Influence of Chemical Treatment on the Physical and Mechanical Properties of Bamboo Fibers as Potential Reinforcement for Polymer Composites

ABSTRACT

The growing concern for environmentally friendly biomaterials has spurred interest in natural fibers as a viable alternative to synthetic fibers in various industrial applications. Chemical treatment of natural fibers is necessary in cases where it is desired to enhance their properties and make them more suitable for various industrial applications. These treatments can remove impurities, increase fiber roughness for better adhesion, and modify surface chemistry, ultimately improving characteristics like tensile strength, thermal stability, and compatibility with matrix materials in composites. In this study, chemical treatments, including Sodium Hydroxide, Ammonium Hydroxide, and Potassium Permanganate, were applied to the Bamboo fibers to modify the fiber structure. The tensile strength, morphological characteristics, and degree of crystallinity of the treated fibers were examined. Results revealed that 5% Sodium Hydroxide treatment for 2 hours significantly improved tensile strength and crystallinity compared to other treatments. Chemical composition analysis, XRD, and FTIR analyses confirmed the removal of impurities and amorphous substances. Density measurements indicated a reduction in volume due to the elimination of low molecular weight impurities, leading to increased fiber density. This research provides valuable insights for the development of sustainable biomaterials in the construction and automotive industries such as wall panels, dashboards and door panels.

摘要

对环保生物材料的日益关注激发了人们对天然纤维的兴趣，天然纤维是各种工业应用中合成纤维的可行替代品. 在希望提高天然纤维的性能并使其更适合各种工业应用的情况下，对天然纤维进行化学处理是必要的. 这些处理可以去除杂质，增加纤维粗糙度以获得更好的附着力，并改变表面化学性质，最终改善复合材料的抗拉强度、热稳定性和与基体材料的兼容性等特性. 在本研究中，对竹纤维进行了化学处理，包括氢氧化钠、氢氧化铵和高锰酸钾，以改变纤维结构. 研究了处理后纤维的拉伸强度、形态特征和结晶度. 结果显示，与其他处理相比，5%氢氧化钠处理2小时显著提高了拉伸强度和结晶度. 化学成分分析、XRD和FTIR分析证实了杂质和无定形物质的去除. 密度测量表明，由于消除了低分子量杂质，体积减少，导致纤维密度增加. 这项研究为建筑和汽车行业的可持续生物材料开发提供了宝贵的见解，如墙板、仪表板和门板.

KEYWORDS:

• Bamboo fiber
• sodium hydroxide
• ammonium hydroxide
• potassium permanganate
• single fiber tensile test
• X-ray Diffraction

关键词:

