Indian Journal of Chemical Technology Vol. 15, May 2008, pp. 277-286 Hibiscus cannabinus and Hibiscus sabdariffa as an alternative pulp blend for softwood: Optimization of soda pulping process J S Upadhyaya a, Dharm Dutt a*, Bahadur Singh b & C H Tyagi a a Department of Paper Technology, Indian Institute of Technology, Roorkee, Saharanpur Campus, Saharanpur 247 001, India b Haryana Pollution Control Board, District Office, Yamuna Nagar 135 001, India Received 13 January 2007; revised 8 February 2008 Due to dearth of forest based raw materials paper technocrats have explored the possibility of alternate cellulosic fibrous raw materials. H. cannabinus and H. sabdariffa agro-based residues bear the characteristics of both, the softwood and hardwood fibers. The bast fibers of H. cannabinus and H. sabdariffa underneath the bark resemble with softwood and core fibers with hardwood. Morphological analysis and chemical composition of H. cannabinus and H. sabdariffa show their suitability for producing paper of various grades. This study provides optimized soda pulping conditions for better utilization of H. cannabinus and H. sabdariffa. Due to identical pulping conditions, H. cannabinus and H. sabdariffa can be delignified together. The optimum cooking conditions for H. cannabinus and H. sabdariffa were found to be as, active alkali 18% (as NaOH), temperature 165 C, time (at temperature) 180 min and wood to liquor ratio of 1:4.5. An AQ dose of 0.05% at an active alkali dose of 13% (as Na 2 O) produces the screening rejects and kappa number similar to that obtained by using 15% active alkali (as Na 2 O). Keywords: Soda pulping, Lignin, Pulp yield, Kappa number, Activation energy, I st order reaction constant, Non-wood plants, Agriculture residues Dearth of good quality of wood fibers in most of the Asian countries including India has compelled the paper technocrats to search for new alternative and hitherto unexploited sources of cellulosic fibers. The search for new alternative source of fiber has been underway for a long time 1. Many fast growing annual and perennial plants have been studied for their suitability for pulp and paper manufacture 2. One potential source of industrial fiber is agricultural crops, either in the form of residues of food crops or plants grown specifically for fiber 3. When the tree supply is becoming sufficiently meager and then kenaf s cost and capability are sufficiently strong to bring it on stream 4. Papermaking fibers from timber sources can be successfully supplemented by fibers from non-woody species 5. Pulps prepared from the bark fraction resemble with softwood pulps in their general papermaking whereas those from the woody fractions are more like hardwood pulps but drain more slowly and have lower tearing strength 6. Nonwood plants offer several advantages including short growth cycles, moderate irrigation and fertilization requirements and low lignin content to alleviate energy and chemicals use during pulping 7,8. Botanically, kenaf (Hibiscus cannabinus) (family Malvaceae) and roselle (H. sabdariffa) are closely related species; cotton (Gossipyium species) also a member of this family 9,10 has been identified by the U.S. Department of Agriculture as a viable substitute of trees in the pulp and paper making process 11,12. Kenaf could provide necessary input to partially alleviate the world s fiber deficit 13. Pulps from kenaf have desirable properties for papermaking and generally possess strength characteristics compatible to commercial coniferous wood pulps 14. Unlike most annual crops kenaf can be harvested for several months, beginning with green kenaf at 120 days after planting 15. Excellent high yielding pulps are easily obtained as kenaf is known as cordage crop 16. In the early 1990s interest in alternative crops re-emerged in the form of a new alternative crops initiative of USDA 17. It consists of two distinct fibers; the softwood-like bast fibers makes up 35-40% of the total dry weight, and the hardwood-like core fibers makes up the balance 18. The low lignin content is reflected in less pulping, chemical and energy consumption and less bleach chemical requirements which make it suitable for mechanical and chemical pulping processes 19. Pulp and paper and structural and non-structural composites are among the products being investigated 20.
