1 Introduction

Sustainability in industrial practices is the order of the day due to unbalance in ecosystems which reflects as global warming; pollution of air, water, and soil; and exhaustion of natural resources [1, 2]. Sustainable practices were further enforced by laws in view to protect and preserve nature and its ecosystem. Any industry that aspires to follow sustainable practices must give utmost care in the selection of raw materials [3]. Many industries were yet to initiate or merely just started their sustainable practices. The composite industry is the one that has initiated its sustainable practices and has been successful in its first steps. This gives scope to composite industries to make their products and processes completely sustainable. Hence, composite industries were in search of eco-friendly, sustainable, and biodegradable raw materials to initiate their sustainability cycle [4]. The identification of the best-suited raw material will help the composite industries to establish sustainable production practices [5, 6]. The main choice that remains viable for composite industries is the fibers existing in natural resources such as plants, minerals, and animals. Fibers from animal sources are not sufficient enough to meet the continuous demand of composite industries; on the other hand, mining of mineral fibers is costlier. For vegetative countries like India, composite industries can rely more on fibers from plants for their raw materials.

Even though the fibers from plants are advantageous in several ways such as minimal cost, easily biodegradable, plenty of sources to obtain from nature, and do not demand harmful and energy-consuming processing techniques, they pose certain hurdles in maximizing the performance of the composite when reinforced [6]. Since these fibers need to be harvested directly from nature, their physical shape cannot be controlled. The fibers of varied physical shapes make the industrialist challenging to achieve specific characteristics for polymer composites with these fibers as reinforcement materials [7, 8]. Further, on dependence of the composite industries on natural fibers as raw materials being available from nature, its supply based on the demand cannot be regulated. If the natural fibers were harvested based on the demand, it might lead to deforestation, imposing another sustainable threat to the environment [9]. On the other hand, several agricultural wastes that are rich in natural fibers remain in landfills and propagate bad odour to the surrounding environment or are fired in open environments creating air pollution [10,11,12]. The usage of these fiber-rich agricultural wastes by composite industries results in better waste management and leads to a circular economy benefitting the farmers.

The necessary traits of natural fibers to be used by composite industries depend on the chemical constituent of the fiber, the weather condition in which the plant or tree is grown, the age of the flora, and the plant part from which the fiber is intended to be utilized [13, 14]. The process adapted to extract the fiber from the plant part also influences the quality of the fibers. Sergius et al. [15] investigated the stem fiber extracted from Ficus benjamina to know its suitability to be used in the textile and composite industries. Their experimentations report that the extracted fibers possessed a cellulose content of 68.71 wt.% and crystallinity of 58.5% which is suitable to be used in the composite and textile industries. Another fiber from the stem of Cissus vitiginea was investigated by Sudhir et al. with a view of utilizing it as a reinforcement material in composite industries [16]. They also noticed a good weight percentage of cellulose content (65.43 wt.%) with acceptable crystalline characteristics (30.5%) and a temperature-withstanding capability up to 304 °C finds scope to be used as support material by composite industries. The fibers extracted from the leaf of the purple bauhinia tree were characterized by Rajeshkumar et al. [17] to know its probable scope in using it as a strengthening material in the composite industries. The extracted leaf fibers possessed a tensile asset of 373.3 MPa which is a boon to be used as a support material in the composite industries. The ability of the fiber to withstand higher temperatures of up to 341 °C identified through their experimentations indicates the ability of the extracted leaf fiber to support the fabrication process of composites.

Licuala grandis L. is a palm category tree that is grown as an ornamental plant and listed under the Arecaceae cluster. The wood of the Licuala grandis L. tree obtained from its trunk after maturity is utilized as a raw material for manufacturing wooden products. But the leaf stalk of the Licuala grandis L. tree which is rich in fiber remains unutilized and retained as landfills or burnt as waste. This natural floral waste rich in eco-friendly fibers requires further examination to verify its suitability to be used as a reinforcement material by composite industries. This inquiry specifies the examination of natural fibers mined from the leaf stalk of the Licuala grandis L. tree, a floral leftover to be used as a reinforcement material by composite industries. The Licuala grandis tree leaf stalk fibers (LGTLSFs) were subjected to physio-chemical and thermal experimentations to portray their mechanical, thermal, and chemical characteristics. The surface features of the LGTLSFs were examined with the help of a scanning electron microscope (SEM). The X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy were performed on the LGTLSF to cross-examine its crystallinity, thermal stability, and existence of functional groups, respectively. The investigations on LGTLSF favour its use as a strengthening material in composite industries to increase the thermal and mechanical characteristics of polymer composites and help formulate the best waste management approach.

