A Pilot Plant Evaluation of Selected Hardwood Pulps for Supercalendered Grade B Paper

Transcription

1 Western Michigan University ScholarWorks at WMU Master's Theses Graduate College A Pilot Plant Evaluation of Selected Hardwood Pulps for Supercalendered Grade B Paper Devendra Kumar Srivastava Western Michigan University Follow this and additional works at: Part of the Wood Science and Pulp, Paper Technology Commons Recommended Citation Srivastava, Devendra Kumar, "A Pilot Plant Evaluation of Selected Hardwood Pulps for Supercalendered Grade B Paper" (1988). Master's Theses This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact maira.bundza@wmich.edu.

2 A rilot PLANT EVALUATION OF SELECTED HARDWOOD PULPS FOR SUrERCALENDERED CRADE B TAPER by Devendra Kumar Srivastava A Thesis Submitted to the Faculty of The Craduate College in partial fulfillment of the requirements for the Degree of Master of Science Department of Paper and Printing Science and Engineering Western Michigan University Kalamazoo, Michigan June 1988

3 A PILOT PLANT EVALUATION OF SELECTED HARDWOOD TULPS FOR SUPERCALENDERED GRADE B PAPER Devendra Kumar Srivastava, M.S. Western Michigan University, 1988 The proliferation of wood free printing and writing papers suggests the evaluation of hardwood kraft and chemithermomechanical pulps for the manufacture of uncoated rotogravure paper. In this study 100% aspen kraft, 100% eucalyptus kraft, and 50% aspen chemithermomechanical with 50% kraft pulps were used to produce rotogravure paper on as 32" trim Fourdriner paper machine under alkaline papermaking condition. The machine runnability was smooth using 100% hardwood furnish for the production of rotogravure paper. The paper produced was found suitable for supercalender grade B applications, such as Sunday magazines, inserts, and flyers. The tensile index and tear index values were satisfactory for the use of paper.

4 ACKNOWLEDGEMENTS I wish to express sincere appreciation to Dr. Richard. B. Valley, Dr. John. F. Bobalek, and Dr. Raja Aravamuthan for their encouragement and suggestions for the improvement of this thesis. In addition, I would like to thank the pilot plant director Mr. Carl Shuster and the crew members for their assistance in running the paper machine & supercalender. I also appreciate the donations of chemicals and chemithermomechanical pulp received from Procomp, Marietta, CA; from EKA Nobel, Surte, Sweden; and from Hercules Inc., Kalamazoo, MI. Many thanks to my sister, Ms. Simmi Kochhar, for her support during my thesis. Devendra Kumar Srivastava

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7 O rder N u m b er 13S3735 A p ilo t p lan t evaluation o f selected hardw ood pulps for supercalendered grade B p a p e r Srivastava, Devendra Kumar, M.S. Western Michigan University, 1988 U MI 300 N. Zeeb Rd. Ann Arbor, MI 48106

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9 PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark V. 1. Glossy photographs or pages 2. Colored illustrations, paper or print 3. Photographs with dark background 4. Illustrations are poor copy 5. Pages with black marks, not original copy 6. Print shows through as there is text on both sides of p a g e 7. Indistinct, broken or small print on several pages 8. Print exceeds margin requirements 9. Tightly bound copy with print lost in spine 10. Computer printout pages with indistinct print 11. Page(s) lacking when material received, and not available from school or author. 12. Page(s) seem to be missing in numbering only as text follows. 13. Two pages num bered. Text follows. 14. Curling and wrinkled pages \ / ^ 15. Dissertation contains pages with print at a slant, filmed as received 16. Other

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11 TABLE OF CONTENTS ACKNOWLEDGEMENTS LIST OF TABLES... LIST OF FIGURES... i i V vii CHArTER I. INTRODUCTION... 1 II. REVIEW OF SELECTED LITERATURE... 3 Uncoated Supercalender Rotogravure Papers... 3 Rotogravure Processes... S Fiber Furnish for Supercalender Papers 9 Market Trend Hardwood Pulp Chracterstics Manufacture of Supercalender Papers Alkaline Paper Making Calcium Carbonate Retention of Size and Filler III. SPECIFIC OBJECTIVES IV. EXPERIMENTAL Summary of Experimental Design Raw Materials Furnish Selection Wet End Additive Paper Machine and Supercalender Determination of Paper Properties iii

12 TABLE OF CONTENTS continued CHAFTER Data Analysis V. PRESENTATION OF RESULTS AND DISCUSSION Comparison of Furnishes B u l k Strength Properties Optical Propreties, Sheet Surface Properties Porosity Printability T e s t VI. SUMMARY OF RESULTS VII. CONCLUS IONS VIII. SUCCESTIONS FOR FURTHER STUDIES REFERENCES APPENDICES A. Fiber Length Analysis by Kajaani FS 100 Fiber Length Analyzer B. Product Data Sheet For Chemicals U s e d C. Supercalendered Uncoated Paper Property Test Results D. Mean Values For Paper Properties E. Clossary of Pulp and Paper Terms BIBLIOGRAPHY iv

