Proximate chemical analysis and effect of age and height of Oxytenanthera abyssinica on �ber morphology and chemical compositions for pulp and paper production potential

This study examined the chemical composition, �ber morphology, and physical properties of Oxytenanthera abyssinica culm to assess its pulping potential. TAPPT and Franklin's methods have been used for experiments. The statistical analysis showed that the chemical composition of Oxytenanthera abyssinica is in�uenced by the age of the plant.The amount of cellulose in the culm increases with age, while ash and extractive content decrease with an increase in age. Thethree-year agedaverage chemical content of the plant was 49.26 ± 0.13, 21.31 ± 0.15, and 20.63 ± 0.12 cellulose, hemicellulose, and lignin contents respectively. There is a signi�cant difference between one, two, and three-year-aged plants (P < 0.05) in cellulose, lignin, ash, and extractive content. The position of the culm also affectsthe �ber morphology of Oxytenanthera abyssinica. The �ber's length, diameter, cell wall thickness, and lumen diameter increase from top to bottom, whereas the �exibility and slenderness ratio decrease. The average �ber morphology of Oxytenanthera abyssinica was �exibility ratio (0.72 ± 0.10), Runkel ratio (0.35 ± 0.10), slenderness ratio (109.98 ± 0.21), lumen diameter (15.63 ± 0.03 µm), cell wall thickness (2.74 ± 0.03 µm), �ber length (2.40 ± 0.10 mm) and �ber diameter (21.83 ± 0.09 µm). The above data showed that the mean value of the �ber length of the plant is greater than 1.5mm, the Runkel ratio was less than 1, and the slenderness ratio was greater than 70 standard values. The result also showed that the average bulk density and the moisture content were 660 kg/m 3 and 9.6%, respectively. Although Oxytenanthera abyssinica is widely grown in the study area, no comprehensivestudies have been carried out on �ber morphology, chemical composition, and physical properties based on age and height. Thus, this research was carried out to study the plant's �ber characteristics to assess its suitability for pulp and paper production.Based on the above data, the three-year aged bottom part of Oxytenanthera abyssinica is recommended for moreyield of pulp and high-quality paper production than the �rst and second-year aged plant.


Introduction
Bamboo is one of the non-wood forest resources with signi cant potential as a substitute for wood resources due to its high productivity, rapid growth, and ease of reproduction [1].It grows rapidly in tropical and subtropical regions and is called "green gold" because of its diversity [2].Bamboo has received much ecological and economic attention in recent decades due to its rapid growth, compact inheritance, and superior mechanical strength compared to other plants [2,3].Around the world, more than 1,500 species of bamboo have been found in 90 genera, it covering 36 million hectares (ha) from latitudes 460 °N to 470 °S, 4000 meters above sea level [4].It occurs in many countries, such as South America (Colombia, Ecuador, and Peru), Central America (Honduras, Mexico, and Costa Rica,) and Asia [5].
In Africa, Ethiopia has the largest bamboo forest [6].Oxytenanthera abyssinica, a commercially and environmentally important bamboo species native to Ethiopia, accounts for around 85 percent of the country's total bamboo acreage [7,8].It covers around 850 000 hectares in the country's center, southwest, and south regions [8].Oxytenanthera abyssinica is a fast-growing, high-yielding renewable resource.It is lowcost, quick-growing, and widely available, and it has physical and mechanical qualities similar to wood [9].
Bamboo ber has been studied as a viable alternative pulp material in various places worldwide [10].Bamboo's productivity and rapid growth, as well as its good ber width (0.01-0.03 mm) and long bers (1-4 mm), can be used to make a wide variety of papers and paper products [11].Compared to other plants, bamboo has higher cellulose content; a study showed that one hectare of bamboo is estimated to contain 6-7 times higher cellulose content than those collected from deciduous or coniferous forests [12].The tear strength of bamboo pulp is comparable to that of pulp obtained from softwood [13].These properties have made bamboo ber widely accepted as an excellent and alternative raw material base for paper and pulp production [14].
The pulping and bleaching process of bamboo ber and the papermaking potential are directly affected by the chemical and physical properties of the raw material [15].The most important aspects determining the characteristics of paper and pulp production are the bamboo species' type, age, and origin [16].Using morphological characteristics of the bamboo species such as wall thickness, lumen width, ber diameter, ber length, and their derivative, such as exibility ratio, theRunkel ratio, as well as slenderness ratio, determine its suitability for pulp and paperproduction [12,17].Chemical composition is another critical factor in determining the suitability of paper and pulpproducts.
The content of the extractives directly affects the yield of pulp.Higher extractive concentrations reduce pulp yields.On the other hand, the concentrations of lignin, cellulose, and hemicelluloses are primarily involved in pulping behavior, and the bers' morphology affects the paper's strength [18].
The rising demand for wood and ber and the decreasing availability of wood supplies have prompted researchers to look for non-wood plants with ber properties similar to wood.As a result, nonwoody plants like bamboo could serve as an alternate source of pulp and papermaking raw materials.The use of nonwoody plants as a source of raw materials for the pulp and paper industries has its own contribution to reducing the greenhouse gas emissions that cause climate change [19].
In order to use bamboo for pulp and paper qualities, it is critical to understand how its chemical composition varies with age and height.The age and height position of the plant affect its properties.Bamboo's chemical composition differs depending on the height of the culm, environment, age of the plant, type of the species, and region in which the plant is found [16].However, Oxytenanthera abyssinica ber morphological variation based on age and chemical property differences caused by culm location have yet to be reported in the study area (western part of Ethiopia, pawi woreda).Hence, this study is conducted on a detailed analysis of the pulping potential of Oxytenanthera abyssinica based on its physical properties, chemical composition, and ber morphological characteristics.