278 INDIAN J. CHEM. TECHNOL., MAY 2008 Experimental Procedure Fiber dimensions H. cannabinus and H. sabdariffa collected from the nearby vicinity of Institute at Saharanpur (India), air dried and leaves and flowers were removed by stroking on a hard surface. Three samples from each stalk were taken at 10% (base), 50% (middle) and 90% (top) of its height/length respectively, similar to an approach followed by Paraskevopoulou 21. For fiber length determination, small slivers were obtained and macerated with 10 ml of 67% HNO 3 and boiled in water bath at 100±2 C for 10 min 22. The slivers were then washed, placed in small flasks with 50 ml distilled water and the fiber bundles were separated into individual fibers using a small mixture with a plastic end to avoid fiber breaking. The macerated fiber suspension was placed on a slide by means of a dropper 11. For fiber diameter, lumen diameter and cell wall thickness, cross-sections were obtained from the same height/length as above and were stained with 1:1 aniline sulphate-glycerin mixture to enhance cell wall visibility by retaining a characteristic yellowish colour. All fiber samples were viewed under a calibrated microscope; a total of 25 randomly chosen fibers were measured from each sample for a total of 250 fiber measurements from each stalks. The slenderness ratio, flexibility coefficient and Runkel ratio were calculated from these derived values 22,23. Proximate chemical analysis Ten samples of each hand-chopped culm of H. cannabinus and H. sabdariffa were boiled with concentrated solution of HCl and sodium chlorite to separate cellulosic fibers together by dissolving middle lamellae separately. The fibers were analyzed for various morphological characteristics as per Tappi Test Methods (T 232 cm-01:2002-03). H. cannabinus and H. sabdariffa were milled separately into powder in a laboratory Wiley mill and a fraction passing through 48 mesh size but retained on +80 mesh size was used for analysis of water solubility (T 207 cm-99), 1% caustic soda solubility (T 212 om-98), alcohol-benzene solubility (T 204 cm-97), holocellulose (T 249 cm-00), lignin (T 222 om-02), ash (T 211 om-93), Ash (T 211 om-93) and pentosan (T 223 cm-01) proximate chemical analysis. Pulping studies H. cannabinus and H. sabdariffa were chopped manually into 15-25 mm long pieces and were digested in WEVERK electrically heated rotary digester of 0.02 m 3 capacity having four bombs of one liter capacity each. The chips of H. cannabinus and H. sabdariffa were cooked at different cooking conditions like maximum temperature from 145 to 175 C, cooking time from 1 to 5 h, active alkali from 12 to 20% (as NaOH) and liquor to wood ratio of 4.5:1. Based on experimental results at optimum cooking conditions, a carbohydrate stabilizer anthraquinone (AQ) was added from 0.0 to 0.15% (based on O.D. raw materials) to study its effect on pulp yield and kappa number. After completion of cooking, the pulps were washed on a laboratory flat stationary screen having 300 mesh wire bottom for the removal of residual cooking chemicals. The pulp was disintegrated and screened through WEVERK vibratory flat screen with 0.15 mm slits and the screened pulp was washed, pressed and crumbled. The pulps were analyzed for kappa number (T 236 cm -85 ), pulp yield and lignin (T 222 om-88) and screening rejects. Preparation of laboratory hand sheets and testing The unbleached pulps of H. cannabinus and