13 LIST OF TABLES 1. North American Consumption of Mechanical Printing Tapers North American Rated Capacity All Uncoated Groundwood SCA and SCB Supplies to U.S / Quality Data for SCA and SCB Comparison of CTMF Versus Chemical P ulp Supercalendering Operation Conditions Alkaline Papermaking Capacity Estimates Refining of P u l p Wet End Additive Machine Condition for 100% Eucalyptus K r a f t Machine Condition for 50% Eucalyptus Kraft + 50% Aspen C T M T Machine Condition for 50% Aspen Kraft + 50% Aspen C T M P Machine Condition for 100% Aspen Kraft Supercalendering Condition for all Rolls Paper Properties to be Evaluated for Rotogravure Paper Probability Values for Effect of Furnishes on the Paper Properties Ranking of Helio Samples v

14 LIST OF FIGURES 1. The Components of BMA and B M B Bar Graph for Basi3 Weight Comparison of Furnishes for B u l k Effect of Filler Content on Bulk for Furnish A and Furnish D Comparison of Furnishes for MD Tensile Index Effect of Filler Content on MD Tensile Index for Furnish A and Furnish D Comparison of Furnishes for CD Tensile Index Effect of Filler Content on CD Tensile Index for Furnish A and Furnish D Comparison of Furnishes for MD Tear I n d e x Effect of Filler Content on MD Tear Index for Furnish A and Furnish D Comparison of Furnishes for CD Tear Index Effect of Filler Content on CD Tear Index for Furnish A and Furnish D Bar Graph for Brightness Bar Graph for Opacity Comparison of Furnishes for Brightness Comparison of Furnishes for Opacity Comparison of Furnishes for Ash content Comparison of Furnishes for Parker Print Surf (10 k g f ) Comparison of Furnishes for Parker Print Surf (20 k g f ) Effect of Filler Content on Smoothness for Furnish A and Furnish D vi

15 LIST OF FIGURES continued 21. Comparison of Furnishes for Gloss Bar Graph for Porosity Comparison of Furnishes for Helio vii

16 CHAPTER I INTRODUCTION Uncoated 3upercalendered <SC) papers have historically been a high volume segment of the European paper industry. Introduction of highly filled uncoated supercalendered papers into the North American manufacturing scheme has occurred in the past seven years. Growth of the paper market is forecast to continue in Europe and make great strides in North America as a result of increased demand and production. To date, the fiber furnishes for these grades have comprised a mechanical fiber fraction (generally groundwood) and a chemical fiber portion (generally kraft). "Wood free" printing and writing papers, those containing less than 10% of mechanical pulp (1), are the most costly grades worldwide. Generally, paper is made from a mix of both softwood and hardwood pulps. Because of increasing paper consumption in Europe, South America, and Asia, the demand for hardwood pulps has increased rapidly. The majority of these are hardwood pulp furnishes used for printing and writing papers. The simplicity of the chemithermomechanical pulping (CTMF) and low cost of production are attractive features of CTMP processes. The most important characteristics of 1

17 this new fiber technology (i.e., C T M D are that, they are adding a new dimension to paper making. Virtually all paper products benefit from the introduction of CTMP in the furnish. For example, replacing groundwood or thermomechanical pulp (TMF) in printing paper gives improved running and printing ability due to less shives, higher brightness and higher strength. Such an increase in strength allows one to use more mineral fillers to further reduce the cost of producing the paper. By replacing chemical pulp, higher opacity and bulk are obtained: and due to higher bulk stiffness and opacity, sheeted paper with lower basis weights can be manufactured. The present study is an initial evaluation of alternative fiber furnishes for the production of one particular grade of printing paper. In this study, fiber furnishes consisting of aspen CTMF, aspen kraft, and eucalyptus kraft pulps were evaluated.

18 CHAPTER II REVIEW OF LITERATURE Uncoated Supercalendered Rotogravure Papers Uncoated supercalender paper for gravure printing was created in the early 1950 in Cermany. Due to the quick expansion of gravure printing mass circulation magazines, the growth in consumption was tremendous in the 1950 and 1960(2.). In Europe the predominant printing process for publication papers is rotogravure. According to the most recent survey by the Gravure Association of America (CAA), publication gravure in U.S.A. was a $7.8 billion industry in 1986, an increase of 56% over 1981 (3.). During recent years modifications and improvement in printing technology have resulted in more stringent demands being made on uncoated rotogravure paper, particularly with regards to sheet consolidation and surface properties. Although the use of CTMF fibers for the production of newsprint papers is now a world wide practice, the use of CTMF fibers for uncoated rotogravure paper has to date only been developed in Europe. The consumption of mechanical printing papers are shown in Table 1, which indicates a projected growth of 5.9% during for SC uncoated papers (4.). The North American rated capacity for all uncoated groundwood

19 4 Table 1 North American Apparent Consumption of Mechanical Printing Papers (4) -Thous. Metric Tons A v g. A n n.% Increase Newsprint % 1.5% Coated Croundwood % 3.9% Uncoated Groundwood % 3.5% SC Uncoated % 5.9% Lightweight % 2.0% Groundwood Forms % 6.3% Other MF Uncoated % -0.6% Table 2 North American Rated Capacity All Uncoated Croundwood (5) {000 Short Tons) MF Croundwood Supercalender Canada U.S.A North America Grade Shift Total %Increase 1988/1985 # 1.5% * 70.3%

