1 Introduction

Being sustainable in industrial operations is the norms due to ecological imbalances, which show themselves as a worldwide climatic change, contamination of water, air and earth, and depletion of ecological sources [1, 2]. Regulations were additionally implemented to promote environmentally friendly methods in order to protect and preserve the environment and its biodiversity. Any sector that wants to employ environmentally friendly practices needs to be very selective about the raw resources it utilizes [3]. Several sectors had either not started using environmentally friendly techniques yet or had just begun to use them. The composite industry was among the earliest to adopt environmentally friendly procedures, and its early endeavors were fruitful. This makes it possible for the composite sectors to continue operating and producing their goods effectively. Composite firms sought for ecologically friendly and decomposable raw materials to begin their sustainable approach [4]. The composite enterprises would benefit from the implementation of environmentally friendly manufacturing procedures if they could find the perfect base material [5]. The fiber derived from minerals, animals, and plants remains the main choice available to composite producers. The persistent needs of the composite sectors cannot be met by animal-based fibers, and the cost of harvesting mineral fibers is higher [6]. Plant fibers may be a more common ingredient used by composite producers in countries with high levels of vegetation, such as India.

Fibers extracted from plants offer several advantages, such as easily biodegradable, low price, abundant prevalence, and less requirement of energy and hazardous intensive processing techniques; however, there are certain obstacles to overcome in order to optimize the composite’s properties when organic yarns are utilized as support material in composites [7]. Meanwhile, these yarns have to be extracted straight away from ecosystem; it is impossible to control their physical form. Since the aforementioned fibers have different geometric shapes, the manufacturer finds it challenging to develop certain properties for composites composed of polymers employing these fibers as reinforcement material [8]. Furthermore, the availability of fibers that are natural is unable to managed based on needs since they come from natural sources. Alternative environmental risk expected is loss of forest area if fibers from trees were removed to cater the market needs [9]. However, some naturally fiber rich waste from agriculture is burned in open air, causing air pollution, or it is dumped in trash dumps, where it emits a foul stench over the neighborhood [10,11,12]. Composite enterprises that take advantage of these agricultural wastes rich in fiber create a circular economy that benefits farmers. Composite enterprises that take advantage of these waste products from agriculture packed with fiber establish an economic cycle that is beneficial to agriculturalists.

The properties of natural fibers that composite enterprises require depend on a variety of factors, including the organic nature of the material, the climate in which the tree or plant is cultivated, the oldness of the plants, and the portion of the herb or tree from which the yarn is harvested. The quality of the fibers is also influenced by the process used to extract it from the source material. Antony et al. [13] extensively characterized the leaf sheath fibers extracted from Licuala grandis tree. The tested yarns had a cellulose proportion of 49.13 wt%, tensile strength of 179 MPa, and with crystallinity index of 48%. The thermal stability of the fibers ensured through experiments ensures its use in composite industries. Manish et al. [14] explored the possibility of using fibers from leaf sheath of areca as sound absorbing material. They observed that the sound absorption capability of the areca leaf sheath fibers prepared as samples varied based on its thickness. The noise reduction coefficient was optimum for a 54-mm-thick sample, and it further increased by the introduction of air gap. With the 54-mm-thick areca leaf sheath sample and airgap of 20 mm, the noise reduction coefficient enhanced from 0.69 to 0.74.

Sekar et al. [15] characterized the leaf sheath fibers extracted from areca tree to know its possible utilization in industries. The fibers had a cellulose content of 56.8 wt%, tensile strength of 401 MPa, and with crystallinity index of 56.5%. The thermal stability was found to be 270˚C, and they suggest the leaf sheath fibers extracted from areca tree to be employed in textile sectors. The leaf sheath fibers extracted from windmill palm tree were investigated by Jing et al. [16] to know its suitable application in composite industries. The interrogated fibers showed a less cellulose content of 35.5 wt%, tensile strength of 132 MPa, and high micro fibril angle of 38.8 with comparable crystallinity index of 49.2%. But the elongation at break is 17.6% with the findings; the authors does not suggest any specific applications. Lami [17] investigated the effect of degumming process using alkali on the leaf sheath fibers extracted from palm tree. The author claims that the degumming process of leaf sheath fibers extracted from palm tree using alkali, hydrogen peroxide as bleaching agent, and silicone as softener improved its mechanical and moisture absorption characteristics.

