**2. Characteristic of bast fibers: structure and chemical composition**

Flax and hemp are the most popular bast fibers, which can be used for textile purpose, including apparels. The lignocellulosic fibers are delivered by yearling plants with potential of multiple applications.

The structure of stem of flax and hemp is very similar; fibers are created as concentric rings around lumen and xylem in the whole length of stem parallel to the stem axis. **Figure 1** shows the cross section of flax and hemp stem [8, 9].

The cellulosic structure inside the secondary cell wall of fiber is schematically presented in **Figure 2**.

Flax and hemp fibers occur in form of bundle called technical fibers containing elementary fibers glued by pectin and lignin as well as naturally connected together due to their arborescent structure (**Figure 3**).

### **2.1 Chemical composition**

Bast fibers contain cellulose, lignin, hemicellulose, pectin, waxes, and fats in their chemical composition. The schematic image of the chemical components distribution in

#### **Figure 1.**

*Structure of flax and hemp stem. (a) Cross section of stem. (b) Fiber bundle.*

#### **Figure 2.**

*Schematic depiction of the microscopic structure of an elementary flax fiber showing the cellulosic structure inside the secondary cell wall (figure redrawn from [10]).*

the cell wall of the fiber is presented in **Figure 4**. The figure illustrates schematically in which way the chemical components of bast fibers are distributed in the fiber structure.

The share of the chemical components depends on the fibrous plant variety and the applied method of fiber extraction. From this reason, different values of the cellulose, lignin, pectin, and hemicellulose waxes are given by different authors in their scientific articles [14–18].

The diversification of fiber chemical composition [19] resulting from fibrous plan variety, applied method of retting, fiber extraction, and subsequent stages of processes is presented in **Table 1**.

*Bast Fiber Textiles Addressed Improvement of Human Life DOI: http://dx.doi.org/10.5772/intechopen.105161*

#### **Figure 3.**

*Real and graphical image of naturally arborescent structure of flax/hemp fibers (based on [11, 12]).*

**Figure 4.** *Schematic image of the section of a hemp cell wall [13].*

The cultivar of fibrous plants, the method of plant growing, and the method of fiber extraction have to be selected taking into account the obtaining of the fiber with chemical composition suitable for textile purpose. The high cellulose content gives softness to the fiber and ensures efficient spinnability in opposite to lignin and pectin. Their big share in the fiber results in low fiber quality, e.g., high stiffness and high linear density coming from inefficient fiber separation, which makes the spin process difficult.
