Introduction

In recent decades the consumption of polymer matrix composites has increased year by year. The versatility of application of these materials, ease of processing and mechanical behavior, drew attention to its use in various industry segments such as automotive, civil construction, naval and aerospace (Manimaran et al. 2018; Sanjay et al. 2018).

Although synthetic fiber materials have been widely used as reinforcement in polymer matrix composites and have some advantages such as high mechanical strength, high thermal resistance, and good compatibility with polymeric matrices (Sathishkumar et al. 2014; Mahato et al. 2017; Kumar et al. 2020). In the face of the global environmental appeal, alternatives to synthetic fibers commonly used as reinforcement in composites, such as, glass fibers, carbon fibers, aramid fibers had their development accelerated. Then several cellulosic fibers like Musa textilis (Abacá), Hibiscus cannabinus (Kenaf) and Boehmeria Nivea (Rami) started to be used as reinforcement in composite materials and applied in different industrial segments such as automotive, building, furniture, marine and aerospace (Müssig 2010; Salit et al. 2015; Delicano 2018; Kan et al. 2019; Thyavihalli Girijappa et al. 2019; Sanjay et al. 2019; Vinod et al. 2020; Mohd Radzuan et al. 2020).

The use of natural fibers to obtain composites has several economic and sustainable development advantages, mainly due to their characteristics which include excellent mechanical properties, low coast, low density, low abrasiveness, ease of processability, abundance, and biodegradability (Al-Oqla 2017; AL-Oqla and El-Shekeil 2019; AL-Oqla 2020).

Additionally, the use of natural fibers combined with biodegradable resins can increase the sustainability of the use of composite materials giving rise to completely green composites (LeSar and LeSar 2013; Koronis and Silva 2018; AL-Oqla and El-Shekeil 2019; Manimaran et al. 2019; AL-Oqla 2020).The fibers obtained from Agave sisalana (Sisal), Sansevieria cylindrica (Saint George’s Spear) and Agave tequilana (Blue Agave), plants of the order Asparagales, have presented promising results as reinforcement in composites. This fact has motivated the search for new species that demonstrate potential for application in polymeric matrix composites (Belouadah et al. 2015; Sreenivasan et al. 2015; Langhorst et al. 2018; Manimaran et al. 2018; Senthilkumar et al. 2018).

The findings about natural fibers revealed their potential as reinforcement material and highlighted their advantages to replace synthetic fibers. The main benefits include the biodegradability, are renewable, present low abrasivity, low cost and low density and have good mechanical properties (Shubhra et al. 2013; Chung et al. 2018; Fangueiro and Rana 2018). As a result, the demand for materials reinforced with natural fibers grew and the search for news fibers for new applications followed in the same way. (Baskaran et al. 2018).

Thus, to increase the range of reinforcement materials with potential applications in polymer matrix composites, a new source of natural fibers obtained from the leaves of Yucca aloifolia L. is presented.

The Yucca aloifolia L. belongs to the order of the Asparagales that possesses 1122 plant genera being at least two of them used in the manufacture of composites, the genus Agave and the Sansevieria. The genus Yucca belongs to the same order and subfamily as the agaves named Agavoideae (formerly classified as Agavaceae) (Chase et al. 2009, 2016; Albers and Meve 2001; Britannica 2015; Kress 2018; Langhorst et al. 2018; Senthilkumar et al. 2018). The Yucca aloifolia L. is one of about 40 species of Yucca cataloged. It is a plant originating from Central and North America, recognized mainly for its resistance to water scarcity and soils devoid of nutrients. Although several Yucca species are of considerable importance to man and have various uses in ancient indigenous civilizations in the United States and Mexico, only a few studies have been recently developed describing potential applications for Yucca aloifolia L., almost exclusively treating the use of the oil extracted from its seeds as a drug (Mokbli et al. 2018) or raw material for the manufacture of biodiesel (Nehdi et al. 2015). Despite this, and for the best of our knowledge, there are not scientific literature describing its application in composites of polymeric matrix. In comparison, some agaves species, such as Sisal and Blue Agave, have been extensively studied and have many publications describing their application in polymeric matrix composites and manufacture of components (Chase et al. 2009, 2016; Albers and Meve 2001; Britannica 2015; Kress 2018; Langhorst et al. 2018; Senthilkumar et al. 2018). Thus, since almost all species of the genus Yucca have considerable potential for crop formation and several species are often cultivated as ornamental plants, having spread and naturalized around the world (Albers and Meve 2001), we decided to investigate one of its species as a source of natural fibers for application in polymeric matrix composites.

