1 Introduction

The demand for eco-friendly, lightweight and high-strength materials for construction and automotive applications is increasing due to industrialization and population growth. In this regard, natural fibers exhibit many benefits compared to synthetic fibers [1]. Lignocellulosic biomass plays a vital role in creating a circular bio-economy and minimizing environmental impact [2]. In global markets, there is a high demand for numerous quality cellulose-based natural fibers; Enset is a source of good-quality fiber, suitable for ropes, twine, baskets, and general weaving [3]. Composites from natural fibers have emerged as materials of interest in important industries, such as packaging, automobiles, and construction [4]. Enset (Ensete ventricosum (Welw.) Cheesman) is grown in the densely populated Ethiopian highlands as a source of food and an appropriate plant with great potential for the production of natural fibers [5].

Fig. 1
figure 1

Enset and its processing for food and fiber: (a) harvestable mature Enset plant (b) pseudostem harvested for leaf sheaths preparation (c) leaf sheath separation from pseudostem (d) harvested leaf sheaths ready for ‘kocho‘ processing (e) manual ‘kocho’ processing (f) fiber extracted as by-product after ‘kocho’ processing (Source: Sisay Buta) 

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Enset is a large fibrous tree-like monocot [6], a multi-use Ethiopian food crop with competitive properties suitable for the production of natural fibers [7,8,9]. Kocho is a fermented, energy-rich food in Ethiopia made from decorticated leaf sheaths of the pseudostem and pulverized corm (true stem) of the Enset plant [10,11,12]. The crop belongs to the order Scitamineae, the family Musaceae, and is a typical monocarpic perennial herb sometimes referred to as the “false banana” [5, 6]and [13]. It grows up to 2 m in dwarf landraces to 10 m tall, with a pseudostem (Fig. 1b) made out of overlapping leaf sheaths (Fig. 1c, d) that encircle each other and an underground true stem, or corm (rhizome) [14]. The Enset plant is found in Uganda, Madagascar, and Vietnam in the wild however, it is only domesticated in Ethiopia. The plant serves as a major staple or co-staple cultural food for at least 20–25% of the country’s population; [13,14,15]. This crop has also been cultivated for animal feed, fiber production, as well as ornamental and traditional medicine [16,17,18].

Enset plants, extensively grown in southern Ethiopia, cover 301,978.68 hectares of land and primarily produce starchy food from their robust pseudostem, corm, and inflorescence stem. Enset fibers are residual agricultural by-products obtained during the processing of pseudostem leaf sheaths for food and are confirmed as a promising eco-friendly fiber source [19]. The pseudostem (false stem) of the Enset plant is formed by overlapping and tightly packed leaf sheaths encircling each other [20, 21]. The processing generates annually about 150,000 tons of Enset fiber bundle residues in Ethiopia [22]. Fibers extracted as a by-product of food or feed crops do not require additional land and reduce the need for additional land [3].

According to Olango et al. [23], farmers consider the production of high-quality fiber to be a very important cultivar criterion. Fibers are used for construction, local rope making, making bags, twines, cordage, ground, table mats, and composites [24]. Furthermore, Enset fibers are possibly used for various industrial applications, including the manufacture of parts for the automotive industry [7]. Nowadays, Enset fiber is also used for the production of fiber-reinforced thermoplastic composites, fiber-reinforced cement composites, hybrid Enset fiber-reinforced, and fiber-reinforced bio-resin composites [4].

The amount of fiber being traded is steadily increasing due to the ongoing construction boom in Addis Ababa and other major cities in Ethiopia. It is essential to analyse the cellulose content and fiber thickness of various Enset landraces [3, 25]. In Hawassa town, Ethiopia, a kilogram of high-quality Enset fiber bundle is typically sold for 100 to 110 birr (equivalent to 1 USD) in retail outlets that sell construction materials (Abulu Gebeyew, pers. comm). The strength and flexibility of the fiber are crucial quality factors for industries such as textiles and paper, which rely on factors like cell length and cell wall chemistry [26]. The size and quality of plant fibers can vary based on factors such as species, location, altitude, nutrients, temperatures, season [27,28,29], climate, plant growth conditions, plant age, maturity at harvest, harvesting methods, fiber refinement, coarseness, chemical composition, structure, extraction and storage methods, and the specific landrace of fibers used [30,31,32]. Murasing et al. [33] found that the highest mechanical strength (breaking strength, elongation at break) was observed at higher altitudes, with the highest tenacity value found at middle altitudes for Grewia fiber.

In terms of mechanical properties, the gauge length affects the tensile strength of fiber, with longer fibers requiring less force to break, resulting in lower strength [34]. Natural fiber mechanical properties are mainly influenced by their chemical composition [35]. Alternatively, domesticated Enset in Ethiopia displays significant phenotypic diversity, with more than 1200 locally named landraces found in a variety of environments, surpassing other local crops in range [36].

