Experimental study of Yushania alpina bamboo fiber

The characteristics of bamboo fiber depend on the source species. This study investigated the properties of Yushania alpina bamboo fibers extracted using mechanical, chemical, and combined methods. Samples from each extraction method were tested for tensile strength. Scanning electron microscopy was used to examine the morphology of the fibers. Fourier transform infrared was used to trace functional group changes. The absorption capacity of the fibers was also examined. The thermal properties of the fibers were investigated using thermogravimetric analysis. The chemical compositions of the fibers were studied using a gravimetric method. In contrast to mechanically and combinedly extracted bamboo fibers, chemically extracted fiber had up to 90.84% and 67.06% increments in tensile strength, respectively. Scanning electron microscopy revealed the removal of attachments on the surfaces of the fibers extracted chemically. The diameter of the fibers extracted chemically was reduced. Fourier transform infrared showed no change in functional groups among the extracted fibers. However, lignin content was reduced in chemically extracted fibers. The absorption capacity of the fibers was encouraging for use in composites. Thermal analysis showed improved thermal properties with the chemical method. Chemical analysis revealed reduced lignin and hemicellulose compositions in chemically extracted fibers. This study suggests bamboo fibers can be used in the construction industry for sustainability.


Introduction
The trend of future construction practices has to be in line with the interest in sustainability.It has been noted that the fulfillment of the needs of the present generation should not compromise the ability of future generations to meet their own needs [1].
On a planet with finite natural resources, the human population is growing from time to time, and therefore the rate of resource consumption, especially those finite natural resources per person, is growing.The current fiber-reinforced concrete construction utilizes intensive fibers obtained from steel, which are a product of finite resources at a faster rate than nature cannot replenish.This has an effect on the environment by creating landscape changes, high energy usage, and more significant carbon emissions.Optional fibers like synthetic fibers and glass fibers are also employed as optional sources of fiber.However, these also pose a threat to the environment as they are not degradable within a short time and negatively affect the atmosphere during their production processes [2][3][4][5][6].
Optional sources for fiber have been under investigation, specifically from sustainable sources called biofibers, whose sources are based on plants.These fibers are environmentally friendly not only during their source plant growth stage but also after their lifetime because they are biodegradable and contribute to the replenishment of soil nutrients [7].
Possible plants with biofibers that were under investigation were sisal, jute, kenaf, and bamboo.Bamboo has the highest fiber yield 3120 kg/ha [8].Fibers extracted from plants like jute and kenaf are finding good applications in substituting glass fibers in the automobile industry.However, employing fiber from only those plants has the potential for supply scarcity, which may result in the assurance of sustainability through the use of the natural resources in question.Due to the difficulty in obtaining free land, efforts to boost plant fiber output by extending cultivation of those plants have been put on hold.Even the cultivation of additional farmlands by removing the present land cover will have a permanent impact on the natural habitat.Here comes the role of bamboo because of its extended coverage that grows naturally, is found abundantly, and easily regrows once cut without changing lands [9].
The other appealing characteristic of bamboo is the context of preserving biodiversity, that is, its unique behavior that can be harvested several times in a growing cycle.On the other hand, the short-term requirement for reaching harvesting is also important.In this framework, bamboo comes into the picture because the complete recovery growth period of bamboo can be done within two to three years before utilization [9].
Owing to its fast growth, acceptable mechanical properties, rapid regeneration, and eco-friendly properties, bamboo fibers have been applied in numerous industries, ranging from pulp, paper, textiles, and parts of automotive through to construction [10,11].According to Roach [12], bamboo uses the least amount of energy to produce per equal unit of load-bearing capability, followed by timber, reinforced concrete, and steel.