Materials and methods

Fibers obtainment

The leaves of Yucca aloifolia L. were collected in the city of Maringá, Paraná State, Brazil. The leaves of Yucca aloifolia L. have two stages described in the literature, at first the leaves are healthy and are in an erect position, forming an angle about 45° in relation to the trunk, in a second stage the leaves start to be curves in direction of the trunk staying in this condition until finally die and dry, remaining attached in the trunk. In this study, the leaves were collected of an adult Yucca aloifolia L. plant which has about twenty years and only adults and health leaves between 35 and 45 cm were utilized. The exact age of the leaves cannot be determined, first because the life cycle of one leaf vary compared to another, and second the plant has not been cultivated (Webber 1895).

After being collected, leaves were washed with soap and water and subjected to extraction of the fibers by mechanical pull-out; The extracted fiber was washed with deionized water, and dried at 60 °C for 24 h. This process is summarized in the Fig. 1.

Fig. 1
figure 1

Fiber extraction of the Yucca aloifolia L. leaf

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Characterization methods

ATR-FTIR

The fibers of Yucca aloifolia L. were characterized using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) technique. The measurement was obtained using a Bruker Optics (RAM II FT-Raman Module Vertex Series) instrument, operating in the region 4000–650 cm−1, with a resolution of 4 cm−1.

XRD

The fibers were characterized by X-ray diffraction using a Bragg–Brentano X-ray diffractometer (Shimadzu XRD-6000), with radiation source Cu Kα (λ = 1.5418 Å). The diffractogram was recorded between 5° and 40° (2θ), the acquisition speed was 0.15°/min, the tension and current utilized was 40 kV and 30 mA, respectively.

To calculate the crystalline index (CrI) of fibers, the Segal method was used (Segal et al. 1959), the CrI is calculated from the height ratio between the intensity of the crystalline peak corresponding to the Miller indices 200 situated between 2θ = 22–24°, and the intensity of diffraction of the non-crystalline material, which is situated at valley between the peaks corresponding to the Miller indices 110 and 200, near 2θ = 18° (Ling et al. 2019).

The diffraction pattern had the data from a blank run, including the sample holder, subtracted from the data of experimental samples (Hermans and Weidinger 1948; Ling et al. 2019; French 2020). In addition, the experimental data was fitted in MAUD software (Lutterotti et al. 2007) utilizing a cellulose Iβ pattern (French 2014), the experimental and fitted curves were exported and plotted in Origin Software where were performed the follow calculus to CrI and crystallite size.

The crystalline index was calculated using the Eq. (1) (Karimi and Taherzadeh 2016):

$$ {\varvec{CrI}} = \frac{{\left( {{\varvec{I}}_{200} - {\varvec{I}}_{{{\varvec{am}}}} } \right)}}{{{\varvec{I}}_{200} }} \times {\mathbf{100}} $$
(1)

where I200 is the maximum peak intensity at 2θ = 22.5° related to the crystalline content and Iam represents the intensity of diffraction of the non-crystalline content in 2θ = 19.14°

The crystallite size was calculated using Scherrer’s Eq. (2) (Scherrer 1912; French and Santiago Cintrón 2013) rather than MAUD crystallite size values, which are larger than those calculated with the Scherrer equation (Ling et al. 2019), the measure was performed utilizing a Gaussian function in Origin software.

$$ {\varvec{\tau}} = \frac{{{\varvec{K}}.{\varvec{\lambda}}}}{{{\varvec{\beta}} \cdot \cos {\varvec{\theta}}}} $$
(2)

where τ is the size perpendicular to the lattice plane, K is the Scherrer’s constant taken as 0.9, λ is the wavelength of the radiation source used (1.5418 Å), β is the peak’s full-width at half-maximum at (200) reflection for cellulose I in radians, θ is the Bragg angle of the diffraction peak.

