Impact of Cultivation Area on the Physical, Chemical, and Mechanical Properties of Banana Pseudo-Stems Fibers in Cameroon

ABSTRACT

Cellulosic fibers were extracted from the pseudo-stem of Musa sapientum cultivated in two different sites in Cameroon. The FBY (Yaounde Banana Fibers) and FBP (Penja Banana Fibers) studied in this work were obtained by a bio-extraction method and characterized. The apparent densities of FBP and FBY were 0.90 ± 0.02 g/cm³ and 1.03 ± 0.04 g/cm³, while the moisture contents were 10.6 ± 0.2% and 12.4 ± 0.3%, respectively. Their chemical compositions were as follows: extracts 15.32% and 17.79%; pectin 5.7% and 14.77%; lignin 10.1% and 9.8%; and cellulose 47.1% and 58.3%, respectively. The water absorption rate at saturation was 140% and 170% by mass and was reached rapidly in the first 30 min of immersion. The tensile strengths of fibers were 743.9 MPa and 730.6 MPa, the elastic moduli were 260 MPa and 242 MPa, and the elongations at break were 2.8% and 2.2%, respectively. From the thermal analysis, the fibers’ stability temperatures were in the neighborhood of 250°C. Only slight differences were noticed in the properties of both fibers. Long outdoor conservation of the banana pseudo-stems before processing provided fibers with properties comparable to the properties of natural fibers reported in the literature. Independently of the harvesting locations, both fibers can be envisaged as cost-cutting fillers in the plastic industry.

摘要

从在喀麦隆两个不同地点种植的Musa sapientum假茎中提取纤维素纤维. 本工作研究的FBY（雅温得香蕉纤维）和FBP（Penja香蕉纤维）通过生物提取方法获得并表征. FBP和FBY的表观密度分别为0.90 ± 0.02 g/cm3和1.03 ± 0.04 g/cm3，水分含量分别为10.6 ± 0.2%和12.4 ± 0.3%. 其化学成分分别为: 提取物15.32%和17.79%; 果胶含量分别为5.7%和14.77%; 木质素10.1%和9.8%; 纤维素含量分别为47.1%和58.3%. 饱和时的吸水率为140质量%和170质量%，并且在浸渍的前30分钟内迅速达到. 纤维的拉伸强度分别为743.9MPa和730.6MPa，弹性模量分别为260MPa和242MPa; 断裂伸长率分别为2.8%和2.2%. 从热分析来看，纤维的稳定温度在250°C左右. 两种纤维的财产只有轻微的差异. 加工前对香蕉假茎进行长时间室外保存，使纤维的财产可与文献中报道的天然纤维的财产相媲美. 与收获位置无关，这两种纤维都可以被视为塑料工业中的成本削减填料.

KEYWORDS:

• Banana pseudo-stems
• cultivation site
• waste recovery
• chemical composition
• crystallization
• mechanical properties

关键词:

• 香蕉假茎
• 栽培地点
• 废物回收
• 化学成分
• 结晶
• 机械财

Introduction

Throughout the globe, there is an increase in agricultural production and a resulting increase in lignocellulosic by-products thanks to the increase in plantation areas and mechanization (Adejumo and Adebiyi 2020). In Cameroon, the non-valorization of these by-products leads to an accumulation of this agricultural waste in the environment. Banana pseudo-stems are one of the most abundant agricultural wastes in Cameroon, produced by both industrial plantations and native farmers. It is estimated that four tons of biomass waste (leaves, pseudo-stem, rhizome, etc.) is released per ton of banana fruit produced, the pseudo-stem being the bulky waste (Karthika1, Varalakshimi, and Babu 2020). The annual production of banana/plantain in Cameroon was about 2.53 million tons in 2007 (Okolle et al. 2009) and grew to about 5.114 million tons in 2018 according to FAO 2021, placing Cameroon among the top 10 world producers in 2018. These pseudo-stems are unexploited and are generally discarded after the recovery of their fruits. They can be valorized in composite materials. Composites reinforced with vegetable fibers have emerged as interesting alternatives to some common synthetic fiber composites, offering new percepts for meeting increasingly stringent regulatory ecological requirements and reduction of greenhouse gas emissions (Al-Maharma, Patil, and Markert 2022; Muhammad et al. 2021).

