Comparison of various eucalyptus species for their morphological, chemical, pulp and paper making characteristics

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1 Indian Journal of Chemical Technology Vol. 18, March 2011, pp Comparison of various eucalyptus species for their morphological, chemical, pulp and paper making characteristics Dharm Dutt* & C H Tyagi Department of Paper Technology, Indian Institute of Technology Roorkee, Saharanpur Campus, Saharanpur , India Received 20 May 2010; accepted 18 January 2011 Eleven eucalyptus species are characterized for morphological, chemical, pulp and paper-making characteristics to get high pulp yield of good strength through social forestry in north Indian topological conditions. Eucalyptus grandis of Bhadrachalam and Saharanpur origins give very good fibre dimensions, especially slenderness ratio, which is directly comparable to Pinus kesiya. Other eucalyptus species have shorter fibres and narrow lumen with thick wall resulting to poorer flexibility, higher Runkel ratio and rigidity coefficient. The chemical analysis of eucalyptus species reveal satisfactory levels of holocellulose (except Eucalyptus camaldulensis) and Klason lignin content (<30%) (except Eucalyptus camaldulensis and E. 348 hybrid). Relatively increased (>25%) lignin content except E. 413 (hybrid) might require additional pulping time and chemical charge compared to other species. Kappa number (<22), pulp yield (>48%) and higher strength properties of E. grandis of Bhadrachalam and Saharanpur origins, Eucalyptus torrelliana, Eucalyptus camaldulensis and Eucalyptus alba showed their suitability for social forestry. Keywords: Eucalyptus species, Fibre dimensions, Chemical analysis, Pulping, Strength properties The effect of fibre properties on paper strength lead to the general belief that paper with desirable strength properties can only be made from long-fibered wood species, i.e., softwood species 1,2. Kellogg and Thykeson 3 and Matolcsy 4 have also pointed out the significance of fibre dimensions in predicting wood pulp mechanical properties. The paper strength also depends on the lignin and cellulose content of raw plant materials; the pulp mechanical strength and especially tensile strength is directly proportional to cellulose content 5. Eucalyptus species grown at different topological conditions affect the morphology, chemical composition, pulping conditions and paper properties due to variation in soil condition and ground water level 6. The present study aims at selecting the different eucalyptus species in north Indian topological conditions where many paper mills are located so that their plantation may be ascertained through social forestry in order to cater the fibrous raw materials demand for paper industry. The criteria for selection of eucalyptus species for plantation are: fibre dimensions, holocellulose, lignin, ash, alcohol-benzene soluble and pentosan contents, their suitability to produce good quality of paper using various indices and are validated by pulping and paper making characteristics. *Corresponding author (E mail: dharm_dutt@rediffmail.com) Materials and Methods Raw materials Eleven eucalyptus species and hybrids of age one year were selected for the study: E. grandis (seedlings collected from Bhadrachalam, District Khammam), E. grandis (seedlings collected from a nursery in Saharanpur), E. alba, E. tereticornis, E. torrelliana, E. europhyllia, E. camaldulensis, E. 413 (hybrid), E. 266 (hybrid), E. 471 (hybrid), E. 348 (hybrid). A representative sample consisting of about five seedlings of different eucalyptus species as mentioned above of the same genotype were grown in an agriculture field located in village Kadarpur which is 26 km away from in Saharanpur (Northern India). The average premonsoon and post-monsoon ground water levels during years 2004 to 2008 was 6.25 and 5.25 m respectively. The average temperature variation in Saharanpur confines to 1 to 45 C. All these eucalyptus were cut after 4 years of cultivation. Fibre dimensions and derived values (indices) Five logs of each eucalyptus species of age 4 years were debarked manually. Three samples from each log were taken at 10% (base), 50% (middle) and 90% (top) of its height/length respectively, an approach similar to that followed by Lal et al. 7 For fibre length determination, small slivers were obtained and macerated with 10 ml of 67% HNO 3 and boiled in a

