© 2017 The Authors. Published by Center for Pulp and Paper, Ministry of Industry, Indonesia
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objective of this study was to investigate the suitability of kenaf core for pulping by assessing its physical, chemical and pulp properties.
MATERIALS AND METHOD
Kenaf core, a variety of V6, four months old and waste from bast extraction, was supplied by Lembaga Kenaf Dan Tembakau Negara (LKTN), Kelantan, Malaysia.
Chemical analysis
An experiment was run to quantify the main chemical components and fibre morphology of kenaf core as described in TAPPI Standards (TAPPI 1994). For chemical composition analysis, the kenaf core was ground into fine fibres using a Wiley Mill. In obtaining a homogenous sample, the ground fibres were then sieved through BS 40-mesh (425 µm) and BS 60-mesh (250 µm) sieve screens to remove fine and rough fibres, as described in Technical Association of the Pulp and Paper Industry (TAPPI) Standards T 257 - Sampling and Preparing Wood for Analysis. The determination of extractives content was carried out based on TAPPI T 204, where ethanol-toluene (1:2) was used as the solvent. Holocellulose content of the extractive-free sample was determined according to Wise et al. (1946). Α- cellulose content, was analysed according to the procedure described in the TAPPI T 203. Pentosan was determined using the method of Savard et al. (1954). The determination of lignin, alkali solubility, water solubility, ash, and silica content were performed as per TAPPI Standards Methods T 222, T 212, T 207, and T 211, respectively. Each analysis was carried out in triplicate. For fibre morphology – length, diameter, lumen and cell wall thickness – image analyser was used for measurements. Fibre slenderness, flexibility and Runkel ratio ware calculated according to available formula (TAPPI 1994).
Pulping
Three pulping processes were used to produce pulps – mechanical, chemical and chemimechanical, represented by refiner mechanical pulping (RMP), soda anthraquinone pulping (soda-AQ), cold soda refiner mechanical pulping (cold soda RMP) and chemimechanical pulping (CMP) respectively.
Refiner Mechanical Pulping (RMP) Process
One (1) kg (oven-dry weight) kenaf core chips were soaked overnight fed into 12-inch single disc laboratory refiner (Sprout Waldron) used in a two-stage operation. The primary stage was operated at a load between 18 and 20 amperes at an inlet consistency of 10% and with the refiner plate (D2A507, Sprout Waldron) clearance set at 0.035 inches. The chips were passed into the refiner using the ribbon-type electric screw feeder. The collected stocks were refined in a secondary stage that was operated with an inlet consistency of 7%, and with the refiner plate clearance set at 0.005 inches. The pulp obtained was thoroughly washed and screened by Somerville fractionators. The total pulp yield was calculated as the sum of the screened pulp yields, and screen rejects. Handsheets preparation and handsheets property measurements were prepared according to TAPPI Standards (TAPPI 1994).
Cold Soda Refiner Mechanical Pulping Process (cold soda RMP)
One (1) kg (oven-dry weight) kenaf core chips were soaked for 18 hours in a 5% solution of sodium hydroxide (NaOH) at room temperature. The liquor to kenaf core ratio was 7:1. After impregnation, the chips were washed to remove all NaOH from the surface. The pre-treatments kenaf core chip was fed into 12-inch single disc laboratory refiner (Sprout Waldron) used in a two-stage operation. The primary stage was operated at a load between 18 and 20 amperes at an inlet consistency of 10% and with the refiner plate (D2A507, Sprout Waldron) clearance set at 0.035 inches. The collected stocks were refined in a secondary stage that was operated with an inlet consistency of 7%, and with the refiner plate clearance set at 0.005 inches. The pulp obtained was thoroughly washed and screened by a Somerville fractionators. The total pulp yield was calculated as the sum of the screened pulp yields, and screen rejects. Handsheets preparation and handsheets property measurements were prepared according to TAPPI Standards (TAPPI 1994).
101 Chemi-mechanical Pulping (CMP) Process
One (1) kg (oven-dry weight) kenaf core chips were soaked for 18 hours in a 5% solution of sodium hydroxide (NaOH) at room temperature before heated to a temperature of 60oC in a rotary digester. The liquor to kenaf core ratio was 7:1. After impregnation, the chips were washed to remove all NaOH from the surface. The pre-treatments kenaf core chip was fed into 12-inch single disc laboratory refiner (Sprout Waldron) used in a two-stage operation. The primary stage was operated at a load between 18 and 20 amperes at an inlet consistency of 10% and with the refiner plate (D2A507, Sprout Waldron) clearance set at 0.035 inches. The collected stocks were refined in a secondary stage that was operated with an inlet consistency of 7%, and with the refiner plate clearance set at 0.005 inches. The pulp obtained was thoroughly washed and screened by a Somerville fractionators. The total pulp yield was calculated as the sum of the screened pulp yields, and screen rejects. Handsheets preparation and handsheet property measurements were prepared according to TAPPI Standards (TAPPI 1994).