This diversity encompasses a wide range of plant morphology [15], food and nutrition traits [37], and fiber quality [3]. Farmers value and actively maintain diverse Enset landraces on their farms [13, 23]. While there are reports of large-scale processing of high-quality fiber in Ethiopia, industrial-scale applications have not yet been developed [25]. The potential use of Enset diversity to extract natural fiber from pseudostem leaf sheaths at different altitudes for product development has not been thoroughly explored. Research on the fiber characteristics of Enset landraces is still limited. We hypothesize that fiber chemical and mechanical properties may vary with altitude, leading to differences in Enset landrace fiber properties at different altitudes.

Therefore, this study assesses how altitude impacts the chemical and mechanical properties of fibers from various qualitative phenotypes (such as the color of leaf lamina, upper and underside color of the petiole and leaf midrib, and leaf tip edge color) of Enset landraces in southern Ethiopia. The results will aid in leveraging Enset diversity for large-scale production of Enset fiber at mid and high altitudes, promoting income security and employment opportunities.

2 Materials and methods

2.1 Study area

For this research, purposive sampling techniques were employed to select the study location, Enset landraces, and altitude. The samples were collected from the main Enset growing belt in the high and middle altitudes of Hulla woreda, central Sidama zone in Sidama National Regional State of Ethiopia. In this study, kebeles (the smallest administrative unit within a woreda (district)) were purposefully selected according to the importance and production of diverse Enset landraces with the inclusion of measurable altitudinal differences in the selected area. Two kebeles were selected for the study, such as Gase kebele from high altitude and Gatama kebele from middle altitude. A total of 128 Enset-growing households were randomly selected in the two kebeles (64 from each). The selected kebeles (Gase geographically located between 6° 5’ 9.0’’ N latitude and 38° 49’ 0.4’’ E longitude with an elevation of 2122 to 2158 m.a.s.l and Getama also located between 6° 5’ 7.9’’ N latitude and 38° 63’ 17.8’’ E longitude, the area has an elevation of 2742 m.a.s.l) to assess possible altitudinal effects on Enset landrace for the study.

2.2 Selection of enset landraces based on qualitative phenotypic attributes

The semi-structured questionnaires and farm visits were conducted in the selected 128 households. For each of the farms visited, the GPS location was recorded using the My GPS Location application downloaded on a smartphone (Galaxy Note8 SM-N950U). Furthermore, phenotypic characteristics such as maturity periods, age, fiber yield, and fiber quality were categorized during household interviews before the selection and tagging of landraces for fiber extraction. Image-based qualitative phenotype data were also included during the survey using a high-resolution camera to differentiate visible characters of the selected landraces. Accordingly, 10 Enset landraces were identified and selected, namely: ‘Ado’, ‘Astara’, ‘Ganticha’, ‘Gedio Ado’, ‘Gossalo’, ‘Keshicha’, ‘Kiticho’, ‘Kulle’, ‘Midasho’, and ‘Uwisha’ for their quality fibers (Fig. 2).The semi-structured questionnaires and farm visits were conducted in the selected 128 households. For each of the farms visited, the GPS location was recorded using the My GPS Location application downloaded on a smartphone (Galaxy Note8 SM-N950U). Furthermore, phenotypic characteristics such as maturity periods, age, fiber yield, and fiber quality were categorized during household interviews before the selection and tagging of landraces for fiber extraction. Image-based qualitative phenotype data were also included during the survey using a high-resolution camera to differentiate visible characters of the selected landraces. Accordingly, 10 Enset landraces were identified and selected, namely: ‘Ado’, ‘Astara’, ‘Ganticha’, ‘Gedio Ado’, ‘Gossalo’, ‘Keshicha’, ‘Kiticho’, ‘Kulle’, ‘Midasho’, and ‘Uwisha’ for their quality fibers (Fig. 2).

At the age of 6 years old, ten qualitative phenotypes (Fig. 2) of Enset plants were selected from different landraces and tagged in a volunteer’s field. Compensation was paid for each selected landrace. Three Enset individual plants were randomly chosen and tagged for fiber extraction to represent a single landrace in each kebele. This resulted in a total of 60 Enset plant samples (10 landraces x 3 Enset plants each x 2 altitudes) that were purchased and used for the study.

Fig. 2
figure 2

Qualitative phenotype different Enset landraces selected for fiber characterization study (Source: Sisay Buta)

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2.3 Pseudostem leaf sheaths preparation for fiber extraction

The Enset plant can grow to be 4 m to 13 m tall with a pseudostem, which is a false stem made of overlapping leaf sheaths that encircle each other to form the pseudostem, ranging from 2 m to 5 m in length [38]. Typically, the wooden scraping board used to separate the pulp from the fiber is no longer than 1.5 m [39]. However, if the pseudostem leaf sheath is longer than 1.5 m, it is cut into two or more parts to match the board’s length, thereby reducing the fiber’s length accordingly [3]. For this study, a 2 m long wooden scraping board was deliberately prepared and used to separate the pulp from the fiber. All sampled Enset plants had their pseudostem leaf sheaths cut at a height of 1.65 m to obtain the longest clean fiber. Subsequently, the pseudostem leaf sheaths (Fig. 1c, d) from the inner-mid part of each landrace were harvested and collected on the spot where they were cultivated in the farmers’ fields, specifically selected for this study.

