3.1. Physical properties of Oxytenanthera abyssinica
3.1.1. 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 three-year-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 significant 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 significant 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 findings from other bamboo species [29]. In the current study, the average moisture content is significantly 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 fibers 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].
3.1.2. 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 significant variation in basic densitybetween the top and middle as well as middle to bottom regions (P < 0.05). However, there was a significant 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 (704.033 kg/m3), middle (691.56 kg/m3), and bottom (563.06 kg/m3) 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].
Table 1
Basic density and moisture content of Oxytenantheraabyssinica
Location
|
Statically value
|
Mean basic
density (g/ml)
|
Mean moisture
content (%)
|
Top samples (TS)
|
N
|
6
|
6
|
x̄ ± STD
|
0.88 ± 0.30 a
|
8.73 ± 0.21a
|
95% CIL
|
0.15
|
8.20
|
95% CIU
|
1.65
|
9.26
|
Middle
samples (MS)
|
N
|
6
|
6
|
x̄ ± STD
|
0.64 ± 0.036b
|
9.40 ± 0.32b
|
95% CIL
|
0.56
|
8.61
|
95% CIU
|
0.74
|
10.2
|
Bottom
samples(BS)
|
N
|
6
|
6
|
x̄ ± STD
|
0.42 ± 0.06c
|
9.99 ± 0.21c
|
95% CIL
|
0.27
|
9.64
|
95% CIU
|
0.58
|
10.34
|
The average value
|
N
|
18
|
18
|
x̄ ± STD
|
0.66 ± 0.11b
|
9.37 ± 0.24
|
95% CIL
|
0.46
|
9.01
|
95% CIU
|
0.86
|
9.73
|
Where: STD: standard deviation, CI: confidence interval, N: number of sample, and x̄: 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 significantly different (P ≥ 0.05), with a confidence limit of 95%.
3.2. Fiber morphology of Oxytenanthera abyssinica
An optical microscope, scanning electron microscope, and 3D optical surface profiler microscope were used to examine the surface of Oxytenanthera abyssinica fiber and its cross-sectional area. Fig.s 3 represent the cross-sectional area of the Oxytenanthera abyssinica bamboo block and the surface of its fiber. 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 fibers beneath and surrounding vascular bundles in most cases. The sclerenchyma surrounding the first cycle of peripheral vascular bundles is not obstructed by interfascicular parenchyma. The Oxytenanthera abyssinica possesses the longest interwoven fiber 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 fiber'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, fiber diameter, and fiber length. These factors determine if Oxytenanthera abyssinica fiber is acceptable for paper and pulp manufacture. The fiber characteristics features of the stem section of the Oxytenanthera abyssinica fiber are shown in Table 2.
Table 2
Fiber dimensions (Top, middle and bottom) of Oxythenantera abyssinica
Position
|
Statically value
|
Fiber
length
(mm)
|
Fiber diameter
(µm)
|
Cell wall thickness µm)
|
Fiber lumen
diameter(µm)
|
Top
|
N
|
14
|
14
|
22
|
20
|
x̄ ± STD
|
2.23 ± 0.01a
|
18.66 ± 0.22a
|
2.51 ± 0.11a
|
14.28 ± 0.04a
|
95% CIL
|
1.91
|
16.87
|
1.86
|
12.71
|
95% CIU
|
2.54
|
20.45
|
3.16
|
15.79
|
Middle
|
N
|
14
|
14
|
20
|
22
|
x̄ ± STD
|
2.38 ± 0.02a
|
21.98 ± 0.01a
|
2.90 ± 1.21b
|
15.54 ± 0.01a
|
95% CIL
|
2.02
|
18.76
|
2.55
|
12.80
|
95% CIU
|
2.75
|
25.20
|
3.25
|
18.28
|
Bottom
|
N
|
14
|
14
|
20
|
20
|
x̄ ± STD
|
2.59 ± 0.25b
|
24.87 ± 0.03a
|
2.91 ± 0.24b
|
17.09 ± 0.03a
|
95% CIL
|
2.22
|
23.12
|
2.11
|
16.34
|
95% CIU
|
2.96
|
26.62
|
3.71
|
17.86
|
Average for a plant
|
N
|
42
|
42
|
62
|
62
|
x̄ ± STD
|
2.40 ± 0.64
|
21.83 ± 0.09
|
2.74 ± 0.03
|
15.63 ± 0.03
|
95% CIL
|
2.20
|
20.18
|
2.53
|
13.84
|
95% CIU
|
2.60
|
23.48
|
2.95
|
17.42
|
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 significantly different (P ≥ 0.05), with the confidence limit of 95%. where: STD: standard deviation, CIL: confidence interval lower, CIU: confidence interval upper, N: number, x̄: mean value
3.2.1. Fiber length