20 is shown in Table 2 (5.), Which predicts a 70.3% increase in supercalendered paper from 1985 to There are two major subgrades, Supercalendered Crade- A (SCA) and Supercalendered Grade-B (SCB). SCA is priced close to light weight coated. Gravure contains up to 30% mineral filler, and an offset, normally with 15-20% filler. SCB is a lower quality, lower filler level grade which fills the gap between machine finished uncoated mechanical pulp printing specialties (LIMITS) grades (i.e. roto news and high brightness) and SCA. It is priced well below low weight coated. These grades were originally developed in Western Europe, whose productive capacity for them is close to 3 million tons per year. European sources supply 40-50% of North American demand (6.). Table 3 shows that about 64% of SCA and SCB are imported from various countries (6.). Table 4 shows the quality data for SCA and SCB (6.). Gravure demands a smooth sheet of low porosity as well as good formation, uniformity, and dimensional stability. The gravure printing process is used for its high quality reproduction, consistent print quality, and superior color. It is especially economical for long runs such as large circulation magazines. The "top 10" magazines (Parade, Reader*s Digest. TV Guide. USA Weekend. Modern Maturity. National Geographic. Better Homes and Gardens, E'amily Circle, Woman* s D a y. and McCalls.) are

21 6 printed by gravure (7.). Table 3 SCA, SCB Supplies to U.S. 1984/85 in 000 of Short Tons/Year (6) Company/Region SCA SCB Total Total 1 Champion, U.S Madison, U.S CIP, Canada Consolidated- Bathurst, Canada * Haindl, Germany Feldmuhle, Germany Holmens, Sweden Stora, Sweden Saugbrugs, Norway Finland Italy Total

22 7 Table 4 Quality Data for SCA &, SCB (6) Particular SCA SCB Basis Weight (g/m2) Density, (g/cm3) : 9 Brightness, % ISO Opacity % Sheffield Roughness (ml/min) Paper Closs % Gravure Print Closs% A s h, % Further, gravure also enjoys a significant ; share in packaging and products printing. Overall, gravure is said to have captured a 20 percent share of printing market-40 percent of that is publication work, 29 percent packaging and 23 percent product gravure work (7.). Catalog publishing today represents what is probably the fastest and most dynamic major market in the printing and publishing industry. A catalog is accepted by definition as a publication of sixteen or more pages, bound, providing advertising and promotion of products or services (8.). Another rapidly expanding publication market and one of growth for gravure has been advertising inserts and

23 flyers. Newspaper inserts are free-standing unbound advertising pieces ranging from a single sheet to a full- size tabloid. Then these inserts are placed into or bound with the main publication. Rotogravure Processes Gravure printing is often done on a web-fed rotary press, which has proven to be an economical means of producing long run.jobs 3uch as newspaper supplements. Gravure printing process is a process in which the image area is etched below the surface of the printing plate and then transferred directly to the paper by means of pressure. The gravure printing unit consists of a printing cylinder, an impression cylinder, an inking system, and a dryer. Ink i3 applied to the printing cylinder by an ink roll or spray, and the excess is removed by the doctor blade and returned to the ink fountain. The impression cylinder is covered with a resistent rubber composition that presses the paper into contact with the ink in the tiny cells of the printing surface. Gravure ink consists of pigment, a resin binder, and a volatile solvent. The ink is quite fluid and dries entirely by evaporation hence only light printing pressures are required (9). Traditionally, the gravure process used chemical etching to prepare the copper cylinders. Frequent

24 corrections on the film or cylinders are required to run the whole process efficiently. In response to thi3 problem, electromechanical engraving was first introduced with the Hell (Kiel, W. Germany) Helioklischograph in This is now the accepted method of engraving cylinders for magazines and periodicals. This has been successful in reducing variabilitjr and improving the predictability and reproduction capability of cylinders. Fiber Furnishes for Supercalender Tapers Chemical pulps are currently an integral but expensive component of all commercial SC furnishes. The chemical pulp yield is only 40-45% as compare to 85-90% yield of CTMT. Chemically produced fibers generally represent 20-35% of SC fiber mixtures. The proportion of chemical pulp in the mixed furnish is often a compromise of several interacting (and often opposing) parameters. Sheet dry and wet tensile strengths are generally improved with increasing chemical pulp content. Paper machine wet-end and press section runnability (especially fourdrinier3> is generally improved at high chemical fiber levels due to improved drainage. Opacity, however, is sacrificed by increasing the amount of chemical pulp in the furnish. The linting has been reported to be reduced as chemical fiber furnish content is increased (10.). Often increased filler loading (to improve costs or

25 printability) is necessarily accompanied by (small) increases in chemical fiber levels. Clearly even incremental increase in chemical fiber contents in the furnish represent a significant increase in raw material costs. Many current producers of SC papers rely on purchased (non-integrated) chemical pulp supplies to satisfy their needs. A paper by Huuseri and Syrjanen at the 1979 International Mechanical pulping conference discussed pilot trials for SC (magazine) paper from thermomechanical pulp (TMP) containing furnishes (li) The article describes paper machine trials to produce SC paper from TMF and TMP/chemical pulp blends, all loaded (to varying degrees) with talc filler. Conclusions of the trials were that cost effective quality SC paper can be produced from TMP. During the past few years, chemical pretreatment of wood chips before mechanical pulping was introduced to reduce the high energy of TMP. While chemical treatment prior to mechanical processing does reduce the specific energy requirement for fiber separation, it can alter fiber surface properties. Specifically, surface area is reduced (1.2). Chemithermomechanical pulping combines thermomechanical pulping technology with sodium sulfite chemical treatment. The chemical treatment can be affected at two different points in the TMP process. The