Chemical composition

The determination of composition of the fibers in terms of amount of cellulose, hemicellulose and lignin was performed according to the Van Soest method (Van Soest 1963; Vaz 2016). The method is carried out applying a neutral detergent solution to dissolve easily soluble materials, such as proteins and lipids. Then, the material is subjected to an acidic detergent solution, resulting in the solubilization of hemicellulose. The residue from the acid detergent solution is then treated with sulfuric acid (H2SO4) to remove cellulose. The final residual substance is taken to a muffle at 550 °C for 4 h, resulting in the fraction corresponding to insoluble minerals. The material in analysis is weighed before and after each stage, the fractions belonging to each constituent were given by mass difference (Van Soest 1963; Vaz 2016).

TGA

The thermal analysis was held in a simultaneous thermal analyzer from Perkin Elmer (STA 6000) with an open platinum crucible and heating rate of 10 °C/min, in the temperature range from 40 to 600 °C, under an atmosphere of nitrogen flow at 20 ml/min.

Tensile test

The fibers were subjected to tensile testing in a Stable Micro Systems (TA.XT. Plus) texturometer with 50 kgf load cell. The data acquisition occurred at a speed of 6 mm/min following a standard method (ASTM International 2013). Twelve samples were randomly chosen and tested, the free length of samples was 25 mm. The values for force (N) and distance (mm) obtained were subsequently used to perform the calculations of tensile strength (T.S.), Young's modulus (Y.M.) and elongation (EL). The cross-section area of the fibers was obtained by microscopy. For the calculation, Excel and Visual Basic® software were used.

SEM

The morphological study was carried out with FEI (Quanta250) SEM equipment. After the tensile test, the samples were identified and covered with gold by sputtering. The images were obtained towards the length of the fiber and used to determine its cross-section, allowing the determination of T.S., Y.M. and EL. For measurement of fiber cross section values was used the software ImageJ (Schneider et al. 2012). Three measurements were performed on the perpendicular direction of fiber alignment for each one of the fibers. The mean value of the measurements was used as the fiber diameter.

Results and discussion

ATR-FTIR

The spectra were divided in two regions, the fingerprint region that comprises the range of 1800 to 800 cm−1 and the region comprised between 3800 and 2750 cm−1. The bands were identified by numbers in Fig. 2. In the region between 2750 to 1800 cm−1 no significant bands were found.

Fig. 2
figure 2

ATR-FTIR spectrum of Yucca aloifolia L. fibers

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The region between 800 and 1800 cm−1 contains the largest number of bands identified, most of which are attributed to plant material as bands associated with cellulose, lignin, and hemicellulose. In the spectra can be observed bands attributed to lignin groups such as bands in 177020 cm−1 attributable to the stretching of C=O bonds in conjugated ketones, 173819 cm−1 attributable to the stretching of C=O bonds in non-conjugated ketones, 161117 cm−1 attributable to the stretching of C = C bonds in the aromatic ring syringyl (S), 150716 cm−1 assigned to the stretch C=C bonds associated with lignin and 12759 cm−1 attributed to C–O bond in aromatic methoxyl groups present in the guaiacyl. Bands attributed to lignin and cellulose present in how 146215 cm−1 assigned to asymmetric C–H deformation OCH3, CH2 in the pyran ring, 142314 cm−1 ascribed to asymmetric C–H deformation –OCH3, 137213 cm−1 flexural CH assigned to cellulose I, II and hemicellulose 133312 cm−1 attributed to C–O bond and flexural bending in CH plan cellulose I and II, 12358 cm−1 assigned to the syringyl ring and stretching C–O in the lignin and xylan, 11566 cm−1 attributable to the asymmetrical stretching C–O–C bond in the cellulose I and II, 11025 cm−1 ascribed to aromatic deformation the typical C–H plan units of S and stretching C=O and 10303 cm−1 attributed to deformation of the C–O bond in the cellulose I and II and finally bands allocated cellulose as found at 131711 cm−1 CH2 bending attributed to the cellulose I and II, 128010 cm−1 assigned to the deformation CH cellulose I and II, 12017 cm−1 assigned to the bending plane –OH unoxidized cellulose, 10524 cm−1 bending attributed to C–O valence linkage, mainly C(3)–O(3)H and 8952 cm−1 assigned to amorphous cellulose. Besides that, bands in 164518 cm−1, assigned to linked water at lignin or cellulose, and in 8751 cm−1, assigned to bending of the aromatic group in the guaiacyl are noted. (Coseri et al. 2015; Chimeni et al. 2016; Liu et al. 2017; Maulidiyah et al. 2017; Achinivu 2018; Hospodarova et al. 2018; Sanjay et al. 2018; Hemmati et al. 2019).