Surprisingly, the outer Enset leaf sheath fibers have a brittle nature, so they were excluded during pseudostem preparation for fiber extraction. The pseudostem of each Enset landrace was further divided into fiber-extractable pseudostem and fiber-non-extractable pseudostem based on farmers’ practice. Starting from the outer kocho extractable middle layers of the pseudostem leaf sheath (Fig. 1c, d), up to the fifth layers of the pseudostem leaf sheath were reserved as fiber-extractable pseudostem leaf sheath for this study without the outermost and deep inner side of the pseudostem leaf sheath. The inner non-fiber-extractable part of the pseudostem leaf sheath was manually removed and discarded before normal pseudostem leaf sheath fiber extraction.

2.4 Fibers extraction process

The sampled fiber-extractable pseudostem’ leaf sheaths of each landrace were separately placed on a wooden board made for food and fiber extraction. The Enset pseudostems leaf sheath were scraped using a sharp locally available, flat steel scraper with a wooden handle (Fig. 3a), and the fibers were carefully extracted manually using traditional tools. The epidermal layer was first removed, and the sheaths were scraped until the fibers were free from soft pithy stuffs, epidermis and other extraneous matter used as input for kocho processing. Kocho processing involves producing fermented, energy-rich food by harvesting, cleaning, scraping the pseudostem leaf sheath (which yields fiber as a by-product) and pulverized corm, and sometimes adding a starter culture (gamancho).

Fig. 3
figure 3

Enset fiber extraction, whole sale to retail point in Sidama Region of Hawassa City, Ethiopia. a Manual Enset fiber extraction using traditional tools, b Extracted Enset fiber, c Enset fiber transportation to Hawassa market, d Enset fiber for sale (Source: Sisay Buta)

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The resulting extracted fiber by-product was collected separately from each Enset plant and then; tagged separately as experimental material. For each landrace selected, three Enset plants were fiber extracted separately at each altitude. The resulting Enset fibers sampled from each landrace were proportionally mixed to create one representative sample (Fig. 3b) and used as a single treatment for each altitude and each landrace. Finally, ten fiber samples from high altitude and ten from middle altitude were collected, resulting in a total of twenty fiber samples prepared from both altitudes representing ten landraces. The fiber samples were then subjected to sun drying separately and carefully to remove excess moisture and facilitate further analysis.

2.5 Fiber sample preparations

The extracted fibers from each landrace were separately cleaned with clean water and sun-dried to remove the water contained in them for further investigation (Fig. 3b). Then, the sun-dried fibers were isolated slightly by hand, sitting patiently. The fiber laminates were allowed to undergo the hand retting process to separate individual fiber strands manually. Then, pure fibers were allowed to dry again at room temperature before weighing and bagging to eliminate any moisture. Afterward, all the fibers were measured for weight and length, as per the required dimensions following the standard method of ASTM D 6612 standard for mechanical testing [40]. Subsequently, for chemical composition analysis, sampled Enset fibers were separately cut into smaller pieces using a manual hand paper cutter to facilitate grinding. Then samples were ground into powder using a 1 mm sieve size with a Retsch MM200 mixer ball mill grinder for 10 min and dried at 105 °C for 24 h in the animal nutrition laboratory of Hawassa University, College of Agriculture campus. Fiber samples from each landrace and altitude were paper-bagged and labelled with the landrace name and altitude in the laboratory for chemical analysis.

2.5.1 Fiber chemical composition analysis

Fiber chemical composition tests were conducted on each Enset landraces at the central Plant and Animal Biotechnology Laboratory owned by Hawassa University, College of Agriculture. For the determination of the chemical composition of Enset as natural fibers, chemical testing was preferred as the method found prominent [41]. The ASTM D629-15 [42] standard was used for checking Enset landraces fiber chemical composition. A selective dissolving method based on the compounds was used to determine the amounts of fiber components. The composition of cellulose, hemicellulose, and lignin was determined by an ANKOM2000 Fiber Analyzer (ANCOM Technology, Macedon, NY) due to its ability to produce equally precise results and help batch processing at lower costs with the highest precision. Following the procedure recommended by the manufacturer, ANKOM Technology automates the principles and methods developed by [43]. The Enset fiber samples were prepared using ANKOM F57 filter bag technology and placed in a bag suspender. The chemical determination was executed by transferring every sample to the filter bag for analysis following the procedure outlined by the ANKOM analyzer company. The technology uses neutral and acid detergent solutions to separate fiber components. The solution was then heated, and solubilisation took place without manual intervention. At that point, the analytical method on the computer controller simply selected, and the button was pushed. The process was commenced in a closed system with F57 filter bags for all cellulose, hemicellulose, and lignin determination in this study. The system automatically added the appropriate chemicals and performed the necessary rinses. Subsequently, the analysis by the fiber analyzer technology completed the bags were simply removed, and a final drying before weighing the samples was finished. The results were automatically yielded by the ANKOM fiber analyser, obtained values, fiber content in the original mass of individual samples, in % (w/w), was calculated, and the data were separately handled for further analysis and interpretation.

