1. BLEACHING OF BAMBOO COLD
SODA PULPS
Results and Discussions
Constant Conditions
Pretreatment with Acid
Pretreatment with Alkali
Bleaching Conditions in Different Stages
Effect of Peroxide in Alkali Pretreatment
Pretreatment with Dye
Bleaching Conditions in Different Stages
Conclusions
Experimental
Raw Materials
Bleaching
2. HIGH YIELD SEMI-CHEMICAL PULPING OF
MIXTURE OF BAMBOO AND
MIXED HARDWOODS
Raw Material
Experimental and Results
Sulphate Semi-Chemical Process
Kraft Green Liquor-Semi-Chemical Process
Neutral Sulphite Semi-Chemical Process
Discussion
Sulphate Semi-Chemical Process
Green Liquor Semi-Chemical Process
Neutral Sulphite Semi-Chemical Process
Conclusion
3. DEVELOPMENT IN HIGH YIELD PULPING PROCESS
Mechanical Process
Semichemical Process
Chemical Process
Alkaline Chemical Process
Sulfite process
Organic Catalyst to High Yield Pulping
AQ Pulping Technology
Polysulfide-AQ Process
Alkaline Sulfite-AQ Pulping
Experimental
4. THERMO-MECHANICAL PULPS FOR NEWSPRINT
MANUFACTURE FROM TROPICAL PINES
Raw Materials
Experimental
Preparation of Thermo-Mechanical Pulps
Results and Discussions
5. A STUDY ON REPLACEMENT OF SODIUM
SULPHATE BY AQ-LARGE SCALE TRIAL
Anthraquinone an Aid to Pulping
Laboratory Scale Investigations at Central Research Laboratory, Dalmianagar
Plant Trial with AQ
Evaluation of Mill Pulp
Discussion and Results
Conclusions
6. ZETA POTENTIAL CONCEPT IN PAPER SIZING
Electro Kinetic (Zeta) Potential-A Concept
The Theory of Electrical Double Layer
Stern’s Modified Double Layer
The Meaning and Limitations in the Application of
Electro Kinetic Theory
to the Paper Sizing
Behaviour of Alum in Water
Electro Kinetic Properties of Alum-rosin
Size Precipitate and the Sized Fibre
Conclusion
Nomenclature
Greeks
7. ECONOMICS OF BAMBOO AND HARDWOOD PULPING
BY ANTHRAQUINONE CATALYSED-KRAFT-PROCESS
Experimental Design & Observations
Results & Discussions
Conclusion
8. EFFECT OF BLEACHED PULP VISCOSITY ON STRENGTH
PROPERTIES OF BAMBOO SULFATE PULP
Experimental
Pulping
Bleaching
Physical Strength Properties
Chemical Analysis
Observations and Discussions
Conclusion
9. ALKALI/OXYGEN DELIGNIFICATION AND
BLEACHING OF SODA BAMBOO PULP
Experimental
Discussions
Conclusions
10. ALKALI/OXYGEN DELIGNIFICATION AND BLEACHING
OF SODA BAMBOO PULP, BAMBOO + MIXED HARD
WOOD PULP (70 : 30) AND MIXED HARDWOOD PULP
Experimental and Results
Discussions
Conclusion
11. SODIUM CARBONATE IN ALKALI EXTRACTION DURING
BLEACHING BAMBOO (D. STRICTUS) PULP
Experimental
Study on Sequentially Chlorinated (H/C) Pulp
Study on Chlorinated Pulp
Results and Discussion
Conclusions
12. EFFECT OF HEMICELLULOSES ON
UNBLEACHED SOFTWOOD KRAFT PULP
Materials and Methods
Enzyme Treatments
Bleaching Experiments
Chemical Composition and Kappa Number Analyses
Microscopic Analysis
Numerical Measurement of Colour
Results and Discussion
Chemical Changes After Enzyme Treatment
Bleaching Experiments
Graff ‘C’ Stain
Numerical Measurement of Colour
Accessibility Changes and Simons’ Stain
Deuterium Oxide Exchange
Simons’ Stain
Conclusions
13. THERMODYNAMIC FUNCTIONS OF THE
REACTION BETWEEN LIGNIN AND
HYDROGEN PEROXIDE DURING BLEACHING
Experimental
Isolation of Thiolignin
Preparation of Hydrogen Peroxide Solution
Reaction of Thiolignin with Hydrogen Peroxide
Results and Discussion
Analysis of Kinetic Data
Order of the Reaction and Variation of Rate
Constant with Reaction Parameters
Validity of Arrhenius Equation (Reaction Rates and
Temperature Changes)
Estimation of various Thermodynamic Functions
Conclusions
14. SEQUENTIAL BLEACHING
Experimental Procedure
Discussions of the Results
Bleach Consumption
Physical and Chemical Properties
Pollution Load of the Filtrate
Conclusion
15. MANUFACTURE OF CORRUGATING MEDIUM PAPER
UTILIZING 100% BAGASSE FURNISH
Process Suggested for Making
Corrugating Medium from 100% Bagasse
Fibre Preparation
Depithing at Paper Mills
Digestion Cycle
Stock Preparation
16. EFFECTIVE UTILIZATION OF CHEMICALS IN
PULP AND PAPER MILLS
Digester House
Chemical Recovery Section
Bleach Plant
Chemical and Stock Preparation
Effluents
17. EFFECTIVE USE AND RECOVERY OF
CHEMICALS IN COLD SODA PULPING
Experimental
Chemical Treatment of E. Tereticornis
Eta Reed Sulphate Pulping
Evaporation and Burning Properties of Kraft and
Cold Soda Spent liquors
Results and Discussions
Chemical Consumption
Pulp Properties
Composition of Liquors
Pollution Loads
Properties of Spent Liquors
Material Balances
Conclusions
18. EFFECTIVE USE AND RECOVERY OF CHEMICALS IN
COLD SODA PULPING WITH PARTIALLY CLOSED SYSTEM
Chemical Treatment of E. Tereticornis
Results and Discussions
Conclusions
19. MAINTENANCE ENGINEERING IN PULP
AND PAPER INDUSTRY
Inspection
Lubrication
Servicing
Maintenance Problems
20. LIMITATION TO SATISFACTORY OPERATION OF
WET END OF PAPER MACHINE
Basis Weight Profile
Head Box Pulsation
Drainage Formation and Sheet Structure
The Head Box
Rectifier Roll Head Boxes
Micro Turbulence Head Boxes
Web Formers
Twin Wire Forming
Schmidt Classification
Norman Classification
High Consistency Forming
Ancillary Equipments
Wet Web Strength
Limitations of Water Removal on Pressing
Conclusion
21. DESIGN AND APPLICATION OF REFINERS
IN STOCK PREPARATION
Conical Refiners
Shallow Angle Refiner
Steep Angle Refiners
Double Disc Refiners
Safety Devices
Influence of Machine Variables on Refining
Batch Refining
Machine Refiners
22. WET FELT DESIGNING TECHNIQUES
Pressing
Case Study
Recommendations
23. MODERNIZATION AND OPTIMUM UTILIZATION OF
EVAPORATORS FOR HARDWOOD BLACK LIQUORS-MILL
EXPERIENCE
Hardwood Black Liquors
Recovery Boilers and Required Liquor
Solids
Original Evaporator Units
Installation of a Pump in Between First
Pass and Second Pass of Concentration Effects of
Both Units
Conversion of Concentration Effect of
First (OLD) Unit to a Finisher
Introduction of a New Finisher Effect
Utilization of Vent Vapour from Finisher
Changing the Liquor Entry from Tangential to Radial and
Modification of Flash Chamber
Utilization of Vapour from Improvised Finisher of
Old Street
Conclusions
24. PAPER MACHINE EFFLUENT
Experimental
Discussions
Mode of Treatment for Paper Machine Effluent
Results
Conclusion
25. CONICAL REFINERS AND WIDE-ANGLE REFINERS IN
CONTINUOUS AND BATCH REFINING SYSTEMS FOR
BAMBOO AND HARDWOOD FURNISH
Introduction
Types of Refining Systems in the Mill
Conical and Wide Angle Refiners Strength, Development and Power Consumption
26. USE OF ‘NO PICK’ ROLL IN PAPER MACHINE PRESS
SECTION BASED ON SHORT-FIBRED TROPICAL
HARDWOODS AND AGRICULTURAL RESIDUES
Theoretical Considerations
The Problem
Press Section Before Modification
Press Section After Modification
Discussion
Conclusions
27. CONSUMPTION OF FURNACE OIL IN
RECOVERY BOILERS
Storage
Viscosity
Velocity
Turbidity & Causticity
Silica
Inverse Solubility
Organic Content and Calorific Value
28. NECESSITY TO RENOVATE AND
MODERNIZE PAPER MACHINE
Fourdrinier Part
Press Part
Dryer Section
Calender Stacks
Pope Reel
Conclusion
29. WET END OPERATION OF A PAPER MACHINE
Approach Flow
Head Box
The Slice
Approach System, Head Box and Slice at W.C.P.M.
Sheet Formation and Drainage on the Fourdrinier
Shake
Suction Boxes
Dandy Roll
The Couch
Conclusion
30. CLEANING SYSTEM-SHOWER FOR PAPER MACHINE
Mechanical Cleaning
Classification of Water Shower
Wire Cleaning Shower
Knock off Shower
Trim Knock-off Shower
Couch Roll Cleaning Shower
Return Roll Cleaning Shower
Dandy Cleaning Shower
Felt Shower
Special Features of Water Showers
Material of Construction
Insert Type Nozzle
Protective Shell
Programming
Filters
31. SUITABILITY OF KENAF CTMP FOR LINERBOARD
Experimental
Raw Material
Particle Size
Reduction and Washing
Injection Process
Fiberizing and Refining
Kraft Pulping
Pulp Testing and Handsheet Formation and Testing
Results and Discussion
Andritz Sprout-Bauer Pulping Trials
FPL Pulping Trials
Kenaf and Loblolly Pine Pulp Blends
Conclusions
32. NEWSPRINT FROM BLENDS OF KENAF CTMP
AND DEINKED RECYCLED NEWSPRINT
Experimental
Results and Discussion
Conclusion
33. FEASIBILITY OF USING KENAF
CHEMITHERMOMECHANICAL PULP IN
PRINTING AND WRITING PAPER
Results and Discussion
Andritz Sprout-Bauer and FPL Pulping Trials
Postbrightened Kenaf Thermomechanical Pulp
Conclusions
Experimental
Raw Material, Particle Size Reduction, and Material Wash
Injection Process
Fiberizing and Refining Process
Testing of Pulp and Forming and Testing of Handsheets
Postbrightening of Kenaf TMP
Brightness Reversion
34. MESTA/KENAF AS RAW MATERIAL FOR KRAFT PULPING
Raw Material
Experimental
Chemical Constituents of Mesta
Pulping and Sheet Making
Discussion
Physical Characteristics
Chemical Constituents
Pulping Bleaching and Black Liquor Characteristics
Morphological Studies
Properties of Pulp Sheets
Fibre Classification Results
Conclusions
35. RESPONSE OF KENAF VARIETY, HC-583
TO DIFFERENT LEVELS OF NITROGEN
Materials and Methods
Results and Discussion
Plant Height
Basal Diameter of Stalk
Dry Yield of Stalk
Increase in Dry Yield of Stalk per Kg. N Applied
Conclusion
36. PREHYDROLYSED KRAFT COOKING OF
JUTE STICK (EFFECT OF PREHYDROLYSIS CONDITION)
Experiments
Raw Materials
Digestion
Bleaching
Chlorine Water Bleaching
Analysis of the Pulp
Results & Discussion
A. Effect of Prehydrolysis Treatment on the Chemical Composition of Jute Stick
B. Loss of -Cellulose and Lignin after Prehydrolysis and Kraft Cooking of Jute Stick
Results of Bleached Pulps
Conclusions
37. HIGH YIELD PULP FROM JUTE STICKS
38. GREASE PROOF PAPERS FROM SULPHITE JUTE STICK PULP
Raw Material
Pulping
Conclusion
39. CHEMICAL RECOVERY BOILERS FOR PULP MILLS
USING AGRICULTURAL RESIDUES AS RAW MATERIALS
Present and Future Prospects of Agricultural Residue Usage in India
Advantages of Use of Agricultural Residues
Special Shelter Type Design for Smaller Units
40. PROBLEMS IN BL EVAPORATION IN INDIAN RAW MATERIALS
Black Liquor Screening
Black Liquor Soap Problem
Carbonaceous Deposits
Scale Formation and its Removal
Results Achieved
Technical
Vapour Side Scale
Method of Feeding Black Liquor
Mixed Feed
Quintuple Effect & Forced Circulation Evaporator
Forced Circulation Evaporator
41. UTILIZATION OF UNCONVENTIONAL RAW MATERIALS
Advantages at a Glance—for New Process
Cooking Liquor and Position of pH (Cold) during Pulping
Pulping Conditions and Delignification
Yield and General Properties of Pulp
Chemical Composition of Unbleached Pulp
Bleaching of Pulp
Paper Making Properties
Black Liquor and Recovery
Environmental Protection
Air Protection
Water Protection
Future Looks
Sulfite Shuttles into Space
42. UTILIZATION OF AGRICULTURAL RESIDUES USING
MECHANO-CHEMICAL PULPING PROCESS
Pilot Plant Trials at Cellulose and Paper Branch,
Forest Research institute and colleges, Dehradun
Production of Rice Straw Pulp
Production of Wheat Straw Pulp
Production of Bagasse Pulp
Production of Paper
Mechano Chemical Pulping on Industrial Scale
Chemical Preparation
Cooking
Search for Alternative Raw Material
Variables in the Process
Modification of Bagasse Pulping by Partial Replacement of
Sodium Hydroxide by Sodium Carbonate
Addition of Sodium Sulphide in Cooking Liquor in
Bagasse Pulping
Conclusion
43. FEASIBILITY OF RECYCLED NEWSPAPERS HARDBOARDS
Experimental Design and Analysis
Materials
Processing
Acetylation
Adhesive Application
Board Manufacture
Testing
Results and Discussion
Static Bending Properties
Tensile Strength Properties
Water Absorption and Thickness Swell
Linear Expansion
Concluding Remarks
44. RESTORING BONDING STRENGTH TO RECYCLED FIBERS
Dry-Fiberized Fiber Characteristics
Mechanical Treatment
Fractionation
Strength Additives
Chemical Treatments
Blending with Virgin Fiber
Papermaking Variables
Wet-Formed Papers
Pressing
Air-Formed Papers
Conclusions
Methods and Materials
45. CHEMICAL MODIFICATION OF AGRO-FIBER FOR THERMOPLASTICIZATION
Experimental Procedures
Esterification Procedure
Thermal Analysis
Pressing of Esterified Fiber
Electron Microscopy of Pressed Fiber
Swelling of Pressed Fiber in Water
Results and Discussion
Esterification of Lignocellulosics
Thermal Analysis
Swelling of Pressed Fiber Pellets in Water
Conclusions
46. POTENTIALS FOR COMPOSITES FROM JUTE AND
ALLIED FIBERS
Plant Utilization for Composites
Potential Composites for Agro-Resources
Geotextiles
Filters
Sorbents
Structural Composites
Non-structural Composites
Molded Products
Packaging
Combinations with Other Resources
Chemical Modification for Property Improvement
Conclusions
47. AN APPROACH TO ‘INPLANT COLOUR REDUCTION’ OF
BLEACH PLANT EFFLUENT USING CALCIUM
HYPOCHLORITE
Experimental
Discussion
48. DESILICATION OF SULPHATE WEAK BLACK
LIQUOR BY THE ADDITION OF LIME
Experimental
Procedure of Desilication
Results & Discussion
49. TREATMENT OF PULP & PAPER MILL WASTES
Pulp and Paper Industry Water
Consumption
Nature and Effect of Impurities
Primary Treatment
Sedimentation Units
Sludge Handling & Disposal
Secondary Treatment
50. DECOLOURIZATION OF WASTE WATER
FROM BLEACHED-KRAFT PULP & PAPER
MILL USING ALUM AND CLAY
Materials and Methods
Results and Discussion
Sludge Blanket
Effluent Quality
Colour Removal
Removal of Suspended Solids
COD Reduction
Conclusion
¬51. REMOVAL OF SOLUBLE SILICA FROM
SULPHATE GREEN LIQUOR
Experimental
Carbonation
Green Liquor Analysis
Results & Discussion
52. TRENDS IN ASH CONTENT OF STRAW
PULPS-AN EXPLANATION
Experimental
53. MINI LIME TREATMENT OF DISSOLVING
PULP MILL COLOURED EFFLUENT
Sources of Colour in the Pulp Mill
Effluent
Present Work
Chlorination of Lime Treated Effluent
Calcining of Effluent Sludge
Causticization Using Lime Obtained from Effluent Sludge
Conclusion
54. COLOUR AND COD REDUCTION OF
BLEACH EFFLUENTS
Experimental
Results and Discussions
Colour of the Effluents
Phenolic Compounds
Rate of Colour Reduction
Chemical Oxygen Demand
Conclusions
55. EFFECT OF pH ON SULPHITE PULPING OF
HOLOCELLULOSE OF E. TERETICORNIS
Experimental
Preparation of Cooking Liquor
Titration of Cooking Liquor
Sulphite Pulping
Neutral Sulphite Pulping
Preparation of Cooking Liquor
Chemical Analysis of Sulphite and
Neutral Sulphite Cooked Holocellulose
Results and Discussion Effect of pH and
Cooking Time on Yield
Effect of pH and Cooking Time on Klason Lignin
Effect of pH and Cooking Time on Alpha-Cellulose
Effect of pH and Cooking Time on
Pentosans
Effect of pH and Cooking Time on
Acidic Sugar
Effect of pH and Cooking Time
On Methoxyl and Acetyl Groups
56. UTILIZATION OF AGRICULTURAL RESIDUES
FOR PULP, PAPER AND BOARD
Rice Straw
Writing and Prints Paper
Grease Proof Paper
Wrapping Paper
Straw Board
Fibre Boards
Wheat Straw
Writing & Printing Paper
Greaseproof Paper
Straw Board
Jute Sticks
Writing and Printing Paper
Wrapping Paper Pulp Yield and Sheet Characteristics
Straw Board
Newsprint Grade Refiner Groundwood Pulp
Constitution of Hemicellulose
Greaseproof Paper, Strength Properties of Standard Sheet
Building Board
Bagasse
Writing and Printing Paper
Wrapping Papers
Rayon Grade Pulps
Greaseproof paper
Straw Board
Fiber Board
Newsprint
Cotton Stem
Writing and Printing Paper
Miscellaneous Raw Materials
Arecanut Husk
Ground Nut Shells
Tea Stem
Caster Stems (Ricinus Communis, linn)
Sun Flower Stalk
Arhar Sticks (Cajanus SP) and Jawar Stalk (Sorghum SP)
Sugar Cane Leaves
Paddy Husk
57. PROVISION OF CAPTIVE POWER GENERATION IN
A 30 TPD AGRO-BASED PAPER PLANT AS A MEANS OF
IMPROVING CAPACITY UTILIZATION
Capacity Utilization
Power Availability
Captive Power Plant
Recommended Scheme
Features of the Scheme
Fixed Costs
Variable Costs
Average Cost of Power Generation
Economics and Discussion
Conclusion
58. ENERGY CONSERVATION IN PULP AND
PAPER INDUSTRY—SOME THOUGHTS
Paper Industry
Deliberations
Total Energy Concept
In-Plant Power Generation
Energy Distribution and Utilization
Overdesign and Capacity Utilization of the Equipment
Energy Aduit
Short Term-Long Term Action Programme
Short Term Schemes
Long Term Schemes
Generation
Short Term
Long Term
Transmission
Short Term
Long Term
Utilization
Short Term
Long Term
Waste Streams
Energy Conservation Approaches
Factor Affecting Energy Efficiency
Research and Development
National Energy Programme
Summary and Conclusions