26 TMF and CTMF yields are 95% and 90% respectively. Chip pretreatment is probably the more recognizable of the two stages. In this process small (2-4% Na2S03 applied) amounts of chemical are reacted with wood chips for a very brief period of time. Normal chip steaming follows as does atmospheric or pressurized refining. Sulphonation facilitates fiber separation (in the S1/S2 layer), but the energy required to produce a freeness value comparable to TMF is greater. Fines content is also reduced, resulting in lower opacity and light scattering (12). Inter-stage treatment of TMF with Na2S03 is an alternative to chip pretreatment. Chemical treatment (at somewhat higher levels and longer reaction times than chip treatment) is enacted either between or after the refining stage. Since the pulp already has a large surface area and a high fines content relative to pulp produced after chip pretreatment, desirable light scattering properties are maintained. The pulp receives no chemical pretreatment before fiberization, hence the separation of the fibers takes place in the S1/S2 layer and not in the middle lamella assuming that sufficient energy is applied during refining (12). Both approaches to produce CTMF may have some dependence on high cost chemical pulps. Additionally, recent work on producing CTMF from Northern hardwood

27 (aspen) opens the doors for additional furnish cost reductions, without sacrificing sheet properties (13). Still, work is under progress for eucalyptus chemi thermomechanical pulp. Market Trend The furnish choice is based on meeting product quality demands, namely runnability and printability at a competitive production cost. The increasing incorporation of refiner pulps (TMF, CTMF) in groundwood printing papers has been driven primarily by efforts at production cost minimization. A trend worth noting is the rate at which production of hardwood market pulps is growing. Total bleached hardwood output rose 5.3% in 1986, to over nine million tons, while bleached softwood grew by 3.7% to 13.5 million tons. Chemithermomechanical pulp, which has been hailed by some as the pulp of the future, saw a 5% growth output, reaching 427,000 tons in 1986 (14.). Chemithermomechanical pulp is a recently developed pulping process. The first mill was opened in Rockhammer, Sweden in 1978 and currently Sweden still leads the world in CTMF production. Current production totals for the world are approximately 1.5 million tons/yr, which is 1% of the global fiber requirement (1JL). Of this world production Sweden now produces approximately one-third

28 (.16.). Hardwood CTMP production stands at around 188,000 tons/yr. while softwood CTMP production is over 1.2 million tons/yr. (16.). It is expected that by the year 1990 CTMP production will top the 10 million tons per year mark (.17.). CTMP developed from thermomechanical pulping. Who actually invented it is difficult to establish (.17.), but it can be said that the mill at Rockhammer was one of the first to produce it. The process started as a modified version of bleaching by adding alkali and peroxide at the refiners. This was later developed into impregnation of the chips with sulfite/alkali, and thus became a true CTMP process. The reason CTMP is such a fast growing pulp is that it makes an excellent replacement for both mechanical and chemical pulps. Hardwood Pulp Characteristics The greatest long term problem facing the pulp and paper industry as a whole is the rising cost and declining supply-demand ratio for softwood & hardwood. A number of companies worldwide are establishing plantations using fast growing species of softwoods and hardwoods (18). Hardwoods, in particular eucalyptus are grown in plantation. Rotation rates of 5-8 years are being used for growing eucalyptus on plantation (.19.). The growth of hardwood is faster than the growth rate for native pine

29 (20.). Today, twelve species of eucalyptus have been planted for the pulp industry in South America and Europe (21). The fibers from various hardwood3 range from 0.6 to 2.0 mm in length as compared with 2.5 to 5.0 mm for the softwoods (22.). In addition to the short length of the fibers hardwoods pulps contain vessel segments and ray cells, many of which are lost in washing and screening operations in the handling of the pulps as well as on the paper machines in their conversion into paper (22.). Hardwood fibers inherently form stable suspensions in water (22.). Because of this characteristic suspensions of these fibers flocculate more slowly than do suspensions of softwood fibers. Consequently, the use of hardwood fibers in the papermaking furnish practically always results in more uniform paper formation. The use of hardwoods is motivated by this characteristic. Hardwood fibers in paper promote opacity more than softwood fibers (2 ). The need for greater opacity in printing papers has been recognized for many years. The opacity of papermaking fibers is reduced as fibers are processed mechanically before they are formed into a 3heet of paper (22.). This is due to short fiber length of hardwoods, which gives better network during formation. The relative strengths of various hardwood pulps are compared in Table 5. Aspen CTMP at 88-91% yield, with

30 good physical characteristics could be produced (23). This indicates that CTMP can be used to partially replace the expensive chemical pulp in paper manufacture. Table 5 Comparison of CTMP Versus Chemical Pulp (23) CTMP Kraft Item Unit Aspen Aspen Freeness CSF Tensile m Burst kpa.m2/g Tear Index mn.m2/g Opacity % Yield % Brightness ISO to 90 Manufacture of Supercalender Papers Historically, SC papers for both rotogravure and offset printing have been made from furnishes comprised of groundwood and chemical pulps. Chemical pulp contents of these furnishes ranges between 20-40%. The fiber composition of furnish is generally formulated based on the printing technique to be used and the paper machine and auxiliary equipment available at the mill (.10.). For example, papers targeted for rotogravure printing require very smooth (on a micro basi3), homogeneous, and

