Physical, Chemical and Mechanical Characterization of Sida Rhombifolia Fibers from the Center Region of Cameroon for their potential use in textiles and composites

ABSTRACT

To substitute synthetic fibers, which are non-biodegradable and environmentally unfriendly, studies have been carried out to exploit vegetable fibers. Within this concept, this work investigates Sida rhombifolia as a case study. Previous studies showed that the fibers could be extracted only by cold water retting, but this study seeks to show that the boiling water extraction technique can also be used. The objective of this study is to characterize Sida rhombifolia fibers from the Center region of Cameroon, extracted with cold and boiling water, and compare their physico-chemical and mechanical properties with those of other vegetable fibers. The standard tests for the different characterizations have been respected. This study showed that the fibers extracted with cold water retting contained 70.16% cellulose, 16.70% hemicellulose, 10.86% lignin, and 1.47% pectin, while the fibers extracted by boiling water technique contained 68.71% cellulose, 17.48% hemicellulose, 11.26% lignin, and 2.01% pectin. Finally, extraction of fibers from the cold water retting technique gave 38.83% extraction yield, 1.33 g.cm⁻³ density, 11.23 tex linear mass, 11.73% water content, 118.53% rate of water absorption, and 21.45% humidity at a relative humidity of 75%. While fibers extracted by the boiling water technique had 33.74% extraction yield, 1.35 g.cm⁻³ density, 13.57 tex linear mass, 13.28% water content, 225.12% rate of water absorption, and 22.06% humidity at a relative humidity of 75%, statistical analysis by Student’s t-test showed a significant difference in the mechanical properties of the fibers depending on the extraction method. Sida rhombifolia fibers can be used in textiles and composites and can be extracted by the boiling water technique.

摘要

为了取代不可生物降解且对环境不友好的合成纤维，人们对开发植物纤维进行了研究. 在这一概念下，本文以菱叶西达为例进行了研究. 先前的研究表明，纤维只能通过冷水脱胶来提取，但本研究试图表明，沸水提取技术也可以使用. 本研究的目的是对喀麦隆中部地区用冷水和沸水提取的菱叶西达纤维进行表征，并将其物理化学和力学性能与其他植物纤维进行比较. 不同特征的标准测试得到了尊重. 研究表明，冷水脱胶提取的纤维中纤维素含量为70.16%，半纤维素含量为16.70%，木质素含量为10.86%，果胶含量为1.47%，沸水提取的纤维含有纤维素68.71%，半纤维素17.48%，木质素11.26%，果胶2.01%. 最后，从冷水脱胶技术中提取纤维，在75%的相对湿度下，提取率为38.83%，密度为1.33 g.cm-3，线性质量为11.23Tex，含水量为11.73%，吸水率为118.53%，湿度为21.45%. 虽然通过沸水技术提取的纤维在75%的相对湿度下具有33.74%的提取产率、1.35 g.cm-3的密度、13.57tex的线性质量、13.28%的含水量、225.12%的吸水率和22.06%的湿度，但通过学生t检验的统计分析显示，纤维的机械性能因提取方法而异. 菱叶丝达纤维可用于纺织品和复合材料，并可通过沸水技术提取.

KEYWORDS:

• Vegetable fibers
• Sida rhombifolia
• extraction technique
• student’s t-test
• textiles
• composites

关键词:

• 植物纤维
• 菱叶西达
• 提取技术
• 学生t检验
• 纺织品
• 复合材料

Introduction

The construction, automotive, goods, and leisure industries, which rely on textile reinforcement, face the challenge of designing and producing composite structures. To overcome this challenge, the recovery of plant biomass through the utilization of their fibers is necessary (Legrand et al. 2020; Mbang et al. 2023; Mewoli et al. 2023). This visibility is justified by the manufacture of composites based on plant fibers obtained from resources such as banana, Sida rhombifolia, hemp, kenaf, Ananas comosus (AC), Triumfetta pentandra (TP), okra, Recktophillum camerunense (RC), and Grewia bicolor (GB) (Ntenga 2007; Nanou and Yousfi 2020; Mazian 2018; Malik, Ahmad, and Gunister 2021; Shih et al. 2017; Nkapleweh et al. 2022; Khan et al. 2009; Rai et al. 2012; Stawski et al. 2020; Beakou et al. 2008; Betene et al. 2020; Ntenga 2007; Mejouyo et al. 2020; Jumaidin et al. 2021; Libog et al. 2023; Ndiwe et al. 2023). The use of plants as fibrous reinforcements for composites has two main advantages: they are widely available and at low cost, and their use allows the reduction of environmental impacts compared to conventional composites since they are renewable and biodegradable materials (Baley 2021).

