Extraction and Characterization of Fiber Treatment Inula viscosa Fibers as Potential Polymer Composite Reinforcement

This research aims to characterize and analysis of newly cellulosic fiber extracted from Inula viscosa bark. The obtained Inula viscosa fibers were also characterized after having been treated with alkali and permanganate treatments. The effect of chemical treatments on the mechanical, physical, chemical and thermal properties of Inula viscosa fibers was investigated by using, X-ray diffraction, thermo gravimetric, scanning electron microscope analysis, optical microscope test, tensile and droplet tests. The treatment with permanganate was found to have the higher density (1.154 ± 0.032 g/cm3) compared to that of the untreated ones (1.040 ± 0.010 g/cm3). The best mechanical properties were also achieved when the permanganate treatment was adopted. In this pretext, tensile strength values and Young modulus were found as 196.99 ± 28.89 MPa and 12.98 ± 2.36 GPa, respectively. It is estimated that the fiber treatments will enable high-quality Inula Viscosa Fiber-reinforced polymer composites for use in the industry.


Introduction
Societal needs for new environmentally friendly materials make scientists to develop materials from nature itself. The increased numbers of research on renewable and biodegradable materials to replace conventional materials [1][2][3]. Researchers and scientists currently focus on green composite materials from plants fibers with good fiber yields, costeffective without compromising mechanical properties [4]. This is justified because, on the one hand, natural fibers have the status of renewable and durable materials; on the other hand, they are abundant, light, of moderate resistance, high specific modulus compared to synthetic ones [5][6][7]. Composite materials reinforced by natural fibers have contributed significantly to the human race's well-being and technological development. The construction industry, vehicle parts, domestic applications, aerospace, sports equipment, and others have been more inclined to use cellulosic fibers because of their benefits [8,9].
The various sections of a plant, such as bark, root, seed, leaf can be obtained from the cellulosic fiber. The latter is one of the most available and inexpensive materials on the planet due to its wide variety of industrial and common applications. When assessing natural fibers' properties, natural fibers properties are also highly influenced by the environment's growth, such as humidity, temperature, soil, and all affect fiber strength, density, and so on. Also, the fibers' extraction (chemical, mechanical, or biological technique) leads to various properties.
It is known that the plants are grown in various regions and are exposed to different environmental conditions. Hence, the characteristics of the fiber are highly dependent on these conditions. Added to this is plant age, quality of soils, etc. [7, 10].
The cellulose's exceptional properties such as low spiral angle, small diameter, and continuous will enhance the properties of the composite. The outer layer of cellulose fiber is covered by non-cellulosic component (hemicelluloses, lignin, pectin, and wax).
The conditions of the natural fiber are based upon the strength of cellulose fiber. Higher tensile strength is achieved by the chemical composition of the cellulose fiber. Therefore, it is necessary to explore new natural fibers, with fiber reinforcement's required strength properties. A wide range of diverse natural fiber is available that offer reinforcing effects to polymer composites. The mechanical efficiency of polymer matrix composite is primarily dependent on interfacial bonding. The fibers may be changed in chemical or physical treatments [11,12]. Also, natural fibers treated with mercerization, silane treatment, benzoylation, potassium permanganate, etc., have significant advantages, such as lower water absorption, increased surface roughness, and higher thermal stability, less amorphous content, improved crystallinity index, and increased crystallite size [13][14][15]. Natural fibers are obtained from various plants such as tree bark such as Azadirachta indica, Ceiba pentandra, Acacia Concinna, Grewia tilifolia, Acacia Nilatica L., Acacia leucophloea, ramie, and yarn have been a focus of research for scientists as reinforcements of composite because of their specific properties and availability [16][17][18][19][20].
The current work focuses on the characterization of new cellulosic fiber extracted from the bark of Inula viscosa plant. Two different chemical treatments, 3% alkaline and 3% permanganate, have been adopted to improve the performance of the obtained Inula viscosa fibers. The physicochemical, morphological, mechanical and thermal properties of the Inula viscosa fibers is investigated for the first time in this work. The fiber surface and fiber structure morphology were observed by using a binocular microscope and scanning electron microscopy (SEM). The surface morphology of Inula viscosa fiber was investigated using a binocular microscope and scanning electron microscopy (SEM). Infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were employed to analyze the chemical and molecular structure of untreated and treated Inula viscosa fibers. The thermal stability was conducted by using Thermo-gravimetric analyzer. The mechanical properties of Inula viscosa fibers were investigated using the single filament test according to the ASTMD3379 standard method. The interfacial shear strength, post-debonding strength and debonding behaviors were studied using a micromechanical droplet approach.