2 Materials and methods

2.1 Extraction of LGTLSFs

The leaf stalks of the Licuala grandis tree were picked from landfills of institutional and organizational campuses in and around Coimbatore, Tamil Nadu, India. The picked leaf stalks were cut to appropriate sizes as shown in Fig. 1 and immersed in water for 14 days to release its fibers [18]. The soaked leaf stalks were raked manually to segregate the LGTLSF from the pulp. The segregated LGTLSFs were splashed with water at several attempts to confiscate the pulp attached in the form of dust particles. Then the LGTLSFs were desiccated in sunshine for 3 days to lessen their wetness and warehoused for further investigation. The LGTLSF was characterized physically, mechanically, chemically, and by thermal means to ensure the possibility of utilizing it as a support material by composite industries.

Fig. 1
figure 1

Extraction of Licuala grandis tree leaf stalk fiber. a Licuala grandis tree, b collected leaf stalks of Licuala grandis tree, c soaking of leaf stalk, d fiber extraction, and e extracted Licuala grandis tree leaf stalk fibers

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2.2 Characterization of LGTLSF

The biochemical proportions of the LGTLSF such as cellulose, wax, lignin, and hemicellulose were accounted for by the well-established procedures followed in the literature [19]. The weight loss technique was followed to identify the moisture content of the LGTLSF. The mass-volume method was adhered to quantify the density of the LGTLSF. A single-fiber tensile test was conducted on LGTLSF as per ASTM D3822-07 norms to appraise its mechanical characteristics [20]. FTIR spectroscopy was performed on LGTLSF at 4 cm−1 resolution and 32 scans/min to identify the occurrence of active groups in the fiber. Similarly, XRD spectroscopy analysis was conducted on LGTLSF with the vertical goniometer movement of 5°/min to plot the XRD spectrum over the Bragg angle (2θ) range of 10 to 80° [21]. The exterior features of the LGTLSF were best understood by viewing through SEM at a hastened power of 8 kV. The thermal nature of the LGTLSF was detailed by performing thermogravimetric analysis (TG and DTA) and differential scanning calorimetry (DSC) experiments by raising the temperature of the LGTLSF samples until 550 °C and 450 °C, respectively, at 10 °C/min [22].

3 Results and discussions

3.1 Chemical study of LGTLSF

The biochemical characteristics of the eco-friendly fibers depend on the weather conditions in which the plant or tree is grown, the age of the flora, and the herbal part from which the support material is mined. The outcomes of chemical investigation of natural fibers help to infer their physio-mechanical, crystalline, and surface texture characteristics. The surface texture of the natural support material plays a vital role in the mechanical assets of the polymer composite when reinforced [23]. Moreover, the specific traits of the natural fiber–strengthened polymer composite are highly dependent on the qualities of the reinforced fibers. The chemical proportions of LGTLSF have been portrayed in Table 1 measured as weight percentage (wt.%). The significant amount of 56.47 wt.% cellulose in LGTLSF, which is equivalent to its competitors, contributes to the fiber’s mechanical properties. The crystalline nature of the LGLSF, which produces adequate hydrophobic properties of the fiber to be employed as support material in polymer composites, benefits from the larger amount of cellulose content.

Table 1 Chemical and physio-mechanical features of Licuala grandis leaf stalk fiber in comparison with its other natural and synthetic counterparts [25]
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When engaged as a strengthening material in polymer composites, the LGTLSF has a minimum hemicellulose concentration of 18.36 wt.%, which benefits the fiber’s mechanical and bonding properties. When engaged as strengthening material in polymer composites, the 12.8 wt.% of lignin in the LGLSF works as a binder and encourages the contact with the matrix [24]. The LGLSF’s fire resistance is supported by its 1.8 wt.% ash content. When engaged as strengthening material in polymer composites, the LGLSF’s thermal durability to withstand damage to polymerization temperature is further supported by the same. Its usage as a strengthening material in polymer composites is encouraged by the satisfactory weight percentages of moisture (10.3 wt.%) and wax (0.27 wt.%).