• 竹纤维
• 氢氧化钠
• 氢氧化铵
• 高锰酸钾
• 单纤维拉伸试验
• X射线衍射

Introduction

Due to the increasing awareness of environmentally friendly biomaterials, there is an increasing demand for natural fibers as a possible substitute for synthetic fibers in the construction and automotive industries. Natural fibers being lightweight, biodegradable, renewable, less expensive and abundantly available, making them as the ideal choice of replacement for synthetic fibers (Chokshi et al. 2022). Chemical treatments are applied to natural fibers to enhance their resistance to moisture, mechanical properties, and adhesion with fiber/matrix interface (Jagadeesh et al. 2021; Koohestani et al. 2019; Madhu et al. 2020; Salih, Zulkifli, and Azhari 2020). Chemical treatments applied to reinforcing fibers can decrease their hydrophilic tendency, leading to enhanced compatibility with the hydrophobic matrix. Alkali treatment is commonly used to modify the molecular structure of natural fibers. This process alters the crystalline cellulose order, creating an amorphous region that enhances chemical penetration. The treatment reduces hydrophilic hydroxyl groups, improving moisture resistance, while also eliminating impurities, resulting in a cleaner and more uniform fiber surface with improved stress transfer capacity between cells (Kabir et al. 2012). Potassium Permanganate treatment, as an oxidization method, improves chemical interlocking at the fiber-matrix interface, enhancing adhesion. The resulting cellulose-manganate formation contributes to increased thermal stability of the fiber, while also reacting with lignin constituents and reducing the fiber’s hydrophilic nature by separating them from the cell wall (Kabir et al. 2012). The main purpose of alkali treatment is to disrupt hydrogen bonds within the fiber structure, creating a rougher surface to enhance compatibility. This effective method also aids in removing lignin and impurities covering the fiber surface while depolymerizing cellulose structures (Madival et al. 2022; Verma and Goh 2021). When fibers are treated with a Potassium Permanganate solution, it generates highly reactive permanganate ions (Mn3+), which then interact with cellulose hydroxyl groups to create cellulose – manganate, initiating graft copolymerization. The formation of cellulose – manganate contributes to increased thermal stability of the fiber. Additionally, it reacts with the hydrophilic -OH groups in lignin constituents, causing their separation from the fiber cell wall and reducing the overall hydrophilic nature of the fiber (Kabir et al. 2012; Madival et al. 2023). The tensile test is used to assess the impact of chemical treatments on the overall strength and performance of fibers. The results provide insights into the effectiveness of the treatments in enhancing the mechanical properties of the fibers (Khan et al. 2022). XRD helps quantify the degree to which the treatments affect the crystallinity of the fibers. Changes in cellulose crystallinity can impact properties like strength, stiffness, and thermal stability (Madhu et al. 2019; Poletto, Ornaghi Júnior, and Zattera 2014; Sanjay et al. 2019). The Fourier Transform Infrared spectroscopy spectrum is used to identify the functional groups and their corresponding fiber components present in the fibers both before and after treatment. FTIR is particularly useful for detecting modifications or removal of lignin, hemicellulose, and other components that influence fiber properties (Madhu et al. 2019; Vijay et al. 2020). By examining SEM images of Bamboo fibers before and after treatment, it is possible to observe structural changes, surface roughness, and the removal of impurities. SEM images can reveal how the treatments alter the fiber’s surface characteristics and provide insights into the mechanisms underlying the observed changes in mechanical and other properties (Hasan, Rabbi, and Maruf Billah 2022; Sanjay et al. 2019). Chen et al. (2017) found that treating Bamboo fibers with higher concentrations of Sodium Hydroxide solution led to a decrease in the modulus of elasticity. Chin et al. (2020) found that treating Bamboo fibers with lower concentration of Sodium Hydroxide led to reduced removal of hemicellulose and lignin leading to reduced degree of crystallinity whereas higher concentrations were effective in removing the amorphous content resulting in a highly crystalline cellulose. While several studies have explored the impact of treatments like Sodium Hydroxide, Ammonium Hydroxide, and Potassium Permanganate on tensile strength, crystallinity, and surface roughness of different natural fibers, there seems to be a lack of study comparing the effects of Potassium Permanganate, Sodium Hydroxide and Ammonium Hydroxide treatment on Bamboo fibers. Furthermore, the existing research primarily focuses on individual properties like tensile strength or crystallinity, rather than providing a holistic view of the interplay between different factors resulting from various treatments. Therefore, a research gap exists in terms of a more integrated investigation that considers how these treatments affect mechanical, structural, and surface properties, providing a clearer understanding of their implications for practical applications in industries like construction, automotive, marine, sports and packaging. A research study was conducted to examine how the tensile strength, morphological characteristics of Bamboo fibers were impacted by alkali and Potassium Permanganate treatments.

Methodology

Materials

The Bamboo fibers used in the current study were procured from Go Green products, Chennai, India. The Sodium Hydroxide, Ammonium Hydroxide and Potassium Permanganate solutions were procured from Vinayaka Agencies, Udupi.

Treatment of fibers

The fibers were made to undergo three different chemical treatments: Sodium Hydroxide, Ammonium Hydroxide, and Potassium Permanganate treatment.

• Sodium Hydroxide treatment: The fibers were soaked in 1%, 3%, 5%, and 7% of Sodium Hydroxide solution for 2 hours at room temperature. Rinsed with distilled water and oven dried for 3 hours at 60°C (Negawo et al. 2019; Bartos et al. 2020).

