The paper and pulp industry consists of four main sectors which are pulp, recovered paper, graphic paper, and packaging. Many different types of raw materials can be used and depending on the materials, the process of paper production changes. It also depends on the quality of the pulp, the type of machinery used and the final treatment applied after the paper has formed.
Many different types of wood can be used to make paper. Softwood, for example, has long fibres which give strength to the paper while the short fibres of hardwoods contribute to the paper having a smooth and shiny surface. Depending on the type of paper product, the combination of pulp used is different. The logging industry is where the process of paper production begins. The trees meant to be used as pulpwood are cut down and cut into specific lengths and are chipped either then and there in the woods or in collection yards or sent whole directly to the pulp mills. Pulp can also be acquired from the waste products of woodworking industries. First the lumber are washed with water to remove debris and then placed on conveyor belts leading to a machine that removes the bark from the logs and cleans the wood, a machine called a barking drum. The logs are then fed into a chipper which swiftly transforms the logs into millions of chips and the chips are automatically sorted by size and the ones that are too big are recycled into the machine and the ones that are too small are used as fuel. Two methods of chipping exist, mechanical pulping and chemical pulping. In mechanical pulping, the barked logs are pressured into a grinder, which uses friction to separate the fibres of the wood. The heat evolved due to the friction allows the fibres to be separated as it softens the lignin in the wood. This type of pulping is used to produce newspaper and other papers that do not need ot last a long time. They are not strong and turn yellow easily and inexpensive to make as most parts of the tree is used and it’s a simple process. In the kraft process, a costly process which only yields about half of the tree and a common chemical process, wood chips are fed into digestors which are like pressure cookers. A solution of different chemicals is used to “cook” the chips and break down the lignin. The pulp then enters a blow tank at high speed where the softened pulp disintegrates into fibre which are then rid of the chemicals and the impurities. The processed fibres of cellulose are now called pulp and they are passed through cleaners and screens before the bleaching process starts. Bleaching makes the paper being produced white and bright. After bleaching, a mechanical process refines the pulp by beating and roughens the surface thus improving the tearing, tensile and bursting strength of the paper. At this point, fillers like clay or talc, are sometimes added to improve certain properties such as brightness, opacity, smoothness, and printing properties of the paper. This type of papers are mainly used in books, magazines, or stationery. More materials, such as resin, wax, starch, and glue, can be added to it to make it more water resistant. And often times dyes are added to give the paper colour. Now to pulp is about 99% water and 1% fibre and is fed into a paper machine, in which pumps spray a thin layer of fibres onto a fast-moving, looping wire screen where the water drops away and the fibres become paper. A press section then presses out the moisture from the damp paper and it is dried by a series of steam drums in the drying section. Now it can be rolled and cut into various sizes. The pulping process varies slightly for recycled paper. A repulper adds water and breaks down the paper into pulp and bleaching agents are used again to remove the colours. The pulp produced now is usually called secondary fibre. This type of paper is most commonly used in newsprint. After completing the papermaking process, the paper can now be sold in sheets or rolls to another industry where they will be used to make the end consumer products, such as stationery, boxes, packaging, newspapers magazines and many more. The papermaking industry is an advanced area with many scientists, engineers and other professionals, and also requires a hefty sum of investment. For example, a new world-class mill can cost up to one billion US dollars. This is the reason why paper and pulp industries are listed in one of the largest companies in the US.