The palm tree Phoenix sylvestris L., also known as the silver date palm in the local dialect, is a member of the Arecaceae family and is planted for its food, medicinal, and ornamental use. In Asian nations, Phoenix sylvestris is found growing in plains and scrublands. Its fruit is used to make pastries and wine. Following fruit harvesting, the leaf sheath remains as agro-wastes. Its trunk is used to make wooden gadgets for household applications. But the leaf sheath of Phoenix sylvestris L. is left out as waste which remains in landfills. The leaf sheath of Phoenix sylvestris L. contains enormous quantity of fibers which currently goes as waste. In a view to utilize Phoenix sylvestris leaf sheath fiber (PSLSF) in composite industries, the characteristics of the fiber was interrogated holistically. The PSLSF was exposed to physio-chemical and thermal testing to illustrate their mechanical, thermal, and chemical properties. SEM was utilized to assess the PSLSF’s surface characteristics. XRD, TGA/DTG, and FTIR interrogations were performed on the PSLSF to evaluate its crystalline, thermal endurance, and functional groups, correspondingly. The most effective waste elimination plan may be developed, and the thermo-mechanical features of composite made of polymers can be enhanced by using PSLSF as a reinforcing material, according to studies on the material.

2 Materials and methods

2.1 Separation of PSLSF

The leaf sheaths belonging to Phoenix sylvestris was gathered from the garbage of corporate and educational sites in and around Chennai, Tamil Nadu, India. The collected leaf sheaths shown in Fig. 1 were soaked in water for 3 days. The soaked leaf sheaths were washed in flowing water 5 or 6 times to separate the PSLSF from the pulp and remove other dust particles [18]. The extracted PSLSF were sundried to diminish its dampness content and stored for further study. The PSLSF was subjected to physical, mechanical, chemical, and thermal evaluations to ensure its suitability for usage as reinforcing material in composite industries.

Fig. 1
figure 1

Separation of Phoenix sylvestris tree leaf sheath fiber. a Phoenix sylvestris tree. b Phoenix sylvestris tree showing leaf sheath. c Collected leaf sheath of Phoenix sylvestris tree. d Water retting of collected leaf sheath. e Extracted Phoenix sylvestris tree leaf sheath fibers

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2.2 Characterization of PSLSF

The chemical constituents of the PSLSF were explained using the standard techniques found in the scientific field, such as Krusher–Hoffer method for cellulose, the Conrad method for wax, the Klason method for lignin, and the Standard NFT 12–008 method for hemicellulose [19]. Using the ASTM E1755-61 norm, the amount of moisture in the PSLSF was ascertained. The density of PSLSF was computed by means of the mass-volume method. For this use, a known-volume container is stuffed with a powdered dry specimen of PSLSF and squeezed until all of the air is extracted. To calculate the fiber mass density, the weight of the container is recorded both with and without the powdered PSLSF specimen. Single fiber tensile test based on ASTM D3822-07 was conducted on PSLSF to assess its strength [20]. In every instance, ten specimens were examined. Using 4 cm−1 precision and 32 scans per minute, FTIR analysis was performed on PSLSF to determine the manifestation of functional clusters in the yarn. XRD spectroscopy was also performed on PSLSF using an upward goniometer displacement of 5°/min to show the XRD band over the Bragg angle (2θ) array of 10° to 80° using copper-K-alpha 1.54 Ang as the source of radiation [21]. The simplest method for comprehending the PSLSF’s external features was to examine them using SEM images at an 8 kV accelerated voltage. The thermal durability of PSLSF was elucidated using TGA/DTG and DSC investigations, which entailed heating specimens to 550 °C and 450 °C, correspondingly, at a speed of 10 °C/min [22].

3 Results and discussions

3.1 Chemical examination of PSLSF

The chemical properties of natural yarns are influenced by the growth environment of shrubs and trees, the age of the vegetation, and the parts of the herb that is used when the fiber is extracted. Environmental fiber’s chemical composition can be utilized to infer specifics about their physio-mechanical, exterior texture, and crystallographic properties. The organic fiber’s exterior texture has a major impact on the mechanical characteristics of the bonded polymeric composite [23]. Furthermore, the properties of the impregnated fibers have a significant influence on the features of vegetative fiber impregnated polymer composites. The chemical properties of PSLSF are presented as proportions of weight (wt%) in Table 1. The substantial percentage of 64.43 weight percent cellulose in PSLSF, that is equivalent with that of its substitutes, affects the mechanical features of the fiber. The crystalline form of PSLSF is aided by the substantial cellulose content, producing enough hydrophobic features for the yarn to be utilized as reinforcing substance in composites made of polymers.