H. sabdariffa were disintegrated in PFI mill (Tappi T 200 sp-96) at different beating levels and drainage time (Tappi T 221 cm-99) was determined. Laboratory hand sheets of 60 g/m 2 were prepared according to Tappi T 221 cm-99 and tested for various physical strength properties, like tear index (T 414 om-98), tensile index (T 494 om-01), burst index (T 403 om-97) and double-fold (T 423 cm-98). Bleaching studies The unbleached soda and soda-aq pulps of H. cannabinus and H. sabdariffa were bleached by CEHH bleaching sequence. Results and Discussion Morphological characteristics Table 1 reveals the morphological characteristics of H. cannabinus and H. sabdariffa. Both the plants have two distinct kinds of fibers long bast fibers, which account for 32.6 and 34.5% of its fibrous part, and short core fibers, which account for the rest respectively. The bast fibers of H. cannabinus and H. sabdariffa are nearly ten times longer than softwood fibers, and it requires additional refining to shorten it to the point where it can duplicate the characteristic of wood. The bast fibers of H. cannabinus and H. sabdariffa have very good derived values as compared to those of some softwood and certainly to
UPADHYAYA et al.: SODA PULPING PROCESS FOR HIBISCUS CANNABINUS & H. SABDARIFFA 279 Table 1 Morphological characteristics of H. cannabinus and H. sabdariffa Particulars H. cannabinus H. sabdariffa 1 Colour Pale white Pale white 2 Average diameter of stalk, cm 1-3.0 1-2.5 3 Average diameter of stalk, m 2 2 4 Bast fiber (o.d. basis), % 32.6 34.5 5 Core fiber (o.d. basis), % 67.4 65.5 6 Presence of residues Hairy thorn and fruity residues 7 Average fiber length of bast fibers, mm 2.84 2.78 8 Average fiber diameter of bast fibers, μm 22.92 24.32 9 Average fiber length of core fiber, mm 0.81 0.79 10 Average fiber diameter of core fiber, μm 30.85 28.42 11 Density, g/cm 3 0.275 0.281 12 Bulk density, kg/m 3 130 137 13 Fiber length of whole plant, (L) mm Average Variation 14 Fiber width of whole plant, (L) μm Average Variation 1.62 0.40-5.68 26.46 15.34-36.32 Hairy thorn and fruity residues 1.56 0.46-5.40 24.18 12.85-35.85 15 Lumen width, (d) μm Average Variation 19.72 4.45-29.75 16 Cell wall thickness, (w) μm Average 6.76 Variation 3.10-10.50 17 Flexibility coefficient (d/d X 100) 74.53 70.06 18 Runkel ratio, (2w/d) 0.69 0.62 19 Miihlesteph ratio 35.20 28.92 20 Ratio of length to width, (L/D) 61.22 64.52 16.94 4.12-26.88 5.28 2.52-9.84 most hardwood 24. Therefore, paper made from H. cannabinus and H. sabdariffa are expected to have increased mechanical strength and thus be suitable for writing, printing, wrapping and packaging purposes 23,25,26. The core fibers are still highly flexible with a good Runkel ratio and low felting power and can thus supplement the higher mechanical strength of the bark fibers 27,28. So, the whole stem of H. cannabinus and H. sabdariffa could produce a pulp of good quality and strength 29,30. The values of flexibility coefficient and ratio of length to width of H. cannabinus and H. sabdariffa are lower as compared to the values of bamboo whereas the values of Runkel ratio are just half. Such fibers, which contain lower Runkel ratio, are readily converted into double walled ribbons and exhibit plastic deformation on pressing and thus, offer more surface contact area for fiber bonding 31. This gives good physical strength and also the rattleness 29. Chemical composition The proximate chemical