Soda-AQ Pulping Process
The conditions employed throughout the experiment were as follows: liquid to material ratio was 6:1, active alkali of 24%, AQ was 0.1% of kenaf (both are based on oven-dried raw material), cooking temperature was 160oC, time to maximum temperature was 90 minutes and time at temperature was 90 minutes. At the end of digestion, the softened pulp was disintegrated for 5 min in a hydropulper, washed on a screen. Disintegrated pulps were screened in the vibratory flat screen, Somerville fractionators, with a slot width 0.15 mm. The total pulp yield was calculated as the sum of the screened pulp and sieves or screen reject yields. Handsheets preparation and handsheets property measurements were prepared according to TAPPI Standards (TAPPI 1994).
RESULTS AND DISCUSSION
The kenaf core chemical content and fibre morphology are tabulated in Table 1 and Table 2.
Table 1. Chemical compositions for kenaf core
Chemical composition Content, %
Alcohol-acetone extractives 2.79
Lignin 20.26
Holocellulose 74.83
Alpha-cellulose 50.15
Hemicellulose 24.68
Ash 1.99
Hot water extractives 6.26
Table 2. Fibre morphological characteristics of core fibres Characteristics
Length (mm) 0.72
Diameter (µm) 29.26
Lumen (µm) 20.87
Thickness (µm) 4.32
Slenderness ratio 25.31
Flexibility coefficient 72.33
Runkel ratio 0.43
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The kenaf core pulp and paper properties are tabulated in Table 3 and Table 4.
Table 3. Pulp properties of kenaf core
Property Process
RMP Cold soda RMP CMP Soda-AQ
Total yield (%) 93.2 85.5 73.6 44.7
Screened yield (%) 77.7 75.5 69.2 44.7
Sieve (%) 15.5 10.0 4.6 0
The pulping process influenced the pulping properties. RMP had the highest total yield whereas soda-AQ had the lowest yield. Soda-AQ pulping had the lowest yield due to the dissolution of lignin and other components during the pulping process. The more the chemicals are involved, the lower the yield and lignin content since chemical action degrade and solubilises components of the kenaf core, especially lignin and hemicelluloses.
Table 4. Paper properties of kenaf core
Property Process
RMP Cold soda RMP CMP Soda-AQ
Density (g/cm3) - 0.49 0.74 0.61
Tensile index (Nm/g) - 0.41 0.78 0.51
Tear index (mNm2/g) - 3.51 6.41 4.98
Burst index (kPam2/g) - 1.85 4.40 2.27
Double fold (800 K.M) - 6.00 530.00 24.00
The pulping process had influenced the paper properties. Paper made from CMP pulp had the highest strength properties while RMP had the lowest. Mechanical pulps are commonly produced from softwood species, which has very long fibre; while the shorter and thinner hardwood fibres are more severely damaged that will form an exceedingly weaker sheet (Smook 1992). CMP pulp gives the strongest paper since the lignin, which interferes with hydrogen bonding of fibres, is largely removed and exposes more hydroxyl and carboxyl groups for interfibre bonding. The removal of lignin will produce fibre that is more flexible and easier to collapse, thus increases interfibre bonding.
CONCLUSION
Technically chemi-mechanical pulping (CMP) process is the best because its pulp produced a paper with the highest quality compared to RMP, soda-anthraquinone (AQ) and cold soda RMP. From the economic and environmental point of views, soda-AQ is the worst compared to CMP and cold soda RMP. The production cost of CMP is lower soda-AQ than because it does not need very high temperature and chemical usage. The total yield of CMP was higher by 29% than soda-AQ. The CMP process was chosen because it is technically suitable for papermaking, economically viable due to its high yield and low heating and chemical cost; and environmentally friendly because its effluent needs least chemical treatment compared to soda-AQ. CMP was chosen for pilot plant trial.
ACKNOWLEDGMENTS
We would like to express our gratitude to FRIM and LKTN for the financial support.
REFERENCES
Ang, L.H., 2006. Cultivation of Kenaf (Hibiscus cannabinus) on Sand Tailings. FRIM Technical Information Handbook, No. 38. FRIM, Kepong.
103 ECER., 2010. Bank aid for ECER kenaf farmers. http://www.ecerdc.com.my/en/news-article/bank- aid-for-ecer-kenaf-farmers/ Accessed 13 March 2017.
Monti, A., and Zatta, A., 2009 From growing kenaf to its industrial use. 1st Workshop Poznàn.
http://www.crops2industry.eu/images/pdf/poznan/6%20UniBO.pdf. Accessed 27 June 2014
Smook, G.A., 1992. Handbook for Pulp and Paper Technologist. 2nd edition. Angus Wilde Publication, Vancouver.
TAPPI., 1994. TAPPI (Technical Association Of The Pulp And Paper Industry) Test Methods 1994- 1995. TAPPI Press, Atlanta.
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© 2017 The Authors. Published by Center for Pulp and Paper, Ministry of Industry, Indonesia