The word ‘paper’ derives from the word ‘papyrus’ and is a thin material produced by the amalgamation of plant fibres, which are subsequently held together without extra binder, largely by hydrogen bonds and to a large degree by fiber entanglement. The fibres used are usually natural and composed of cellulose. The most common source of these kinds of fibres is wood pulp from pulpwood trees, largely softwoods such as spruce. However, other vegetable fibre materials including cotton, hemp, linen, and rice may be used.
Processing of the fibers
Wood or plant cell walls are composed of fibers bound together. During pulping, these fibers are separated from each other and carbohydrate surfaces (cellulose or hemicellulose) are exposed. It is hydrogen bonding between these carbohydrate surfaces that provides paper strength. Fibers can be separated either chemically or mechanically.
Most chemical pulp is made using the Kraft process. The purpose of a chemical pulping process is to break down the chemical structure of lignin and render it soluble in the cooking liquor, so it may be washed from the cellulose fibers. Because lignin holds the plant cells together, chemical pulping frees the fibers and makes pulp. After Kraft pulping the pulp can be used directly for bags and boxes or further delignifed, during bleaching, to produce white pulp for printing and writing. Chemical pulps tend to cost more than mechanical pulps, largely due to the low yield, 40-50% of the original wood. Since the process preserves fiber length, however, chemical pulps tend to make stronger paper. Another advantage of chemical pulping is that the majority of the heat and electricity needed to run the process is produced by burning the lignin removed during pulping.
There are two major mechanical pulps, thermomechanical pulp (TMP) and groundwood. In the TMP process wood is chipped and then fed into large steam-heated refiners where the chips are squeezed and fiberized between two steel discs. In the groundwood process debarked logs are fed in into grinders where they are pressed against a rotating stones and fiberized. Mechanical pulping does not remove the lignin, so the yield is very high, > 95%, but also causes paper made from this pulp to yellow and become brittle over time. Mechanical pulps have rather short fiber lengths and produce weak paper. Although large amounts of electrical energy are required to produce mechanical pulp, it costs less than chemical pulp.
Paper made from either chemical or mechanical pulp can also be recycled. By mixing with water and applying mechanical action the hydrogen bonds in the paper can be broken and fibers separated again.
Drying
After the paper web is produced, the water must be removed from it in order to create a usable product. This is accomplished through pressing and drying. The methods of doing so vary between the different processes used to make paper, but the concepts remain the same.
Pressing the sheet removes the water by force. Once the water is forced from the sheet, another absorbant material must be used to collect this water. On a paper machine this is called a felt (not to be confused with the traditional felt). When making paper by hand, a blotter sheet is used.
Drying involves using air and or heat to remove water from the paper sheet. In the earliest days of papermaking this was done by hanging the paper sheets like laundry. In more modern times, various forms of heated drying mechanisms are used. On the paper machine, the most common is the steam-heated can dryer. These dryer cans heat to temperatures above 200ºF and are used in long sequences of more than 40 cans. The heat produced by these can easily dry the paper to less than 6% moisture.
The paper may then undergo “sizing” to alter its physical properties for use in various applications.
Today, paper includes a wide range of products with very different applications: communication, cultural, educational, artistic, hygienic, sanitary, as well as for storage and transportation of all kinds of goods. It’s almost impossible to imagine a life without paper.
The significance of paper and paper-products in modern life is obvious to everyone; no manufactured product plays a more meaningful role in every area of human activity. The uses and applications of paper and paper products are virtually limitless.
EXAMPLES OF PAPER USES
Agriculture
Sacks, seed packets
Building
Wallpaper, damp-proof courses, roofing, flooring, flame resistant papers, plasterboard, decorative laminates for furniture, abrasive base paper, decorative crepe paper, felt paper for vinyl floor covering.
Business
Computer tapes, print-out sheets, advertisements, circulars, catalogues, filing systems, sales and service manuals, brochures, shop-till paper,
Money, Finance and Security
Money, insurance forms, cheque books, travellers’ cheques, postal orders, cash bags, papers that contain special markings which are only visible when subjected to ultra-violet light, diazo paper, thermal paper
Office paper
Photocopying paper, graph papers, paper twine and string, blotting paper, carbonless paper, box files, folders, envelopes,
Cars
Fascia boards, door and roof liners, filters, the Highway Code
Communication
Writing, typing, printing, envelopes, publishing, accounts, receipts, stamps, newspapers, magazines, greeting cards, calendars, diaries, telephone directories, embossing paper,
Domestic Products
Wrapping and boxes for cleaning materials, domestic tissues, paper plates and cups, kitchen towels, table napkins, lampshades.
Education
Books, exercise books, instruction books, maps, wall-charts, report cards, Braille paper, stationery, stencil base paper, rice paper, pyroxylin coated paper for book cover, decorative,
Entertainment and Sport
Menu cards, paper hats, crackers, fireworks, programmes, playing cards, board games, kites, model aircraft, football coupons, race cards
Food Packaging
Wrapping for bread, flour, tea, sugar, butter, margarine, sweets, deep frozen food etc., milk cartons, egg boxes, foil wrappings, tea bags, sausage skins, cigarette paper, flexible packaging, twisting paper for candy wrap, paper cup, lace paper, tablecloth paper, metallized paper, molded boxes for egg tray, apple tray, etc.,
Identification
Gummed labels, identity cards, tamper-proof labels for supermarkets, release base paper,
Industry
Presentation, wrapping, packaging and protection for all manufactured goods, transfer sheets for decorating chinaware, flame retardant paper, cores, paper tubes, fiber drum, composite cans, gypsum board liner, decalcomania paper for ceramic/glass, electrical insulation paper, condenser tissue paper, glass fiber paper for filtering process,
Electrical
Special insulating boards, electrolytic condenser paper, wrapping and identification for electrical cables, printed circuits, battery separators
Filtration
Filters for water air, coffee, medicine, beer, oil and for mechanical uses.
Impregnated Papers
Polishing, waxing, cleaning.
Protective Papers
Grease proof and corrosion-resistant products, sleeves for compact discs.
Medical
Packaging to keep instruments and equipment sterilized, bandages, plasters, clothing for nurses, face masks, surgeons’ caps, disposable bed pans, sheets, pillowcases, medical packaging,
Personal
Facial and toilet tissue, towels, sanitary products, tableware, sheets, disposable nappies, confetti, carrier bags, gift wrapping, diapers,
Photographic
Films, photographs, enlargements, mounts, lens cleaners, extrusion paper for photographic purpose,
Record keeping and other documentation
Legal documents, birth, marriage and death certificates, wills, history, scientific data
Travel
Tickets, passports, maps, charts, luggage labels, timetables, fiber for suitcases.
