Sudanese Dicots as Alternative Fiber Sources for Pulp and Papermaking

The suitability of the stems from two Sudanese dicotyledonous annual plants, namely castor bean (Ricinus communis) and Leptadenia pyrotechnica (L. pyrotechnica) were investigated for pulp and papermaking. Chemical compositions, elemental analysis, fi ber dimensions, paper physical properties and morphology revealed a relatively high α-cellulose content (46.2 and 44.3 %) and low lignin (19.7 and 21.7 %) in the stems of castor bean and L. pyrotechnica, respectively. The average fi ber length of castor bean and L. pyrotechnica is 0.80 and 0.70 mm with fi ber width of 16.30 μm and 18.20 μm, respectively, which makes them acceptable candidates. SodaAQ pulping of castor bean stem led to a higher pulp yield of 43.2 % at kappa number 18.2 compared to 40.3 % at kappa 20.3 for L. pyrotechnica. This yield is less than that obtained for wood plants and similar to that observed for annual plants. Paper handsheets produced from castor bean showed better mechanical properties than L. pyrotechnica. SEM images indicated that the produced papers were quite homogeneous, compact, closely packed, and well assembled.


INTRODUCTION 1. UVOD
The annual world consumption of paper and paperboard is growing 2.1 % and it will reach an estimated 490 million tonnes by 2020 (Dutt et al., 2008).However, ~ 4 billion trees are cut across the globe for pulp and paper manufacturing often raising ecological and climatic issues (Kamoga et al., 2016) and leading to a demand for alternative pulp and papermaking raw materials.In some countries, pulp and paper industries have been facing some challenges due to the shortages of forest resources (Ferhi et al., 2014b).However, non-wood species or annual plants and agriculture residues are likely the best candidates as alternative sources of cellulosic fi bers (Kamoga et al., 2016).Furthermore, as these cellulosic fi ber materials have identical properties, they could be used as wood fi bers for pulp and papermaking (Mechi et al., 2016), textile, boards, and green composite materials (Mansouri et al., 2012).
Castor bean (Ricinus communis) is a tropical annual and fast-growing plant.Leptadenia pyrotechnica (L.pyrotechnica) is an important multipurpose non-wood species of tropical and sub-tropical arid regions.Mojumder et al. (2001) investigated the chemical composition of L. pyrotechnica, and determined that it consists of 4.93 % of lignin, 75.26 % of α-cellulose and 2.77 % of ash.However, the results reveal that castor and L. pyrotechnica residues are a good alternative for the pulp and paper industries since they are plants of high cellulose content.This work investigated the chemical components and fi ber properties of castor bean (Ricinus communis) and L. pyrotechnica stems after soda-AQ pulping.

Materijali
Castor bean (Ricinus communis) and L. pyrotechnica stems were collected from North Kordofan State, west of Sudan (latitudes 12˚ 30 North and longitudes 29˚ 30 East) in March 2017.Materials were randomly selected according to TAPPI standard methods.A part of the material was chipped to 1.5×1.5×2cm and ground to powder with a mesh size of 40-60 in a laboratory by using a Wiley mill grinder for determining their chemical components.Hydrogen peroxide (H 2 O 2 ), sodium hydroxide (NaOH), sodium oxide (Na 2 O), acetic acid and anthraquinone (AQ) were acquired from Sinopharm Chemical Reagent Co., Ltd.(Shanghai, China).

Morphological characteristics 2.2.2. Morfološka obilježja
For the measurements of fi ber dimensions, samples were macerated in a mixture of 30 % hydrogen peroxide and acetic acid (1:1).Fiber length, width and kinked and curled index were measured with FQA device (OpTest, Canada), model LDA-02 according to T271 om-07.Lumen diameter and wall thickness were measured by Leica DMLB (Leica Microsystems GmbH, Wetzlar, Germany) connected to a video camera Leica DFC490 (Leica Microsystems GmbH, Wetzlar, Germany) at 400× magnifi cations.Fibers morphology and elemental composition (Carbon (C), Oxygen (O), Aluminium (Al), Nitrogen (N), silicon (Si), magnesium (Mg), and Calcium (Ca)) were determined using a scanning electron microscope (SEM-EDS) by (OCTANE 9.88/1114658 AMETEK ® (USA)).Before the test, the paper specimens were coated with gold-palladium in a Sputtergerät SCD 005 sputter coater (England).A sputter current of 60 mA, sputter time 90 s, and fi lm thickness of 20 nm to 25 nm were chosen as the coating conditions.was continued for 120 min at the maximum temperature of 170 °C.At the end of pulping, pressure was relieved to atmospheric pressure; pulp was taken out from the digester, disintegrated and washed by continuous water fl ow.Pulp was screened on a 0.15 mm laboratory slot vibratory screener and the yield was determined gravimetrically.Pulp yield was determined as dry matter obtained on the basis of o.d.raw material.The pulp was subjected to mechanical beating using the PFI mill according to T248 sp-00, kappa number was determined according to T 236 cm-85 (Sarker et al., 2017), while pulp viscosity was determined according to T 230 om-04 (Feria et al., 2012).Moreover, a totally chlorine-free bleaching was carried out.According to Moral et al. (2016) 10 % pulp concentration is bleached in two stages by 4 % hydrogen peroxide (H 2 O 2 ) in 0.2 % sodium hydroxide (NaOH) at 80 °C for 2 h of each stage.The pulp was washed properly until neutralization in every stage.