Test results of tensile strength and elastic modulus of fibers obtained from different bamboo species gave results in the range of 140.1 MPa to 862 MPa and 17 GPa to 55 GPa, respectively.These variances are caused by the extraction procedure used to obtain the fiber as well as the intrinsic species variety [6,8,9,13,14].
Fiber from bamboo culms can be extracted using mechanical, chemical, and a combination of mechanical and chemical methods.There is no clear-cut advantage among different extraction methods.There are pros and cons to every fiber extraction technique.Their effects span from the quality of fiber that can be obtained to the costs of the selected type of extraction method [10,13,14].
Different studies ended up with mixed results on the tensile strength of fiber extracted from bamboo.Shah et al 's [15] study presented that the steam explosion method was the optimum way to extract fiber from bamboo.Phong et al [10] obtained bamboo fiber with the highest tensile strength when the mechanical method was employed for the extraction.On the other hand, the research results of Rawatan et al's [9] showed that bamboo fiber had a tensile strength increment due to the alakline treatment.Among the several bamboo fiber treatments, the alkaline treatment is the most basic and effective at increasing mechanical interlocking or bonding between the fiber and the matrix [16].This is accomplished by roughening the smooth outer surface and decreasing the fiber diameter, hence increasing the aspect ratio.Sodium hydroxide removes hemicelluloses, wax, lignin, oils, and other impurities attached to the plant fibers' outer surface and reacts with the hydroxyl group.Because of this, the water absorption capacity is also reduced.However, the alkaline treatment has to be within some percentage of concentration so that the fiber will not be degraded, and that will reduce the tensile strength [6,[15][16][17][18].
The effect of an alkaline environment on the composition of biofibers, which include hemicellulose, lignin, cellulose and impurities, is an important consideration in the study of natural fibers.Jing et al [19] showed the alterations of physical, chemical, and mechanical qualities of palm fiber due to the alkaline environment.Moreover, the study revealed that behavior of the fibers varies due to the interactions that occur in the alkaline environment.
The main chemical elements of bamboo fiber are cellulose, hemicellulose, and lignin, with various percentages of composition.Moreover, bamboo fiber has various kinds of sugars, fats, protein substances, and a small amount of ash elements [25,26].
The extraction method employed results in changes in plant fiber behavior.This is manifested through changes in absorption, tensile strength, morphology, and the removal or reduction of the chemical makeup of the fiber.Subash et al [13] studied and elaborated in detail on the impact of extraction methods on bamboo characteristics and also the methods of bamboo fiber extraction.
The alkali retting technique using NaOH in the extraction of fiber from bamboo gave long fibers of good quality without any damage.Accordingly, Ramprasad et al [27] pointed out that because of the alkali retting method, long fibers of good quality were extracted without any damage; hence, this process of extracting was recommended.
Around 67% of African bamboo forest coverage, which is 7% of the world's total, is available in Ethiopia.The species types of those bamboo are Yushania alpina (highland) bamboo and Oxytenanthera abyssinica (lowland) bamboo.These species are indigenous [28,29].
Therefore, these resources could be considered an optional, potentially environmentally friendly source to get fiber and utilize them to improve mechanical characteristics of concrete [5,30].
However, unlike bamboo species present in other nations, the influences of fiber extraction techniques on chemical composition, water absorption, tensile strength, morphology, thermal property and functional groups in the fiber obtained from indigenous species were not examined.Moreover, within species, no similarity is attributed to the specific location where the sample is collected.
Hence, to address those gaps, the extracted fibers using various methods were examined to investigate the chemical composition, tensile strength, absorption capacity, morphology, thermal property, and chemical functional groups.