31 compressible surfaces. Offset papers, especially for web fed processes, require a 3trongly bonded fiber matrix, both internally (and on the surface) for press runnability. Dusting or linting during offset printing is probably the single most important technical factor considered by a printer, if he was to choose between a SC roll or a light weight coated roll. The properties required in the pulp used for printing paper are, in most cases, related to functional criteria. These tend to be evaluated subjectively, rather than objectively, or cannot readily be defined in terms of physical or chemical measurements. The major division in this field has traditionally involved two classifications; furnish containing mechanical pulps, and furnish that is described as being completely wood-free. Clever Swedish entrepreneurs recently have had some sucess in changing the traditional meaning of "woodfree." Now a days, grades having less than 10% of mechanical pulp are considered as woodfrees (1.). The challenge of improving the performance and reducing the costs of all components of a paper stock system is not new. For many years, papermakers and suppliers have made great progress in developing new paper furnishes and chemical additives to make better paper more economically. New chemical additives are being introduced in large numbers to fine-tune wet end processes and to

32 increase the performance and economics of the entire system (24)(25)(26 ). The latest advances in wet end improvements are now coming from products developed specifically to improve the performance of other additives, thereby lowering overall costs even further. Cost reduction comes about by a reduction in use of chemical additives in general, as well as through clearer white water systems and improved operating performance (26.). Traditionally, fourdrinier machines have been used to produced both SC gravure and offset papers. However, in an effort to address the paper symmetry requirements of the graving applications, new machines are often twinwire. A more complete review of the role that twin-wire and hybrid formers play in SC paper quality can be found in an article by Hujala (27.). The market for uncoated papers is currently changing as newspaper producers and other printers are increasing their use of two- and four-color printing. Customers that once relied almost exclusively on machine calendered papers now have a need for improved grades offering better smoothness and printability. Supercalendering as a part of the papermaking process plays an important role in improving the surface characteristics of uncoated groundwood papers. The three most important factors (28.) in supercalendering are:

33 1. the temperature of the calender rolls, 2. the moisture content of the paper when it enters the calender, 3. the pressure at the first nip of supercalender. Of these three points, moisture and temperature are the most important factors in supering while the speed is only critical for rotogravure printing. Typical operating conditions employed at Madison Paper Industries Maine are presented in Table 6 (28.). Table 6 Supercalendering Operating Conditions (28) Parameter Value Base Moisture 7.5 <V /O Steam Quantity 2500 lb/hr Temperature 260 F Pressure 25 psig Roll Water Temperature Top Zone 210 F Bottom Zone 260 F Bottom Nip Pressure 1600 pli Operating Speed 1950 fpm Tension Unwind 1.5 pli Windup 1.9/1.1 pli Off-line supercalenders are used with increasing frequency for premium quality uncoated printing papers. The paper is calendered in soft nips, between hard and

34 soft rolls. The soft rolls are covered (or filled) with compressed paper, which will deform somewhat to let floes pass through the nip without crushing them. Supercalendered (SC) paper has a uniform high gloss and low bulk (29). Alkaline Paper Making Alkaline paper making has been practiced in Europe fairly widely since the 1950s. The introduction of a relatively inexpensive ground calcium carbonate filler to U.S. market in the 1970s, along with improvements in alkaline sizing agents, has increased interest in alkaline paper making. It is evident from Table 7, that the alkaline papermaking with calcium carbonate has significant share and demand in market (30.). It has been estimated that U.S. production of coated and uncoated wood free alkaline paper will increase to approximately 55% by This conversion to alkaline paper making technology in North America will significantly increase the demand for calcium carbonate (30.). The basic reasons for process conversion from traditional acid to alkaline paper making technology is as follows: 1. Alkaline paper making provides an opportunity to substitute higher levels of lower cost mineral fillers for expensive bleached fiber. 2. The conversion is chemical in nature and no significant capital investment is required.

35 20 Table 7 Alkaline Papermaking Capacity Estimates Coated and Uncoated Free Sheet Printing and Writing Papers (30) (Tpy) (000 ommitted) Particular Coated Free Sheet Total Capacity Alkaline Capacity % Alkaline 50% 61% 74% Uncoated Free Sheet Total Capacity 10,100 10,800 11,300 Alkaline Capacity % Alkaline 15% 22% 49% Composite Market Total Capacity 12,800 13,900 15,200 Alkaline Capacity 3,000 4,300 8,400 % Alkaline 23% 31% 55% Calcium Carbonate Demand The chemistry of alkaline technology is compatible with the use of calcium carbonates for paper coating and filling, the least cost high brightness, high opacity pigments. Sizing is used to retard the penetration of liquids into the paper structure. Internal sizing is added during the papermaking process by depositing materials onto the