^ Top

Bleaching of Bamboo Cold Soda Pulps

Bleaching studies were carried out on bamboo cold soda pulp, with a view to attain a brightness of about 50% ISO, for use in making newsprint. The present investigations were undertaken at the instance of the National Newsprint and Paper Mills Limited, Nepa Nagar. Results of the laboratory investigations are presented in this report.

As is the case with chemi-mechanical pulps, lignin content in the pulp is high i.e. most of the lignin is retained in the pulp.

Bleaching experiments were carried out with increasing dosages of hypochlorite. The bleaching conditions and results are given in Table 2.

Even with 25% hypochlorite, the brightness attained was only 45% ISO. During the bleaching experiments it was observed that the brightness development in the initial stages was rapid and then, brightness decreases with prolonging time. The effect of retention time on brightness in hypochlorite bleaching is given in Table 3.

It can be observed that pre-extraction improves the brightness and extraction at 80ºC seems to be optimum.

Effect of Peroxide in Alkali Pretreatment

Use of 0.5% H2 O2 in alkali pre-extraction improves the brightness of the subsequent two-stage hypochlorite bleached pulp. The results are given in table 5. The sequence E3P0.5 provides the maximum brightness.

Pretreatment with Dye

The unbleached pulp has 53% yellowness, which hinders in brightening of the pulp. With a view to reduce the yellowness of the pulp, the pulp was treated with 0.05% to 0.75% victoria blue dye at 2% consistency in a disintegrator, thoroughly mixed and dewatered prior to bleaching with two-stage hypochlorite. Though addition of dye reduces the yellowness of the pulp considerably, further bleaching does not improve the brightness more than that achieved in the absence of dye.

Addition of dye for the final bleached pulp, to reduce the yellowness and then use of optical whitening agent (Ranipal) to improve the brightness further was also not effective significantly.

H2 O2 Treatment

The pulp was given pre-edta treatment, to complex the metal ions and then bleached with increasing dosages of H O2. Bleaching conditions and results are given in Table 6.

The bleaching conditions and results are given in Table 7. It can be observed that sequence with peroxide gives maximum brightness of 48% with 20% hypochlorite and 41.8 with 15% hypochlorite. With increasing brightness bleached pulp yield drops down. Bleached pulp yield for two-stage hypochlorite is 97% whereas with pre-extraction in presence of peroxide it is 91%. So, for attaining 6 points gain in brightness, about 5-6% yield has to be sacrifised. The unbleached and bleached pulp strength properties are given in tables 8 to 10 and strength properties are compared at 200 ml CSF in Table 11.

It can be observed, that strength properties of pulps bleached by different sequence are similar, though bleached pulps with pre-extraction possess somewhat higher burst and tensile strength.

Minimum bleaching time just sufficient for complete exhaustion of hypochlorite has to be given coupled with efficient mixing. In two-stage hypochlorite bleaching, 15 minutes was found sufficient for first stage in the laboratory trials. Prolonging the bleaching time after exhaustion of hypochlorite reduces the brightness.

High Yield Semi-Chemical Pulping of Mixture of Bamboo and Mixed Hardwoods

Paper industry has tremendously increased in India in the last 20-30 years. At present the total paper production capacity in India is about 12.35 lakhs tonnes as against the installed capacity of 18-16 lakhs tonnes, which will be increased to 22 lakh tonnes by 1986, 28 lakhs tonnes by 1991 and 42.5 lakhs tonnes at the end of this century. To fulfill this requirement lot of cellulosic raw material will be required whereas our forest (the main resources of raw material) is limited and it is decreasing day by day. The paper maker’s are aware of this from longback and hence efforts have been made from time to time to develop some new sources of fibrous raw material as well as new methods of pulping so that more paper may be obtained from the same amount of raw material.