Sida rhombifolia is a perennial shrub that belongs to the family Malvaceae and the genus Sida, which has more than 200 species found in tropical and subtropical zones worldwide (Gopinath et al. 2016). It is a plant whose fibers can be extracted with great rigidity and is available in all regions of Cameroon (Mejouyo et al. 2020). This plant also has extraordinary medicinal properties (Ekramul Islam, Ekramul Haque, and Mosaddik 2003; Mah, Teh, and Ee 2017). The only technique used so far for extracting fibers from this plant has been cold water retting. This is a technique that allows the fibers to be extracted after two weeks of soaking (Dydimus Efeze et al. 2012; Gopinath et al. 2016). This technique takes quite a long time, and there is a risk of air pollution due to the strong odor released, which can cause illness. Therefore, an alternative extraction technique using boiling water has been used (Bezazi et al. 2022; Chengoué et al. 2020; Libog et al. 2021; Wimberley and Rocky 2022). These authors’ studies showed that the boiling water technique allows for quick fiber extraction without weakening their properties. Sida rhombifolia fibers that have already been studied come from the southwest region of Cameroon (Dydimus Efeze et al. 2012) and India (Gopinath et al. 2016). These fibers were extracted using cold water retting, and extraction using boiling water has not yet been studied. To strengthen the literature on the study of fibers, the objective of this study is to characterize Sida rhombifolia fibers from the Center region of Cameroon, extracted with cold and boiling water, and compare the properties (physical, chemical, and mechanical) with other plant fibers.

Materials and methods

Fiber extraction and yield

Sida rhombifolia’s stems were harvested in Yaoundé, in the Center Region of Cameroon, and the fibers were extracted using both the cold-water retting technique (Figure 1) and the boiling technique (Figure 2). The cold water retting technique involved cutting the stems into short lengths ranging from 30 cm to 40 cm and soaking them in containers filled with water (Figure 1a) at a room temperature of 25°C ± 2°C for 3 weeks. During this period, microbial degradation occurred, and the outer layer became soft. Subsequently, the fibrous layers were gently extracted by hand (Figure 1b), then washed repeatedly in abundant water (Figure 1c), and finally sun-dried.

Figure 1. Extraction of sida rhombifolia fibers by cold water retting; (a) Dipping; (b) extraction (c) washing.

Figure 2. Extraction of Sida Rhombifolia fibers by boiling water; (a) cooking the stems; (b) isolated bark of the stems (c) scraped bark.

The boiling water technique for fiber extraction involved cutting the Sida rhombifolia stems into the same lengths as those used for cold-water retting and introducing them into an autoclave (Figure 2a). The autoclave was set at 121°C for 20 minutes. After this duration, the barks became soft, and fibers were isolated from the stems (Figure 2b). The fibrous mass obtained was then washed in water and dried.

The fiber extraction yield for each technique was determined by Equation 1(1) $\mathrm{E}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}=\frac{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\mathrm{s}\mathrm{o}\mathrm{b}\mathrm{t}\mathrm{a}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{d}\mathrm{a}\mathrm{f}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{e}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\mathrm{I}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{m}}\times 100.$(1) :

(1) $\mathrm{E}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}=\frac{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\mathrm{s}\mathrm{o}\mathrm{b}\mathrm{t}\mathrm{a}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{d}\mathrm{a}\mathrm{f}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{e}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\mathrm{I}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{m}}\times 100.$(1)

Determination of physical properties

Density

The determination of the density of the fibers was carried out at the Pycnolab Laboratory in the Littoral Region of Cameroon using the pycnometric method with toluene (${\rho }_{\mathrm{t}}$ = 0.866 g.cm⁻³ at a room temperature of 24 ± 2 ◦C) as the immersion liquid, according to ASTM D 2320–98 (2003). Before measurements, 10 samples of fibers were cut into 5 mm lengths and then dehumidified at 105°C for 24 h in a forced-air drying oven (Obame et al. 2022; Betene et al. 2022). The measurements were carried out using a scale balance with a sensitivity of 0.1 mg, and Equation 2(2) $\rho ={\rho }_{\mathrm{t}}\frac{{\mathrm{m}}_2-{\mathrm{m}}_0}{\left({\mathrm{m}}_1-{\mathrm{m}}_0\right)-\left({\mathrm{m}}_3-{\mathrm{m}}_2\right)}$(2) was applied to calculate the density ρ.

(2) $\rho ={\rho }_{\mathrm{t}}\frac{{\mathrm{m}}_2-{\mathrm{m}}_0}{\left({\mathrm{m}}_1-{\mathrm{m}}_0\right)-\left({\mathrm{m}}_3-{\mathrm{m}}_2\right)}$(2)

Where: ${\mathrm{m}}_0\hspace{0.17em}$is the mass of the empty pycnometer; ${\mathrm{m}}_1\hspace{0.17em}$is the mass of the pycnometer filled with toluene at room temperature; $\hspace{0.17em}{\mathrm{m}}_2\hspace{0.17em}$is the mass of the pycnometer containing the fiber samples; and m₃ is the mass of the pycnometer filler with toluene and fiber at room temperature.

