Paper is made by pressing together moistfibers and drying them intoflexible sheets.
Therefore, any material from whichfibers can be obtained could also be used for making paper. In practice, this is not so as factors such as the abundance offibers, strength of thefiber,flexibility of thefiber and the length of thefibers in the source material determine whether or not a raw material can be used to process paper. The
172 6 Pulp and Paper Technology
Table 6.1 The various types of paper
Type of paper Use Characteristics of paper
Bank paper It is used for typewriting and correspondence
Thin strong writing paper of less than 50 g/m2
Bond paper It is used for letterheads, electronic printing, graphic work and other stationery
The quality is similar to bank paper.
However,
the weight greater than 50 g/m2. It is made from rag pulp
Book paper (publishing paper)
Used specifically for the publication
of printed books
Traditionally, book papers are off white or low white papers
(easier to read), are opaque to minimize the show through
of text from one side of the page to the other and are (usually)
made to tighter caliper or thickness specifications, particularly
for case bound books. Typically, book papers are light weight
papers 60–90 g and often specified by their caliper/substance
ratios (volume basis) Construction
paper (sugar paper)
Used for projects and crafts Construction paper or sugar paper is a type of coarse colored
paper typically available in large sheets.
The surface is characterized
by rough texture, the presence of small particles and looks unfinished Cotton paper Due to its durability, it is used for
printing
and storing important documents such as dissertation
or thesis, bank notes and legal documents. It is also
sometimes referred to as cotton rag or ragged paper
Cotton paper is made from 100% cotton fibers. It is superior
to paper made from wood pulp in strength and durability.
It can last for several hundred years without fading, discoloring or deteriorating
Electronic paper or E-paper
It mimics the appearance of ordinary ink paper and used mainly in display technology
Reflects light like ordinary paper. It can hold text and images
indefinitely without drawing electricity, while allowing the image
to be changed later. It portrays other characteristics like ordinary
paper, e.g. it can be bent and crumpled Inkjet paper Mostly used for printing in inkjet
printers
It is paper with good dimensional stability, good surface strength and no curling. It is classified by its brightness, smoothness,
and sometimes by its opacity Photo paper It is used specifically for
reproduction of photographs
The best of these papers, with suitable pigment-based ink systems,
can match or exceed the image quality and longevity of traditional
materials used for printing color photographs. For printing monochrome photographs, traditional sliver-based
(continued)
6.3 Raw Materials for Making Paper 173
Table 6.1 (continued)
Type of paper Use Characteristics of paper
papers are widely felt to retain some advantage over inkjet prints Kraft paper It is used for paper grocery bags,
multi-wall sacks,
envelopes and other packaging
This type of paper is strong and relatively coarse. It is usually of brown color but can be bleached to produce white paper. It is produced from wood pulp by the Kraft process
Laid paper It is used as a support for charcoal drawings
It has a ribbed texture imparted to it as part of the manufacturing process Tyvek Example applications include,
medical packaging, envelopes, car covers, air and water intrusion barriers (house wrap) under house siding, labels, wristbands, mycology, and graphics
Tyvek is a brand offlash spun high-density polyethylenefibers, a synthetic
material; the name is a registered trademark of the DuPont Company.
It is a very strong material permeable by water vapor but not liquid water Paper towel It is a disposable product made of
paper. They are often chosen to avoid the contamination of germs
This is high moisture absorbency, soft paper with properties similar to conventional towels used for drying hands, dusting and wiping windows Wall paper Wallpaper is a material that is used
to cover and decorate
the interior walls of homes, offices, and other buildings
The surface of this type of paper is either plain so it can be painted or has graphic patterns. Wallpaper printing techniques include surface printing, gravure printing, silk screen-printing, and rotary printing.‘Wallpaper’is also a term for computer wallpaper. Wallpapers are usually sold in rolls and are put onto a wall using wallpaper paste
Washi (Japanese paper)
It is used in traditional arts mostly in Japan where it originated from. It is also called Wagami
Washi is commonly made usingfibers from the bark of the gampi tree, the mitsumata shrub (Edgeworthia papyrifera), or the paper mulberry, but also can be made using bamboo, hemp, rice and wheat. It is generally tougher than paper made from wood pulp Wax paper Used in cooking, for its non-stick
properties. It is also used for wrapping
food for storage, as it keeps water out or in. Another area of use is in the in arts and crafts industry
This is a moisture proof paper achieved by the application of wax. The practice of oiling parchment or paper in order to make it semi-translucent or
moisture-proof goes back at least to medieval times
Coated paper For printing purposes, e.g.
Newspaper insert, advertising materials,
catalog, security papers, magazines
The surface of this type of paper is coated to impart certain qualities to the paper, such as surface gloss, smoothness, ink absorbency and protection against ultraviolet radiation. The coating materials used are mostly inorganic compounds, e.g. Kaolinite
Wove paper It is used mainly as a writing paper It has a uniform surface and is neither ribbed nor watermarked
174 6 Pulp and Paper Technology
common raw materials used to make paper include, esparto-grass, straw, wood,flax (linen), hemp, jute and rags-cotton and linen.
The process of paper manufacture consists of two main steps, namely, pulp making and the conversion of pulp into paper. During the first step, i.e. pulp making,fibers are extracted from the raw materials. In the second stage, the pulp in stage one is converted into paper proper ready for the market. Linen and cotton rags having already undergone a process of manufacture, consist of almost purefibers with the addition of fatty and coloring matters, which can be got rid of by simple boiling under a low-pressure steam with a weak alkaline solution. On the other hand, esparto, wood, straw, flax, hemp and jute as they are from the soil/wood contain all the intercellular matter in its original form, which should be dissolved by strong chemical treatment under a high temperature in other to free thefiber for subsequent use.
Wood-pulp has grown to be one of the most importantfibers for paper-making purposes. Scandinavia, Germany, the United States and Canada are the countries that mainly use wood as a material for paper-making, owing to their possession of large forest areas. These countries are the source of wood-pulp used by many other countries. Trees of medium age are usually selected, varying from 70–80 years’ growth and running from 8 to 12 in. in diameter. They are fell in winter and reach the mill in logs about 4 ft long. After being freed from the bark and the knots taken out by machinery, the logs are cut into small cubical chips about 2 in. in size by a revolving cutter. The chips are then bruised by being passed between two heavy iron rolls to allow a boiling solution to thoroughly penetrate them, and are conveyed to boilers over a screen of coarse wire-cloth, which separates out thefine sawdust as well as any dirt or sand. In the soda process, the wood is boiled in large revolving or upright stationary boilers to extract thefiber.
Most kinds ofstrawcan be utilized for making into paper, the varieties generally used arerye, oat, wheat and barley. Oat and rye are the most important, as they give the largest yield infiber. Germany and France are the two principal users of straw, which closely resembles esparto in its chemical constitution and is reduced to a pulp by a somewhat similar process. Fibers like jute, hemp and manila are chiefly used for the manufacture of coarse papers where strength is of more importance than appearance, such as wrapping papers, paper for telegraph forms, etc. The boiling processes for these are similar to those used for esparto and straw.