The Study Area
Lowland Ethiopian bamboo (Oxytenanthera abyssinica), one to three year age stems, were taken from the west part of Ethiopia, Metekel zone in Pawe woreda (Fig. 1).It is located at an elevation of 1120 meters above sea level, with longitudes of 36° 20' to 36°32' and latitudes of 11°12 to 11°21'.It has a humid and hot climate, with temperatures ranging from 19.4°C to 37.6°C [20].

Sample collection, identi cation and use
According to TAPPI standards 2002 [21], twenty Oxytenanthera, abyssinica plants with an average age of three years, were randomly selected from a natural forest found near village 7 town, pawe woreda for ber characterization test.The plant's culms (9 meter) were cut above the second node, or around 30 cm, because cutting the culms below this height will slow the growth of the remaining culms.The culms were divided into three equal lengths, each measuring 3m, for the bottom, middle, and top segments to examine the culms' ber characteristics.
For proximate chemical analysis, age (1, 2 and 3 year), Oxytenanthera abyssinica were randomly identi ed and selected based on age.The culms of identi ed Oxytenanthera abyssinica were cut with axes, after removing the branches and top parts of the plant, the culms were rinsed repeatedly with water and then chopped into chips with a planer machine.The chips were dried in the sun for 2 weeks.The dried chips of Oxytenanthera abyssinica were crushed, and the mesh size of over 60 mesh and under 40 mesh size were collected and stored in polyethylene bottle for proximate chemical analysis.
The identi cation of the plant species was carried out by taxonomists at Addis Ababa University, College of Natural Sciences Department of Biology and Biodiversity Management and the use of plant parts in the present study comply with international, national, and/or institutional guidelines [22].A permission was received from the Pawe Woreda Agricultural and Rural Development O ce to harvest plant material.

Physical properties of Oxytenanthera abyssinica 2.4.1. Moisture content
Sample blocks representing the 3 years Oxytenanthera abyssinica, at the top, middle and bottom position with 6 replicates were used to measure moisture content.All sample blocks were cut from fresh culms with a wall thickness of 10 x10 mm x culms.They were weighed and dried in a 105°C oven for 48 hours until a consistent weight was achieved.Afterward, the sample blocks were placed in a desiccator for 30 minutes to cool down before being re-weighed.The samples were weighed using a digital scale with a 0.001 gm precision and oven-dried at 105 o C for 72 hours to achieve a constant weight value.The moisture content was determined using ASTM 5229 using Eq.(1) [23].

Moisture content = ……………….(1)
Where: GW = green weight (the weight of sample before drying); ODW = the weight of a sample after drying with oven (Oven dry weight)

Basic density
Sample blocks representing the 3 years Oxytenanthera abyssinica, at the top, middle and bottom position (3 cm each) with 6 replicates were used to measure moisture content (Fig. 2).After removing the outer part of the plant samples, the middle region of each internode was taken fromthe top, middle, and bottom culms segments for basic density tests.Six sample block was cut to a culms wall thickness of 30cm x 30cm

× 100%
GMoven−ODW ODW for each position.The sample blocks (18 samples) were oven-dried for 48 hours at 103°C until they attained a predetermined weight.The dry weight of the oven was calculated by measuring the weight of the sample block.The oven-dry weight and green volume were used to calculate density.The water displacement method was used to determine the green volume of the sample.Eq. ( 2) was used to compute basic density [23].
2.5.Fiber morphology of Oxytenanthera abyssinica TAPPT standards performed proximate chemical analysis were used: TAPPI T203 om 99 for alpha-cellulose content, TAPPI T211 om-93 for ash content, TAPPI T207 cm-99 for water solubility, TAPPI T222 om-02 for lignin content, TAPPI T212 om-98 for 1% NaOH solubility and TAPPT T204 cm-97 for alcohol-benzene solubility.The wise technique was used to analyze holocellulose.The cell lumen, cell wall thickness, ber breadth, and ber length were all measured after ber maceration using Franklin's method.Three derived values were also computed based on the ber dimensions such as slenderness ratio ( ber length ber diameter), exibility ratio [( ber lumendiameter ber diameter)⋅100], and Runkel ratio [(2 ⋅ ber cell wall thickness) berlumen diameter] [24,25].The ndings were then examined to see if Oxytenanthera abyssinica might be used to make pulp and paper.

