1 Introduction

Synthetic fiber–based materials have been primarily employed for structural applications in most of the sectors, in the last few decades [1]. However, the current environmental policies looking over sustainable materials that cannot create any socio-ecological issues but ensure superior qualities, on the other hand. Since a revolution is necessary at this eco-concerned scenario to produce sustainable and biodegradable materials to replace traditional synthetic materials [2], natural plant fibers are one among the choice due to their cost-effective, biodegradable, renewable, and lightweight nature, which could be used for the fabrication of fiber reinforced polymer composites [3, 4]. Plant-based fibers provide several advantages while their ready availability is a major driving force in their increased adoption. Despite their low density, lower cost, eco-friendliness, and good thermal property, plant fibers have seen an uptick in use in recent years [5]. Sisal, jute, hemp, and cotton are just a few examples of plants that are grown primarily for their fiber, which has high economic importance. However, some fibers are obtained from agro-industrial residues as coir, maize stalk fiber, and sugar cane waste fibers [6]. The former ones are termed as primary fiber-yielding plants and later ones are termed as secondary fiber-yielding plants. Wood, silk, bamboo, hemp, sisal, flax, kenaf, and other common plant fibers were successfully reinforced with polymers, and the resulting composites exhibited better competitive properties [7].

However, the usage of low-quality plant fibers is limited in several domains due to the concerned issues including poor temperature resistance, excessive water captivation, incompatibility, and aggregation tendency. Since identifying novel high-quality fibers is still a challenging task because of the variations in the fiber components particularly, cellulose, hemicellulose, lignin, and moisture content among different fiber sources [8]. The majority of the time, fibers are utilized not in their raw or unprocessed states but rather in the form of blends. Blends of fiber and polymers exhibited good qualities when compared to synthetic fibers. Ropes, insulations, textiles, and polymer composites are just few of the many products that find usage for plant fibers in their raw/blended forms. Flax and jute fibers are often used in direct rope-making methods [9]. Yarns, on the other hand, found in things like clothes, purses, and even carpets, and they are often woven from a variety of plant fibers. Needle felts made from coir fibers are great for absorbing sound and blocking out unwanted noise when used as acoustic soundproofing [10]. Biodegradable flower pots, briefcases, bookshelves, table tops, disc holders, seats, and even wind generators, vehicles, airplanes, etc. all make use of natural fibers, which are widely acknowledged as reinforcing materials in the composites sector [11].

Fiber-reinforced composites are often produced by reinforcing two or more materials together, which ultimately leads in the production of a composite with desirable qualities extracted from the usual materials that were blended [12]. In most cases, it will be made up of a material that has a continuous phase, into which one or more discontinuous phase (reinforcing phase) components will have been placed. The discontinuous phase of composites is created by the reinforcing material or fibers, which are typically reinforced into the matrix in a scattered manner. Because the matrix ensures that the reinforcement remains precisely where it should be in order to provide the composite with sufficient mechanical properties [13]. Furthermore, the surface roughness of the fiber has a significant impact on the interfacial bonding between the fiber and matrix. Even though, a composite’s ultimate strength is dependent on the reinforcements’ qualities, distribution, interactions, as well as the proportion by weight or volume that used to fabricate the composite, where the geometry of the reinforcing phase as shape, size, and distribution are profoundly have influence on composite properties. Thermoset and thermoplastic polymer matrices may be used as continuous phase for composite fabrication through any of the injection molding, compression molding, melt-extrusion, and hand lay-up techniques [14].