The region between 3800 and 2750 cm−1 is mainly related to the stretching of OH and CH groups. In this region, it possible to observe bands of 292222 cm−1 ascribed to the symmetrical stretching CH aromatic methoxyl groups and methyl groups and methylene side chains and 285121 cm−1 attributable to the asymmetrical stretching CH aromatic methoxyl groups and methyl groups and methylene side chains. The wideband in 333023 cm−1 is assigned to stretching of the OH bond of hydroxyl groups, the increase in the intensity of this band indicator longer exposure OH (Coseri et al. 2015; Chimeni et al. 2016; Liu et al. 2017; Maulidiyah et al. 2017; Achinivu 2018; Hospodarova et al. 2018; Sanjay et al. 2018; Hemmati et al. 2019). With the basis of the analysis results, it is possible to confirm the presence of the main constituents of lignocellulosic fibers, cellulose, hemicellulose and lignin in Yucca aloifolia L. fibers. The summary of the band’s positions and assignments are presented in Table 1.

Table 1 IR assignments for Yucca aloifolia L. fibers
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X-ray diffraction analysis

In the X-ray diffractogram of Yucca aloifolia L. fibers in Fig. 3 is possible to observe the presence of peaks related to the crystalline planes at the following Bragg angles (2θ): 15.5° (1 \(\overline{1 }\) 0); 16.7° (110); 22.5° (200); and 34.8° (004) (Yue et al. 2012; French and Santiago Cintrón 2013; French 2014; Ling et al. 2019; del Cerro et al. 2020). The peaks related at planes (1 \(\overline{1 }\) 0) and (110) has overlapped reflection, the overlapped of reflections is influenced by crystallite size which is very small in cellulose samples, about 20–50 Å (Thygesen et al. 2005), the accomplished refinement helped to make them distinguishable. The peaks found are related to crystallographic planes of the cellulose Iβ (French 2014). The preferred orientation is an inherent factor in cellulosic samples, in this work the relative heights between the overlapping peaks and the peak (200) can be an indicator of its occurrence (Ling et al. 2019; French 2020).

Fig. 3
figure 3

Diffractogram pattern of Yucca aloifolia L. fibers and the Rietveld fitted pattern

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The crystallinity of natural fibers is directly linked to the mechanical behavior, higher cellulose crystallinity results in increased of properties as Young’s modulus, tensile strength and hardness (Latif et al. 2019; Rongpipi et al. 2019; Todkar and Patil 2019). In this way these features can be very desirable when it is intended to use natural fibers as a reinforcement in polymeric matrix composites (Sanjay et al. 2018; Lotfi et al. 2019; Gholampour and Ozbakkaloglu 2020). However, it is an extremely important factor, various authors report that the measured crystallinity of cellulose can differ significantly depending on the technique and analysis approach used, limiting the results comparison, even when the same data was used (Karimi and Taherzadeh 2016; Rongpipi et al. 2019).

The CrI of Yucca aloifolia L. fibers calculated by Segal method was 69.43% and according to Scherrer equation the crystallite size is approximately 24.6 Å for Yucca aloifolia L. fibers. The experimental and fitted data are shown in Fig. 3.

Chemical composition analysis

The chemical composition in weight percent (wt%) of the Yucca aloifolia L. fibers (F-Yucca) is shown in Table 2.

