Investigation on Mechanical characterization of abutilon indicum fiber nonwoven fabric reinforced epoxy composite materials

Natural fibres find their way into many engineering applications in the automobile and aerospace sectors owing to their eco-friendly nature. Natural fiber produced from agricultural residue, is capable of enhancing the mechanical and thermal properties of composite materials while lowering their overall cost. The main aim of the current study is to investigate such natural fiber, nonwoven fabric reinforced composites. In this work, samples reinforced by non-woven Abutilon indicum (AI) fibre are manufactured with varying fibre weight percentages, such as 20%, 25%, 30%, 35%, 40%, using the hand layup method and needle-punching process to make the fabric and composite. Mechanical tests such as tensile, flexural, and compressive tests were using a universal testing machine, and impact tests were performed using an izod impact tester, in addition to morphological and thermal studies were performed on the above composites and their respect compositions. The effect of the fibres on FTIR and TGA was also investigated. In order to understand the bonding behaviors and the fractured composite specimens were examined by a scanning electron microscope (SEM). The findings revealed that the highest values of tensile and flexural strength were observed to be 39.796 MPa and 62.329 MPa at 35 wt% fibre and maximum impact strength and compressive strength were 0.441 joules and 47.45 Mpa at 35 wt% fibre.


Introduction
The effects of environmental degradation of synthetic fibres in composites have paved the way for the utilization of natural fibres in strengthening composites [1]. Normally, the natural fibers, namely bagasse, jute, kenaf, ramie, flax, and banana fiber, are preferred in reinforcing the composites owing to their significant properties such as high mechanical strength, low density, and being recyclable and economical in nature [2][3][4][5]. In addition, the fibres are renewable and ecofriendly [6,7]. The application of these composites is mostly found in the construction and automobile sectors [8]. Due to the new societal and environmental policies, there is a need to promote the utilization of biodegradable ingredients (both matrix and fiber) in commercially feasible composites. Therefore, attention is focused on utilizing natural fibres in developing natural composites for commercial applications owing to their greater strength [9,10], biodegradability, less weight [11], good corrosion resistivity [12], lower wear rate [13], and good stiffness [14].
Natural fibres must be used as reinforcement while developing composites in order to ensure proper fiber/ matrix adhesion. Krishnudu et al [15] evaluated and recommended the ideal weight percentage of fibre content required to improve the mechanical strength of the composites. Even though lignocellulosic fibres are the most preferred fibres in manufacturing eco-friendly composites, a lot of hurdles have to be faced while developing natural fiber-reinforced composites due to their complicated nature. There are a few drawbacks observed during processing, such as aggregate formation, poor fiber-matrix compatibility, high moisture absorption, and being highly affected by microbial attack [16]. The literature review reveals that the applications of reinforced composites are mostly found in the automotive and aerospace industries, where weight reduction in components plays an important role [17].
Nonwoven permeable structured sheets are manufactured from liquid plastic, films, or independent fibers. The fibres are treated thermally or mechanically to obtain porous structures in nonwoven fabrics. The nonwoven requires less fortification for composites compared to regular and woven fabrics developed for specific uses. Normally, fibres are manufactured by different methods like hot calendaring, stitch bonding, hot-air thermal bonding, needle punching, etc. Among these methods, needle punching is largely used for fibres to be manufactured into nonwoven form. In polypropylene composites, jute fibre used as needle punched non-woven fabric exhibits excellent sound absorption [18]. In a needle-punched texture arrangement, metal needles are used, and different fibre mixers or filaments can be used, especially for extreme strands.
The polyethylene strands are widely used in non-woven fabrics, from form cover to superior geotextiles. Non-woven-textures are used in composites, which offer great compressive and inter-laminar shear properties [19]. Nonwoven geotextiles and structures from flax and polyester strands are manufactured through a needlepunched method. It was found that flax geotextiles are less thick as compared with fabricated mat. These types of composites can be used in hot framework applications. The findings from the literature reveal that enhancing thermo-mechanical and functional properties [20][21][22]. This work overcomes the limitations described earlier by using a simple needle punching technique to make a non-woven fibre fabric as a reinforcement material in natural composites. These products are the first of their kind, developed in a variety of forms using natural fibers. Krishnudu et al [23] examined the optimization of the reinforcement ratios, and the optimum values of reinforcement are recommended in order to increase the mechanical characteristics [24][25][26][27][28].
Abutilon indicum (also known as Indian mallow and thuthi in Tamil) is a medicinal shrub of the Malvaceae family, is occasionally grown for decorative purposes in southern Indian states. This plant, which is frequently used medicinally, is regarded as invasive on several tropical islands. By passing through the water retting process, it may be utilized as a plant fibre due to its availability as a renewable supply and biodegradability. AI is used for Ayurveda and fully employs the root, bark, blooms, leaves, and seeds for medical reasons in the southern region of India. AI is typically prescribed by Ayurvedic doctors for joint discomfort and facial paralysis [29]. Alkalitreated Abutilon indicum fiber-reinforced composites were investigated by Mohana Krishnudu et al [30]. Venkateshwar Reddy et al [31] evaluated the mechanical and wear characteristics of AI based NFC. This prompts us to research its beneficial features in the context of natural composites.
Based on the literature survey, few investigations were carried out on AI-based NFCs. The main aim of the current study is to investigate such natural non-woven fabric-reinforced composites in order to enhance the mechanical and thermal properties of composite materials while lowering their overall cost.