Many applications of natural fibers, especially those from banana pseudo-stem, are found in literature. Some of these applications include their use in printed circuit boards (Guna et al. 2016); dielectric applications (Bhuvaneswari et al. 2017); epoxy and hybrid epoxy composites (Balaji et al. 2022; Karthick et al. 2018; Prabhu et al. 2022; Prabhu, Karthikeyan, and Balaji 2021); and in three-dimensional cups, plates, and boxes developed by compression molding of banana fibers – wheat gluten films (Nataraj et al. 2018). However, before considering the use of these fibers in their various applications, research work needs to be done to study the variations in fiber properties with their region of origin, adopted agricultural practices, and the duration between the harvest and time of processing of the fibers. It is known in the field of wood science that the properties of a wood species vary with the growing area and even also within the same tree. Banana pseudo-stem is a lignocellulosic material such as wood, so the hypothesis of research was related to the question to know if the two different above described agricultural practices can considerably impact the chemical, physical, thermal, and mechanical properties of banana fibers (Saha Tchinda 2015).

In this work, long fibers were extracted from pseudo-stems of the banana species Grande-Naine which belongs to the Musa family. These banana pseudo-stems were harvested in the Littoral region of Cameroon (Njombe-Penja), with a very sunny climate and high temperatures throughout the year (over 24°C) (Gaymard, Kay, and Etoundi 2015), and in the Center region (Yaoundé) where the climate is tropical, with precipitation amplitude of 270 mm and the average temperature of 23.7°C (Gaymard, Kay, and Etoundi 2015). This research works aim to compare the chemical, physical, thermal, and mechanical properties of the raw fibers prepared from these pseudo-stems for their applications in the preparation of eco-friendly composite materials. Given the agricultural management practice implemented by the operating companies (use of chemical fertilizers, watering), the pseudo-stems collected from agro-industrial plantations in Penja were considered to originate from fast-growing plants compared to the pseudo-stems from native farms in Yaoundé. The volcanic-type soil in Penja has developed fertile arable lands suitable for intensive banana cropping (Ako et al. 2011), while the soil in Yaoundé is ferrallitic (Yerima and Ranst 2005). In this study, the pseudo-stems were kept in outdoor atmospheric conditions and exposed to natural biodegradation for about 1 month before processing.

Materials and methods

Biomass and fibers’ extraction

Figure 1 shows the fibers extraction protocol. The banana pseudo-stems were harvested, shelled, sliced, and preliminarily exposed to natural biodegradation in the outside ambient conditions (25 ± 5°C) for 1 month (30 days).

Figure 1. Banana pseudo-stems raw fibers extraction procedure.

The raw biomasses were then soaked in cold tap water for 14 days to soften the fibers and allow a natural bacterial breakdown of the organic layers binding the fibers. The slices were mechanically defibrillated with a metallic comb. The fibres were then washed with tap water to remove dust and other solid residues and air-dried under indoor ambient conditions (25 ± 5°C) until constant mass (about 1 week). The obtained fibers were kept in plastic bags for further characterization. A part of the fibers was crushed with a blade Retsch crusher using a 1 mm sieve, and the powder sieved passing a 160-μm sieve for determination of chemical compositions.

Characterization

Moisture content

The protocol described by Baley (2013) was used to determine the moisture content, which was calculated using Equation (1):

(1) $\mathrm{\%}H=\frac{M_i-M_f}{M_f}\times 100$(1)

Where Mi is the initial mass of species and Mf is the mass of species after drying in an oven.

Apparent density

The water immersion method described by the NF P 94–053 standard was used to determine the bulk density ρ of the fibers. A mass (m) of fibers was weighed and covered with paraffin (density of paraffin ρ = 0.88 g/cm³ determined also by using the water immersion methods) and reweighed. The mass of the paraffin was deduced, and the volume of the paraffin was calculated (V_p). The samples covered with paraffin were then all immersed, avoiding the appearance of bubbles. From the volume of water displaced in the test tube, we have the volume V _(p + f) of the fiber and paraffin. The volume V of each fiber bundle is determined by equation (2), and the bulk density in g/cm³ was calculated using equation (3):

(2) $V=\hspace{0.17em}{V}_{p+f}-V_p$(2)

(3) $\hspace{0.17em}{\rho }_a=\hspace{0.17em}\frac{m}{V}$(3)

