The effects of species on the thermomechanical pulping of balsam fir, black spruce, red spruce and white spruce

Transcription

1 T161 The effects of species on the thermomechanical pulping of balsam fir, black spruce, red spruce and white spruce By S. Johal, B. Yuen and P. Watson Abstract:There were no significant differences in refining energy consumption, fibre properties, or physical and optical properties between black, red or white spruce. Balsam fir required considerably less refining energy to a given freeness than any of the three spruces, and was consistently lower in sheet density, and significantly weaker in strength properties. However, balsam fir thermomechanical pulps have significantly superior optical properties than those from the three spruces. T REE AGE, juvenile/mature wood content, site quality, genetic origin, and environmental factors all strongly influence mechanical pulping and pulp quality. Canadian spruces are regarded worldwide as the benchmark wood species for thermomechanical (TMP) pulping. The superiority of the spruces has been attributed to its favourable fibre properties (fibre length, fibre coarseness and fibre wall structure), low extractives content, high wood density, and high brightness of the wood [1], resulting in good strength, optical and surface properties in paper. In eastern Canada, Balsam fir is usually mixed with spruces. In general, certain pulp properties (tensile index and brightness) of firs are slightly inferior to spruce mechanical pulps [1]. There is limited published literature to relate the wood characteristics of either spruce or balsam fir to mechanical pulping [2-5]. Although spruce/balsam fir chip mixtures are widely used in TMP pulping, published literature is scarce on the properties variability for mixtures of these species. Wood costs, coupled with increasing demands for improved pulp quality, are creating significant challenges for the pulp and paper industry. In order to reduce pulp process and properties variability, it is essential to understand wood quality variability within and between species. Once such information is developed, it will be possible to quantify the costs associated with species variability, and hence better optimize the supply chain. This report will describe the fibre and sheet properties of TMP pulps from balsam fir, black spruce, red spruce and white spruce species. An attempt was made to relate fibre and sheet properties to within and between species differences. Fibre and sheet properties of TMP pulps from selected balsam fir/white spruce and balsam fir/red spruce chip mixtures have also been determined. EXPERIMENTAL Site and Tree Selection: Balsam fir, black spruce, red spruce and white spruce trees were sampled from three sites in Quebec and two sites in New Brunswick [6-7]. The spruce species were identified by gross morphological differences; tree form, needle and cone size and shape [8]. The trees chosen for this investigation were selected on the basis of field determination of site index, age, wood density, fibre length and fibre coarseness obtained from breast height (BH) increment cores from a total of 432 tree samples within 37 sample plots [6]. Location and site index (a standardized measure of an area s productive capacity) of each sample selected for this study has been given elsewhere [6]. Chip Preparation: The bolts selected from nine balsam fir, four black spruce, four red spruce and eight white spruce trees were debarked, and then segregated by a portable sawmill to produce mature wood (over 40 years old) sections. Only mature wood (MW) sections were chipped using a CM&E 10-knife disc chipper as representative of sawmill residual chips. Each of the 25 chip samples were well homogenized, and then screened on a Burnaby Machinery and Mill Equipment Ltd. two-deck laboratory chip classifier to remove oversize (>32 mm) and the fine (<8 mm) material. The solids contents of the chip samples used for mechanical pulping were in the range of 40.5 to 71.5% wet wood basis. Thermomechanical Pulping: In first-stage refining a 30.5-cm Sunds Defibrator TMP 300 singledisc laboratory refiner was used. A Bailey Network 90 system was used to control and/or monitor the refining variables. A high freeness pulp sample from each of the 25 first-stage TMP pulps was given one or two further passes in a 30.5-cm Sprout Waldron open-discharge laboratory refiner equipped with type D2A507 plates at 15-17% refining consistency. Each sample was refined at three energy levels in the freeness range from 62 to 190 ml CSF. After pulp latency removal, each pulp was screened on a six-cut laboratory flat screen to determine screen rejects. Bauer-McNett fibre classifications were determined on screened pulps. Representative samples from each of the 75 pulps were analysed for fibre length using a Kajaani FS- 200 instrument. Handsheets were prepared with white-water recirculation to minimize the loss of fines and tested for structural, mechanical and optical properties using PAPTAC standard methods. Handsheet roughness was measured by S. JOHAL, B. YUEN, P. WATSON, pwatson@paprican.ca PULP & PAPER CANADA 107:7/8 (2006) 41

