Extraction and Characterization of Cellulosic Fibers from Jenfokie and Doby Stems: Effect of Extraction Methods on Physicochemical, Mechanical, and Thermal Properties

ABSTRACT

This experimental study aims to explore natural lignocellulosic fibers from Jenfokie and Doby plants. The effect of the fiber (water-retted and non-retted) extraction methods on physical, mechanical, thermal, chemical, and crystallinity properties were experimentally investigated for fibers collected from the eastern highlands of Ethiopia. The chemical composition (cellulose, hemicellulose, lignin, extractives, etc.) was determined after different treatment processes. The tensile strength maximum of up to 72 cN/tex and 56 cN/tex, and cellulose content up to 85% and 81% were obtained for Jenfokie and Doby retted extracted fibers, respectively. There was small difference lignin extracted by Klason method and the alkaline hydrogen peroxide (APH) method. Each step-wise extracted fiber was characterized to cognize the intrinsic changes during the multi-step extraction process. The diameters were determined by Optical Microscope (OM), the removal of non-cellulosic materials by Fourier Transform Infrared (FT-IR) spectroscopy, the thermal stability (up to 375°C) by thermogravimetry (TGA), and the crystallinity index (up to 73%) by using X-ray Diffraction (XRD). An improvement in cellulose content, density, moisture absorption, tensile strength, thermal stability, and crystallinity of Jenfokie (unstudied or new) and Doby plant retted fibers would be promising for composite and textile materials.

摘要

本实验旨在探索Jenfokie和Doby植物的天然木质纤维素纤维. 实验研究了从埃塞俄比亚东部高地采集的纤维（水浸和非浸）提取方法对物理、机械、热、化学和结晶性能的影响. 在不同的处理工艺后，测定了化学成分（纤维素、半纤维素、木质素、提取物等）. Jenfokie和Doby retted提取纤维的最大拉伸强度分别高达72 cN/tex和56 cN/tex，纤维素含量分别高达85%和81%. Klason法和碱性过氧化氢法提取木质素差异较小. 对每一步提取的纤维进行表征，以识别多步提取过程中的内在变化. 通过光学显微镜（OM）测定直径，通过傅立叶变换红外（FT-IR）光谱测定非纤维素材料的去除，通过热重分析（TGA）测定热稳定性（高达375°C），通过X射线衍射（XRD）测定结晶度指数（高达73%）. Jenfokie（未研究的或新的）和Doby植物脱胶纤维在纤维素含量、密度、吸湿性、拉伸强度、热稳定性和结晶度方面的改善将有望用于复合材料和纺织材料.

KEYWORDS:

• Natural fiber
• Jenfokie fiber
• Doby fiber
• retted
• non-retted
• chemical composition
• mechanical property
• crystallinity

关键词:

• 天然纤维
• 詹福基纤维
• 多比纤维
• 脱胶
• 不脱胶
• 化学成分
• 力学性能
• 结晶度

Introduction

The various environmental changes caused by the use of synthetic materials over the past few decades have promoted the use of biomaterials. Under these conditions, bio-composites are manufactured by using lignocellulose fibers derived from plants, which are cheaper, more abundant in nature, and more renewable than aramid, carbon, and glass fibers (Moudood et al. 2019). Recent environmental awareness has made the development of natural fiber composite materials (Sanjay et al. 2019). The attractive features of natural fibers have been their low cost, lightweight, low environmental impact, high specific modulus, and relatively good mechanical properties compared to the health hazards of composites reinforced with synthetic fibers (Rokbi et al. 2011).

Numerous natural fibers, such as flax, hemp, jute, oats, rye, cane, grass reeds, kenaf, ramie, nettle, sisal, and coir, have been studied in plastics (Memon et al. 2019). Among many natural fibers, stinging nettle (Urtica dioica) is a well-known herbaceous plant that groups 30–45 species that are considered as weeds in intensive agriculture (Suryawan et al. 2019). One of the primary interests of nettle is that the complete plant can be used for a range of purposes, such as food, fodder, medicine, cosmetics, biodynamic agriculture, and textile production (Ilyas et al. 2018). Doby –Girardina bullosa (steudel) wedd. – is one among those nettle plants with hollow tapered stems, seasonal, fine hairs, and it grows in the highlands of Ethiopia 2–3 m in length and 60–120 mm in external diameter and cause skin irritation when touched by the human body (Kale, Getachew Alemayehu, and Gorade 2020).