2.5.2 Ash content (%) determination

The ash contents of the Enset landraces fiber were determined by placing about 2 g of sample on pre-weighed crucibles and placed in the furnace at 575 ºC for 3 h and cooled. The crucibles were placed in desiccator and weighed until the difference of two successive weights are less than 1 mg, as recommended by in [44]. The percentage of ash contents were calculated using the below Eq. 1.

$$\%\:\text{of Ash content}=\frac{Initial\:sample\:weight}{Final\:ash\:Weight}\times100$$
(1)

2.5.3 FTIR analysis

Fourier transform infrared spectroscopy (FTIR) is a powerful analytical technique that leverages the unique vibrational properties; for the identification of different functional groups in terms of their structure and composition. The analytical studies were conducted with the assistance of FTIR. FTIR provides information about molecular fragments, the presence or absence of specific functional groups, and can offer deeper insight into the fiber structure, indicating relative proportions of elements such as carbon, hydrogen, and oxygen [45]. Solid sample FTIR testing was carried out in Hawassa University’s central laboratory to determine the functional group components present in Enset landraces fiber samples. The fiber samples were measured, and 1 mg of extractive-free samples was obtained and then ground using a cutter-type mill with a 1 mm screen size in a Retsch MM200 mixer ball mill grinder for 10 min and dried at 105 °C for 24 h. Subsequently, the powdered product (10 Enset fiber samples from mid-altitude and 10 Enset fiber samples from high altitude) were separately mixed with 100–200 mg of dry, IR-transparent matrix called dry potassium bromide (KBr) and pressed into a pellet for analysis. Then, potassium bromide pellets were analyzed as solid samples. FTIR analysis was conducted, and the functional group components were identified using an FTIR spectrometer PerkinElmer, Model: Spectrum 3 MIR/NIR/FIR, USA. Spectrum 10 software was utilized for the analysis. The infrared spectra were recorded in the range of 4000 to 500 cm-1 with a resolution of 4 cm-1 and 64 scans accumulation for the qualitative and quantitative determination of biomass components in the mid-IR region.

2.5.4 Mechanical properties test

2.5.4.1 Sample conditioning

Mechanical property analysis of the sampled fibers was conducted at the Ethiopian Textile and Garment Industry Research and Development Center’s Physical Testing Laboratory in Addis Ababa, Ethiopia. Upon the arrival of all 20 Enset fiber samples at the Addis Ababa Physical Testing Laboratory, the samples were individually coded and conditioned at 22 °C and 63% relative humidity in a standard atmosphere before being tested in the laboratory for 24 h, following the ASTM D 6612 standard [40].

2.5.4.2 Fiber linear density

Each individual sample fiber mass was measured using an electrically sensitive commodity analytical balance with an accuracy of 0.001 (Model: FA2104B, Accuracy Grade: I). A total of 10 strands of fiber with an initial length of approximately 500 mm from each sample were selected for fiber count. Subsequently, the length in meters and mass in grams were used to calculate the count following the ASTM D 6612 standard [40] methods for each Enset landrace bundle of fiber. Then, the linear density was calculated considering the length of each Enset fiber as 500 mm, and the mass of it was also measured. The data of the linear density in count was recorded in (tex) Table 1 and was used during mechanical testing using Eq. 2.

The Eq. 2 was used to calculate the linear density of fiber:

$$\text{Fiber}\:\text{ linear}\:\text{ density} =\text{ Length (m)}/\text{Mass (g)}\times 0.59$$
(2)

Where: 0.59 is the correction factor (constant) for fiber ASTM D 6612 standard [40].

2.5.5 Fiber mechanical testing

The fiber samples were tested following ISO 2062 universal tensile strength tester (STATIMAT ME + tensile tester) (ISO 2062–2013) protocols. The mechanical fiber properties such as elongation at break (%), tensile force (N), and breaking tenacity (cN/tex) were determined following the Uster-5000 standard testing method using an automated tester machine (Textechno STATIMAT ME+) with a 100 N load cell at room temperature. A total of 10 strands representing each sample of fibers were cut with an initial length of approximately 500 mm sections and separately handled. According to [3], the required fiber length for mechanical strength assessment was 500 mm, whereas 15 mm was added for gouge knotting dedications for the tester machine. According to ASTM D 6612 standard [40], the tester has a minimum and maximum travel gauge length of 50 mm and 860 mm, respectively, with a draw-off clamp speed of 1–5000 mm/min. The tester machine meets the requirements of all important national and international standards. A total of sixty Enset plants acquired 20 Enset fiber samples from high and mid altitudes land were tested. Breaking tenacity measures the strength of a fiber expressed by the maximum tensile force (breaking force) divided by the linear density of the fibers and articulated in centi Newton/tex (cN/tex). The sampled fibers, similar to the fiber linear density measurement, were prepared with a 500 mm length to fit an intermediate of the minimum and maximum standard gauge length of 50 mm and 860 mm, respectively, and were linked to a computer-mounted automatic tester machine. Subsequently, the test fibers were placed with clips between two oscillating gauges separately and tested. We have used the maximum gauge length of 500 mm for this Enset fiber study and executed. A tensile force was applied to the individual fiber for breakage. Each Enset landrace fiber test was repeated 5 times after inserting each and every count for each sample fiber. The tester machine automatically provides test results for elongation at break (%), tensile force (N), and breaking tenacity in (cN/tex). Breaking tenacity is expressed in centi Newton/tex (cN/tex). Tex is a unit of measure for the linear mass density of fibers (Table 2), yarns, and thread and is defined as the mass in g per 1,000 m [3].