3.2 FTIR analysis of LGTLSF

The FTIR observations of LGTLSF are displayed in graphical form in Fig. 2. The graphical plot provides an idea on the presence of notable functional groups in the LGTLSF. The trench seen at a frequency of 532 cm−1 attributes to the oscillations of alkyl halide which is an organic functional cluster [26]. The deep trench viewed at the wavelength of 1018 cm−1 belongs to the oscillating alkene cluster which is again an organic functional group symbolized as = C-H. The instabilities in the FTIR plot visible until 1377 cm−1 ensure the existence of polysaccharides of cellulose in the LGTLSF [27]. The carbonyl functional cluster symbolized as C-O is indicated by the trench at 1603 cm−1. The oscillations in the FTIR spectrum in the wavelength range between 1848 and 2124 cm−1 represent the occurrence of lignin and hemicellulose in the LGTLSF [28]. The prevalence of alkaline functional cluster promotes the symmetric bending of C-H which is represented by the trench at 2898 cm−1. The broader trench seen at 3288 cm−1 in the FTIR plot of LGTLSF is attributed to the flaring of OH impregnated around the cellulose. The observations of FTIR analysis ratify the outcomes of the chemical analysis of LGTLSF.

Fig. 2
figure 2

FTIR spectrum of Licuala grandis tree leaf stalk fiber

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3.3 Morphological and anatomical analysis of LGTLSF

The LGTLSF’s physical characteristics are shown in Table 2. These values were obtained by repeating the experiment at least thrice. Lignin and cellulose make up the secondary and primary cell walls of the LGTLSF, which heavily influences the physical features of the eco-friendly material [29]. The neighbouring cells in the LGTLSF are connected by the lignin and hemicellulose found in the lamellae, which act as connective tissue. When mined, support materials are used to strengthen polymer composite materials; the lumen, or empty space inside the cells of the LGLSF, aids in the natural fibers’ ability to retain less density and adds to the lightweight nature of the polymer composite.

Table 2 Physical features of Licuala grandis leaf stalk fiber
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Figure 3 displays the exterior and cross-sectional views of the LGTLSF as seen via SEM. When utilized as a support material in polymer composites, the observations from Fig. 3a demonstrate that the surface of the LGTLSF is rough with greater crest and trough, which favours the bonding of LGTLSF with the matrix [30]. On strengthening in polymer composites, the LGTLSF exterior with more crest and trough enhances the surface area of contact between the LGTLSF and matrix, which is beneficial for having stronger interfacial bonding properties. The SEM pictures also show the presence of lignin, a binder substance, and tiny fibrils that connect parenchyma cells. The microfibril angle has an influence on the physical nature of the LGTLSF as well. The microfibril angle of LGTLSF is calculated using Eq. (1) and is 6.01° ± 0.12°.

$$\varepsilon=\ln\left[1+\frac{\Delta L}{L_0}\right]=-\ln\;(\cos\alpha)$$
(1)

where ε is the strain, α is the microfibril angle (°), ΔL is the elongation at break (mm), and Lo is the gauge length (mm). When reinforced in polymer composites, LGTLSF’s microfibril angle must be as small as possible in order for the matrix and LGTLSF to transfer stress effectively.

Fig. 3
figure 3

SEM image of Licuala grandis leaf stalk fiber: a parallel view 2000 × and b cross-sectional view 500 × 

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3.4 XRD study of LGTLSF

The XRD observations of LGTLSF are displayed in graphical form in Fig. 4. The graphical plot provides an idea on the crystalline characteristics of the LGTLSF. The semi-crystalline features of LGTLSF were endorsed by the resilient crown at a Bragg angle (2θ) of 21.3° [31]. The preceding peak of mild intensity seen at a Bragg angle (2θ) of 15.8° is attributed to the amorphous components in the LGTLSF. The broader peak at 21.3° of 2θ corresponding to the crystalline contents of LGTLSF belongs to the crystallographic plane (2 0 0). The cellulose in this crystallographic plane possesses a monoclinic structure belonging to the category cellulose-I [32]. On the other hand, the peak at 15.8° of 2θ relating to the amorphous contents of LGTLSF fits the (1 1 0) crystallographic plane. The crystallinity index (CI) of the LGTLSF was quantified by Eq. (2) [32] as 49%. The higher CI value obtained among its counterparts ensures the stiffness of the LGTLSF.