Climber plants (more than 110 families) are a group of vascular plants that germinate on the ground by winding, adhering to other plants to attain great stature, which share nearly one-quarter of the total vascular plants (He and Paul Chen 2014; Hossain, Sayedur Rahman, and Ahammad Khan 2015). Forty-two percent (42%) of the trees in the forest carried climbers’ liana (thick-stemmed) and vines (weak and thin stemmed) (Muoghalu and Okerinmola Okeesan 2005). The Jenfonkie, an Asclepiadaceae (Artemisia abyssinica Sch.Bip. ex A. Rich) climber plant, has a solid stem, non-flowering, separate joints or internodes, and the fibers were extracted between the internodes. It grows throughout the year and in rich soils up to 18 m in length and 8–22 mm in external stem diameter (middle) and releases a small amount of milky-like liquid substance between the core and the bark.

The objective of this study focused on the extraction and characterization of Ethiopian Highland Jenfokie and Doby herbaceous plant fibers for engineering application. The study further investigated the effects of extraction (retted and non-retted) method on the physical, mechanical, thermal, chemical, and crystallinity properties of Jenfokie and Doby fibers. This study contributes the new fiber from the Jenfokie plant for engineering applications.

Materials and methods

Sample preparation

Jenfokie and Doby plants were harvested from the highland of Dima Wuchale kebele, Arsi Zone, Oromia Regional State, Ethiopia with two different traditional fiber extraction methods (i.e., water retted and non-retted), as shown in Figures 1–4. The details of fiber extraction steps are shown in the supplementary materials, Figures S1 and S2.

Figure 1. Jenfokie fiber unretted extraction process (a & b) Jenfokie plant, (c) bark with fiber, (d) Jenfokie fibers, (e) alkali treated fiber, and (f) bleached cellulose.

Figure 2. Jenfokie fiber water retted extraction process (a) Jenfokie plant, (b) internodes cut and water pre-retted Jenfokie stem (c) fiber (d) alkali treated fibers, and (e) bleached cellulose.

Figure 3. Doby fiber unretted extraction process (a and b) doby plant, (c) bark, (d) fiber, (e) alkali treated fibers, and (f) bleached cellulose.

Figure 4. Doby fiber water retted extraction process (a) doby plant, (b & c) pre-retted stem and bark, respectively, (d) water retted bark fiber separation from amorphous parts, (e) fiber (f) alkali treated fibers, and (g) bleached cellulose.

Reagents used

Chemicals such as toluene AR (99.9%) and sulfuric acid (assay: 98%); sodium hydroxide pellets LR (98%); ethanol absolute (99.8%), and hydrogen peroxide LR (H₂O₂, 30%) in aqueous solution were purchased from Fine General Trading, Ethiopia.

Fiber yield and density measurements

The bark and fiber yield were measured dividing the extracted bark by stem and fiber by bark, respectively (Nguyen, Pirak, and Yildiz 2019). The Archimedes principle was used for the density measurement with the help of pycnometer and distilled water (Ahmed et al. 2019; Lokantara et al. 2020).

(1) ${\rho }_{\mathrm{f}}=\frac{\left(m_2-m_1\right)}{\left(m_3-m_1\right)-\left(m_{4-}{m}_2\right)}\times {\rho }_{\mathrm{w}}$(1)

where ρ_f is the density of the fibers, ρ_w is the density of the distilled water (1 g/cm³) in the pycnometer, and m₁ is the mass of the pycnometer when it is empty, m₂ is the mass of the pycnometer when it is filled with fiber, m₃ is the mass of the pycnometer when it is filled with water and m₄ is the mass of the pycnometer filled with fiber and water.

Fiber moisture content analysis

The weight of the sample was measured (M₁) in three replicates after exposure. The samples were placed in an oven at 105°C for 24 h and were subsequently weighed (M₂). The percentage of moisture content was weighed using the following formula:

(2) $Moisturecontent\left(\mathrm{\%}\right)=\frac{M_1-M_2}{M_2}\times 100\mathrm{i}\mathrm{n}\mathrm{\%}$(2)

Single fiber tensile test and diameter measurement

A single fiber tensile test was conducted using the TEXTECHNO STATIMAT ME+ machine at the Ethiopian Textile Industry Development Institute according to the ASTM-D-2256 method in five replicates. The diameter of both Jenfokie and Doby fibers was determined using an Optical Microscope (OM) by taking two different fibers and cutting them at three different points along their length.