Sample preparation
The bamboos utilized in this study were sourced from Ethiopia, specifically from Hagereselam town, located within the Sidama regional state, at an altitude of 2600 meters above mean sea level.These bamboos were determined to be three years old based on the extensive experience of the planters and by adhering to the guidelines outlined by researchers [28,31].The chemical type used for chemical and combined mechanical and chemical fiber extraction methods is NaOH in a 1 kg container with a small pallet shape.The bamboo preparation process for the extraction is presented in figure 1.
Once the bamboo is sliced to 2 mm to 3 mm thick, the extraction process is continued to get the fibers from five approaches.
• The first way was to immerse the sliced bamboo in pure water for five days, then was beaten and combed, which is identified as a mechanical method.The extracted fibers were exposed to sun drying for three days and then further put in an oven for three hours at 60 °C.
• The second approach was that the portion of the fiber obtained from the first approach was further exposed to a 4% NaOH solution for 12 h, which is called the combined method.Once the fibers are extracted, they are exposed to the sun for three days and then put in an oven for three hours at 60 °C.
• In the third, fourth, and fifth methods, the slices of bamboo were immersed for three days in a NaOH solution with 3%, 6%, and 9% concentrations, respectively.After the duration of retting, the slices of bamboo were continuously washed and beaten with a hammer.The loosened bamboo was combed to obtain the fibers.These are categorized as chemical methods.The extracted fibers were exposed to the sun for drying for three days and then put in an oven for three hours at 60 °C.
The samples from both the chemical and combination techniques were rinsed with continuously flowing water for one hour and tested with a PH meter to ensure that the sodium hydroxide was substantially eliminated.

Chemical analysis
The chemical compositions of the dried bamboo fibers were determined by chopping them into very small pieces.The gravimetric methods proposed by Ayeni et al [32] were used for the determination of cellulose, hemicellulos and lignin content in the fibers.

Moisture content and absorption
The moisture content was determined based on a sample in the order of 1 gram obtained after being sun-dried for three days.The samples from each extraction process were placed in a 60 °C oven for 5 h before being weighed.The samples are then returned to the oven for an additional 1 h at 60 °C to verify the weight variation.This procedure was done until two consecutive oven-dried weights came closer to zero.The absorption capacity was determined based on the weight of the oven-dried fiber and the weight of the fiber after immersion for 24 h.The percentage of the moisture capacity is the ratio of the difference between the sun-dried weight and the ovendried weight to the oven-dried weight.The absorption capacity is the ratio of the difference between the immersed weight and the oven-dried weight to the oven-dried weight [33,34].

Tensile testing
The tensile testing was done using a TEXTECHNO STATIMAT ME+ machine with a load cell of 100 N and a loading rate of 1 mm per minute [7,35].The gage length was fixed to 25 mm as per ASTMC 1557.The crosssectional area is computed once the density is known [36,37].
The fiber cross-sectional area used to obtain tensile strength is calculated using the density, length, and mass relationship.For this purpose, the length and mass of each fiber were measured using a ruler and balance, respectively.The density was measured using a density measurement apparatus.All these measurements and experiments were conducted at room temperature within the laboratory.
The value of the density of M (mechanically extracted fiber) is 0.8 g /c .c., MC (fibers extracted using the combined method) is 0.9 g /c .c., C3 (fibers extracted using the chemical method of 3% NaOH) is 1 g /c .c., C6 (fibers extracted using the chemical method of 6% NaOH) is 1 g /c .c., and C9 (fibers extracted using the chemical method of 9% NaOH) is 1 g/c.c.The reasons for the increment in density of fiber extracted using chemical techniques are the internal structure rearrangement of the fiber, the reduction of materials with less density, and the effect on pores due to the alkaline solution effect [38][39][40].
From each extraction technique, 15 fibers were picked, and tensile testing was conducted on 75 fiber samples.The tensile strength of each tested fiber was computed based on the values obtained from the readings of the tensile testing machine, balance, ruler, and density apparatus.The tensile stress data has to be checked for confidence that the outliers are excluded in the subsequent data analysis.The IQR (interquartile range) criterion is used to identify and then reduce outliers.After the data is ordered in descending order, the five parameters will be taken.These are the lowest values (Dl), the median of the whole data (M), the median of the lower half data below the median (Q1), the median of the upper half data above the median (Q2), and the highest value (Du).The data within Q1-1.5 * IQR to Q2+1.5 * IQR are used for the data analysis where IQR = Q2-Q1 [41,42].Because no data was identified as an outlier, all of the recorded data were used for the subsequent mean tensile computation.
An analysis of variance (ANOVA) was performed to determine if the methods of extraction employed had caused significant tensile strength variation among the bamboo fibers.Tukey's standardized test was also conducted at a 95% probability level to identify which method of extraction was significant.

