Reviewof Related LiteratureThischapter presents information and studies conducted related to the project. Thefollowing reviews are obtained from different sources such as books, journals,reports and other related works:Paperis defined by Noah Webster as “a substance made in the form of thin sheets orleaves from rags, straw, bark, wood, or other fibrous materials for varioususes.
” With the abundance of paper used today throughout the world in books,magazines, and newspapers and for writing, it is difficult to conceive thatthere was a period of thousands of years when true paper did not exist. At thepresent time it would be impossible for civilization to endure, even for a day,the total lack of paper – a material that is as little understood by theaverage consumer at it is indispensable. (Hunter et.al, 1974)Theword paper itself originates from the name of the papyrus plant, which inancient times was common along the Nile River in Egypt.
Papyruses, producedusing slender cuts of this plant, are squeezed, dried, and after that utilizedas a substrate for the written word, in a procedure that jam the firstappropriation of cellulose fibres, and which came to associate with over twocenturies before the revelation of paper. The creation of paper is without adoubt the most vital innovation of humanity amid the principal thousand years.Since paper generation spread everywhere throughout the world, the commitmentto oddity has crossed all fringes.
Just from the mid-nineteenth century on waswood considered as a crude material for papermaking. Pulping, the detachment ofcellulose from wood, has a short, however incredible history: endless newinnovations were created in a brief timeframe. The utilization of paper hastouched diverse regions of regular day to day existence. To address theassorted variety of uses, paper needs more fixings alongside cellulose fibres.(Hagiopol, 2012)Usedin a wide variety of forms, paper and paperboard are characterized by a widerange of properties. In the thousands of paper varieties available, someproperties differ only slightly and others grossly. The identification andexpression of these differences depend upon the application of standard testmethods, generally specified by industry and engineering associations in thepapermaking countries of the world.
Accordingto Ghosh, no manufactured product plays a more critical part in every of humanactivity than paper and paper items. It’s essential in regular daily existenceis clear from its utilization in recording, stockpiling, and scattering ofdata. Basically, all written work and printing is done on paper. It is the mostbroadly utilized wrapping and bundling material, and is essential for auxiliaryapplications.
The utilizations and applications for pulp and paper items areessentially boundless. (2011)Thefirst sheet of paper was not proposed for mass utilization but rather offeredascension to a procedure that would deliver billions of huge amounts of paperutilizing billions of huge amounts of wood which touches another worldwideissue: wood is a standout amongst the most imperative materials of ouropportunity. It is a crude material for some different ventures and anadjusting variable of climate. (Hagiopol et. al., 2012)Papermaking,formation of a matted or felted sheet, usually of cellulose fibres, from watersuspension on a wire screen.
Paper is the basic material used for writtencommunication and the dissemination of information. In addition, paper andpaperboard provide materials for hundreds of other uses, such as wrapping,packaging, toweling, insulating, and photography. Inthis study, the strength and durability of the paper that will be producedshall be taken into account.
The strength of paper is determined by thefollowing factors in combination: (1) the strength of the individual fibres ofthe stock, (2) the average length of the fibre, (3) the interfibre bondingability of the fibre, which is enhanced by the beating and refining action, and(4) the structure and formation of the sheet. Resistance to rupture whensubjected to various stresses is an important property in practically allgrades of paper. Most papers require a certain minimum strength to withstandthe treatment received by the product in use; but even where use requirementsare not severe, the paper must be strong enough to permit efficient handling inmanufacture. Tensile strength is the greatest longitudinal stress a piece ofpaper can bear without tearing apart. The stress is expressed as the force perunit width of a test specimen. Since the weight of the paper and the width ofthe test specimen affect the force of rupture, a conventional method ofcomparing inherent paper strength is the breaking length—that is, the length ofa paper strip in metres that would be just self-supporting.
(Britt, 1999)Optimalproperties of the paper that will be produced shall also be considered. Opticalproperties pertain to brightness, color, opacity, and gloss. The termbrightness has come to mean the degree to which white or near-white papers andpaperboard reflect the light of the blue end of the spectrum (i.e., theirreflectance).
This reflectance is measured by an instrument that illuminatespaper at an average angle of incidence of 45° and a wavelength of 457?(microns). Brightness measured in this way is found to correlate closely withsubjective estimates of the relative whiteness of paper. Opacity is one of themost desired properties of printing and writing papers. Satisfactoryperformance of such papers requires that there be little or no “show-through”of images from one side of the sheet to the other. Satisfactory opacity inprinting papers requires that white mineral pigments be incorporated with thepaper stock or applied as a coating. The terms gloss, glare, finish, andsmoothness are used in describing the surface characteristics of paper.