Treatment of fibers with caustic soda

The treatment of the fibers with sodium hydroxide was carried out using the method described by Ganapathy et al. (2019) and Parre et al. (2020). Commercial sodium hydroxide with a purity of 98% was used for this work. It was provided by ONYX Bricolage (France). Twenty grams of fiber (dried at 103°C.) of each sample was treated in a sodium hydroxide solution at different concentrations of 2.5%, 3%, or 5% (m/v) for 24 h at room temperature. After this processing time, the fibers were removed, pressed, and washed with distilled water, then with an acetic acid solution (1%) until neutral pH (7). They were then dried in an oven at 75°C overnight ((12 ± 2) h) and weighed. The extraction rate was calculated using Equation (4):

(4) $t_e=\hspace{0.17em}\frac{m_i-m_f}{m_i}\times 100$(4)

Where t_e (%) is the fiber extraction rate, m_i is the initial anhydrous mass in grams, m_f is the mass in grams after treatment

Water vapor and water absorption

The fibers used for these experiments were tied in bundles to prevent fiber loss and dried at 105°C to constant mass. The adsorption of water vapor was studied in a closed chamber with distilled water at the bottom; the samples were not in contact with water. The relative humidity of a chamber containing pure water is around 100% at 25°C. The experiment was carried out at room temperature (25 ± 5°C) and the bundles were weighed at different exposure times. The absorption of water was carried out using the protocol described by Sellami (2015). Water absorption tests were done by immersing and weighing the fiber bundles after defined immersion times. The fiber bundles were mopped with clean tissue paper to remove excess water (until no trace of water is observed on the paper) before each mass measurement. The moisture content as a function of time was determined by the following relation (5):

(5) $W=\frac{W_t-W_o}{W_o}\times 100$(5)

Where W (%) is the moisture content, W_t is the mass at t, and W_o is the mass of dried fiber bundles before immersion (at t = 0).

Chemical analyses

The chemical analysis was carried out according to the TAPPI standard (T 222 om-88). Ten grams of anhydrous fiber (powder) was taken for all experiments. The chemical composition was determined according to the methods described by Chokouadeu Youmssi et al. (2017) and Sango et al. (2018).

Fourier transform infrared (FTIR) analysis

FTIR analyses were carried out using the Perkin Elmer Frontier attenuated total reflectance (ATR) apparatus equipped with a Diamond/ZnSe crystal. Two milligrams of grounded powder was deposited on the crystal device. Each spectrum was obtained by 32 scans with a resolution of 4 cm⁻¹ from 4000 to 600 cm⁻¹. The samples were scanned five times, and the average of these spectra was studied in the fingerprint region between 1800 and 600 cm⁻¹.

Mechanical properties of fibers

The machine used for the mechanical test was equipped with two jaws (one mobile and the other fixed) (Figure 2).

Figure 2. Single fiber tensile test procedure.

The single-fiber tensile test was performed using a universal tensile testing machine (LDW-1KN, China). The machine was equipped with a 40 N load cell and operated at a constant tensile rate of 2 mm/min. The ends of the fibers were glued in sandpaper before being placed in the jaws to avoid direct contact of the jaws with the fiber which can cause scratches and tears of the fiber. The mean diameter of the fibers determined by analysis of more than 100 fibers was 0.14 mm

Thermal analysis

The thermal behavior of FBY and FBP was studied by thermo gravimetry (TG-DTG) and differential scanning calorimetry (DSC) using a LINSEIS STA-PT 1000. Twenty to 22 mg of each type of fiber sample was placed in an alumina crucible. The fine powder samples were heated up steadily at a rate of 10°C/min from 24 to 1000°C under atmospheric air, and at an isotherm at 900°C for 30 min in an argon medium. The TG experimental procedure and heating up to 1000°C were applied to determine the ash content (remaining residue) of the fibers. The values obtained were comparable to those obtained by Tappi T 413 standard.

Scanning electron microscopy analysis

A Hitachi S-300N SEM microscope working at 15 kV was used for the analyses. The fibers were covered with a gold film before analysis.

Results and discussions

Equilibrium moisture content and bulk density of FBP and FPY

The equilibrium moisture content and bulk density of the fibers are shown in Table 1.

