Overview of Kapok Fiber

Kapok fiber mainly refers to the floss inside the fruits of three plant species: Bombax ceiba and Bombax insigne of the Bombax genus, as well as Ceiba pentandra of the Ceiba genus. Kapok fiber comes in three colors: white, yellow and yellowish-brown. A mature kapok tree can yield 5 to 8 kilograms of kapok fiber, with the global annual output reaching approximately 200,000 tons.

Structure and Properties of Kapok Fiber

1、Chemical Composition

Kapok fiber contains approximately 64% cellulose and 13% lignin. It also includes 8.6% moisture, 1.4~3.5% ash content, 4.7~9.7% water-soluble substances, 2.3~2.5% xylan, and 0.8% wax. The degree of polymerization of kapok fiber is around 10,000, which is comparable to that of cotton fiber.

2、Appearance, Morphology and Properties

Kapok fiber has a cylindrical longitudinal appearance with a smooth surface and no natural twist, presenting a good luster. Its cross-section is round or oval, with a thicker middle section, a blunt rounded root end and a slender closed tip end. When the cross-sectional cells remain intact, they form an airbag structure; after rupture, the fiber becomes flat and ribbon-shaped.

The interior of the cells is filled with air. The hollowness of kapok fiber reaches 80~90%, with a thin and nearly transparent cell wall, resulting in low relative density and excellent buoyancy. A mass of kapok fiber can bear 20 to 36 times its own weight in water without sinking. The surface of kapok is rich in wax substances, which makes the fiber smooth, water-repellent, less prone to tangling, and insect-resistant.

What’s more Kapok fiber length ranges from 8 to 34 mm. The diameter of the fiber mid-section is 18–45 μm, with an average of 30–36 μm, and the cell wall thickness is 0.5–2 μm. The fiber fineness is 0.9–3.2 dtex. The density of single kapok fiber is only 0.29 g/cm³, compared with 1.53 g/cm³ for cotton fiber.

3、Chemical Properties

Since Kapok fiber can be dyed directly with dyes. However, as kapok fiber contains a large amount of lignin and hemicellulose, these components intertwine with cellulose and interact through intermolecular forces. This blocks part of the hydroxyl groups on cellulose and hinders the smooth penetration of dye molecules, resulting in a dye uptake rate of only 63%, compared with 88% for cotton under the same conditions.

so Kapok fiber possesses good chemical properties with excellent acid resistance. Dilute acids have no effect on it at room temperature, nor do weak acids such as acetic acid.

since Kapok fiber is soluble in 75% sulfuric acid at 30°C and 65% nitric acid at 100°C, and partially soluble in 35% hydrochloric acid at 100°C.

It also shows good alkali resistance; sodium hydroxide (NaOH) has no impact on kapok fiber at room temperature.

Applications of Kapok Fiber

Blended yarn made from kapok and cotton can be widely used in such as knitted underwear, fleece garments, sweaters, woven casual outerwear, bedding products, socks and other fields.