However, identification of a high-quality fiber or reinforcement is still recognized as a challenge in fiber-based material research. The identification of a suitable fiber source, optimization of extraction procedure, fiber modification through pretreatments, and its characterization are the main milestones of fiber research. Generally, water retting and dew retting are used widely for the extraction methods for plant fibers. In this study, water retting method was employed for the extraction of fibers. Fiber pretreatment is effective in case of many fibers to improve their specific properties by delignification. Pretreatments separate non-cellulosic components as lignin, wax, and hemicelluloses from the lignocellulose network. However, the cost of pretreatment techniques relies as the constraint of this aspect. Many researchers are evaluating plant fiber-reinforced polymer composites to evaluate their performance and appropriateness in a variety of applications [15]. This high demand for cellulosic fibers has prompted the authors to look over Hibiscus canescens stem for fiber extraction and its characterization to establish the feasibility of relevant fibers for composite applications. There is no study reported on the characterization of H. canescens stem fiber still now. Although, this article compares H. canescens stem fiber to other plant fibers in terms of its density, diameter, tensile qualities, chemical composition, crystallographic properties, thermal properties, and surface morphological features to establish the efficacy of proposed fiber for composite applications.

2 Materials and methods

2.1 Plant collection and fiber extraction

Hibiscus canescens is a dicotyledonous shrub commonly named as grayish Hibiscus, which is native to warm, temperate, subtropical, and tropical regions. They belong to the family Malvaceae and are widely distributed in Africa and South Asia, especially in certain regions of India. The mature H. canescens plants were gathered from a Village in the Madurai district of Tamil Nadu of South India. Water retting method was employed in this study to extract fibers from H. canescens stem. For that, the collected plant stems were made devoid of all other plant parts and washed thoroughly to remove external particles, if any. After being washed, the plant stems were submerged in the water filled in a container for 2 weeks. This could result microbial degradation and consequently fibers enclosed with retted material were detached through manual combing using a metal brush. Subsequently, the fibers obtained through retting procedure were taken out of the container and rinsed carefully with purified water to get rid of any remaining contaminants. The fibers were then sun dried for 7 days and further dried in an oven for 24 h to eliminate the residual moisture content [16]. Figure 1 depicts the plant that is utilized for fiber extraction (a), retted material obtained after water retting (b, c) and fibers attained after manual combing (d).

Fig. 1
figure 1

Hibiscus canescens plant (a), retted material (b, c), and extracted fibers (d)

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2.2 Characterization of Hibiscus canescens stem fiber (HCSF)

For determining the fiber’s appropriateness for lightweight purposes physical examination is necessary in terms of density and diameter analysis. Insights on understanding the fiber’s composition, functional groups, and crystallinity, chemical analysis is admirable. The mechanical and thermal properties of the fiber can be determined with sufficient accuracy using the tensile and thermal tests. To measure surface roughness characteristics of the fiber to assess its inter-bonding capability, morphological investigation is preferred. Since the extracted raw fibers (HCSF) were subjected for a group of tests mentioned above to determine its suitability for use in diverse composite formulation.

2.3 Physical properties analysis

The diameter of and the density of were the two different aspects of its physical make-up that were looked at during this study utilizing the procedures that were outlined below. The cross-sectional area of the HCSF fiber was measured at four different places along its length by subjecting it an Auslese 7 LCD digital optical microscope. A total of 20 fiber samples were tested, and the average diameter of the specimens was determined using the image-pro program due to its irregular cross-sectional area. For density measurement, a pycnometer was used, where methylbenzene was cast-off as a known density liquid instead of toluene. The following equation was used to calculate density (1) of HCSF; specifically, m1 represents the mass (kg) of the unoccupied pycnometer, m2 represents the weight (kg) of the pycnometer after being subjected to fiber, m3 represents the mass (kg) of the pycnometer after being filled with methylbenzene, m4 represents the density (kg) of pycnometer which is filed with HCSF and methylbenzene, and ρMAPF (g/cm3) corresponds to the density of HCSF [17].

$${\rho}_{\left(\textrm{MAPF}\right)}=\left(\frac{m_2-{m}_1}{\left({m}_3-{m}_1\right)-\left({m}_4-{m}_2\right)}\right){\rho}_m$$
(1)

