Pulp and Papermaking Characteristics of South Sudanese Cordia Africana (Gambil) Wood

Objective The wood of an important indigenous Sudanese hardwood species, Cordia africana lam, was examined to determine its suitability for pulp and papermaking. Basic density, bark-to-wood ratio, ber dimensions and chemical composition were studied. Results Pulps were evaluated and papermaking characteristics were tested. C. africana wood showed medium basic density (410 kg m -1 ). The average bark-to wood ratio by mass (6.82%) and volume (11.67%) were in the normal average for pulpwood and could be used for production of high grade pulp. The bers of C. africana were long with an average ber length of 1.13 mm, average ber diameter was 30 µm with an average lumen diameter 20 µm and cell wall thickness of 5 µm. the wood showed high ash content (2.7%), high pentosans (25%), relatively medium lignin content (23.9%).C. africana pulped with 12-15% alkali charge as Na 2 O for two hours at 170 0 C gave good Kappa numbers with normal and relatively high yield with very low rejects. The addition of 0.13% anthraquinone (AQ) in cooking liquor reduced the active alkali consumption by 2-2.3%, increased the pulp yield and reduced bleachable Kappa numbers. The pulp produced suitable for wrapping paper and paperboard.

The wood of Cordia africana is utilized for timber production, farm equipment, household utensils and fuel [12][13][14][15][16], and also used in construction and manufacturing of toys [16] Amhara tribes in Ethiopia use this tree in rituals of orthodox religion [17].
Although Sudan was politically divided into two countries in 2011, the social scienti c relations still continuing, the border between the two countries open with more or less similar environmental, ecological conditions and plant tree composition [18 and 19].
South Sudan is largely dependent on the imports of paper products. The demand for these products have grown rapidly with continuous development. Pulp can be produced in many different yields depending on the suitability of the raw material and pulping conditions. Wood as raw material for pulp and papermaking has offered precious services to man and decisively contributed to development [20]. Sudan and South Sudan is rich in different hardwood species many of which could be a good source of pulp production [21]. The study of such wood species is important to determine their suitability for pulp production. Among the important indigenous Sudanese hardwood species is Cordia Africana. The species is naturally distributed in western Darfur (Jebel Marra), Blue Nile and southern Kordofan, and in South Sudan (Equatoria, Upper Nile and Bahr el Ghazal).
This study aimed to investigate the pulping and paper properties of Cordia. Africana stem with reference to ber dimensions and chemical composition.
Main Text Five C. Africana trees with average age six years, were randomly selected according to TAPPI standards 2002 [22], from Jelhag natural forest (Upper Nile state, South Sudan). The trees were felled and branches were removed, transported to Khartoum capital of Sudan by bus, stored in National Centre for Research NCR). Leaves, owers fruits and seeds were collected for identi cation with taxonomists of Medicinal and Aromatic Plants Research Institute National Center for Research, Sudan [18].
Five logs of 100 cm long were exposed to air dry under sun, prepared according to TAPPI standard (T 257-cm-02 [22], chipped with hands and packed in plastic bags for further analysis. The average basic density was determined using wood specimens according to the British standards [23]. Wood bers were macerated using a mixture of 30% hydrogen peroxide and acetic acid (1:1). Fiber dimensions were determined microscopically at X100 and X 300 magni cations according to (TAPPI-232cm-01) after staining with aqueous safranin [24]. Standard deviation and arithmetical mean were used to determine ber properties Morphological indices. The heat value of C. Africana wood was carried out using a Krocher oxygen bomb calorimeter [25].
After negotiations and suggestions with other coauthors the pulping conditions and cooking parameters were decided according to physical properties Cordia africana wood and mainly on its chemical components. The Soda and soda-anthraquinone conditions were 12-15% as Na 2 O on oven dry weight of wood, the maximum temperature was kept constant at 170 0 C. Time to maximum temperature was 60 minutes for all cooking trials, the time at maximum temperature was 120 minutes kept constant for all trials under study. tearing resistance (TAPPI-414 om-98), and Tensile (TAPP-404-cm-92).Hand sheets were prepared using a rapid-Kothen sheet forming machine and tested using TAPPI standards.
