Each test is carried out using bagasse extracted from sugar cane cut in the field, then treated at atmospheric pressure, with the following parameters:

· Soda concentrations: 0.1 N; 1N; 2N;

· Solvents used: salt water and distilled water;

· Bath temperature: room temperature (25˚C);

· Agitation: manual.

The pre-treatment and extraction protocols were developed, according to Davina [11], then adapted for bagasse particles, with the preferential objective of long, fine fibres. The extraction was carried out following six different protocols, presented in Table 1.

The aspect obtained is presented in Figure 2.

It appears from Figure 2 that: the higher the concentration of soda, the more intense the color of the bath. This is mainly due to the amount of lignin extracted: the more intense the bath, the more lignin is extracted [11].

In this technique, the experimental protocol is simple: it is a question of introducing the fibres into a beaker containing a certain amount of water. In this work, two protocols presented in Table 2.

Extraction by combing

In this technique, a wire brush used; the extraction principle here consists of brushing the inside of the bagasse walls in order to obtain the fibres. The wire brush passed on the internal part of the bagasse bark which allows the fibres to dissociate from this internal wall and then collected.

To determine the external average diameter of the fibres, an optical microscope was used and two glass slides between which the fibre was placed on the graph paper.

The microscope being connected to the computer and using the screen allows us to visualize the morphological aspect of the fibre in Figure 3.

1) Determination of the apparent density

Density is an important data since it makes it possible to define the rate of reinforcement necessary for the resistance and the rigidity of the desired final composite [2]. The apparent density is calculated by measuring the mass, length and diameter of several fibres. To have the masses and lengths of the fibres, respectively, a 10⁻⁴ precision balance of Sartorius brand and a digital calliper was used (Figure 4).

The apparent density is obtained using the following formula:

ρ = m v

With: ρ apparent volumetric mass in g/cm³,

m: fibre mass (g),

v: fibre volume (cm³).

1) Recovery rate

The recovery rate is defined as the amount of water present in the air that can absorb 100 grams of dry matter under well-determined hygrometric conditions [11]. This test was carried out according to the gravimetric method Based on the standard NF G08-001-4. The formula giving the recovery rate is as follows:

R % = M h − M s M s * 100

Mh: the wet mass under the given humidity and temperature conditions (in grams);

Ms: dry mass (in grams).

2) Water content

The water content or humidity of a material is defined as the amount of humidity contained in 100 grams of wet matter under well-defined climatic conditions [11]. This test was carried out according to the gravimetric method Based on the standard NF G08-001-4. The equation giving the water content is as follows:

Q % = M h − M s M h

The tensile tests were carried out at the scientific and technical service center in Food Processing, Packaging, Environment and Textile (Celabor) in Herve in Belgium. The test conditions were as follows:

· Applied standard: DIN EN ISO 13934-1;

· Device: Zwick 10 kN cell;

· Test speed: 100 mm/min;

· Distance between tools for initial position: 100 mm.

1) Experimental Protocol

The method used is that of the conventional tensile test. The sugar cane bagasse fibre is glued to paper to ensure its linearity and placed between the fixed and movable jaws of the mechanism. The central unit makes it possible to collect the data of the standard force until rupture as a function of the elongation. The Figure 5 presents the appearance of the stress-Elongation curves as a function of the extraction method.

2) Method for determining the mechanical properties of bagasse fibres

Figure 5 below shows the appearance of the stress-strain curves as a function of the extraction method. From the measured force/displacement data at each instant of a tensile test, we calculate the following:

- Maximum standard stress

σ max = F max S 0

- Standard failure stress

σ r = F r S 0

- Young’s Modude

With:

· σ : stress in MPa;

· F: strength in N;

· S 0 : Initial fibre section in mm²;

· ε: strain in %.

1) Young’s Module

The histogram in Figure 10 below shows the comparison of the Young’s moduli obtained by different methods of fibre extraction.

It can be seen from this graph that the chemical extraction method (1N-BPD) has the highest Young’s module (53.17 GPa); and the chemical extraction method (0.1 N-BPD) has the lowest Young’s module (1.9 GPa).

2) Stress at rupture

The histogram in Figure 11 below shows the comparison of the breaking stress obtained by different methods of fibre extraction.

The graph in Figure 12 shows that: the chemical extraction method (1 N-BPD) has the highest breaking stress (1231.83 MPa). Therefore, fibres treated with soda are more resistant than untreated fibres. This conclusion was also

observed by Sedan [12].

3) Maximum stress

The histogram in Figure 12 below shows the comparison of the maximum resistances obtained by different methods of fibre extraction.

The graph in Figure 13 shows that: the chemical extraction method (1 N- BPD) has the highest breaking stress (1289.89 MPa). It was noticed that when soda is too concentrated, for example the case of 2 N, it almost destroys the structure of the fibre, making it less resistant mechanically. When there is also a low concentration of sodium hydroxide, for example the case of 0.1 N, there is no great influence on the mechanical properties.

4) Elongation at rupture

The histogram in Figure 13 below shows the comparison of the elongations at rupture point obtained by different methods of fibre extraction.

It appears from this graph that the chemical extraction method (0.1 N-BPD) has the highest elongation at break (5.6%), and the chemical extraction method (2 N BPS) has the lowest elongation at break (1.8%).

At the end of this analysis, we discovered that the best method that produces ductile fibres is the chemical extraction method (1 N-BPD). Because it permits generally to obtain the best mechanical characteristics. This result is also demonstrated for other vegetable fibres which when treated with 6% NaOH and incorporated in a mortar, increase the flexural strength [12] and other properties like compressive strength of the mortar [12] [13] [14] [15]. Thus, the overall characteristics (mechanical, physical) retained for our bagasse fibres are shown in Table 3 below.

In this section, the results from laboratory experiments was presented, and some

conclusions have been drawn: The sugarcane bagasse fibres has a fine geometry compared to many fibres encountered in literature with an average diameter which is around 0.19 mm. Its hygrometry (recovery rate and water content) is encouraging because it revealed that the bagasse fibres absorb less water (the water content and the recovery rate being 10.18% and 11.32% respectively) compared to many other vegetable fibres that have been incorporated into a mortar [16] [17]. The fibres obtained by the chemical extraction method (1 N-BPD) had the best characteristics. This result means that with this percentage of soda (NaOH), the residual mechanical strength of the fibres increases. This was also mentioned by Toledo et al. [18]; this is all the more consistent because according to Van de Weyenberg et al. [19], the treatment of plant fibres with NaOH changes their structure.

This result could be exploited in the study of the durability of mortars in which bagasse fibres are introduced; as several authors have shown, in this case Sedan et al [12], plant fibres treated with 6% NaOH are sufficient to improve the flexural strength of at least 39% of mortars in which these fibres are incorporated.

It should also be noted that the extraction methods used each have their advantages and disadvantages. Natural methods: Combing and retting have the advantage that they are less expensive, and do not require a lot of equipment and expertise to implement; but the fibres from these methods do not have the best characteristics. On the other hand, the chemical method with soda (NaOH) is more expensive and requires more expertise than natural methods, but it allows to extract more fibres with the best characteristics.