2.4 Thermal performance of HCSF

The thermal study was performed to establish the appropriateness of fiber for high temperature necessitate dealing and applications, specifically to identify the thermal stability and maximum degradation temperature of the proposed material. This investigation was carried out using a NETZSCH STA 449F3 thermal analyzer, in which a 5.458mg of HCSF sample was placed in an alumina plate and heated from 32 to 600°C at a rate of 10°C/min [18]. Nitrogen gas (N2) was infused into the system at a rate of 30 ml/min to uphold an inert atmosphere that assist to overcome oxidation effects during inspection[19, 20]. The resultant TG/DTG curves were recorded which displays the thermal degradation profile of HCSF in terms of weight loss of HCSF against increasing temperature ranges. Furthermore, the kinetic activation energy of the material (Ea) was estimated through Briodo’s curve in accordance with Broido’s equation (2). In Broido’s equation, the universal gas constant is represented as R that is equal to 8.314 J/mol K, temperature in Kelvin is signified by T, reaction constant is embodied by K and the normalized weight (weight at any time (Wt)/initial weight (Wi)) is indicated by y [21].

$$\ln \left[\ln \left(\frac{1}{y}\right)\right]=-\left(\frac{E_a}{R}\right)\left[\left(\frac{1}{T}\right)+K\right]$$
(2)

2.5 Tensile characterization

Mechanical behavior of HCSF was investigated with the aid of Zwick/Roell universal testing equipment. For that, fiber samples were prepared as per ASTM D3822-07 specifications 1kN load cell, Instron 5500 R testing machine was used at room temperature condition with a total of 20 single fiber samples with a gauge length of 50 mm were investigated for understanding the variations in tensile properties, due to the uneven nature of fiber. All the samples were run at a crosshead speed of 2.5mm/min during the examination [15]. The reliability of tensile characteristics of 20 fiber samples were evaluated through Weibull distribution curves using the software Minitab-17 [22]. The microfibril angles (α) of HCSF was further determined using the following relation (3) [23]. Of which, strain is represented by the symbol ε, microfibril angle (°) is given as α, while the change in length-at-break is shown by ΔL (mm).

$$\varepsilon =\ln \left(1+\frac{\Delta \textrm{L}}{50}\right)=-\ln \left(\cos\ \alpha \right)$$
(3)

2.6 Chemical examination

2.6.1 Chemical composition of raw MAPF

Through the use of conventional chemical analysis procedures, the composition of various chemical components of HCSF were detected. According to Kurshner and Hoffer’s method, the amount of cellulose in the HCSF was determined [24]. Hemicellulose content was evaluated using the neutral detergent fiber method, as per [25]. Estimation of the sample’s lignin concentration followed the standard approach established by APPITA P11s-78 [26, 27]. The wax concentration in the HCSF was investigated using the Conrad method, for that, the waxy residue obtained after treating crushed fiber samples with ethanol and then chloroform was weighed [28]. Similarly, ash fraction of the material was determined using the TAPPI (Technical Association of the Pulp and Paper Industry) standard [29]. A Mettler Toledo HS153 moisture analyzer was employed to check the moisture percentage of HCSF, and the average moisture content was noticed while analyzing 10 trials for each fiber samples[30, 31].

2.6.2 FT-IR characterization

FT-IR analysis was used to study the major functional groups associated with each individual chemical component of HCSF in order to determine the chemical conformation of the compound. This procedure was done with the aid of a Jasco FT-IR 6300 type-A spectrometer, to which a thin film of HCSF powder and potassium bromide (1:10) being subjected. During examination, 32 scans were taken per minute at a resolution of 4 cm−1, within a wave number range of 4000 to 500 cm−1 [32]. All scans were performed at a constant 2 mm/s scanning speed and 45° incidence angle [1]. The conduction percentage of diverse functional groups occupied in the material was recorded as FT-IR spectra, which was used to authenticate the constituent parts of the fiber [33].