Fiber dimensions measurement procedure
The width and length of the bers were examined using the following methods (Fig. 3).The maceration processwas performed using amatch-size sample and nitric acid (50%).For ber separation, matchstick-sized samples were placed in test tubes, and immersed in nitric acid solution, and kept at 70 o C for 5-6 hours.After cooling, the nitric acid was drained, and the bers were rinsed in distilled water before being separated on the Whatman grade 1 lter paper [26].A Motic BA210 microscope with a camera was used to take the images.

Cell dimension measurement
Slices with a thickness of 20m were cut with a Leica sliding microtome for cell measurement [27].To eliminate excess safranin solution, the slices were soaked for one minute in a safranin solution (1 gram/100 ml water) and alcohol concentrations of 25%, 50%, and 75%, respectively.Slices were submerged in xylene for 1 minute before being placed on a standard 7.5cm x 2.5cm slide.Finally, a small amount of Canada balsam was dropped and left to dry before applying the slide cover.The lumen diameters and cell wall thickness were measured using Motic software and an image was recorded with a camera attached to a Motic BA210 microscope (Fig. 3).

Scanning Electron Microscopy (SEM) Analysis
Scanning electron microscopy (high-vac.,SED PC-std, 15 kV) was used to obtain SEM images of extracted cellulose.ImageJ software analysis was used to examine the size image of the samples.

Statically analysis
Analysis of variance (one-way ANOVA), p-value, con dence limit (CI) and standard deviation (SD) on the results was performed using Origin 8 and Microsoft excels software.Measurements for cellulose, lignin, hemicelluloses, ash, extractives, solubility in alcohol, benzene, 1% NaOH, hot water, and cold water were performed three times (n = 3) for 1, 2, and 3 year age plants.For each sample, more than 14 readings were taken from the bottom, middle, and top positions of the plant to measure the ber morphology (Table 2 and Table 3).Six repetitions of each experiment were utilized to measure physical properties such as basic density and moisture content.We put the average result with standard deviations (SD) in the manuscript.A 95% con dence limit of Pvalue less than or equal to 0.05 was used to determine signi cance.Mean comparisons were performed using Tukey Test.

Moisture content
The species type, the age of the culm, the place of growth, the length of the culm, and the thickness of the culm wall all affect how much moisture is present in a particular bamboo species [28].This study measured the moisture contents at the top, middle, and bottom of a threeyear-old Oxytenanthera abyssinica bamboo species.The result showed that 9.37 ± 0.24 percent mean moisture contentwas observed.The proportion of moisture content decreased from the bottom to the top as the culm height of Oxytenanthera abyssinica increased.The top, medium, and bottom parts of Oxytenanthera abyssinica moisture content were 8.73 ± 0.21, 9.4 ± 0.32, and 9.99 ± 0.21 percent, respectively.There was no signi cant variation (p < 0.05) in moisture content between the top, middle, and bottom parts of the plant.This showed that the position of the culm does not show a signi cant effect on the content of moisture.The moisture content of the culm dropped as the height of the culm increased, which is consistent with previous ndings from other bamboo species [29].In the current study, the average moisture content is signi cantly lower than other bamboo species, such as Dendrocalamus asper, Bambusa vulgaris, Gigantochloa scortechini, and Schizostachyum grande.For instance, the moisture content of the top section of the above bamboo species was found to be 20.83,15.29, 16.09, and 23.36, respectively [30].This shows that, in comparison to the other bamboo species described above, Oxyrenanthera abyssinica has a higher potential for paper production.This is because moisture reduces the bonds between the bers formed in the papermaking process and reduces paper strength [31].According to studies, paper loses 50% of its strength when it has a moisture level of 14%, which may be achieved by conditioning the paper at 90% relative humidity [31].

