Extraction and physicomechanical characterisation of Typha Australis fibres: Sensitivity to a location in the plant

ABSTRACT Typha Australis is a problematic invasive plant in Senegal. This study aims to promote the valorization of this plant in the field of biocomposites for furniture, door panels or automobiles. Thus, Typha Australis fibers obtained by manual extraction with plastic comb are subdivided into three zones: top, middle, and bottom. Physicomechanical properties such as density, water content, tensile strength and Young’s modulus are measured. The results show an average density of 1.53 g/cm3 in the three zones, the same order of magnitude as lignocellulosic fibers. The water content of the different fibers obtained is between 6% and 10%. To determine mechanical properties, a tomographic analysis is performed for each fiber to accurately know the section at any point before the tensile test. Of the three studied areas, the middle fiber shows the best mechanical characteristics with a maximum stress of 103.5 MPa, elongation at break of 0.5% and Young’s modulus of 5.6 GPa. These results are promising as they show a lightweight material with better values in its middle part that can be effectively used as reinforcement.


Introduction
More and more scientists are in the search of strategies to facilitate a more innovative, resourceefficient and competitive society that reconciles the sustainable use of renewable resources for industrial purposes while ensuring environmental protection. In this context of eco-design, the use of composites based on plant fibers, whose vocation, in the long term, is to replace part of the traditional composites based on synthetic fibers, becomes essential.
Natural fibers such as flax, jute, cotton, etc., are resources found in abundance and are easily decomposable, biodegradable, and renewable (Jeyapragash, Srinivasan, and Sathiyamurthy 2020). They are more available than synthetic fibers, with low cost, low density, and desirable aspect ratios (Chokshi et al. 2020) despite a large dispersion noticed in their different properties (physical, mechanical, chemical).
In Senegal, the Typha Australis plant is found in the Senegal River basin and its presence was exacerbated by the effects of the construction of the Diama anti-salt dam in 1986. Overall, in the river basin, the figures on affected areas vary widely and are estimated to be between 60,000 and 80,000 ha according to research (PNEEB 2014). And its progression, which varies according to the environment, can reach 15% per year on average Typha Australis is an aquatic perennial plant found in wetlands belonging to the Typhaceae family (Dieye et al. 2017) and can grow up to 1 to 3 meters long with spongy, strap-like leaves (Ponnukrishnan, Chithambara Thanu, and Richard 2014). The invasion of this plant along the river basin is causing problems related to public health, water supply security, biodiversity, economic activities . . . (Diatta et al. 2011). To overcome these problems and to avoid the destruction of this biomass at the risk of spending a lot of financial resources and time, this plant is used in construction as an aggregate with clay (Niang et al. 2018(Niang et al. , 2019, with cement (Gaye et al. 2021) or in biofuel for the manufacture of charcoal (Henning and GbR 2002). Another possibility is to use Typha Australis fibers as reinforcement in biocomposites for the various end applications such as furniture's, door panels, shelves or automotive dashboards (Sabarinathan et al. 2020).
It is within this framework that this study focuses on the determination of the physical and mechanical properties of Typha Australis fibers to check their capability.
The study of the characteristics of the fibers allows a relevant comparison between synthetic and biosourced fibers. A better understanding of the potential of Typha fibers will enable them to be positioned in the family of the most widely used natural fibers. However, it is important to identify extraction techniques that preserve the chemical and physical properties of the fibers while being economical interesting (Bezazi et al. 2014), (Rao and Rao Rao and Mohana Rao 2007).
Some authors have carried out a retting process of the fibers from the Typha Domingensis leaf followed by extraction with the manual extraction machine (Ramesh et al. 2020) or decortication by hand . In our case, a direct manual extraction of the fibers is performed from the fresh leaf using a plastic comb.
Results of physical properties show that linear density of Typha leaf fibers is between 10 and 30 tex with a diameter between 141 and 496 μm. The bigger value of the average diameter of untreated fibers (486 μm) resulted from layers of wax and fatty substances on their surface and a large number of micro fibrils in one fiber bundle. So, in order to obtain a thin fiber, extraction conditions need to be severe (Sana, Mounir, and Slah 2014). It is also seen that the Typha fibers (d = 50 µm) are polygonal in shape and multicellular in nature like other vegetable fibers. The microscopic photographs of the extracted fibers show that finer fibers can be obtained because of the proper extraction process (Moghaddam and Majid Mortazavi 2016). Concerning the mechanical properties, the tensile strength of the Typha Domingensis leaf fiber is very good (38.63 g/tex) and is comparable to flax fiber. The elongation properties are also found similar to flax (Pandey, Jose, and Kumar Sinha 2020).
The main objective of this study is to characterize Typha Australis fibers manually extracted to evaluate their potential as reinforcement in composites. To do so, physical properties results like density and water content are given and mechanical properties namely strength, Young's modulus and elongation at break are well known and compared to other researches.