36 fibers which are capable of importing a low free surface energy to the paper. Little sizing material is usually required, % by weight (31)(32)(33). The alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) are used as a synthetic sizing agent in alkaline papermaking. The AKD molecule consists of two hydrocarbon chain each of 16 to 18 carbon atoms in length, attached to a 4-membered lactone ring (34.). It reacts with a cellulose hydroxyl group to form a stable ester linkage. AKD is insoluble in water, so it is used in emulsion form with cationic starch which imparts a net positive charge to the particles formed. AKD emulsions are retained with the addition of additional cationic material. Cationic starch or cationic low molecular weight resins are used. The low melting point of AKD permits the sizing agent to spread over the fiber surfaces very extensively during the elevated temperature drying of paper. The AKD emulsion particles are larger in diameter than rosin particles, 0.2 to 2.0 urn versus 0.1 urn. As a result, the attractive forces are weaker than are generated using the rosin-alum precipitate and they spread over the fiber surface in a layer of molecular dimensions (35). This very efficient coverage is one reason for the high efficiency of alkaline sizes. The anchoring step with alkaline sizes results from the formation of a

37 covalent bond between the size and the cellulose. This attachment accounts for the ability of alkaline sizes to provide good resistance to a wide variety of penetrants. Calcium Carbonate By 1985, over 50% of the wood free papers produced in Europe were made using alkaline technology. Calcium carbonate became the European filler of choice in alkaline papers, because of its compatibility with the alkaline process and the availability of extensive, high quality commercial deposits (30.). The calcium carbonates used in the United States fall into two general categories, ground limestone (GL) and precipitated calcium carbonate (PCC). Trecipitated calcium carbonate is found in various crystalline forms. The common types are calcite, rombohedral (barrel-shaped); calcite, scalenohedral (rosette-shaped); and aragonite, acicular (needle-like) (36.). The advantages of using precipitated calcium carbonate are as follows: 1. ph buffering of the aqueous papermaking mixture in the correct range for efficient alkaline sizing. 2. An economical increase in paper opacity and brightness. Retention of Size and Filler A good retention of size is especially important in

38 an alkaline system because of the small amount of expensive synthetic size being added to the stock. To increase the retention of size on the fibers, retention aids are employed. Retention aids are essentially large molecules (e.g., polyacrylamide) with polar groups (anionic, cationic, nonionic or a mixture called "amphoteric") scattered along the backbone of the polymer. The polar groups have an affinity for colloidal particles in inverse order of size. They are therefore, generally attracted first to fillers, then fines, and finally fibers. The strength of attraction is increased if the electrokinetic charge of the particle is unlike that of the retention aid (e.g. the retention aid is anionic and the particles are cationic) (37.). Synthetic size emulsions are relatively unstable because the cationic stabilizer is usually not firmly bound to the particle surface. When these emulsions are exposed to excessive shear, high temperatures an repeated cycling through the system, there is a tendency for the stabilizer to separate from the emulsified particles and cause breakdown of the emulsion. This can result in low retention and hydrolysis. Both of these processes detract from sizing efficiency and runnability. A number of retention aid chemicals are available to the papermaker since these chemicals act mainly through the mechanism of flocculation. Moberg (38.) has described

39 the optimization of wet end chemistry. At wet end, any change to improve one property affects several other properties. Hence, an integrated approach is needed, including one that considers the interaction from wet end operations to the end customer. Today*3 papermaking operations require wet end control. Fortunately, steady improvement has been made in wet end chemicals and their application. These include synthetic sizes, improved pigments, and two-component retention aids. It has been shown (39.) that it is possible to use multi-functional wet end chemical system for improved quality and also for better paper machine operations. The name of the chemical system is compozil. Compozil consists of two components, which are added to the stock at separate points. The components of Compozil are shown in Figure 1 (39.). One component, called BMB, is a cationic potato starch, which reflects a nitrogen content of 33% to 36%. This is higher than the majority of wet-end starches. Except for its high cationic charge, BMB is similar to typical cationic wetend starches, and is a material with which paper makers are familiar. The second component, BMA, is anionic colloidal 3ilica. The important features of BMA are its higher charge density, its low molecular weight, and its large surface area. A detailed study for the application of Compozil has been discussed by Bengtsson and

40 BMA COLLOIDAL SILICA ANIONIC OH 0 BMB CATIONIC STARCH CATIONIC Figure 1. The Component of BMA. and BMB

41 Kramer (40.). Most of the rotogravure paper is manufactured using a blend of softwood and hardwood. The time when all available sources of softwood for pulping will have been used may rapidly be approaching. New plantation programs are gradually increaseing the amounts of available softwoods, but not at a rate to meet increasing demands of paper consumption. The short fall will have to be met from the various sources of hardwoods available: 1. Mixed aspen and poplar resources in the Northern coniferous belt. 2. Mixed species including beech, poplars, maples, alder, etc in temperate zones. 3. Mixed tropical hardwood species. 4. New plantations of genetically improved hardwoods, especially eucalyptus species. Keeping all these in mind, it was decided to evaluate furnishes using hardwood pulps. The goals of the study are described in Chapter III.

42 CHAPTER III SPECIFIC OBJECTIVES The forgoing review of the literature has shown that uncoated supercalendered paper properties are a function of several complex phenomena and interactions between these phenomena. Among the factors involved are the furnishes and wet end additives used. Numerous authors have attempted to elucidate the importance of furnishes used in the development of uncoated supercalendered paper. As discussed in Chapter II, only a few studies have attempted to evaluate SC paper properties as a function of CTMr hardwood furnishes. The objectives were as follows: 1. To determine if 100% hardwood furnish can be run on a pilot paper machine and produce paper with properties that approximately those of commercial SCB grade. 2. To determine if two different hardwood pulps yield significantly different paper properties under similar alkaline papermaking conditions. 3. To evaluate the effect of different hardwood furnishes on SCB paper properties, on the replacement of 50% hardwood Kraft pulp by CTMP aspen. 4. The properties were also compared to commercial grade uncoated supercalendered paper. It was not the purpose of this study to attempt to match current 27

43 commercial SC uncoated rotogravure paper. 5. The experimental portion of this study was designed to examine several commonly measured SC paper properties (tensile, tear, smoothness, helio, brightness, opacity, and ash) as a function of various furnishes.