Bamboo is the main raw material for Indian Paper Industry. New Bamboo areas even at high cost are being trapped. Looking the future shortage of this valuable raw material more and more of hardwoods and many short rotation plants like agricultural residues, some variety of grasses and Bagasse. Gunny bags, Jute sticks etc. are being used these days to meet the growing demand.

The semi-chemical process, which was first developed by United States Forest Product Laboratory, Madison in 1926, is now being gradually adopted in other countries in order to conserve the fibrous resources, to bring down the cost of production and to make the paper product more competitive with other materials.

The primary objective in the development of semi-chemical process was not only to utilize hardwoods to obtain higher yield of usable pulp than could be obtained by the conventional pulping process, but also to counteract the steadily increasing raw material cost. Semi-chemical pulping is a two-stage process involving chemical treatment of wood chips to obtain a softening and partial removal of ligni-cellulosic bonding material followed by mechanical treatment to complete the fiber separation.

This process is attractive economically because of the high yield attainable, low chemical consumption and because the process lends itself to small units and a minimum of plant investment. In this case because the action of cooking liquor and bleaching agents is directly selectively on the lignin, bleached hardwood pulp could be obtained in higher yields also. It also produces a stronger pulp than could be obtained by fully chemical cooking, when the hardwoods species are used. Unbleached semi-chemical pulps at present are used for making corrugating board, speciality board. Newsprint and wrapping papers and may have possibilities of being used as liner and towelling. The bleached semi-chemical pulps at present are being used for making Books, Magazines (coated and uncoated) Bond, Writing, Glassine, Grease-proof paper, Food board, Speciality and may have possibilites of being used as waxing carbonizing and towelling tissue etc.

Literature survey revealed that some valuable work has been done on high yield pulping. Jauhri, used sulphate Semi- chemical process to produce high yield pulp from Dendrocalmus strict us. Nicolas used the cold soda pulping for Philippine Bamboo to obtain high yield pulp. Beckker used neutral sulphite-semi chemical pulping for corrugating medium. A comparative study of neutral sulphite and green liquor semi-chemical pulping for corrugating medium has been done by Raymond Michael conducted N.S.S.C. pulping of young European black alder, Yuichiro and Yuiko prepared high yield pulp containing no fiber bundles. Worster and Mc Candless prepared semi-chemical pulp using kraft green liquor. Agrawal and Singh prepared semi-chemical pulp from a mixture of hardwoods using neutral sulphite semi-chemical process and sulphate semi-chemical process. Guha, Singh and Grover used sulphate and neutral sulphite semi-chemical process to produce high yield pulp from a mixture of Maharastra hardwoods.

With these ends in view and to increase the yield, investigation were undertaken to find the suitability of mill chips (comprising of 60.70% Bamboo and 30-40% mixed hardwoods) for the production of semi-chemical pulp using sulphate semi-chemical, green liquor semi-chemical and neutral sulphite semi-chemical processes. The study also includes to find out the suitability of bleached semi-chemical pulp for the production of bleached grade writing and printing paper after blending with bleached chemical mill pulp.

Raw Material

Chips were collected from the Silo conveyor belt of the chipper house section of our mill. Chips comprised of 60-70% bamboo and 30-40% mixed hardwoods like sal, salai etc. These were air dried before starting the pulping experiments.

Experimental and Results

The chips were processed by sulphate semi-chemical process, Kraft green liquor process and neutral sulphite semi-chemical process.

A. Sulphate Semi-Chemical Process

Trials were carried out by the sulphate process in a stationary forced circulation type electrically heated autoclave of 30 liter capacity. 25kg O.D. chips were taken in each digestion. The material to liquor ratio was kept as 1: 4. The chemical percentage was kept as 5, 8 & 11% as Na2O. The time of the digestion was 3½ hrs. (Including 3 hrs. to rise to 170°C). The softered chips were washed and refined in the Sprout Waldren disc refiner using plate no. D2 A-501. The power consumption during refining was determined. The unbleached pulp yield and permanganate number of the pulp were also determined. The spent liquor was collected and analysed for R.A.A. Tweddle, pH and calorific value of the liquor was also determined. The digestion and refining condition, pulp yield, permanganate number and black liquor analysis are recorded in Table 1A.

The pulp obtained (of cook No. 3) was beaten in laboratory valley beater to a freeness of 25, 35, 45 and 55°SR and standard sheets were made and tested for their strength properties according to Tappi standards. The results are recorded in Table 2A

The pulp of the cook no 3 was bleached by conventional multi-stage bleaching under C/E/C/E H sequence. Bleached yield of the pulp, brightness, copper number, viscosity, post colour number of the pulp were determined. Bleaching condition, bleached yield, brightness, copper number, viscosity and post colour number are recorded in Table 3.

The fiber classification of bleached pulp was carried out in Bauer Mc Nett fiber classifier. Results are recorded in Table 4.

The bleached pulp was beaten in laboratory valley beater to a freeness of 25, 35, 45 and 55°SR and evaluated for strength properties. Results are recorded in Table 5.

Bleached semi-chemical pulp (beaten to 45°SR) was blended in different proportions with mill bleached chemical pulp (beaten to 45°SR) and the blends were evaluated for strength properties. The strength values of the blends are given in Table 6.

Kraft Green Liquor—Semi-Chemical Process

Pulping trials were also carried out using Kraft green liquor in similar manner as in A. The total chemicals applied were as Na20% on total active alkali basis. As in sulphate semi-chemicals process pulp obtained with 11% alkali was proceeded further. The results are recorded in Table 1B, 2B, 3, 4, 5 and 7.

Neutral Sulphite Semi-Chemical Process

Pulping trials were also carried out by the N.S.S.C. process in a similar manner as in A. The ratio of sodium sulphite to sodium carbonate was kept as 7:1. The percentage of chemicals was calculated as Na2O. As in sulphate semi-chemical process pulp obtained with 11% alkali was proceeded further. The results are recorded in Table 1C, 2C 3, 4, 5 and 8.

Discussion

Sulphate Semi-Chemical Process

It is observed in Table 1-A that power consumption decreases from 380 KWh/Tonne to 100 KWh/Tonne and the yield of the pulp decreases from 75.4 to 55.13 when the percentage of alkali is increased from 5 to 11%. With this increase in alkali, the permanganate number decreases from 36.1 to 34.1 and R.A.A. increases from 6.20 to 9.30g/l. This indicates that the softening of the chips is more as the percentage of chemicals is increased as expected. The calorific value is satisfactory. Table 2 A indicates that unbleached pulp of cook no. 3 can be readily beaten upto 55°SR freeness in 59 mts. The physical strength properties of the unbleached pulp are encouraging. The tear factor of the pulp decreases with increase in °SR where as other strength properties increase in °SR freeness. Table 3-A shows that the total chlorine requirement is 26.6% and caustic demand is 6.6% to obtain a brightness of 73% PV. The total shrinkage of the pulp during bleaching is 20%. This pulp has a satisfactory viscosity post colour number and copper number indicating that it is not degraded and has a satisfactory keeping quality.

The fiber classification of bleached pulp recorded in Table 4A shows that the fiber percent retention on 70 mesh is maximum. From Table 5-A, it is observed that on bleaching the beating time is reduced and the physical strength properties improved considerably, this improvement in strength is due partly to the removal of lignin from the fibers and partly to the increase in specific surface which tends to increase inter fiber bonding.

The results recorded in Table 6 indicates that bleached sulphate semi-chemical pulp is of superior quality in comparison to the mill bleached chemical pulp in respect of strength properties, hence with the increase in proportions of semi-chemical pulps, the properties of blends are better than the mill pulp.

Green Liquor Semi-Chemical Process

It is observed in Table 1 B that power consumption decreases from 240 KWh/Tonne to 120 KWh/Tonne and the yield of the pulp decreases from 70 percent to 58.8 percent when the percentage of alkali is increased from 5 to 11%. With this increase in alkali the permanganate number decreased from 36.48 to 34.78 and R.A.A. increases from 9.30 to 13.95 g/l. This again indicates that the softening of the chips is more as the percentage of chemical is increased. The calorific value is normal. In Table 2-A, it can also be seen that unbleached pulp of cook no. 6 can be readily beaten upto 55°SR freeness in 28 mts. The strength properties increases with increase in °SR freeness except in case of tear factor.

From Table 3-B it is observed that total chlorine requirement is 23.5 percent and caustic demand is 6.65 percent to obtain a brightness of 72 percent PV. The total shrinkage of pulp during bleaching is 17.7 percent. This pulp has satisfactory viscosity copper number, post colour number indicating that it is not degraded and has a satisfactory keeping quality. The fiber classification of bleached pulp recorded in Table 4-B indicates that maximum fibre percent retention is on 70 mesh. From Table 5-B it is observed that after bleaching, the beating time is reduced and physical strength properties improve considerably.

The results recorded in Table 7 indicates that bleached green liquor semi-chemical pulp is superior in comparison to the mill bleached chemical pulp in respect of strength properties, hence with the increase in proportions of semi-chemical pulps, the properties of blends are better than the mill pulp and the brightness of the blends decreases from 78 to 68 percent PV with the increase amount of semi-chemical Pulp in the blends, however, this brightness is sufficient for writing and printing grade paper where higher brightness is not needed.

Neutral Sulphite Semi-Chemical Process

From Table 1-C it is observed that power consumption decreases from 180 KWh/Tonne to 120 KWh/Tonne and the yield of the pulp decreases from 77.60 to 68.60 when the percent of alkali is increased from 5 to 11% as Na2O (10.16 to 22.33% as Na SO3 respectively). With this increase in alkali the permanganate number decreases from 36.64 to 35.58 and R.A.A. increases from 4.65 to 10.85 g/l as Na2O. This indicates that the softening of the chips is more as the percentage of the chemicals is increased as expected. The pH of the spent liquor remains around 7.5 to 8.5 and calorific value is normal.

In Table 2-C it can also be seen that unbleached pulp of cook no. 9 can readily be beaten upto 55 SR freeness in 29 minutes only. The physical strength properties of the pulp decreases with increase in °SR freeness whereas other strength properties increases with increase in °SR. The pulp has very good bulk (1.7 to 1.68).

From Table 3-C, it is evident that the total chlorine requirement is 24.71% and caustic demand is 6.35% to obtain a brightness of 70.5% PV. Total pulp shrinkage during bleaching is 20.8%. This pulp has satisfactory viscosity, copper number and post colour number indicating that it is not degraded and has a satisfactory keeping quality.

The fiber classification of bleached pulp recorded in Table 4C shows that fiber percent retention on 20 mesh is maximum. From Table 5-C it is observed that on bleaching the beating time is reduced and the strength properties are improved considerably N.S.S.C bleached semi-chemical pulp has very good bulk (2.12 to 1.61). From Table 8, it is observed that bleached neutral sulphite semi-chemical pulp is superior in comparison to the mill bleached pulp, as the bleached semi-chemical pulp has better breaking length stretch and burst factor, hence with the increase in proportions of bleached semi-chemical pulps, the properties of the blends are better than the mill pulp (Except when 20% and 40% bleached semi-chemical pulp are mixed in the blends in this case strength properties of these blends are camparable with the mill pulp).

Brightness of these blends decreased from 78 to 67.5% PV, with the increase amount of bleached semi-chemical pulp in the blends; however, these brightness are satisfactory for printing and writing grade paper where too high brightness is not needed.