analysis of H. cannabinus and H. sabdariffa are presented in Table 2. The water Table 2 Chemical composition of H. cannabinus and H. sabdariffa Particulars H. cannabinus H. sabdariffa 1 Cold water solubility 4.56 5.81 2 Hot water solubility 6.42 8.24 3 Alcohol-benzene 4.28 3.88 solubility (1:2 v/v) 4 1% NaOH solubility 28.50 25.80 5 Lignin 18.50 19.20 6 Pentosan 17.30 18.45 7 Holocellulose 71.80 71.40 8 Hemicellulose 25.05 22.80 9 α-cellulose 46.75 48.60 10 β-cellulose 10.24 9.56 11 γ-cellulose 11.50 13.20 12 Ash 1.56 1.40 13 Silica 0.35 0.28 solubility estimates a part of extraneous components, such as inorganic compounds, tannins, gums, sugars and coluoring matter present in the wood and hot water estimates, in addition, starches. The values of water of H. cannabinus and H. sabdariffa solubility
280 INDIAN J. CHEM. TECHNOL., MAY 2008 are lower as compared to hardwoods and nonwoods 29. The alcohol-benzene solubility, which estimates low-molecular-weight carbohydrates, salts, and other water soluble substances 32 is comparable to bamboo but higher than Eucalyptus tereticornis 29,33. Carbohydrate composition is important in determining its response to processing conditions and the development of physical properties 34. H. cannabinus has higher cellulose content than H. sabdariffa. Hardness, bleachability, and other pulp properties are associated with the lignin content 35. Klason lignin contents are also at satisfactory level (<20%) for H. cannabinus and H. sabdariffa. It requires milder cooking conditions leading to satisfactory delignification levels 23,29. H. sabdariffa contains higher α-cellulose than H. cannabinus; plant materials with 34% and over α-cellulose content are characterized as promising for pulp and paper manufacture from a chemical composition point of view 10. The pentosan content indicates the retention or loss of hemicellulose in general during pulping and bleaching processes, and since hemicellulose contributes to the strength of paper pulps, high pentosan content is desirable 36. H. cannabinus and H. sabdariffa contain higher pentosan content than that of bamboo and Eucalyptus tereticornis but lesser than that of bagasse 29. Ash (CO - -, Ca, K and some d- block elements) and silica contents are lower in H. cannabinus and H. sabdariffa than that of bagasse and bamboo but slightly higher as compared to hardwoods. The ash content is undesirable, as trace elements interfere with H 2 O 2 and O 2 bleaching and alkali earth metals pass into the pulp. On the other hand, high silica content shows damaging effect on the processability of wood. Influence of temperature and time Figure 1 reveals the curves plotted between residual lignin and reaction time at different reaction temperatures. The curves indicate that each curve can be approximated by two straight lines at each temperature investigated. The curves with steeper slopes are pertaining to rapid solubilization of bulk of lignin (bulk delignification), whereas the part of curves with more gentle slopes pertain to the slow solubilization of the residual lignin (residual delignification). Both parts of these curves are having different velocity constants. These curves also clearly indicate that as the temperature is decreased from 175 to 145 C, the reaction time to reach transition from bulk to residual delignification phase and the lignin Fig. 1 Percentage of lignin versus reaction time at maximum cooking temperture during