2 146 INDIAN J. CHEM. TECHNOL., MARCH 2011 water bath (100±2 C) for 10 min 8. The slivers were then washed, placed in small flasks with 50 ml distilled water and the fibre bundles were separated into individual fibres using a small mixer with a plastic end to avoid fibre breaking. The suspension is diluted to a consistency of about 0.05%. The macerated fibre suspension was finally placed on a slide (standard, 7.5 cm 2.5 cm) by means of a medicine dropper 9. The slides were prepared as per IS: 5285:1998 Fiber analysis of paper and board methods of test. For fibre diameter, lumen diameter and cell wall thickness determinations, cross-sections of thickness 25 µm obtained from the same height/length were cut on Leitz base sladge microtome 1300 and were stained with 1:1 aniline sulphate-glycerine mixture to enhance cell wall visibility (cell walls retain a characteristic yellowish colour). All fibre samples were viewed under a binocular type compound microscope equipped with a graduated mechanical stage, Abbe condenser, triple nosepiece and an optical equipment consisting of two eyepieces of 10 magnification and three objectives of 48 mm, 16 mm and 4 mm focal length calibrated microscope (Leica, Houstan); a total of 75 randomly chosen fibres were measured from each sample for a total of 75 fibre measurements from each log. To properly calibrate reticle (eyepiece micrometer)) with a stage micrometer, align the zero line (beginning) of the stage micrometer with the zero line (beginning) of the reticle. Now, carefully scan over until we see the lines line up again. We can then use a simple ratio to determine the value that each line represents in reticle. Three derived values were also calculated using fibre dimensions: wall fraction as twice cell wall thickness/fibre diameter, flexibility coefficient as (fibre lumen diameter/fibre diameter) 100 and Runkel ratio as (2 fiber cell wall thickness)/lumen diameter 12,13. Three derived values were also calculated using fibre dimensions: slenderness ratio as fibre length/fibre diameter, flexibility coefficient as (fibre lumen diameter/fibre diameter) 100, Runkel ratio as (2 fiber cell wall thickness)/lumen diameter and rigidity coefficient (2 fiber cell wall thickness/ fibre diameter) Proximate chemical analysis The whole debarked eucalyptus species (4 years old) logs were disintegrated in to chips in Veco Plan Chipper. The trunk is cut into three pieces at 4 m length from the base and was converted in to chips in laboratory chipper. 25 g wood chips from each part of the trunk were milled into powder in a laboratory Wiley mill, mixed properly and fraction of mesh size was used for holocellulose (T249 cm 00), lignin (T222 om 02), alcohol-benzene solubility (T204 cm 97), Ash (T211 om 93) and pentosan (T223 cm 01) as per Tappi Standard Test Methods 11. Differences in values of each chemical component of different species are statistically significant at P < 0.05 (Turkey grouping). This approach provides a more accurate picture of standard error and allows a direct visual comparison of means for analyses within each species. Pulping studies The logs of all the eucalyptus species were disintegrated individually into chips in Veco Plan Chipper at Star Paper Mills Ltd., located in the vicinity of institute. These chips were digested in WEVERK electrically heated rotary digester of 0.02 m 3 capacity having four bombs of one litre capacity each by kraft pulping process at different cooking conditions like, 16% active alkali (as Na 2 O), time from ambient temperature to 165 C: 105 min, time at 165 C: 90 min, maximum cooking temperature 165± 2 C, liquor to wood ratio 2.8:1 and digester pressure 6.5 kg/cm 2. 