Thebroad term finish refers to the general surface characteristics of the sheet.Smoothness refers to the absence of surface irregularities under either visualor use conditions. Gloss refers to surface lustre and connotes a generallypleasing aspect.
(Britt, 1999)Brighteningis first of all a by-product of cleaning, of the removal of dirt andimpurities. Of all man-made products, most likely fabrics were the first onesto be bleached with purpose. Laundering and the treatment with soap remove fat,waxes, and stains. The removal of stains is an essential prerequisite ofdrying. Only uniform products react with dyestuff into a homogenously coloredproduct. (Suess, 1947)Bleachingleads to brighter (whiter) paper, this gives better contrast between the printand the paper. Other reasons for bleaching is cleanliness, as bleaching removesimpurities that otherwise turn up in the paper as dots, and age-preservation,as bleaching can remove chemical structures in the pulp material that otherwisewould in time make the paper yellow. Some paper products require a white paper.
One reason is the print quality. A whiter paper gives a better contrast betweenthe paper and the print, the cleanliness of the paper is another reason forbleaching. Impurities in the pulp may otherwise turn up on the paper as dots,deteriorating the printing. A third reason for bleaching is the ability ofpaper resist ageing. Substances in the pulp can turn the paper yellow andbrittle as time goes by, mainly substances connected to lignin.
(Ek et.al,2009)Hydrogenperoxide is a rather widely used bleaching agent for high yield pulps. It hasbeen also demonstrated that it can partially or totally replace chlorine orchlorine dioxide in the bleaching of chemical pulps. (Hendry et.
al, 1985)Kraftpulping is a full chemical pulping method using sodium hydroxide and sodiumsulfide at pH above 12, at 160 to 180oC, corresponding to about 800kPa steam pressure, for 0.5 to 3 hours to dissolve much of the lignin woodfibers. It is useful for any wood species, gives a high strength pulp, istolerant to bark, and has an efficient energy and chemical recovery cycle.
(Bierman, 1996)Accordingto Ek, Kraft cooking is the dominant chemical pulping method globally. Thecooking chemicals used are sodium hydroxide, and sodium sulphide. By leavingout the sodium sulphide and only used sodium hydroxide as the cooking chemical,the process is called soda cooking. (2009)Inthe United States and Canada, about portion of the wood delivered is utilizedas timber, fundamentally for development; the sawdust and other waste shaped inpreparing the sheets is changed over to molecule board and pulp.
The followingmost broad utilization of wood is for pulp, which in addition to other thingsis changed over by different procedures to paper, manufactured ?bers, plastics,and tile. (Bidlack, 2003)Asignificant number of us are aware of ways we can utilize assets economically,make things ourselves, and esteem the articles in our lives by making them withour own particular hands. In any case, we don’t really think about the paper weuse consistently and the immense measures of vitality and water devoured by paperfactory mills.Grassesinvolve a more prominent territory of the world’s land surface than some otherplant family, happening in relatively every earthbound condition and giving acrucial source of nourishment for people and animals.
(Cheplick, 1998) Paperhas been made from grasses and other non-wood materials for over 1900 years.Wood is relatively new papermaking fibre, only 100 years old. Today, thecommercial non-wood pulp production accounts for 6% of the global pulpproduction. (Pahkala, 1994)Theearliest information about usage of grass as a writing material dates back to3000 BC in Egypt where the pressed pith tissue of papyrus sedge was the mostwidely used writing material. In the 20th century, wood became themain raw material for paper. (Atchison et.
al, 1987)Inmany countries, the wood supplies are not large enough for the rising demand ofpulp and paper, but on the other hand, the availability of agroresiduals ishigh. (Paavilainen, 1996)Accordingto Hagiopol, the structure of chemicals for paper must accommodate not only thediversity of demands for paper quality but also the papermaking process. Paperchemicals must not react unintentionally with water and must be adsorbed on thecellulose fiber in the presence of water. The interactions between chemicalsand cellulose (solubilization, adsorption, chemical reactions) must take placein the temperature ranges from 20oC to about 105oC andmoisture from 99.
5% to 5%. Thus, it is obvious that there are no twopapermaking systems alike and there is no paper chemical that serves allfunctions and performs under every set of conditions. Paper chemistry isdeveloped by keeping in mind not only the paper performances and costs, butalso the wood preservation and the environment protection. Thus, paperadditives have recently become more significant. The organic chemistry of paperchemicals must be seen as parts of the papermaking process where chemicalengineering, colloid, and surface science, and materials science must also beconsidered. The manipulation of the paper chemical composition, within thepaper making process, using organic chemistry is the background of Hagiopol’sbook. (2012)Cellulosefibers are recovered from wood through a process called pulping. During woodextraction with water, only <5% of soluble material goes into the waterphase (as in thermo-mechanical pulp).