Basic density
Table 1 shows the basic density of Oxytenanthera abyssinica's at different heights.The average basic density was 0.66 ± 0.114 kg/ml, which varies between 0.362 to 1.245 g/ml.The table showed that, unlike moisture content, the basic density increased from bottom to top with values of 0.88 ± 0.25, 0.64 ± 0.034, and 0.42 ± 0.06 g/ml, respectively.There was no signi cant variation in basic densitybetween the top and middle as well as middle to bottom regions (P < 0.05).However, there was a signi cant difference between the top and bottom portions (p < 0.05) (Table 1).Yushania alpine (Ethiopian highland bamboo species), recorded the basic density at the top (704.033kg/m 3 ), middle (691.56 kg/m 3 ), and bottom (563.06kg/m 3 ) parts [32].It has a lower basic density at the top position than Oxytenanthera abyssinica's.The current plant's basic density was lower in the center and bottom than Yushania alpina (Table 1), indicating that it has a higher pulping capability than highland bamboo.Because a low-density basic wood creates a paper with a lower beating resistance, high folding strengths, bursting, and sheet density [33,34].Where: STD: standard deviation, CI: con dence interval, N: number of sample, and x: mean value.All data were examined more than three times, and the mean value ± SD was used.Values in the same column with the identical alphabetical letter are not signi cantly different (P ≥ 0.05), with a con dence limit of 95%.

Fiber morphology of Oxytenanthera abyssinica
An optical microscope, scanning electron microscope, and 3D optical surface pro ler microscope were used to examine the surface of Oxytenanthera abyssinica ber and its cross-sectional area.Fig.s 3 represent the cross-sectional area of the Oxytenanthera abyssinica bamboo block and the surface of its ber.The cross-sectional structure of the bamboo culm is represented by many vascular bundles implanted in the scleral and parenchymal basal tissues (Fig. 4a).Parenchymalcells are characterized by thin walls and numerous simple holes that connect them.Pits can be seen mainly on the longitudinal walls.Sclerenchyma cells, on the other hand, have thick walls.Sclerenchyma produces bundles of bers beneath and surrounding vascular bundles in most cases.The sclerenchyma surrounding the rst cycle of peripheral vascular bundles is not obstructed by interfascicular parenchyma.The Oxytenanthera abyssinica possesses the longest interwoven ber bundle coupled with cementing-like material to give great strength, as shown by SEM and optical imaging in Fig. 4.
Fiber characteristics are one of the most critical variables in determining a ber's suitability as a pulp and paper raw material [35].Thus, the purpose of this study component was to provide basic information on the morphological characteristics of Oxytenanthera abyssinica for the potential of pulp.Lignocellulosic materials have cell wall thickness, lumen width, ber diameter, and ber length.These factors determine if Oxytenanthera abyssinica ber is acceptable for paper and pulp manufacture.The ber characteristics features of the stem section of the Oxytenanthera abyssinica ber are shown in Table 2.All data were examined in triplicate, and the mean value ± SD was used.Values in the same column with the identical English alphabetical letter are not signi cantly different (P ≥ 0.05), with the con dence limit of 95%.where: STD: standard deviation, CI L : con dence interval lower, CI U : con dence interval upper, N: number, x: mean value

Fiber length
The ber length is the number of binding sites available on ber to create an interwoven network of bers.It is calculated by measuring ber from one end to the other [8].In this study, ber length of Oxytenanthera, abyssinica was measured, and the main result was recorded in Fig. 5.The result showed that the ber length of Oxytenanthera abyssinica ranged from 1.32 to 3.55 mm, averaging 2.40 mm, with a 95% CI value of 2.20-2.60.Therefore, the expected ber length is classi ed as long ber(> 1.5 mm).The ber length of Oxytenanthera abyssinica is comparable with the length of European red pine (2.15 mm), coniferous tree bers (2.55 mm), jute (2.35 mm), kenaf (2.35 mm), and sisal (2.5 mm), [36,37].The top and bottom parts of Oxythenanteraa abyssinica have signi cantly different (P < 0.05) ber lengths.However, the length of the bers in the top and middle parts is not signi cantly different (Table 2).The largest mean ber length of Oxytenanthera abyssinica was found at the bottom of the plant, with a mean of 2.59 ± 0.25 mm, while the shortest (2.23 ± 0.01mm) was found at the top (Table 2).The plant`s ber length decreased as it climbed from the bottom to the top.This result was comparable to the work of Wahab et al. (2009) [29].
According to their ndings, the longest ber was found near the bottom of the Bambusa vulgaris plant, while the shortest ber was found at the top.However, according to Sharma et al. (2014) [38] and Aderounmu and Adelusi (2019) [39] nding, the axial section of the bamboo species, such as Bambusa vulgaris and Dendrocalamu sstrictus stems did not affect the length of the bers.Differences in ber lengths extracted from the axial section of Oxytenanthera abyssinica may be due to differences in internode lengths in different regions, as ber lengthscorrelate with intermodal lengths [40].Because Oxytenanthera abyssinica has long bers greater than 1.5 mm, it can build a stronger and larger network in the pulp than in short bers, resulting in increased paper strength [41].Oxytenanthera abyssinica possesses a higher ber length when compared with a fast-growing grass called Arundo donax ( ber length of 1.73 mm), which has been used as an excellent raw material for handmade paper production [42].For the production of paper, long ber lengths are preferred.Long bers produce a sheet structure that is more open and less uniform.The stronger the paper's resistance to tearing, the longer the bers are.The paper industry prefers long ber materials for their excellent product [8,43].Thus Oxytenanthera abyssinica can be a good source for the pulp industry.