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 (T236 cm-85), pulp yield and screening rejects as per Tappi Standard Test Methods 11. The black liquor generated was analyzed for residual alkali, organic, inorganic and total solids (T625 wd-99). Preparation of laboratory hand-sheets and testing The unbleached pulp was beaten in PFI mill (T200 sp-96) at 40 0 SR. Laboratory hand sheets of 60 g/m 2 were prepared (T221 cm-99) on British sheet former, pressed, air-dried in atmospheric conditions, conditioned at 27±2 C and 65±2% relative humidity and tested for various physical strength properties like, tear index (T414 om-98), tensile index (T494 om-01), burst index (T403 om-97) and bulk (T426 wd-70) 15. Results and Discussion Fibre dimensions and derived values (indices) E. grandis fibres of Saharanpur origin are comparatively longer (0.92 mm), wider (20.12 µm)

3 DUTT & TYAGI: COMPARISON OF EUCALYPTUS SPECIES FOR ITS PULP & PAPER CHARACTERISTICS 147 and have wide lumen (14.32 µm) with thin cell wall (2.80 µm) (Table1). E. grandis fibres of Saharanpur origin have low Runkel ratio which is expected to have an inevitably positive effect on tensile and bursting strengths as well on folding endurance 8. The short and thin walled fibres exhibit plastic formation, thus they offer more surface contact and fibre bonding 6. The fibres with Runkel ratio below 1.0 are considered as thin walled fibres 12 and good mechanical strength properties are usually obtained when Runkel ratio is below 1.0. Runkel ratio is also related to paper conformability 13,14 and pulp yield 15. E. grandis fibres from Saharanpur origin have slenderness ratio comparable to softwood like Pinus kesiya. The short and thin fibres produce a good slenderness ratio, which is related to paper sheet density and to pulp digestibility 15 and, in turn, increase tearing resistance. This is partly because short and thin fibres are readily collapsed to double walled ribbons and produce good surface contact and fibre-to-fibre bonding 8. Fibre diameter and wall thickness governs the fibre flexibility. Thin walled fibres favourably affect the bursting and tensile strengths and folding endurance of paper. A decrease in these variables, which are measures of the flexibility and wet plasticity of fibres, results in higher degree of conformability within the sheet, which gives rise to a sheet of a higher density or lower bulk. This gives good physical strength properties with more opaque sheet and less porosity. Therefore, papers made from E. grandis fibres of Saharanpur origin are expected to have an increased mechanical strength and thus be more suitable for writing, printing, wrapping and packaging purposes 10,16. On the other hand, E. grandis fibres of Bhadrachalam origin are comparatively longer (1.06 mm), less wide, narrow, with thick cell wall compared to E. grandis fibres of Saharanpur origin. The fibres with good slenderness ratio, high Runkel ratio and low flexibility are expected to have negative effect on pulp mechanical strength 17 because short and thick fibres do not readily collapse to ribbons and provide less surface contact for bonding (Fig. 1). Fig. 1 (A) Thick walled tend to retain its tubular structure and provide less surface area (B) Thin walled fibres are readily converted into ribbons and provide more surface contact area for bonding. Name of eucalyptus species Table 1 Morphological characteristics of fibres from different 11 species of eucalyptus Fiber length (L), mm Fiber width (D), µm Cell wall thickness (w), µm Morphological characteristics Lumen diameter (d), µm Runkel ratio, 2w/d Flexibility c oefficient (d/d) 100 Slenderness ra tio, L/D Rigidity coefficient 2 w/d E. grandis * 1.06± ± ± ± E. grandis ** 0.92± ± ± ± E. alba 0.88± ± ± ± E. tretecornis 0.85± ± ± ± E. torrelliana 0.81± ± ± ± E. europhyllia 0.85± ± ± ± E. camaldulensis 0.80± ± ± ± E. 413 (hybrid) 0.75± ± ± ± E. 266 (hybrid) 0.71± ± ± ± E. 471 (hybrid) 0.67± ±1.4 4± ± E. 348 (hybrid) 0.71± ± ± ± Pinus kesiya ± standard deviation, E. grandis * = Bhadrachalam (District Khammam) origin, E. grandis ** Saharanpur origin

