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Both Sustainable and Functional: Kapok Fiber

Kapok tree, also known botanically as Ceiba Pentandra, belonging to the malvaceae family, is commonly grown in Asia, Africa and South America. Among the exporters of kapok fiber, which has been produced as an agricultural product since the 10th century, are countries such as Indonesia, Thailand and the United States; Japan, China and Hong Kong are among the countries that import kapok fiber.

Kapok fibers, which have extraordinary properties that are not even found in many synthetic fibers, are not a fiber type known as textile fiber today. Kapok fibers are often compared with cotton fibers in terms of fiber structure and fiber properties, since cotton is the first natural fiber that comes to mind when it comes to seed fiber, and both are seed fibers. However, unlike cotton fibers, kapok fibers are not very suitable for weaving and spinning with their thin and easily broken structure. Often, they are used in mixtures with various fibers to form a textile surface. Kapok fibers, which stand out with their hollow fiber structure, lighter-than-water specific gravity, and oil-absorbing character, exhibit a profile quite different from known natural fiber types. Kapok fibers are unicellular fibers like cotton fibers.

Kapok fibers are a textile material that is very suitable for use as a filler in materials such as quilts, pillows and toys, with its light and anti-allergic structure. In addition, it has been used for many years in the production of products that are required to float on water, such as life jackets, thanks to its non-sink feature. With the widespread use of synthetic textile materials, synthetic fibers have become more preferred in the areas of use of kapok fibers. Cheaper cost of synthetic fibers, ease of maintenance of synthetic products unlike natural products, resistance to detergents and washing; played an active role in the preference of synthetic fibers as filling fiber. However, in recent years, with the introduction of the concept of sustainability into industrial life and the transfer of this awareness to the consumer, the search for contributing to a sustainable future has begun in the textile industry, as in all industrial areas. Although there are many parameters to be considered for a sustainable textile production, the use of environmentally friendly, renewable and biodegradable natural materials instead of petroleum-derived synthetic materials as raw materials is among the methods that support sustainability. At this point, kapok fibers have the potential to be a very important raw material source in the production of textile materials with functional properties such as technical textiles. The fact that the fibers do not sink in water, provides sound and heat insulation and has a high oil absorbing feature in contrast to their hydrophobic feature makes kapok fibers superior to many synthetic fiber types.

Kapok Tree

Kapok trees with the botanical name Ceiba pentandra; They are tropical trees, often called majestic, that belong to the Malvaceae family (formerly the Bombacaceae family). Kapok trees are among the tallest trees in the tropical forest and reach 70 meters in height. The diameter of flat, cylindrical, smooth and gray colored trunks of Kapok trees can reach 3 meters. Young trunks and branches are equipped with thick, conical spines and are often green due to photosynthetic pigments. Its flowers are usually white, pinkish white and red. They have skin-like textures.

Kapok fruits are large ellipsoid-shaped capsules that can be as long as 20 cm and contain 5 woody jaws which, when opened, reveal numerous soft kapok fibers in which many tiny brown-black seeds are embedded. Kapok fibers are not attached to the seeds and the surface of the fibers is covered with a waxy substance that aids in water repellency. The seeds between the Kapok fibers can be used in oil production, as in the cotton plant.

Kapok trees grow in regions with subtropical and tropical climate conditions. Mexico, Peru, Bolivia and Brazil in the Americas; In Asia, it is widely found in countries where the climate is suitable such as India, Thailand, Indonesia, Philippines, Vietnam and Sri Lanka. Kapok fibers are grown in Asia mainly to obtain fiber. The flowering of Kapok trees is directly related to the climatic conditions of the region where they are grown. It is observed that kapok trees, which bloom sparsely (every 5 years) in environments with high precipitation and humidity, bloom more frequently on forest edges or in dry regions. In our country, the south-west Aegean and Mediterranean regions provide suitable climatic conditions for the cultivation of the kapok tree plant.