2 T162 thermomechanical pulps TABLE I. Properties of thermomechanical pulps from balsam fir, black spruce, red spruce, and white spruce at a given freeness of 100 ml CSF. Balsam Fir F3-14 F3-16 F3-21 K1-7 K1-9 & K5-1 & K5-2 & P2-1 P2-4 K1-16 K5-3 K5-5 Specific Refining Energy (MJ/kg) Rejects (% od Pulp) Apparent Sheet Density (kg/m 3 ) Burst Index (kpa m 2 /g) Tensile Index (mn m 2 /g) Tear Index (mn m 2 /g) Sheffield Roughness (SU) Brightness (%) Scattering Coefficient (cm 2 /g) R-48 Fraction (%) Fines (P-200) (%) Length Weighted Average Fibre Black Spruce Red Spruce K6-2 & K6-15 & K7-1 & K7-2 & K1-1 K1-20 K7-4 & K7-12 & K6-13 K6-16 K7-10 K7-5 K7-13 K7-14 Specific Refining Energy (MJ/kg) Rejects (% od Pulp) Trace Apparent Sheet Density (kg/m 3 ) Burst Index (kpa m 2 /g) Tensile Index (mn m 2 /g) Tear Index (mn m 2 /g) Sheffield Roughness (SU) Brightness (%) Scattering Coefficient (cm 2 /g) R-48 Fraction (%) Fines (P-200) (%) Length Weighted Average Fibre White Spruce F3-14 F3-25 K1-14 K1-22 K5-4 K5-8 P2-7 P2-8 Specific Refining Energy (MJ/kg) Rejects (% od Pulp) Trace Apparent Sheet Density (kg/m 3 ) Burst Index (kpa m 2 /g) Tensile Index (mn m 2 /g) Tear Index (mn m 2 /g) Sheffield Roughness (SU) Brightness (%) Scattering Coefficient (cm 2 /g) R-48 Fraction (%) Fines (P-200) (%) Length Weighted Average Fibre Sheffield instrument and values expressed in Sheffield Units (SU). The raw data for the TMP pulps are available upon request. RESULTS, DISCUSSION Analytical Methods: In general, appropriate baseline values of pulp freeness are commonly used to monitor mechanical and optical properties of TMP pulps. Therefore, to facilitate data analysis and discussion, the raw data were standardized by interpolation or extrapolation to a freeness of 100 ml CSF, Table I. The standardized data at 100 ml CSF was used to perform analysis of variance (ANOVA) to determine energy consumption, fibre properties, strength and optical properties differences between the spruce samples [9]. The summary of this analysis and Fig. 1 show that there were no significant differences in energy consumption, fibre properties or sheet properties between black spruce, red spruce and white spruce. Since the three spruce species have a similar range of fibre and handsheet properties, the standardized data at 100 ml CSF was used again to find differences between three spruces and balsam fir. The summary of this analysis has been given elsewhere [9]. Energy Consumption: At a given freeness of 100 ml CSF, the three spruces required a similar range of refining energy as shown in Fig. 1 and confirmed by ANOVA [9]. The specific energy consumption for balsam fir, black, red and white spruce to reach a given freeness in the range from 60 to 190 ml CSF is shown in Fig. 2. The corresponding values standardized to 100 ml CSF are shown in Table I. As expected, because of between-tree, between-site, and between-species differences, the data in Fig. 2 show considerable scatter. This highlights the importance of multiple tree assessments when describing the wood, :7/8 (2006) PULP & PAPER CANADA

3 T163 FIG. 1. At a given freeness there are no significant differences in refining energy, tensile strength, fibelength, sheet density or scattering coefficient between black, red and white spruce. FIG. 2. Specific refining energy vs. unscreened freeness for all four species shows that balsam fir requires the least energy to a given freeness. FIG. 3. At a given freeness significant differences exist between balsam fir and spruces at the fundamental fibre, strength and optical properties level. FIG. 4. At a given freeness of 100 ml CSF, low chip density balsam fir requires considerably less energy than high-density black, red and white spruce. fibre and pulping characteristics of any species. Among all four species, balsam fir consistently needed the least energy to reach a given freeness. The significant difference in refining energy between balsam fir (8.94 MJ/kg) and spruces (12.01 MJ/kg) is clearly shown in Fig. 3, and is further confirmed by analysis of variance [9]. As most TMP operations target a pulp freeness, this 34% variation in specific refining