Table 1. Physical and mechanical properties of FBY and FBP fibers.

Fiber	Moisture %	Density (g/cm^3)	Tensile strength (MPa)	Elastic modulus (MPa)	Elongation at break (%)
FBP	10.6 ± 0.2	0.9 ± 0.02	730.6 ± 0.3	242.0 ± 0.2	2.2 ± 0.03
FBY	12.4 ± 0.3	1.03 ± 0.04	743.9 ± 0.1	260.0 ± 0.3	2.8 ± 0.02

At equilibrium, FBY appeared to contain more water than the FBP with ambient moisture. These values are in the same range as the results reported by Manimaran et al. (2018) and Lim et al. (2018). Most of the moisture in lignocellulosic materials is retained by hydrogen bonds with hydrophilic components such as cellulose and hemicellulose. The high moisture content in BFY can be explained by density measurements. The bulk density of FBY was higher than that of FBP, with an increase of about 10% ((1.03 ± 0.04) g/cm³ for FBY against (0.9 ± 0.02) g/cm³ for FBP) corresponding to a higher mass concentration of components per unit volume of fibers. For banana fibers, Manimaran et al. (2018) reported a density of 0.99 g/cm³ and Puriman and al. (2018) reported 1.023 g/cm³. The lower density for FBP may be due to agricultural practices in industrial plantations that result in the fast-growing of the plants. As reported by Dewi, Tihurua, and Wulansari (2022), when compared to fast-growing plants, slow-growing plants exhibit different anatomical and physical wood characteristics, one of which is low density.

Chemical composition of FBY and FBP

The chemical composition of the fibers is shown in Table 2.

Table 2. Chemical composition of FBP and FBY fibers.

Fiber	Extracts (%)	Pectin (%)	Lignin (%)	Cellulose (%)	Hemicellulose (%)	Ash (%)
FBP	14.8 ± 0.3	14.8 ± 0.8	10 ± 2	58.3 ± 0.7	12 ± 2	8.0 ± 0.4
FBY	14.6 ± 0.4	5.7 ± 0.3	10.1 ± 0.3	47 ± 3	16 ± 2	9.0 ± 0.4

From the analysis of the results presented in Table 2, it appears that the FBP contains less mineral matter compared to FBY: 8.0% for FBP compared to 9.0% for FBY. These values are in line with those reported in literature wherein mineral contents of banana fibers range from values as high as 9.11% found by Kathirselvam et al. (2019) to even higher and unexpected values such as 60.73% found by Puriman and al. (2017). The ethanol/benzene and water total extractives were 14.8% and 14.6%. The lignin content of the fibers was (9.8 ± 2.2)% and (10.1 ± 0.3)% for FBP and FBY, respectively. These values are comparable to those of Puriman et al. (2017) and Manimaran et al. (2018). The cellulose content was higher in FBP fibers (58.3 ± 0.7)% than in FBY fiber (47.1 ± 2.6)%. The hemicellulose content determined by subtracting the cellulose content from the holocellulose content was in the opposite trend: higher in FBY ((16 ± 2)%) than in FBP ((12 ± 2)%). These values are close to those of the other fibers given by Shanmugasundaram, Rajendran, and Ramkumar (2018). The fibers from banana plants grown in the FBP industrial area appeared to be richer in cellulose and poorer in minerals when compared to fibers from native farms. The plants grown in the industrial area are considered fast-growing plants, due to the use of fertilizers.

Water vapor adsorption and liquid water absorption

Figures 3a–b show the increase in moisture content W (%) of the fibers when exposed to 100% relative humidity and to liquid water, respectively. The objective of this test was to evaluate the intrinsic water absorption properties of fibers such as water absorption rate and saturation time.

Figure 3. (a) Water vapor adsorption and (b) liquid water absorption behaviors of FBP and FBY crude fibers.