The fiber length is the number of binding sites available on fiber to create an interwoven network of fibers. It is calculated by measuring fiber from one end to the other [8]. In this study, fiber length of Oxytenanthera, abyssinica was measured, and the main result was recorded in Fig. 5. The result showed that the fiber 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 fiber length is classified as long fiber(> 1.5 mm).The fiber length of Oxytenanthera abyssinica is comparable with the length of European red pine (2.15 mm), coniferous tree fibers (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 significantly different (P < 0.05) fiber lengths. However, the length of the fibers in the top and middle parts is not significantly different (Table 2). The largest mean fiber 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 fiber 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 findings, the longest fiber was found near the bottom of the Bambusa vulgaris plant, while the shortest fiber was found at the top. However, according to Sharma et al. (2014) [38] and Aderounmu and Adelusi (2019) [39] finding, the axial section of the bamboo species, such as Bambusa vulgaris and Dendrocalamu sstrictus stems did not affect the length of the fibers. Differences in fiber lengths extracted from the axial section of Oxytenanthera abyssinica may be due to differences in internode lengths in different regions, asfiber lengthscorrelate with intermodal lengths [40].Because Oxytenanthera abyssinica has long fibers greater than 1.5 mm, it can build a stronger and larger network in the pulp than in short fibers, resulting in increased paper strength [41]. Oxytenanthera abyssinica possesses a higher fiber length when compared with a fast-growing grass called Arundo donax (fiber 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 fiber lengths are preferred. Long fibers produce a sheet structure that is more open and less uniform. The stronger the paper's resistance to tearing, the longer the fibers are. The paper industry prefers long fiber materials for their excellent product [8, 43].Thus Oxytenanthera abyssinica can be a good source for the pulp industry.
3.2.2. Fiber width
Figure 6 shows the fiber width of Oxytenanthera abyssinica fibers. A fiber's width or diameter is usually measured from one end to the other, usually measured across thefiber 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% confidence interval of 20.18–23.48. Between the top and bottom parts, there was a significant difference in fiber 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 finding is different from the work of Wahab et al. (2009) [29]. According to their result, the middle part of Bambusa vulgaris had a larger fiber diameter (18.6 ± 0.20) than the top (16.5 ± 0.15) and bottom (15.8 ± 0.13) parts. Oxytenanthera abyssinica has a wider fiber 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 officinerum (21.4 µm) (non-wood plant) have lower fiber diameters (19.00–20.00 µm) than Oxytenanthera abyssinica [47]. The fiber 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 fiber width) [48] and Caesalpinia decapetela (softwood plants with 18.63µm fiber width) [49]. This gives the idea that Oxytenanthera abyssinica also can be used as an excellent raw material for pulping.The increase in fiber 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 fiber.This is because paper made from fibers with a diameter of 20–40 µm frequently has high sheet density and surface properties [51]. According to the fiber diameters found in this work, the pulp will have few void spaces, resulting in fine-surfaced paper sheets with acceptable density [51, 38].
3.2.3. Cell wall thickness
Figure 7 shows the cell wall thickness of Oxytenanthera abyssinica fibers. 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% confidence 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 significant (P > 0.05) change in their value. However, the top and bottom (2.91 ± 0.24µm) sections had significant 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].