2.6.3 Crystallinity analysis

X-ray diffraction (XRD) analysis was conducted to authenticate the existence crystalline and amorphous fractions in the fiber sample. This examination was executed in an X’ Pert PRO diffractometer, where powdered HCSF sample was subjected to a sample holder, followed by X-rays (CuK) with an intensity of 1.5406A passed through the material, and the corresponding diffracted rays were recorded using an X-ray detector in the 2θ range (10°–50°) with a scan rate and speed rate of 10.0231° to 80.9231°, 1°/m, respectively. According to peak height method, the crystallinity index (CI) of the HCSF was derived through Siegal’s formula (4). Of which, Iam is given to represent the intensity of amorphous peak at 18o, I002 signify the possession of the crystalline peak at 23° [34]. Additionally, the crystallite size of HCSF was determined using Sherrer’s formula (5), where β denotes the whole width at half maximum of the peak at 23°, λ represent the radiation intensity, K denotes the universal constant (0.89), and θ is the Bragg angle [35].

$$\textrm{CI}=\left(1-\frac{I_{\textrm{am}}}{I_{002}}\right)\times 100\%$$
(4)
$$\textrm{CS}=\frac{K\lambda}{\beta \textrm{Cos}\theta }$$
(5)

2.7 Surface topographies of MAPF

The imaging techniques as SEM (scanning electron microscopy), EDX (energy-dispersive X-ray spectroscopy), and AFM (atomic force microscopy) were used to evaluate the fiber’s roughness characteristics and elemental dispersal [5]. The methods used to inspect surface properties of HCSF are explicated in the following sections.

2.7.1 SEM investigation

The surface features of the HCSF sample were accomplished in the longitudinal direction by using a SEM model FEI Quanta FEG 200. In order to increase the conductivity of the fiber and thus to lower the over shielding effect of electrons, the specimens were coated with a thin film of gold prior to examination. Then, high-resolution images of HCSF surface were captured at four different magnifications as 200×, 500×, 1000×, and 2000×. The experiment was conducted in the low-vacuum mode (50 Pa) at an accelerating voltage of 15kV. It was probable to identify the microstructures present on the exterior part of the fiber using obtained images. Also, the images were sufficient to establish the surface roughness/smoothness and its inter-bonding capacity to a certain extent [36].

2.7.2 EDX spectroscopic analysis

The energy-dispersive X-ray spectroscopy (EDX) was used to reveal the most notable elements present on the exterior part of the fiber. The elemental quantification was performed using an EDX spectrometer type NCAPentaFET83 coupled with a high-resolution SEM equipment. The resultant spectrum was obtained through an EDX detector, which shows the prominence of individual elements existing on the fiber surface, in term of atomic and weight percentage [37].

2.7.3 Atomic force microscopic (AFM) examination

Using an AFM (Park, Korea, model XE-70), quantification of diverse surface roughness parameters was done. The examination has realized with non-contact mode, where a shielding frequency of 293 Hz and an accuracy of 1nm was used. The acquired 3D/2D images were further processed with XEI image processing software that is connected to the AFM. The parameters as average surface roughness (Ra), root mean square roughness (Rq or Rrms), 10-point average roughness (Rz), surface skewness (Rsk), surface kurtosis (Rku), and maximum peak-to-valley height (Rt) were quantified through this way and which was adequate to describe the peripheral roughness of HCSF [38].

3 Results and discussion

The physico-chemical, mechanical, thermal, and morphological characteristics of HCSF are described in detail in this session. The significant research outcomes are presented in the form of figures and tables, where appropriate comparisons are made with existing fibers to explore the position of proposed fiber.

3.1 Physical properties of HCSF

The diameter variations of four randomly selected regions of a HCSF are depicted in Fig. 2, which is an optical microscopic view. Due to the irregular weaving of the fibers, an average diameter of 441.32 μm was calculated after analyzing 20 separate HCSF samples. Generally, fibers with moderate diameter are favored due to the fact that moderate diameter offer good tensile properties, whereas high diameter leads to fiber-matrix incompatibility and low diameter causes reduced tensile strength. The diameter found to be moderate when compared to other investigated fibers such as Tamarindus indica (564–789 μm), Prosopis juliflora (20 μm), Phaseolus vulgaris (535.6 μm), Sisal (50–300 μm), Coccinia grandis (27.33 μm), date palm rachis (520 ± 72 μm), Ficus religiosa root (0.09–0.12 μm), kenaf (65–71 μm), Pongamia pinnata (62.34 μm), Ramie (50 μm), Juncus (3300 μm), Cissus quadrangularis stem (770–870 μm), purple Bauhinia purpurea (511± 3.07 μm), and Cissus quadrangularis root (610–725 μm). The density (1425 kg/m3) of HCSF beheld promising when compared to other fibers including purple Bauhinia purpurea (1460 kg/m3), Coccinia grandis (1517 kg/m3), Cissus quadrangularis root (1510 kg/m3), flax (1500 kg/m3), pine apple leaf fiber (1440 kg/m3), hemp (1500 kg/m3), sisal (1500 kg/m3), cotton (1600kg/m3), and glass fibers (2500 kg/m3) [17, 39]. A low density and a reasonable diameter of fibers are essential requirements in the making of lightweight products. These two studies, however, demonstrate the physical suitability of fiber for use in lightweight composites. Table 1 presents the physical properties of HCSF and other comparable fibers, along with their other specific properties.