Table 2 Chemical composition of Yucca aloifolia L. fibers
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The comparison among the values obtained to cellulose, hemicellulose and lignin, for other untreated fibers and Yucca aloifolia L., is presented in Table 3. The cellulose, lignin and hemicelluloses content are close to those found in the kenaf fibers, that are widely used in polymer matrix composites (Nematollahi et al. 2019; Radzuan et al. 2019; Mohd Radzuan et al. 2020). Compared with the sisal fibers, that belongs to the same order and subfamily (Agavoideae), the Yucca aloifolia L. fibers have cellulose content 14.3% lower, while the hemicellulose and lignin have higher values, 43.9% and 20%, respectively.

Table 3 Typical chemical compositions for natural fibers
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Generally, fibers with high cellulose content have higher mechanical properties compared to fibers with less cellulose. A high hemicellulose and lignin content is undesirable for use in polymer matrix composites, because they are more susceptible to thermal degradation and act as igniters increasing the thermal degradation of cellulose (Fan and Fu 2017; Jawaid et al. 2019). However, several factors may be related to the contents of the components found in natural fibers, among them are climatic factors, environmental, or even the age of the plant (Fan and Fu 2017; Jawaid et al. 2019).

Thermogravimetric analysis

TG-DTG curves of the Yucca aloifolia L. fibers (F-Yucca) are shown in Fig. 4. It is possible to observe that fibers have four weight loss stages. In the first stage, which occurred below 100 °C, the evaporation of water and volatile compounds present in the fibers occurred, being 4% of the weight lost in this step (Ornaghi et al. 2014). Lower weight loss on this temperature range indicates lower hydrophilicity of the fibers, this being a factor beneficial for use in polymer composites (Fernandes et al. 2013; Chandrasekar et al. 2017). In the second stage, the weight loss presented a maximum rate at 294.7 °C, in this temperature range occurs the depolymerization of glycosidic bonds in hemicellulose and pectin (Fernandes et al. 2013; Indran and Raj 2015; Chandrasekar et al. 2017). The third step of weight loss is related to cellulose degradation that occurred between 310 and 390 °C, with maximum degradation rate at 357.7 °C. Higher temperatures of cellulose degradation are related to the greater thermal stability of the fiber (Fernandes et al. 2013; Indran and Raj 2015; Chandrasekar et al. 2017). The fourth step occurred over to 390 °C, is related to oxidative degradation of lignin and residual of fibers carbonized, corresponding of 18% of the total weight at the end of the process at 591.8 °C. (Indran and Raj 2015; Jordá-Vilaplana et al. 2017; Wang et al. 2018).

Fig. 4
figure 4

TG-DTG curve of Yucca aloifolia L. fibers

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Thermal characterization of the natural fibers is particularly important when it is aiming to apply them in composite materials since in various manufacturing processes are used high temperatures. Thus, the evaluation of the thermal behavior at different temperatures is fundamental and can help to determine the optimum thermal condition to fiber application in different polymeric matrices preventing it from occurring thermal degradation (Belouadah et al. 2015).

The temperature at which the degradation of hemicellulose and pectin begins in the fibers of Yucca aloifolia L., around 193 °C, is higher than the melting temperature of several polymeric materials, allowing the fibers to be applied in a wide range of polymeric materials without suffering thermal degradation. Thermoplastics, such as polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC), as well as thermosets, such as epoxy, phenolic and polyester resins (Callister and Rethwisch 2015), are widely used in obtaining composites reinforced with natural fibers (Chauhan et al. 2019) and can be reinforced with Yucca aloifolia L. fibers.

Tensile properties

Based on the fiber diameters obtained by SEM images, the fiber mechanical properties are shown in Table 4. The high variability found in the results is expected in mechanical tests of natural fibers. It is related to the characteristics of this type of fiber, such as structural imperfections, cross-sectional variability along the length of fiber, shown in Fig. 7, and variability of the geometric profile (Alves Fidelis et al. 2013; Noda et al. 2016). The stress/strain patterns are shown in Fig. 5.

Table 4 Tensile properties of Single fibers of Yucca aloifolia L
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Fig. 5
figure 5

Single fibers stress/strain curves of Yucca aloifolia L.