Determination of chemical composition

The chemical composition analysis was done through gravimetric method as shown in Figure 5 (Manimaran et al. 2021). The AOAC (Cheung 1996; Idris, Abosede Wintola, and Jide Afolayan 2019), method was used to determine the ash content and the lignin was burned to determine in ash content in the in the lignin. The acid-insoluble lignin was determined by the TAPPI T222 om–88 method (Paschoal et al. 2015). By assuming that extractives, hemicellulose, lignin, ash, and cellulose are the only components of the total biomass, the cellulose content (%w/w) was estimated by difference, i.e. [% Cellulose = 100 − (% extractive + % ash + % acid-insoluble lignin + % hemicelluloses)] (Ayeni et al. 2015; Lin et al. 2010).

Figure 5. Chemical composition determination of Doby and Jenfokie plant fibers.

Delignification using Alkali Hydrogen Peroxide (AHP)

After toluene-ethanol and alkali pre-extraction, the sample was followed by AHP treatment in a water bath at a temperature of 85°C for 2 h using 30% H₂O₂ with a dosage of 10% (w/w) at an initial pH of 11.5 (adjusted with 5 M NaOH) (You et al. 2017) keeping the solid-to-liquid ratio constant at 1:10. Then, the sample was washed using distilled water and the weight loss (W_l) of lignin in three replicates.

(3) $W_l=\frac{W_1-W_2}{W_1}\times 100$(3)

where W₁ and W₂ represents the dry weight of the fiber before and after bleaching, respectively.

Fourier transform infrared (FT-IR) spectroscopy analysis

The functional groups of both Jenfokie and Doby fibers samples (raw, extractive free, alkali treated, and bleached) were performed on Spectrum 65 FT-IR (PerkinElmer) in the range of 4000–400 cm^{− 1} with four scans at a resolution of 4 cm^{− 1} using KBr pellets.

Thermogravimetric analysis

The thermal stability of Jenfokie and Doby fibers was characterized by using a thermo-gravimetric analyzer (TG-DTA, HCT-3, Beijing Henven Instruments, China) under constant nitrogen flow, from room temperature to 700°C, at a heating rate of 20°C/min. Approximately 10 mg of each sample was used.

Crystallinity index by X-ray diffraction (XRD)

Powdered milled samples were analyzed by an X-ray diffractometer (XRD-7000S) equipped with a Cu Kα radiation source operated at 30 mA and 40 kV, scanned in the 2θ range between 5° and 80°, at a scan speed of 3°/min. The crystallinity index was determined using the amorphous subtraction method after baseline subtraction (Douard et al. 2021), where A_cryst is the area of all the crystallinity peaks, and A_total is the total area under the diffractogram (Ovalle-Serrano, Blanco-Tirado, and Combariza 2018) Eq. (10).

(4) $\mathrm{C}\mathrm{I}=\left(\frac{A_{\mathrm{c}\mathrm{r}\mathrm{y}\mathrm{s}\mathrm{t}}}{A_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}}\right)\times 100$(4)

Result and discussion

Fiber characterization

Effects of extraction techniques on Jenfokie and Doby fiber yield

Three replications were done and the average yield measurement values were evaluated at the bark level and fiber level, as shown in Table 1. The retting was done after four, seven, and ten days, and the maximum fiber yield was at seven days for both fibers chosen for this experimental investigation. Retted extracted fibers had greater uniformity and fiber quality than non-retted fibers due to the removal of pectin and water-soluble constituents from the fibers’ surface (Jankauskienė et al. 2015).

Table 1. Jenfokie and Doby bark and fiber yield.

Fibre	Bark yield (%)	Fibre yield (%)	Fibre	Bark yield (%)	Fibre yield (%)
JU – R	39.07 ± 1.09	39.82 ± 1.09	JR – R7	39.07 ± 1.09	35.66 ± 1.97
DU – R	42.59 ± 1.69	57.98 ± 3.27	DR – R7	59.00 ± 1.69	58.94 ± 2.68
JR – R4	39.07 ± 1.09	27.84 ± 1.04	JR – R10	39.07 ± 1.09	21.75 ± 3.20
DR – R4	42.59 ± 1.69	50.78 ± 2.68	DR – R10	42.59 ± 1.69	49.47 ± 4.77

JU-R unretted Jenfokie raw fibers; DU – R unretted Doby raw fibers; JR-R retted Jenfokie raw fibers; DR-R retted Doby raw fibers; ⁴ four days water retted; ⁷ seven days water retted; and ¹⁰ ten days water retted.