Table 1 Physical, chemical, and mechanical characteristics of Phoenix Sylvestris leaf sheath fiber in contrast with its ecofriendly counterparts [25]
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On utilizing as reinforcements in polymeric composite materials, the PSLSF’s minimum hemicellulose content of 10.36 weight percentage enhances the yarn’s morphological and interaction features. On applying as reinforcements in composite with polymers as the base material, the 13.2 content % of lignin in the PSLSF functions as an adhesive and encourages contact with the substrate [24]. The fireproofing of the PSLSF is attributed to its 1.5 weight percent ash content. If utilized as reinforcing substance in polymeric composite materials, the PSLSF’s thermal endurance to withstand deterioration at polymerization heat is further strengthened by the ash content. Its application as reinforcements in composites made of polymers is supported by the acceptable weight proportions of wax (0.21 wt%) and dampness (10.3 wt%).

3.2 FTIR analysis of PSLSF

The FTIR findings of PSLSF are presented visually and tabulated in Fig. 2 and Table 2, respectively. The chemical architecture of PSLSF is shown by the FTIR spectrum. Chemical identification is aided by the distinct spectral patterns that each molecule produces. The visual plot provides insight into the presence of significant functional categories in the PSLSF. The valley that fluctuates at an oscillation rate of 1093 cm−1 is caused by an organic chemical cluster known as an alkyl halide [26]. The narrow valley perceived at a wavelength of 1389 cm−1 is caused by the wavy alkene group, a different organic functional cluster represented by = C-H. The apparent discrepancies in the FTIR graph up to 1493 cm−1 warrant the presence of sparsely distributed carboxylic group in the PSLSF. The carbonyl operational group, denoted by C-O, is symbolized by the valley at 1701 cm−1 [27]. In the FTIR spectrum, undulations in the frequency of 2883 cm−1 indicate the presence of cellulose in the PSLSF. The broader valley shown at 3318 cm−1 in the FTIR spectrum of PSLSF is caused by the continuing presence of OH absorbed surrounding the cellulose. The alkali operational group predominates, which results in fluctuations around 3607 cm−1, which signifies the symmetric expansion of C-O [28]. The insights from the FTIR study corroborate the findings of PSLSF's chemical examination.

Fig. 2
figure 2

FTIR spectrum of Phoenix sylvestris leaf sheath fiber

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Table 2 FTIR peak positions of Phoenix sylvestris leaf sheath fiber
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3.3 Anatomical and morphological study of PSLSF

The physical features of the PSLSF, as seen by micro method to view the inner makeup of the yarn, are shown in Table 3. The cellulose and lignin that make up the PSLSF’s primary and secondary cell walls, accordingly, significantly affect the mechanical properties of the fiber [29]. In the PSLSF, cells next to one another are joined by the lignin and hemicellulose adhering in the lamellae, which serve as tissues of connection. On utilizing as strengthening substance in composite made of polymers, the lumen, which is a void inside the PSLSF cells, enables the fibers from nature to retain a lower density and augments to the polymeric composite's lightweight quality.

Table 3 Physical entities of Phoenix sylvestris leaf sheath fiber
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Figure 3 depicts the PSLSF’s external and cross-sectional perspectives as perceived by SEM. On utilizing as reinforcing component in polymeric composites, the coarse surface of the PSLSF, with its greater peak and valley, improves the interaction of the PSLSF with matrix, according to the findings from Fig. 3a [30]. The circumferential region of the boundary between the PSLSF and matrix is increased in the polymeric composite with reinforcing component that has greater peak and valley, which is beneficial for improving the bonding across interfaces. The mechanical properties of the PSLSF are further influenced by tiny fibrils that connect parenchyma cells and lignin, an organic substance that acts as a binding agent. The micro fibril angle well connected to the mechanical properties of the PSLSF. Utilizing Eq. (1), the micro fibril orientation of PSLSF is arrived to be 4.27° ± 0.13°:

Fig. 3
figure 3

SEM imageries of Phoenix sylvestris leaf sheath fiber: a surface view and b cross-sectional view

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$$\upvarepsilon =\text{ln}\left[1+\frac{\Delta L}{{L}_{0}}\right]=-ln\left(cos\alpha \right)$$
(1)

where ε is the strain, α is the micro fibril angle (degree), ΔL is the Elongation at break (mm), and Lo is the gauge length (mm). The computed micro fibril inclination is more in line with the 4.95° ± 0.32° estimate of the Cissus quadrangularis stem fiber [30]. When reinforced in polymeric composites, PSLSF’s having low micro fibril angle enables the matrix and PSLSF to distribute stress appropriately.