On the whole it can be observed that when the same amount of chemicals as Na2O are used, the yield by the sulphate semi-chemical process are lower than that of neutral sulphite semi-chemical process but the strength properties are better. The pulps obtained by neutral sulphite semi-chemical process are bulkier than the pulp obtained by the sulphate process. The physical strength properties of sulphate semi-chemical unbleached pulp are also superior in comparison to the green liquor semi-chemical unbleached pulp, however, the physical strength properties of green liquor semi-chemical unbleached pulp are equivalent to neutral sulphite semi-chemical unbleached pulp. Power consumption during refining is towards higher side in sulphate semi-chemical in comparison, to the neutral sulphite and green semi-chemical process. Similar trends are observed during beating of unbleached pulp as beating time is more in sulphate semi-chemical process comparatively. Sulphate semi-chemical and green liquor semi-chemical unbleached pulps are darker as compared to the neutral sulphite semi-chemical unbleached Pulp. As recorded in Table 3 sulphate semi-chemical green liquor, semi-chemical, and neutral sulphite semi-chemical pulp could be bleached upto a brightness of 70% in multi-stage bleaching following C,E/C/E/H sequence. In case of green liquor semi-chemical process total chemical, requirement for bleaching is 23.5%, which is lower in comparison to the sulphate semi-chemical process (26.6%) and neutral sulphite semi chemical process (24.71%). The bulk and strength properties of sulphate semi-chemical bleached pulp are lower than that of neutral sulphite semi-chemical and green liquor semi-chemical bleached pulp. After bleaching beating time is reduced in all pulps. In case of sulphate semi-chemical unbleached pulp beating time is higher as compared to other pulps.

It is also observed that green liquor semi-chemical pulp are equivalent to neutral sulphite semi chemical pulp in strength characteristics, however, they may result in denser sheets.

The physical strength properties of all the blends of sulphate semi-chemical, green liquor semi-chemical and neutral sulphite semi-chemical pulps are satisfactory. However, the exact quantity of the pulp to be blended depends upon the strength values and brightness of the finished sheet. The brightness can be improved further by the addition of suitable fillers.

Development in High Yield Pulping Process

The scarcity of raw material is being felt a serious problem all over the world, specially in developing countries. In our country, the pulp and paper production is below the normal needs due to growing population and more demand of paper and its products. Our forest resources are limited. In this context, high yield pulping offers one way to the solution of the problem of scarcity of raw material. This makes a way to minimize the gap between availability and requirement of raw material.

Mechanical Process

The main factors to this process are the absence of chemicals costs and the almost quantitative yield from wood, the yield losses being only 2-5 percent. Mechanical pulping in grinders has several drawbacks resulting to the pulp of low purity and inferior strength.

To achieve acceptable grade of mechanical pulp from lower priced hardwood and softwood saw mill waste, methods have been developed which start from chips and use of disc refiners of various types. Various types of chemical pre-treatments have also been tried from simple addition of sulfite and bisulfite in the refiner to achieve somewhat brighter as well as stronger pulps. In order to reduce energy consumption with or without chemicals, thermal softening of the inter-fibre bonds can be utilized. Hence, during last 10 years, thermomechanical, chemimechanical and chemithermomechanical pulping processes are being developed to overcome the drawbacks of mechanical pulp. Ultra-high yield pulps are also attracting, increasing commercial interest.

Semichemical Process

Semichemical process involves with chemical treatment followed by the treatment in advanced mechanical fiberizing equipment. By addition of chemicals to the grinder showers, it is possible to achieve certain effect. These processes are representing a transitional stage to semichemical. As impregnation was found to be one of the main problems in semichemical pulping of bolts, interest soon concentrated on the treatment of chips. Hydrolysis of wood has been studied from different angle and thermal softening has been considered the main purpose of this rocess. However, the treatment in cold alkali lie at concentrations of 7-8 gpl NaOH followed by mechanical fiberizing, gives cold caustic straw pulps in 75-85 percent yield, suitable for Corrugating board.

To obtain acid sulfite pulp in high yield, pulping conditions should be chosen to give somewhat slower reactions. Slower reaction is achieved by lower temperature or higher combined SO2 (lower acidity). The semi chemical Kraft pulps are obtained in 55-70 percent yield, corresponding to Roe number 17-31 for American softwoods. The yield of hardwoods pulps is somewhat higher than 55 percent.

Pulping in neutral or alkaline sulfite solutions was already suggested and then repeatedly investigated. A semi chemical process using the neutral sulfite process had been worked out by the U.S. Forest Products Laboratory. The most common yield range of 85-70 percent for well-buffered neutral sulfite cooks. Neutral sulfite pulps from eucalyptus give very interesting paper characteristics. Hardwood pulps made from this process are frequently stronger than chemical hardwood pulp. Extremely mid neutral sulfite cooks, giving pulp yield of 85-95 percent from both hardwood and softwoods, are also of interest for newsprint.

Chemical Process

Mc Govern has reported that there are three general approaches to high yield chemical pulping process.

(i) Improved uniformity of delignification adopting optimization of pulping conditions.

(ii) Stabilization of Carbohydrate fraction.

(iii) Resorption of polymeric carbohydrates in early stages of cooking.

The attack of chemicals on cellulose and hemicellulose depends on the type and concentration of chemicals employed in cooking. The extent of attack on the particular fraction of carbohydrate may be dependent on its degree of polymerization, manner of combination with other carbohydrates as well as lignin.

Alkaline Chemical Process

High yield kraft pulps in the yield range of 60-70 percent have been obtained by various worker by optimizing the pulping conditions. The increase in yields of practical interest, attempt have been made with the use of inorganic chemicals. A systematic search for oxidents and reductantes have been tested. Sodium dithionite and Sodium, tetrahydroborate are investigated. The increase in yield was found to originate entirely from an increase in gluco-mannan yield, 6 percent of wood and possibly some increase in cellulose yield, 1 percent of wood.

Polysulfide pulping is one of the recent innovations in the field of high yield pulping. Data of Kleppe based on the experience of mill scale polysulfide pulping indicate that yield could be increased by 1.5-2.0 times the amount of added sulfur when 20-30 kgs. of sulfur per metric ton of pulp dissolved in white liquor charged to a dual vessel Kamyr digester although the sulfidity of cooking liquor was 4-5 percent. An increase of 63 percent in the pulp yield was observed with addition of 2-5 percent polysulfide sulfur to the cooking liquor.

Sulfite process

The removal of lignin was significantly more by sulfite cooking while the attack on extractive was considerably less. The carbohydrates of sulfite cook are subjected to several changes and the most important reaction of which is acid hydrolysis of the glycosidic bonds. The extent of carbohydrate decomposition is largely controlled by three factors time, temperature and acidity. On the increasing of pH of the cooking liquor, and thereby bysulfite ion concentration, more favourable conditions for the preservation of acid-sensitive carbohydrates are secured. Therefore, only significant higher yields at certain degree of delignification are secured on increasing the combined SO2 charge from the normal level.

Organic Catalyst to High Yield Pulping

Recently trials have confirmed the benefits to be gained by employing the organic catalyst in digester. Various quinones and amines have been tried to accelerate the delignification with stabilization in carbohydrate fraction. The cost and availability of the catalyst could prove limiting factors. Acceptance of anthraquinone (AQ) as an attractive means of improving Pulping economics has been faster than is typical in the paper industry.

CIL Laboratory results showed that 0.05 percent AQ increased the yield of southern softwood pulp by 2-3 percent. At this time there are about 10 Companies in the world, which are operating AQ pulp mills. In Japan, AQ producer Kawasaki Kasei chemicals has patented and commercialized its technology concurrently with CIL.

What Holtan does predict is that one of the optimum ways of using AQ will be as a combination to reduce the H factor as well as the alkalinity in order to control its effects. A 10-15 percent reduction in the amount of active alkalinity or in H-Factor is possible at standard AQ application rates. AQ can and will be used in many different way and as Holtan says, “The reasons chosen by actual mills will be as unique as the mill themselves”.

AQ Pulping Technology

AQ is only effective in alkaline pulping where it accelerates delignification and also improves pulp yield of between 2.5-4 percent. Laboratory results indicate that larger reductions in alkali charge could be made and that use of yield gains of as much as 2-3 percent on wood at constant kappa number for southern pine chips. Ghosh et al., reported that addition of small amounts of AQ resulted in significant increases in the delignification and pulp yield, and reduction of rejects without significant losses in strength for hard-woods. Virkola et al., presented the details of NS AQ pulping, then its potential application. The alkaline liquor consists mostly of Na2So3 plus some Na2Co3 and NaOH, the apparent optimum Na2So3 proportion being 80-85 percent of the total alkali. Light coloured unbleached softwood pulp is achieved with a big yield advantage over conventional kraft pulp (7-10 percent points higher than total yield at - 410 kappa number). The yield gain is primarily due to better retention of hemicellulose NS-AQ pulp at about 80 kappa, is about 19 percent points higher yield than kraft. With maritine pine, Alcaper provides 2 percent higher yield than kraft at 30 kappa adopting a new technique by combining the catalytic effect of anthraquinone and the delignifying capability of hydrogen peroxide into a single process.

Polysulfide-AQ Process

Glen Brown of Head Corp. spoke about pilot-scale trials of maxy polysulfide pulping with and without AQ and also about AQ’s effect on the soda and kraft processes. Brown’s Key piece of information about AQ in polysulfide pulping: “The yield increases of polysulfide and AQ the Kraft process are additive.” First describing results on mixed hard-woods, Brown provided that 0.1 percent AQ on wood gave upto 3.5 percent greater yield in soda pulping, and about 1.4 percent higher yield in the kraft and polysulfide processes. The observation with a pine spruce mixtures were similar upto 2 percent higher yield using 0.15 percent AQ in either kraft or polysulfide processes.

Alkaline Sulfite-AQ Pulping

Paper units are facing a problem of high cost of production. This problem is due to ever increasing cost of raw material, cooking, bleaching and pollution treatment chemicals. One way to solve this problem is to investigate an alternate high yield pulping process which will result to high yield of semibleached pulp. In this direction, an attempt has been made in our laboratory using wheat straw as a raw material.

The cooking liquor for alkaline sulfite pulping consists NaOH and Na2SO3. The cooks were conducted to achieve the optimum Na2SO3 proportion with and without AQ. The optimum Na2SO3 proportion was found to be having 65-70 percent of the total alkali for wheat straw. The effect of AQ charge was studied and optimum charge was found to be 0.05 percent on old straw. Soda and Kraft like alkali concentration and material to, liquor ratio were used. It is observed that in the study of alkaline sulfite pulping, the pH of cooking liquor drops quickly during the early part of the cook and most of the pulping is progressed at pH 9.5-10.2. The temperature was kept 150°C for two hours. The pulps so formed are 60-65 percent yield having Kappa number 20-25. In this study, it is interesting to note that the pulps are light yellow in colour having the brightness 55-60º GE. The properties of the pulp are shown in Table No. 1.

Thermo-Mechanical Pulps for Newsprint Manufacture from Tropical Pines

To meet the expanding demand of newsprint, it will be essential to identify the suitability of pulps from alternative raw materials. Tropical pines in this regard cannot be overlooked. Considerable work done on plantations of tropical pines has revealed that these could be grown in several parts of the country. Pande has indicated that vast potential exists in the various states like Andhara Pradesh, Madhya Pradesh, Orissa, Tamilnadu, Uttar Pradesh, West Bengal for growing tropical pines. Table 1 gives the area estimated under tropical pine plantations in India.

Besides above, some plantations have also been raised in the states like Kerala, Karnataka and Bihar, but the details and potential are not yet available.

Conventionally newsprint is made from a blend of mechanical pulp and chemical pulp. High yield pulping processes like cold soda process is of particular interest for production of newsprint grade pulps from hardwood and cold soda pulps. The two new mills being set up viz. Mysore Paper Mills and Kerala Newsprint will utilise eucalyptus, bamboo and eta reed.

Thermo-mechanical pulping process (TMP) is the most recent mechanical process yielding a strong pulp having all the essential requirement for newsprint production. The key feature of this process is reduction or complete elimination of chemical pulp in the furnish, thus not only eliminating one pulping street but also pollution arising out of chemical pulp mill.