Fig. 2
figure 2

Diameter variations of HCSF

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Table 1 Physico-chemical composition of HCSF in comparison with other natural fibers
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3.2 Thermogravimetric analysis of HCSF

The weight loss feature of HCSF owed by thermal degradation is depicted in Fig. 3 (a, b, c), which illustrates the TG/DTG curves (a) and differential thermal analytic (DTA) curve (b). It is clear from the outcomes that the initial stage of mass loss was occurred around 70°C, and is indicative of the evaporation of existing water content from the HCSF. Between the temperature range of 200–321°C, the degradation of hemicellulose component is validated and which indicates the second stage of degradation. In 2020, Palai and Sarangi observed a similar deterioration pattern in plant fiber. The third phase of weight loss occurred in between 375 and 500°C that represent the elimination of cellulose fractions. Hence the thermal stability of HCSF is identified as 375°C. Even after being heated to 500°C, maximum degradation of sample has been occurred around 550°C. Similar pattern of degradation was observed through DTA analysis that also validated TGA results in terms of proving the complete hemicellulose and cellulose degradation drift at 321°C and 454–486°C. In addition, this experiment established that HCSF is stable up to 250°C, an essential attribute that makes the fiber suitable for high heat environments. However, the thermal stability of HCSF is promising than the thermal resistance of Tamarindus indica (238°C), Ricinus communis (225°C), Passiflora foetida (320°C), Pongamia pinnata (332°C), Phaseolus vulgaris (328.5°C), Phoenix dactylefera L. leaf sheath (245.1°C), Cissus quadrangularis root (230°C), Cissus quadrangularis stem (270°C), Prosopis juliflora (217°C), Coccinia grandis (213.4°C), Cymbopogon flexuous (253.17°C), Zmioculus zamiifolia (310 ± 2.64°C), Ficus religiosa (325°C), Phaseolus vulgaris (328.5°C), sisal (250°C), hemp (225°C), Juncus effuses L. (200°C), cotton (265°C), Altheria officinalis L. (320°C), Tridax procumbens (195°C), and Thespesia populnea (245.4°C) (Table 2). Moreover, the revealed thermal stability of HCSF is imperative since that allow the fiber to be appropriate for high thermal settings. Kinetic activation energy (Ea), on the other hand, is the minimal amount of energy needed to commence the disintegration of cellulosic fibers and is used to evaluate the degradation pattern of plant fibers. A typical range of kinetic activation energy of plant fiber is 60–170 kJ/mol. The kinetic activation energy of HCSF (65.66 kJ/mol) calculated using Broido’s plot (c) is in the required range, which was almost closer to the activation energy reported for Grewia damine (65.29 kJ/mol) (Indran et al., 2014; Umashankaran and Gopalakrishnan, 2019).