Effect of extraction techniques on absorbing moisture of Jenfokie and Doby fibers

The moisture absorption of both Jenfokie and Doby chopped fibers was evaluated after exposed to an open atmosphere of humidity ranging from 25% to 54% Table 3. As a result, the increased moisture absorption of non-retted Jenfokie and Doby fibers may be attributed to the failure to remove pectin components, which are primarily found in the middle lamella (Baley, Morvan, and Grohens 2005; Martin et al. 2013).

Table 2. Mean mechanical test results of both retted and unretted Jenfokie and Doby fibers.

Test parameters	Fibres
	JU – R	JU – R	JR – R	JR – R	DU – R	DU – R	DR – R	DR – R
Gauge length (cm)	10	20	10	20	10	20	10	20
Elongation at break (%)	2.60	1.79	2.80	1.28	2.58	1.18	3.24	2.61
Force to break (N)	4.58	3.16	4.88	5.60	2.43	1.05	4.20	3.14
Tenacity (cN/tex)	62.07	48.14	72.7	37.95	36.69	16.01	56.84	21.29
Elastic modulus (cN/tex)	2245.8	1159.22	3275.7	1904.63	1674.3	805.1	1669.19	991.3

Table 3. Chemical composition and physical properties result obtained from Jenfokie and Doby fibers.

Fibres	Cellulose (wt.%)	Hemicellulose (wt.%)	Acid insoluble Lignin (wt.%)	Extractives (wt.%)	Ash (wt.%)	Density (g/cm^3)	Diameter (µm)	Moisture absorption (%)
JU – R	79.43 ± 1.13	7.13 ± 1.03	4.53 ± 0.20	6.78 ± 0.51	2.13 ± 0.71	1.52 ± 0.25	149.66 ± 10.79	6.0 ± .67
JR – R	84.87 ± 1.37	5.33 ± 0.61	4.80 ± 0.31	4.33 ± 0.34	0.67 ± 0.29	1.77 ± 0.48	124.56 ± 10.67	4.44 ± .77
DU – R	73.90 ± 0.83	8.67 ± 0.61	3.73 ± 0.23	8.00 ± 0.33	5.70 ± 0.58	0.88 ± 0.25	102.49 ± 7.69	7.33 ± .67
DR – R	81.20 ± 2.51	7.87 ± 0.23	3.93 ± 0.50	5.67 ± 1.53	1.33 ± 0.29	1.39 ± 0.08	90.44 ± 8.71	4.67 ± .66

Effect of extraction techniques on Jenfokie and Doby fiber density and diameter

The density of non-retted and retted Jenfokie fibers (1.5–1.77 g/cm³) was slightly greater than Cotton (1.5–1.6 g/cm³), Flax (1.4–1.5 g/cm³) and Ramie (1.0–1.55 g/cm³) fibers, while the density of non-retted and retted Doby fibers (0.88–1.39 g/cm³) is comparable with Bamboo (0.6–1.1 g/cm³) fibers (Dittenber and GangaRao 2012). The increase in density of water retted Jenfokie and Doby fibers compared to non-retted was due to the removal of less dense surface impurities such as pectin, fats, waxes, etc., which causes increase in cellulose crystallinity and packing density, as recommended in previous study (KılınÇ et al. 2018).

Some of the fiber’s diameters measured are shown in Figure 6. Jenfokie fiber diameters range from 131.85 to 258.90 μm and from 110.17 to 134.36 μm for non-retted and retted fibers, respectively. The fiber diameter of Doby measured varies from 89.05–109.60 µm and 75–99.74 µm for non-retted and retted fibers, respectively. The diameters of Jenfokie and Doby fibers are in the range of other bast fibers such as Acacia leucophloea (168 µm), Coir (280–380 µm), Chloris barbata (180–200 µm), Epipremnum aurem (105–150 µm), Thespesia populnea (120–200 µm), Enset (333.97 µm) and Sisal (474.4 µm) (Bekele, Lemu, and Jiru 2022; Seki et al. 2022). A slight increase in the average diameters of non-retted Jenfokie and Doby fibers observed in this study might be from the non-removal of pectin (middle lamellae) and other substances from the surface of the fibers, as noted by (Dey et al. 2021).

