobicity of banana fiber. Although acetylation of some natural fibers has been reported, attempts on banana fibers are scant. Teli and Valia (2013) used acetic anhydride and N-bromosuccinimide for solvent-free acetylation on banana fibers to improve oil absorption. The acetylation found on banana fibers contributed to a significant increase in acetyl groups. Therefore, the modified fiber was found to have better water resistance and thermal stability.

Did You Know?

The researchers mixed jute fibers, which are mainly used in packaging materials, with gray and bleached banana fibers in different proportions. They found that yarns mixed with bleached banana fibers were much more productive than yarns mixed with gray banana fibers. The researchers also developed a blend of naturally dyeable jute and banana fibers and tested various aspects of its physical and mechanical properties, such as strength and tensile rate, which showed that it is resistant to color loss, has good quality, and is resistant to abrasion.

Uses

Banana fiber is blended with other fibers to make jackets, jeans, and other clothing.

Because of its light weight, luster, and high water absorption, banana fiber is also used in home textiles such as curtains, towels, and bed linens.

Hand-peeled banana fibers can be used to produce handbags.

Sources

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