3.1. Density measurement
Density measurement of the natural fibers is essential to evaluate the potential density of composite materials that use certain fibers. Various factors affect the density of cellulosic fibers such as the soil plant conditions, humidity present, fiber 's age, the fiber extraction process, etc.
The density value for 3 % alkali and 3% permanganate treated was IVFs (1102 ± 33.42 kg/m3), (1154 ± 13.22 kg/m3) which is a slight density increment compared to untreated IVFs (1040 ± 10.54 kg/m3). This is possibly attributed to the pores and voids in the fiber surface consisted grafted molecules during chemical treatments [33-35]. From this testing, it was noted that the density of novel fiber IV was lower than other natural fiber such as jute (14800 kg/m3), sisal (1500 kg/m3), Alfa and Sabra fibers (1.40 g·cm−3 ± 0.02), banana (1350 kg/m3) , Cyperus pangorei (1102 kg/m3). Thus, IVs could be the candidate fiber reinforcement for composite lightweight.
3.2. Diameter measurement
The average diameters of the untreated raw fiber, 3% alkaline and 3% permanganate treated IVs fiber as shown in Figure 5. The diameter of untreated raw fiber (93.50 ± 2.75 µm), 3% alkaline (80.41 ± 1.63 µm), and 3% permanganate treated (78.60 ± 1.82 µm)., respectively.
3.3. Scanning electron microscopy (SEM)
The surface morphology of fibers can be determined using the Scanning Electron Microscopy (SEM) method to examine the surface morphology of fibers. Scanning electron micrographs of untreated, alkaline, and permanganate-treated fibers are presented in Figure 6. Figure 6 (a) shows the SEM micrograph of untreated fibers, the surface of IVs showed absence of impurities such as wax and grease, and internal fibrils . At higher magnification, Figure 6 (b) shows that the removed waxes and oils from the fibers' surface were removed by 3% alkaline treatment, thus enable surface roughness on the fiber surface [41, 42]. The alkaline treatment showed the differences compared to raw fiber. In this case, the fiber's surface was smoother than the raw fiber due to removing surface impurities. For permanganate-treated fibers, Figure 6 (c), it can be observed that the fiber became cleaner, with a rougher surface, as impurities were removed from the surface of the fiber . This rough surface may improve interfacial bonding when IV fibers are used as reinforcing materials.
3.4. Energy-dispersive X-ray spectroscopy analysis (EDX)
The EDX technique relies on the sample's major interaction and the X-ray excitation source. The qualitative findings on the quantity of major elements (carbon, oxygen, calcium, manganese, etc.) provided by the fiber surface of untreated and treated IVFs are shown, Figure 7. In addition, the presence of C and O elements tends to be the most prominent in the EDX continuum since they are the critical components of the architectures of natural fibers .
The EDX study of both untreated and handled IVFs in terms of atomic percentage and weight is provided in Table II. It has been found that untreated IVF comprises almost 97.56 percent carbon weight, however, the carbon proportion is decreased to 97.32 percent and 75.08 percent for alkaline and potassium permanganate treatments, respectively, since chemical treatments could have eliminated the outer layer of the treated fiber . This would be due to the IVF's more non-cellulosic components.
3.5. Thermogravimetric analysis
The thermal properties of untreated and treated IVF fibers are analyzed using TGA. Figure 8 demonstrate the TGA and DTG curves of these lignocellulosic fibers, an essential feature in biocomposite based on these fibers . The first stage of decomposition was similar to untreated raw and chemically treated (IV) fibers, indicating the weight loss process. At the range between 30 ℃ and 125°C, a small weight loss (6.15%) was demonstrated, which is agreed by several authors [43, 44].