• Ammonium Hydroxide treatment: The fibers were soaked in 1%, 3%, 5%, and 7% of Ammonium Hydroxide solution for 2 hours at room temperature. Rinsed with distilled water and oven dried for 3 hours at 60°C (Rajulu et al. 2003; Santhiarsa 2016).

• Potassium Permanganate treatment: The fibers were soaked in 0.25%, 0.5%, 0.75%, and 1% of Potassium Permanganate solution for 3 minutes at room temperature. Rinsed with distilled water and oven dried for 3 hours at 60°C (Imoisili and Jen 2020).

Single fiber tensile test

The single fiber tensile test was carried out according to ASTM C1557 on Shimadzu EZ-SX Universal Testing machine. The equipment had maximum load capacity of 500 N and crosshead speed range of 0.001 to 1000 mm/min. The test was carried out for 10 samples each having a gauge length of 25 mm and cross head speed of 1 mm/min. The fiber diameter of 0.787 ± 0.042 mm was measured using a tool room microscope. Tabs were made using a cardboard sheet as shown in Figure 1.

Figure 1. Single fiber tensile test sample.

Density

The density of the fibers was calculated as per ASTM D3800. The density of the fibers is determined by measuring the weight of the fibers in air and in acetone. The density of the fibers is calculated using equation 1(1) $\mathrm{Density}\mathrm{of}\mathrm{fiber}=\frac{\left(M_3-M_1\right){\rho }_L}{\left(M_3-M_1\right)-\left(M_4-M_2\right)}$(1) .

(1) $\mathrm{Density}\mathrm{of}\mathrm{fiber}=\frac{\left(M_3-M_1\right){\rho }_L}{\left(M_3-M_1\right)-\left(M_4-M_2\right)}$(1)

Where ρ_L is the density of acetone (g/cm³),

M₁ is weight of wire in air,

M₂ is weight of wire in acetone,

M₃ is weight of wire plus fiber in air,

M₄ is weight of wire plus fiber in acetone.

Chemical composition

The mass content of lignocellulosic elements such as cellulose, hemicellulose, and lignin in Bamboo fibers were measured as per analytical methods proposed by (Li et al. 2004; Varma and Mondal 2016). The process used to estimate the mass percentage of cellulose, hemicellulose, lignin, and extractives is shown in Figure 2.

Figure 2. Pictorial depicting the process followed to obtain the mass percentage of chemical constituents in Bamboo fibers.

The experiment involved taking dried Bamboo fibers that weighed m₀ grams and immersing them in a mixture of Benzene and Ethanol in a 2:1 ratio. The mixture was heated to 60°C for 3 hours. The fibers were rinsed with distilled water and dried in a hot air oven at 105°C. Then, the fibers were weighed, and their weight was recorded as m₁ grams. Finally, the percentage of extractives is calculated using equation 2(2) $W_1=\frac{m_0-m_1}{m_0}\times 100$(2) .

(2) $W_1=\frac{m_0-m_1}{m_0}\times 100$(2)

To determine the mass percentage of hemicellulose, the dried fibers weighing m₁ grams were boiled for 3.5 hours in 150 ml of Sodium Hydroxide solution (20 g/L) using reflux equipment. After rinsing with distilled water, the fibers were dried in a hot air oven. The weight of the dried fibers was measured as m₂ grams and the hemicellulose percentage is determined using equation 3(3) $W_2=\frac{m_1-m_2}{m_0}\times 100$(3) .

(3) $W_2=\frac{m_1-m_2}{m_0}\times 100$(3)

To determine the percentage of lignin in a sample, the extractives were first dried and weighed as m₃ grams. The sample was then mixed with 30 ml of 72% (v/v) sulfuric acid and left for 24 hours. Three hundred milliliters of distilled water was added and the mixture was boiled in reflux equipment for 1 hour. The residue was then filtered and rinsed with distilled water before being left to cool. Finally, the residue was dried in a hot air oven and weighed as m₄ grams. The percentage of lignin is calculated using equation 4(4) $W_3=\frac{m_4\left(1-W_1\right)}{m_3}\times 100$(4) .