Extraction of Typha Australis fibres
Typha Australis studied comes from the Hann Maristes basin in Dakar-Senegal. The young plant was harvested according to the standard NS 02-061 (Homologuée 2014) of Senegalese cutting. The leaves separated between them are then subdivided into three zones: the bottom, the middle and the top (Charlet et al. 2009) as shown in Figure 1 to observe the influence of the location of the fiber on physical, mechanical properties.
The extraction of the fibers represented on Figure 2 is manually done with a plastic comb (Rao and Mohana Rao 2007). The spacing between the teeth of a plastic comb was 1 mm.
The fibers obtained are then sun-dried to take maximum advantage of the sun during the day. After 3 days, the moisture of the fibers disappears (Ramesh et al. 2020).

Density measurement
The tests were performed using a Micromeritics AccuPyc II 1340 helium pycnometer.
The measurements, repeated ten times, are performed by applying a pressure of 19.5 bars with a stabilization criterion of 0.0065 g/min. A sample holder of 10 cm 3 is used. The absolute fiber density (ρ) is given by Equation 1, where V represents the volume occupied by the fiber sample and m the fiber mass tested.

Water content measurement
The water content (W) is determined according to the French standard NF EN ISO 665 2020. It corresponds to the loss of mass that the sample undergoes when it is dried in an oven at 105°C until it reaches a constant mass. According to the NF EN ISO 665 standard, the determination of the mass of cotton seeds begins after three hours of drying. On this basis, the drying times of the Typha samples were 120, 150, 180, 210, and 240 minutes. The fibers were weighed with a Mettler Toledo electronic balance with a precision of 0.01 g. The tests were repeated three times. Figure 3(a-c) above illustrates the dried Typha fibers.

Tensile testing
We used the Instron 68SC-2 tensile/torsion machine with a 100 N load cell. As shown in Figure 4 , the fiber to be tested is glued into a paper frame hollowed out in the center with a cut on each side just before the test is initiated (Ilczyszyn 2013). A pre-tension of 1 N is applied before starting the test.
The fibers are tested with a traverse speed of 5 mm/min and a gauge length of 20 mm according to ASTM 3822-07 (Properties 2007).
To determine the stress, a tomographic analysis of each fiber was made on the gauge's whole length to know the fiber's section at any point. A total of 1440 sections were obtained for maximum accuracy.
Once the specimen is broken, the fracture zone is located, and the surface of the image in questionobtained by X-ray thanks to the tomograph -is measured by image processing using Image J software (Postdam 2017). An example of a fiber section obtained by tomography is given in Figure 5 respectively. The Young's modulus is the slope of the line in the elastic part.

Density
The average absolute densities of Typha fibers are compared to those of other natural fibers is given in Table 1.

Water content
The results are presented in Table 2 and illustrated in Figure 6. Missing measurements are related to the availability of the experimental setup.

Tensile strength
The tensile curves obtained for the bottom, middle and top fibers are plotted in Figures 7, 8 and 9. The average values of the elastoplastic parameters from fiber traction in each of the three zones are given in Table 3 for comparison. The standard deviations and the coefficients of variation (CV) of the fibers are also given.

Density
The low standard deviations obtained (0.016-0.026 g/cm 3 ) show the excellent repeatability of the measurements made. The slight difference between the values could be related to the physicochemical properties differing from one area to another or could be due to experimental bias. The highest density (1.605 g/cm 3 ) is observed on the bottom fibers. Indeed, these fibers are heavier and full of much more sap released during combing. The top fibers are lighter and more fragile with a lower density (1.478 g/   cm 3 ). A same observation was made by Charlet et al. (Charlet et al. 2009) on flax fibers. They explained that the bottom and top fibers have a higher porosity than the middle ones. In addition to that, the bottom ones are in direct contact with the soil hence exposed to harsh environmental conditions. However, the density of the middle fiber of Typha (1.519 g/cm 3 ) being closer to that of flax. The average obtained from the three Typha zones, which is 1.53 g/cm 3 , is of the same order of magnitude as the density of flax and that of lignocellulosic fibers, which is about 1.53 g/cm 3 (Delannoy 2019).   Comparing the results with the density of Munja fibers (1.423 ± 0.067 g/cm 3 and 1.487 ± 0.053 g/ cm 3 in distilled water and diesel, respectively) (Lila et al. 2022) the difference is not too great and these results are closer to those of the top fiber.