Papermaking and testing 2.2.4. Proizvodnja i ispitivanje papira
All pulps were beaten to 5000 revolution at 35°SR in a PFI mill T248 sp-00, and papers of 60 grams were made according to the T205sp -95 in a laboratory handsheet machine (PTI laboratory Equipment, Vorchdorf, Austria).The physical properties of the samples were determined according to common standards: burst index T403 om-10, tear index T414 om-04 and tensile index T494 om-06 (Rudi et al., 2016).The brightness and opacity were determined according to T525 om-92 and T425 om-96 (Tutuş et al., 2016), respectively.

Flexibility coeffi cient = (fi ber lumen diameter ÷ fi ber diameter)×100
(2) Runkel ratio = (2×fi ber cell wall thickness) ÷ lumen diameter (3) Rigidity coeffi cient = (cell wall thickness×100) ÷ fi ber diameter (4) Felting power = fi ber length ÷ fi ber width (5)  (Saeed et al., 2017b).On the other hand, L. pyrotechnica show a higher amount of hemicellulose (22.15 %) compared to castor bean value of 20.50 %.This result may explain the higher solubility of L. pyrotechnica in alkali solution (1 % NaOH), because it is adequate to dissolve the fragile branched components of the cellulosic chain, such as hemicelluloses (Mattos et al., 2016).However, these results are not in line with vine stems (Mansouri et al., 2012) and A. armatus (Ferhi et al., 2014a).Lignin content was found to be higher in L. pyrotechnica (21.70 %), while it was 19.70 % in castor bean.However, these results are comparable with those of the listed annual plants and hardwoods (17-26 %) and lower than those of softwoods (25-32 %) (Ates et al., 2008).Castor bean and L. pyrotechnica showed almost the same ash contents, 2.60 and 2.40 %, respectively, which is the range (1-3 %) for hardwoods and less than those of the materials listed in Table 1.However, high ash content is undesirable, as trace elements interfere with bleaching chemicals and alkali earth metals in the pulp will cause problems in chemical recovery.Moreover, high ash content may lead to damage in wood during processing (Dutt et al., 2009, López et al., 2012).The basic parameters that affected the physical properties of the paper are fi ber dimensions including fi ber length, fi ber width and fi ber cell wall thickness (Albert et al., 2011).The average fi ber length of castor bean and L. pyrotechnica are 0.80 and 0.70 mm, respectively.They are less than that of softwood (2.7-4.6 mm) and in the range of hardwood (0.7-1.6 mm) (Comlekcioglu et al., 2016) and they are considered as short fi ber species (Jahan et al., 2008).These fi bers were similar to A. armatus (Ferhi et al., 2014a) and longer than vine stems (Mansouri et al., 2012) and prunus amygdalus (Mechi et al., 2017).It is expected that paper handsheets produced from L. pyrotechnica pulp with relatively short fi bers may give a smoother paper than that of castor bean because short fi bers will fi ll the voids in the paper sheet, while the paper handsheet formed from castor bean pulps would result in higher strength properties and less fi ne sheet structure (Nasser et al., 2015).Moreover, the higher the fi ber length, the better will be the tearing resistance of paper (Agnihotri et al., 2010).Therefore, paper made from these materials showed good mechanical strength and can be suitable for producing writing and printing papers as well as wrapping and packaging paperboard.On the other hand, L. pyrotechnica showed a thicker fi ber with the width of 18.20 μm compared to the 16.30 μm of castor bean.However, the observed fi bers are thinner than those of A. armatus (Ferhi et al., 2014a), and those of Prunus amygdalus (Mechi et al., 2017) are thicker than those of I. tinctoria (Comlekcioglu et al., 2016).Cell wall thickness of castor bean (6.40 μm) is lower compared to that of L. pyrotechnica (7.00 μm) and I. tinctoria (Comlekcioglu et al., 2016), However, longer fi ber with lower cell wall thickness showed signifi cant advantages in physical properties of the produced paper (Tutus et al., 2010).
Values derived from the fi ber dimensions, important for determining the suitability of the material for paper production, are listed in Table 2. Castor bean showed a relatively high felting power of 49 compared to 38.46 for L. pyrotechnica.However, these values are similar to those of hardwood (40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55) and lower than those of softwood (60-80) (Comlekcioglu et al., 2016).If the felting power of a fi brous material is lower than 70, it is suitable for the pulp and paper industry (Tutus et al., 2010).The values of the rigidity coeffi cient negatively infl uence tensile, tear, burst and double fold resistance of the paper (Anoop et al., 2014).Both castor bean and L. pyrotechnica fi bers showed higher rigidity coeffi cients of 38.04 and 38.46, respectively, compared to 30.44 of cymodocea serrulata (Syed et al., 2016) and 26.40 of I. tinctoria (Comlekcioglu et al., 2016).Moreover, it was reported that, if the slenderness ratio of fi brous material is less than 70 and higher than 33, the lignocellulosic material is considered to be good for pulp and paper production (Shakhes et al., 2011a;Syed et al., 2016).Both castor bean and L. pyrotechnica showed slenderness ratios of 49.00 and 38.46, respectively.Castor bean had a relatively high fl exibility coeffi cient of 63.19 compared to 62.64 and 47.2 of L. pyrotechnica and I. tinctoria, respectively.Previous The physical properties of the pulp obtained from the studied materials are summarized in Table 3.The results reveal that castor bean shows higher total pulp yield of 43.20 % with an acceptable kappa number of 18.20 compared to that of 40.30 % with kappa number of 20.30 of L. pyrotechnica.The low pulp yield of L. pyrotechnica is attributed to a relatively high content of extractives, especially in hot and cold water compared to that of castor bean (Ferhi et al., 2014a) as well as low cellulose content (Gonzalo et al., 2017).These values are higher than those of A. armatus (Ferhi et al., 2014a) and I. tinctoria (Comlekcioglu et al., 2016) and lower than those of vine stems (Mansouri et al., 2012) and A. armatus (Ferhi et al., 2014a).However, the differences in kappa number could be attributed to differences in lignin content in the materials.The value of viscosity is an indicator of fi ber length and degree of polymerization (Kamoga et al., 2016).However, caster bean showed higher viscosity (6.46 mP•s) compared to that of L. pyrotechnica (5.12 mP•s) and prunus amygdalus (5.28 mP•s) (Mechi et al., 2017) but lower than that of vine stems (8.50 m mP•s) (Mansouri et al., 2012).