It was shown that the first curve trend in DTG curves were decline in DTG curves, Figure 8 (b), it is proven that the water evaporation after 3% alkaline, 3% permanganate treatment. The same observation was found in Figure 8 (a). This is due to the reduction of the cellulose fiber's hydrophilic nature when the chemical treatment was employed on the IV fiber as the acquired for fiber reinforced polymer composites. Thus, the reduction moisture loss percentage in the both treated fibers could be the higher of crystallinity properties of the IV fiber .When the temperature rises up to ℃, no significant peak is observed in the DTG curve and the similar was agreement with others work . Beyond this temperature, thermal stability is decreasing and the fiber decomposition is happened, Figure 8 (a).
The second stage decomposition at 190℃ until 290℃ corresponds to hemicellulose decomposition and the third decomposition at 290°C-400°C correspond to cellulose and lignin decomposition. It was reported by another study  the least thermally stable was hemicellulose, the intermediate was cellulose and the lignin was the most resistant.
The untreated IV fibers started to degrade at around 200℃ as shown in the degradation profile. The first degradation peat at 285°C correspond to the depolymerization of hemicellulose, pectin and glycosidic linkages of cellulose by 18.71% of weight loss. The 3% alkaline and 3% permanganate treated IVs. the peak was not visible, proving the complete removal of hemicellulose from the fiber. The major second peak was observed at 365.51℃ due to degradation α-cellulose by 80.87% weight loss for untreated raw fiber , whereas 3% alkaline treatment and 3% permanganate -treated at 363℃ and 350 with 67.7 % and 62% weight loss respectively . It can be noted that surface modification by both treatments reduced the thermal stability properties of the IV fibers, our findings are consistent with previous works [49, 50]. From ambient to higher temperatures at 600℃, the lignin degradation whose structure is a complex composition of aromatic rings with different branches may occur at a very low weight loss .
3.6. Fourier transforms infrared spectroscopy (FTIR)
The comparison of FTIR spectra of untreated raw fiber and chemically treated with 3% alkaline and 3% permanganate of Inula Viscosa (IV) fibers presented in Figure 9, shows absorption bands of chemical groups characteristic of lignocellulosic fiber compounds. The main characteristics of the spectrum of the untreated IVs at the peaks 3329, 2919, 2851, 1731, 1638, 1592, 1423, 1325, 1239, and 1028 cm-1 are a-cellulose, hemicelluloses, lignin, pectin, and water molecules contents. From the large absorption band observed around 3329 cm-1 is linked to OH and CH stretching of cellulose  . The strong adsorption peaks depicted at 2919 cm-1 and 2851 cm-1 are related to C-H stretching vibrations from CH and CH2 in cellulose and hemicellulose, respectively . An observable peak around 1731 cm-1 corresponds to the C=O stretching of hemicelluloses [21, 54]. The band around 1638 cm-1 was related to the O–H bending of water absorbed into cellulose fiber structure The peak around 1592 cm-1 corresponds to the aromatic ring C=C of the phenyl propane group in lignin . Also, a small peak near 1423 cm-1 belongs to the aromatic skeletal vibrations and ring breathing with C–O stretching in lignin . The peak observed at 1325 cm-1 is attributed to C-H and C-O groups' bending vibration of the aromatic ring in polysaccharides. Additionally, A small peak around 1239 cm-1 belongs to the acetyl group's C–O stretching in hemicelluloses . A visible peak at 1028 cm-1 is related to the stretching of C–O groups of cellulose . The fibers' FTIR spectra confirm the compositional changes in permanganate and alkali-treated fibers, Figure 9. The two peaks at 1239 cm−1 and 1731 cm−1 were observed in FTIR of untreated fibers, which correspond to hemicelluloses, disappeared in the spectrum of the permanganate and alkali-treated fibers. This result could be explained by the elimination of the residual hemicellulosic materials after the treatment. The removal of an important amount of lignin by the chemical treatment can be noticed through the disappearance of the peaks located at about 1325 cm−1 and1423 cm−1. It is to demonstrate that the removal of hemicelluloses and lignin from the treated (IV) supports the results of the chemical analysis.