energy between these species explains a major source of production variability and has significant cost implications. The influence of wood density on refining energy consumption in thermomechanical pulping is not clear. In general, wood density has been found not to have the dominant effect on refining energy [3, 10-12]. Wood density is an indicator but not a predictor of energy consumption [13]. Even for a given species with the same wood density, energy consumption to a given freeness can vary as much as 30% [14]. In this study, we found that the specific refining energy required to refine chips to a given freeness decreased with increasing chip density, Fig. 4. Earlier, Miles and Karnis had postulated that the energy consumption to a given freeness depends on the initial fibre properties, especially the coarseness and the length of fibres in wood [13]. The results of this investigation do not support their hypothesis, since the initial kraft pulp coarseness and fibre lengths of all four species were more-or-less similar [7]. The relative energy requirement ranking between different wood species with different wood densities, and fibre properties is more complex than the current knowledge would allow, and thus fibre cell wall properties, (perimeter, thickness and microfibril angle) must also be considered. In Fig. 4, the species differences are very clear and each set of points is surrounded by envelopes rather than a bestfit line or curve. The raw data for black, red, and white spruce show considerable scatter because of wide range of chip densities (317 to 406 kg/m 3 ) observed compared to the relatively narrow range (298 to 336 kg/m 3 ) for balsam fir. Two white spruce samples had exceptionally low chip densities. Such differences in wood density also have significant implications for mill production costs. Fibre Properties: Figure 3 and Table I show clearly that at a given freeness of 100 ml, CSF balsam fir length-weighted average fibre length (LWAFL) values were significantly lower than three spruces. It is interesting to note that the initial fibre length and coarseness values from kraft pulping study of these four softwood species were more-or-less similar [7]. However, at a given freeness LWAFL, and long-fibre fraction values for balsam fir TMP pulps were consistently lower than that from the three spruces, which suggests fibres were cut in balsam fir. However, the onset of balsam fir fibre shortening during the refining process did not increase the fines content P-200 (passed through the 200-mesh screen of a Bauer- McNett fibre classifier). On the contrary, the data in Fig. 5 shows that balsam fir thermomechanical pulping consistently produced less fines than black, red and white spruce. This implies that balsam fir from these locations would provide an opportunity to tailor-make mechanical pulps with sheet density, strength, and optical properties distinctly different from those black, red and white spruce. Refin- PULP & PAPER CANADA 107:7/8 (2006) 43

4 T164 scattering coefficient between spruces and balsam fir has been postulated most likely due to the lower wall thickness of balsam fir compared to spruces [14-15]. In addition, some balsam fir samples are known to give very poor quality pulps due to the variability inherent in this species [15]. This variability can be significantly reduced by refining at lower intensities [15]. These data clearly show that balsam fir would provide a more opaque sheet than those from black, red and white spruce at the same freeness but at a lower sheet conthermomechanical pulps FIG. 5. At a given freeness, balsam fir TMP pulps consistently produced less fines than black, red and white spruce TMP pulps. FIG. 6. Within the freeness range from 60 to 205 ml CSF, black, red and white spruce TMP pulps give denser sheets than balsam fir TMP pulps. FIG. 7. At a given freeness, balsam fir TMP pulps are considerably superior in scattering coefficient than those from the three spruces. ing at lower refining intensity would preserve the length of balsam fir fibres [15]. This might be a way to fully benefit from the characteristics of these fibres. Sheet Consolidation and Strength Properties: The development of sheet density with freeness is shown in Fig. 6. As expected, sheet density increased with decreasing freeness. Figure 6 also shows that at a given freeness balsam fir consistently gave less dense sheets than black, red, and white spruce. Analysis of variance [9], and standardized sheet density analysis at a given freeness of 100 ml CSF (Table I) confirm that these balsam fir TMP pulps gave less dense sheets than the corresponding black, red and white