From Figure 3a, the adsorption of water vapor is a slow process that continues even after five (5) days of exposure. The water vapor is mainly fixed by the cell walls and their adsorption causes swelling of the fibers and opens new sites for further fixation of water. The ingress of water in the cell wall is progressive. The moisture content after 5 days of fiber exposure was higher in FBP (32.6%) than in FBY (24.5%). The equilibrium moisture content of natural fibers is a function of the relative humidity of the exposed medium and the nature of the fibers. For instance, moisture contents above 30% were reported for coir, whereas in the same conditions, flax fiber values were around 20% (Hill, Norton, and Newman 2009). The water vapor adsorption values of FBP were higher than those for FBY. This same trend was observed with liquid water. The moisture content values of FPB increased with time. FBP appeared to be slightly more sensitive to water than FBY. The moisture content of the fibers increased rapidly at early exposure and reached a fairly steady state (Figure 3b). Similar results for natural fibers are reported in literature (Saikia 2010). The slight decrease in moisture content after long exposure times was attributed to the dissolution of fiber extracts in water. The fibers appeared as bundles of microfibers with tube-like structures as shown in the micrographs in Figure 4. The micrographs obtained with both fibers were similar. Only SEM images of FBP are then shown here.

Figure 4. SEM micrographs of the cross section and surface of the fibers (FBP).

The fibers were bundles of small fibers. The result is consistent with the preparation procedure which does not cause the binder phase to dissolve between individual fibers. The open porosity explains the rapid penetration of water inside the material. The values of liquid water absorbed by FBP and FBY were between 140% and 170%, revealing the high hydrophilic nature of the fibers. Untreated natural fibers are highly hydrophilic due to the presence of various hydroxylic groups in their structure.

FTIR analyses

The spectra of the raw banana pseudo-stem fibers are shown in Figure 5.

Figure 5. Fourier transform infrared spectra of raw and NaOH processed fibers: (a) FBY, (b) FBP.

The spectra of the raw fibers (FBY and FBP) exhibited general characteristic features of lignocellulosic material. The assignments of the vibration bands to the main functional groups and chemical components of the materials can be found in literature (Fan, Dai, and Huang 2012; Xu et al. 2013). The presence of a relatively high number of extractives did not introduce manifestly new bands probably because the extractives contain mainly the same functional groups as the main components. The peak centered around 1740 cm⁻¹ was attributed to the stretching of carbonyl groups (C=O) in hemicellulose and lignin. The two bands at 1600 cm⁻¹ and 1500 cm⁻¹ assigned to carbon–carbon double bonds of aromatic cycles are proof of the presence of lignin in the fibers. The region between 1500 cm⁻¹ and 800 cm⁻¹ is known as the fingerprint of lignocellulosic materials with various peaks associated with vibrations of C-H, C-O, C-O-C, C-C-O groups in cellulose, hemicellulose, and lignin (Wu et al. 2014). The results are in line with the chemical composition and confirmed that the lignocellulosic nature of the fibers was preserved by the extraction procedures applied. Long-term outdoor exposure of the pseudo-stems does not seem to considerably affect the fibers, which is why there is a certain flexibility for transporting and processing the pseudo-stems after the harvest.

Mechanical properties

The tensile mechanical characteristics (mechanical strength (Mpa), elastic strength (Mpa), and elongation at break (A%)) of the banana pseudo-stem fibers were determined according to the ASTM D3822–07 standard and shown in Table 1. The results were compared to those of other fibers in the literature (Table 3).

Table 3. Comparison of the chemo-mechanical characteristics of raw FBY and FBP fibers with other natural fibers.

Natural fibers	Physical properties		Chemical properties (mass %)						Mechanical properties		Reference
	Diameters (µm)	Density (kg/m^3)	Cellulose	Hemi-cellulose	Lignin	Wax	Moisture content	Ash rate	tensile strength (MPa)	Elongation at break (%)
Pseudo-stem banana fibers (FBY)	0.84–0.14	1021	47.07 ±2.6	15,52 ± 2,3	10.1 ± 0.3	-	12.43±0.3	9 ± 0,42	743.9	2.8	This study
Pseudo-stem banana fibers (FBP)	0.75–0.13	991	58.27 ±0.7	12.08 ± 1.8	9.80± 2.2	-	10.57±0.2	8.02 ±0,3	730	2.2
Pseudo-stem banana fibers	0.81–0.14	1020	/	/	/	/	11.8±0.15	/	816.6	2.83	Chengoué Mbouyap et al. (2020)
Aerial roots of Banyan tree fibers (Raw)	0.09–0.14	1234	67.32	13.46	15.62	0.81	10.21	3.96	19.37±7.72	1.8±0.4	Ganapathy et al. (2019)
Aerial roots of Banyan tree fibers treated 5% NaOH	0.08–0.12	1269	70.4	10.74	12.7	0.69	9.91	5.86	20.45±12.2	1.6±0.5
Salago fibers (genus Wikstroemia spp.)	0.00623	1023	79.05	13.6	10.13	-	50.21	60.93	1187	2.48	Pouriman et al. 2017
Red banana peduncle fibers	150–250	990	72.90	11.01	15.99	0.32	9.36	2.79	440±13.4	1.57±0.04	Manimaran et al. (2018)
Prosopis juliflora bark fibers	20	580	61.65	16.14	17.11	0.61	9.48	5.2	558±13.4	1.77±0.04	Saravanakumar et al. (2013)
Areca Palm Leaf Stalk Fibers	285–330	1090±24	57.49±0.66	18.34±0.24	7.26±0.12	0.71±0.024	9.35±0.15	1.43±0.019	364.66±21.46	3.47±1.15	Shanmugasundaram, Rajendran, and Ramkumar (2018)

