Home Research PapersReview of Related Literature This chapter presents information and

Review of Related Literature This chapter presents information and

Review
of Related Literature

This
chapter presents information and studies conducted related to the project. The
following reviews are obtained from different sources such as books, journals,
reports and other related works:

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Paper
is defined by Noah Webster as “a substance made in the form of thin sheets or
leaves from rags, straw, bark, wood, or other fibrous materials for various
uses.” With the abundance of paper used today throughout the world in books,
magazines, and newspapers and for writing, it is difficult to conceive that
there was a period of thousands of years when true paper did not exist. At the
present 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 the
average consumer at it is indispensable. (Hunter et.al, 1974)

The
word paper itself originates from the name of the papyrus plant, which in
ancient times was common along the Nile River in Egypt. Papyruses, produced
using slender cuts of this plant, are squeezed, dried, and after that utilized
as a substrate for the written word, in a procedure that jam the first
appropriation of cellulose fibres, and which came to associate with over two
centuries before the revelation of paper. The creation of paper is without a
doubt the most vital innovation of humanity amid the principal thousand years.
Since paper generation spread everywhere throughout the world, the commitment
to oddity has crossed all fringes. Just from the mid-nineteenth century on was
wood considered as a crude material for papermaking. Pulping, the detachment of
cellulose from wood, has a short, however incredible history: endless new
innovations were created in a brief timeframe. The utilization of paper has
touched diverse regions of regular day to day existence. To address the
assorted variety of uses, paper needs more fixings alongside cellulose fibres.
(Hagiopol, 2012)

Used
in a wide variety of forms, paper and paperboard are characterized by a wide
range of properties. In the thousands of paper varieties available, some
properties differ only slightly and others grossly. The identification and
expression of these differences depend upon the application of standard test
methods, generally specified by industry and engineering associations in the
papermaking countries of the world.

According
to Ghosh, no manufactured product plays a more critical part in every of human
activity than paper and paper items. It’s essential in regular daily existence
is clear from its utilization in recording, stockpiling, and scattering of
data. Basically, all written work and printing is done on paper. It is the most
broadly utilized wrapping and bundling material, and is essential for auxiliary
applications. The utilizations and applications for pulp and paper items are
essentially boundless. (2011)

The
first sheet of paper was not proposed for mass utilization but rather offered
ascension to a procedure that would deliver billions of huge amounts of paper
utilizing billions of huge amounts of wood which touches another worldwide
issue: wood is a standout amongst the most imperative materials of our
opportunity. It is a crude material for some different ventures and an
adjusting variable of climate. (Hagiopol et. al., 2012)

Papermaking,
formation of a matted or felted sheet, usually of cellulose fibres, from water
suspension on a wire screen. Paper is the basic material used for written
communication and the dissemination of information. In addition, paper and
paperboard provide materials for hundreds of other uses, such as wrapping,
packaging, toweling, insulating, and photography.

 

In
this study, the strength and durability of the paper that will be produced
shall be taken into account. The strength of paper is determined by the
following factors in combination: (1) the strength of the individual fibres of
the stock, (2) the average length of the fibre, (3) the interfibre bonding
ability of the fibre, which is enhanced by the beating and refining action, and
(4) the structure and formation of the sheet. Resistance to rupture when
subjected to various stresses is an important property in practically all
grades of paper. Most papers require a certain minimum strength to withstand
the treatment received by the product in use; but even where use requirements
are not severe, the paper must be strong enough to permit efficient handling in
manufacture. Tensile strength is the greatest longitudinal stress a piece of
paper can bear without tearing apart. The stress is expressed as the force per
unit width of a test specimen. Since the weight of the paper and the width of
the test specimen affect the force of rupture, a conventional method of
comparing inherent paper strength is the breaking length—that is, the length of
a paper strip in metres that would be just self-supporting. (Britt, 1999)

Optimal
properties of the paper that will be produced shall also be considered. Optical
properties pertain to brightness, color, opacity, and gloss. The term
brightness has come to mean the degree to which white or near-white papers and
paperboard reflect the light of the blue end of the spectrum (i.e., their
reflectance). This reflectance is measured by an instrument that illuminates
paper at an average angle of incidence of 45° and a wavelength of 457?
(microns). Brightness measured in this way is found to correlate closely with
subjective estimates of the relative whiteness of paper. Opacity is one of the
most desired properties of printing and writing papers. Satisfactory
performance 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 in
printing papers requires that white mineral pigments be incorporated with the
paper stock or applied as a coating. The terms gloss, glare, finish, and
smoothness are used in describing the surface characteristics of paper. The
broad term finish refers to the general surface characteristics of the sheet.
Smoothness refers to the absence of surface irregularities under either visual
or use conditions. Gloss refers to surface lustre and connotes a generally
pleasing aspect. (Britt, 1999)