Fiber width
Figure 6 shows the ber width of Oxytenanthera abyssinica bers.A ber's width or diameter is usually measured from one end to the other, usually measured across the ber length [8].The data showed that theaverage width was 21.83 µm with a range of 13.38 to 29.78 µm with a 95% con dence interval of 20.18-23.48.Between the top and bottom parts, there was a signi cant difference in ber diameter (p < 0.05).
Fiber diameter increased from the bottom (24.87 ± 0.03 µm) to the top (18.66 ± 0.22 µm) (Table 2).This nding is different from the work of Wahab et al. (2009) [29].According to their result, the middle part of Bambusa vulgaris had a larger ber diameter (18.6 ± 0.20) than the top (16.5 ± 0.15) and bottom (15.8 ± 0.13) parts.Oxytenanthera abyssinica has a wider ber diameter than other bamboo species, such as Bambusa vulgaris (14.8m) [44], Dendrocalamus gignteus (21.34 µm) [45], Gigantochioa apus (14.5 µm) [45], Melocanna baccifera (17.1 µm) [46].Eucalyptus grandis (wood plant) and Bagasse of Saccharum o cinerum (21.4 µm) (non-wood plant) have lower ber diameters (19.00-20.00µm) than Oxytenanthera abyssinica [47].The ber width of Oxytenanthera abyssinica (21.83 µm) is greater than that of two other plants that have been tested for pulp and paper properties such as Melia azedarach (hardwood plants with 13.45 µm ber width) [48] and Caesalpinia decapetela (softwood plants with 18.63µm ber width) [49].This gives the idea that Oxytenanthera abyssinica also can be used as an excellent raw material for pulping.The increase in ber diameter has been connected to the many chemical and physiological changes in cell walls during the growth processes and in the vascular cambium [50].The paper's sheet density and surface properties are affected by the diameter of the Oxytenanthera abyssinica ber.This is because paper made from bers with a diameter of 20-40 µm frequently has high sheet density and surface properties [51].According to the ber diameters found in this work, the pulp will have few void spaces, resulting in ne-surfaced paper sheets with acceptable density [51,38].

Cell wall thickness
Figure 7 shows the cell wall thickness of Oxytenanthera abyssinica bers.The cell wall thickness of Oxytenanthera abyssinica ranged from 1.12 to 5.255 µm, with a mean value of 2.74 µm and a 95% con dence interval of 2.53-2.95.The thickest cell walls were found at the bottom, while the thinnest were found at the top.The top (2.51 ± 0.11 µm) and middle (2.90 ± 1.21 µm) sections have no signi cant (P > 0.05) change in their value.However, the top and bottom (2.91 ± 0.24µm) sections had signi cant changes in cell wall thickness (P < 0.05) (Table 2).Oxytenanthera abyssinica cell wall thickness is comparable to some wood plant cell wall thickness.It was demonstrated that eucalyptus grandis and Ficus exasperate, had average cell wall thicknesses of 2.94 µm and 2.0-3.0 µm, respectively [47,52].The plant's cell wall thickness is, however, less than that of Rhizophora harrisonni (~ 8.8 µm) and Rhizophora racemosa (~ 9.0 µm) [53].Other bamboo species with thicker cell walls than the current plant, include Bambusa beecheyana (6.82 µm), Bambusa vulgaris (5.06 µm), Ochlandra travancorica (6.00 µm), and Dendrocalamusasper (5.69 µm) [54,10].Arundo donax, which has been utilized as an excellent raw material for producing handmade paper, has a cell wall thickness of 5.36 µm.In contrast, Oxytenanthera abyssinica has a smaller thickness of 2.74 µm [42].This demonstrated the plant's greater potential for producing pulp and paper.Plants having thinner cell wall help to make high-quality paper [55].