Countries where the Kapok tree is grown

Kapok trees grow fast in places with a lot of light, so if there is a seed source nearby, they will act as pioneers by colonizing areas cleared of other vegetation. Many trees have adapted to dry conditions and can store water in cortical cells in their trunks. The harvesting of Kapok fibers is carried out by collecting the capsules one by one. Since the flowering of the tree takes about 1 month, the maturation of the fibers does not occur at the same time. For this reason, the harvesting of kapok fibers is also carried out over time from September to November. Since it is of great importance for fiber quality that the fiber is not harvested before it reaches sufficient maturity, the harvesting of kapok fiber is done in 2-3 times, as is the case with cotton fiber. Kapok fibers are first separated from the cores by hand or by machines. The machines used to separate the kapok fibers from the seed kernels are ginning machines similar to the machines used in cotton fiber. After the ginning process, kapok fiber is stored in bales as in cotton fiber. Performing the baling process at an average pressure (5 kg/cm²) is of great importance in order to preserve the various fiber properties, especially the elasticity of the fibers, without deterioration.

Structure and Properties of Kapok Fibers

Kapok fibers are a type of cellulosic fiber with a soft and silky touch. However, it differs from other cellulosic fibers with its hollow tube-shaped fiber structure. Kapok fibers keep mold and harmful insects away, as the fibers contain a large amount of lignin and wax. Kapok fibers, which are yellowish or light brown in color, have a silky sheen. Kapok fibers, which are also odorless and soft, are non-toxic or allergenic and resistant to decay. Kapok fibers have similar characteristics with silk grass fibers both in terms of appearance and general characteristics. Silk grass fibers are a type of seed fiber that has a hollow fiber structure, low fiber density, and exhibits hydrophobic and oleophilic fiber properties like kapok fibers.

SEM images of (a) Kapok fiber longitudinally (at 100x magnification), (b) cross-section (at 1855x magnification)

Kapok fibers consist of natural microtubules (approximately 8-10 µm diameter and approx. 0.8-1.0 µm wall thickness) in the form of hollow thin tubes. One end of the fiber tapering to a point is closed and the other end has a curved shape. A flat and cylindrical surface is seen in the longitudinal view of the Kapok fiber, while a large internal cavity is observed in the cross-sectional view. When the waxy structure on the surface of Kapok fibers is removed, the unique hollow structure of the fibers increases the specific surface area of the fiber, giving the fiber a superior moisture transfer feature. Since the hollow structure, which is generally imparted to synthetic fibers during production, is a characteristic feature of kapok fibers, it is possible to characterize these fibers as an environment-friendly fiber type, both because of their natural structure and because they are an alternative to synthetic fibers.

Kapok fibers have not been seen as a textile material that can be spun into yarn due to their large internal spaces filled with air, smooth surfaces, low cellulose ratios and low strength values. Although 100% spinning of kapok fibers is not possible beyond the lap forming stage, as a result of the development of technology, it has become possible to improve the spinnability and tactility of kapok fibers by sizing or blending.

Studies on the spinning of kapok fibers by blending them with various fibers show that the amount of kapok fiber is not less than 50%, and it is made suitable for spinning by blending it with cotton fibers. It has been stated that yarn durability and resistance decrease, while yarn extensibility increases with the increase in the amount of kapok in the blend in the spinning processes carried out by mixing in various ratios such as 80:20 cotton/kapok, 70:30 cotton/kapok, 60:40 cotton/kapok and 50:50 cotton/kapok. In addition, as the amount of kapok in the blend increased, a significant decrease was observed in the total manufacturing cost of the yarns.

In a study examining the performance properties of cotton/kapok blended fiber woven fabrics, it was concluded that cotton/kapok fiber blended woven fabrics meet the basic fabric properties required for garment textiles. In the study comparing the air permeability, abrasion resistance, heat retention ability, crease-free angle, draping and strength properties of Kapok/cotton fiber fabrics with 100% cotton fabrics; cotton/kapok blend fabrics have better air permeability and heat retention ability (especially for plain woven fabrics) than 100% cotton fiber fabrics; However, it has been noted that the abrasion resistance and crease-free angle of the kapok/cotton blended fiber woven fabrics are lower than the 100% cotton fiber fabrics. Considering the air permeability and heat retention capabilities of kapok/cotton fiber blended fabrics, it was stated that it would be more appropriate to choose woven fabrics with a satin weave structure to produce fabric suitable for summer, and woven fabric with a plain weave structure to produce fabric suitable for winter.