The wood cell has a heterogenousstructure and consists primarily of three polymeric materials: cellulose(42%-45%), hemicellulose (27%-30%), and lignin (20%-28%). Fibers within woodare glued together with a natural phenolic resin. The pulping process involveshigh temperatures, high pressure, and chemical compounds. Water as aplasticizer, high temperatures of 120oC to 130o, andcorresponding pressure are the regular conditions helping to free cellulosefibers.
Wood pulping must prevent not only the degradation of valuablematerial, but also reduce the environmental issues. During wood pulping, an”unintentional chemical modification” of the cellulose may take place (such as peraceticacid and chlorine dioxide) may oxidize indiscriminately all the woodcomponents. The changes in the composition and chemical structure of cellulosefibers should be taken into account when interaction with paper chemicals isconsidered. The fiber porosity decreases with increasing the pulping yield andthe fiber swelling wall increases with the number of carboxylic groups.(Hagiopol, 2012)Thepresence of certain components in the cell contents can significantly affectboth the behavior of pulp source during pulping and the behavior of pulp duringthe manufacturing of paper. These effects will require closer attention in thefuture.
The control for the number of polyphenols formed is desirable for manyreasons. For example, pulp and paper manufacturers require raw materialcontaining the minimum number of extractives, if the pulp and paper makingproperties are suitable. (Hillis, 1962)Manufacturingof pulp starts with raw material preparation. This includes debarking,chipping, and other processes such as depithing.
Cellulosic pulp ismanufactured from the raw materials using chemical and mechanical means. Themanufacture of pulp for paper and board employs mechanical, chemi-mechanical,and chemical methods. Each pulping process has its advantages anddisadvantages.
The major advantages of mechanical pulping are its high yield offibers – up to 90%. Chemical pulping yields approximately 50% but offers higherstrength properties. (Bajpai, 2013)Theincreasing demand in wood fiber consumptions especially in pulp and papermaking has pushed forward the search for alternative fiber resources. Non-woodderived fiber could be good candidates due to its abundance in availability.Agriculture residues, are good potential fiber resource for pulp and papermaking. The worldwide consumption of pulp and paper products has tremendouslyincreased due to the population growth, development of communication andindustrialization in many developing countries. Conventional pulp and paperproduction utilizes fiber from wood has inevitably resulted in the depletion ofwood resources. Therefore, it is of the main concern and interest to seek foralternative fiber resources derived from non-wood plants.
Non-wood fibers offerseveral advantages including its abundance in volume, a short cycle growth,cheaper cost of production and environmentally friendly. (Kassim, 2015)Accordingto a tabulated data of chemical compositions of non-wood and wood fibers fromKassim, cellulose percentage from wood fibers are higher than all of non-woodfibers. Cellulose percentage from fibers of Eucalyptus globulus and Pinepinaster are 53% and 55.9%, respectively. While Cogon grass, Vine stems, CynaraCardunclus, and Canola straws contains 37.13%, 35%, 40.5% and 48.
5%,respectively. From this study, the cellulose percentage from wood fibers, canbe as greater as 37.39% compared from non-wood fibers. (2015)Froma study of pulp production from elephant grass by Gomes et. al, elephant grasshas a beneficial characteristic for pulp production, such as high fibersproduction and its chemical composition. Some works have shown contents of 40%,30%, and 17.7% for cellulose, hemicelluloses, and lignin, respectively. Thesevalues are good for pulp production, especially the low lignin content,suggesting high pulpability of this material in cooking processes.
Theirexperiment showed that elephant grass showed good potential for pulpproduction. (2013)Pulpconsists of fibres, usually acquired from wood. The pulping processes aim firstand foremost to liberate the fibres from the wood matrix. In principal, thiscan be achieved in two ways, either mechanically or chemically. Mechanicalmethods demand a lot of electric power, but on the other hand they make use ofpractically the whole wood material, i.e. the yield of the process is high. Inchemical pulping, only approximately half of the wood becomes pulp, the otherhalf is dissolved.
The pulp obtained is coloured, the degree of colouringdepends on the pulping process. For certain paper grades, the dark pulp has tobe bleached. Inthe board industry, papermakers are facing demands for products possessingconflicting properties, such as resistance not only to water but also to oilsand gases.
There are broadly two generic reasons for applying chemicals to thesurface of paper: first, to provide the particular characteristics required bythe variety of end uses to which paper products are subjected; and second, tohide undesirable variation and contamination. (Brander et.al, 1997)Thefeasibility of cogon grass (Imperata cylindrica) as substitute for cardboardfood packaging was studied in a research project of DOST.