Materials
Dittrichia viscose (L.) or Inula viscosa (IV) owes its name to the Greek "inaein" which means purged. This plant is known in Algeria as "Magraman". It is an undemanding plant in the Mediterranean region and widespread in northern Algeria. It grows in grassy places, in fields, and is also found along roadsides and paths. It belongs to the family Asteraceae, Class: Magnoliopsida; Genus: Inula Species: Inula viscosa. It is a wild, perennial, taprooted, reasonably large (up to 1.50 m tall) plant. Its stems are fairly branched and have dense foliage. The leaves, alternate, elongate to lanceolate, are inserted directly on the stem, without petioles. The whole plant is coated with glandular hairs that release an odoriferous and sticky resin, with a smell of camphor, Fig. 1.

Fiber Extraction from the Plant
Fresh Inulaviscosa plant was collected from Hodna region (Algeria) in April 2019. First all, leaves were separated from their stem. After that, IV stems were completely immersed into the container filled with tap water and covered for five weeks to detach outer skin from the stem using biological retting technique [21,22]. Next, the inner layer was manually removed from the outer layer. The inner layer of the bark yielded fine fibers. The extracted fibers were washed in running water to eliminate unwanted contaminants left behind the fiber surface, then dried in an oven at 70 °C for 6 h, Fig. 1.

Chemical Treatments
Two different chemical treatments were used in this investigation. The 3% alkaline and 3% permanganate were used to alter the Inulaviscosa fibers' surface and foster a stronger bonding between them and the resin.

Alkaline Treatment
IV fibers were immersed in distilled water with a 3% sodium hydroxide solution, for 3 h. The fibers were immersed in water prior to having neutral pH reached. After rinsing, the fibers were dried for 48 h before being characterized.

Permanganate Treatment
For the permanganate treatment, the pretreated with alkaline fibers as in "Alkaline Treatment" section were soaked 1 3 in 3% of Potassium permanganate (KMnO 4 ) solution for 3 min [23]. These fibers were washed and dried in the air.

Scanning Electron Microscopy
The surface morphology of the three types of IV fibers were analyzed using a Scanning Electron Microscope (SEM) machine Model HITACHI S-3400N. The SEM instrument was set up at an emission current of 58 μA. The working distance was set to 6.2 mm, and the acceleration voltage of 5.0 kV. Before taken microscopic image, the fibers were coated with a thin gold layer to avoid electrical charges during the examination.

Energy-Dispersive X-Ray Spectroscopy Analysis (EDX)
The EDX involves an analytical method was employed for the element analysis of a sample attached with SEM images. This approach allows elements from the whole element of periodic table to be detected of the three types of IVFs, except for H, He, and Li. Therefore, the Hydrogen can't be observed by this technique which represents the major constituents of natural fiber (Table 1).

Fourier Transform Infrared Spectrometry (FTIR)
The FTIR analysis was carried out for untreated the three types of IVFs by using an FTIR machine (SHI-MADZU81001, Japan). The purpose of using FTIR analysis to distinguish the changes in functional groups on the fiber surfaces of IVs. All spectra were recorded in the range from 4000 to 500 cm −1 .The sample preparation for this testing, the fibers were chopped and were ground into powder form.

X-Ray Diffraction Analysis (XRD)
The degree of crystallinity and crystalline size of cellulosic fibers IVs were tested by using an X-ray diffraction test [24]. The XRD testing is non-destructive and rapid testing. The tests were carried out for the three types of IVFs. In this testing, the Copper was used as the anode material with monochromatic Cu Kα radiation with a wavelength of 0.154 nm and a current of 30 mA and voltage of 30 kV. The continuous scanning mode, 2θ range varying from 5° to 60° with a step size of 0.02° at 25 °C. The Segal empirical technique  and Scherer's equation were used to determine, the degree of crystallinity and crystallite size of the three types of IVFs as displayed in Eqs. (1) and (2).
where, I c represents the maximum intensity of the crystalline phase peak and I am represents the amorphous phase's intensity in the cellulose present in the fiber [25].
where K = 0.89 is Scherer's constant, β is the peak's fullwidth at half-maximum, λ is the wavelength of the radiation, and θ is the corresponding Bragg angle [26].

Thermogravimetric Analysis (TGA)
The thermal stability and thermal decomposition of the three types of IVFs were obtained by using Thermogravimetric analysis by using GA machine Model (TGA Q 500 TA Instrument, USA). The specimens were measured under room temperature ranging from 30 to 600 °C.