4 148 INDIAN J. CHEM. TECHNOL., MARCH 2011 The short fibres of E. Elba (0.88 mm) and E. 471 (hybrid) (0.67 mm) are rigid (rigidity coefficient 0.50 and 0.59 respectively) and less flexible with high slenderness ratio due to high cell wall thickness (4.80 and 4.0 µm respectively) with narrow lumen. On contrary to this, fibres from E. tretecornis (Fig. 2), E. torrelliana, E. europhyllia, E. camaldulensis, E. 413 (hybrid), E. 266 (hybrid) and E. 348 (hybrid) have Runkel ratio more than 1.0 will be stiffer, less flexible and form bulkier paper of lower bonded area. The paper made from this type of fibres will be bulky, coarse surfaced and containing a large amount of void volume. Due to lower value of fibre length to width ratio (slenderness ratio), there will be lower fibre flexibility and a poor chance of forming well bonded paper. Similarly, increase in rigidity of fibres results in decrease in fibre bonding. Fibre lumen diameter affects the beating of pulp. Narrower the fibre lumen diameter poorer will be the beating of pulp because of the penetration of liquids in to empty spaces of the fibres. The properties of such type of fibres may be used for manufacturing of base paper for pictorial circuit board 18, seed germination paper 19 and tea bag paper 20. Chemical compositions Proximate chemical analysis (ash, alcohol: benzene soluble, lignin, pentosan and holocellulose) of various eucalyptus species are presented in Table 2 in order to assess their suitability for pulp and papermaking. The total ash (SiO 2, Ca, K, Mg, Fe, Co and Mn) in E. grandis of Saharanpur origin is higher (2.87%) compared to other species of eucalyptus. High ash contents are undesirable for pulping as they affect normal alkali consumption and give problems at recovery of the cooking liquor (evaporation, combustion, and lime mud reburning) and operational problems in material handling, pulp washing and pulp beating. In this case, the high quantity of ashes cannot be considered as problematic, in the context of pulping and papermaking processes, since the silicabased salts are negligible. Ash as trace elements interferes with H 2 O 2 and O 2 bleaching and alkali earth metals pass in the pulp 21. The chelation treatment with DTPA/EDTA and NaHSO 3 (Q stage) is quite effective at removing transition metals from kraft pulps 22. To conclude a comparison with eucalyptus species shows that chemical ash varies from 0.36 to 1.96%, as shown in Table 2. The alcohol-benzene solubility in E. grandis of Saharanpur origin, which estimates polyphenols, mainly in the polymerized form, ellagic acid, gallic acid and ellagitannins, gallotannins, flavonoids and their polymers, lowmolecular-weight carbohydrates, salts, and other water soluble substances 23, is comparable to Fig. 2 Scanning electron micrograph of E. tereticarnis Table 2 Proximate chemical analysis of different 11 species of eucalyptus Name of eucalyptus Chemical compositions, % species Ash Alcohol-benzene soluble Lignin Holocellulose Pentosan E. grandis 2.87 (0.25) E. grandis 1.59 (0.20) E. alba 0.36 (0.10) E. tretecornis 1.12 (0.12) E. torrelliana 1.89 (0.20) E. europhyllia 0.98 (0.10) E. camaldulensis 1.26 (0.17) E. 413 (hybrid) 0.72 (0.14) E. 266 (hybrid) 0.75 (0.16) E. 471 (hybrid) 0.94 (0.16) E. 348 (hybrid) 1.96 (0.21) Differences in values of each chemical component of different species are statistically significant at < 0.05 (Turkey groupings). Values in bracket show silica content.