The reported study was undertaken to evaluate pulping characteristics of P. patula and P. caribaea by thermo-mechanical pulping process. The results reported are very encouraging. On pilot plant, newsprint grade paper was also made from 100% Thermo-mechanical pulp from P. patula. The runnability on experimental pilot plant was good.

Raw Materials

P. patula logs were supplied from 1972-73 plantation of Kanasar-6 plantations by Silviculturist, Sal region U.P. The logs were 10-15 cm in diameter and 2-2.5 m. in length. The specific gravity  of wood as received was 0.343.

Pinus caribaea logs were supplied from experimental plantation of Forest Research Institute by Director, Forestry Research, Forest Research Institute Dehra Dun. The plantations were raised in 1963. The specific gravity of wood as received was 0.400. The chip density of P. patula and P. caribaea was 170 and 165 (o.d. kg/m3) respectively.

Experimental

The detailed description of the Thermo-mechanical pulp pilot plant was reported in an earlier publication.

A Study on Replacement of Sodium Sulphate by AQ-Large Scale Trial

The kraft pulping process has several well established advantages in providing good quality pulp, high chemical and energy efficiency etc. Moreover, it is capable of pulping any cellulosio raw material. But the deficiencies of the process in terms of inferior yield coupled with economic and environmental pressure provide strong incentive for further search of superior processes. The efforts have been aimed at alternative processes capable of eliminating the deficiencies of the Kraft process while retaining its advantages.

The importance of Soda process as a viable alternative was realized if however, the basic drawbacks of the process viz. low pulp yield, inferior quality, longer cooking time, high temperature and caustic charges could be overcome by the use of suitable additives.

Anthraquinone an Aid to Pulping

The suitability of a process incorporating very small amount of Anthraquinone-2-mono-sulphonate sodium salt (AMS) into the system was indicated in the year 1972 by Bach and Fiehn. The additive was effective both in Kraft and soda processes and it resulted in improved yield, a reduction in rejects and accelerated delignification without any adverse effect on physical strength properties of the pulp produced. Holton in 1977 found that Anthraquinone alone instead of its derivative was extraordinarily effective in pulping wood chips and was superior to (AMS).

Kraft liquor is already a moderately effective delignifying agent hence greater effectiveness of anthraquinone was expected in soda process and was established. Holton observed that the small amounts of Anthraquinone so dramatically accelerated the soda pulping process that it was thought that it could effectively compete with or surpass the sulphate process in some respect. Moreover its application does not require any special technique and equipments.

The concept of pulping by incorporating Anthraquinone into the system has drawn worldwide attention.

It has eliminated or reduced the pollution caused by sulphur and its compound.

Investigations have also shown that the addition of Anthraquinone did not enhance the toxicity of untreated bleached kraft effluents and that no difference in treatability or effluent characteristics were observed between the two effluents.

Research and investigations carried out in different parts of the world have corroborated the findings of Holton.

Investigations carried out in different laboratories and mills of our country have revealed following facts about anthraquinone usage.

—       Soda Anthraquinone process gives yield and pulp quality similar to Kraft level and better than soda level in case of pulping Eucalyptus and pine wood.

—       In case of pulping of Eucalypus hybrid it was observed that for identical pulping conditions addition of anthraquinone resulted in reducing the Kappa number of pulp by 10-15. It was also observed that anthraquinone is more effective in smaller dosages. There was improvement in physical strength properties of the resulting pulp.

—       Work done on bamboo (D. strictus) at the Research Centre of West Coast Paper Mills reveals that the benefits in the terms of increase in yield, reduction in H-factor and lowering of sulphidity can be obtained (either singly or in combination) by the addition of as small as 0.05% AQ on the basis of raw material during kraft pulping.

—       AQ is also effective on mixed tropical hardwoods. For 0.05% dosage, there was reduction in active alkali charge by 2.0 to 2.4% producing pulp of kappa number 32 approx. Simultaneously there was increase in yield by 1.5%. If active alkali charge is not reduced, there is 16% saving in H factor (cooking time reduced) for 31-32 kappa number. Simultaneously the gain in yield is by 1.2%. If active alkali charge or h factor are not reduced, for a constant kappa no. of 34 there is scope for reducing the sulphidity from 25 to 5% by using AQ. No adverse effect has been observed in the bleachability, beating characteristics and strength properties of the pulp obtained by AQ pulping. Black liquor properties are also not affected.

—          Anthraquinone is effective in reducing active alkali charge, H-factor and chlorine requirement in bleaching. At the same time it increases yield. But it was found economical only when active alkali charge was reduced for maintaining mill kappa number at the same level. (Raw material-bamboo and mixed hardwoods).

—       Plant trial with AQ at Central Pulp mills has indicated that use of anthraquinone during cooking helps to reduce reject percentage which in turn gives rise to higher pulp yield. It is possible to maintain a higher kappa number in pulp with easy bleaching characteristics. Cost saving are possible as the sulphidity range as low as 12-15% can be maintained enabling replacement of costly salt cake by other less expensive sodium make up.

Laboratory Scale Investigations at Central Research Laboratory, Dalmianagar

Investigations were carried out in the laboratory to see the effect of anthraquinone on pulp yield, bleachability and strength properties of both Soda and Sulphate pulps of our normal commercial chips. Commercial chips consisting of 70% bamboo and 30% hardwoods were taken for laboratory trials. Soda and Sulphate cooks with and without anthraquinone were carried on chips from same lot and under identical cooking conditions, (Table 1). The pulping was done in 15 litre capacity laboratory rotary digester. The cooked material was screened on a 7 mesh screen with water jet pressure. The material passing through the screen are termed screened pulp and that retained on the screen as the reject. Screened unbleached pulp yield and percentage rejects were evaluated. The unbleached pulp was bleached under conventional multistage bleaching system consisting of CEHH sequence. Total chlorine consumption and bleached pulp yield were also determined. The unbleached and bleached pulps were beaten in the laboratory valley beater to 45º S.R. freeness, standard sheets were made on the British Standard Sheet making machine and the sheets tested for various physical strength properties. The cooking data are presented in Table 1 and unbleached and bleached pulp characteristics in Table 2.

Following inferences are drawn from the experimental results:

—       There is increase in yield of screened unbleached pulp and bleached pulp in case of AQ pulping.

—       Under identical conditions of cooking the reject percentage is reduced by the use of AQ. The reduction is 4.9 and 0.4 percent respectively in soda and sulphate process.

—          Anthraquinone is more effective in delignification in soda pulping than sulphate pulping. For 0.05% charge of AQ the drop in permanganate are 4.7 units in soda pulping as compared to 1.8 units in sulphate pulping under similar cooking condition.

—       The reduction in permanganate number by the use of AQ has resulted in lower consumption of bleaching chemicals. This reduction being 3.0 and 1.1 percent respectively in soda and sulphate process.

—       The strength properties of pulp are more or less uneffected by the use of AQ.

—       The soda-anthraquinone pulping results are nearer to normal sulphate pulping.

Plant Trial with AQ

On the basis of investigational results large-scale trial in the mill, with a view to eliminate the use of sodium sulphate was undertaken. Accordingly, two tonnes Anthraquinone was procured from M/s. Indian Dyestuff Industries. Nearly 4000 tonnes of bone dry chips were cooked during the trial. The anthraquinone corresponded to 0.05% on b.d. chips was charged. The furnish during the trial was 70% Bamboo and 30% hardwoods. Anthraquinone was added to the digester when half of the digester was loaded with the chips. Other operational conditions of cooking and bleaching were similar to those maintained during normal sulphate pulping (Table 3). The use of sodium sulphate in the soda recovery plant was completely stopped during the trial period. The sulphidity dropped to 3.0% during the trial.

Evaluation of Mill Pulp

The consumption of different chemicals on b.d. chips and pulp characteristics like permanganate number, copper no. and brightness are given in Table 3 and 4. Samples of both unbleached and bleached pulp were collected in the factory, round the clock. The composite samples were evaluated in the laboratory as per TAPPI. Standards for various characteristics. The pulp evaluation results along with those of similar pulp produced during the period preceeding the AQ trial are incorporated in Table 5. These comparative figures speak of the relevance of AQ addition. Summary of Paper and board characteristics produced with and without AQ pulp are given in Table 6.

Zeta Potential Concept in Paper Sizing

Internal sizing of paper with alum-rosin size is one of the most important and yet one of the most complex process of paper making, For a better understanding of this sizing, it is important to have an exact mechanism whereby alum “sets” the rosin size on the fibre can precisely be defined. The chemistry of alum-rosin size reaction, the complex products therein formed, and its subsequent adherence to the fibre surface deserves further study so as to put certain modification to the existing theories. Precipitation is a charge transfer phenomenon and adherence of precipitate on the surface is a surface phenomenon involving adsorption/ absorption. The application of the above said phenomenon, fully to the water-fibre-rosin size-alum system without some reservations has been restricted because of the polyphase nature of the system and also by the wide variation of acidity, which effect many radical charges in the system. Based on the critical evaluation of the different theories, it seems that the sizing of paper can satisfactorily be explained through “Electro Kinetic Theory”. Since the Electro Kinetic Theory deals with the surface phenomena, it should be remembered that not only the surface chemistry of the fibre, but also the surface of suspension containing viz. rosin, aluminium rosinate and aluminium hydroxide are also important. An attempt has been made in this review to highlight the role of Electro Kinetic Potential (Zeta Potential) as a means of evaluating the water-fibre-rosin size-alum system and to delineate the individual roles of the variables so as to project a coherent theory.

Electro Kinetic (Zeta) Potential-A Concept

A colloidal particle in a polar liquid can get the electrical charge by a number of mechanisms, one of them is through “ionization”. The other mechanism being the adsorption of a cation or an anion from the bulk liquid, having a specific affinity to the particle. The Dipole-Dipole adsorption is yet another mechanism which results in the specific orientation of particular charge towards the outside of the particle, giving the particle specific residual and surface charge. The particle once in possession of a particular charge, the like charges are repelled away and the opposite charges are attracted towards it. So at any time, with reference to a particular charge on the particle, there will be on the average more ions of opposite than like sign in the vicinity of the charged particle. The excess opposite charge accumulates as a differential ionic layer called “Guoy-Chapmann” layer.

The distribution of this diffuse ionic layer of “Gegenions” (the Guoy-Chapmann Layer) in the liquid surrounding the ion species, strictly follows Poisson-Boltzmann’s equation. The movement of diffuse layer in the liquid creates a potential difference between the charged mobile layer and the surrounding bulk liquid. The Zeta Potential is then defined as the integral of the work done to transport an unit charge from an infinite source to a chosen arbitary plane of shear. For simplicity it has been assumed that the infinite source is the interior of the liquid and the arbitary plane of shear is a point near the solid substance.

Representing a pad of fibrous mass as equivalent to a mass of fine capillaries. Quinkie observed electric osmotic phenomenon. He further observed that if the liquid is allowed to flow through the pad by the application of a pressure gradient, a flow of electrical charges occur.

The generated streaming current and its relationship, with the streaming potential and the resistance of the pad is given by Von Helmoltz, which is modified and generalized afterwards by Smoluchowski, as follows.

Indicating the stream potential to be independent of the dimensions and conditions of the packing pad. The origin of surface electrical conductance, in addition to electrolytic conduction, depend on the electro osmotic transfer of current. So the value z in equation (3) is always too high. By replacing the electrolyte with the one of high concentration Briggs found the value of (z) and Briggs value of z has taken as the source of most of the Zeta Potential data reported for fibres.

But Briggs failed to take account of the following complications. In the equation the dimensions of the pad is eliminated. Bikerman pointed out that the pads get swollen in the electrolyte and that the paths for the ionic transfer and fluid flow are unlikely to be identical as given in equation (2) So an appreciable amount of electricity can flow through as well as around the fibres. A second but less serious complication arises from the ultra low frequency dispersion of electrical resistance.