soda pulping of H. cannabinus and H. sabdariffa. content of the pulp, corresponding to this transition point both increase. Table 3 also reveals that at lower temperature range, the residual lignin contents decrease sharply, while at higher temperature, the magnitude of decrease in lignin content are not so pronounced. Moreover, at higher temperature, the degradation of carbohydrate fractions also increased, thereby reducing the pulp yield 37. The ratio of lignin to solubilized carbohydrate is about 1:0.75 during bulk delignification, whereas this ratio is about 1:7.0 during residual delignification, i.e. about ten times greater. This loss of carbohydrates related to the dissolved lignin is observed in the residual delignification 37. The nature of curves after transition points are almost horizontal lines, clearly indicating
UPADHYAYA et al.: SODA PULPING PROCESS FOR HIBISCUS CANNABINUS & H. SABDARIFFA 281 Table 3 Effect of temp on residual lignin and pulp yield during soda pulping of Hibiscus cannabis and Hibiscus sabdariffa at 18% active alkali (as NaOH) Time at Temp, (H) Time at temperature, C 145 155 165 175 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 3 4 3 4 3 4 3 4 1 1.0 15.2 62.6 15.2 62.2 14.2 61.5 13.9 58.8 12.2 56.4 12.2 61.4 11.9 63.5 11.6 59.0 2 1.5 13.4 61.2 13.5 60.5 12.1 57.0 11.7 56.5 10.7 54.5 9.80 59.6 8.75 52.0 8.45 57.2 3 2.0 12.2 59.5 12.0 57.9 9.80 53.6 10.0 55.0 7.50 52.8 7.10 57.4 6.25 47.9 6.65 53.4 4 2.5 10.7 56.2 10.7 55.4 8.00 49.5 7.90 54.1 5.25 50.9 5.05 55.3 3.15 44.5 4.00 50.8 5 3.0 9.70 54.8 9.50 51.9 6.50 47.8 4.95 52.0 2.33 48.8 2.50 53.6 1.60 40.0 2.00 46.7 6 3.5 8.25 53.0 7.95 50.2 4.90 46.5 4.40 50.2 2.10 46.4 2.40 52.0 1.48 36.8 1.68 44.8 7 4.0 7.35 51.5 6.50 48.8 4.25 46.0 4.00 46.2 1.90 43.8 2.10 50.1 1.15 35.0 1.45 43.2 8 5.0 6.20 48.8 6.15 48.0 3.90 45.0 3.85 45.4 1.65 41.6 1.85 46.4 1.00 34.4 1.30 40.5 1= Lignin, 2 Yield, 3= Hibiscus cannabinus, 4 = Hibiscus sabdariffa Pulping conditions Time from ambient temp to 105 C = 45 min Time from 105 C to max temp = 45 min that the bulk deliginification are over up to these transition points and it is not economical to continue the cooking operation beyond this optimum temperature of 165 C. Therefore, based on experimental data, a maximum cooking time of 3 h at 165 C may be considered as an optimum cooking condition for the soda pulping of H. cannabinus and H. sabdariffa. The Arrhenius activation energy 38 of bulk delignification in kraft pulping of H. cannabinus and H. sabdariffa were calculated and are presented in Table 4 which is very low in comparison to softwoods and hardwoods 39 whereas for residual delignification was only about two thirds of this value. This explains either the existence of an association between lignin and carbohydrate in wood 40 or the formation of bonds during pulping 37-41. Influence of alkali charge Table 5 reveals that screened pulp yield decreases with increasing active alkali from 12 to 18% (as NaOH) and then tends to decline sharply, whereas both kappa number and screening rejects decline sharply up to an alkali dose of 18% and beyond that both of these parameters practically remain constant. The screened pulp yield of H. cannabinus and H. sabdariffa were found to be 49.2 and 48.4% at kappa number of 30.2 and 29.9 respectively at an active alkali charge of 18% (as NaOH), which may be considered as optimum cooking dose for H. cannabinus and H. sabdariffa. During