The cogon grass wascut, boiled, and crushed in order to get the pulp. The pulp was then subjectedto five different treatments before it was made into a cardboard-like material.The amount of resin and other additives were kept constant while the amount ofstarch was varied in every treatment. (Gabieta et.al,)Opportunitiesfor improved energy utilization exist in virtually all aspects of the pulpingand papermaking process, and higher efficiency pays off. Cost reduction methodsshould, of course, always be a part of mill culture.
On this study, efficiencyof energy usage is important since this machine will contain a grinding, pulping,and drying process. There are opportunities to save energy cost at every stepin the overall process, starting from the harvesting of the primary materials,through the chipping, screening, pulping, and stock preparation areas prior tostock delivery to the paper machine. Even greater opportunities are foundduring papermaking, where the paper web is formed, consolidated, pressed, anddried. In addition, a number of converting operations can be carried out priorto the reel or in subsequent processes off the paper machine. Most improvementsoccur incrementally, building on existing technology. For example, Voith Paperhas recently developed hydrodynamically optimized spoiler rotors that reducepower consumption by a reported 15-20% over conventional rotors. (Baum, 2008)Thereare three basic steps in the paper manufacturing process (1) forming (2)pressing and (3) drying. Contact drying with steam heated cylinders is thepredominant method of drying in paper and paperboard machines.
Besidesconductive heat transfer between hot cylinder surface and the wet web, the roleof air that is either the drying medium or surrounds the drying atmosphere isvery significant. Paper drying is associated with both heat and mass transfer.The heat energy released when steam condenses is transmitted through the dryershell to the wet paper and this constitutes the heat transfer aspect of drying.The air receives the water vapor evaporated from the paper.
The removal of thisvapor from the sheet into the air steam constitutes the mass transfer aspect ofpaper drying. As a result, the operation of a dryer section must be optimizedin terms of both heat transfer and water removal. The factors which most influencepaper drying operation are (1) steam pressure and temperature; (2) temperatureand humidity of air; (3) energy content of steam and (4) heat and mass transfercoefficients. In paper drying, mass transfer occurs after a sufficient amountof heat energy has been transmitted to the web, resulting in the transfer ofmass of water from the paper to the air in dryer section. The mass transferoccurring in paper drying can be described as molecular diffusion. (Ghosh,2011)Froma study of University of British Columbia, drying in papermaking serves twofunctions.
First, it removes the remaining water in the web that cannot beremoved by vacuum or pressing. Second, it causes fibres to bond together byhydrogen bonding. As free and imbibed water are removed from the web, strongsurface tension forces develop between fibres, causing them to come intointimate contact. This leads to molecular bonding. These forces also causefibre straightening and microcompressions at bonding sites. This starts at aconsistency of about 20%. The hydrogen bonding provides all the strength neededfor most papers, i.
e., adhesives are not added. Drying is achieved by raisingthe web temperature in the web to a level at which the vapour pressure of waterin the paper exceeds the partial pressure of water vapor in the ambient. Thispressure difference is the driving force for the evaporation of water from theweb.Thedrying process consists of heat transfer to the web and mass transfer of vaporfrom the web. The first stage is a warm up stage and the second stage is aconstant rate stage.
The second stage is where the drying rate is constantbecause sufficient water remains in the web that heat and mass transfer withinthe web are not controlling steps. The third stage is the falling rate stage.Here is when there is an insufficiency of water to completely fill the web.Water near the paper surface in contact with the hot roll evaporates, causingcomplex mass transfer of vapor and liquid diffusion within the web. Water nearthe hot surface evaporates and diffuses outward.
Some liquid flows towards thehot surface. The final point of evaporation takes place from both surfaces.Itis well known that the use of cellulose fibers for papermaking results inchanges to the fiber when compared to a virgin state. Fibers are subjected to amultitude of operations during the papermaking process that may affect thestructure and properties of the fiber itself. Two important phenomena thatoccur during papermaking that can significantly impact fiber properties are (1)heating without water removal and (2) drying.
For instance, in paper drying,the wet fiber web can be considered heated in the presence of water early inthe drying operation (referred to as the heat-up zone) and then dried later in theoperation (referred to as the constant drying rate and the falling dryingrating zones). It is of interest to understand how these two phenomena affectfiber swelling and pore behavior as well as fibre strength and the condition ofcellulose within the fibre. The effect of heating fibres without drying hasbeen investigated in order to separate the effects of water removal and heattreatment. By boiling pulp suspensions, heating alone without drying was shownto decrease the swelling and water uptake of fibres. Other research has shownthat thermal treatment of pulp in water results in increase in crystallinity.
Heating without water removal has also been found to affect the fiber strength.It is found out that bleached sulfate pulp heated above 120oC in thepresence of water became brittle, reflected in the observation that thefreeness of the pulp was unacceptable after refining to a desired tensilestrength. (Welf et.al, 2005)