3.4 XRD study of PSLSF

The XRD findings of PSLSF are shown graphically in Fig. 4. The crystalline characteristics of the PSLSF are understood from the pictorial representation. The partially crystalline properties of PSLSF are supported by the strong spike at Bragg angle (2θ) of 22.3° [31]. The prior small intensity spike found at 2θ of 16.7° is caused by the amorphous substances in the PSLSF. Regarding the crystalline elements of PSLSF, the larger spike at 22.3° of 2θ correlates to the crystallographic layer (2 0 0). The identified cellulose in this crystalline layer is categorized as cellulose-I and has a monoclinic structure. On the other hand, the amorphous substance spike of the PSLSF is located on the (1 1 0) crystallographic layer at 16.7° of 2θ. The PSLSF’s crystallinity index (CI), as determined by Eq. (2) [32], was 53.6%.

Fig. 4
figure 4

XRD spectrum of Phoenix sylvestris leaf sheath fiber

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

where Ic is the maximum intensity of crystalline peak at 2θ = 22.3° and Iam is the intensity of amorphous peak at 2θ = 16.7°. The analyzed CI number of the PSLSF guarantees that it possesses the requisite physical characteristics, such as crystallinity, to function as a reinforcing substance in composites made of polymers. Applying Scherrer’s formula (3) [32], the crystallite size (CS) of the PSLSF was computed and arrived to be 3.13 nm.

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

where K = 0.89 is Scherrer’s constant, λ is the wave length 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. Table 4 displays PSLSF’s CI and CS numeric in relation to other fibers found in the available research. The measured number of the CS amply supports its less hydrophilic nature, allowing PSLSF to be used as a reinforcement component in composites including polymers as the substrate.

Table 4 XRD outcomes of Phoenix sylvestris leaf sheath fiber in comparison with other fibers in the literature
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3.5 Physico-mechanical study of PSLSF

Table 1 provides an overview of the PSLSF’s physico-mechanical properties. Pulverized fibers were firmly stuffed in a tubular container of specified weight in order to calculate the PSLSF’s density. The result was that the mass-volume density of the PSLSF was found to be 1.45 g/cm3. When utilized as reinforcement, the natural fiber strengthened composite of polymers will have a lower density because of the PSLSF [33]. PSLSF strengthening contributes to the creation of materials with particular properties in polymer matrix composites. Employing image J software and an optical microscope, the diameter of the PSLSF was ascertained. Table 5 shows that the diameter of the PSLSF varied from 191.60 to 256.47 μm. Considering its irregular size and form, the PSLSF’s cross-section is taken into consideration as round to facilitate the calculation of diameter using Eq. (4):

Table 5 Mechanical characteristics of Phoenix sylvestris leaf sheath fiber
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$${\text{D}}_{\text{f}}=\sqrt{\frac{{L}_{f}}{9000\times {M}_{d}\times 0.7855}}$$
(4)

where Df is the LGPF’s diameter; Lf is its linear mass density in denier, which is a measure of the LGPF’s fineness determined in accordance with ASTM D1577-07 standard; and Md is its mass density in grams per cubic centimeter. The diameter of the PSLSF obtained from Eq. (4) is 223.81 μm, falling within the permitted range determined by using the image J software.

The PSLSF’s tensile strength, which ranges from 192 to 239 MPa, is shown in Table 5 together with the stress–strain graph in Fig. 5. Similar to other plant-based fibers (such as Dorris scandens stem and the leaves of pineapple fiber) used as reinforcement in composites with polymers as the matrix, PSLSF shows equivalent tensile strength values [34,35,36]. There were five attempts at every experimentation. The PSLSF’s cross-section, which varies in dimensions and shape throughout its span, is the reason for the discrepancy in physical properties observed along the gauge length change. The strain to failure estimates listed in Table 5 are supported by the PSLSF stress–strain graph shown in Fig. 5, which further highlights the examined fiber’s fragility. The stress–strain curves start with the steep linear curve which is the elastic region of the PSLSFs. Following the elastic region, the PSLSFs exhibit a plastic region where the stress decreases and finally results in rupture of the PSLSFs showcasing a brittle failure. The higher Young’s modulus and adequate elongation at break numerics of the PSLSF comprehend its exceptional load-withstanding ability [35]. The PSLSF can be used as reinforcing material in composites made of polymers due to its assessed and actual physico-mechanical features. Since organic yarns make up the majority of the load-bearing component of environmentally friendly composites made from fibers with polymers serving as the matrix, PSLSF with enhanced tensile features may be a suitable reinforcing substance.