Linear mass

The linear mass of the fiber was determined gravimetrically according to ASTM D 1577–96. Thirty samples of fibers were cut to a size of 20 ± 0.1 cm and dried in a non-forced air oven for 24 hours at a temperature of 105 ◦C. Each sample was weighed on a balance with a sensitivity of 0.1 mg at a room temperature of 24 ± 2°C. Equation 3(3) $\mathrm{L}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\left(\mathrm{t}\mathrm{e}\mathrm{x}\right)=\frac{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{d}\mathrm{r}\mathrm{i}\mathrm{e}\mathrm{d}\mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\left(\mathrm{g}\right)}{\mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}\left(\mathrm{K}\mathrm{m}\right)}$(3) was used to calculate the linear mass.

(3) $\mathrm{L}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\left(\mathrm{t}\mathrm{e}\mathrm{x}\right)=\frac{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{d}\mathrm{r}\mathrm{i}\mathrm{e}\mathrm{d}\mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\left(\mathrm{g}\right)}{\mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}\left(\mathrm{K}\mathrm{m}\right)}$(3)

Water content

Ten fiber samples with an initial undried mass of m₁ = 5 ± 0.1 g were weighed using a scale with 1 mg sensitivity, then dried in a non-pulsed air drying oven for 24 hours at a temperature of 105°C. After drying, the mass m₂ was read using the scale, and Equation 4(4) $\mathrm{W}\mathrm{C}\left(\mathrm{\%}\right)=\left(\frac{{\mathrm{m}}_{1-\hspace{0.17em}}{\mathrm{m}}_{2\hspace{0.17em}}}{{\mathrm{m}}_1}\right)\times 100\hspace{0.17em}$(4) (Klaai et al. 2021) was used to determine the moisture content $\hspace{0.17em}\left(\mathrm{W}\mathrm{C}\right)$ according to the AFNOR B 51004 standard.

(4) $\mathrm{W}\mathrm{C}\left(\mathrm{\%}\right)=\left(\frac{{\mathrm{m}}_{1-\hspace{0.17em}}{\mathrm{m}}_{2\hspace{0.17em}}}{{\mathrm{m}}_1}\right)\times 100\hspace{0.17em}$(4)

Water absorption rate

The samples used for this test were fiber clusters conforming to ASTM D 2402 : 2001. The fibers were dried in a forced-air oven at 105°C in the laboratory of the Faculty of Medicine of University of Yaoundé 1. The samples were dried for 3 hours to make them anhydrous, then conditioned and cooled for 3 hours. Ten fiber clusters of initial mass m_i = 100 ± 5 mg in the dry state were weighed using a 1 mg sensitivity scale and further immersed in distilled water at a temperature of 32 ± 2°C for 24 hours. Once removed from the water, a dry cotton cloth was used to wipe the excess water off the surface. The method used in this test was the gravimetric method, and Equation 5(5) $\mathrm{W}\mathrm{A}\left(\mathrm{\%}\right)=\left(\frac{{\mathrm{m}}_{\mathrm{f}}}{{\mathrm{m}}_{\mathrm{i}}}-1\right)\times 100\hspace{0.17em}$(5) was used to calculate the water absorption rate (WA).

(5) $\mathrm{W}\mathrm{A}\left(\mathrm{\%}\right)=\left(\frac{{\mathrm{m}}_{\mathrm{f}}}{{\mathrm{m}}_{\mathrm{i}}}-1\right)\times 100\hspace{0.17em}$(5)

Where: $\hspace{0.17em}{\mathrm{m}}_{\mathrm{f}}\hspace{0.17em}$ is the mass of the sample saturated with water;$\hspace{0.17em}{\mathrm{m}}_{\mathrm{i}}$ is the mass in the anhydrous state.

Moisture absorption rate at 75% relative humidity

The test was carried out according to NF G 08-001-4. The samples were oven-dried at a temperature of 105°C for 3 hours to make them anhydrous. Then, the fibers were weighed using a digital scale with a sensitivity of 0.1 mg to obtain their different initial masses. The samples were conditioned in a sodium chloride enclosure (solubility of 357 g/L, 8 g in 20 ml of water for a relative humidity of 75% at 20°C) for 24 hours (Betene Ebanda 2012) and reweighed to determine their various final masses. The enclosure was saturated with salt for 24 hours before the start of the test. Equation 6(6) $\mathrm{M}\mathrm{U}\left(\mathrm{\%}\right)\hspace{0.17em}=\hspace{0.17em}\frac{{\mathrm{M}}_{\mathrm{f}}\hspace{0.17em}-\hspace{0.17em}{\mathrm{M}}_{\mathrm{i}}}{{\mathrm{M}}_{\mathrm{i}}}\times 100\hspace{0.17em}$(6) was used to determine the percentage of moisture uptake (MU) by the fibers. Ten samples of fiber were used.