Materials used
Abutilon indicum (AI) plants were taken from Chettipalayam, Coimbatore, India and the isolated fibers of Abutilon indicum, obtained after the microbial degradation process as shown in figure 1(a). Fibers of the plant stem were soaked in water for 21 days to permit microbial breakdown. The soaked stems were then cleansed with distilled water and kept in an open space for a week for the drying purpose. The extracted fibre and socked fibre as can be seen in figures 1(b) and (c). Finally, the fibres were removed by the combing method using a wire brush. The chemical characteristics of abutilon indicum fibre are presented in table 1.

Needle punching technique
To make the fabric, a needle-punching process (available at PSG College of Technology, Coimbatore, India) was applied to mechanically entangled webs or batts of 30 mm long fibers. This was accomplished by interlocking the strands with reciprocating barbed (felting) needles. Through inter-fiber friction, the consolidated structure retained its integrity. For punching, a triangular needle with 9 barbs spaced evenly in a 300 mm long blade was used. An 8 mm depth of punch penetration and a density of 100 punches per cm 2 were chosen as the optimal parameters. Figure 1(d) depicts the needle punch method of producing Abutilon indicum fibre nonwoven fabric.

Composite laminate fabrication
The compression moulding method was used to make the composite laminates for this study. The specimens were prepared for 20%, 25%, 30%, 35% and 40% reinforcement by weight, and the percentage of different fibers was modified to fabricate the different composites. The mould surfaces were first coated with a releasing agent (wax). The Abutilon Indicum fiber composite fabric was fabricated by the hand layup method by stacking the laminates on a flat mould and applying the resin in between each layer.
After the completion of the layup process, the top die was placed. Then the mould was closed and 1500 PSI of pressure was applied to it. The composite was maintained at 80°C for an hour for complete curing of the fabrics. Next, the laminated fabric was removed from the mould and the test specimens of the required dimensions were prepared.

FTIR spectroscopy and thermogravimetric (TGA) analysis
The functional compound of the fiber was measured by using FTIR machine (make and model: Perkin-Elmer Spectrum 100 FTIR Spectrometer) was used to observe the spectra in the range of 4000 to 500 cm -1 . To measure the infrared of CTF fiber, The materials were crushed into tiny pellets by potassium bromide (KBr) due to the transparent nature of KBr. The spectrum was used to identify the various functional groups of the specimens of the composites. The scan rate of FTIR spectrometer was 32 per min and resolution of 2 per centimetre in the  wave number region range of 400-4000 cm −1 at a room temperature of 30°C and RH of 65% was documented in absorbance mode as a function of the wave. The thermal stability of the fiber reinforced composites was evaluated using TGA. TGA analysis is a paramount important one for the experiment of thermal permanence of the constituents of the natural fiber considers the functioning temperature limit of the composite made with similar fibers [33][34][35]. The thermogravimetric analyzer (make and model: TG/DTA -EXSTAR/6300, available at the Avinashlingam Institute for Home Science and Higher Education for Women, Coimbatore, India) was used to test the thermal stability of the composite. To avoid undesired oxidation, 2-5 gm of sample was heated from 24°C to 980°C in an alumina pan at an average rate of 10°C per min. The entire process is carried out in an environment in which nitrogen flows at a constant rate.

Mechanical characterization
All test samples were prepared using a hydraulic shearing machine. Tensile test samples were prepared as per ASTM standard D3039. The strength of each sample was determined and stress strain curve was obtained using a universal testing machine (make and model: Kalpak UTM and 121101), which has a crosshead speed of 2 mm min −1 . Next, unnotched Izod impact testing was conducted in accordance with the ASTM D256 standard. The highest energy of the hammer employed for testing polymer composites is 5 J. In addition, the flexural and compression properties of the specimen were determined in accordance with ASTM D790 and D3410 standards, respectively. The surface morphologies of the specimens were analyzed using SEM (make and model: Carl Zeiss V18). The surface is gold coated before analyzing the morphology [36].