Where b is the effective volume of the swollen fibre, m, the density of the pad.

From the relation between the and m, the Zeta Potential d is calculated at the n=O intercept point. The specific volume ß and the specific surface s are calculated from the slope and intercept of the rectilinear form of the Kozency-Carman permeability equation.

In contrary to the belief of Helmoltz, Guoy showed that due to the presence of excess counter ions near the charged colloidal particle, the electrostatic attraction of the counter ions, further away from the particle are screened, and hence instead of a sharp potential gradient at the interface, the potential drops rapidly at first and then slows down with the increasing distance, coming to a Zero charge at distance infinite away from the particle surface. As to be expected, the attraction of the central colloid is the greatest, of course, close to itself. Due to this fact, the neutralizing counter ions are concentrated much more at these regions and becomes negligible as the distance further away. In addition to this the furtherance of the diffuse layer from the central colloid depends upon the charge of the bulk liquid and also on the concentration of the simple salts, which gives the charge to this electrical system. An interesting aspect of this phenomenon is that the increase in the valency of the counter ions significantly affect the diffusion layer, because both the screening effect and the electrical attractions are magnified. This is an important point in dealing with the sizing of the paper as a whole electro kinetic system, because the effect of polyvalent ion has as will be discussed later, a profound effect on the sizing efficiency.

Stern's Modified Double Layer

Stern pointed out that Guoy Chapmann, double layer theory, contains certain omissions and the assumptions made are not consistent to the charge evaluated for the system. He pointed out that all the counter ions and solvent molecules are not mobile. The narrow layer of counter ions always fixed to the surface at a closer distance. He has applied a correction for the finite size of the ions in the first layer adjacent to the charged surface. Due to the electrostatic and Van der Wall’s forces, a specific ion adsorption is possible. This results in a compact layer of counter ions attached to the surface. According to him the double layer is in two parts: One, the layer which has approximately a single ion thickness, and remains fixed to the solid surface. The potential drop in this layer is therefore very sharp. The second part of the layer extends some distance into the liquid phase in diffused state. The free movement of the ions in this regions are affected by the thermal agitation but the distribution of positive and negative ion is not uniform, because of the preferential attraction of ions of opposite sign. The result is a gradual fall of potential into the bulk liquid where the charge distribution is uniform. The fixed layer to the surface is called Stern’s rigid layer and the diffuse layer is called Guoy-Chapmann (Fig. 2).

Economics of Bamboo and Hardwood Pulping by Anthraquinone Catalysed-Kraft-Process

While developing a certain pulping process, the cost design has to be always kept in mind: and the question “Shall we realise profit from this venture?” needs satisfactory solution. An effort has been made by the authors to answer this question, particularly with reference to Kraft—AQ pulping of bamboo and tropical mixed hardwoods, (MHW) which are the major raw material source to paper industry in developing countries like India.

Holton found that even small quantities of Anthraquinone (AQ) in Kraft cooking liquor improve pulp yield, reduce sulphidity demand and produce pulp of better quality. With various wood species, use of AQ in pulping has been found to have a marked catalytic effect leading to lower chemical and energy demands. Besides enhancing the rate of delignification, AQ is said to stabilise carbohydrates and at comparable kappa numbers, unbleached yield is reported to be higher for Kraft-AQ pulps with seemingly no adverse effect on bleachability, beating characteristics and strength properties of bleached and unbleached pulps.

With a view to study the economy of pulping using AQ, the present work was undertaken. Following approaches of immediate interest have been made in the present work to study how far AQ would be useful in reducing the cost of pulp manufacturing:

Results & Discussions

Approach—1

Active alkali reduction with simultaneous yield gain; —With 14% AA and 1330 H-factor, Bamboo was cooked to 31.8 kappa number with 46.5% yield (control cook B-1). Under the same conditions, kappa number was found to be reduced by 5.2 units with 0.05% AQ (cook B-2). AA charge was then reduced in steps of 1% from 14% to 11% maintaining H-factor the same. It was observed that kappa number gradually increased from 26.5 to 38.3. On figure 1 by drawing a 13 no. cooks were carried out in all, under cooking conditions mentioned below & detailed in Table 1. Dilution ratio was so maintained that all the chips remained submerged in liquor.

Horizontal line at control-cook kappa number of 31.8, it was found that the line intersects the curve at 12.2% AA charge indicating a possible reduction of 1.8% in AA or 18Kg. AA/Ton bamboo using 0.5 Kg. of AQ/Ton OD Bamboo for maintaining kappa number at the same level.

Also at 12.2% AA & 0.05% AQ, the yield was more by 2-3% as compared to control cook B-1, as seen by the intercept of vertical line OQ with yield versus alkali curve.

Fig. 2. Pulping Parameters of Tropical Mixed Hard Woods for AQ Catalyzed Kraft Process.

This reduction may require Rs. 35 × 5 × 300 × 50 = 26, 25, 000/- worth of AQ in one year which is even more than the total initial capital savings. Even the increased yield is not much to offset this price.

Reduction of bleaching chemical consumption: —Using a 0.05% dosage of AQ in pulping at the same AA charge, kappa no, was found to be reduced by about 5.2 units in both the raw materials. This reduction if observed in kappa no. & the mill Kappa no. is controlled at 26.5, the chlorine consumption is expected to be reduced by about 2.1% on unbleached pulp of 21 kg per ton unbleached pulp or approximately 10 kg on OD RM.

Effect of Bleached Pulp Viscosity on Strength Properties of Bamboo Sulfate Pulp

The physical strength properties of paper depend on the quality of raw material, its pulping, bleaching and subsequent paper-making process. The bleached pulp viscosity gives a relative indication of the extent degradation of raw material during the various stages of processing and ultimately reflects on the strength properties of paper. This is because the viscosity of pulp is also a measure of the average degree of polymerization and has a direct bearing on the strength properties of pulp. However, some anomalies exist in this relationship. For instance two pulps of the same raw material prepared by different processes of bleaching will not show the same viscosity-strength relationship, although the % lignin removed may be more or less same in these samples. On the other hand these pulp samples bleached with any given process will show a reproducible trend of viscosity-strength relationship.

The viscosity test is less cumbersome and quick as compared to the laboratory evaluation of pulp for physical strength properties, as a guide for further processing. However no Conclusion can be drawn about pulp strength properties from viscosity results unless previous investigations have identified the relationship. Khanna & Coworkers reported the relation of bleached pulp viscosity for a mixture of Bamboo and Eucalyptus with its strength properties. But the variation in bleaching pulp viscosity was one by varying the cooking conditions to get the unbleached pulp of varying Kappa nos. and viscosity and then bleaching under optimum conditions. Pai and Meshramkar reported the variation of pulp viscosity at every stage of bleaching (CEHH), for bamboo, Eucalyptus and Mixed hardwoods. The lower mechanical properties of bleached sulphate pulps for low viscosity values were also reported by other authors.

This study has been undertaken to establish a correlationship between the various strength properties of Bamboo (Dendrocalamus strictus) and the pulp viscosity after bleaching. The variation of pulp viscosity is made by changing the bleaching conditions and chemicals for a pulp brightness of 75-80%.

Experimental

Sound bamboo (Dendrocalamus strictus) chips were collected and classified in Williams chips classifier. The chips classification data are recorded in Table 1.

Pulping

The pulping was carried out using a 15 lit. capacity electrically heated rotary digester. The chemical and conditions were adjusted to obtain a pulp of 35+2 Kappa No. The conditions of cooking and results are recorded in Table 2.

Bleaching

A CEH sequence was used for bleaching the pulps. In order to get the variation in the pulp viscosity, several small scale (50 g OD) bleachings were carried out under different conditions, in a laboratory set up and then large scale bleachings (500 g OD each) were carried out under the optimized conditions of bleaching. The bleaching conditions and results are recorded in Table 3.

Observations and discussion

1. For this study unbleached pulp of a high Kappa No. was selected because of its high initial viscosity, so as to obtain a wide range of bleached pulp viscosities for subsequent studies.

2. The variation in pulp viscosity was obtained by varying chlorine charge during chlorination and hypo stage as well as by selectively adding NaOH in the hypo stage. But in the alkali extraction stage optimum alkali was added to get a final pH of 9.5

3. It can be observed from Fig. 1 and Table 4 that with increasing viscosity (4-10 cps) all the properties i.e. burst factor, tear factor, double fold and breaking length increase. However, after a viscosity of 8 cps the increase in strength properties is not significant. It was not possible to obtain a pulp with viscosity < 11 cps in the given brightness range.

4. Fig. 2 shows that with increasing pulp viscosity the alpha cellulose content increases, upto about 90% and then levels off.

Alkali/Oxygen Delignification and Bleaching of Soda Bamboo Pulp

Molecular oxygen is a unique oxidizing agent. In the normal form of oxygen the electronically stable form two of the electrons are unpaired. It has a strong tendency to react with organic substances and radial chain reactions are initiated. Several intermediate i.e. peroxides, organic radical and hydroxy radicals are formed. These intermediates are non-specific oxidative agents and in pulp bleaching it is necessary to control their formation if severe degradation of the cellulose is to be avoided.

In the middle of 1950’s the Soviet Researchers commenced investigations into the possibilities of using molecular oxygen together with alkali for the bleaching and refining of dissolving pulps. Further development on the oxygen bleaching was started in France at the beginning of 1960’s. The object was to improve the process in such a way that it would be applicable to the bleaching of paper pulps and the detrimental effect of oxygen-alkali treatment on the strength would be eliminated. Robert and associates, worked on several inorganic chemicals for inhibiting the formation of several intermediate compounds i.e. peroxide, organic radicals and hydroxy radical, which have higher degradation effect on cellulose. They observed that MgCO3 was the best.

Other researchers also found that Magnesium salts addition as carbonhydrate degradation inhibitors is necessary in maintaining the strength properties of oxygen pulp at acceptable levels, especially for unbleached grades. It was also pointed out by others that if MgCo3 was mixed up with pulp prior to NaoH, the viscosity and strength properties were improved quite substantially.

Environmental considerations are having a substantial influence on the development of technology for existing plants and new installations in the pulp and paper industry. At the same time, raw material and processing cost are on the increase. These problems have promoted much interest in search for novel sulfur free pulping process which could offer the desired higher pulp yields and qualities and which are less polluting then the conventional Kraft process. Among the various approaches investigated during the past two decades, the two stage oxygen pulping system seem to offer the most promising alternative to the existing kraft process in terms of yield and pulp qualities. Most of the recent work consists of soda cook to high yield followed by defibrization prior to oxygen delignification in one or several stages. Preliminary work on oxygen bleaching has been carried out at Forest Research Institute on soda pulps from Eucalyptus Hybrid and Kinetics of oxygen-alkali delignification of high yield pulps. In the present study the effect of oxygen bleaching on high Kappa no. soda cook and low kappa no. soda cook has been carried out and compared with conventional bleaching sequence.

Experimental

Caustic cooking of Bamboo chips (-22+10 mm size) was carried out using 15.0%, 16.0% 17.0%, 19.0% and 21.0% alkali and bath ratio 1:4. Cooking conditions and results are recorded in Table 1. The resulting pulps were passed through sprout waldran disc refiner at a clearance of 254 microns using refiner plate D2A-501. The refined pulps were analysed for Kappa number and yield (%).

Bamboo pulp of cook no. 5 (Table 1, Kappa no. 45.4) was bleached with oxygen at 7% consistency, using 2%. 3%, 4% and 5% alkali respectively MgCo3 (0.5%) was added as inhibitor to check degradation of cellulose. Oxygen was injected at 120°C 9.0 Kg/ cm2 pressure) for 90 mts. through a non-return valve connected with the side flange of the digester. Shrinkage of pulp (%), Kappa No. and brightness of the pulps are given in Table 2. These oxygen pulps (Expts. No. 2-5) were beaten at 25, 35, 45 and 55 SR freeness in a laboratory valley beater. Standard sheets were made as per Tappi standards. Physical strength properties of oxygen bleached pulps are represented in Fig. 10-12.