Density Measurement
The densities of the three types of IVFs was calculated by a liquid pycnometer for solids with immersion liquid known as the methanol (methanol, ρ = 0.791 g/cm 3 at 21 °C). The liquid pycnometer was based on direct measurement of specimen's volume. The accuracy of electronic weighing machine was checked at 0.00001 g before the weight measurement of the fiber. The sample of IVFs were cut with the length of 1 mm to suit in the pycnometer [27] and were placed in an oven at 60 ℃ until the moisture content was reduced to below 5% before testing [28]. The densities of the three types of IVFs (ρIVFs) were calculated through the following Eq. (3) [27] where ρ IVF is the density of IVFs (g/cm 3 ), ρ E is the density of methanol (g/cm 3 ), m 1 is the mass of empty pycnometer (g), m 2 is the mass of pycnometer with fibers (g), m 3 is the mass of pycnometer with methanol (g), and m 4 is the mass of pycnometer with fibers and methanol (g) [29].

Diameter Measurement
A diameter test was carried out on a single fiber of the three types of IVFs at room temperature by using Olympus, BX51 optical microscope (Japan) with a magnification of 5X, three replicates were measured for each untreated and treated IV fiber by placing the fiber over a glass plate and taping down its end to obtain a clear image [30].

Tensile Test
Tensile testing of the three types of IVFs was evaluated by Instron universal testing machine (UTM)at a speed of 1 mm/ min according to ASTM D 30393. The fibers were then fixed and glued to the tab shape, which was performed with the gauge length of 30 mm fibers then inspected to remove the crack, Fig. 2. The tensile strength of fibers was calculated from the following Eq. (4) [31].
where, T tensile strength in Pa, F force to failure in N, A average fiber area in m 2 .

Droplet Test
In the droplet test, a thin metal rod was chosen to place microdroplets of epoxy resin on single fibers that were fived to a paper frame and left to solidify. Before testing, the paper frame was cut away when a sample was connected to the tensile testing machine equipped of 5kN (INSTRON UTM). The interfacial shear strength (IFSS) which evaluate the adhesion in specific fiber matrix system according to the following Eq. (5) [32] where τ is the interfacial shear strength (MPa), F max is the maximum pull-out force; D is the fiber diameter and L is the embedded length. Both parameters were measured using an optical microscope equipped with a high resolution before testing, Fig. 3a. The schematics of the microdroplet test are shown in Fig. 3b.
The ten samples for each untreated raw fiber, 3% alkaline and 3% permanganate-treated were tested. The fiber diameter measurement was obtained from the point nearest to the droplet to both sides' fiber contacts.

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 cellulosic fibers' density, such as the soil plant conditions, humidity present, fiber's age, the fiber extraction process, etc. The densities values for 3% alkali and 3% permanganate treated fibers are 1.102 ± 0.33 g/cm 3 and 1.154 ± 0.13 g/cm 3 respectively which are slight densities increment compared to untreated one (1.040 ± 0.10 g/cm 3 ). This is possibly attributed to the pores and voids in the fiber surface consisted grafted molecules during chemical treatments [33][34][35]. It was noted that the density of novel IV is lower than other natural fiber such as jute (1.4800 g/cm 3 ) [36], sisal (1.500 g/cm 3 ) [37], Alfa and Sabra fibers (1.40 g/cm 3 ) [34], banana (1.350 g/m 3 ) [38], Cyperus pangorei (1.102 g/cm 3 ) [39]. Thus, IVs could be the candidate fiber reinforcement for composite lightweight.

Diameter Measurement
The average diameters of the three types of IVs fibers are shown in Fig. 4. The investigated untreated, alkali and permanganate treated fibers were found to have the diameter of 93.50 ± 2.75 µm, 80.41 ± 1.63 µm and 78.60 ± 1.82 µm, respectively. As indicated, significant changes were observed in the fiber diameter after chemical treatment. These results are in agreement with those obtained by Rokbi et al. [29]. In their work, they concluded that the chemical treatment improves the quality of treated fibers, following the partial removal of lignin, hemicellulose, and adhering non-fibrous materials that link the elementary fibers. As a result, thinner and lighter fibers were obtained.

Scanning Electron Microscopy (SEM)
The surface morphology of fibers can be determined using the Scanning Electron Microscopy (SEM) method to examine fibers' surface morphology. Scanning Electron Microscopy of the three types of IV fibers are presented in Fig. 5. Figure 5a shows the SEM micrograph of untreated fibers, the surface of IVs showed absence of impurities such as wax and grease, and internal fibrils [40]. At higher magnification, Fig. 5b 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, Fig. 5c shows that the fiber became cleaner, with a rougher surface, as impurities were removed from the surface of the fiber [35]. This rough surface may improve interfacial bonding when IV fibers are used as reinforcing materials.