$${\text{CI}}=\frac{({I}_{{\text{c}}}-{I}_{{\text{am}}})}{{I}_{{\text{c}}}}$$
(2)

where Ic is the maximum intensity of crystalline peak at 2θ = 21.3°, and Iam is the intensity of amorphous peak at 2θ = 15.8°. The assessed CI numeric of LGTLSF ensures its crystalline nature and required physical qualities to be castoff as a support material in polymer composites. Equation (3) [32] proposed by Scherrer was used to assess the crystallite size (CS) of the LGTLSF as 1.14 nm. The lesser CS value obtained for LGTLSF when compared with its counterparts enhances the mechanical and hydrophobic characteristics of the fiber.

$${\text{CS}}=\frac{K\lambda }{\beta \mathrm{cos\theta }}$$
(3)

where K = 0.89 is Scherrer’s constant, λ is the wavelength of the radiation, β is the peak’s full-width at half-maximum (FWHM) expressed in radians, and θ is the Bragg’s diffraction angle. The numerical value quantified for CS endorses the hydrophobic nature of the LGTLSF which is sufficient to be castoff as a strengthening material in polymer composites.

Fig. 4
figure 4

XRD spectrum of Licuala grandis tree leaf stalk fiber

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3.5 Physicomechanical study of LGTLSF

Table 1 summarizes the physicomechanical parameters of the LGTLSF. Powdered LGTLSF specimens were securely crammed in a cylindrical flask with an identified mass in order to calculate the LGTLSF’s density. As a result, 1.36 g/cm3 was calculated as the LGTLSF’s density on a mass-volume basis. When employed as reinforcement, LGTLSF’s lower density guarantees that the natural fiber–reinforced polymer composite will be lightweight [33]. LGTLSF reinforcement in polymer matrix composites aids in the fabrication of composites with certain properties. With the aid of the ImageJ program and an optical microscope, the diametric width of the LGTLSF was measured. As shown in Table 3, the diameter of the LGTLSF varied from 397.96 to 442.37 µm. Despite the LGTLSF’s cross-section’s non-uniform size and shape, it is assumed to be circular for the purposes of calculating the diameter using Eq. (4).

$${D}_{f}=\sqrt{\frac{{L}_{f}}{9000\times {M}_{d} \times 0.7855}}$$
(4)

where Df is the LGTLSF’s diameter, Lf is its linear mass density in denier, which is a measure of the LGTLSF’s fineness determined in accordance with ASTM D1577-07 norm, and Md is its mass density in grams per cubic centimeter. Equation (4) yields a diameter for the LGTLSF of 436.12 µm, which is within the range of values discovered using the ImageJ program.

Table 3 Mechanical assets of Licuala grandis leaf stalk fiber attained as per ASTM norms
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The tensile asset of the LGTLSF, which is shown in Table 3, ranges from 312 to 354 MPa. Comparable to other eco-friendly support materials used as strengthening components in polymer composites, LGTLSF has tensile strength values [34]. The LGTLSF’s cross-section varies in size and form over its length, which accounts for the variability in physical features detected over the variation in gauge length. The lower Young’s modulus and higher elongation at break values of the LGTLSF demonstrate the LGTLSF’s superior load-bearing capacity [35]. The LGTLSF is capable of serving as a strengthening material in polymer composites due to its estimated and measured physicomechanical properties. Since natural fibers are the primary load-bearing component of eco-friendly, mined, support-material-strengthened polymer composites, the LGTLSF with higher tensile characteristics can be an appropriate reinforcement material.