kraft pulping, the consumption of active alkali was found to be constant over a wide range of alkali charge 42. It was found that the excessive active alkali charge which remains unconsumed during the course of pulping adversely decreases the pulping viscosity. Table 4 First order rate constant for bulk delignification in soda pulping of H. cannabinus and H. sabdariffa Temp, C Rate constant KS -1 H. cannabinus H. sabdariffa 1 145 0.6310 10 4 0.6933 10 4 2 155 1.1160 10 4 1.2738 10 4 3 165 2.3710 10 4 2.5300 10 4 4 175 3.1470 10 4 3.3420 10 4 5 Activation energy kcal/mole kj/mole 19.73 82.47 19.29 80.63 Figure 2 reveals that all the curves can be approximated by two straight lines at each alkali doses investigated. The steeper slope is related to bulk delignification and the gentler one to the residual delignification and is having different velocity constants. The nature of curves indicates that at the transition point, lower pulp lignin content is obtained at higher alkali doses than lower alkali doses. The degree of delignification is calculated after 3 h at 12, 14, 16, and 20% active alkali doses and is found that degree of delignification remains practically constant beyond 18% active alkali dose in all cases for H. cannabinus and H. sabdariffa. Influence of anthraquinone Table 6 shows the effect of different doses of AQ viz., 0.025 and 1.0% on pulp yield, kappa number and screening rejects at higher alkali levels for soda pulping of H. cannabinus and H. sabdariffa. The addition of AQ brings down the kappa number by 15-20 units, the drop being more at lower alkali levels than 18% active alkali level. The higher dose of AQ
282 INDIAN J. CHEM. TECHNOL., MAY 2008 Fig. 2 Percentage of lignin versus reaction time at different alkali doses during soda pulping of H. cannabinus and H. sabdariffa Table 5 Effect of alkali charge at 165 C on residual lignin, kappa number and pulp yield during soda pulping of Hibiscus cannabis and Hibiscus sabdariffa Active alkali (as NaOH) Time at 165 C (H) Lignin, % H. cannabinus H. sabdariffa Kappa no. Yield, % Lignin, % Kappa no. Yield, % 12 1 15.80 15.50 2 13.25 13.00 3 10.10 58.0 55.3 11.25 59.0 56.0 4 8.00 8.25 5 7.45 7.25 14 1 14.35 14.00 2 11.75 11.45 3 8.00 48.9 53.0 7.90 50.5 53.5 4 6.15 6.35 5 5.25 5.40 16 1 13.50 13.25 2 9.50 9.45 3 6.65 42.0 51.8 6.55 42.5 52.1 4 5.00 4.85 5 4.00 3.75 18 1 12.00 12.15 2 7.75 7.80 3 2.45 30.2 49.2 3.00 29.9 48.5 4 2.00 2.00 5 1.45 1.60 20 1 10.50 10.15 2 5.80 5.95 3 1.75 24.8 45.5 2.00 25.0 44.5 4 1.00 1.25 5 0.70 0.90 Pulping conditions Time from ambient temp to 105 C = 30 min, Time from 105 C to 165 C = 60 min, Wood to liquor ratio = 1:4.5 reduces the kappa number further but this reduction is marginal. The addition of AQ apparently does not increase the pulp yield at all levels of active alkali though the kappa numbers are reduced substantially. These results reveal that it is possible to obtain the same kappa number of pulp with higher yield if AQ is added to the system at lower alkali charge. The screening rejects in the pulp are also found to be lower with increasing AQ doses. This shows that addition of AQ results in faster delignification