Figure 6. Optical microscope diameter images (a) unretted Jenfokie, (b) retted Jenfokie, (c) unretted Doby, and (d) retted Doby.

Effect of the gauge length and extraction techniques on the tensile strength of Jenfokie and Doby fibers

Table 2 shows the summary of the mechanical properties in which the highest tensile strength and Young’s modulus were obtained for both retted extracted fibers due to the higher cellulose content in the fibers, respectively. This observation is in line with the results reported in previous studies (Tarabi, Ghasemloo, and Mani 2016). An increased amount of hemicellulose and extractive content in the non-retted fibers also contributed to the reduction in tensile strength. The tensile strength result obtained in this study were Jenfoki 62.07−72.7 cN/tex and Doby 36.69–56.84 cN/tex fibers at lower gauge length is comparable with other fibers such as Caster oil (57.8 − 86.9 cN/tex), Flax (57 cN/tex) fibers, etc. (Belachew, Gebino, and Haile 2021).

As the gauge length increased from 10 cm to 20 cm, the elongation of both retted and non-retted fibers decreased (Tamanna et al. 2021). The lower elongation percentage of retted fibers may be due to the smaller diameter of the fiber bundles compared to non-retted fibers, which resulted from the removal of some constituents from the fibers’ surface. This result is in-line with previous reports (Dey et al. 2021).

Effect of Jenfokie and Doby fibers extraction methods on the chemical composition

The number of extractives of non-retted fibers was more significant than the amount of water-retted extracted fibers due to the removal of some constituents like fats, pectin, etc., from the fiber surface during the retting process as shown in Table 3 (Mazian et al. 2018).

The greater the ash content found in non-retted than retted Jenfokie and Doby fibers was due to the presence of pectin, as reported in previous study (Nguyen, Pirak, and Yildiz 2019). A slight increase in lignin content of both retted fibers is probably due to substantial loss of carbohydrates, soluble extractable, etc., as recommended in previous study (Placet, Day, and Beaugrand 2017). As noted and studied by (Wang et al. 2019), the reduction of hemicellulose content for retted Jenfokie and Doby fibers was with slight glucose loss after the retting process. The cellulose content obtained for Jenfokie (79.43–84.87 wt%) and Doby (73.90–81.20 wt%) is comparable with other higher cellulose content plant fibers such as Ramie (68.6–85 wt%), PALF (70–83 wt%), Nettle (86 wt%) and Cotton (82.7–90 wt%) (Asmare and Technol 2017; Dittenber and GangaRao 2012). A slight increase in cellulose content was found in the case of water-retted fibers in this study, probably due to the removal of pectin and non-cellulosic substances in the water phase (Brindha et al. 2019).

Effect of AHP extraction on delignification of Jenfokie and Doby fibers

The delignification weight loss after AHP extraction were 3.1%, 3.2%, 3.0%, and 3.2% for JU – AHP, JR – AHP, DU – APH, and DR – APH, respectively. A small difference between acid-insoluble lignin extracted by 72% H₂SO₄ and lignin extracted by the AHP process might be that some amounts of lignin were removed during alkali extraction, and acid-soluble lignin was not considered in this study which probably increases the amount Klason lignin (Wang et al. 2019).

FT-IR spectroscopy result

Effect of Jenfokie and Doby fibers extraction techniques on the chemical composition

The chemical functional group changes at each extraction step (raw, toluene-ethanol, alkali, and AHP bleaching) of both Jenfokie and Doby fibers are shown in Figure 7 from FT-IR analysis. The OH stretching vibrations of the hydrogen-bound hydroxyl groups from cellulose, hemicellulose, and lignin are represented by the absorption bands in the range of 3346–3440 cm^{− 1} seen in the spectra of all the fibers. The band from 2899 to 2925 cm⁻¹ is characteristic of C – H stretching in cellulose, hemicellulose, and lignin. The spectra on both Jenfokie and Doby fibers had an absorption band from 1727 to 1744 cm⁻¹ which is associated with the C=O bond of the acetic and ester groups of the hemicelluloses, and carboxyl aldehyde in lignin. Additionally, waxes and fats exhibit absorbance in the C=O (1727–1744 cm^{− 1}) bond region from the ester group. After alkali treatment and bleaching, the peaks decrease and disappear due to the removal of hemicellulose and lignin content from the surface of the fibers (Li et al. 2015).