Application Areas of Kapok Fibers

Textile Made Products

Kapok fibers are mostly used as fillers for home textiles such as beds, quilts, pillows and toys, since it is very difficult to turn them into textile surfaces such as yarn and fabric due to their fragile structure. With its water-resistant, anti-allergic, bacteria and fungi-resistant structure, kapok fibers are mostly seen in the natural organic products catalog today. However, in recent years, there have been studies investigating the use of kapok fibers in automobile seats instead of polyurethane foam. The fact that Kapok fibers provide not only environmental benefits, but also advantages in terms of moisture management and comfort creates an alternative area of use for fibers.

It is possible to obtain textile surfaces such as yarn, weaving or knitting in mixture of Kapok fibers with different fiber types. Fabrics obtained from Kapok fiber blend yarns have the potential to be used in clothing production. At the same time, it has been observed that nonwoven surface structures with kapok fiber can also be produced for filter, insulation material and similar purposes.

In a study on the separation of oil from aqueous solutions and the recovery of oil material, it was noted that kapok fiber nonwoven surface filters produced by air-laying-bonding method were used. It has been stated that these filters, which have the potential to absorb oil at a high rate, perform the separation process in a qualified way and ensure that both oil and water can be reused, as well as the filter can be used repeatedly in the developed system.

Buoyant Products

Thanks to its excellent hydrophobic and oleophilic properties and very low fiber density, kapok fibers have been used for many years in the production of products that require the ability to not sink in water. has been started. Although it is not widely used in these areas today, it has a wide potential as an alternative natural raw material that can be used in technical textile products that are not required to sink on water.

Oil Absorbing Products

The hydrophobic and oleophilic characters of Kapok fibers give very successful results in the separation of fatty substances from aqueous solutions. In particular, kapok fiber filters produced for the separation of oil and similar spills from sea water are both very durable and can be used very effectively in the separation process. Considering that approximately 10 million tons of petroleum and its products are used in the world every year, it is obvious how high the probability of contamination of water resources such as sea, lake and ocean is during the use or transportation of these products. Cleaning the oil and its derivatives contaminating water resources causes very serious costs. Filters produced with Kapok fibers, on the other hand, can provide a more efficient and more economical alternative to filters produced mostly from synthetic materials.

Thermal and Acoustic Insulation

Unlike many natural fiber types, kapok fibers with wide lumen and thin cell wall show a superior sound absorption performance by increasing the friction between sound waves and fibers thanks to this special structure. When environmental-friendly, biodegradable and renewable ecological features are added to the superior sound absorption ability of Kapok fibers; It becomes inevitable to prevent noise pollution and become widespread in the production of products that provide acoustic insulation. In addition, kapok fibers are also used in the manufacture of products that provide thermal insulation, thanks to their low thermal conductivity.

Fiber Reinforced Composites

Composite materials are encountered in many areas of life today. Natural or synthetic fibers can be added to the structure in order to improve the strength and flexibility of these structures, which can be used in a wide variety of areas from airplanes to buildings. With the use of sustainable and renewable resources becoming the reason for preference, the usability of natural fiber types in composite structures has become a subject that attracts the attention of many researchers. Cellulose-rich natural fibers have high polarity because they contain abundant hydroxyl groups. Therefore, natural fibers can form hydrogen bonds by interacting with resin matrices, and natural fibers can be used to reinforce thermoset and thermoplastic polymer matrices. Kapok fibers are among the natural fiber types used in composite structures. Researches on the use of Kapok fibers in composite structures show that these fibers have a suitable use in reinforcing composite structures. Kapok fibers can be used as a single fiber in the composite structure, as well as sisal, glass fibers, etc. as reinforcing elements. It can also be used with various fibers. Researches on the production of lighter cars, in particular, show that in recent years, kapok fibers have become a preferred material type in automotive interior composites together with natural fibers such as jute and sisal.

What do you think? Can Kapok fiber really contribute to sustainability in the industrial sense? Can it be preferred to synthetic alternatives in technical textiles? You can share your opinions with us and express your suggestions in the comments section or in the dialog box below.



Kemal Bilal TURKOGLU, Ece KALAYCI, Ozan AVINC, Arzu YAVAS. "Oleofilik Buoyans Özellikli Kapok Lifleri ve Yenilikçi Yaklaşımlar". Bilim ve Teknoloji Dergisi. 2018

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