5 DUTT & TYAGI: COMPARISON OF EUCALYPTUS SPECIES FOR ITS PULP & PAPER CHARACTERISTICS 149 E. grandis of Bhadrachalam origin and slightly higher than E. alba. Alcohol-benzene extractable can precipitate upon pulping, retard drainage due to chocking of Fourdrinier wire and leave stains in the resulting paper sheets. Hardness, bleachability and other pulp properties are associated with the lignin content 24. Klason lignin contents were also at satisfactory levels (about 28±2%) for all the eucalyptus species except E. camaldulensis (33.2%) and E. 348 (hybrid) (31.3%). This, in practice, means that most of eucalyptus species need, in general, milder pulping conditions (lower temperatures and chemical charges) than that of E. camaldulensis in order to reach a satisfactory kappa number. It also indicates the potential of these eucalyptus species to undergo bleaching more easily and with the utilization of fewer chemicals. Examples of milder pulping conditions leading to satisfactory delignification levels are abundant in the literature. Lal et al. 7, report such conditions for Anthocephalus cadamba, Malik et al. 24, for Leucaena leucocephala, López et al. 25, for Leucaena diversifolia and Jahan et al. 26, for Trema orientalis. Carbohydrate composition is important in determining its response to processing conditions and the development of physical properties 27. All the eucalyptus species contain holocellulose in the range of 62±2% except E. camaldulensis (55.6%), E. 413 (hybrid) (67.80%), E. 266 (hybrid) (67.20%) and E. 471 (hybrid) (66.50%). The pentosan content indicates the retention or loss of hemicelluloses during pulping and bleaching processes, and since hemicelluloses contributes to the strength of paper pulps, high pentosan content is desirable in general 28. Pentosan content is the on higher side in E. europhyllia (16.47%), E. torrelliana (16.57%) and E. grandis of Bhadrachalam origin (18.66%) and 12±2% in other species of eucalyptus except E. 471 (hybrid) (8.66%) which is on the lower side. Pulping, black liquor characteristics and paper properties Table 3 presents the results of pulping, black liquor characteristics and paper properties of 11 species of eucalyptus. Screened pulp yield of E. grandis of Saharanpur origin is 51.02% at kappa number of with screening rejects of 0.51%. It may be explained based on facts that most of the alkali is consumed during the heating-up stage. Thus, such cooking conditions do not cause much cellulose depolymerization but may vary the amount of dissolved hemicelluloses at different cooks, resulting in characteristic variations in pulp yields 29. Screened pulp yield of E. grandis of Bhadrachalam origin slightly decreases (49.75%) with an increase in kappa number (22.25) and screening rejects (0.98%). The decrease in pulp yield may be due to lower ash content and high pentosan content in E. grandis of Bhadrachalam. The high solubility of pentosan (hemicelluloses) due to alkaline hydrolysis (depolymerization) of the polysaccharide chains and further degradation reactions (secondary peeling) is probably ascribed to their relatively low molecular masses 30. The pulping results of E. torrelliana, E. 348 (hybrid) and E. camaldulensis resemble to that of E. grandis of Saharanpur origin. However, the kappa number of E. 348 (hybrid) is on the higher side (i.e. 24). The low screened pulp yields of E. europhyllia (45.05%), E. 413 (hybrid) (47.48%), E. 266 (hybrid) (46.84%) and E. 471 (hybrid) (45.93 %) may be due to variation in chemical compositions and peeling reactions. Residual lignin left after kraft pulping depends on various factors, i.e., extractives in wood, polysaccharides of low molecular masses and heart wood to sap wood ratio 31. Total solids of black liquor which represents mass ratio of dried black liquor to unit of black liquor before drying are about 13±1% in all the eucalyptus species. The higher the total solids, the less water the black liquor contains and the hotter the adiabatic combustion temperature. Organic in black liquors generated in different eucalyptus species varies from to 64.48% and inorganic from to 44.60%. Combustion of the organic portion of