*3.8.2 Bio-physical properties of natural tropical fibers*

**Table 2** shows great variability in the data related to natural fibers, which is explained by the morphology and composition of each fiber, whether treated or not. Five types of tropical natural fibers were specifically investigated which are palm oil flower (POFl), palm oil fruit (POFr), coconut from the outer shell (Cn), sugar cane bagasse (Sc) and banana stem (Bs) fibers. These fibers are taken from the state of Tabasco in Mexico. Sugarcane fibers are separated into coarse (Scg) and fine (Scf) fibers for the study. Palm oil flower and fruit fibers are also separately considered even if some of their properties are closely related, see **Table 3**. They were not processed but extracted manually. Only the banana rachis required soaking in water and then drying of the isolated fibers.


#### **Table 3.** *Some bio-physical properties of palm oil flower and fruit fibers.*

*Recycling of Tropical Natural Fibers in Building Materials DOI: http://dx.doi.org/10.5772/intechopen.102999*

**Figure 15.** *Tensile strengths observed on typical tropical fibers from Mexico.*

**Figure 16.** *Typical stress-strain relationships for different tropical fibers.*

**Table 3** shows the bio-physical properties of palm oil fibers such as density, water absorption, thermal conductivity, cellulose content and area. The low density of fibers makes them a suitable additive in manufacturing lightweight building composites. Natural fibers are hydrophilic materials and higher water absorption of fibers in composite leads to micro-cracks growth in composites. Natural fibers have a low thermal conductivity which has a positive influence on the thermal behavior of building materials. Higher cellulose content of fibers contributes significantly to the tensile strength of fibers. The area of fibers is important to study the mechanical characteristics of fibers such as tensile strength. Tensile strength of fibers is heavily influenced by the area of fibers as technical fibers tested in this study are consist of the number of elementary fibers.

#### *3.8.3 Bio-physical properties of natural tropical fibers*

The five types of fibers were subjected to a tensile test. The length of the fiber chosen is 20 mm (free or gauge length) for a total length of 30 mm. The constant test speed was 0.5 mm/min at a room temperature of 22 ± 2°C and relative humidity of 40–50%. A minimum of 10 fibers were tested for each series. The minimum, average and maximum tensile strength of Mexican tropical fibers is presented in **Figure 15**. The tensile and strain loading curves reveal different mechanical behaviors depending on the fiber. Pseudo-elastic, visco-elastic or elasto-plastic behavior with a strainhardening effect can be observed in **Figure 16**.

The tensile strength of fibers discussed in **Figures 15** and **16** is one of the most important parameters for their use in bricks as fibers act as reinforcement. The higher tensile strength of fibers increases the tensile strength of building composites.