Figure 7. FT-IR spectral of stepwise extracted lignocellulose (a) unretted Jenfokie fibers, (b) retted Jenfokie fibers, (c) unretted Doby fibers, and (d) retted Doby fibers.

JU – R unretted Jenfokie raw fiber; JU – E unretted and toluene-ethanol extracted Jenfokie fiber; JU – A unretted and alkali extracted Jenfokie fiber; JU‒AHP unretted and alkali hydrogen peroxide bleached Jenfokie fiber; JR – R retted Jenfokie raw fiber, JR – E retted and toluene-ethanol extracted Jenfokie fiber; JR – A retted and alkali extracted Jenfokie fiber; JR – AHP retted and alkali hydrogen peroxide bleached Jenfokie fiber; DU – R unretted Doby raw fiber; DU – E unretted and toluene-ethanol extracted Doby fiber; DU – A unretted and alkali extracted Doby fiber; DU – AHP unretted and alkali hydrogen peroxide bleached Doby fiber; DR – R retted Doby raw fiber; DR – E retted and toluene-ethanol extracted Doby fiber; DR – A retted and alkali extracted Doby fiber; and DR – AHP retted and alkali hydrogen peroxide bleached Doby fiber.

Both fibers in the spectra in the range of 1601–1644 cm^{− 1} represents, the OH bending vibration of absorbed water. These bands, further in the spectrum of both Jenfokie and Doby samples, are attributed to lignin C – H deformation. With the removal of lignin, these bands become weak and narrow. The bands of 1424‒1444 cm^{− 1}, the characteristic absorbance of aromatic C=C stretching and CH₂ bending found in lignin (Viju and Thilagavathi 2021) showed that the alkali treatment slightly affected and disappeared after bleaching with alkaline hydrogen peroxide in both Doby and Jenfokie fibers.

Effect of extraction techniques on Jenfokie and Doby fibers thermal stability

The thermal stability of Jenfokie and Doby fibers was determined with the aid of Thermogravimetric (TGA) and its Differential Thermogravimetric (DTG) analysis curves after stepwise extraction. For each progressively extracted retted and non-retted fiber, Figure 8 illustrates the mass loss by TGA and the rate of degradation by DTG as a function of temperature. According to (Shahedifar and Masoud Rezadoust 2013), hemicelluloses degrade between 180°C and 350°C, cellulose degrades between 250°C and 380°C, and lignin degrades between 250°C and 500°C.

Figure 8. TGA/DTG curves of both retted and unretted Jenfokie and Doby fibers (a) unretted Jenfokie fiber, (b) retted Jenfokie fiber, (c) retted Doby fiber, and (d) retted Doby fiber.

When the temperature ranged from room temperature (RT) to 140°C, weight loss ranged from 6.1% to 13.3%, which represents moisture evaporation and the decomposition of volatile extractives, as shown in Table 4. The highest weight loss for both non-retted raw fibers could be due to the presence of volatile extractives on the surface of the fibers (Sadrmanesh and Chen 2019). The second weight loss of both raw fibers was recorded between 226.1°C and 407.5°C attributed to the degradation of hemicellulose, pectin and cellulose. Non-retted fibers degrade at a lower temperature than retted extracted fibers because the decomposition of the chemicals starts at the surface.

Table 4. Thermal degradation temperatures and residual weight of the investigated Jenfokie and Doby lignocellulose.