Fourier transform infrared (FTIR)
Fourier transform infrared (FTIR) spectroscopy relies on the absorbance or transmittance of infrared light.When a sample is exposed to IR radiation, some of the radiation is absorbed by the sample and some is transmitted.The resulting spectrum represents the molecular absorption or transmission, creating a unique molecular pattern in the sample.It helps in identifying key components of the fiber and provides information on fiber quality and chemical changes due to processing or treatments.Accordingly, the FTIR spectra of bamboo fibers extracted through the prescribed methods were obtained from a thermo-scientific IS50 ABX spectrometer of German origin within the range of 4000-400 cm −1 , with a resolution of 16 cm −1 and 32 scans.The FTIR used was attenuated total reflectance (ATR) which does not require complex sample preparation.

Thermogravimetric analysis (TGA)
The thermal stability of the extracted bamboo fibers was examined by thermogravimetric analyzer (Model HCT-1) with the temperature ranging from 25 °C to 800 °C at a rate of 20 °C per minute in an air atmosphere.

Scanning electron microscope (SEM)
SEM is an instrument that uses electrons for image formation to study the surface morphology, structure, and composition of materials.Through high-resolution imaging, it is possible to view factors such as size, surface roughness, and the presence of contaminants or flaws.In this experiment, the bamboo fibers obtained through those techniques were further examined to know about their morphology using a scanning electron microscope (SEM).A Joel scanning electron microscope, model JCM 6000 PLUS at X1000, was used to study fiber surface morphologies.Before examination, the fiber samples were sputter-coated with a thin layer of gold in a vacuum chamber.The sputter-coating conductive material avoids the accumulation of electrons on the surface of the fiber, resulting in better image formation.

Chemical analysis of bamboo fibers
As presented in table 1, chemical compositions of bamboo fibers extracted by mechanical, chemical, and combined techniques have shown different proportions.Because of the reduction of lignin and hemicellulose, the percentage of cellulose showed an increase in the case of fibers extracted chemically.Therefore, chemical composition of bamboo fiber varied according to the extraction method.Chemical compositions of natural fibers were influenced by factors such as fiber sources, locality in which it grows, extraction process and maturity [43].
The chemical composition study revealed that fibers exposed to an alkaline environment during the extraction process had less lignin and hemicellulose content.Similarly, Martijanti et al [26] conducted a chemical composition study on the fibers of the Gigantochloa apus and Bambusa tuldoides bamboo species.Due to the use of a NaOH solution for fiber extraction, hemicellulose and lignin showed a reduction, while cellulose showed an increment.The hemicellulose, lignin, and cellulose contents of those species were in the range of 16.21%-19.15%,16.93%-21.30%,and 46.91%-55.68%,respectively.
The mechanical properties of bamboo fiber have a relationship with the composition of hemicellulose, cellulose, and lignin content.Studies showed that, due to a reduction in lignin content, there was an increase in tensile strength [44].