(6) $\mathrm{M}\mathrm{U}\left(\mathrm{\%}\right)\hspace{0.17em}=\hspace{0.17em}\frac{{\mathrm{M}}_{\mathrm{f}}\hspace{0.17em}-\hspace{0.17em}{\mathrm{M}}_{\mathrm{i}}}{{\mathrm{M}}_{\mathrm{i}}}\times 100\hspace{0.17em}$(6)

M_i: Anhydrous mass of the fibers in grams;

M_f: Mass of the fibers after removing from the enclosure.

Chemical characterization

Chemical composition

The ASTM D 1104, ASTM D 1106, and ASTM D 1287 standards carried out the determination of the composition of the fibers, such as cellulose, hemicelluloses, lignin, pectin, and waxes. The method used involved successive extraction of the fiber components with solvents from 2 g of crushed and dried fibers. The first extraction was done with an alcohol-toluene mixture, which dissolved the waxes and fats. The second extraction was carried out with hot water at 90°C, which made it possible to determine the quantity of mineral salts as well as the low percentage of tannins, starch, and polysaccharides. Then the third extraction was done for the separation of the pectins using an aqueous solution of extraction with ammonium oxalate. The lignins were dissolved in a solution of sodium chlorite and glacial acetic acid. Finally, the hemicelluloses were solubilized with a potassium hydroxide solution and then with a soda solution. By elimination, it was possible to determine the percentage of cellulose and hemicellulose. The values obtained were the average of three repetitions of the rate of the constituents of the fibers (Mewoli et al. 2020).

FTIR-ATR spectrometry analysis

The main objective of this analysis was to identify the functional groups of Sida rhombifolia fibers. The spectra were recorded using a Bruker Alpha-P spectrometer, equipped with an Attenuated Total Reflectance (ATR) module with a diamond crystal and controlled by the Opus/Mentor software. The fibers were dried at 50°C for 24 hours and powdered to sizes of 315 μm according to (Libog et al. 2021). A few milligrams of powder from the plant fibers studied were deposited on the diamond crystal of the ATR module. The acquisitions were made by scanning over a spectral range of 4000 to 400 cm⁻¹.

Mechanical properties and statistical analysis

The determination of Young’s modulus, tenacity, and strain at the break of the fibers was carried out on 30 fiber samples from each extraction method using an LDW-5 tensile testing machine with a load capacity of 100N at a controlled temperature of 23°C ±1, relative humidity of 50%, and a speed of 2 mm/min, according to the recommendation of the NFT 25 501–2 standard (Betene et al. 2022; Obame et al. 2022; Soppie et al. 2023).

The fibers were separated by hand and fixed to cardboard (Figure 3). A little glue was applied to two edges on each side of the hole to hold the fibers in place and allow it to dry for a few minutes.

Figure 3. Single fiber support.

The different experimental points were obtained and analyzed in the Microsoft Excel 2016 software. The Equation 7(7) $\mathrm{S}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{i}\mathrm{n}\mathrm{a}\mathrm{t}\mathrm{b}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{k}=\frac{\mathrm{E}\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\mathrm{I}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}}.$(7) to (Equation 9(9) $\mathrm{Y}\mathrm{o}\mathrm{u}\mathrm{n}{\mathrm{g}}^{\prime }\mathrm{s}\mathrm{m}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{l}\mathrm{u}\mathrm{s}\left(\mathrm{M}\mathrm{P}\mathrm{a}\right)\hspace{0.17em}=\mathrm{T}\mathrm{e}\mathrm{n}\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{t}\mathrm{y}\times \mathrm{d}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}.$(9) ) made it possible to plot the tenacity-strain curves, giving rise to the equation Y = Ax+B, where the slope and the ordinate at the origin of the regression line are represented by A and B, respectively. The calculation of A, representing the slope of the regression line, is simply the specific Young’s modulus (N.tex⁻¹).

(7) $\mathrm{S}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{i}\mathrm{n}\mathrm{a}\mathrm{t}\mathrm{b}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{k}=\frac{\mathrm{E}\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\mathrm{I}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}}.$(7)

(8) $\mathrm{T}\mathrm{e}\mathrm{n}\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{t}\mathrm{y}\left(\mathrm{N}.{\mathrm{t}\mathrm{e}\mathrm{x}}^{\text{-}1}\right)\hspace{0.17em}=\frac{\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}}{\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{d}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}}.$(8)

(9) $\mathrm{Y}\mathrm{o}\mathrm{u}\mathrm{n}{\mathrm{g}}^{\prime }\mathrm{s}\mathrm{m}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{l}\mathrm{u}\mathrm{s}\left(\mathrm{M}\mathrm{P}\mathrm{a}\right)\hspace{0.17em}=\mathrm{T}\mathrm{e}\mathrm{n}\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{t}\mathrm{y}\times \mathrm{d}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}.$(9)

A statistical analysis was performed on Microsoft Excel 2016 software on the mechanical properties of the fibers. A student’s t-test was applied for a 95% confidence level on the samples of both extraction techniques. The hypothesis that was made was that the extraction technique does not affect the mechanical properties of Sida rhombifolia fibers. If the probability of this hypothesis is less than 5%, then the hypothesis is not verified; otherwise, it can be considered verified. The Student’s t-test takes into account the dispersion (standard deviation) of the compared populations and the number of tests performed.