Fig. 3
figure 3

TGA/DTG curves (a), DTA curve (b), and Broido’s plot (b) of HCSF

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Table 2 Mechanical and thermal composition of HCSF in comparison with other natural fibers
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3.3 Tensile features of HCSF

Usually, different fibers beheld different tensile properties that dramatically affects the mechanical strength of its reinforced polymers. Hence, tensile characterization of HCSF was done, where the fibers with 40mm length showed maximum tensile features as displayed in Table 3. The tensile strength of the 40mm HCSF is identified as 394.9 ± 14.42 MPa, which is higher than the mechanical strength of Ricinus communis (356 ± 2.387 MPa), Juncus (31 ± 8 MPa), Coccinia grandis (273 ± 2.74 MPa), Juncus effuses L. (113 ± 36 MPa), Tridax procumbens (25.75 MPa), Acacia concinna (302.1 ± 16.78 MPa), Zmioculus zamiifolia (34.92 ± 5.47 MPa), Pongamia pinnata (322 MPa), purple Bauhinia purpurea (373.3 MPa), and Grewia damine (375.6 ± 16.58 MPa). Significant tensile modulus was recognized for HCSF (30.29 ± 4.365 GPa) because of its superiority over the average tensile modulus of Tamarindus indica (11.23 ± 2.72 GPa), Juncus (0.7 ± 0.1 GPa), Pongamia pinnata (9.67 GPa), Coccinia grandis (10.17 ± 1.26 GPa), Zmioculus zamiifolia (0.135 ± 0.052 GPa), kenaf (25.1 GPa), Acacia concinna (8.544 ± 0.210 GPa), Juncus effuses L. (4.38 ± 1.37 GPa), purple Bauhinia purpurea (5.31 GPa), and Tridax procumbens (0.94 ± 0.09 GPa). The strain at break of HCSF was found to be 5.32 ± 0.34% and a microfibril angle of 18.53 ± 0.582° was noted. Recent studies on manau rattan (Calamus manan) fibers revealed the utility of fibers for optical fiber production due to its good thermal resistance (332°C), tensile (273–482.6MPa), and transparent features. Similar thermal (321°C) and tensile features (394.9 ± 14.42MPa) noted for HCSF too. Moreover, all the potential mechanical and thermal features observed have disclosed that HCSF could be a better candidate for such kind of composite preparation.

Table 3 Tensile properties of HCSF with different length proportion
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The Weibull distribution plots corresponding to diameter (a), tensile strength (b), tensile modulus (c), and stress–strain rate (d) are presented in Fig. 4, which clearly show how dramatically plant fibers tensile properties can alter. All the four tensile value deviations were found to be within the Weibull range, proving that HCSF may be successfully used as reinforcement in polymer composites. The amount of surface porous and chemical constituents’ integrity, the critical length of this HCSF at 40mm were observed. This 40-mm fiber length can be used as a discontinuous reinforcement with polymeric composite materials.

Fig. 4
figure 4

Weibull plots of diameter (a), tensile strength (b), tensile modulus (c), and stress–strain rate (d) for HCSF

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3.4 Chemical components of HCSF

High cellulose content of 68.46 wt.% observed for HCSF suggesting it holds excellent crystallinity along with good thermal and tensile properties, as already established through thermal and tensile tests. Compared to other cellulosic fibers such as Grewia damine (57.78 ± 3.56 wt.%), Ficus religiosa (55.58 wt.%), Acacia concinna (59.43 wt.%), purple Bauhinia purpurea (60.54 ± 4.31 wt.%), Zmioculus zamiifolia (41.12 ± 3.32 wt.%), Coccinia grandis L. (63.22 wt.%), Phoenix dactylefera L. leaf sheath (43.50 wt.%), Prosopis juliflora (61.65 wt.%), Tridax procumbens (32 wt.%), Cymbopogon flexuous (68.13 wt.%), Ricinus communis (65.5 wt.%), Pongamia pinnata (62.34wt.%), Altheria officinalis L. (44.6 wt.%), Phaseolus vulgaris (62.17 wt.%), and jute, HCSF (58–63 wt.%) was promising due to its high cellulose content [6]. The proportion of other components in HCSF were 14.36 wt.% (hemicelluloses), 12.48 wt.% (lignin), 0.28 wt.% (wax), 10.44 wt.% (moisture), and 5.34 (ash). In fact, the low hemicellulose and lignin concentration found in fiber point towards its high tensile and lower moisture absorption properties; which also indicate that the fiber possess less amorphous fraction and is resistant to water or moisture [9, 17]. At the same time, low moisture (10.44 wt.%) content was detected for HCSF that disclosed the long-term durability of fiber, which is advantageous than typical fibers as jute (10.99 wt.%), hemp (10.8 wt.%), sisal (11 wt.%), Tridax procumbens (11.2 wt.%), Thespesia populnea (10.83 wt.%), and pineapple leaf fiber (11.8 wt.%) [59, 60]. In general, the bonding effectiveness between plant fibers and polymer resin could be lower when a higher wax content is present in the fibers. Since low wax concentration (0.28 wt.%) noted for HCSF is an additional feature that portends well for its bonding with matrix, a relatively low ash concentration of 5.34 wt.% is found in fiber, which also reveals that the fiber possesses low amorphous content. The chemical make-up of HCSF is displayed in Table 1 along with those of similar fibers for easy comparison. In order to verify the accuracy of these qualitative results, further chemical validations were done using FT-IR, XRD, and NMR analysis.