Results and discussions
3.1. FTIR-abutilon indicum fiber nonwoven fabric epoxy composites The FTIR spectra of Abutilon Indicum fiber nonwoven fabric epoxy composites are shown in figure 2. the peaks observed for 35 wt% with 1701 cm −1 is specifically assigned to C=O stretching in hemicelluloses of Abultilon Indicum fiber woven fabric epoxy composites. In addition, the peaks of 1565 cm −1 are assigned to aromatic skeleton vibrations of lignin and [33]. Abultilon Indicum fiber woven fabric epoxy composites at around 1398 cm −1 are assigned to CH deformation in lignin.
These results prove that the constituents of Abultilon Indicum fiber woven fabric epoxy composites contain cellulose, lignin, and hemicelluloses in their chemical structure. The region 3500-2500 cm −1 is related to OH and CH2 groups. The peaks located at 2990 cm −1 are attributed to (CH) and CH2 groups for 35 wt% of Abutilon Indicum fiber woven fabric epoxy composites. The peaks at 3012 cm −1 belong to the C-H stretching of cellulose of 35 wt% of composites [5].

TGA-abutilon indicum fiber nonwoven fabric epoxy composites
The thermal stability of the fiber reinforced composites was evaluated using TGA. The TGA and DTG curves of the composites are presented in figure 3 indicates a plot between weight loss percentage and temperature ranges between 30 and 700°C. The composites indicated weight loss in two stages It is observed that the weight loss percentage of the Abutilon Indicum fiber composite specimen decreases with increasing temperature and revealed an initial region of weight loss between room temperature and 250°C, which was mainly due to the evaporation of carboxyl, moisture, and water-soluble hydroxyl particles of the material [30,37].
The major degradation takes place in the temperature range of 250°C to 500°C. A remarkable loss in weight of about 71.65% and 68.57% for 20 wt% and 35 wt% fiber composites is observed due to the decomposition of α-cellulose content [38]. Beyond 500°C and upto 680°C only a minor loss in weight is observed due to the decomposition of residual products shows a slow degradation profile. Final residual of 10.31% and 7.52% of 20wt% and 35wt% respectively. The critical temperature of the specimen with 35 wt% is 423.43°C and 20 wt% is 438.07°C. The DTG curves of 35% fiber composites with the peak temperature of 380°C is observed from figure 3(b) [39,40]. Figure 4(a) shows the influence of fibre weight percentage on the tensile characteristics of Abutilon Indicum nonwoven specimens. The Abutilon Indicum 35 wt% nonwoven composites exhibit a greater tensile strength (39.765 MPa) than the 20 wt% composites (27.478 MPa). Thus, the 35 wt% specimen can be declared as the optimal fibre content of the nonwoven composites. Since the Abutilon Indicum fibres have a lower aspect ratio and a smaller surface area, they require less matrix for effective wetting. In the present work, we have observed that the 35 wt percent sample exhibits the highest strength compared to the 40 wt% specimen [41].  The entanglement between fibres was efficient at 35 wt% fibre concentration, implying that the matrix wetted the fibres efficiently. The composite was stiff at this point due to an excellent binding between fibres resulting from the matrix's firm hold on the fibres. The entwining of fibres and the effectiveness of wetting, reduced as the matrix content declined with the increase in fibre weight percentage from 35% to 40 wt%. This caused the slippage between fibres, resulting in a decrease in the tensile strength of the material.

Tensile behavior
The decrease in tensile strength of the 40 wt% Abutilon Indicum fibre nonwoven composite was predicted earlier due to insufficient matrix wetting of fibres, resulting in poor fiber-matrix bonding [42]. The breakout pattern and fibre pull out seen in the SEM images corroborated the idea that composite tensile strength is influenced by insufficient matrix wetting of the fibers. The stress-strain curve for tensile properties of composites as can be seen in figure 5(a).

Flexural behavior
For lignocellulosic reinforced polymer composites to have acceptable mechanical properties, especially flexural strength, compatibility between the fibres and matrix is critical. The matrix in composites acts as a stress transmission interface between the reinforcement fibres. The flexural strengths of Abutilon Indicum nonwoven fabric composites are shown in figure 4(b). The Abutilon Indicum nonwoven composites' optimal flexural strengths were attained at a fibre content of 35 wt%. At this concentration, the significant matrix wetting of fibres allows the load to be diffused and distributed among the fibres, yielding the maximum flexural strength. Due to inadequate wetting of the matrix on the reinforced fibres, flexural strength decreases at 40 wt% fibre concentration. The stress-strain curve for flexural properties of composites as can be seen in figure 5(b).
The reinforcement in composites was found to reduce due to the inadequate moistening of fibres. The poor matrix dispersion due to the poor wetting thus resulted in creation of weak spots at the region of interface [43]. The Abutilon Indicum nonwoven composites required a 35 wt% fibre content to obtain optimum flexural strength, as shown in figure 4(b). Since the Abutilon Indicum fibre's thickness was significantly high and aspect ratio was quiet low, less matrix was required for dispersion and wetting due to a lower surface area of the composite. In nonwoven composites, the structure and the fibre surface characteristics greatly influence the interaction between the fibre and matix material. The flexural strength of 35 wt% Abutilon Indicum test sample was found to be the highest (62.293 MPa). The strength started to decrease beyond 35 wt% and was found to be 60.225 MPa for the 40 wt% sample. Flexural strength of Abutilon Indicum nonwoven composites, on the other hand, improved linearly as fibre content increased [44]. The mechanical properties of composite samples listed in table 2.