Results and discussions

Table 1 presents the physical properties of some fibers from the literature as well as of the Sida rhombifolia fiber.

Table 1. Properties of sida rhombifolia fibers compared to other plant fibers.

Fibers	Density (g.cm^−3)	Water absorption (%)	water content (%)	References
Sisal	1.5	190–250	5–10	(Asim et al. 2015; Beakou et al. 2008)
Banana tree	0.32–0.66	232–396	11.26–13.20	(Libog et al. 2021)
Ananas Comosus (AC)	1.256–1.526	188.64	12–12.21	(Asim et al. 2015; Betene et al. 2020; Uddin et al. 2017)
Triumfeta Cordifolia (TC)	1.16–1.477	342.3	-	(Mewoli et al. 2020)
Triumfeta Pentandra (TP)	0.351	183.31	11.23	(Nkapleweh et al. 2022)
Sida Rhombifolia	1.32–1.38	-	10.54	(Dydimus Efeze et al. 2012; Gopinath et al. 2016)
Recktophillum Camerunense (RC)	0.63–0.947	198.17	7.5–9.37	(Betene et al. 2020)
Neuropeltis Acuminata (NA)	0.843–0.918	276.16	10.36	(Betene et al. 2020)
Cotton	1.5–1.6	-	8–25	(Aizi 2017; Asim et al. 2015)
Hemp	1.15–1.45	-	6.2–12	(Aizi 2017; Asim et al. 2015)
Sida Rhombifolia Fibers extracted by cold water (SDR-R)	1.330 ± 0.03	118.53 ± 16.97	11.73 ± 0.44	Present Study
Sida Rhombifolia Fibers Extracted by boiling water (SDR-C)	1.351 ± 0.048	225.12 ± 15.67	13.28 ± 0.61	Present Study

Fiber yield from the two (2) methods of extraction

Figure 4 shows the physical appearance of the fibers obtained after extraction.

Figure 4. Sida rhombifolia fibers extracted by cold water retting (SDR-R) and boiling water (SDR-C).

Extraction with cold water retting presents clear, flexible fibers. However, the extraction time is relatively long, and the water resulting from the operation is nauseating and full of microbes. On the other hand, extraction with boiling water has a relatively short extraction time, and the process is hygienic. However, the fibers are less clear than those obtained by cold-water retting. This observation is similar to the work of (Chengoué et al. 2020; Libog et al. 2021). In addition, the fiber extraction yield of Sida rhombifolia obtained using cold water retting is 38.83%, which is slightly higher than that obtained from boiling water extraction (33%). This significant difference in the yield of the fibers is due to the more efficient removal of extra cellulosic materials in the case of cold-water extraction compared to boiling-water extraction.

Fiber bundles obtained by cold water extraction are clear and have a color close to white. Fibers extracted with boiling water, on the other hand, are obtained without bundles and have a color close to off-white yellow. The effect of boiling water could be at the origin of this color difference. We can conclude that cold-water-extracted fibers will absorb fewer chemicals during finishing operations than boiling-water-extracted fibers.

Physical properties

Density

Table 1 shows that for the cold and boiling water extractions, the density of Sida rhombifolia is 1.330 ± 0.03 g.cm⁻³ and 1.351 ± 0.048 g.cm⁻³, respectively. These values are similar to those reported by (Dydimus Efeze et al. 2012; Gopinath et al. 2016). When compared to other plants, Sida rhombifolia fibers have a higher density than banana tree, Recktophillum camerunense (RC), Neuropeltis acuminata (NA), and Triumfetta pentandra (TP) fibers (Libog et al. 2021; Betene et al. 2020; Nkapleweh et al. 2022). However, they have a lower density than cotton, sisal, hemp, Triumfetta cordifolia (TC), and Ananas comosus (AC) fibers (Aizi 2017; Beakou et al. 2008; Asim et al. 2015; Mewoli et al. 2020; Betene et al. 2020). Due to their lightweight nature, Sida rhombifolia fibers can be used in composites and textile applications.

Linear mass

The linear mass of the fibers extracted by the cold and boiling water methods in this study is 11.23 tex ±1.1 and 13.57 tex ±0.95, respectively; these values are close to those of (Dydimus Efeze et al. 2012) for Sida rhombifolia and (Dydimus Efeze et al. 2020) for banana stem (13.33–17.33 tex for unbleached fibers and 9.33–14.66 tex for bleached fibers). A difference in linear density values was observed between the two extraction techniques. The main reason is that during cold-water extraction, lignin is effectively removed, making the fibers very susceptible to separation into finer fibers, and their fineness is lower than that of fibers obtained with boiling water. The linear mass of Sida rhombifolia fiber is higher than that of AC and jute fibers (Asim et al. 2015; Betene et al. 2020; Betene et al. 2022; Beakou et al. 2008) and lower than that of banana (Sango et al. 2018). Sida rhombifolia can be used in textile applications.