Brightening
is first of all a by-product of cleaning, of the removal of dirt and
impurities. Of all man-made products, most likely fabrics were the first ones
to be bleached with purpose. Laundering and the treatment with soap remove fat,
waxes, and stains. The removal of stains is an essential prerequisite of
drying. Only uniform products react with dyestuff into a homogenously colored
product. (Suess, 1947)

Bleaching
leads to brighter (whiter) paper, this gives better contrast between the print
and the paper. Other reasons for bleaching is cleanliness, as bleaching removes
impurities that otherwise turn up in the paper as dots, and age-preservation,
as bleaching can remove chemical structures in the pulp material that otherwise
would 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 between
the paper and the print, the cleanliness of the paper is another reason for
bleaching. Impurities in the pulp may otherwise turn up on the paper as dots,
deteriorating the printing. A third reason for bleaching is the ability of
paper resist ageing. Substances in the pulp can turn the paper yellow and
brittle as time goes by, mainly substances connected to lignin. (Ek et.al,
2009)

Hydrogen
peroxide is a rather widely used bleaching agent for high yield pulps. It has
been also demonstrated that it can partially or totally replace chlorine or
chlorine dioxide in the bleaching of chemical pulps. (Hendry et.al, 1985)

Kraft
pulping is a full chemical pulping method using sodium hydroxide and sodium
sulfide at pH above 12, at 160 to 180oC, corresponding to about 800
kPa steam pressure, for 0.5 to 3 hours to dissolve much of the lignin wood
fibers. It is useful for any wood species, gives a high strength pulp, is
tolerant to bark, and has an efficient energy and chemical recovery cycle.
(Bierman, 1996)

According
to Ek, Kraft cooking is the dominant chemical pulping method globally. The
cooking chemicals used are sodium hydroxide, and sodium sulphide. By leaving
out the sodium sulphide and only used sodium hydroxide as the cooking chemical,
the process is called soda cooking. (2009)

In
the United States and Canada, about portion of the wood delivered is utilized
as timber, fundamentally for development; the sawdust and other waste shaped in
preparing the sheets is changed over to molecule board and pulp. The following
most broad utilization of wood is for pulp, which in addition to other things
is changed over by different procedures to paper, manufactured ?bers, plastics,
and tile. (Bidlack, 2003)

A
significant 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 with
our own particular hands. In any case, we don’t really think about the paper we
use consistently and the immense measures of vitality and water devoured by paper
factory mills.

Grasses
involve a more prominent territory of the world’s land surface than some other
plant family, happening in relatively every earthbound condition and giving a
crucial source of nourishment for people and animals. (Cheplick, 1998)

 

Paper
has been made from grasses and other non-wood materials for over 1900 years.
Wood is relatively new papermaking fibre, only 100 years old. Today, the
commercial non-wood pulp production accounts for 6% of the global pulp
production. (Pahkala, 1994)

The
earliest information about usage of grass as a writing material dates back to
3000 BC in Egypt where the pressed pith tissue of papyrus sedge was the most
widely used writing material. In the 20th century, wood became the
main raw material for paper. (Atchison et. al, 1987)

In
many countries, the wood supplies are not large enough for the rising demand of
pulp and paper, but on the other hand, the availability of agroresiduals is
high. (Paavilainen, 1996)

According
to Hagiopol, the structure of chemicals for paper must accommodate not only the
diversity of demands for paper quality but also the papermaking process. Paper
chemicals must not react unintentionally with water and must be adsorbed on the
cellulose fiber in the presence of water. The interactions between chemicals
and cellulose (solubilization, adsorption, chemical reactions) must take place
in the temperature ranges from 20oC to about 105oC and
moisture from 99.5% to 5%. Thus, it is obvious that there are no two
papermaking systems alike and there is no paper chemical that serves all
functions and performs under every set of conditions. Paper chemistry is
developed by keeping in mind not only the paper performances and costs, but
also the wood preservation and the environment protection. Thus, paper
additives have recently become more significant. The organic chemistry of paper
chemicals must be seen as parts of the papermaking process where chemical
engineering, colloid, and surface science, and materials science must also be
considered. The manipulation of the paper chemical composition, within the
paper making process, using organic chemistry is the background of Hagiopol’s
book. (2012)