(4) $W_3=\frac{m_4\left(1-W_1\right)}{m_3}\times 100$(4)

The percentage of cellulose is calculated using equation 5(5) $W_4=100-\left(W_1+W_2+W_3\right)$(5) .

(5) $W_4=100-\left(W_1+W_2+W_3\right)$(5)

X-ray Diffraction (XRD)

X-ray Diffraction analysis was carried out on Rigaku Miniflex 600 for Bamboo fiber samples. The step scan is used at 0.015° per step with 1 second allowed for each step. The 2θ values range from 0° to 80°. The degree of Crystallinity (%) is calculated based on Segal empirical method (Segal et al. 1959) using equation 6(6) $\mathrm{Degree}\mathrm{of}\mathrm{Crystallinity}=\frac{{\mathit{I}}_{002}-I_{\mathit{am}}}{I_{002}}\times 100$(6) .

(6) $\mathrm{Degree}\mathrm{of}\mathrm{Crystallinity}=\frac{{\mathit{I}}_{002}-I_{\mathit{am}}}{I_{002}}\times 100$(6)

Where, I₀₀₂ is the peak intensity of cellulose content and I_am is the peak intensity of amorphous content.

Fourier Transform Infrared Spectroscopy (FTIR)

The functional groups present in the fibers are studied using FTIR spectrum. The FTIR spectrum is obtained using Shimadzu IR Spirit spectrophotometer. Fine particles of Bamboo fibers are mixed with Potassium Bromide powder. The mixture is die pressed to obtain pellets which will be placed in the FTIR spectrometer to obtain the spectrum. The spectrum is obtained within the wavelength range of 400 cm⁻¹ to 4000 cm⁻¹.

Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS)

To analyze the effect of chemical treatment on the morphology of the fiber surface SEM images were captured on EVO MA18 with Oxford EDS system having a magnification range of 1x to 1,00,000x. The Bamboo fiber samples were made to undergo sputtering to improve the electro transmittance. The images of the fibers were captured at various locations and magnifications. The atomic and weight percentages of elements present in the fiber surface are estimated using the EDS spectrum.

Results and discussion

Single fiber tensile test

Figure 3 shows the results of the tensile test conducted on Bamboo fibers treated with 1%, 3%, 5%, and 7% of Sodium Hydroxide and Ammonium Hydroxide. From Figure 4 it can be seen that 0.5% is the optimal concentration of Potassium Permanganate treatment. The tensile strength was found to be higher for the 5% Sodium Hydroxide and 1% Ammonium Hydroxide treatments compared to those with different weight percentages of Sodium Hydroxide and Ammonium Hydroxide. Moreover, the tensile strength of 0.5% Potassium Permanganate treated fibers and untreated fibers were compared with those treated with 5% Sodium Hydroxide and 1% Ammonium Hydroxide as shown in Figure 5.

Figure 3. Tensile strength of sodium hydroxide treated and ammonium hydroxide treated bamboo fibers.

Figure 4. Tensile strength of potassium permanganate treated bamboo fibers.

Figure 5. Comparison of tensile strength of treated and untreated bamboo fibers.