UPADHYAYA et al.: SODA PULPING PROCESS FOR HIBISCUS CANNABINUS & H. SABDARIFFA 283 Plant species Table 6 Results of soda-aq additive pulping for Hibiscus cannabis and Hibiscus sabdariffa Alkali doses, (as NaOH) AQ doses Kappa number Pulp yield Hibiscus cannabinus Rejects Kappa number Pulp yield Hibiscus sabdariffa Rejects 1 12 0.000 45.8 52.3 2.10 47.0 52.8 1.95 0.025 38.5 51.8 1.60 39.0 52.5 1.45 0.050 35.0 51.7 1.40 35.7 52.4 1.40 0.075 32.5 51.5 1.30 34.5 52.3 1.30 0.100 32.0 51.5 1.30 33.7 52.3 1.30 2 13 0.000 42.0 51.8 1.65 42.5 52.1 1.55 0.025 35.2 51.6 1.30 34.6 51.7 1.25 0.050 32.3 51.5 1.25 30.5 51.6 1.20 0.075 30.5 51.8 1.20 29.8 51.6 1.20 0.100 29.8 51.3 1.20 29.2 51.6 1.20 3 14 0.000 35.4 51.3 1.25 35.6 51.5 1.35 0.025 30.0 50.9 1.00 30.2 51.2 1.10 0.050 27.4 50.8 0.95 27.5 51.0 1.05 0.075 26.8 50.7 0.92 27.0 49.8 0.98 0.100 26.5 50.7 0.88 26.6 49.8 0.84 4 15 0.000 30.2 49.2 0.90 30.0 48.5 1.10 0.025 25.6 49.5 0.65 26.0 48.1 0.92 0.050 22.7 49.4 0.62 23.2 48.0 0.80 0.075 22.1 49.3 0.60 22.7 47.8 0.74 0.100 21.8 49.3 0.58 22.3 47.7 0.75 Pulping conditions Time from ambient temp to 105 C = 30 min, Time from 105 C to 165 C = 60 min, Wood to liquor ratio = 1:4.5 Table 7 Mechanical strength properties of unbleached soda pulps of Hibiscus cannabis and Hibiscus sabdariffa Beating time, (min) Beating level, ( SR) Drainage time, (s) Apparent density (g/cm 3 ) Burst index, (kpam 2 /g) Tensile index (Nm/g) Tear index (mnm 2 /g) Porosity Bendtsen (ml/min) Soda pulp H. cannabinus 0 18 3 0.61 0.93 17.46 7.26 1500 8 5 28 12 0.65 2.43 38.26 8.83 610 85 10 42 17 0.71 3.39 53.96 8.14 260 170 15 54 24 0.75 3.97 62.29 6.97 200 345 20 62 38 0.78 4.10 63.80 6.67 140 450 H. sabdariffa 0 19 4 0.63 1.05 18.22 7.36 1550 5 5 29 14 0.65 2.75 39.00 9.02 600 90 10 42 18 0.73 3.53 55.28 8.34 250 240 15 55 25 0.78 4.02 65.64 6.87 180 340 20 65 40 0.81 4.15 67.28 6.45 140 400 Soda-AQ pulp H. cannabinus 0 18 4 0.65 1.16 21.00 7.32 1530 10 5 30 13 0.67 2.75 48.05 9.00 650 95 10 42 18 0.70 3.65 55.48 8.25 280 190 15 55 26 0.74 4.30 63.96 7.30 210 390 20 65 43 0.78 4.36 65.00 7.08 150 460 H. sabdariffa 0 18 5 0.64 1.14 22.10 7.58 1520 8 5 29 13 0.67 2.94 50.40 9.25 640 110 10 43 17 0.69 3.68 57.50 8.40 300 210 15 56 25 0.73 4.26 65.82 7.35 220 400 20 64 45 0.77 4.32 66.20 6.92 160 470 Double fold ()
284 INDIAN J. CHEM. TECHNOL., MAY 2008 Table 8 Bleaching conditions and results of soda pulps of Hibiscus cannabis and Hibiscus sabdariffa Particulars H. cannabinus H. sabdariffa Soda pulp Soda-AQ pulp Soda pulp Soda-AQ pulp 1 Unbleached pulp kappa number 30.20 30.30 29.90 30.00 2 Chlorination stage (C) Amount of Cl 2 added on pulp, % 4.90 5.00 5.10 5.15 Amount of Cl 2 consumed on pulp 4.87 4.96 5.05 5.12 Amount of Cl 2 consumed on Cl 2 basis, % 99.39 99.20 99.02 99.42 Final ph 1.95 1.98 2.00 2.04 3 Alkali extraction stage (E) NaOH added on pulp, % 1.50 1.50 1.50 1.50 Initial ph 11.65 11.60 11.63 11.59 Final ph 10.31 10.30 10.27 10.18 4 Hypochlorite I st stage (H 1 ) Hypo added as avail Cl 2 on pulp, % 2.00 1.98 2.02 2.00 Hypo consumed as avail Cl 2 on pulp, % 1.87 1.85 1.90 1.86 Hypo consumed on Cl 2 basis, % 93.50 93.43 94.06 93.00 Final ph 8.20 8.18 8.12 8.22 5 Hypochlorite 2 nd stage (H 2 ) Hypo added as avail Cl 2 on pulp, % 1.50 1.48 1.50 1.52 Hypo consumed as avail Cl 2 on pulp, % 1.40 1.35 1.33 1.40 Hypo consumed on Cl 2 basis, % 93.33 91.22 88.67 92.11 Final ph 8.10 8.12 8.13 8.08 6 Total Cl 2 added on pulp, % 8.40 8.46 8.62 8.67 7 Total Cl 2 consumed on pulp, % 8.14 8.16 8.28 8.38 8 Bleaching losses, % 9.77 9.85 10.10 10.00 9 Pulp brightness (Elrepho), % 77.00 77.00 78.50 79.00 10 Viscosity, CED (0.5%) Cp 9.45 10.00 9.60 10.05 Bleaching conditions C E H 1 H 2 Consistency, % 3 10 