Water content

The water content of the Sida Rhombifolia fibers for cold and boiling water extraction techniques is 11.73% ± 0.44 and 13.28% ± 0.61, respectively (Table 1). These values are higher than those of (Dydimus Efeze et al. 2012) which are 10.54%. This difference can be attributed to the difference in harvesting sites; moreover, the relative humidity of the Center region of Cameroon is higher than that of the southwest region of Cameroon. The presence of free hydroxyl groups makes it possible to attribute this sensitivity to wet steam. Sida rhombifolia fiber has a higher water content than any of the plant fibers listed in Table 1. His sensitivity to wet vapor could be attributed to the presence of free hydroxyl groups (Mohammed et al. 2015; Nkapleweh et al. 2022; Uddin et al. 2017). The water content of fibers obtained with boiling water is higher than with cold water. This may be explained by the hemicellulose content, which may be higher than that of boiling water.

Rate of water absorption

Based on different techniques of extraction, there is a significant difference in the rate of water absorption. The fibers extracted by cold water retting showed a water absorption of 118.53% ± 16.97, while boiling water showed a value of 225.12% ± 15.6 (Table 1). These values are high (above 100%), and this difference could come from the effect of the heat that the stem of the plant undergoes to make its outer layer soft to extract the fibers. This can also be seen in the difference in color of the fibers after extraction. Sida Rhombifolia fibers have a high water absorption and are therefore hydrophilic in the same way as the fibers of Recktophillum Camerunence (RC), Ananas comosus (AC), Neuropeltis acuminatas (NA), Triumfeta cordifolia (TC), and TP (Betene et al. 2020; Mewoli et al. 2020; Nkapleweh et al. 2022). This hydrophilic character is generally affected by the presence of hemicelluloses in the fiber due to their numerous branchings (Betene et al. 2020; Legrand et al. 2020; Mewoli et al. 2020). This ability to absorb most often leads to cracking and a reduction in the rigidity of the composite material (Mewoli et al. 2020). This characteristic can be improved by using a coupling agent and surface treatments (Betene et al. 2020; Libog et al. 2021).

Moisture absorption rate at 75% relative humidity

The water absorption rate is the ability of a dry material to absorb water when soaked in a water-containing enclosure, whereas the moisture absorption rate at 75% relative humidity is the ability of a dry material to absorb moisture in a 75% relative humidity enclosure during which a dry material absorbs moisture. The anhydrous fibers of Sida Rhombifolia absorbed water in an enclosure at 75% relative humidity for 24 hours, and the values obtained for cold and boiling water extraction were 21.45% ± 2.19 and 21.02% ± 2.83, respectively. The difference is not significant. These values are close to those of RC fiber (Betene Ebanda 2012). So Sida rhombifolia fiber can be used in the same field of application as RC.

Chemical properties

FTIR-ATR spectrometry analysis

Figure 5 presents the FTIR spectrum of the fibers studied, which represents the absorbance of the said fibers as a function of the wave number$\sigma \left(\mathrm{c}{\mathrm{m}}^{-1}\right)$. These spectra are characteristics of lignocellulosic materials and are identical for the two fiber extraction techniques. The broadband for fiber extracted by cold and boiling water techniques was observed in the spectra at 3334.06 cm⁻¹ and 3317.60 cm⁻¹, respectively. This represents the stretching vibration of the hydroxyl group ($-$OH) cellulose and hemicellulose (Mpon et al. 2012; Sango et al. 2018; Subramanya, Satyanarayana, and Pilar 2017). The peaks 2909.11 cm⁻¹ and 2887.81 cm⁻¹ are the characteristic peaks for the C-H stretching vibration of cellulose and hemicellulose components (Barreto et al. 2010; Becker et al. 2013; Betene et al. 2020; Bilba, Arsene, and Ouensanga 2007; Gopinath et al. 2016; Guimarães et al. 2009; Ibrahim et al. 2010; Libog et al. 2021). The peaks at 1731.85 cm⁻¹ and 1730.28 cm⁻¹ represent the symmetrical elongation of acetyl and carboxyl (C=O) groups present in hemicelluloses (Betene et al. 2020) waxes, and pectins (Taallah 2014). The symmetric elongation of the aromatic groups (C=C) of lignin is represented by the peaks 1511.72 cm⁻¹ and 1505.37 cm⁻¹ (Betene et al. 2020; Gopinath et al. 2016). The peaks 1422.44 cm⁻¹ and 1423.23 cm⁻¹ represent the agitation of the CH₂ present in the lignin and the hemicellulose. The bending vibration of the CH and CO groups of the aromatic ring of hemicelluloses and lignin shows peaks at 1019.80 cm⁻¹ and 1023.65 cm⁻¹ (Gopinath et al. 2016). The modes at 894.40 cm⁻¹ and 898.74 cm⁻¹ indicate the symmetrical stretching of CH and OH bonds in cellulose and lignin. The analysis of this FTIR spectrum shows sufficiently that Sida rhombifolia contains cellulose, hemicellulose, lignin, and pectins without any precision on their content, whatever the fiber extraction technique.