Tensile strength of bamboo fibers
The mean tensile strengths of the samples in each category of extraction methods are presented in table 2. The number in the parentheses denotes the standard deviation.Such deviations were common behaviors observed in fibers extracted from plant sources [10,45].Unlike factory products, this is due to the non-uniformity among fibers attributed to the extraction process and the intrinsic fiber variation within the plant.
The mean tensile strength value of bamboo fiber extracted using the mechanical technique (M) is 205.5 MPa, and there is a slight improvement when the combined method (MC) is employed for the extraction.The tensile strengths of bamboo fibers extracted chemically are higher than those produced by other methods.
The tensile strength of fibers recovered by retting in a 6% NaOH solution rose by 90.84% when compared to mechanical methods.In comparison to the mechanical approach, retting in the 9% NaOH solution increases the tensile strength of the bamboo fiber by 88.72%.The tensile strength of the bamboo fiber obtained by retting in the 3% NaOH solution increased by 87.77% in comparison with the result attained from the mechanical method.
The tensile strength of the bamboo fibers extracted by the combined method is greater by 14.23% than the mechanical method.The combined method produced fibers with less tensile strength than the chemical method.
In comparison to the mechanical approach, the diameter of bamboo fibers obtained by retting in 3% NaOH, 6% NaOH, and 9% NaOH was reduced by 31.81%,39.89%, and 38.52%, respectively.These agree with the recommendation that the use of a higher alkaline concentration for extraction can reduce the diameter of the fiber.This is because the alkaline environment washed away waxes and other impurities attached to the fibers.On the other hand, the obtained tensile strength of the bamboo fiber was found in the high-performance natural fibers range [45].
The ANOVA analysis showed a statistically significant (p < 0.05) increase in the tensile strength of bamboo fiber when the chemical method was used.Tukey's standardized test revealed that there are no statistically significant variations among the tensile strengths obtained using the chemical method.However, this test proved that the use of a 6% NaOH solution for extracting bamboo fiber has a significant effect on the tensile strength in comparison with the mechanical method.As shown in table 3, the absorption capacity is on the decline when retting in a solution of NaOH is used to get the fibers.This is because the reduction of impurities and other hydrophilic constituents in the fiber when exposed to alkaline environment during the extraction process [20,21,24].
The experiment demonstrated that the diameter of the bamboo fibers obtained by the chemical method was reduced.This implies an increase in surface area, as a result of which more moisture will be lost as vapor to the atmosphere when exposed to the sun for drying.The other important parameter to consider when applying it to the concrete is its absorption capacity because this will affect the mix design process.The fibers obtained from the chemical extraction method showed a lesser absorption capacity.The values obtained in this experimental study are comparable with previous findings, and the result is encouraging for use in composite applications [46].

Fourier transform infrared (FTIR) analysis of bamboo fibers
The FTIR spectra of bamboo fibers extracted using the employed techniques are presented in figure 2 below.
In FTIR analysis, the appearance, disappearance, and reduction of peak values at various wave numbers are used to trace changes among the samples collected.Accordingly, the conducted FTIR experiment reveals that fibers obtained from the species Yushania alpina contain free hydroxyl alcohol, which is an O-H stretching bond functional group whose peak value fell in the range of 3300 cm −1 to 4000 cm −1 like other species.However, unlike other species, the studied samples did not show additional peaks within the range [47] as shown in table 4.
The other peak value was observed at 1729.49cm −1 on fiber obtained by mechanical method or retting in pure water, and this peak disappears on other extraction methods.The disappearance of peaks at this value is attributed to the NaOH solution used for the extraction.The absence of a peak at this value is due to the removal of hemicellulose, which is the carbonyl group [49].The other range where the peak is within 1640cm −1 to 1680cm −1 is C=C alkenes, the indicator range for lignin.In this experiment, there is a peak at 1640.07 cm −1 in the case of fiber obtained from the pure mechanical method, which shows a reduction in fibers extracted using the combined method and the chemical method [50].This indicates the reduction of lignin due to the fiber exposed to the NaOH solution.The reduction of lignin contributes to an increment in the tensile strength, as suggested by scholars [51].Generally, there was a resemblance among the FTIR spectra of all the samples due to the absence of new functional groups [52].