Cellulose
fibers are recovered from wood through a process called pulping. During wood
extraction with water, only <5% of soluble material goes into the water phase (as in thermo-mechanical pulp). The wood cell has a heterogenous structure and consists primarily of three polymeric materials: cellulose (42%-45%), hemicellulose (27%-30%), and lignin (20%-28%). Fibers within wood are glued together with a natural phenolic resin. The pulping process involves high temperatures, high pressure, and chemical compounds. Water as a plasticizer, high temperatures of 120oC to 130o, and corresponding pressure are the regular conditions helping to free cellulose fibers. Wood pulping must prevent not only the degradation of valuable material, but also reduce the environmental issues. During wood pulping, an "unintentional chemical modification" of the cellulose may take place (such as peracetic acid and chlorine dioxide) may oxidize indiscriminately all the wood components. The changes in the composition and chemical structure of cellulose fibers should be taken into account when interaction with paper chemicals is considered. The fiber porosity decreases with increasing the pulping yield and the fiber swelling wall increases with the number of carboxylic groups. (Hagiopol, 2012) The presence of certain components in the cell contents can significantly affect both the behavior of pulp source during pulping and the behavior of pulp during the manufacturing of paper. These effects will require closer attention in the future. The control for the number of polyphenols formed is desirable for many reasons. For example, pulp and paper manufacturers require raw material containing the minimum number of extractives, if the pulp and paper making properties are suitable. (Hillis, 1962) Manufacturing of pulp starts with raw material preparation. This includes debarking, chipping, and other processes such as depithing. Cellulosic pulp is manufactured from the raw materials using chemical and mechanical means. The manufacture of pulp for paper and board employs mechanical, chemi-mechanical, and chemical methods. Each pulping process has its advantages and disadvantages. The major advantages of mechanical pulping are its high yield of fibers – up to 90%. Chemical pulping yields approximately 50% but offers higher strength properties. (Bajpai, 2013) The increasing demand in wood fiber consumptions especially in pulp and paper making has pushed forward the search for alternative fiber resources. Non-wood derived fiber could be good candidates due to its abundance in availability. Agriculture residues, are good potential fiber resource for pulp and paper making. The worldwide consumption of pulp and paper products has tremendously increased due to the population growth, development of communication and industrialization in many developing countries. Conventional pulp and paper production utilizes fiber from wood has inevitably resulted in the depletion of wood resources. Therefore, it is of the main concern and interest to seek for alternative fiber resources derived from non-wood plants. Non-wood fibers offer several advantages including its abundance in volume, a short cycle growth, cheaper cost of production and environmentally friendly. (Kassim, 2015) According to a tabulated data of chemical compositions of non-wood and wood fibers from Kassim, cellulose percentage from wood fibers are higher than all of non-wood fibers. Cellulose percentage from fibers of Eucalyptus globulus and Pine pinaster are 53% and 55.9%, respectively. While Cogon grass, Vine stems, Cynara Cardunclus, and Canola straws contains 37.13%, 35%, 40.5% and 48.5%, respectively. From this study, the cellulose percentage from wood fibers, can be as greater as 37.39% compared from non-wood fibers. (2015) From a study of pulp production from elephant grass by Gomes et. al, elephant grass has a beneficial characteristic for pulp production, such as high fibers production and its chemical composition. Some works have shown contents of 40%, 30%, and 17.7% for cellulose, hemicelluloses, and lignin, respectively. These values are good for pulp production, especially the low lignin content, suggesting high pulpability of this material in cooking processes. Their experiment showed that elephant grass showed good potential for pulp production. (2013) Pulp consists of fibres, usually acquired from wood. The pulping processes aim first and foremost to liberate the fibres from the wood matrix. In principal, this can be achieved in two ways, either mechanically or chemically. Mechanical methods demand a lot of electric power, but on the other hand they make use of practically the whole wood material, i.e. the yield of the process is high. In chemical pulping, only approximately half of the wood becomes pulp, the other half is dissolved. The pulp obtained is coloured, the degree of colouring depends on the pulping process. For certain paper grades, the dark pulp has to be bleached. In the board industry, papermakers are facing demands for products possessing conflicting properties, such as resistance not only to water but also to oils and gases. There are broadly two generic reasons for applying chemicals to the surface of paper: first, to provide the particular characteristics required by the variety of end uses to which paper products are subjected; and second, to hide undesirable variation and contamination. (Brander et.al, 1997) The feasibility of cogon grass (Imperata cylindrica) as substitute for cardboard