Physical properties of C. africana wood were shown in (Table 1 supplementary materials). The average basic density was (410kg m -1 ) and bark-to-wood ratio were in the medium range for tropical hardwoods [28]. This will not cause wear on chipper knives in pulp mills with normal liquor-to wood ratio (usually 4:1), impregnation will be easy as yield of pulp per unit volume is related to basic density. The heat value was 18187 K j Kg -1 indicating their suitability in coal rewood production and indicated a high lignocellulosic materials could be expected.
The ber length for C. Africana (1.31 mm) as presented in Table 1 was considered as medium bred species, therefore it does not need to be mixed with other long bered wood pulp to obtain good paper properties very good tear resistance could be expected from this raw material. The comparatively wide lumen and ber diameter indicated that to collapse easily and produce good surface contact between adjacent bers of C. africana, this supported further with morphological indices ( Table 1).
The chemical constituents of C. africana wood were re ected in Table 2, the inorganic components (ash and silica) were high (5.84% and 2.65% respectively) may cause an increase in alkali consumption and negatively affect the black liquor recovery. The average cellulose content (48.7%) was in normal range for tropical hardwoods and good pulp yields could be expected from C. Africana wood, it is well known that Kurschner-Hoffer cellulose gave less percentage when compared to alpha cellulose thus may results of high yield of this raw material if appropriate cooking conditions used. The lignin content was medium (23.9%) which indicated normal deligni cation of wood chips. However 1% NaOH soluble (20.2%) re ected normal cooking parameters should be applied.
The cooking conditions and yield for C. africana wood were given in Table 3. At same pulping conditions C. africana chips have shown lower screened yield (41.5 and 44.7%) when cooked with soda process, whereas the screened yield was increased with addition of 0.13% AQ to 47.7% and 53.6%. The bleachable pulps resulted when soda-AQ cooking were used [29][30][31][32]. These results indicated clearly the superiority of soda cooking when anthraquinone applied as catalyst, thus improve yield, and reduce rejects with bleachable Kappa numbers although the initial ISO brightness more or less similar during soda pulping with or without anthraquinone.
The unbleached pulps evaluation was given in (Table 2 supplementary materials), indicated that when hand sheets of C. africana tested at both 25 and 40 0 SR gave high tensile index, tear index, burst index and folding endurance ( Figure 1 and 2 supplementary materials), all the mechanical strength properties were increasing with increase of beating degree showed that still bers were strong enough even at high degrees of beating and pulps of this raw material can be used for wrapping paper and paperboard.

Limitations
Based on physical and morphological properties, the wood of Cordia Africana could be considered as medium range pulpwood. The use of soda-AQ pulping process for C. africana wood has accelerated deligni cation and beating rate, decreased the alkali consumption and increased yield.
The nal products of pulping with this raw material is strong enough for wrapping paper and paperboard.
Cordia africana tree is hard wood distributed in both Sudan and South Sudan, it is grown naturally, it is fast growing species, with all promising results of physical properties, chemical composition, ber morphology and pulping with low cost soda with anthraquione cooking conditions could be one of tree species to establish integrated pulping industry between the two neighboring countries. However due to lack of equipment of bleaching stages were not carried out. The di culty of transportation will one of limitations for integrated pulp and paper industry between two neighboring countries, and lack of industrial polices to establish pulp and paper mills as of promising economical investment sector.

Declarations
SOT carried out practical and technical work and revised the draft manuscript. OTE designed the work and review the draft manuscript, TOK wrote the draft manuscript. All authors read and approved the nal manuscript.

Competing interests
Not applicable.

Availability of data and materials
We have already included most of data in the manuscript, the lab and data, some data not included in the manuscript attached as Additional le.