The tensile strength and elongation at break were comparable for the fibers from FBY and the fibers from FBP. The results are also close to those reported for banana pseudo-stem fibers harvested at other locations in Cameroon as reported by Chengoué Mbouyap et al. (2020) and Sango et al. (2018). The fibers from Banana pseudo-stems of the same species seemed to be chemically and mechanically consistent irrespective of the location of cultivation and the agricultural practices. The tensile strength and elongation at break are in the same range as those of other tropical fibers such as flax, hemp, and bamboo reviewed in Raja et al. (2017) and the fibers shown in Table 3. The fibers exhibit high tensile strengths generally between 300 MPa and 1200 MPa and weak elongation at break between 1% and 3%.

Thermal analysis

The ATG-DTG curves of the fibers are shown in Figure 6.

Figure 6. ATG-DTG curves of raw fibers: (a) FBP, (b) FBY.

The FBP (Figure 6a) had three main phases of mass loss. The first mass loss of 9.79% by weight is located between 40°C and 100°C and has a peak around 69°C, it corresponds to the evaporation of the adsorbed and free water present in the fiber (Manimaran et al. 2016). The second mass loss is 73%, observed between 200°C and 325°C, with two DTG peaks: 283°C and 305°C. It was assigned to the degradation of polysaccharides (hemicelluloses and cellulose) in the fiber (Ahmed et al. 2018). The third loss of 9.45% observed between 325°C and 480°C and a peak around 424°C represents the loss of lignin and charcoal residues (Milani and al. Milani, Samarawickrama, and Kottegoda 2016). The residue at 600°C was 7.76% by mass of the sample

The thermal behavior of FBY (Figure 6b) was similar to that of FBP. The FBY sample had a first loss located between 40°C and 100°C and having a peak around 73°C and attributed to the evaporation of adsorbed moisture corresponded to a mass loss of 8.56%. The second loss located between 225°C and 325°C with a peak around 295°C assigned to the degradation of the polysaccharides (hemicelluloses and cellulose) in FBY corresponded to a mass loss of around 67.49% and 2.76%. When compared to FBP, the mass loss in FBY was lower in this stage probably because of the low holocellulose (cellulose + hemicellulose). The mass loss in the third stage was attributed to further degradation of cellulose and lignin was also high in FBY and was observed at lower temperatures between 363°C and 485°C with a peak around 390°C. The residue content at 600°C was 8.53% by mass. When comparing both thermal behaviors, the thermal resistance of FBY fiber appeared to be greater than that of FBP fiber, given that their main degradation appeared at 295°C and 283°C, respectively.