food packaging was studied in a research project of DOST. The cogon grass was cut, boiled, and crushed in order to get the pulp. The pulp was then subjected to 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 of starch was varied in every treatment. (Gabieta et.al,) Opportunities for improved energy utilization exist in virtually all aspects of the pulping and papermaking process, and higher efficiency pays off. Cost reduction methods should, of course, always be a part of mill culture. On this study, efficiency of energy usage is important since this machine will contain a grinding, pulping, and drying process. There are opportunities to save energy cost at every step in the overall process, starting from the harvesting of the primary materials, through the chipping, screening, pulping, and stock preparation areas prior to stock delivery to the paper machine. Even greater opportunities are found during papermaking, where the paper web is formed, consolidated, pressed, and dried. In addition, a number of converting operations can be carried out prior to the reel or in subsequent processes off the paper machine. Most improvements occur incrementally, building on existing technology. For example, Voith Paper has recently developed hydrodynamically optimized spoiler rotors that reduce power consumption by a reported 15-20% over conventional rotors. (Baum, 2008) There are three basic steps in the paper manufacturing process (1) forming (2) pressing and (3) drying. Contact drying with steam heated cylinders is the predominant method of drying in paper and paperboard machines. Besides conductive heat transfer between hot cylinder surface and the wet web, the role of air that is either the drying medium or surrounds the drying atmosphere is very significant. Paper drying is associated with both heat and mass transfer. The heat energy released when steam condenses is transmitted through the dryer shell 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 this vapor from the sheet into the air steam constitutes the mass transfer aspect of paper drying. As a result, the operation of a dryer section must be optimized in terms of both heat transfer and water removal. The factors which most influence paper drying operation are (1) steam pressure and temperature; (2) temperature and humidity of air; (3) energy content of steam and (4) heat and mass transfer coefficients. In paper drying, mass transfer occurs after a sufficient amount of heat energy has been transmitted to the web, resulting in the transfer of mass of water from the paper to the air in dryer section. The mass transfer occurring in paper drying can be described as molecular diffusion. (Ghosh, 2011) From a study of University of British Columbia, drying in papermaking serves two functions. First, it removes the remaining water in the web that cannot be removed by vacuum or pressing. Second, it causes fibres to bond together by hydrogen bonding. As free and imbibed water are removed from the web, strong surface tension forces develop between fibres, causing them to come into intimate contact. This leads to molecular bonding. These forces also cause fibre straightening and microcompressions at bonding sites. This starts at a consistency of about 20%. The hydrogen bonding provides all the strength needed for most papers, i.e., adhesives are not added. Drying is achieved by raising the web temperature in the web to a level at which the vapour pressure of water in the paper exceeds the partial pressure of water vapor in the ambient. This pressure difference is the driving force for the evaporation of water from the web. The drying process consists of heat transfer to the web and mass transfer of vapor from the web. The first stage is a warm up stage and the second stage is a constant rate stage. The second stage is where the drying rate is constant because sufficient water remains in the web that heat and mass transfer within the 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, causing complex mass transfer of vapor and liquid diffusion within the web. Water near the hot surface evaporates and diffuses outward. Some liquid flows towards the hot surface. The final point of evaporation takes place from both surfaces. It is well known that the use of cellulose fibers for papermaking results in changes to the fiber when compared to a virgin state. Fibers are subjected to a multitude of operations during the papermaking process that may affect the structure and properties of the fiber itself. Two important phenomena that occur 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 in the drying operation (referred to as the heat-up zone) and then dried later in the operation (referred to as the constant drying rate and the falling drying rating zones). It is of interest to understand how these two phenomena affect fiber swelling and pore behavior as well as fibre strength and the condition of cellulose within the fibre. The effect of heating fibres without drying has been investigated in order to separate the effects of water removal and heat treatment. By boiling pulp suspensions, heating alone without drying was shown to decrease the swelling and water uptake of fibres. Other research has shown that 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 the presence of water became brittle, reflected in the observation that the freeness of the pulp was unacceptable after refining to a desired tensile strength. (Welf et.al, 2005)  

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