Fibers	1st degradation		2nd degradation		3rd degradation		Maximum degradation (Tmax) (°C)	Residue at 700 (°C)
	Temperature (°C)	Weight loss (%)	Temperature (°C)	Weight loss (%)	Temperature (°C)	Weight loss (%)
Raw fibers
JU – R	RT–118.8	13.3	236.4–400.5	57.1	400.5–521	20.8	345.1	8.30
JR – R	RT–124.3	7.6	238.1–407.5	60.5	407.5–542	20.4	355.8	7.50
DU – R	RT–140.0	13.1	226.1–387.9	50.8	387.9–610	27.3	323.5	8.01
DR – R	RT–130.1	6.4	232.5–387.8	59.0	387.8–572	23.8	347.6	7.80
After Toluene-Ethanol extraction
JU – E	RT–115.2	6.1	244.6–407.4	60.7	407.4–542	24.6	363.9	7.12
JR – E	RT–124.3	6.4	252.2–415.2	64.0	415.2–586	21.3	363.1	5.80
DU – E	RT–134.2	10.2	240.7–415.4	55.0	415.4–578	24.3	350.1	7.03
DR – E	RT–130.8	12.5	237.6–423.2	62.0	423.2–609	27.7	358.8	6.70
After Toluene-Ethanol & 17.5% NaOH alkali extraction
JU – A	RT–118.6	10.2	237.7–410.5	52.4	410.5–595	31.9	368.1	4.21
JR – A	RT–137.2	6.7	238.8–421.4	54.0	421.4–610	31.8	375.7	5.02
DU – A	RT–128.4	8.7	243.4–412.2	53.2	406.5–625	30.3	365.4	5.04
DR – A	RT–134.2	9.1	246.6–406.5	55.4	412.2–603	32.2	369.0	4.10
After Toluene-Ethanol, 17.5% NaOH & APH extraction
JU – AHP	RT–105.8	9.8	241.2–410.3	50.3	410.3–568	32.9	366.1	1.13
JR – AHP	RT–135.9	4.7	217.4–416.6	52.5	416.6–593	37.7	368.9	2.40
DU – AHP	RT–128.2	7.2	241.6–405.2	52.4	405.2–610	35.6	353.4	1.50
DR – AHP	RT–133.8	9.8	212.9–405.5	53.4	405.5–648	32.6	363.9	1.80

The degradation temperature of extractive free samples was increased for both retted and non-retted fiber due to the thermal depolymerization of hemicelluloses and the breakdown of glycosidic linkages of cellulose. The major weight loss of up to 55.4% is related to the degradation of cellulose. The TGA curve for both fibers shifted to a higher temperature after they were bleached with hydrogen peroxide compared to raw fibers.

The third degradation occurs between 387.8°C and 625°C due to the breakdown of non-polysaccharides. The rate of thermal degradation after alkali extraction was higher than that of the raw fibers attributed to the removal of hemicelluloses as reported by (Martin et al. 2013; Xiao et al. 2015). Lastly, the residual ash and char levels were decreased for both retted and non-retted Doby and Jenfokie lignocellulose fibers due to high char contributors of lignin and hemicellulose, as recommended in previous study (Dizbay-Onat et al. 2018). The maximum decomposition temperature of Jenfokie (345.1–355.8°C) and Doby (323.5–347.6°C) raw fibers are comparable with other natural fibers such as Jute (283°C), Okra (359°C), Hemp (390°C), Curaua (335°C) and Kenaf (284°C) even though this result is increased after alkali treatment and bleaching (Sampathkumar et al. 2015). An increase in cellulose content for retted Jenfokie and Doby fibers is observed might be due to the removal of non-cellulosic materials (Mazian et al. 2020).

Effect of extraction techniques on Jenfokie and Doby fibers crystallinity

XRD patterns of both retted and non-retted Jenfokie and Doby (raw, treated with alkali, and bleached) powder fibers are represented in Figure 9. The deconvolution of XRD pattern shows major crystalline peaks around 2θ = 15.5°, 16.5°, and 22.94° for retted and non-retted raw fibers corresponding to (1$\bar{1}$0), (1 1 0), and (2 0 0) planes, respectively. The beginning peak around 15.5° indicates the diffraction of cellulose type I, which represents the crystalline constitute of cellulose (Araújo, Vilarinho, and Machado 2019). While crystalline peaks for alkaline extracted and bleached are around 2θ = 12.5°, 20.4°, and 22° can be attributed to the planes of (1$\bar{1}$0), (1 1 0), and (0 2 0) due to cellulose II, respectively (Gong et al. 2017). Strong alkali extraction in combination with bleaching treatment is known to induce a partial transformation of cellulose type I to cellulose type II structure. The crystallinity index is increased after alkali treatment and bleaching in both Jenfokie and Doby fibers, this is most probably due to the removal of amorphous materials such as waxes, lignin, and hemicellulose (Dalle et al. 2021).