Caustic soda treatment of fibers

Caustic soda aqueous solutions are usually applied to dissolve the binding phase and liberate individual fibers from raw fibers bundles (Chand and Fahim 2021; Sango et al. 2018). The treatment, also called mercerization, changes the fine structure, dimension, morphology of the fibers, and increases the reactivity of their surface hydroxyl groups (Chand and Fahim 2021). The treatment of the fibers in sodium hydroxide solutions leads to a considerable reduction of the mass of the fibers. Raw fibers were treated with 2.5%, 3%, or 5% of aqueous NaOH solutions. It was noticed that the caustic soda treatment reduced the weight of the lignocellulosic raw material, by dissolving some components: mainly, lignin, hemicelluloses, and extractives. The FTIR spectra of the treated fibers were recorded and shown in Figure 5 for comparison. The spectra of the fibers treated in low-concentration sodium hydroxide solutions were globally comparable to the spectrum of the raw fiber, suggesting that the chemical structure of the fibers was not considerably affected by the treatment. The peaks of carbonyl (C=O) groups at 1740 cm⁻¹ and aromatic rings at 1600 cm⁻¹ and 1500 cm⁻¹ are still visible in the spectra of the treated fibers. Nevertheless, the intensities are low when compared to the raw fibers, showing that lignin and hemicelluloses are only partially removed (Fengel 1992; Mouhoubi et al. 2012; Ouajai and Shanks 2005). The fiber percent yields were between 59% and 64% for the FBP and between 72% and 73% for the FBY. The better yields obtained with FBY could be related to the higher density of these fibers. The concentration of the aqueous sodium hydroxide solutions had only little effect on fiber yield. An increase in the concentration was supposed to decrease the yield by increasing the proportion of dissolved components; rather, the reverse was observed. These results are in agreement with works carried out by Ganapathy et al. (2019), who showed treating fibers with a 5% aqueous sodium hydroxide solution is better than treating with a 3% solution. A high concentration of sodium hydroxide can lead to the mercerization of cellulose. However, the efficacy of the treatment could be dependent on the quality of the fiber treated. For the FBY, a good yield was obtained using the 3% sodium hydroxide solution. The yield with the 5% sodium hydroxide solution was lower than with the 3% solution for this fiber. For the FBP fiber, we found that the yield increased as a function of the sodium hydroxide concentration. A good yield was obtained with a 5% solution. The result can be explained by the difference in cellulose and hemicelluloses contents of the fibers. An increase in sodium hydroxide concentration in FBY led to an increase in the amount of dissolved hemicellulose given the relatively higher content of this component in the fiber. Hemicelluloses are known to be soluble to some extent in sodium hydroxide solutions. The high content of insoluble cellulose in FBP could also stabilize to some extent hemicelluloses and lignin in this sample, increasing the stability of the fibers toward alkaline degradation. In this study, when comparing the properties of the fibers extracted with and without NaOH treatment, extraction with NaOH reduces the fiber yield without significantly increasing the mechanical performance of the materials. The mechanical properties of the fibers were globally in the same range as other fibers and can be used without further treatment.

Conclusion

Banana pseudo-stem fibers were mechanically extracted from raw stems harvested at two different cultivation sites using a comb-like metallic instrument. The chemical composition of the fibers from the industrial plantations of Penja (FBP) was different from that of the fibers from native farms in Yaoundé (FBY). A considerable difference was observed with the contents of cellulose and hemicellulose. Compared to FBP, FBY exhibited lower cellulose content, higher hemicellulose content, higher density, and lower water absorption rate at saturation. The range of density of fibers FBY (0.991 g/cm³ and 1.021 g/cm³) is much lower than that of synthetic fibers but closer to the average density of other plant fibers. The fibers rapidly absorbed liquid water because of their tube-like structures as revealed by SEM micrographs. The mechanical properties of FBY fibers were slightly superior to those of FBP fibers: tensile strength of 743.9 MPa and 730 MPa, elastic moduli of 260 MPa and 240 MPa, and elongation at break of 2.8% and 2.2%, for FBY and FBP, respectively. The fibers with low cellulose and high hemicellulose contents had slightly better mechanical properties. Globally, the results show that the banana growing site, i.e., a fast-growing industrial site or a slow-growing traditional site, has a low impact on the fiber characteristics. The raw material for an industrial composite application can be collected from any of these sites. There is a time flexibility for the transport of the pseudo-stems which can be stored outside for 1 month before processing. ATG and DTG results show that FBP and FBY can be used as reinforcing agents in many thermoplastic materials, given that their degradation temperature is higher than the processing temperature of polymer matrices such as poly(lactic acid), polyethylene, or polypropylene.

Highligths

• Fibers obtained from banana pseudo-stems, cultivated with or without chemicals was investigated.

• Fibers were obtained by bioextraction.

• Fibers obtained can be used as reinforcing agent for many thermoplastic materials.

Disclosure statement

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

Additional information

Funding

This project did not receive any funding. The research was financially supported by the contribution of all authors.