Oxygen delignified pulps of (expts. No. 2-5) were further bleached under C/E/H sequence. The alkali stage effluents were analysed for BOD5 and COD. The bleached pulps were analysed for copper no. viscosity, P.C. no. and brightness. Bleaching conditions and results are recorded in Table 3.

Unbleached bamboo pulp (Cook no. 5) was also bleached under C/E/H sequence for comparison with O/C/E/H sequence bleached pulps. Bleached bamboo pulps were also beaten in laboratory valley beater at 25, 35, 45 and 55°SR freeness. Physical strength properties of oxygen bleached pulps, O/C/E/H sequence bleached pulps and C/E/H Sequence bleached Pulp are represented in Figs. 13-15.

Bamboo pulp of expt. No. 2 having higher Kappa No. (Table 1, Kappa No. 71.5) was also bleached with oxygen (Oxygen pressure 9.0 Kg/cm2) using 7% alkali, pulp consistency (7%) and reaction temperature 120°C. Oxygen was injected for a period of 90 minutes. Magnesium carbonate (0.5%) was added to avoid pulp loss. Shrinkage of pulp (%) Kappa No. and brightness of the pulp are recorded in Table 4. Oxygen bleached pulp was further bleached under C/E/H sequence using 9% chlorine in the first stage and 4% hypochlorite in the third stage bleaching BOD, COD and pH of alkali extracted effluent was also analysed (Table 5). The number of double folds of alkali/oxygen delignified pulp, O/C/E/H bleached pulps of lower & higher Kappa No. are recorded in Table 6 along with double folds, of C/E/H bleached pulp of lower Kappa number. Bleached pulp was analysed for copper number, viscosity, P.C, No. and brightness. Oxygen bleached Pulp and O/C/E/H bleached pulps were evaluated for physical strength properties. Physical strength properties of oxygen pulp and O/C/E/H pulps are represented in Figs. 16-18.

Two competing reactions delignification and carbohydrate degradation occur simultaneously during oxygen bleaching. Degradation of wood polysaccharide occurs due to oxidative hydrolysis which depends on both temperature and alkali concentration. Bamboo refined pulp (Kappa No. 45.4) was delignified with alkali/oxygen using 2.0%, 3.0%, 4.0% and 5.0% alkali to find out optimum alkali dose (Table 2). The effect of alkali addition in oxygen delignification on Kappa No. of pulp and brightness is shown in Fig. 3. Kappa No. of the pulp reduced sharply with 2% alkali and then steadily upto 5% alkali. The brightness of the pulp improved moderately which is caused by delignification and not by lignin bleaching. The effect of alkali/oxygen delignification on pulp shrinkage (%) is represented in Fig. 4.

Alkali/oxygen delignified pulps were evaluated for physical strength properties. The effect of beating these pulps at different freeness on tensile index depicted in Fig. 10, shows that tensile index decreased with increase in alkali percentage. Burst index of these pulps increased with increase in alkali percentage (Fig. 11). Tear index was much affected in alkali/oxygen delignification as depicted in Fig. 12. Lower tear index is being a property which is adversely affected by oxygen bleaching treatment. Double folds of alkali/oxygen delignified pulps increased with increase in alkali addition.

Oxygen stage bleaching is the only solution when the aim is for complete removal of colour, lowering of BOD and toxic elements in effluent from fully bleached pulps. Application of chlorine chemicals results in higher brightness pulps. Therefore alkali oxygen delignified pulps were bleached with different chlorine and hypochlorite dosages in First and Third stage respectively. After alkali extraction the caustic extracted effluents of these pulps were analysed for BOD 5 and COD as per standard methods. The effect of chlorine addition on COD and BOD 5 of caustic extracted effluent is represented in Fig. 5 & 6 respectively. Blank experiment for bleaching the soda bamboo pulp under C/E/H sequence was also carried out. COD and BOD 5 of caustic extracted effluent of blank experiment are depicted by dotted lines in Fig. 5 & 6 respectively, COD reduction in O/C/E/H sequence (Expt. No. 2-5) was 25.5% 44.3%, 50.5%, and 55.7% respectively, whereas BOD 5 reduction was 31.9%, 50.0%, 63.6% and 72.7% respectively as comped to C/E/H sequence. The total chlorine consumption in Blank experiment under C/E/H sequence was higher as compared to O/C/E/H sequence bleached pulps (Table 3).

The effect of total chlorine addition on viscocity & copper no. of O/C/E/H sequence bleached pulp projected in Fig. 7 & 8 (Dotted lines of these figures indicated viscosity & copper no. of C/E/H sequence bleached pulp) show that viscosity of O/C/E/H pulps was higher than C/E/H pulp and reverse trend was observed with copper no. & P.C. No. Oxygen bleached pulps have better brightness stability than conventional bleached pulp. The total pulp shrinkage in O/C/E/H sequence was higher than C/E/H sequence.

This shown that the pulps degrade to a lesser degree when oxygen stage of bleaching is applied.

Sodium Carbonate in Alkali Extraction During Bleaching Bamboo (D. Strictus) Pulp

In recent years, Pulp and Paper Industry in India is also facing the world wide inflation and escalation of cost of chemicals. This makes the Industry to look for alternative cheaper chemicals, wherever possible. In this paper an attempt has been made to study the viability of using sodium carbonate as an extraction chemical to substitute sodium hydroxide.

Though, the alkaline chemistry of sodium hydroxide and sodium carbonate is almost similar in several respects, the weak basicity of sodium carbonate has limited its use.

Singh have reported that the extraction stage delignification follows two distinct phases, (i) a rapid initial phase and (ii) a slower second phase. The change in the Kappa number or the rate of delignification during the second phase was found to have a linear relationship with the caustic soda consumption, which is effected by the temperature of the system. They also observed that the caustic soda consumption is a zero order reaction for first twenty minutes and then becomes negligible. The drop in Kappa number in the rapid phase amounted to 65% of the total drop consuming only 13% of sodium hydroxide. The consumption of caustic soda in both phases is around one fifth of its addition, indicating thereby that the amount of alkali utilized in delignification is quite less and the rest is utilized in maintaining the pH of the system so as to avoid lignin redeposition.

Peter Axegard observed the Kappa number to never reach a constant level, but continue to decrease even after a long period. Thus, in the slower reaction phase, the very slow rate of delignification within a defined period of about two hours put the reaction as an independent function of the alkali consumption following a zero order reaction in hydroxyl ion concentration. The initial rapid and the later slower phase reactions are two separate first order reactions with respect to the Kappa number of the pulp. He also opined that the chlorinated lignin upon extraction yields lignin of two types-eliminated easily and with difficulty. It is likely that in the rapid phase, a favoured topographical condition exposes a maximum amount of lignin to chemical attack, accelerating the delignification upto a short period. Afterwords the residual lignin is so difficult to reach, that the reaction slows down considerably. He also believed the rapid phase delignification to be a function of hydroxyl ions following a reaction order between zero and one. Thus this mechanism though different from that of Singh et al, indicates the initial rapid phase delignification to depend on the alkalinity, temperature and chlorination of the pulp.

Coniferyl aldehyde, the main constituent of soft wood lignin, being quite resistant to alkaline hydrolysis, a strong alkali may be necessary to extract it, but bamboo lignin contains mostly syringyl groups which are not so resistant to alkaline hydrolysis. Further, soft wood hemicelluloses contain 1: 4 glucan which can undergo isomerisation to 1: 4 mannan during alkaline hydrolysis to get stability, whereas bamboo hemicelluloses, which contain 1: 4 xylan do not undergo this change. They get removed during sodium hydroxide extraction. Hence, a milder alkali can possibly reduce the alkaline hydrolysis of bamboo hemicelluloses and preserve them.

Emll Heuser has believed that a certain amount of alkalinity is being maintained during extraction with the same delignification irrespective of the type of alkali used. Chang reports the isolated lignin from unbleached pulp equally soluble in sodium hydroxide as well as sodium carbonate. Arnold et al., have found sodium carbonate and ammonium hydroxide to be at par in efficiency when compared to sodium hydroxide. All this is of relevance to the present study. As the literature though limited, is confined to temporal soft and hardwoods, authors initiated this study on the possibility of sodium carbonate as a substitute for sodium hydroxide.

Experimental

After encouraging results were obtained from preliminary studies on the use of sodium carbonate as a substitute for sodium hydroxide in alkali extraction, detailed studies were carried out.

Study on Sequentially Chlorinated (H/C) Pulp

Extraction of sequentially chlorinated pulp (H/C) was done at 55°C using sodium carbonate and sodium hydroxide alone, as well as in a 50: 50 mixture, both expressed as NaOH. Hypo stage bleaching was then carried out, substracting 1.0% chlorine on the weight of unbleached pulp, in form of hypochlorite, added during sequential bleaching, from the total demand of chlorine for achieving 80+1° Elrepho brightness. The pulps were tested for their chemical and physical properties. The conditions maintained and results obtained are tabulated in Table 1.

Study on Chlorinated Pulp

Extraction of chlorinated pulp was carried out at 55°C with sodium carbonate and sodium hydroxide as above. The pulps were subsequently bleached with hypochlorite to get a brightness of 80+1° Elrepho and tested for their chemical and physical properties. The conditions maintained and the results obtained are in Table 1. Effluent characteristics of the filtrate from alkali extraction stage were studied and are in Table 1.

For all tests, Standard Procedures were followed. The pulp was beaten in valley beater to a freeness of 40° SR. A plant trial was taken to confirm the results of bench scale studies. Results are tabulated in Table 2.

Results and Discussion

From Table 1 it is obvious that the pulp extracted with sodium hydroxide has shown a slightly lower permanganate number than the carbonate extracted pulp, probably for the following reasons.

(i) The carbonate extracted pulp contains more of hemicelluloses which consume permanganate and show a higher number,

(ii) After the removal of rapid phase lignin, the residual lignin content in the pulp is higher in the case of carbonate extracted pulp.

The sequentially chlorinated as well as chlorinated pulps, when extracted with sodium carbonate (or a 50: 50 Na2CO3 & NaOH mixture) show a tendency for less shrinkage as compared to the NaOH extracted pulp. This can probably be attributed to less degradation of hemicelluloses owing to the milder action of sodium carbonate. The extracted pulp on subsequent hypochlorite bleaching, gave practically same brightness, physical and chemical properties as that of NaOH extracted pulps.

The pH of the pulp during the carbonate extraction has a comparatively lower value than during hydroxide extraction (Table 1 & 2). This can be explained since the alkalinity provided by sodium carbonate is weaker than that of NaOH at equivalent concentrations. In the case of carbonate extracted pulp, the addition of buffer during the hypochlorite bleaching is also reduced indicating a better pH stabilization in the system. From the effluent characteristics (Table 1) it is observed that the effluent generated from carbonate extracted pulp at the extraction stage is less polluted in terms of total solids and COD.

Results of the plant scale trials, conducted in an integrated pulp and paper mill, using bamboo and following sequential chlorination confirmed the findings of the bench scale studies (Table 2).

The advantage of using sodium carbonate in terms of cost benefit is two fold, viz. (a) it is substantially cheaper than sodium hydroxide and (b) it is more readily available.

Effect of Hemicelluloses on Unbleached Softwood Kraft Pulp

Pretreating unbleached kraft pulp with polysaccharides minimizes or eliminates formation of undesirable chloro-organic by-products during chlorination. Exactly how these enzymes break down lignin during bleaching, however, is not understood.