2.6 Statistical analysis

The results of the chemical analysis and mechanical properties test data were statistically evaluated by Analysis of Variance (ANOVA, P < 0.05) using R version 4.2.2 statistical software. Enset landraces and location were used as independent variables, and the chemical and mechanical properties of Enset landraces fiber were considered as dependent variables. The data from the study underwent normality and variance homogeneity tests using the Shapiro-Wilk test and Levene’s test, respectively. The data were found to be normal and the variances were homogeneous. The obtained results of the study were compared with the results of other scholars in the literature as a control. Tukey’s HSD Post-Hoc test was used for means separation at a 5% significance level. Graphs and tables were created using MS-Excel. Error bars in all graphs represent 95% confidence intervals to provide a more accurate depiction of the standard error and enable a direct visual comparison of means.

3 Results

3.1 Enset landraces fiber chemical composition

The cellulose, lignin, hemicellulose, and ash are the most common fiber chemical compositions that affect the physical, chemical, and mechanical properties of natural fibers. As illustrated in Table 1, the results show the chemical compositions of varied landraces Enset fiber sampled from mid and high altitudes. The results of the chemical analysis exhibited that the variation in the percentage of ash, cellulose, hemicellulose, and lignin composition significantly varied among the Enset landraces (p < 0.001) (Table 1). Cellulose is an important component of plants and is often enclosed by matrices of other structural polymers such as lignin and hemicellulose. The results of the chemical analysis revealed that the Enset landrace ‘Kiticho’ fiber from the middle altitude had the significantly highest ash (8.61%) composition, and the least (3.38%) was recorded for ‘Uwisha’ from high altitude (Fig. 4). This might be due to the inherent composition of specific soil minerals present in the Enset plant fiber from which the fiber is derived. This suggests that specific minerals presence in the ash and their distribution within the fiber may affect the mechanical properties. ‘Ado’ and ‘Keshicha’ fiber from the middle altitude scored the significantly highest cellulose content (respectively 52.72% and 51.68%). The smallest cellulose content (26.54%) was recorded for the ‘Kulle’ landrace from high altitude. The overall average ash content of the Enset landraces was 5.73%. This recorded cellulose content may be due to the nature (genetic makeup) of the landrace to accumulate, the content specifies that Enset landraces fiber is a material with valuable characteristics, making it suitable for various applications where strength, durability, and biodegradability are important.

‘Kiticho’, ‘Uwisha’, and ‘Ado’ contained the highest hemicellulose content (20.29%, 20.22%, and 20.09%) from high, middle, and middle altitudes, respectively, and also the least hemicellulose content (13.14%) was recorded for the ‘Gedio_Ado’ landrace from high altitude.

Table 1 Interaction effects of qualitative phenotype of different Enset landraces and altitudes on fibers chemical composition
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‘Ganticha’ landrace from high altitude comparatively had significantly highest lignin (3.90%) content and the lowest lignin (1.74%) content was obtained from ‘Keshicha’ landrace from middle altitude. This vast difference in chemical composition is not surprising may be because natural fibers are dully component parts of the plants in nature have more amount of cellulose than hemicellulose, lignin and others and their accumulation may be affected by the altitude where they grow.

Fig. 4
figure 4

Interaction effects of Enset landraces and altitudes on ash (%) content. Mean values of each bar followed by the same letter(s) are not statistically significant at p < 0.0001

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3.2 FTIR test result

The functional groups within the spectrum range from 4000 cmto 1 to 500 cm−1 was considered for the FTIR analysis. From the FTIR graph of Enset landraces fiber from mid and high altitudes test as illustrated in (Fig. 5a and b), a broad band around 3000–3710 cm−1 was present in all mid and high altitudes obtained Enset landraces sample fiber. A peak at 2875 cm−1 is also recorded in both the mid and high altitude obtained Enset landraces sample fiber. Other sharp peak was also observed at 1640 cm−1 on both mid and high altitude Enset landraces fiber samples. Another peak at 1460 and 1100 cm−1 was recorded on both samples. Both of the two altitudes obtained Enset fiber samples may exhibit the characteristics peaks of natural fiber (Fig. 5). This result may indicate the presence of functional groups within the samples in both the altitudes obtained fiber samples, which again related to the chemical composition of the cell wall of the Enset fiber from which it is made from and also the nature of the Enset landraces building up materials.