3.5 Crystalline possessions of HCSF

X-ray diffraction spectra of HCSF sample reveals three significant peaks at 18.14°, 22.11°, and 34.59°, as seen in Fig. 5. The peak at 18.14° related to the lattice plane (1 1 0), and another peak between 22.11° relates to the cellulose I plane (2 0 0). An alignment of the fiber bundles was seen to produce minor peaks at 34.59° [4, 41]. Desired cryatallinity index (CI) and crystallite size was measured for HCSF as 48.78%, 1.59nm, respectively. At higher crystallinity, the cellulose chains become more consistently oriented, enhancing the mechanical qualities and makes them appropriate for biocomposites. Larger crystalline size affects cellulosic fiber absorption and chemical reactivity. Thus, the observed cryatalline properties of this fibers were significant when compared to the other investigated natural fibers such as Grewia damine (30.35%, 5.09nm), Ficus religiosa (42.92%, 5.18nm), Acacia concinna (27.5%, 4.17nm), Zmioculus zamiifolia (25.75 ± 2.34%, 2.54 ± 0.24nm), Prosopis juliflora (46%, 2.8nm), Tridax procumbens (34.46%, 25.04nm), Cymbopogon flexuous (46.02%, 13.96nm), Pongamia pinnata (45.31%, 5.43nm), Juncus (43%), Cissus quadrangularis stem (47.1%), Juncus effuses L. (33.4%, 3.6nm), and Thespesia populnea (48.17%, 3.57nm) [9, 61, 62]. Moreover, the obtained diffractogram was appropriate to prove the occurrence of crystalline and amorphous components in the sample, which was also predicted through chemical composition analysis.

Fig. 5
figure 5

X-ray diffractogram of HCSF

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3.6 Functional groups of HCSF

Figure 6 displays the FT-IR spectrum of HCSF, demonstrating ten prominent peaks in different wavenumber zones, each of which is connected with a distinct functional group in the compound’s chemical make-up. The first two peaks noted at 3335cm-1 and 2916 cm-1 is coupled with the cellulose component of fiber, which was attributed by the OH and CH stretching of cellulose [13]. The presence of α-cellulose in the fiber was sensed by noticing the peak at 2832 cm-1 that corresponds to the associated C-H stretching of alkanes. The following peak located at 2317cm-1 indicates C≡C groups due to the existence of wax in the sample. Likewise, the C=O (1611cm-1) and C-OH (1021cm-1) stretching noted in the FT-IR spectra is linked with the lignin residues in the material. The existence of hemicellulose has been confirmed by the peaks positioned at 1304cm-1 (CH2 stretching) and 1239cm-1 (C=O stretching). Finally, the peak noted around 598cm-1 is attributed by the C-OH stretching of cellulose in the fiber. Multiple concomitant investigations also observed similar FT-IR signatures that described in this study [63]. Although, this chemical investigation was sufficient to validate all other chemical characterization outcomes. Different functional groups and associated chemical component of HCSF was tabulated in Table 4.