Fig. 5
figure 5

Stress–strain curve of Phoenix sylvestris leaf sheath fiber

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3.6 TGA study of PSLSF

The PSLSF’s thermal behavior was visually depicted in Fig. 6. The thermal endurance of the PSLSF is made clear by the graphic depiction. The PSLSF loses water as the temperature increases, as seen by the thermogravimetric profile, which indicates decreased mass of 6.1% up to 109 °C. Following dehydration of the PSLSF, the fiber sample exhibited satisfactory temperature endurance up to 242 °C, suggesting a 2.9% weight drop that signaled the start of the depolymerization phase [36]. The key component materials of the PSLSF, such as hemicellulose, lignin, and cellulose, initiated to decompose via the depolymerization process after a further increase in temperature. Up to 293 °C, this causes the PSLSF sample to lose mass by about 14.2%. The mass reduction of the PSLSF specimen in the temperature span of 294 °C to 378 °C indicates the complete cellulose disintegration in the processed fiber specimen [37]. The mass decrease that occurs after 379 °C designates that portion of the lignin and waxes has been detached from the extracted fiber sample.

Fig. 6
figure 6

TGA-DTG curve of Phoenix sylvestris leaf sheath fiber

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The DTG graph variations show that the cellulose in the PSLSF suffers pyrolysis and molecular framework deterioration, with an acute point at around 331 °C and a mass difference of about 51.32%. The leftover char at 550 °C (15.57%) can be used to forecast the fire resistance of the PSLSF. The thermal properties of the PSLSF are shown in Table 6 together with those of different natural fibers found in the available literature. Using Broido’s formula (5) [38], the kinetic activation energy (E) of the PSLSF was determined to be 72.36 kJ/mol. In Fig. 7, the Broido’s graph was also displayed.

Table 6 Thermal properties of Phoenix sylvestris leaf sheath in comparison with other natural fibers
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Fig. 7
figure 7

Broido’s plot of Phoenix sylvestris leaf sheath fiber

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

where R is the universal gas constant (8.314 J·mol−1K−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 × 10−23J·K−1). An important metric for assessing the PSLSF’s capacity to facilitate polymerization in the process of creating polymeric composites is the estimated E value. When the surrounding temperature is elevated, the utilization of PSLSF augmented composite polymers is supported by the PSLSF’s thermal evaluations.

3.7 DSC study of PSLSF

The DSC results of PSLSF were visually displayed in Fig. 8. The visual representation shows the amount of heat transfer across the PSLSF sample as the temperature increases. The DSC plot’s endothermic curve illustrates how the cellulose-bound water molecule enables the PSLSF sample to lose wetness. The water particles that were firmly bonded in the cellulose of the PSLSF start to evaporate as temperatures get nearer to 100 °C [39]. The temperature of the PSLSF specimen subsequently rises even more, attaining 114.6 °C, which is the endothermic section of the DSC profile, where the dehydration of liquid droplets that are intimately adhered to cellulose takes place. The degradation of the wax in the PSLSF samples is designated by the exothermic profile at 169.7 °C [40]. The PSLSF specimen’s damaged cellulose is due to the endothermic spike, which was detected at 223.6 °C. Pyrolysis is a process that occurs in hemicellulose and lignin, and it results in exothermic surges at 287.5 °C and 342.7 °C, correspondingly. At higher temperatures, further endothermic and exothermic fluctuations in the DSC profile indicate the lignin and hemicellulose degradation in the PSLSF [41]. The endothermic and exothermic variations observed in the PSLSF specimen after heating guarantee the use of PSLSF augmented composites of polymers in workplaces with greater ambient temperatures.

Fig. 8
figure 8

DSC plot of Phoenix sylvestris leaf sheath fiber

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4 Conclusions

The outcomes of the PSLSF investigations clearly suggest that the composites sector will use this substance as a reinforcing agent in composites made of polymers. This initiates a more effective agro-waste administration strategy and assists composite companies in addressing sustainability issues with their products and processes. A 64.43 weight percent content of cellulose was found in the PSLSF after chemical analysis, favoring the mechanical properties required to be employed as a strengthening ingredient in composites using polymer as the substrate. The results of the chemical investigation were further supported by the FTIR evaluation that identified important functional compounds in the PSLSF. The density (1.45 g/cm3) and tensile strength (192–239 MPa) of the PSLSF serve as examples of its exceptional mechanical qualities. It is confirmed that the PSLSF is adequately hydrophobic by the predicted CI number of 53.6%. High ambient temperature applications can benefit greatly from PSLSF integrated composites of polymers due to their endothermic and exothermic activity and thermal endurance up to 242 °C. The thermal and mechanical evaluations of PSLSF support the use of PSLSF enhanced polymer composites in frames that are lightweight under high ambient temperature circumstances. To determine the PSLSF strengthened polymeric composites’ particular usefulness in sectors like building and automotive manufacturing, more research must be done on their characterization.