Figure 9. X–ray diffraction pattern of Jenfokie and Doby fibres. (a) Unretted Jenfokie fibres, (b) retted Jenfokie fibres, (c) unretted Doby fibres, and (d) retted Doby fibres.

The XRD result showed an increase in the CI after alkali extraction and bleaching of both retted and non-retted fibers as shown in Table 5. The peaks were more defined after dewaxing, alkali, and hydrogen peroxide extraction which might be resulted from the removal of the amount of non-cellulosic materials such as contributors such as hemicellulose, lignin, and wax (Kamali and Meghdad 2022). The crystallinity index after stepwise extraction up to 65.23–73.33% for Jenfokie and 68.62 − 70.53% for Doby cellulose obtained is comparable with other natural fibers such as Sansevieria cylindrica (60%), Acacia planifrons (65.38%), Jute (71.39%), and Sisal (62.8%) (Totong et al. 2022; Vinod et al. 2021).

Table 5. The CI of both retted and unretted Jenfokie and Doby fibers.

Samples	CI (%)	Samples	CI (%)	Samples	CI (%)	Samples	CI (%)
JU – R	48.79	JR – R	50.84	DU – R	58.51	DR – R	56.08
JU – A	58.37	JR – A	64.58	DU – A	60.69	DR – A	61.9
JU – AHP	65.23	JR – AHP	73.33	DU – AHP	68.62	DR – AHP	70.53

The higher CI of retted Jenfokie and Doby fibers might be due to the degradation of non-cellulosic compounds during the water-retting process (Mazian et al. 2019). After stepwise extraction, the CI was increased, which might be due to the decrease in non-cellulosic materials that promote an increase in cellulose content (Marques et al. 2020; Pereira et al. 2021).

Conclusion

This study, shows the extraction method highly influences most of the fiber properties. Pre-retting improves the ease of removal of the bark from the stem. Water retted Jenfokie and Doby fibers had higher cellulose content up to 85% and 81%, respectively. Water retted Jenfokie and Doby fibers showed better tensile strength (72.7 cN/tex and 56.84 cN/tex), and flexural strength (3275.7 cN/tex and 1669.19 cN/tex) at lower gauge lengths, respectively

An increase in CI was observed for both retted extracted fibers. The TG curves for both retted and non-retted extracted fibers show an increase in thermal stability after toluene-ethanol (up to 363.9°C), alkali removed (375.7°C), and alkali hydrogen peroxide (368.9°C) treated fibers compared to the raw (355.8°C) fibers. Finding a new (Jenfokie) fiber having the highest quantity of cellulose content, tensile strength, and thermal properties would be a promising material for the next level of engineering applications.

Highlights

In this work, the fibers and cellulose were extracted from the natural lignocellulosic fibers of Jenfokie and Doby plants. The extraction of fibers and cellulose from Doby plants is compared with Jenfokie (relatively unstudied/new) plants. The key highlights of this work are mentioned below:

• Water-retted extraction of both Jenfokie and Doby fibers improved the physicochemical, mechanical, and chemical properties compared to unretted/dry retted extraction process.

• An increase in thermal stability and crystallinity index was observed for both retted-extracted Jenfokie and Doby fibers.

• The high cellulose content of retted-extracted fibers ensures good physical, mechanical, and thermal properties.

• Tensile strength maximum up to 72 cN/tex and 56 cN/tex and the cellulose content of up to 85% and 81% were obtained for Jenfokie and Doby retted extracted fibers, respectively.

• An improvement in cellulose content, density, moisture absorption, tensile strength, thermal stability, and crystallinity of Jenfokie plant (unstudied or new) fiber would be a promising material for composite and textile applications.

We confirm that neither the manuscript nor any parts of its content are currently under consideration or published in another journal.

Credit author statement

Solomon Estifo Wossine: Data collection, Testing, Investigation, Methodology, Result analysis, Writing-original draft. Thothadri Ganesh Conceptualization, Methodology, Supervision, Review & Editing and validation. Habtamu Beri Tufa Conceptualization, Methodology, Validation and Supervision.

Acknowledgements

The first author’s PhD study was made possible and supported by Wachamo University and Adama Science and Technology University (ASTU), both in Ethiopia, the authors acknowledge.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15440478.2023.2229518

Additional information

Funding

There was no specific external support for this study.