3.6 TGA study of LGTLSF

The thermal observations of LGTLSF are displayed in graphical form in Fig. 5. The graphical plot provides an idea on the thermal stability of the LGTLSF. The dehydration of the LGTLSF with a rise in temperature is reflected as weight loss until 108 °C in the thermogravimetric curve. After dehydration of the LGTLSF, the fiber sample showed good resistance to temperature until 218 °C indicating a minor weight loss [36]. The components of the LGTLSF such as cellulose, lignin, and hemicellulose started to disintegrate on a subsequent increase in temperature through the depolymerisation method. This incurs a reduction in the weight of the LGTLSF sample of about 13.9% until 291 °C. An extensive reduction in weight of the LGTLSF sample in the temperature array of 292 to 367 °C represents the comprehensive dilapidation of cellulose in the mined fiber sample [37]. The weight loss witnessed after 368 °C indicates the deprivation of a portion of lignin and wax in the mined fiber sample.

Fig. 5
figure 5

TGA-DTG curve of Licuala grandis leaf stalk fiber

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The variations of the DTG plot designate an infliction point at about 331.5 °C accompanied by a difference in mass of about 51.63% representing that the cellulose in the LGTLSF undergoes pyrolysis and breakdown of molecular structure. The fire retardant ability of the LGTLSF is predictable from the residual char attained at 550 °C which is quantified as 14.31%. Broido’s Eq. (5) [38] was utilized to estimate the kinetic activation energy (E) of the LGTLSF as 72.71 kJ/mol.

$${\text{ln}}\left[{\text{ln}}\left[\frac{1}{y}\right]\right]=-\left(\frac{E}{R}\right)\left[\left(\frac{1}{T}\right)+K\right]$$
(5)

where R is the universal gas constant (8.314 J·mol−1 K−1), T temperature in Kelvin, y normalized weight (wt/wo), wt weight of the sample at any time t, w0 initial sample weight, and k Boltzmann’s constant (1.3806 × 10−23 J·K−1). The estimated E-value guides to finalize the capability of the LGTLSF to bear the polymerization process during the fabrication of polymer composites.

3.7 DSC study of LGTLSF

The DSC observations of LGTLSF are displayed in graphical form in Fig. 6. The graphical plot provides an idea on the heat flow in the LGTLSF sample with a rise in temperature. The dehydration of the LGTLSF sample associated with the water particles attached to cellulose is shown as an endothermic curve in the DSC plot. The reluctantly attached water particles in the cellulose of the LGTLSF get dehydrated closer to above 100 °C [39]. Subsequently, further rise in temperature of the LGTLSF sample dehydrates the water particles which are closely attached to cellulose until 129.8 °C representing the endothermic part of the DSC curve. The degeneration of wax in the LGTLSF sample is indicated by the exothermic curve at 169.4 °C [40]. The damage caused to cellulose in the LGTLSF sample is attributed to the endothermic peak at 267.2 °C. The pyrolysis experienced by hemicellulose and lignin affiliates to the exothermic peaks at 283.7 and 379.1 °C, respectively. Further endothermic and exothermic fluctuations seen at higher temperatures in the DSC curve denote the degeneration of hemicellulose and lignin in the LGTLSF [41]. The endothermic and exothermic fluctuations witnessed in the LGTLSF sample on heating ensure that the LGTLSF-strengthened polymer composites can be employed in industrial environments having higher ambient temperatures.

Fig. 6
figure 6

DSC plot of Licuala grandis leaf stalk fiber

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4 Conclusions

The observations of the experimentations on LGTLSF strongly suggest its use as a support material in polymer composites by composite industries. This aids in minimizing the sustainability issues in their products and processes by composite industries and initiates a better agro-waste management approach. The 56.47 wt.% of cellulose content in the LGTLSF identified through chemical analysis supports the adequate mechanical physiognomies to be castoff as a support material in polymer composites. The results of chemical analysis were further endorsed by the identification of major functional groups through FTIR analysis. The abrasive surface texture of the LGTLSF aids in making interlocking bonds with the polymer matrix when reinforced. The tensile strength (312–354 MPa) and density (1.36 g/cm3) of the LGTLSF reveal its specific mechanical characteristics. The appraised CI value of 49% confirms the adequate hydrophobic nature of the LGTLSF. The endothermic and exothermic behaviour on the rise in temperature of the LGTLSF and thermal stability until 218 °C favours LGTLSF-embedded polymer composites in high ambient temperature applications. The thermo-mechanical observations of LGTLSF warrant the use of LGTLSF-supported polymer composite in lightweight structural applications in high ambient temperature environments.