Fiber lumendiameter
Figure 8 shows the ber lumen diameter of Oxytenanthera abyssinica bers.For several ber sample measurements, the ber lumen width for Oxytenanthera abyssinica ranged from 6.40 to 37.79 µm, with a pooled mean width of 15.63 µm with 95% con dence limit of 13.84-17.42.The ber lumen diameters at the top (14.28 ± 0.04µm), middle (15.54 ± 0.01 µm), and bottom (17.09 ± 0.03µm) were all of them were signi cantly different (p 0.05).The sample with the greatest value was at the bottom, while the sample with the lowest value was at the top.The average ber lumen diameter in our study is larger than the ber lumen diameter of Bambusa vulgar as reported by Wahab et al. (2009) [29].However, the resulting value decreased from the top (2.6 ± 0.11) to the bottom (2.4 ± 0.15).Oxytenanthera abyssinica also possess a larger ber lumen diameter than other bamboo species, such as Dendrocalamus strictus (4.33 µm), Dendrocalamus lati orus (3.44 µm), Dendrocalamus giganteus (5.66 µm), Dendrocalamus asper (3.97 µm), Bambusa vulgaris (3.81 µm) and Bambus abeecheyana (3.55 µm) [10].This showed that Oxytenanthera abyssinica has a greater potential for pulping than the bamboo mentioned above species becausethe bigger the ber lumen width, the better the beating of pulp will be because liquids can permeate unoccupied holes in the bers [8].The width of the ber lumen affects the beating of the pulp.The bigger the ber lumen width, the better the beating of pulp will be because liquids can permeate unoccupied holes in the bers.The difference in lumen diametercould bedue to the increase in physiological development and cell sizeof the wood as the plant grows in girth [53].
Because the species studied in this work had a broader lumen and thinner walls than the above bamboo species, They will quickly collapse during the beating process to generate pulp with stronger elasticity, burst strength, compression, and tensile.During the beating process, bers with thinner walls and broader lumens collapse more quickly and form networks strongly with one another than those with thicker walls and narrower lumens beating process [56].Thewall thickness, lumen diameter, and ber diameter of Oxytenanthera abyssinica were generally larger at the bottom and smaller at the top.This showed that changes in ber characteristics along the bamboo culm are caused by maturity; the older the culm segment, the better its morphological traits.Because the internodes at the bottom and middle of the bamboo plant spread and develop more quickly than those at the top, the bers in those areas are often superior to those at the top [57].

Runkel ratio
The Runkel ratio of wood ber is one of the characteristics of wood that has been recognized as essential for pulp and paper properties [58].
Table 3 showed that Oxytenanthera abyssinica had an averageRunkel ratio value of 0.35 with 95% con dence interval of 0.24-0.35.The maximum Runkel ratio was found in the middle of the plant (0.37 ± 0.01), and the minimum was found in the bottom (0.34 ± 0.01).No signi cant difference (P 0.05) between the top, middle, and bottom regions.
A high pulp yield will be obtained if the Runkel ratio is less than one [59].Low Runkel ratio bers are often thin-walled and have greater strength properties, inter-ber bonding, and greater conformability [60,61].The Runkle ratio of bers from all portions of Oxytenanthera abyssinica's is less than 1, thus, it is satisfactory to recommend the plant for producing exible pulp and paper with good mechanical properties [44,62].

Flexibility ratios
The exibility ratio indicates how easily bers link and, as a result, how strong the tensile and bursting strength are generated [63].Table 3 showed that Oxytenanthera abyssinica had an average exibility ratio value of 0.72 with 95% con dence interval of0.64-0.80.There was a signi cant variation in the exibility ratio between the central and lower parts of Oxytenanthera abyssinica (P 0.05).The results also showed that it decreased from the top (0.76 ±0.1) to the bottom (0.69 ± 0.1) along the culm.The exibility ratios of Oxytenanthera abyssinica bers werebetween 0.50 to 0.75 in all portions of the plant; this showedthat the plant possesses elastic properties [43].Elastic bers commonly recommend for manufacturing packing papers [47,64].According to studies, the higher the ber length-to-width ratio, the more exible the ber is and the more likely it is to produce a well-bonded paper [65].All data were examined in triplicate, and the mean value ± SD was used.Values in the same column with the identical English alphabetical letter are not signi cantly different (P ≥ 0.05), with a con dence limit of 95%.Where: STD: standard deviation, CI L : con dence interval lower, CI U : con dence interval upper, N: number, x: mean value.

Comparison of ber characteristics with other bamboo species
In comparison to two well-known bamboo species such as green bamboo and Moso bamboo, Oxytenanthera abyssinica has a longer ber length (2.40 mm) and diameter (21.83 mm), as well as a smaller Runkel ratio (0.350) (Fig. 9)[66].However, the Runkel ratio of green bamboo and Moso bamboo were greater than one (> 1), with values of 2.96 and 4.53, respectively.This indicates that the papermaking potential of Oxytenanthera abyssinica is higher than the two bamboo species because a low Runkel ratio means larger ber lumen width and a thin ber wall.A thin ber wall is desirable for high-quality, strong, well-formed paper.Moreover, the beating of pulp, which involves liquid penetration into gaps within the ber, is positively in uenced by large lumen size.Thus, bers having a high Runkel ratio are less exible, stiffer, and produce bulkier, low-bounded-area paper [67].For the production of high-quality paper, long ber lengths are preferred.Long bers produce a sheet structure that is more drainable and less uniform.The exibility, tensile, and burst strength of paper are all improved by thin cell walls [67,68].This also indicates that Oxytenanthera abyssinica has a higher potential for papermaking properties than the other two bamboo species (Fig. 9).