Treatment with 5% Sodium Hydroxide, 1% Ammonium Hydroxide, and 0.5% Potassium Permanganate were identified as optimal based on the achieved tensile strengths. Subsequent analysis will compare these treatments with untreated Bamboo fibers. The experimental results indicate that treating Bamboo fibers with a 5% Sodium Hydroxide solution for 2 hours resulted in an enhanced tensile strength when compared to treatments with different weight percentages of Sodium Hydroxide and Ammonium Hydroxide. Sodium Hydroxide proved to be an effective alkali treatment when compared to Ammonium Hydroxide. The removal of contaminants like hemicellulose and lignin caused the fiber to shrink after treatment, resulting in increased fiber density and tightly packed structure (Kore et al. 2021). The untreated fibers exhibited the lowest tensile strength due to the presence of higher percentages of non-cellulosic elements such as lignin and hemicellulose, as confirmed by the chemical composition analysis presented in Table 1. All alkali-treated fibers and fibers treated with Potassium Permanganate had better tensile strength than untreated fibers. The contaminants in the fibers were eliminated as the Sodium Hydroxide concentration increased, which led to an increase in the relative cellulose content (Jayabal et al. 2012). As a result, fibrils were rearranged along the direction of the tensile force, increasing the tensile strength (Hossain et al. 2013; Kore et al. 2021). Additionally, the hydroxyl groups of cellulose, hemicellulose, and lignin were separated by a NaOH solution from the inter- or intramolecular hydrogen bonds (Kore et al. 2021). The close packing of cellulose chains caused by the fiber fibrillation and collapse of the cellular structure boosted the tensile characteristics (Chowdhury et al. 2015; Rokbi et al. 2011). Ammonium Hydroxide treatment resulted in partial delignification, which caused the cellulose chain to be slightly constrained (Kore et al. 2021). This resulted in a reduced packing density of cellulose molecules, which in turn resulted in reduced strength (Zhang, Wang, and Keer 2015). Seven percent Sodium Hydroxide treated fibers had reduced tensile strength due to excess delignification which damaged the fiber (Kabir et al. 2012).

Table 1. Chemical constituents of treated and untreated bamboo fibers.

Samples	Cellulose (%)	Hemicellulose (%)	Lignin (%)	Extractives (%)
Untreated Bamboo fibers	38.91	23.84	30.05	6.49
5% Sodium Hydroxide treated Bamboo fibers	47.72	15.26	27.78	7.58
0.5% Potassium Permanganate treated Bamboo fibers	44.39	17.62	29.02	7.18

Density

Density of the fibers was measured using Archimedes principle and calculated using equation 1(1) $\mathrm{Density}\mathrm{of}\mathrm{fiber}=\frac{\left(M_3-M_1\right){\rho }_L}{\left(M_3-M_1\right)-\left(M_4-M_2\right)}$(1) . As per the results obtained, the highest density was obtained for Sodium Hydroxide treated Bamboo fibers (1.26 g/cc) followed by Potassium Permanganate treated (1.23 g/cc) and untreated Bamboo fibers (1.22 g/cc). The treatment of fibers resulted in removal of hemicellulose, lignin, and impurities having low molecular weight leading to a reduction in the volume of the fibers, while the change in mass is minimal. Hence, the density of fibers increased upon treatment (Ariawan et al. 2020; Saheb and Jog 1999).

Chemical composition

The mass percentages of extractives, hemicellulose, lignin, and cellulose were calculated using equation 2(2) $W_1=\frac{m_0-m_1}{m_0}\times 100$(2) , 3(3) $W_2=\frac{m_1-m_2}{m_0}\times 100$(3) , 4(4) $W_3=\frac{m_4\left(1-W_1\right)}{m_3}\times 100$(4) and 5(5) $W_4=100-\left(W_1+W_2+W_3\right)$(5) respectively. The mass percent of chemical constituents of Bamboo fibers are shown in Table 1.

The percentage of chemical constituents of untreated fibers was in the range obtained by Reddy et al. (2014). The treatment of Bamboo fibers increased the percentage of cellulose compared to the untreated Bamboo fiber. The treatment of fibers with 5% Sodium Hydroxide solution resulted in 22.64% increase in cellulose content whereas the treatment with 0.5% Potassium Permanganate solution resulted in 14.08% increase in cellulose content. Cellulose provides strength to the fibers and increasing the cellulose content increases the strength of the fiber (Guo, Sun, and Satyavolu 2019). Sodium Hydroxide treated fibers had 13.39% and 4.27% less hemicellulose and lignin than Potassium Permanganate treated fibers, respectively. Alkali treatment was more effective in removing lignin and hemicellulose compared to Potassium Permanganate treatment. Hence, a higher tensile strength was observed for 5% Sodium Hydroxide treated Bamboo fibers.