Handsheet physical properties 3.1. Fizikalna svojstva listova papira
The physical and optical properties of handmade paper sheets produced from soda-AQ pulps of the studied annual plants are listed in Table 4.The paper handsheets produced from these species had good formation with basis weights of 63 and 65 g/m 2 and thicknesses of 115 and 117 μm for castor bean and L. pyrotechnica, respectively.Hand sheet formed from castor bean showed higher values of tensile, tear and burst index compared to those of paper produced from L. pyrotechnica and Prunus amygdalus (Mechi et al., 2016).Castor bean and L. pyrotechnica papers showed a lower tearing index than that of A. armatus (Ferhi et al., 2014a) and vine stems (Mansouri et al., 2012).Remarkably high brightness of 75.20 and 69.20 % was achieved for caster bean and L. pyrotechnica with a preliminary bleaching sequence.This high brightness predicts good bleachability of the pulps from these two annual plants, meaning that lower chemical charges are required.

Morphological analysis of papers obtained
from castor bean and L. pyrotechnica 3.2.Morfološka analiza papira proizvedenoga od stabljika ricinusa i L. pyrotechnica Paper handsheets were observed by SEM and SEM-EDS analysis, as presented in Fig. 1.Handsheets were magnifi ed at 500 x.SEM images indicated that the produced papers are quite homogeneous, compact,

Figure 1 1 .
Figure 1 Scanning electron microscopy of (A) L. pyrotechnica, (B) castor bean Slika 1. Slike dobivene skenirajućim elektronskim mikroskopom (A) L. pyrotechnica, (B) ricinus It belongs to the Euphorbiaceae family that is grown across the world (de Assis Junior et al., 2011; Udoh and Abu, 2016).Vasconcelos et al. (2014) investigated the physical and chemical properties of fi brous residues of castor bean, and they found that castor bean stems consist of 50.46 % of cellulose, 29.64 % of hemicelluloses, 17.34 % of lignin and 1.48 % of ash.

Table 2
(Shakhes et al., 2011b)tor bean, L. pyrotechnica and some annual plants Tablica 2. Obilježja vlakanaca ricinusa, L. pyrotechnica i nekoliko drugih jednogodišnjih biljaka Liu, Lucia, Chen: Sudanese Dicots as Alternative Fiber Sources for Pulp... studies stated that higher Runkel ratio fi bers are stiffer, less fl exible, and form bulkier paper of lower fi ber to fi ber bond than lower Runkel ratio fi bers.High average fi ber length and low Runkel ratio result in good pulp strength properties(Shakhes et al., 2011b).Both castor bean and L. pyrotechnica showed high Runkel ratio of 1.20 and 1.23 compared to that of 1.1 of I. tinctoria.