Chemical Composition
The results of the proximate chemical analysis of Oxytenanthera abyssinica at 1, 2, and 3 years of age were reported in Table 4.The average cellulose, hemicelluloses, and lignin content in three-year-old Oxytenanthera abyssinica were 49.26 ± 0.13, 21.31 ± 0.15, and 20.63 ± 0.12, respectively.The percentage of cellulose content increase when the ages of Oxytenanthera abyssinica become older.Themean cellulose content at ages 1, 2, and 3 were 49.26 ± 0.13, 48.87 ± 0.15, and 48.21 ± 0.15, respectively.The mean cellulose content of the 3-year-old, 2-yearold, and 1-year-old Oxytenanthera abyssinica samples differed signi cantly (P < 0.05).However, the average cellulose content of the 2 and 1year-old bamboo samples did not differ signi cantly.The current studies have shown that the cellulose content of Oxytenanthera abyssinica is higher than that of all hardwoods and softwood plants [69].
The hemicellulose content of Oxytenanthera abyssinica in the ages of 1,2 and 3 years old are 21.31 ± 0.15, 23.17 ± 0.11, and 21.05 ± 0.22% respectively.The hemicellulose content of the 3-year-old and 2-year-old bamboo samples did not differ signi cantly (P .However, the content of the 1 and 2-year-old and 1and 3-year-old bamboo samples differed signi cantly (P 0.05).As can be seen in Table 3, the hemicellulose content was highest at 2 years old compared to Oxytenanthera abyssinica at ages 1 and 3.The hemicellulose content in the current study was lower than the softwood content [69].The average percentages of lignin content in Oxytenanthera abyssinica at ages 1, 2, and 3 are 20.63±0.12,23.54±0.33,and 23.03±0.24,respectively.There was a signi cant difference in lignin content between bamboo samples aged 3 and 2, and 3 and 1 years.Like hemicellulose, Oxytenanthera abyssinica has the highest lignin content at 2 years of age.The average percentages of extractives and ash content at ages 1, 2, and 3 are (6.8 ± 0.15, 7.16 ± 0.15 and 7.67 ± 0.15) and (2.645 ± 0.11, 4.505 ± 0.17 and 6.63 ± 0.153) in a respective manner.As the plant becomes older, the percentage of ash and extractive content decrease.
The content of cellulose, hemicelluloses, and lignin of the Oxytenanthera abyssinica is in the range of hardwood content.The content of lignin in the plant in this study showed a lower value than softwood and hardwood [69] when compared to wood; this showed a more e cient deligni cation under the same cooking conditions.This means that to achieve a suitable kappa value, Oxytenanthera abyssinica would require milder pulping conditions (lower chemical charges and temperatures) than hardwoods and softwoods, which could reduce chemical consumption and energy usage.
Three aged Oxytenanthera abyssinica bamboo species has got higher solubility in hot water(11.67± 0.15), cold water (9.56 ± 0.15), alcohol benzene (4.51 ± 0.15), and 1% NaOH solubility (20.4 ± 0.15) than two and one-year aged bamboo species.There was no signi cant difference (P > 0.05) in value of cold water and alcohol-benzene solubility between one, two and three year samples (Table 4).Oxytenanthera abyssinica has a greater alcohol-benzene solubility of 4.51 ± 0.153 than green bamboo (Dendrocalamopsis oldhami) species (3.3-3.9%)[66] which is used for pulp and paper-making.This indicated that Oxytenanthera abyssinica has a higher concentration of salts, low molecular weight carbohydrates, non-volatile hydrocarbons, phytosterols, resins, lipids, waxes, and other water-soluble substances than green bamboo.This information con rmed that the study plant has higher pulp and paper potential.Solubility in 1% NaOH solution of Oxytenanthera abyssinica was (20.4 ± 0.15).The value is higher than the other solubility such as cold water solubility (9.56 ± 0.15), hot water solubility (11.67 ± 0.15), and alcohol-benzene solubility (4.51 ± 0.15).Solubility in a 1 percent NaOH solution indicates the degree of fungal decay or degradation of wood. 1 percent NaOH solubility also indicates the degree of solubility of extractive chemicals, some lignin, and low molecular weight hemicellulose [70].All data were examined in triplicate, and the mean value ± standard deviationwas used.Values in the same column with the identical English alphabetical letter are not signi cantly different (P ≥ 0.05), with a con dence limit of 95%.STD: standard deviation, CI L : con dence interval lower, CI U : con dence interval upper, N: number, x: mean value.
The alpha-cellulose content of 3 year aged Oxytenanthera abyssinica was (48.8 ± 0.23) (Table 5).This value is higher than the value of seven Indonesian bamboo species studied by Maulana et al. (2020) [70].According to their study, the alpha-cellulose content of Ando bamboo and Ampel bamboo is less than 40%, and the alpha-cellulose content of Senbiran bamboo and Kunin bamboo is 40-45%.Begun bamboo, Hitam bamboo, and Tari bamboo have high alpha-cellulose content greater than 45%.This showed that Oxytenanthera abyssinica couldhave a higher potential for pulping and paper production than Indonesian bamboo species.Because α-cellulose has a positive effect on the pulp yield [71].Further research has been conducted to link the amount of cellulose to pulp yields.For instance, according to Dillner et al. (1970) [72], cellulose contents and kraft pulp yields of Eucalyptus globulus wood were closely connected and Wallis and coal.(1996)[73] demonstrated that eucalypt wood samples with a high cellulose content produced more pulp.