spruce. Figure 3 and analysis of variance [9] show that at a given freeness balsam fir TMP pulps had significantly lower tensile index than those from the three spruces, reflecting the lower sheet density of balsam fir. It is interesting to note that even though the strength properties of balsam fir are significantly lower than spruces, these strength properties compare favourably with other softwood species. Optical Properties: When compared at a given freeness, Fig. 7, or refining energy consumption [9] balsam fir TMP pulps were consistently superior in scattering coefficient properties than those from black, red and white spruce, with one exception. This is not surprising given the significant differences in fibre properties suggested by the refining energy and pulp strength properties. In general, scattering coefficient is greatly influenced by the quantity and quality of fines. Miles and Karnis reported that for a given amount of fines of a given quality (specific surface), the scattering coefficient of balsam fir was higher than that of black spruce and jack pine [14]. The differences in the FIG. 8. At a given freeness of 100mL CSF, the effects of balsam fir content on refining energy, tensile index, long-fibre fractions and fines content are as expected :7/8 (2006) PULP & PAPER CANADA

5 T165 solidation level. In general, the brightness values for the four species were somewhat similar. Thermomechanical Pulps from Balsam Fir/Spruce Chip Mixtures: Balsam fir and spruce chips are usually co-refined in varying mixtures in thermomechanical pulping process in eastern Canada. This necessitated the determination of energy consumption and sheet properties of TMP pulps from carefully controlled balsam fir/spruce mixtures. Based on fibre and sheet properties of TMP pulps from pure species, seven different chip mixtures consisting of balsam fir/white spruce and balsam fir/red spruce were used to prepare TMP pulps using the same refining conditions as described earlier in this report. The wood samples used were matched to the location from which they were obtained. Appropriate quantities of chips were used on an oven-dried weight basis to prepare the desired chip mixtures. The raw data were standardized by interpolation or extrapolation to 100 ml CSF and has been given elsewhere [9]. Increasing the balsam fir amount in the spruce furnish did not significantly reduce the energy requirements to a given freeness except when the balsam fir content reached very high levels [9]. The long-fibre fraction R-48, Fig. 8, fines content (P-200) (Fig. 8), and fibre length [9] decreased regularly with increasing balsam fir content in the balsam fir/red spruce chip furnish. TMP pulps from balsam fir/white spruce chip mixtures showed little or no change in either sheet density [9] or tensile index (Fig. 8) with increasing balsam fir substitution at given freeness. However, for TMP pulps from balsam fir/red spruce chip mixtures both sheet density [9] and tensile index (Fig. 8) decreased regularly with increasing balsam fir content in the chip furnish at a freeness of 100 ml CSF. Scattering coefficient increased regularly with increasing balsam fir content in both white and red spruce chip furnishes [9]. The ability to calculate the pulp properties from different chip mixtures is necessary to both predict and optimize the end product properties. Therefore nonlinear regression analysis, employing a second-order polynomial, was used to fit both pulp properties at 100 ml CSF, for example refining energy or tensile index, and balsam fir content (bfc) in chip mixtures over a range of combinations. The regression equations shown below describe the effect of balsam fir substitution in the chip furnish and also indicate that the trends are conclusive because of relatively high values of their coefficient of determination (R 2 ). Balsam fir/white spruce: Refining energy (MJ/kg) = (bfc, %) (bfc, %) ; R 2 = Tensile index (N m/g) = (bfc, %) (bfc, %) ; R 2 = Sheet density (kg/m 3 ) = (bfc, %) (bfc, %) ; R 2 = Scatt. coefficient (cm 2 /g) = (bfc, %) (bfc, %) ; R 2 = Balsam fir/red spruce: Refining energy (MJ/kg) = (bfc, %) (bfc, %) ; R 2 = Tensile index (N m/g) = (bfc, %) (bfc, %) ; R 2 = Sheet density (kg/m 3 ) = (bfc, %) (bfc, %) ; R 2 = Scatt. coefficient (cm 2 /g) = (bfc, %) (bfc, %) ; R 2 = Although there is no mechanistic model that can relate the sheet properties of pulps produced from various chip mixtures to the properties of the fibres of the individual components, the non-linear regression equations shown above can be used to predict the properties of balsam fir/white spruce and balsam fir/red spruce chip mixtures. CONCLUSION