3.2.4. Fiber lumendiameter
Figure 8 shows the fiber lumen diameter of Oxytenanthera abyssinica fibers. For several fiber sample measurements, the fiber lumen width for Oxytenanthera abyssinica ranged from 6.40 to 37.79 µm, with a pooled mean width of 15.63 µm with 95% confidence limit of 13.84–17.42. The fiber 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 significantly different (p \(\le\)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 fiber lumen diameter in our study is larger than the fiber 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 fiber lumen diameter than other bamboo species, such as Dendrocalamus strictus (4.33 µm), Dendrocalamus latiflorus (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 fiber lumen width, the better the beating of pulp will be because liquids can permeate unoccupied holes in the fibers [8]. The width of the fiber lumen affects the beating of the pulp.The bigger the fiber lumen width, the better the beating of pulp will be because liquids can permeate unoccupied holes in the fibers. 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, fibers 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 fiber diameter of Oxytenanthera abyssinica were generally larger at the bottom and smaller at the top. This showed that changes in fiber 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 fibers in those areas are often superior to those at the top [57].
3.2.5. Fiber-derived of Oxytenanthera abyssinica
3.2.5.1. Runkel ratio
The Runkel ratio of wood fiber 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% confidence 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 significant difference (P \(\le\)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 fibers are often thin-walled and have greater strength properties, inter-fiber bonding, and greater conformability [60, 61]. The Runkle ratio of fibers from all portions of Oxytenanthera abyssinica's is less than 1, thus, it is satisfactory to recommend the plant for producing flexible pulp and paper with good mechanical properties [44, 62].
3.2.5.2. Flexibility ratios
The flexibility ratio indicates how easily fibers link and, as a result, how strong the tensile and bursting strength are generated [63]. Table 3 showed that Oxytenanthera abyssinica had an averageflexibility ratio value of 0.72 with 95% confidence interval of0.64-0.80. There was a significant variation in the flexibility ratio between the central and lower parts of Oxytenanthera abyssinica (P \(\le\)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 flexibility ratios of Oxytenanthera abyssinica fibers werebetween 0.50 to 0.75 in all portions of the plant; this showedthat the plant possesses elastic properties [43]. Elastic fibers commonly recommend for manufacturing packing papers [47, 64]. According to studies, the higher the fiber length-to-width ratio, the more flexible the fiber is and the more likely it is to produce a well-bonded paper [65].
3.2.5.3. Slenderness ratio
Table 3 showed that Oxytenanthera abyssinica had a Slenderness ratio mean value of 109.98 with 95% confidence interval of104.2-115.76.The difference in the slenderness ratio was significant (P 0.05) between the bottom (104.14±0.31), the middle (108.28±0.12), and the top (119.00 ±0.22) sections. The slenderness decreased from the top (119.00±0.22) to the bottom (104.14±0.31) along the culm.The fibers from all parts of Oxytenanthera abyssinica have a slenderness ratio greater than 70.This suggests that the fibers create high-quality sheets for packing and other applications [63].
Table 3
Fiber-derived (top, middle and bottom) part of Oxytenanthera abyssinica
Position
|
Statically value
|
Flexibility ratio
|
Slendernessratio
|
Runkelratio
|
Top
|
N
|
14
|
14
|
14
|
x̄ ± STD
|
0.76 ± 0.10a
|
119.0 ± 0.22a
|
0.35 ± 0.01a
|
95% CIL
|
0.66
|
104.96
|
0.32–0.38
|
95% CIU
|
0.86
|
133.04
|
|
Middle
|
N
|
14
|
14
|
14
|
x̄ ± STD
|
0.71 ± 0.10b
|
108.28 ± 0.12a
|
0.37 ± 0.01a
|
95% CIL
|
0.47
|
96.8
|
0.22
|
95% CIU
|
0.95
|
119.75
|
0.59
|
Bottom
|
N
|
14
|
14
|
14
|
x̄ ± STD
|
0.69 ± 0.10b
|
104.14 ± 0.31a
|
0.34 ± 0.01a
|
95% CIL
|
0.46
|
80.4
|
0.26
|
95% CIU
|
0.92
|
127.91
|
0.42
|
Mean
|
N
|
42
|
42
|
42
|
x̄ ± STD
|
0.72 ± 0.10
|
109.98 ± 0.21
|
0.35 ± 0.10
|
95% CIL
|
0.64
|
104.2
|
0.24
|
95% CIU
|
0.80
|
115.76
|
0.35
|
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 significantly different (P ≥ 0.05), with a confidence limit of 95%. Where: STD: standard deviation, CIL: confidence interval lower, CIU: confidence interval upper, N: number, x̄: mean value.
