Paper and Pulp
Paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distributed on the surface, followed by pressing and drying. It is a versatile material with many uses, including printing, painting, graphics, signage, design, packaging, decorating, writing, and cleaning. It may also be used as filter paper, wallpaper, book endpaper, conservation paper, laminated worktops, toilet tissue, currency and security paper, or in a number of industrial and construction processes.
Pulp
A commercially fibrous raw material (cellulose) for paper manufacture obtained from bamboo or other wood by mechanical and chemical methods. The process of producing pulp from fibres is called pulping.
Raw materials
- Softwood: eg. pines, firs, spruces
- Hardwood: eg. eucalyptus, mulberry, rubber plant wood
- Grass and reeds: eg. lemon, situ, panni, bamboo
- Straw: eg. rice, wheat, barley
Bamboo
It is an ideal raw material which can be used alone or can be blended with other sources like
hardwood. For high-grade paper, fibre should be ideally long, with high cellulose content and low lignin
content.
Stages in the production of paper/ Paper Production Stages
1. Timbering: The quality of the paper depends upon the quality of the timber. Timber comes from well-managed forests where more trees are planted.
2. De-barking: It is the process of removing the bark of trees. The bark is stripped(removed) from the logs by knife, drum, abrasion or hydraulic barker. The stripped bark is used for fuel or soil enrichment.
3. Chipping: Stripped timbers are chipped into small pieces by knives in a massive chipping machine. Chips are then stored in huge bins.
4. Pulping: One or more of the following pulping processes are applied:
- Chemical pulping: Chips from the storage bins are fed into the digestor. The wood chips are then cooked to remove lignin. Lignin is the binding material that holds the cellulose fibre together. It uses sulfate pulping (Kraft), sulphite or soda pulping. Here, hydrogen peroxide or sodium hypochlorite is used for bleaching.
- Mechanical pulping: Rotating steel discs with teeth are used to tear wood parts in mechanical pulping.
- Hydropulping: The wood fibres are brought into the circular tank containing water. This has a very powerful agitator at the bottom which breaks up the bales(wooden fibre) into small pieces.
5. Blend chest: Chemicals can be added to obtain the required characteristics of the paper. Dyes are also added to get colour paper.
6. Waste paper: Waste paper is collected from waste paper banks and commercial dumps. The waste paper represents 67% of raw materials. Paper not suitable for recycling is removed.
7. De-inking: Before the printed paper can be recycled, the ink needs to be removed. It is done by washing and floatation.
8. Refining: This is where the cellulose fibre passes through a refining process. Cellulose is shifts and inflexible before refining.
9. Screening and cleaning: Pulps contain undesirable fibrous and non-fibrous materials which should be removed. Cleaning involves removing small particles of dirt and grit using rotating screens and centrifugal cleaners.
10. Papermaking machine: A slurry of fibre is drained to create a continuous paper web. After it, the wet web passes through the press section to remove excess water and then the press web passes through a heated drying section to obtain dry and quality paper.
Quality of Paper
- Weight: The grammage is, in short, the weight of the paper per square meter. Depending on the grammage, it is possible to obtain a higher quality in different functionalities but, above all, in prints.
- Volume: Volume is the amount of air in the paper. The more air it contains, the lighter it will be, but it must be taken into account that it will also take up more space.
- Paper thickness: Thickness refers to the stiffness and stability of the material. It is established by multiplying the grammage by the volume. This thickness, as can be assumed, is what determines the width of the paper between the two sides. The thicker the paper, the more useful it will be for applying different varieties of aqueous paints.
- Roughness: Roughness is a fundamental property when selecting the type of paper. This property affects the tracing of the ink in the process of printing or writing on the paper’s surface. Therefore, the roughness and the type of ink that will be placed on the paper must be considered if you want a good-quality print or drawing. Different types of paper with the name
- Opacity: Opacity has to do with how light the colour of the paper is, affecting how visible the ink applied to it is.
Depending on its opacity, the color applied in the print may vary, causing what is seen on the monitor and the final printed result to differ significantly or not.
As its name suggests, the opacity of the paper is related to the amount of light that is projected on
this material and, the higher the opacity, the greater the contrast with the impression obtained.