Fig. 5
figure 5

Enset landraces fiber FTIR, (a) FTIR spectrum of mid altitude Enset landraces fiber samples and (b) FTIR spectrum of high altitude Enset landraces fiber samples

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3.3 Mechanical properties of enset landraces fibers

Measuring the linear density of Enset fibers is crucial for predicting their mechanical characteristics. Linear density, defined as the mass per unit length of the fibers, directly affects their strength, flexibility, and performance in various applications. By assessing the linear density of fibers, individuals can select the most suitable fibers for their purposes and improve their products to meet specific mechanical standards.

Table 2 Qualitative phenotype different Enset landraces from mid and high altitudes fiber calculated linear density (tex) for mechanical testing
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Moreover, the linear density of fibers plays a role in their capacity to absorb impact energy, with thicker fibers providing greater resistance. In light of this advice, we have calculated the linear density of Enset fibers (Table 2).

3.3.1 Elongation at break (%)

A summary of the elongation at break (%) properties of Enset landraces fibers is presented in Fig. 6. The analysis of mechanical properties revealed significant differences among Enset landraces fiber elongation (p < 0.05). ‘Ganticha’ from high altitude exhibited the highest elongation at break (2.93%), followed by ‘Uwisha’ and ‘Ado’ (2.18% and 2.092% respectively).

The minimum elongation at break % (0.86 and 0.88) was recorded for ‘Astara’ and ‘Uwisha’, respectively, at middle altitude. The lowest elongation at break (0.88% and 0.856%) was recorded for ‘Uwisha’ and ‘Astara’, respectively, at middle altitude. This result indicates that altitude affects the elongation at break of Enset landraces fiber, which may be due to the slow growth at high altitudes. The higher recorded elongation at break value of Enset landraces may be attributed to the fiber’s capacity to stretch further before breaking, suggesting increased flexibility when stretched.

Fig. 6
figure 6

Interaction effects of qualitative phenotype varying Enset landraces and altitudes on fiber elongation at break (%).*Mean values of each bar followed by the same letter(s) are not statistically significant at p < 0.0001

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3.3.2 Mean tensile force (N)

As shown in (Fig. 7), there was a highly significant difference in the tensile force among Enset landraces.

The mean tensile force (N) produced by ‘Gossalo’ from high altitude (13.36 N) was higher than the fibers of other Enset landraces.

It was also observed that the second-highest tensile force (10.92 N and 10.47 N) was recorded for ‘Ganticha’ and ‘Midasho’ landraces, respectively, from middle and high altitudes. The overall average tensile force was 6.53 N for both the high and middle altitude Enset landraces fibers. This result indicates that the property may be primarily linked to the Enset landraces’ high cellulose content and may be the genetic makeup interaction with the environment.

Fig. 7
figure 7

Interaction effects of qualitative phenotype variation in Enset landraces and altitudes on tensile force (N) of fibers. Mean values of each bar followed by the same superscript letter(s) are statistically non-significant at p < 0.0001

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3.3.3 Breaking tenacity (cN/tex)

The highest fiber breaking tenacity (104.56 cN/tex) was recorded for ‘Gossalo’, followed by ‘Gedio_Ado’ (52.41 cN/tex), ‘Ganticha’ (48.31 cN/tex), and ‘Midasho’ (46.30 cN/tex) at high altitudes (Fig. 8). In the middle altitude, the highest was recorded for ‘Gossalo’ (49.43 cN/tex) and the least was recorded for ‘Uwisha’ (19.092 cN/tex). The mean breaking tenacity obtained was 39.69 cN/tex. A higher tenacity cN/tex value recorded signifies that Enset landraces fiber is a stronger fiber; it could withstand more force before breaking. This may be linked to the lower linear density (tex) value of the fiber and/or the altitude effect on landraces as well as may be together with the genetic performance of landraces (Table 2).

Fig. 8
figure 8

Interaction effects of qualitative phenotype varying Enset landraces and altitudes on tenacity (cN/tex) of fibers. Mean values of each bar followed by the same superscript letter(s) are statistically non-significant at p < 0.0001