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The comparison between the values for tensile strength, Young's modulus and deformation of other natural fibers and Yucca aloifolia L. fibers are shown in Table 5. The values obtained portray that the tensile strength obtained is the fourth largest among the compared fibers, being smaller than typical values founded for pineapple, ramie and Curauá fibers. Therefore, it can be concluded that Yucca aloifolia L. fibers have mechanical characteristics similar to the other fibers applied in polymer matrix composites.

Table 5 Typical average mechanical properties of natural fibers
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SEM

The morphological analysis revealed the presence of parenchymal cell residues and that the fiber structure is completely joined by lignin, forming uneven and continuous filaments along the length of the fiber (Neto et al. 2012; Ramphul et al. 2017). Fiber morphology is a determining factor in its application as reinforcement in composite materials (Indran and Raj 2015). Although the low roughness observed on the surface of the fibers and the significant presence of non-cellulosic constituents indicates that the fibers need to undergo surface modification, such as a fiber cleaning process, before to be applied in polymeric matrix composites. A fiber surface treatment is essential for achieving good interfacial adhesion between the fiber and the matrix (Moshi et al. 2020).

Prior knowledge of the fiber's morphological characteristics is extremely important to decide the best treatments and applications in composite materials. Analyzing the treatments applied to the fibers that belong to the same family of Yucca aloifolia L. as Agave Sisalana (Senthilkumar et al. 2018; Melkamu et al. 2019) and Agave Americana L. (Ben Sghaier et al. 2012; El Oudiani et al. 2012; Madhu et al. 2020), very desirable results can be observed in the fibers that have gone through the mercerization process, which in some cases was able to provide cleaning of the fibers while maintaining their mechanical characteristics in addition to provide improvement in its thermal resistance characteristics. The scanning electron micrographs of the Yucca aloifolia L. fibers are shown in Fig. 6.

Fig. 6
figure 6

SEM images of Yucca aloifolia L. fibers

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The cross-sectional analyses of Yucca aloifolia L. fibers revealed a large variation in the dimensions of the sections when compared to each other, which is expected in natural fibers and may influence their mechanical behavior. The variations in the section of the fibers are mainly related to the way the fibers were extracted, to the species of the plant and to factors related to its growth such as the environment where the plant grown and its age (Baskaran et al. 2018; Lotfi et al. 2019; Manimaran et al. 2019; Vinod et al. 2020). Section micrographs of the Yucca aloifolia L. fibers are shown in Fig. 7. The fracture region of fiber after tensile test were presented in Fig. 8.

Fig. 7
figure 7

SEM images of sectional variation of Yucca aloifolia L. fibers

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Fig. 8
figure 8

SEM image of fracture region of Yucca aloifolia L. fiber

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Conclusion

Physicochemical, thermal, mechanical and morphological analyses revealed that the fibers extracted from the leaves of Yucca aloifolia L., compared with other natural fibers already used, have the potential for application in polymeric matrix composites.

The results obtained in the ATR-FTIR characterization showed the presence of the main constituents of lignocellulosic fibers, cellulose, hemicellulose, and lignin in the fibers of Yucca aloifolia L. The chemical characterization indicates that the fibers are constituted by a high amount of cellulose, about 52.5%, being the crystallinity index of the cellulose obtained through XRD analysis of 69.43%. The thermal analysis performed through TGA, reveals excellent thermal stability of the fibers up to temperatures of 193.4 °C, allowing the fibers to be applied in various polymeric materials.

The mechanical characterization of the fibers pointed to a very desirable mechanical behavior in reinforcements applied in composites obtaining high average values in comparison with other natural fibers such as 801 MPa for tensile strength and 39 GPa for Young's module, the elongation of 2%, the mechanical properties found for Yucca aloifolia L. fibers exceed those found in fibers commonly used in polymeric composites such as sisal, jute and hemp.

The images captured in SEM analyses revealed the presence of a large amount of non-cellulosic constituents present on the surface of the fibers.

Based on the obtained results, it can be stated that the fibers of Yucca aloifolia L. have potential application in composites of polymeric matrix.