Compressive behavior
As shown in figure 6(a), the Abutilon Indicum fibre nonwoven composites with a 35 wt% fibre content had comparable compression strength. The identical compression strength is most likely due to the fibres' tensile strength and elongation. According to Hasan and Wei [45], the elongation of the reinforcement fibres affects the compression strength of nonwoven composites, with lower elongation fibres failing earlier and higher elongation fibres transferring the residual load. These two characteristics of the fibres are believed to be responsible for the similarity in compression strength patterns of the 35 wt% Indicum fibre samples.

Impact behavior
Factors such as fiber-matrix bonding and fibre reinforcing toughness have a substantial impact on energy in materials. The impact energy of the Abutilon Indicum fibres nonwoven composite is depicted in figure 6(b). The figure shows that composite impact energy increases significantly up to 35 wt% fibre loading, but then falls to 0.441 J at 40 wt% fibre loading. At 20 wt% and 25 wt% fibre loading, respectively, the impact energy was 0.363 J and 0.385 J. As the fibre loading rises from 30% to 35%, the impact energy rises from 0.407 J to 0.441 J.
The enhancement of the composite properties is due to the improved fibre and matrix adhesion. The molecular interface chain's flexibility allowed for easy load dispersion and a steadfast avoidance of crack initiators, resulting in the enhancement of the composite's shock-absorbing capacity. The reinforcing effect, which allows for a uniform stress distribution from matrix to fibre phase, is responsible for the first increase in impact strength. A similar finding was made for natural fiber-reinforced composites with a large volume fraction. The results concluded that crucial fibre weight percent plays a significant role in mechanical properties analysis.

Scanning electron microscope analysis
The interface between fiber and matrix can be thought of as a three-dimensional boundary. The interaction occurring at the interface is the influencing factor that dictates the composite quality. Micromechanical interlocking or mechanical locking, physical coupling such as electrostatic interaction or Vander Waals forces, and interfacial bonding are the three techniques that can be used to achieve this relationship. Figures 7 (a)-(b) shows the cracked interface of the SEM investigation of the Abutilon Indicum fibers nonwoven composite specimen for 20 wt%. The micrograph displays primarily matrix holes and peeling at 20% fibre concentration. This indicates that matrix failure dominated the failure of the samples, resulting in poor composite specimen strength. A meagre improvement in the interfacial bonding of the sample was found when the fiber weight percentage was changed to 35. The fiber pullout in the test specimen confirmed that the stress transfer from matrix to fiber was very marginal [46][47][48].  Similarly, figures 7(c)-(d) shows SEM images of tensile and flexural composite specimens of Abutilon Indicum fibres. Similar to broken tensile composite specimens, the micrograph indicated a similar pattern and it shows the most common failures, which include fibre pullout, fibre breakage, fiber fracture, and fiber matrix good bonding [47]. However, even after the fracture, the nonwoven composite structure was visible at 35 wt% fibre content. This demonstrates excellent fiber-to-matrix bonding, resulting in increased strength. Meanwhile, matrix holes were seen when the fibre level reached. This was due to a lack of matrix and the creation of agglomerations. As a result, the strength has been diminished.

Conclusion
From the finding, the AI fibres nonwoven composite has improved mechanical properties at 35 wt% fiber. Tensile, flexural, compression, and impact strengths of AI fibre nonwoven composites clearly increase up to 35 wt%, then begin to decrease, and strength increased by 4.75%, 3.32%, 4.23%, and 6.57%, respectively, when compared to 40 wt%. The thermal stability of the Abutilon Indicum fibre reinforcement improved significantly in all fibre composites. The deterioration temperature of the composite with 35 wt% fibre content started at 349.06°C and terminated at 438. 07°C. When comparing to the other composite combination, the thermal degradation range increased to 35 wt% fiber content. The SEM analysis of the composite samples also supports at the strong fibre matrix adhesion and enhanced fiber-matrix interaction. The author suggested that the alkali treatments, wear studies for various application like door panels, window panels, partition boards, and ceilings for future research directions.

Data availability statement
All data that support the findings of this study are included within the article (and any supplementary files).