3.2.6. Comparison of fiber 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 fiber 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 fiber lumen width and a thin fiber wall. A thin fiber wall is desirable for high-quality, strong, well-formed paper. Moreover, the beating of pulp, which involves liquid penetration into gaps within the fiber, is positively influenced by large lumen size. Thus, fibers having a high Runkel ratio are less flexible, stiffer, and produce bulkier, low-bounded-area paper [67]. For the production of high-quality paper, long fiber lengths are preferred. Long fibers produce a sheet structure that is more drainable and less uniform. The flexibility, 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).
3.3. 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-year-old, and 1-year-old Oxytenanthera abyssinica samples differed significantly (P < 0.05). However, the average cellulose content of the 2 and 1-year-old bamboo samples did not differ significantly. 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 significantly (P\(\ge 0.05)\). However, the content of the 1 and 2-year-old and 1and 3-year-old bamboo samples differed significantly (P \(\le\)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 significant 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 efficient delignification 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 significant 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 confirmed 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].
Table 4
Chemical composition value of Oxytenanthera abyssinica at1, 2 and 3 year aged
Age of the
Plant
|
Statically
value
|
Cellu-
lose
|
Lig-
nin
|
Hemi
cellulose
|
Ash
|
Extractives
|
Solubility
|
Hot water
|
1% NaOH
|
Alcohol benzene
|
Cold water
|
3 year
|
N
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
x̄ ± STD
|
49.26 ± 0.13a
|
20.63 ± 0.120a
|
21.31 ± 0.15a
|
2.64 ± 0.11a
|
6.8 ± 0.15a
|
11.67 ± 0.15a
|
20.4 ± 0.15
|
4.51±
0.15a
|
9.56 ± 0.15a
|
95% CIL
|
47.39
|
18.73
|
16.06
|
2.09
|
5.18
|
9.25
|
16.89
|
1.02
|
3.30
|
95% CIU
|
51.13
|
22.52
|
26.55
|
3.19
|
8.41
|
14.08
|
23.90
|
7.99
|
15.82
|
2 year
|
N
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
x̄ ± STD
|
48.87 ± 0.21b
|
23.54 ± 0.33b
|
23.17 ± 0.11b
|
4.50 ± 0.17b
|
7.16 ± 0.153b
|
9.11±
0.93b
|
17.42±
1.03
|
4.40±
0.71a
|
9.49±
0.71a
|
95% CIL
|
44.21
|
21.21
|
20.03
|
3.78
|
6.28
|
5.92
|
11.33
|
2.46
|
6.48
|
95% CIU
|
53.53
|
25.87
|
26.30
|
5.23
|
8.03
|
12.30
|
23.50
|
6.34
|
12.50
|
1 year
|
N
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
x̄ ± STD
|
48.21 ± 0.12b
|
23.03 ± 0.24b
|
21.05 ± 0.22a
|
6.62 ± 0.15c
|
7.67 ± 0.153c
|
7.54±
0.76c
|
14.56±
1.42
|
4.21±
0.55a
|
9.01±
0.71a
|
95% CIL
|
44.17
|
19.00
|
17.43
|
1.68
|
3.89
|
1.86
|
10.19
|
4.14
|
7.07
|
95% CIU
|
52.25
|
27.00
|
24.66
|
11.57
|
11.44
|
13.21
|
18.92
|
4.27
|
10.32
|
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 significantly different (P ≥ 0.05), with a confidence limit of 95%.STD: standard deviation, CIL: confidence interval lower, CIU: confidence interval upper, N: number, x̄: 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.