If residual lignin is covalently bonded to hemicellulose, and chemical evidence indicates that it is, enzymatic cleavage of hemicellulose-glycosidic bonds could solubilize lignin with fewer lignin bonds cleaved by the bleaching agents. Physical association of hemicelluloses with cell wall lignin may pose a barrier to delignification by hindering the accessibility of bleaching reagents to lignin or restricting diffusion of degraded lignin from the cell wall. Enzymatic hydrolysis could remove this barrier. One hypothesis considers the reprecipitated xylan to be a physical barrier. In softwood kraft pulps, the main hemicelluloses are xylan and mannan, thus, xylanase and mannanase are used to degrade xylan and mannan.

To determine the effect of xylanase and mannanase on kraft pulp, the study reported here used classical microscopy stain methods combined with chemical composition analyses and other physical techniques. The chemical and physical interpretation of the stain results was investigated.

Materials and Methods

Enzyme Treatments

Enzymes used for the treatment of unbleached kraft pulp samples included CARTAZYME HS xylanase (Sandoz Chemicals Corporation, Lexington, MA) and a mannanase enzyme solution (Sandoz Chemicals Biotech Research Corporation, Lexington, MA). The starting unbleached kraft pulp was obtained from mill in the northeastern United States and consisted primarily of spruce, fir, larch, and pine, with about 1% hardwood. The kappa number of the pulp was 24.3 mL/g. The pulp was treated with xylanase at three levels (1.6 and 10 units/g), mannanase at two levels (5 and 10 units/g), and a mixture of the two enzymes (1 xylanase plus 5 mannanase units/g) (Table 1). The pulp samples were incubated at 50°C, pH 4.8, for 2 to 18 h. The samples were then either washed with water or extracted with a 2.0% sodium hydroxide solution for 1 h at 70°C. Control pulp samples were prepared the same as enzyme-treated samples, except that the enzyme solution was replaced with water. The wet pulps were refrigerated until analyzed.

Bleaching Experiments

Control and enzyme-treated pulps were subjected to a standard CDED1 ED2 bleaching sequence with 10% chlorine dioxide substitution in the chlorination stage.

The CD stage was carried out at 3.5% consistency for 1 h at 25°C with active chlorine charge of 4.8% (% on pulp =0.22 × kappa number). Chlorine and chlorine dioxide were premixed before addition to the pulp samples. Extraction stages were carried out at 10% consistency and 70°C for 1 h with a caustic loading of 0.6 times the active chlorine used in the CD or D stages. During the first chlorine dioxide stage (D1), pulp samples were bleached with 0.8% C102 and 0.35% NaOH at 10% consistency for 3 h at 70°C. The chlorine dioxide charge for the second stage (D2) was 0.4% under the previously stated conditions.

At three stages during the enzyme/chemical bleaching sequence, ISO brightness values were determined.

Chemical Composition and Kappa Number Analyses

Freeze-dried samples were ground in a Wiley mill, hydrolyzed and analyzed for the five major wood sugars. The high performance liquid chromatography (HPLC) was performed with a Dionex model chromatograph using a CARBO-PAC PA-I column. Kappa numbers were determined by the TAPPI microkappa number analysis method (UM246). The microkappa number was used because the available sample size was limited.

Microscopic Analysis

Slides were prepared according to the TAPPI T401 om-88 procedure. Graff ‘C’ stain was purchased from Integrated Paper Service. Three drops of the stain were applied to the fiber field on a microscope slide. The wet fibres were covered with a cover glass and allowed to stand 1.5 min. The surplus stain solution was drained off, and the fibers were examined immediately.

Direct blue 1 and direct orange 15 dyes for Simons’ stain were provided by Pylam Products, Inc. under the commercial names Pontamine Sky Blue 6BX and Pontamine Fast Orange 6RN. Separate solutions, one consisting of 1% direct blue 1 dye and the other of 0.2% high-molecular-weight (>25,000) direct orange 15 dye, were prepared. The solutions were mixed in a ratio of 1 : 1, Eight drops of the mixed dye solution were applied to the fibers on a slide. The slide was dried at 75°C, washed with water, and examined.

The quantitative microscopic analyses were performed following the TAPPI T401 om-88 procedure using an Olympus research microscope, model AH-2.

Numerical Measurement of Colour

Photomicrographs of Graff ‘C’ stained fibers were taken at preset locations on the slide for randomization. The L*a*b* system color values were measured from the photographs with a Minolta Chroma Meter CR-200 at preselected points to provide further randomization. About 300-400 data were obtained from each sample for analysis. (The b* values were not absolute, but relative. Because of the large head size on the Chroma Meter, we modified the procedure by measuring the colored fiber through a 3-by 6-mm hole in white paperboard.)

Results and Discussion

Chemical Changes After Enzyme Treatment

The enzyme treatment did not result in a large hemicellulose loss. After xylanase treatment, the xylan content decreased from 6.8% of the total polysaccharides to 6.2%. After mannanase treatment, the mannan content decreased from 7.9% to a low of 6.8%. Xylanase and mannanase treatments each resulted in losses of their respective hemicelluloses on the order of 10%. The mannanase effected somewhat more of a loss of mannan than xylanase did of xylan. For both xylanase and mannanase, a high dosage of enzyme resulted in more xylan or mannan loss, and 18 h of treatment resulted in more xylan and mannan loss than 2 h. The alkali extraction removed somewhat more xylan after xylanase treatment, but the mannan content was unaffected by alkali extraction after mannanase treatment.

Most of the lignin loss occurred with the alkali extraction with or without enzyme treatment. The treatment with both xylanase and mannanase released slightly more lignin, especially at the higher enzyme dosages and 18 h treatment time. It appeared that the mixture of xylanase and mannanase resulted in more lignin loss than the additive effects of the individual treatments. The magnitude of the difference, however, was about that of the experimental error.

Bleaching Experiments

The results of bleaching experiments with various enzyme treatments are shown in Table 2. In terms of brightness gain, the improvement brought about by enzyme pretreatment was apparent after the CDE stage and carried through to the fully bleached pulp. This implied that the improved bleaching was related to an easier delignification in the first stage.

Graff ‘C’ Stain

Graff ‘C’ stain, an iodine stain consisting of potassium iodide, iodine, aluminium chloride, calcium chloride, and zinc chloride, is used extensively in microscopic fiber analysis. This stain is sensitive to the chemical composition of fiber. For unbleached kraft pulp, the stained fiber colour ranges from yellow through green to blue depending on the degree of cooking. Raw or slightly cooked fibers with high lignin content stain yellow, medium cooked fibers with medium lignin content stain green to brown, and well-cooked fibers with little or no lignin content stain gray to blue. This stain was used to analyze the enzyme-treated pulp by counting the number of fibers in each colour category (Table 3).

After enzyme treatment, the percentage of yellow fibers decreased from 20.3% to 17.2% for xylanase and to 13.2% for mannanase, while the percentage of green fibers increased from 15.4% to 17.6% for xylanase and to 222% for mannanase. The relative number of brown fibers and gray-blue fibers remained unchanged after either xylanase or mannanase treatment. For both xylanase and mannanase treatment, changes occurred between the yellow and green fibers. These changes indicated that lignin was lost primarily from high lignin content fibers.

Numerical Measurement of Colour

Instead of sorting the fibers by color subjectively color can be expressed numerically according to a system adopted by the International Commission on Illumination. In their L*a*b* system, color is expressed in three dimensions as L*a*, and b* values. The numerical scales for a* and b* are shown in Fig. 1.

The b* value decreases from positive values to negative as the color changes from yellow to blue. This is similar to the fiber color stained with Graff ‘C’ stain, which is yellow when the lignin content is high and blue when the lignin content is low. Therefore, the b* value of a Graff ‘C’ stained fiber indicates lignin content-the higher positive b* values represent high lignin content, and the negative b* values represent low lignin content.

The exact color of fibers stained Graff ‘C’ stain depends on the structure and conformation of the polysaccharides as well as the lignin content (Yu, in preparation). Nevertheless, for a given pulp, the influence of lignin on the colour appeared to dominate, and we used the b* value to describe the lignin content change in kraft pulp after enzyme treatment (Table 4, Fig. 2).

After enzyme treatment, the average b* values decreased from 3.3 to 2.9 for xylanase and to 2.4 for mannanase. The b* distribution showed that for both xylanase and mannanase, b* distribution narrowed at the expense of fibers with higher b* values. These results corroborated those of the more subjected visual examination of Table 3. The b* value analysis also suggested that upon enzyme treatment, the lignin content distribution narrowed at the expense of fibers with the highest lignin content.

Accessibility Changes and Simons’ Stain

Deuterium Oxide Exchange

Deuterium oxide exchange measures fiber accessibility. It is generally believed that hydroxyl hydrogens in the less crystalline regions and on the surface of the crystalline regions of cellulose are accessible deuterium oxide, while the hydroxyl hydrogens in the highly crystalline regions are not (12). After treatment with deuterium oxide, the accessible hydroxyl hydrogen’s exchanged with deuterium, and the hydroxyl absorption peak in the infrared moved from 3300 cm-1 to 2500 cm-1. The inaccessible, unexchanged hydroxyl absorption remained the same. Therefore, the ratio of absorbance at 2500 cm-1 (A2500) to absorbance at 3300 cm-1 (A3300) indicated the fiber’s accessibility (Table 5).

Enzyme treatment did not increase the A2500/A3300 ratio, but rather decreased it slightly. Thus, neither xylanase nor mannanase opened the crystal lattice in the fiber. The slight decrease of A2500/A3300 after enzyme treatment was probably due to the loss of some xylan and mannan that was accessible to deuterium oxide in the control pulp.

Simons’ Stain

Simons’ stain (9,13,14) consists of two direct dyes; direct blue 1, which has a well-defined structure with a molecular weight of 992.82, and direct orange 15, a polymeric mixture containing a high molecular weight fraction. This stain is relatively independent of the chemical composition of the fiber but is sensitive to its physical structure. The Simons’ stain is used to measure the size of the fiber cell wall micropores the same way that the solute exclusion technique does. The accessibility measured is not the same as that measured by deuterium oxide exchange. Fibers with pores accessible to the high molecular weight fraction of the orange dye stain orange or yellow. Fibers with pores accessible to the blue dye, but not accessible to the high molecular weight fraction of the orange dye, stain blue [14]. In a given fiber, there may be some areas that are accessible to the high molecular weight orange fraction while some areas are inaccessible. Such fibers will stain a mixture of orange and blue, and will appear green Table 6.

Thermodynamic Functions of the Reaction between Lignin and Hydrogen Peroxide during Bleaching

Kinetic investigations provide valuable information regarding the mechanism of the reactions. Thus from time to time, the kinetic studies of the several types of reactions involving organic substrates have been made to provide the necessary data for deciding the mechanism of a reaction. The advancements in this Branch of chemistry are associated with the advances in separation procedures new analytical techniques, physical measuring devices and in chemical theories. The governing notion of Arrhenius, that the activation of some kind is essential for chemical change, is of universal validity and has dominated the subject of chemical kinetics since the days of Arrhenius.

An important aspect of kinetic study is to show how the reaction rates vary with temperature. The role of solvent in reaction kinetics has been explained by Eyring’s theory of absolute reaction rates Kinetic is regarded as the science of motion. It will not be out of place to contrast thermodynamics with its static view point with that of chemical kinetics representing the dynamic view point. Thermodynamics is interested in the initial and final states of a system and an important fundamental postulate of thermodynamics is the state principle, which leads directly to the concept of an equation of state. Because of the greater rigour of thermodynamic methods, there has been considerable effort in the last thirty-five years to approach kinetics from the thermodynamic viewpoint, particularly combined with the methods of statistical mechanics. The important feature of this effort is to treat reaction rates as involving an equilibrium between average molecules and high energy molecules which are aligned and activated ready for reaction or between molecules in the initial state and in the so called “transition state” or “activated complex”. Even in such a treatment a fundamental problem remains: calculating for rate of decomposition of the activated complex. Only quantum mechanics