44 CHAPTER IV EXPERIMENTAL Summary of Experimental Design It was intended that this 3tudy of hardwood pulp furnishes should have practical application in the paper industry. As much of the experimental work as possible was done under typical paper machine operating conditions. All of the experimental runs were made and applied using the pilot equipment operated by the Department of Paper and Printing Science and Engineering at Western Michigan University. In this study, three pulps were evaluated; kraft eucalyptus, kraft aspen, and CTMP aspen. The paper was sized under alkaline conditions. Hercon-48, Albaglos and compozil were used as wet end additive. All operating conditions were maintained as constant as possible. The primary variable studied included the effect of various furnishes on the paper properties. The paper produced were compared to commercial grades. Over- all nine different trial runs were made to compare the effect of chemicals on each furnish. While this method may not prove practical for commercial applications, it does provide a convenient way to examine the effect of furnishes without changing the chemical addition rate. 29

45 The effects of furnishes on paper properties were studied. Analysis of variance was used to determine the significance of furnishes on paper properties. Also two commercial grades of SC papers were studied to compare with the paper produced. Raw Materials All the pulps used in this study were samples from commercial bales received directly from the manufacturers. They were fully bleached pulps available as dry laps. The pulps used together with the respective manufacturer were as follows: bleached 100% eucalyptus kraft pulp (Aracruz Cellulose, Brazil), bleached 100% aspen kraft (Prince Alberta, Canada) and bleached 100% aspen CTMP pulp (Rochhammar Bruks Aktiebolag, Sweden). Fiber length distributions on these pulps were performed using a Kajaani FS-100 fiber length analyzer. The results are listed in Appendix A. The average fiber lengths were as follows: 1. Kraft eucalyptus mm 2. Kraft aspen ram 3. CTMP aspen mm Furnish Selection The furnishes for this study was fixed with 100% kraft aspen, 100% kraft eucalyptus, 50% kraft aspen + 50%

46 CTMP aspen, and 50% kraft eucalyptus + 50% CTMP aspen. The replacement of hardwood kraft was studied at the 50% level with CTMP aspen. Since CTMP eucalyptus is not being manufactured commercially it was decided to use CTMP aspen with kraft eucalyptus. To reduce the variability in stock preparation the degree of refining was maintained as shown in Table 8. The degree of refining was expressed in terms of Canadian Standard Freeness (C.S.F.). The refining of furnishes used was done with a Claflin refiner. Table 8 Refining of Pulp Particular Initial C.S.F. Final C.S.F % Kraft eucalyptus % Kraft aspen % Kraft aspen + 50% Aspen CTMP % Kraft eucalyptus + 50% Aspen CTMP Note: 1. Freeness of Pulp - TAPPI method T410 om Pulp Consistency - TAPPI method T240 om-81 The furnishes of the commercial grades sampled were analyzed by light microscope techniques. The sample

47 analyzed by light microscope techniques. The sample analysis confirmed as 100% groundwood pulp. The fiber furnish was as follows: 1. Commercial grade 1: 100% softwood 2. Commercial grade 2: 75% softwood + 25% hardwood Wet End Additive The chemicals used were Hercon-48 (Hercules Incorporated, DE), Compozil (Procomp, GA) and Albaglos (Pfizer Incorporated, PA). The product data sheets for each of these are given in Appendix B 1-4. To maintain the symmetry between all the furnishes, the addition rates were fixed as shown in Table 9. Because of limited available paper machine run, it was decided to use the levels of chemical addition determined by previous studies (39.) (40). The filler addition levels decided were 20%, 25%, and 30%. Paper Machine and Supercalender The pilot plant paper machine was used for four 8 hour shifts to accomplish the nine trial run3 with each 'furnish. These nine runs represents the chemical additions at different levels with run Ptl as a blank run. The details of these trial runs were already shown in Table 9. The run time for each trial wa3 30 minutes and the time to stabilize the trial run was 10 minutes.

48 33 Table 9 Wet End Additive Trial No. Particular Addition Level 1. Furnish: A - 100%, Kraft eucalyptus B - 50% Kraft eucalyptus + 50% CTMP aspen C - 50% Kraft aspen + 50% CTMP aspen D - 100%, Kraft aspen 2. Trial BMB BMA Hereon 48 Nil 20 lb/t 2 lb/t 1 lb/t 3. Trial 2. + Albaglos 20% 4. Trial 2. + Albaglos 25% 5. Trial 2. + Albaglos 30% 6. Trial BMB BMA Hereon lb/t 3 lb/t 2 lb/t 7. Trial 6. + Albaglos 20% 8. Trial 6. + Albaglos 25% 9. Trial 6. + Albaglos 30% Note: 1. BMB 1% solids at I mixing box. 2. BMA 1% solids at II mixing box. 3. Hercon-48 added 1% solids at I mixing box. 4. Albaglos added 30% solids at II mixing box.