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4 Discussion

The main finding of this comparative study of chemical composition and mechanical properties indicates that Enset landraces’ fiber from mid and high altitudes varies significantly. The chemical composition analysis results showed significant variations in the percentage of ash, cellulose, hemicellulose, and lignin content. The ‘Kiticho’ landrace from the middle altitude (Fig. 5) shows significantly (p < 0.001) higher ash content (8.61%), and the overall averaged ash content of this study was estimated to be 5.73%, which was higher than the ash content (5.66%, 3.8%, 4.34% − 4.9%, and 2.69% − 3.37%) in different studies of Enset reported by [46,47,48]; respectively. This finding suggests that Enset fiber ash is a good candidate as alternative filler in hot mix asphalt reported by the author [49]. One of the important constituents of fiber that provides strength and stability to the cell walls and fiber is cellulose. In contrast, hemicellulose can reduce the strength of the fiber, and the presence of lignin also affects the flexibility of the fiber [50]. Cellulose is arranged as microfibrils in the cell wall among hemicellulose and bounded by lignin, but their content varies and depends on the kind of plant, usually 40–50%, 25–40%, and 15–35%, respectively [51, 52]. It is demonstrated that these compositions make up 93% of Enset fiber’s total chemical constituents. In our study, the percentage of cellulose content was significantly (p < 0.001) highest (52.72%, 51.68%, and 52.62%) obtained from the middle altitude ‘Ado’, ‘Keshicha’, as well as ‘Uwisha’ from high altitude respectively (Table 1). The result of this study is found in the range of 40–55%, which is in agreement with the concluded result of cellulose content reported by [51, 52] ranging from [40–55%] normally found in plant tissue. A different result (64.46%) was reported for Enset plant fiber [17]. The overall average percentage cellulose content (42.87%) is significantly higher than the content of other commonly used natural fibers worldwide such as Kenaf, Bamboo, Rice husk, Hibiscus, Coconut tree, and Coir (31–39%, 26–43%, 41.5%, 28%, 27%, and 37.5%) respectively summarized by [53].

In another way, the significantly highest content of hemicellulose (20.29%) and lignin (3.90%) was recorded for high-altitude landraces ‘Kiticho’ and ‘Ganticha’, respectively. According to [54], the lower cellulose percentage and higher hemicellulose and lignin can affect the fiber strength by accumulating moisture in amorphous areas of Enset fiber. The hemicellulose analysis result (20.29%) is higher than the result (13%) reported for Enset by [54] and also lower than the result (27.88%) obtained by another Enset study concluded by the author [46]. The hemicellulose (20.29%) content of Enset landraces’ fiber is lower than other commonly used natural fibers such as abaca, banana, and bamboo (17.5–25%, 19-29.1%, and 20.5–30%) content observed by several authors [4, 17, 46], respectively. However, the highest lignin content (3.9%) was recorded for the high-altitude ‘Ganticha’, which is higher than the reported result (2.21%) for Enset in a study by [55]. Even the overall average lignin content (2.79%) is relatively higher than the result (2.21%) reported by [55] and also lower than different Enset study results (5%, 5.5%, 10.53%, 12.21%, and 9.5-12.29%) obtained and concluded by [17, 48, 53, 56] respectively. According to Saragih et al. [57], abaca fiber contains (7-15.1%) lignin, which is higher than our study result. According to Wei and Meyer [58], high cellulose content of fiber provides high tensile strength and resistance to chemical attacks. Similarly, our chemical composition analysis results show that Enset landraces’ fiber used in this study show moderate to high cellulose content, comparatively lower hemicellulose and lignin content, which satisfies the general criteria of natural fiber and are suitable for the production of all types of pulp and cellulosic nanocrystals. Highly significant variations (p < 0.001) were obtained from the mechanical properties analysis results.

The identification of the chemical composition found in Enset landraces fiber samples obtained from mid and high altitudes was studied using Fourier-transform infrared spectroscopy (FTIR). FTIR is a versatile materials analysis technique, and the test results also indicated that our mid and high altitude obtained landraces sample fibers exhibit natural fiber characteristics. As demonstrated in Fig. 5, the FTIR of Enset landraces fiber samples from (a) mid-altitude obtained Enset landraces fiber sample and (b) the high-altitude collected Enset landraces fiber sample. Conspicuously, a broad band peak at 3415 cm−1 was observed, indicating group frequencies and the presence of hydrogen-bonded O–H stretching vibration in alpha cellulose, suggesting the abundance of hydroxyl groups. A peak at 2875 cm−1 corresponds to the presence of C–H stretching vibration in methyl and methylene groups in cellulose, hemicellulose, and lignin, which also contribute to the C-H stretching region. Another smaller peak at 2350 cm−1 can be attributed to the triple bond C–H stretching of hemicellulose and lignin, which might also be present due to the complex structure of cellulose. Another peak at 1460 cm−1 indicates C-H bending vibrations connected to CH2 and CH3 groups, which may be indicative of the presence of these types of groups in the fiber [59]. Besides, peaks at 1250 cm−1 were also observed, which may contribute to the C-O stretching vibrations in this region. The 1250 cm−1 peak found in the “fingerprint region,” which generally lies around 1500–700 cm−1, is mainly used to evaluate the amounts of hemicellulose related to cellulose. Another peak at 1100 cm−1 was also documented and associated with C-O stretching vibrations linked to polysaccharides such as cellulose and hemicellulose, which are common in natural fibers. Our FTIR result of mid and high altitude obtained landraces Enset fiber sample analysis is in line with the report of [47, 59, 60].