X-Ray Diffraction analysis

XRD analysis was carried out for 1% Ammonium Hydroxide, 5% Sodium Hydroxide, 0.5% Potassium Permanganate treated and untreated Bamboo fibers. XRD spectrum of Intensity (cps) vs 2θ (°) was obtained as shown in Figure 6, respectively. Degree of crystallinity (%) was calculated from the spectrum using equation 6(6) $\mathrm{Degree}\mathrm{of}\mathrm{Crystallinity}=\frac{{\mathit{I}}_{002}-I_{\mathit{am}}}{I_{002}}\times 100$(6) and the values obtained are shown in Figure 7.

Figure 6. XRD spectrum of treated and untreated bamboo fibers.

Figure 7. Degree of crystallinity of treated and untreated bamboo fibers.

The presence of amorphous components in Bamboo fibers was shown by the first multiple and wide peak. The amorphous zone comprising hemicellulose and lignin is indicated by the peak at 16 degrees. However, the cellulose content of the fibers is represented by the peak at 22° (Júnior et al. 2015; Sánchez, Patiño, and Cárdenas 2020). The presence of higher concentrations of amorphous elements is the cause of the low degree of crystallinity in untreated fibers (Rahman et al. 2017). The Bamboo fibers were treated to eliminate contaminants and amorphous substances like hemicellulose and lignin. As a result, cellulose chains are better packed and under less stress (Wang et al. 2018). Due to the small amounts of hemicellulose and lignin that were eliminated, fibers treated with Potassium Permanganate and Ammonium Hydroxide had a reduced degree of crystallinity. As more hemicellulose and lignin were removed, Sodium Hydroxide-treated fibers showed the highest degree of crystallinity (Chin et al. 2020; Madival et al. 2023).

Fourier transform infrared spectroscopy

Comparing the FTIR spectra of untreated, Sodium Hydroxide treated, and Potassium Permanganate treated Bamboo fibers provides valuable information about the changes induced by the different treatments. The FTIR spectrum of the untreated and treated Bamboo fibers are shown in Figure 8.

Figure 8. FTIR spectrum of treated and untreated bamboo fibers.

In the case of untreated fibers, the peak at 3300 cm⁻¹ shows the O-H stretching vibration of hydroxyl groups in cellulose, hemicellulose, and lignin. The peak at around 2916.22 cm⁻¹ corresponds to the C-H stretching vibration in cellulose and hemicellulose. The presence of acetyl functional groups in lignin is indicated by the peak at 1219.25 cm⁻¹. The reduction in hydroxyl groups of cellulose, hemicellulose, and lignin due to the NaOH solution and KMnO₄ disrupting hydrogen bonds can be reflected in change in width in the peaks at 3300 cm⁻¹ and 2916.22 cm⁻¹. Upon treatment the bands became broader indicating the removal of hemicellulose and lignin. The bands observed at 1022 cm−1 wavenumber corresponds to the ester bonds and the stretching of C-O and C-C bonds in lignin and hemicellulose. The bands shifted to 1028 cm⁻¹ for Sodium Hydroxide treated fibers and it became broader for Potassium Permanganate treated fibers indicating a reduction in hemicellulose and lignin. The peak at 775 cm⁻¹ indicates the beta-glycosidic linkage between glucose units in cellulose whose intensity remains unchanged after treatment indicating the cellulose remains intact. The bands got shifted to 770 and 774 cm⁻¹ for Sodium Hydroxide and Potassium Permanganate treatment respectively due to increased exposure of cellulose (Chin et al. 2020). Alkali-treated fibers, on the other hand, have different locations and intensities of distinctive peaks than untreated fibers. The broadness of peaks of chemically treated Bamboo fiber was different from that of untreated Bamboo fiber due to a new type of hydrogen bonding interactions between -OH group of fibers and the chemicals used for treatment (Júnior et al. 2015; Kore et al. 2021; Madival et al. 2023).

Scanning electron microscopy

The effect of 5% Sodium Hydroxide treatment, 1% Ammonium Hydroxide treatment and 0.5% Potassium Permanganate treatment on the surface morphology of Bamboo fibers are shown in Figure 9.