Thermal analysis of bamboo fibers
The thermal degradation behaviors of the bamboo fibers were examined using TGA and presented in figure 3. The thermal degradation phase comprises moisture loss, hemicellulose degradation, cellulose degradation, and lignin degradation.
The first phase of weight loss was observed within the range from 25 °C up to 180 °C, associated with the evaporation of water in the fibers.Then the degradation of cellulosic chemicals followed; that happened from 200 °C to 550 °C.The degradation of hemicellulose ended around 400 °C.Lignin degradation started at a temperature less than 200 °C and extended to a wide range up to the end temperature, which contributed to the acceleration of the reaction of hemicellulose and cellulose [53,54].The third degradation, which is cellulose, ended around 500 °C.The last phase of degradation was lignin.
As shown in the graph, there was shifting towards the right when the bamboo fibers were exposed to the solution of sodium hydroxide associated with the method of extraction.Because of this, the bamboo fibers extracted by the combined and chemical methods showed better thermal properties than those obtained mechanically [54].Referring to figure 4(a), the fiber obtained using the physical or mechanical extraction technique has an accumulation of soft tissue, which is due to the attachment of wax and impurities [48].On the other hand, fibers obtained by passing through the combined method have impurities attached to the surface of the fiber, as shown in figure 4(b).As shown in figure 4(c), residuals of impurities are observed on the bamboo fiber extracted using the chemical method when retting in a solution of 3% NaOH concentration is used.Fibers obtained by the chemical method with retting in 6% NaOH concentrations showed a nearly clean and rough surface, as shown in figure 4(d).Figure 4(e) shows fibers obtained by the chemical method with retting in a 9% concentrated solution of NaOH.These fibers were found to have a rough surface, and holes appeared, which agrees with previous research outputs [55][56][57][58].The surfaces of the fibers obtained using chemical extraction became clean.Removal  of impurities and the appearance of some roughness on bamboo fibers obtained through the chemical method is good for utilization in composites because there will be better adhesion with the matrix [52].

Conclusions
This study dealt with the effect of extraction techniques on the various properties of the fiber obtained from Yushania alpina available in Ethiopia, Sidama Regional State, and around Hagere Selam Town.
The following findings are drawn from the study: • The chemical method of extraction gave tensile strength improvement by more than 90% than that of the mechanical method.The mechanical method, combined method, and chemical method gave the tensile strength of bamboo fiber in ascending order.
• The diameter of the fibers obtained through the chemical method was less than that obtained through the mechanical method.
• The chemical extraction process by itself can be considered one way to find treated bamboo fiber to get better properties, which is important for its subsequent application in composite.The absorption capacity was in the range of the other species studied, and the result is encouraging for utilization in composites.
• The FTIR study proved that there was no new functional group created because of the chemical NaOH used for the extraction of the fiber.On the other hand, impurities, waxes, and lignin are removed.Removal of these substances enhances the bond in the application of composites.The reduction of lignin in fibers extracted by applying chemical methods contributed to an increase in tensile strength.
• Bamboo fibers obtained using the chemical method of extraction showed reduced lignin and hemicellulose and increased cellulose in their composition.
• The mass loss attained in the case of mechanically extracted fibers was higher than the other methods at the specified range of temperatures, and the graph was dragged in the left direction.This implies that chemical and combined methods of bamboo fiber extraction showed improved thermal properties.
• The morphology of the bamboo fiber was found to be roughened as the concentration of NaOH used increased for its extraction.However, excess concentration affects the fiber.When using a NaOH concentration of 9% for the extraction, the surface became rougher and holes appeared.
• The tensile strength of this bamboo fiber was found in the high-performance natural fiber range.
The chemical method of extraction gave the bamboo fiber a higher mean tensile strength, improved thermal property, and better morphology, which have encouraging implications for application in composites.Therefore, bamboo fiber will play a great role in achieving sustainable construction.Moreover, this is very helpful for countries to exploit their bamboo resources for composite construction by reducing their dependence on imported, environmentally unfriendly fibers.

Figure 2 .
Figure 2. Fourier transform infrared spectroscopy analysis of bamboo fibers.

Table 2 .
Tensile properties of Bamboo Fiber obtained by different extraction methods.

Table 1 .
Bamboo fibers main chemical constituents.Moisture content and absorption capacity of bamboo fibers The moisture content and absorption capacity of the bamboo fibers obtained by passing through the techniques employed are shown in table3.

Table 3 .
Moisture content and absorption capacity.
3.6.Scanning electron microscope (SEM) analysis of bamboo fibersThe morphology of the bamboo fibers was examined using the scanning electron microscope (SEM), and the obtained image is shown below in figure 4.

Table 4 .
Characterization spectral analysis of bamboo fiber.