3.7. XRD analysis
Figure 10 illustrates the XRD pattern of the 3% alkaline, 3 % permanganate treated and raw fibers specimen of IV and the corresponding planes involved. From the Figure 10, it was shown that each specimen showed two peaks, respectively. For 3% permanganate and 3 % alkaline treatment, the first peak represents the amorphous peak demonstrated at 2θ = 15.96˚, 16.45° and 16.06˚ at lattice plane (110). respectively. While for the second-high intensity peak the 3% alkaline , 3% permanganate and untreated IV fibers represents the crystalline peak observed at 2θ = 22.48˚, 22.52° and 22.08˚ respectively, belongs to the (200) plane of cellulose . The value of crystallinity index (CI) was higher for 3% permanganate at 55.93% followed by 3% alkaline treatment at 54.25% and untreated raw fiber at 51.63%. It was shown that chemically treated with alkaline and treatment were improved compared to untreated.
The increase in CI with permanganate and alkali treatments is related to the loosening of cellulosic chains resulting in the disappearance of excess amorphous constituents, such as lignin, hemicellulose, etc. .This result was agreed with SEM morphology the impurities of fiber was removed with chemical treatment.. Furthermore, the crystallite size (CS) of the untreated raw, the 3% alkaline and the 3% permanganate-treated of the IVFs were obtained as 0.8 nm, 1.85 nm and 2.0 nm, respectively. The crystallite size may reduce the chemical activity and the water absorption capacity of the fibers.
3.8. Tensile test
The study of mechanical properties of natural fiber reinforced polymer composites is important to understand their potential for various structural applications. Figure 11 (a), depicts the impact of untreated raw, 3% NaOH and 3% permanganate-treated IVFs on the tensile strength of IVFs. From the graph, the tensile strength trend was increasing for 3% permanganate, followed by 3% alkaline treatment compared to untreated raw fiber with the value of 195.88MPa, 173.047 MPa and 163.60 MPa, respectively. The increased tensile strength of chemically treated IV fibers due to the elimination of impurities from the IV fiber surface. Previous research shows the values of tensile strength from plants fiber was approximate with IVs fiber such as sisal (274-526 MPa) , date palm (170-275 MPa) , Lygeum Spartum (LS) (113 MPa) , pineapple leaf fiber (PALF), and Arundo Donax 248 MPa . The strain rate of untreated fibers and alkali and permanganate treated IVFs is 1.172%, 1.439 %, and 1.562% respectively, which directly affects the micro fibrillation angle of the IVFs Figure 11 (b). The Young modulus of raw natural fibers and fibers treated with alkali and permanganate is 11.407 GPa, 11.596 GPa, and 12.25 GPa, respectively, Figure 11 (c). The tensile modulus of IV fibers with 3% alkaline and 3% permanganate was higher than untreated raw fiber. The values are quite approaching to other plant fiber such as artichoke (11.6 GPa), sisal (9.4 - 22 GPa) and bamboo (11-17 GPa) .
3.9. Droplet test
This work evaluated the bonding strength between the IV fiber and epoxy resin by a droplet test. As shown in Figure 12, the IFFS interfacial shear strength was obtained from the test results. Unlike other fiber pull-offs, this technique allows the average shear stress to be calculated once the fiber is peeled off by force (Fd).
It should be noted that the apparent adhesive force measured with micro bonding tests varies greatly. The variability causes this in the IV fiber dimension that have different diameters. The mechanism of droplet test showed that when the increase of load to pull out the IV fiber, the easily IVs fiber to break. From this result, the higher interfacial shear strength was permanganate-treated fiber with 4.50 MPa, followed by alkaline treatment, and untreated of IVs fiber with 3.36 MPa and 2.93 MPa, respectively. The increased value of t IFFS for permanganate was 53.58% and alkaline treatment by 11,26 % compared to untreated IVs fiber. The data obtained is comparable to the IFFS of flax, hemp, and sisal . The adhesion between the epoxy resin and the Inula Viscosa fiber was improved by permanganate treatment and alkalization. According to the results, the adhesion between the treated Inula Viscosa fiber/epoxy was better than the adhesion bonding between the untreated Inula Viscosa fiber/epoxy.