Figure 9. SEM images of (a) untreated bamboo fibers, (b) 5% sodium hydroxide treated bamboo fibers, (c) 1% ammonium hydroxide treated bamboo fibers and (d) 0.5% potassium permanganate treated bamboo fibers.

The SEM image of untreated Bamboo fibers shows a surface with a significant presence of impurities, irregularities, and debris. These impurities include residual lignin, hemicellulose, and other contaminants from the natural fiber source (Hasan, Rabbi, and Maruf Billah 2022; Madival et al. 2022). The SEM images of alkali treated Bamboo fibers indicate removal of impurities, hemicellulose, wax, pectin, lignin from the fiber surface leading to an increase in surface roughness. Sodium Hydroxide treatment caused an increased fiber roughness can be attributed to the alkali treatment’s effect on removing impurities and potentially causing slight swelling of the fiber surface. As impurities are eliminated and the surface is modified, the exposed fibrils or microfibrils contribute to the observed higher roughness (Hasan, Rabbi, and Maruf Billah 2022; Hossain et al. 2013; Madival et al. 2022). In the case of Ammonium Hydroxide treated fibers, the surface roughness is lower in comparison to the Sodium Hydroxide treated fibers. The Ammonium Hydroxide treatment appears to cause less swelling or fibrillation on the fiber surface, leading to a relatively smoother appearance. Potassium Permanganate treatment has removed a significant amount of impurities and contaminants, resulting in a cleaner and smoother appearance and a slightly detached fibrils. The surface roughness appears to be comparatively low (Hasan, Rabbi, and Maruf Billah 2022; Madival et al. 2022).

Energy dispersive spectroscopy (EDS)

The atomic and weight percentages of different elements present on the surface of the fibers are studied using EDS. The EDS spectrum of chemically treated and untreated Bamboo fibers are shown in Figure 10.

Figure 10. EDS spectrum of (a) untreated bamboo fibers, (b) 5% sodium hydroxide treated, (c) 1% ammonium hydroxide treated and (d) 0.5% potassium permanganate treated bamboo fibers.

The percentages of different elements present on the fiber surface are shown in Table 2. The percentage of carbon increased whereas oxygen percentage decreased after chemical treatment due to the conversion of phenolic hydroxyl groups to phenolic ethers (Madival et al. 2023; Zhang et al. 2018). Sodium atoms were detected in 5% Sodium Hydroxide treated Bamboo fibers. Nitrogen atoms were detected in 1% Ammonium Hydroxide treated Bamboo fibers. Potassium and Manganese were detected in 0.5% Potassium Permanganate treated Bamboo fibers.

Table 2. Elements present in chemically treated and untreated bamboo fibers.

Elements	Untreated bamboo fibers		5% Sodium Hydroxide treated		1% Ammonium Hydroxide treated		0.5% Potassium Permanganate treated
	Weight %	Atomic %	Weight %	Atomic %	Weight %	Atomic %	Weight %	Atomic %
C	46.67	53.82	47.21	54.61	47.05	54.15	47.38	56.66
O	53.33	46.17	50.75	44.15	52.30	45.2	42.99	40.69
Na	-	-	2.04	1.24	-	-	-	-
N	-	-	-	-	0.65	0.65	-	-
K	-	-	-	-	-	-	0.64	0.24
Mn	-	-	-	-	-	-	8.99	2.41

Conclusions

The effect of alkali and Potassium Permanganate treatment on the mechanical, chemical properties of Bamboo fibers were studied and the following conclusions were drawn:

• The tensile strength was found to increase by 41.41% after treatment with Sodium Hydroxide, 22.02% after treatment with Ammonium Hydroxide, and 21.18% after treatment with Potassium Permanganate.

• Treatment with 0.5% Potassium Permanganate increased the density by 0.81% whereas the treatment with 5% Sodium Hydroxide increased the density by 3.27%.