Water content
The water content of our fibers ranges from 6% to 10% as shown in Figure 7. In detail, the lowest contents are measured for the bottom fibers, despite their larger standard deviation. According to studies (Baley, Morvan, and Grohens 2005) and (Charlet 2008), water represents about 8-10% of the mass of flax fiber. These observations are verified for our middle fiber with an 8.44 ± 0.52% content beyond 3 hours of drying. In addition, data available in works (Bismarck et al. 2002;Mohanty, Misra, and Hinrichsen 2000), and (Tserki et al. 2005) show that the mass moisture content of flax fibers stored under ambient conditions is generally between 6% and 10%, as shown in Figure 6 of our Typha Australis fibers.

Tensile strength
A large dispersion noted in the top and the bottom zone is already observed on natural fibers and quantified by Bezazi et al. (Bezazi et al. 2014). Despite its low Young's modulus, tensile stress and elongation are greater for the middle fiber.
The experimental results indicate a sensitivity of the tensile strength to the location of the fiber with the area in the middle showing the highest average value of this property. The difference between the stresses of the middle and top fibers is 22% and 16% respectively.
The mechanical properties of plant fibers depend on several factors such as cultivation and weather conditions, conditioning, etc. (Almusawi 2018;Ilczyszyn 2013). In this study, the age of the Typha and the extraction method used played an essential role in the mechanical values obtained. Indeed, extraction with a comb does not individualize the fibers enough, but it can also damage the fibers, as mentioned by Silva et al. (de Andrade Silva, Chawla, and de Toledo Filho 2008). Other authors have confirmed this hypothesis by reporting that the presence of natural defects (intrinsic) and those related to the fiber extraction process (extrinsic) influence the measured properties. These extrinsic defects (micro-cracks) can be caused by defibration, especially mechanical defibration, which damages the fiber, thus reducing its mechanical resistance to rupture (Goutianos et al. 2006;Ilczyszyn 2013;Shah et al. 2012).
Typha fibers have mechanical properties close to those of coir fiber, as shown in Table 4, which positions Typha fibers in relation to other natural fibers already studied in the literature.
Insert Table 4 here (Delannoy 2019;Jeyapragash, Srinivasan, and Sathiyamurthy 2020). However, it should be noted that the result of combing, which is called a fiber, is, in fact, a bundle of several fibers, as shown in Figure 5. This can explain the low elongation value at break of the Typha "fibers" since there is quickly a disassociation between fibers, causing the test to stop. This phenomenon induces a low value of the maximum stress at break.

Conclusion
The use of natural plant reinforcements to replace synthetic ones in various fields due to certain verified properties is one of the reasons for the interest in Typha Australis from the Senegal River. Typha Australis harvested in the Maristes basin and extracted manually with a plastic comb is studied to determine its characteristics and its possible use as composite reinforcements The physical properties determined show some similarities to those of flax, namely a water content of between 6% and 10%; an average density of the three zones of 1.53 g/cm3 of the same order of magnitude as that of lignocellulosic fibers From a mechanical point of view, these fibers show some sensitivity to location showing better results for a fiber from the middle zone with a maximum tensile stress and a Young's modulus of 103.5 MPa and 5.6 GPa respectively.
The results obtained on the studied fibers in relation to those commonly used do not present any contraindication on the possible use of Typha as composite reinforcements.
Thus, these observations point to the possible use of Typha Australis fibers from Senegal as reinforcements for composites in sectors that use more wood, such as home and office furniture, which are also sectors with a high import rate, the use of suspended ceilings but also the replacement of aluminum panels with Typha biocomposites as office partitions.
However, it is essential to consider the age of the Typha plant at the time of its harvest for more satisfactory results and the extraction method for a better individualization of the fibers while not attacking them. A subdivision of the fibers in different zones also limits the dispersion of the results. Our work shows that the results obtained for the middle zone are better than those of the other zones.
• Valorisation of Typha Australis fibers from Senegal as composite reinforcements • Calculation of mechanical parameters like Young's modulus and tensile strength of fibers using real breaking section obtained by tomography • Measurement of absolute density of Typha Australis fibers with helium pycnometer • Evolution of water content depending on drying time in Typha Australis fibres • Subdivision of Typha Australis fibers into three zones to obtain their specific characteristics

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
The work was supported by the WORLD FEDERATION OF SCIENTISTS [+41227679957].