Figure 5. Evolution of the FTIR spectrum of Sida Rhombifolia fibers extracted according to the extraction technique; (a) fibers extracted with boiling water; (b) fibers extracted with cold water retting.

Chemical composition

The chemical composition of Sida rhombifolia fibers, regardless of the extraction technique, was compared to plant fibers from the literature presented in Table 2.

Table 2. Chemical composition of plant fibers.

Fibers	Cellulose (%)	Hemicellulose (%)	Lignin (%)	Pectin (%)	References
Sisal	65.8	12	9.9	0.8	(Youmssi et al. 2017)
Banana tree	37.5	27.6	15	5.15	(Sango et al. 2018)
Ananas Comosus (AC)	68.11	4.9	12.01	4.15	(Betene et al. 2020)
Triumfeta Cordifolia (TC)	44.4	30.8	18.9	3.3	(Mewoli et al. 2020)
Linen	64.1	16.7	2	1.8	(Baley 2021)
Sida rhombifolia	75.09	15.43	7.48	-	(Gopinath et al. 2016)
Recktophillum camerunense (RC)	65.15	7.42	16.2	3.45	(Betene et al. 2020)
Triumfeta Pentandra (TP)	61.10	14.30	17.73	5.65	(Nkapleweh et al. 2022)
Neuropeltis Acuminata (NA)	36.08	15. 33	25.15	7.69	(Betene et al. 2020)
Sida Rhombifolia Fibers extracted by cold water retting (SDR-R)	70.16	16.70	10.86	1.47	Present Study
Sida Rhombifolia Fibers Extracted by boiling water (SDR-C)	68.71	17.48	11.26	2.01	Present Study

The fibers of Sida rhombifolia consist of cellulose, hemicellulose, lignin, and pectin, as the results presented in Table 2 show. These results are different from those of (Gopinath et al. 2016). This difference can be explained by the difference in the place of harvest of the plant as well as the maturity of the plant. The cellulose content of Sida rhombifolia fiber is higher than that of sisal, banana tree, AC, NA, TP, RC, linen, and TC (Baley 2021; Betene et al. 2020; Mewoli et al. 2020; Nkapleweh et al. 2022; Sango et al. 2018; Youmssi et al. 2017). Hemicellulose is lower than TC and banana trees (Mewoli et al. 2020; Sango et al. 2018). Lignin is lower than NA (Betene et al. 2020), and pectin is higher than sisal (Youmssi et al. 2017).

Mechanical properties

Figure 6 presents the general mechanical properties of Sida rhombifolia extracted by retting (SDR-R) and boiling water (SDR-C).

Figure 6. Mechanical tensile behavior of Sida Rhombifolia fibers; (a) fibers extracted by cold water retting; (b) fibers extracted by boiling water; (c) linear regression line for a sample of fiber extracted by cold water retting.

Figures 6a & 6b show that the mechanical behavior of Sida rhombifolia fibers is fragile, as reported by (Dydimus Efeze et al. 2012). The regression line y = 9.2083x + 0.0328 presented in Figure 6c for a sample of Sida Rhombifolia extracted by retting showed a linear determination coefficient (R²) of 0.9967 and a specific Young’s modulus of 9.2083 N.tex⁻¹.

Figure 7 presents the diagram of the 2D distribution of each characteristic and that of the evolution of the mechanical properties of the fibers under study as a function of the extraction technique.

Figure 7. Evolution diagram of the mechanical properties of fibers;(a) tenacity and Young’s modulus; (b) strain at break.

It is observed in this study that Young’s modulus of Sida Rhombifolia fibers varies between 8.47 ± 1.28 and 9.58 ± 2.21 GPa; as for tenacity, it varies between 0.45 ± 0.13 and 0.54 ± 0.12 N.tex⁻¹; as regards strain, it varies between 0.0453 ± 0.0102 and 0.0611 ± 0.0147. Table 3 shows the mechanical properties and the obtained probabilities (P-value).

Table 3. Student’s t-test: difference between cold and boiling extraction techniques in mechanical properties.