• Treating fibers with 5% Sodium Hydroxide solution increased cellulose content by 22.64%, while treatment with 0.5% Potassium Permanganate solution resulted in a 14.08% increase. Sodium Hydroxide treatment reduced hemicellulose and lignin content by 35.98% and 7.55%, respectively, compared to untreated fibers, whereas Potassium Permanganate treatment reduced hemicellulose and lignin content by 26.09% and 3.42%, respectively.

• The degree of crystallinity was found to increase by 37.46% after treatment with Sodium Hydroxide, 27.46% after treatment with Ammonium Hydroxide, and 12.53% after treatment with Potassium Permanganate.

• Fourier Transform Infrared Spectroscopy revealed that the chemical treatments primarily affected the surface morphology of the Bamboo fibers, removing hemicellulose, lignin, and impurities without introducing new functional groups. This, in turn, influenced the tensile properties and crystallinity of the fibers.

Overall, the study demonstrates that specific chemical treatments, particularly using a 5% Sodium Hydroxide solution, can effectively enhance the tensile strength and structural properties of Bamboo fibers, making them potentially suitable for various applications that require high-strength natural fibers. These findings contribute to the understanding of how different chemical treatments can influence the properties of Bamboo fibers, offering valuable insights for the development of sustainable and high-performance Polymer composites. The future scope of work involves the fabrication of Bamboo fiber-reinforced composites to comprehensively evaluate their mechanical and thermal properties. This will include treating Bamboo fibers with chemicals such as Sodium Hydroxide, Ammonium Hydroxide, and Potassium Permanganate to understand their effects on the overall performance of the composites. Furthermore, the study can explore the potential enhancement of certain properties such as vibration damping or acoustic absorption by hybridizing Bamboo fiber reinforced composites with synthetic or natural fibers and varying the stacking sequence and fiber orientations based on their specific applications. The applications can include interiors of automobiles, interior panels of auditoriums or theaters, etc. A study can be conducted to determine the diffusion kinetics of chemical treatment on the fiber.

Highlights

• The physical and mechanical properties of alkali, Potassium Permanganate treated and untreated Bamboo fibers were investigated.

• Five percent Sodium Hydroxide-treated fibers showed the highest density of 1.26 g/cm³.

• Five percent Sodium Hydroxide treatment led to a 37.46% rise in the degree of crystallinity, indicating improved packing and alignment of cellulose chains within the fibers, contributing to enhanced mechanical properties.

• Sodium Hydroxide treatment, notably, proves to be a effective approach for enhancing the tensile strength and structural characteristics of bamboo fibers, making them suitable for reinforcement in polymer composites

Author contribution

Abhijit Kudva: Conceptualization, specimen preparation, experimentation, data analysis, and manuscript writing.

Mahesha GT: Supervision, review, editing, and proofreading.

Dayananda Pai: Ideation, supervision, analysis, editing, and proofreading.

Consent

All the authors have granted their approval for the publication of the article.

Ethical approval

The article follows the ethical guidelines provided by the journal.

Acknowledgments

The authors would like to express their sincere gratitude to Go Green Products, Chennai, India, for providing the bamboo fibers used in this research. The support and assistance from Vinayaka Agencies, Udupi, in procuring the necessary chemical solutions are greatly acknowledged. The authors also extend their appreciation to the staff and facilities of Manipal – Government of Karnataka Bioincubator, Advanced Research Centre, Manipal Academy of Higher Education, Manipal, for their assistance in conducting the single fiber tensile tests. The authors are thankful to the Central Instrumentation facility, Innovation Center, Manipal Academy of Higher Education, Manipal, for providing access to the X-ray Diffraction analysis equipment. Gratitude is also extended to the Department of Chemistry, Manipal Institute of Technology, Manipal, for their support in conducting the chemical composition analysis and Fourier Transform Infrared Spectroscopy. This research was made possible through the resources and facilities provided by the institutions mentioned above.

Disclosure statement

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

Data availability statement

The data used to support the findings of this study are included within the article.

Additional information

Funding

The authors reported there is no funding associated with the work featured in this article.