9 9 Temperature, C 25±2 55±2 45±2 45±2 Reaction time, minute 40 60 60 120 resulting in lower kappa number. It was observed that kappa number and screening rejects obtained at 18% active alkali (as NaOH) are similar to that obtained by using 16% active alkali (as NaOH) along with 0.75% AQ. At the same time, the screened pulp yield was higher by about 3% than in later case which means substantial saving on raw materials and chemicals. Mechanical strength properties Table 7 reveals the mechanical strength properties of soda and soda-aq pulps H. cannabinus and H. sabdariffa at optimum cooking conditions. The results indicate that the initial freeness and drainage time of both the pulps are found to be higher in comparison to that of bamboo pulp 43. The sheets formed from unbeaten pulps are of higher density about 0.60 to 0.65 g/cm 3. These values are found to be on higher side when compared with hardwoods and bamboo. All the mechanical strength properties increase with increasing beating level up to 45 SR except tear strength. Keeping in view the combined effect on strength properties, the optimum beating level of 45 SR as shown in the table may be considered as optimum. The physical strength properties of soda-aq pulp show an improvement over soda pulps at the same kappa number. Bleaching Table 8 shows the bleaching response of soda and soda-aq pulps of H. cannabinus and H. sabdariffa towards CEHH bleaching sequence. The unbleached pulp brightness was found to be 35-38% (Elrepho). The final brightness of soda and soda-aq pulps of H. cannabinus and H. sabdariffa were observed to 77 and 79% (Elrepho) respectively and the CED viscosity of bleached pulps of H. cannabinus and H. sabdariffa are quite comparable to that of bamboo and hardwoods 44. Conclusions The present investigation helps to provide optimized pulping conditions for better utilization of
UPADHYAYA et al.: SODA PULPING PROCESS FOR HIBISCUS CANNABINUS & H. SABDARIFFA 285 H. cannabinus and H. sabdariffa as an alternative raw material for expensive softwood fibers as these agricultural residues bear the characteristics of some softwoods and certainly to most of the hardwoods. Morphological analysis and chemical composition of H. cannabinus and H. sabdariffa show its suitability for producing paper of various grades. Due to identical pulping conditions, H. cannabinus and H. sabdariffa can be delignified together. The optimum cooking conditions for H. cannabinus and H. sabdariffa were found to be as, active alkali 18%, temperature 165 C, time (at temperature) 180 min and wood to liquor ratio of 1:4.5. An AQ dose of 0.075% at an active alkali dose of 16% (as NaOH) produces the screening rejects and kappa number similar to that obtained by using 18% active alkali (as NaOH). The maximum kappa number reduction was observed 16% active alkali. Both the raw materials show good response towards CEHH bleaching sequence and viscosity is comparable to those of bamboo and hardwoods. The maximum mechanical strength properties are obtained at optimum beating level of 45 SR and the physical strength properties of soda- AQ pulp show an improvement over soda pulps at the same kappa number. References 1 Nelson G H, Clark T F, Wolff I A & Jones Q, Tappi J, 49(1) (1966) 40. 2 Cunningham R L, Clark T F, Kowlek W F, Wolff I A & Jones Q, Tappi J, 53(9) (1970) 1967. 3 McCloskey J M, A review about non-woods? 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