There were no significant differences in energy consumption, fibre properties, or sheet properties between the black, red and white spruce samples assessed in this trial obtained from similar geographic locations. At a given freeness value the use of balsam fir from these locations would reduce energy cost since it requires considerably less energy than any of the three spruces from these locations, however the low chip density of balsam fir might adversely affect production rate. At a given freeness balsam fir consistently produced sheets with lower density than spruces. Balsam fir TMP pulps were somewhat weaker in strength properties than those of the spruces, but exhibit superior optical properties. Non-linear regression equations were shown to be necessary to predict the properties of balsam fir/white spruce and balsam fir/red spruce chip mixtures. ACKNOWLEDGEMENTS The authors are grateful to Derek Dranfield, Shanley Pitts and Maxwell McRae for their extensive field work in obtaining the wood samples used for this study. Special thanks to Paul Bicho and Ashif Hussein for their help in conducting the statistical analysis reported here. The authors would also like to thank Andy Garner, John Wood, Keith Miles and Ingunn Omholt for reviewing this manuscript. LITERATURE 1. VARHIMO, A., TUOVINEN, O. Papermaking Science and Technology. Mechanical Pulping. Chapter 5. ED. Jan Sundholm. Atlanta: Finnish Paper Engineer s Association and TAPPI (1999). 2. DE MONTMORENCY, W.H. The Relationship of Wood Characteristics to Mechanical Pulping. Pulp Paper Mag. Can. 66(6), T (June 1965). 3. BRILL, J.W. Effects of Wood and Chip Quality on TMP Properties. Proc., Intl Mech. Pulp. Conf., Stockholm, (1985). 4. KÄRENLAMPI, P. Spruce Wood Fiber Properties and Mechanical Pulps. Pap. Ja Puu, 74(8): (1992). 5. KÄRENLAMPI, P. Spruce Pulpwood Quality Parameters. Pap. Ja Puu 74(10): (1992). 6. PITTS, S. WATSON, P. The Application of Stand Level Information to the Prediction of Fibre Quality in Eastern Spruces and Balsam Fir. Pointe Claire, QC: PRR 1594 (2002). 7. HUSSEIN, A., GEE, W.Y. WATSON, P. Kraft Pulping Characteristics of Eastern Spruces and Balsam Fir Mixtures. Pointe Claire, QC: PRR 1706 (2004). 8. FARRAR, J.L. Trees in Canada. Natural Resources Canada. Ottawa: Fitzhenry & Whiteside Limited and Canadian Forest Service (1997). 9. JOHAL, S.S., YUEN, B., WATSON, P. The Effects of Species on the Thermomechanical Pulping of Balsam Fir, Black Spruce, Red Spruce, and White Spruce. Proc., 91st PAPTAC Annual Meeting, Montreal, C55-63 (2005). 10. CORSON, S.R. Wood Characteristics Influence Pine TMP Quality. Proc., Intl Mech. Pulp. Conf., Minneapolis, MN, (1991). 11. HATTON, J.V. JOHAL, S.S. Managed Jack Pine Forests: III. Refiner Mechanical Pulps from Juvenile, Mature, and Top Wood, and their Relationships with Wood and Fibre Properties. Pointe Claire, QC: PPR 879 (1991). 12. HATTON, J.V., JOHAL, S.S. Managed Jack Pine Forests: IV. Chemithermomechanical Pulps from Juvenile, Mature, and Top Wood. Pointe Claire, QC: PPR 945 (1992). 13. MILES, K.B., KARNIS, A. Wood Characteristics and Energy Consumption in Refiner Pulps. JPPS 21(11): J (1995). 14. MILES, K.B., KARNIS, A. Energy Consumption in Mechanical Pulping the Effect of Wood Supply. Pointe Claire, QC:, PPR 1015 (1993). 15. McDONALD, D., MILES, K., AMIRI, R. The Nature of Mechanical Pulping Process. Pointe Claire, QC: PPR1577 (2002). Résumé: Nous n avons noté, entre les épinettes noire, blanche ou rouge, aucune différence importante dans la consommation d énergie pour le raffinage, les propriétés des fibres, ou les propriétés physiques ou optiques. Le sapin baumier a requis beaucoup moins d énergie de raffinage pour obtenir un indice d égouttage donné que n importe lequel des trois types d épinettes, la densité de la feuille était beaucoup plus faible, et la résistance était significativement plus faible. Toutefois, les pâtes thermomécaniques de sapin baumier possèdent des propriétés optiques de beaucoup supérieures à celles des trois types d épinettes. Reference: JOHAL, S., YUEN, B., WATSON, P. The effects of species on the thermomechanical pulping of balsam fir, black spruce, red spruce, and white spruce. Pulp & Paper Canada 107(7/8): T (July/August, 2006). Paper presented at the 91st Annual Meeting in Montreal, QC, on February 7 to 10, Not to be reproduced without permission of PAPTAC. Manuscript received on November 23, Revised manuscript approved for publication by the Review Panel on August 9, Keywords: THERMOMECHANICAL PULPS, PULP PROPERTIES, ABIES BALSAMEA, PICEA MARIANA, PICEA RUBENS, PICEA ENGELMANNII, HAND SHEETS, EQUATIONS. PULP & PAPER CANADA 107:7/8 (2006) 45