Fibers	Young’s modulus (GPa)	Tenacity (N.tex^−1)	Strain at break
Sida Rhombifolia Fibers Extracted by boiling water (SDR-C)	9.58 ± 2.21	0.45 ± 0.13	0.0611 ± 0.0147
Sida Rhombifolia Fibers extracted by cold water retting (SDR-R)	8.47 ± 1.28	0.54 ± 0.12	0.0453 ± 0.0102
	P-value = 0.025	P-value = 0.033	P-value = 0.015

Table 3 shows that the probabilities are less than 5%, which makes it possible to reject the hypothesis that the extraction technique does not influence the properties of the fibers, so we can say that the mechanical properties obtained by boiling water extraction are higher than those of cold water retting, except tenacity. This observation was made by (Bezazi et al. 2022; Chengoué et al. 2020; Libog et al. 2021; Wimberley and Rocky 2022). Whatever extraction technique is used, fibers have properties higher than those of (Dydimus Efeze et al. 2012); This difference can be explained by the difference in the botanical origin of the fibers. Sida rhombifolia fibers have inferior properties to jute fibers (Dydimus Efeze et al. 2012; Mohammed et al. 2015). Table 3 presents several mechanical properties of some plant fibers from the literature as well as those of the Sida Rhombifolia fibers from the study.

The studied fibers have a lower Young’s modulus than the fibers presented in Table 4 and a higher tenacity than the fibers of cotton and linen (Mohammed et al. 2015) a strain at break close to that of cotton fibers (Mohammed et al. 2015). Sida rhombifolia fiber can be used in textiles as well as composites.

Table 4. Comparison of sida rhombifolia fiber properties with literature.

Fibers	Young’s modulus (GPa)	Tenacity (N.tex^−1)	Strain at break	References
Cotton	12	0.14–0.43	0.07–0.08	(Dydimus Efeze et al. 2020; Mohammed et al. 2015)
Jute	10–30	1.5–1.8	0.0012–0.0024
Linen	60–80	0.17–0.55	0.027–0.032
Ramie	-	0.24	0.036–0.038
Sida Rhombifolia	9.173	-	0.0989	(Dydimus Efeze et al. 2012)
Banana pseudo stem	6.60–34.74	-	0.009–0.0283	(Chengoué et al. 2020; Libog et al. 2021, 2023)
Sida Rhombifolia Fibers Extracted by boiling water (SDR-C)	9.58 ± 2.21	0.45 ± 0.13	0,0611 ± 0.0147	Present Study
Sida Rhombifolia Fibers extracted by cold water retting (SDR-R)	8.47 ± 1.28	0.54 ± 0.12	0.0453 ± 0.0142	Present Study

The mechanical properties of fibers depend mainly on cell wall structure and chemical composition (Singh et al. 2022). In particular, the percentage of cellulose present in the fibers (Sheferaw et al. 2023). Cold-water-extracted fibers have a higher tenacity than boiling-water-extracted fibers. This can be explained by their higher cellulose content compared with fibers extracted by boiling water. On the other hand, the higher lignin content of boiling water-extracted fibers could explain their superior stiffness and deformation.

Conclusion

This investigation led to the understanding that Sida rhombifolia fibers could not only be extracted by the cold water retting technique but also by the boiling water technique. The results of the physical (density, moisture absorption rate at 75% relative humidity) and chemical tests discussed do not show a significant difference, but the Student’s t-test showed a significant difference at a 95% confidence level on the mechanical properties of the two extraction methods. The fibers can be extracted in only 20 minutes by boiling water instead of two weeks by cold water retting. Sida rhombifolia fibers can be used in composites and textiles. It will be important to complete this study by performing X-ray diffraction (XRD) and thermogravimetric analysis (TGA).

Major points

• The extraction of Sida rhombifolia fibers by a new technique, which is the boiling of water,

• The fibers come from the central region of Cameroon,

• The influence of the extraction techniques on the properties (physical, mechanical, and chemical) of the fibers in the study is noted,

• The fiber of Sida rhombifolia can be used in composites and the textile field.

Author’s Contribution

Téclaire Ngoup: Interpretation of results, drafting and reading of manuscript; Nkemaja Dydimus Efeze: Supervision of work, validation of tests and reading of manuscript; Thomas Kanaa: Methodology, reading of manuscript; Jonas Peequeur Essome Mbang: Interpretation of results , drafting and reading of manuscript; César Segovia: Investigation into methodology, reading of manuscript; Nnanga nga: Reading of manuscript; Ebenezer Njeugna: Reading of manuscript and supervision of work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Acknowledgement

The authors would like to thank Dr. Njom Abel for carrying out the FTIR analysis of the fibers. We would also like to thank Mrs.Younga Ngolle Alida Sidonie (PLEG bilingual letter, English language teacher at GTHS Kekem), Mrs. Yungong Blessing Menkan (textile and clothing industry teacher and researcher at the University of Douala's mechanics laboratory), and Mr. Noubissie Tchoko Romuald Loic (researcher at the University of Douala's mechanics laboratory) for their contributions in proofreading this English-language manuscript. We would like to thank all the reviewers of this manuscript for the quality of their expertise.