49 Seperate rolls were made for each trial run to minimize the variability. Each roll was calendered using the pilot plant supercalender machine. The operating parameters were fixed using the spare rolls of 100% hardwood paper. The operating parameters used for the paper machine and supercalender are shown in Tables Table 10 Machine Conditions for 100% Eucalyptus Kraft Run 1 O u Stock Valve Opening (%) Headbox Flow (gpm) Headbox ph st Tress Front Pressure Back psi 2nd Press Front Pressure Back Temperature (F) First dryer Temperature (F ) First Dryer Section Temperature (F) Sec. Dryer Section Note : 1. Wire Speed (fpm) Vacuum Box (in. Hg) Couch Vacuum (in. Hg) Dry Line (in. from Head Box) - 90

50 5. Calender Speed (fpm) 6. Pt of Nips on Calender Table 11 Machine Conditions for 50% Eucalyptus Kraft +50% Aspen CTMP Run Stock Valve Opening (%) Headbox Flow (gpm) Headbox ph st Tress Front Pressure Back psi 2nd Press Front Pressure Back Temperature (F ) First dryer Temperature (F) First Dryer Section Temperature (F) Sec. Dryer Section Note : 1. Wire Speed (fpm) Vacuum Box (in. Hg) Couch Vacuum (in. Hg) Dry Line (in. from Head Box) Calender Speed (fpm) K of Nips on Calender - 3

51 36 Table 12 Machine Conditions for 50% Aspen Kraft +50% Aspen CTMP Run Stock Valve Opening (%) Headbox Flow (g p m ) Headbox ph st Press Front Pressure Back psi 2nd Press Front Pressure Back Temperature (F ) First dryer Temperature (F) First Dryer Section Temperature (F) Sec. Dryer Section Note : 1. Wire Speed (fpm) Vacuum Box (in. Hg) Couch Vacuum (in. Hg) Dry Line (in. from Head Box) Calender Speed (fpm) ft of Nips on Calender - 3

52 37 Table 13 Machine Conditions for 100% Aspen Kraft Run 1 2 O 4 R Stock Valve Opening (%) Headbox Flow (g p m ) Headbox ph st Fress Front Pressure Back psi 2nd Press Front Pressure Back Temperature (F) First dryer Temperature (F) First Dryer Section Temperature (F) Sec. Dryer Section Note : 1. Wire Speed (fpm) Vacuum Box (in. Hg) Couch Vacuum (in. Hg) Dry Line (in. from Head Box) Calender Speed (fpm) PI of Nips on Calender - 3

53 33 Table 14 Supercalendering Condition for all Rolls Particular Condition Speed, fpm 100 Temperature, F 160 Steam Temperature, F 225 Pressure on rolls, pli 1700 No. of Nips 9 Determination of Paper Properties The samples were drawn from the various rolls to minimize the variability in sampling technique. The number of tests performed with their standard methods are shown in Table 15. All testing was performed after conditioning the samples at 50% relative humidity and 21 C (70 F) for at least one week. The Parker Print Surf Roughness Tester was used to measure smoothness of all the papers. A hard cork backing was used in conjunction with two clamping pressures; 980 kpa and 1960 kpa (10 and 20 kgf) respectively. The smoothness of the sheet is reported in microns. The IGT printability tester was used to run the Helio tests. The Helio test is a measure of the rotogravure printability of a paper sample. The Helio test uses an

54 39 Table 15 Paper Properties to be Evaluated Rotogravure Paper Particular TAPPI Standard Basis Weight g/m2 T 410 om-83 Bulk cm3/g T 411 om-83 Tensile Index MD N.ra/g CD T 404 om-82 Tear Index mn.m2/g MD CD T 414 om-82 Brightness % T 452 om-82 Opacity % T 425 om-81 Sheffield Porosity T 538 pm-82 Gloss % T 480 os-78 Ash % T 413 om-80 Note: Following tests are described earlier. 1. Parker Print Surf Microns 2. Helio Ft Missing Dots/440mm 10 kgf/cm2 20 kgf/cm2 etched printing disk on the IGT printability tester and roughness is characterize by the distance (in mm) along the wedge in which the first twenty dot skips occurs. The operating conditions were as follows: 1. Speed (constant) - 1 m/sec 2. Pressure - 40 kgf

55 40 3. Roto proofing Ink cp Data Analysis The data of all experiment were analyzed by an Unbalanced Incomplete Block Design. Analysis of Variance (ANOVA) was applied to determine the significant effect of independent variables on the properties of paper. The null hypothesis selected was zero between the difference of the mean. The significance level was compared at the 5% level. The bar charts and line graphs were used to compare the particular paper sample with the commercial grade results obtained by ten (10) observations for the respective property. This analysis was designed to evaluate furnishes at constant levels of chemical addition for the production of SC uncoated rotogravure paper. The furnishes selected were 100% eucalyptus kraft, 100% aspen kraft, 50% eucalyptus kraft + 50% aspen CTMP, and 50% aspen kraft + 50% aspen CTMF. The paper samples were collected on various rolls to minimize the variability in sampling technique. The rolls made on the paper machine were subsequently run on the supercalender. The statistical anlysis of this study was performed using the computer facilities at Western Michigan University, Kalamazoo.