3.4. Chemical composition comparison to the other bamboo species
The chemical composition of other bamboo species with the current study were compared in Table 5. The table showed that the cellulose content (49.26wt%) of three year age of Oxytenanthera abyssinica was higher than other bamboo species such as Dendrocalamus brandisii (47.24wt%)[74], Bambusa blumeana (40.3–45.1 wt%) [75], Bambusa tuldoides (35.2 wt%) [76, 45], Gigantochloa levis (33.8wt%) [76], Passiflora edulis (44.64%)[77] and Daphniphyllum oldhami (47.1 wt%) [66]. This showed that Oxytenanthera abyssinica has a great potential for pulp yield and papermaking properties than the mentioned bamboo species.
Table 5: Chemical composition of Oxytenanthera abyssinica to other bamboo species
Samples
|
Alpha cellulose
|
Holocellulose (wt %)
|
Lignin
(wt %)
|
Hemicellulose (wt %)
|
Cellulose (wt%)
|
Ash
(wt %)
|
Reference
|
Oxytenanthera abyssinica
|
48.8±
0.23
|
70.57± 0.28
|
20.63± 0.12
|
21.31±
0.15
|
49.26± 0.13
|
3.30± 0.11
|
This study
|
Phyllostachys heterocycla
|
__
|
|
26.1
|
__
|
49.1
|
1.3
|
[78]
|
Phyllostachys nigra
|
__
|
|
23.8
|
__
|
42.3
|
2.0
|
[78]
|
Phyllostachys reticulata
|
__
|
|
25.3
|
__
|
25.3
|
1.9
|
[78]
|
Bambus ablumeana
|
__
|
65.70
|
20.50
|
__
|
40.3
|
__
|
[75]
|
Bambus atuldoides
|
__
|
67.20
|
25.5
|
32.0
|
35.2
|
3.70
|
[76]
|
Dendrocalamus asper
|
48.60
|
68.25
|
25.27
|
__
|
__
|
2.13
|
[79]
|
Dendrocalamus brandisii
|
__
|
__
|
23.84
|
23.85
|
47.24
|
1.37
|
[74]
|
Dendrocalamus giganteus
|
46.88
|
65.96
|
23.85
|
__
|
__
|
3.70
|
[79]
|
Gigantochloa apus
|
47.56
|
63.23
|
22.41
|
__
|
__
|
6.09
|
[79]
|
Gigantochloa brang
|
51.18
|
79.94
|
24.83
|
__
|
51.58
|
1.25
|
[80]
|
Gigantochloabrang(outer part)
|
56.94
|
80.05
|
38.75
|
__
|
__
|
0.78
|
[81]
|
Gigantochloa levis
|
33.81
|
85.08
|
26.50
|
__
|
33.8
|
1.30
|
[77]
|
Gigantochloa levis
(outer part)
|
36.96
|
89.80
|
35.98
|
__
|
__
|
1.19
|
[81]
|
Gigantochloa robusta
|
44.36
|
56.81
|
23.86
|
__
|
__
|
1.66
|
[79]
|
Goniothalamus scortechinii
|
46.87
|
74.62
|
32.55
|
__
|
46.87
|
2.84
|
[80]
|
Goniothalamus scortechinii (outer part)
|
61.31
|
75.35
|
43.68
|
__
|
__
|
1.50
|
[81]
|
Melocanna baccifera
|
|
73.5
|
25.2
|
21.1
|
52.78
|
2.45
|
[82]
|
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 fiber-to-fiber 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 fibers [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 influence the chemical composition of lignocellulosic materials [88].