Fig. 6
figure 6

FT-IR profile of HCSF

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Table 4 Different functional groups and associated chemical component of HCSF
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3.7 SEM/ SEM-EDX observations

The surface roughness or coarseness of HCSF was detected by the high-resolution SEM images captured at four different magnifications as 250×, 500×, 1000×, and 2000× (Fig. 7 (a–d)). It is clear from the picture that the cementing elements such as hemicellulose and lignin are used to bind many of the fiber bundles together. The corresponding hemicellulose, lignin, wax, and other impurities are visualized as small patches on the surface (Fig. 7 (a–c)). Rarely smoothened area was found that might be owed by the existence of small amount of wax and other impurities. Only fewer micro voids, holes, and fissures were observed, but uneven, mostly rough nature of the surface was noted as a most desired feature for inter-bonding with matrices. Figure 7(d) confirmed that the fiber posses good surface roughness since that can be a preferred option for composite preparation in future. The energy-dispersive spectrogram of HCSF is seen in Fig. 8 (a, b); that revealed that there are three major elements are widely distributed on the fiber surface, which are carbon (C) and oxygen (O), and potassium (K). It is renowned that carbon and oxygen constitute the backbone of biomacromolecule like cellulose in all plants [64]. The prominence of potassium might be due to the existence of non-cellulosic materials on fiber surface. Moreover, few other elements were found to be in but minute quantities or negligible levels. This is due to contaminations or amorphous fractions present on its surface [24]. Presence of different elements on the surface of HCSF is provided in Table 5.

Fig. 7
figure 7

(a, b, c, d) SEM images of HCSF at 250× (a), 500× (b), 1000× (c), and 2000× (d) magnification

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Fig. 8
figure 8

(a, b) SEM-EDX image of HCSF (a) and relevant spectrogram (b)

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Table 5 Presence of different elements on the surface of HCSF
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3.8 Roughness parameters of HCSF

Figure 9 (a–d) shows 2D/3D pictures, line profile, and specific roughness features of HCSF. Of which, 2D/3D images and line contour clearly present the roughness profile of HCSF that is favorable for appropriate fiber–matrix adhesion. Figure 9(d) explore the specific roughness properties of HCSF. The average roughness (Ra) of the fiber is identified as 7.2 nm, which was higher than the average roughness of Symphirema involucratum (6.647nm) [65]. The negative Rsk value (−0.528) indicates that the fiber surface has very little holes or fissures, that would provide a beneficial effect on creating interfacial bonds. Conversely, the required Rku value (2.553) below 3 indicates that the fiber has good surface roughness [66, 67]. The remaining roughness parameters as Rz (33.937nm), Rt (42.624nm), and Rq (8.683nm) once again proved the roughness nature of fiber surface. These morphological topographies demonstrate that the surface roughness of HCSF is good as to consider it for composite formulations in future.

Fig. 9
figure 9

(a, b, c, d) 2D/3D AFM images (a, b), line profile (c), and roughness parameters (d) of HCSF

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4 Conclusion

This study intended to identify a new plant fiber from Hibiscus canescens stem and to characterize it using standard protocols to establish its potential for use in polymeric composites. For that, plant stems were collected and soaked in water for an allotted amount of time to extract the fibers of interest. Physical, chemical, morphological, thermal, and mechanical methods were then used to further characterize the samples. The chemical characterization studies were pertinent to establish the chemical nature of the material; which proved that the material partakes high cellulose content (68.46 wt.%), good crystallinity index (48.78%), desired crystallite size (1.59nm), and more crystalline fractions than amorphous fractions. It is also reflected in the thermal and tensile profiles that the fiber’s high cellulosic crystalline fractions leads to good thermal stability (375°C) and tensile properties (394.9±14.42 MPa; 30.29±4.365 GPa). Along with this, low moisture content (10.44 wt.%) noted revealed that the fibers are strong enough to resist water or microbial attack. The density of the HCSF (1425 kg/m3) is sufficient to ponder it for lightweight and structural applications. The topographical examination revealed rough surface of HCSF with an average roughness of 7.200nm that guaranteeing strong adhesion qualities while composite fabrication. Hence, the current study recommends the extensive utilization of H. canescens stem fiber for composite based applications in future.