Chemical composition comparison to the other bamboo species
The chemical composition of other species with current study were compared in Many researchers have claimed that cellulose concentration and pulp production are directly related.Kiaei et al. (2014) [68] found a positive link between cellulose concentration and pulp quality.High cellulose concentration yields high pulp yield, according to Khoo and Peh. (1982) [83].The hemicelluloses content of Oxytenanthera abyssinica is higher than that of Dendrocalamus brandisii [74], Bambusa vulgaris [83], Phyllostachys edulis [77], and Daphniphyllum oldhami [83].This also explains why the plant has a higher potential for pulp yield than the plants mentioned above.The amount of hemicellulose has a positive relationship with pulp yield.Higher hemicellulose values, for example, lead to increased pulp yield and paper strength (mainly fold strength, burst, and tensile) [84].The current study's lignin content of Oxytenanthera abyssinica exhibited the lowest lignin content among the other ten bamboo species listed in table 10 except Bambusa blumeana.This provides information on how suitable the plant is for pulp and paper production because the amount of lignin negatively affects pulp yield [85,47]. Lignin causes ber-to-ber bonding to be delayed in the paper, and all of its properties have a negative impact on paper production; as a result, high-quality papers are made from lignin-free bers [86].Extractives from raw materials are undesirable because they can interfere with the pulping and bleaching processes.High extractive concentration, according to Ates et al. (2008) [50], will indicate low pulp production as well as increased chemical usage in pulping and bleaching [87].Different soil types, age and maturity levels, and raw material sources could explain the variances in cellulose, lignin, hemicelluloses, ash, and extractives reported in this bamboo species (Table 5).Genetics, age, location, growth conditions, anatomic structure, and plant maturity level also in uence the chemical composition of lignocellulosic materials [88].

Conclusion
In this study, we examined the chemical composition and ber characteristics of Oxytenanthera abyssinica to assess its compatibility for pulp and paper production.The result indicated that the average Runkel ratio was 0.350 (< 1) with 95% CI of 0.24 to 0.35, the slenderness ratio was 109.98 (> 70) with 95% CI of 104.2 to 115.76, and the ber length was 2.40 (> 1.5) with 95% CI of 2.20 to 2.60.The experimental data showed that the amount of cellulose in the culm increases and the amount of ash and extractive decreases as it becomes older (from 1 year to 3 years).However, the highest amount of lignin and hemicellulose content was found in two years, followed by 3 and 1 year.The three-year aged average chemical content of the plant was 49.26 ± 0.13 (95% CI of 47.39 to 51.13), 21.31 ± 0.15 (95% CI of 16.06-26.55),and 20.63 ± 0.12 (95% CI of 18.73 to 22.52) cellulose, hemicellulose, and lignin contents respectively.The bulk densities of Oxytenanthera abyssinica were 660 kg/m3, and its moisture content was 9.37%.Thus, the above data showed that Oxytenanthera abyssinica could have pulp and paper-making potential.The three-year-aged bottom part of the plant is more preferable to the middle and top part of one-year and two-year-aged Oxytenanthera abyssinica.The current study employed samples up to three years old; therefore, future research should focus on samples older than three years because a plant's characteristics rely on its age, culm height, environment (whether it is farmed or natural), type of soil it grows in, and the area in which it is found.The surface of Oxytenanthera abyssinica ber under an optical microscope (a and c), scanning electron microscope (b)    Fiber morphological comparison between Oxytenanthera abyssinica, green bamboo, Moso bamboo.Where L: ber length; D: ber diameter; W: cell wall thickness; l: ber lumen diameter; RR: Runkel ratio and FR: exibility ratio.

Figures Figure 1 A
Figures

Figure 2 Procedures
Figure 2

Figure 6 Fiber width of Oxytenanthera abyssinica Figure 7
Figure 6

Table 1
Basic density and moisture content of Oxytenantheraabyssinica

Table 2
Fiber dimensions (Top, middle and bottom) of Oxythenantera abyssinica

Table 3
Fiber-derived (top, middle and bottom) part of Oxytenanthera abyssinica

Table 4
Chemical composition value of Oxytenanthera abyssinica at1, 2 and 3 year aged

Table 5 :
Chemical composition of Oxytenanthera abyssinica to other bamboo species