A significantly higher elongation at break result (2.93%) was recorded for ‘Ganticha’ from high altitude compared to most of the assessed Enset landraces in this study (Fig. 6). This result is higher than cotton fiber elongation at break (1.6 to 1.87%) and lower than sisal fiber elongation at break (2–3%) result as summarized by [55]. Our obtained result for ‘Ganticha’ of high altitude is higher than the elongation at break (1.92%) of Enset fiber in another study. Our result implies that the fibers from Enset landraces may have a flexibility character than cotton, which has lower elongation at break (1.6 to 1.87%) values. The test result of ‘Gossalo’ fiber from high altitudes showed significantly highest tensile force (13.36 N) than other Enset landraces assessed in our study (Fig. 7). The significantly highest breaking tenacity test result was recorded for the landrace ‘Gossalo’ fiber (Fig. 8) obtained from high altitude. This result is higher compared to abaca varieties, namely ‘Laylay’, ‘Inosa’, ‘Linawaan’, and ‘Sinamok’, with breaking tenacity results of 77.3, 70.7, 68.8, and 61.6 cN/tex, respectively, as assessed and reported by [61]. Ortega et al. [62] reported a maximum breaking tenacity of 49.3 cN/tex for virgin banana fibers, which is comparatively lower than our result. Our result is in line with [26] in another study of Enset, who stated that Enset fiber has higher strength than abaca. This study’s results indicate that Enset fiber’s higher elongation at breaking and higher tenacity value show the capability to resist variations in its shape without any change or crack, making it a strong candidate for fiber-requiring industries and applications. Our findings also indicate that the best-performing landraces in terms of mechanical properties were obtained from high-altitude locations, highlighting the influence of location on the fiber properties of Enset landraces compared to those from middle-altitude locations. The ‘Gossalo’ result was higher than the results recorded for Enset and abaca fibers in terms of tenacity values (54–72 and 67 cN/tex, respectively) as concluded by [63, 64]. Furthermore, the test result of ‘Gossallo’ was significantly higher than the tenacity value of untreated banana fibers (42.8 cN/tex) as reported by [62]. The breaking tenacity of nettle fiber ranges from 24 to 62 cN/tex, which is higher than cotton, silk, and wool fibers but lower than the average value of this study. The overall average tenacity value (39.69 cN/tex) of this study (Fig. 8) was higher than the values recorded for commonly used natural fibers (cotton, hemp, jute, and banana) with values of 24–36, 23.6, 23.9–27.6, and 30.6 cN/tex, respectively, as summarized by [64,66,67,68] in respective order. Similarly, the ‘Gossalo’ test result value (104.56 cN/tex) is the highest in terms of tenacity compared to flax (59.9), sisal (57.2), and rayon (56), and Colombian plantains (47) as reported by [69,70,71], respectively. According to Bezuneh [72], Enset and abaca (Musa textilis) fibers were reported to have similar strength and quality. The abaca fiber variety Laylay showed the highest tenacity value of 77.3 cN/tex [61]. Adamu et al. [73] also reported that Ficus thonningii fiber extracted using the water extraction method exhibits a tenacity of 37.83 cN/tex, which is lower than our mean tenacity result (Fig. 8). Nevertheless, our research results indicate that Enset fiber has higher strength compared to abaca fibers. The study findings suggest that different Enset landraces exhibit variations in fiber chemical composition and mechanical properties, in line with previous research [30], indicating differences in fiber quality depending on the Enset landrace. Similarly, our results support the conclusion of previous studies [74] that the mechanical and physical properties of Enset bundle fibers are influenced by variations in fiber quality among different Enset plants and the position of the fiber along the stem. Enset is a highland crop cultivated in the range of 1200 to 3100 m.a.s.l., with optimal performance observed at elevations of 2000 to 2750 m [75]. Our study also found that high-altitude landraces demonstrate superior mechanical properties and chemical composition compared to middle-altitude landraces, highlighting Enset as a high-altitude crop that thrives best in its natural habitat for optimal growth and fiber quality. Additionally, Enset fiber shows potential in applications such as cellulosic nanocrystals for biomedical and optoelectronic fields [76, 77] and other technical products [17]. Based on previous research and our own findings on chemical composition and mechanical properties, Enset fiber could serve as a viable alternative to commonly used natural fibers in various applications such as pulp and paper production [19], dissolving pulp and cellulosic nanocrystals [31], textiles, bioplastic products [78], automotive and aerospace interior parts [7], biocomposites [4], and packaging [31].

5 Conclusion

This study examined the impact of mid and high-altitude Enset landrace fibers on their chemical and mechanical properties. The results of the chemical analysis showed that the ‘Kiticho’ landrace from mid-altitude had the highest ash content, while the ‘Ado’ landrace from mid-altitude had the highest cellulose content. The ‘Kiticho’ landrace from high altitude had the highest hemicellulose content, and the ‘Ganticha’ landrace from high altitude had the highest lignin content.

In terms of mechanical properties, the ‘Ganticha’ landrace from high altitude had the highest elongation at break, while the ‘Gossalo’ landrace from high altitude had the highest tensile force and tensile strength. These results indicate that high-altitude landraces may offer superior chemical and mechanical properties compared to mid-altitude landraces.

Enset fiber, with its high cellulose content, holds promise for use in producing microcrystalline cellulose, contributing to a circular economy by converting agricultural waste into valuable products. Further research is needed to explore the potential of Enset fiber for various industrial applications using different landraces and gauge lengths. This will help determine its suitability as a natural fiber substitute in future value chain opportunities.