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, Fig. 6. 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 [40].
The EDX study of both untreated and handled IVFs in terms of atomic percentage and weight is provided in Table 2. It has been found that untreated IVF comprises almost 97.56 percent carbon weight, however, the carbon proportion is decreased to 97.32% and 75.08% for alkaline and potassium permanganate treatments, respectively, since chemical treatments could have eliminated the outer layer of the treated fiber [42]. This would be due to the IVF's more non-cellulosic components.

Thermogravimetric Analysis
The thermal properties of the three types of IVFs are analyzed using TGA. Figure 7 demonstrate the TGA and DTG curves of treated and untreated IV fibers, an essential feature in biocomposite based on these fibers [30]. 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, Fig. 7b, it is proven that the water evaporation after 3% alkaline, 3% permanganate treatment. The same observation was found in Fig. 7a. 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 higher in the IV fiber's crystallinity properties [11]. When the temperature rises up to ℃, no significant peak is observed in the DTG curve and the similar was agreement with others work [45]. Beyond this temperature, thermal stability is decreasing and the fiber decomposition is happened, Fig. 7a.
The second stage decomposition at 190 ℃ until 290 ℃ corresponds to hemicellulose decomposition and the third decomposition at 290-400 °C correspond to cellulose and lignin decomposition. It was reported by another study [46] the least thermally stable was hemicellulose, the intermediate was cellulose and the lignin was the most resistant.
The untreated IVFs started to degrade at around 200℃ as shown in the degradation profile. The first degradation peat at 285 °C corresponds to the depolymerization of hemicellulose, pectin and glycosidic linkages of cellulose by 18.71% of weight loss. The 3% alkaline and 3% permanganate treated IVFs. 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 [47], whereas 3% alkaline treatment and 3% permanganate -treated at 363 ℃ and 350 with 67.7% and 62% weight loss respectively [48]. 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 [51]. The Thermal stability of IV fiber is compared with some other natural bark fibers in Table 3.

Fourier Transforms Infrared Spectroscopy (FTIR)
The comparison of FTIR spectra of the three types of IVFs presented in Fig. 8, 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 [52]. 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 [53]. An observable peak around 1731 cm −1 corresponds to the C=O stretching of hemicelluloses [19,54]. 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 [55]. Also, a small peak near 1423 cm −1 belongs to the aromatic skeletal vibrations and ring breathing with C-O stretching in lignin [56]. The peak observed at 1325 cm −1 is attributed to C-H and C-O groups' bending vibration of the aromatic ring in polysaccharides [57]. Additionally, A small peak around 1239 cm −1 belongs to the acetyl group's C-O stretching in hemicelluloses [54]. A visible peak at 1028 cm −1 is related to the stretching of C-O groups of cellulose [43]. The fibers' FTIR spectra confirm the compositional changes in permanganate and alkali-treated fibers, Fig. 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 permanganate spectrum 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. Figure 9 illustrates the XRD pattern of the three types of IVFs and the corresponding planes involved. From the Fig. 9, 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 [40]. 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.

XRD Analysis
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. [58].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. A comparison of crystallinity properties of IV fiber with other natural bark fibers is given in Table 3.

Tensile Test
The study of mechanical properties of natural fiber reinforced polymer composites is important to understand their potential for various structural applications. Figure 10a, depicts the impact of the three types of IVFs on the tensile strength. 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 196.99 ± 28.89 MPa, 172.35 ± 32.20 MPa and 166.5 ± 44.83 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) [59], date palm (170-275 MPa) [60], Lygeum Spartum (LS) (113 MPa) [43], pineapple leaf fiber (PALF), and Arundo Donax 248 MPa [30]. The strain rate of untreated fibers and alkali and permanganate treated IVFs is 1.17 ± 0.16%, 1.43 ± 0.15%, and 1.54 ± 0.144% respectively, which directly affects the micro fibrillation angle of the IVFs Fig. 10b. The Young modulus of raw IVfibers and that treated by alkali and permanganate is 10.95 ± 2.72 GPa, 11.38 ± 2.29 GPa, and 12.98 ± 2.36 GPa, respectively, Fig. 10c. 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) [30]. A comparison of mechanical and physical IV fiber with other natural bark fibers is given in Table 4.

Droplet Test
This work evaluated the bonding strength between the IV fiber and epoxy resin by a droplet test. As shown in Fig. 11, 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 (F d ).
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 droplet test mechanism 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 4.53 ± 1.36 MPa, followed by alkaline treatment, and untreated of IVs fiber with 3.22 ± 0.47 MPa and 2.87 ± 0.69 MPa, respectively. The increased value of 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 [61]. 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.   This finding showed that chemical fiber treatment leads to the studied natural fiber enhanced properties. The future researches' will investigate this new bark fiber as fabric that has not been studied so far.