liquor in a recovery boiler will form sodium sulphide and sodium carbonate and thus, produce heat. Then, the heat produces high pressure steam to generate electricity and low pressure steam for process use. Table 3 presents the paper properties of different eucalyptus species. As the bulk of paper sheet increases from 1.76 (E. grandis of Saharanpur origin) to 1.79 (E. 266 hybrid), there is an insignificant decrease in burst and tear indexes with a slight improvement in tensile index. The higher bulk is mainly due to thick cell wall thickness which provides less surface contact for bonding. Similar trends are observed in case of E. grandis (Bhadrachalam origin) (1.52 cm 3 /g), E. camaldulensis (1.55 cm 3 /g), E. torrelliana (1.61cm 3 /g), and E. tretecornis (1.66 cm 3 /g). However, the bulk of E. europhyllia,

6 150 INDIAN J. CHEM. TECHNOL., MARCH 2011 Parameters Table 3 Pulping and black liquor characteristics and strength properties of paper made from different species of eucalyptus Eucalyptus species and hybrids Pulp evaluation Screened pulp yield, % Screening rejects, % Kappa number Black liquor characteristics Residual alkali, g/l Total solids, % Organics, % Inorganics, % Paper properties Final 0 SR Bulk, cm 3 /g Burst index, kpam 2 /g Tear index, mnm 2 /g Tensile index, Nm/g Cooking conditions: Active alkali 16% (as Na 2 O), Time to temp 105 min, Time at temp 90 min, Max temp 165± 2 C, Liquor to wood ratio 2.8:1 1= E. grandis, 2= E grandis, 3= E. torrelliana, 4= E. europhyllia, 5= E. camaldulensis, 6= E. tretecornis, 7= E. alba, 8= E. 413 (hybrid), 9= E. 266 (hybrid), 10= E. 471 (hybrid), 11= E. 348 (hybrid) E. 348 (hybrid) and E. alba are the same but marginal difference in strength properties may be due to variation in Runkel ratio, flexibility and rigidity coefficient. E. 413 (hybrid) and E. 471 (hybrid) show the similar trends of bulk with strength properties but variation in tensile index and burst index is due to difference in morphological characteristics. Change in trend of some properties may be due to the fact that the strength properties of paper also depends upon other factors like: formation and density of fibres, fibre orientation and the relative bonded area and upon the geometrical and strength properties of the fibre themselves. Conclusions The analysis of fibre dimensions and chemical investigation of various eucalyptus species with hybrids along with the use of certain indices showed that E. grandis of Bhadrachalam and Saharanpur origins are suitable for social forestry in north Indian climatic condition to produce pulp mainly for writing and printing grades. Low kappa number, high pulp yield and good strength properties validates promotion of E. grandis of Bhadrachalam and Saharanpur origins, E. torrelliana, E. camaldulensis and E. alba for pulp production. Social forestry provides cellulosic fibrous raw materials of high biomass (<48%) by selecting fast growing selected eucalyptus species so that India could almost rely on its own raw materials for the production of all newsprint, writing and printing and tissue papers at reasonable costs. References 1 Barefoot A C, Hitchings R G & Ellwood E L, Tappi, 47(6) (1964) Dadswell H E & Wardrop A B, Appita, 12 (1) (1954) Kellogg R M & Thykeson E, Tappi, 58 (4) (1975) Matolcsy G A, Tappi, 58 (4) (1975) Madakadze I C, Radiotis T, Li J, Goel K & Smith D L, Biores Technol, 69 (1999) Dutt D, Upadhyaya J S, Malik R S & Tyagi C H, Cellulosic Chem Technol, 39 (1-2) (2005) Lal M, Dutt D, Tyagi C H & Upadhyay J S, Tappi, 3 (2010) Ogbonnaya C I, Roy-Macauley H, Nwalozie M C & Annerose D J M, Ind Crops Prod, 7 (1997) Han J S, Mianowski T & Lin Y, in Kenaf Properties, Processing and Products, edited by Sellers T & Reichert N A, (Mississippi State University), 1999, Saikia S N, Goswami T & Ali F, Wood Sci Technol, 31(1997) Anonymous, Tappi Test Methods (Tappi Press, Atlanta, USA), Istek A, Cellulose Chem Technol, 40(6) (2006) DuPlooy A B J, Appita, 33 (1980) Bamber R K, Appita, 38 (1985) Ona T, Sonoda T, Ito K, Shibata M, Tamai, Y, Kojima Y, Ohshima J, Yokota S & Yoshizawa N, Wood Sci Technol, 35 (2001)

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