Fibre to board Fibre to board Today’s processes of separating fibre and making paper- compost and road-building material. Using the entire tree board take place in facilities characterised by capital is an important part of our ambition to carry out sustain- intensity, high production volumes and the application of able production. the latest techniques of materials handling, continuous production and process control. From timber to fibre – the pulping process In many cases, including the mills of Iggesund Paper- The timber logs which are delivered to the pulp mill are first board, the production of pulp and the manufacture of debarked, since bark does not contain fibre suitable for paperboard are carried out on the same site in a continu- pulp manufacture. Bark is removed by friction, as logs are ous integrated process, giving benefits in quality, efficiency tumbled together in a rotating drum. The bark is then used and economy. as a fuel within the mill or composted to create garden soil. Managed forests provide the primary source of cellulose The next process depends on the type of separation or fibre from wood varieties such as spruce, pine and birch. defibration process used. The fibre is separated by mechanical or chemical pulp- ing and the whiteness and purity may subsequently be Pulp manufacture improved by bleaching. Basically the choice is between long fibres (spruce and Processing on the paperboard machine starts with the pine) and short fibres (birch). The boardmaker optimises formation of a layer of entangled fibres on a moving wire sheet forming, appearance and performance properties or plastic mesh from which water is removed by drainage. with an appropriate choice and blend of fibres to meet the Further layers of pulp are usually combined in the wet state. needs of particular products. More water is subsequently removed by pressing and dry - ing. Paperboard is coated on-line or off the machine to improve the printing surface. Large diameter, full machine- width reels are produced by the machine. These reels are subsequently cut into smaller reels or sheeted, labelled, and wrapped prior to dispatch to the customer. The forestry cycle The virgin fibre for paperboard is derived from naturally occurring species such as spruce, pine and birch, which provide fibres with suitable characteristics. These species are supplied by managed forestry operations in Sweden and other parts of Europe. To maintain sustainable development, including the re- quirements for biological diversity, modern forest manage- ment makes use of several combined methods. Detailed planning is done at both a county and local level. Natural regeneration, planting and sowing are used. Biologically sensitive areas and old growth forests are protected ac- cording to the local conditions. Another important characteristic is that managed for- PLANTING 0-3 years estry is an integrated operation whereby wood for pulping HARVESTING CLEANING 30-50 years UK 3-15 years UK is harvested with wood for the timber industry. Thinnings, 80-120 years 3-30 years Sweden the smaller diameter trees taken from the forest at vari- Sweden ous stages to allow other trees room to mature, are used sawn timber to produce pulp. When mature trees are harvested, the thicker part of the trunk is used as sawn timber, and the pulpwood tapered top goes to the pulp mill. This ensures maximum use of the harvested timber. Making the best use of raw materials is a key principle THINNING pulpwood within Iggesund Paperboard. The trees supplied to the 15-30 years UK mills are transformed into paperboard – but also into the 30-80 years Sweden energy that drives the production process, heats nearby homes and dries sawn timber. Other end products are soil 26 Reference Manual | IGGESUND PAPERBOARD Fibre to board IGGESUND PAPERBOARD | Reference Manual 27 Fibre to board Mechanical pulp characteristics which the debarked logs are first converted into small flat This process gives a very high yield from the timber. The chips. These chips, with a moisture content of 25–30 %, presence of lignin has a number of implications – the fibre are forced between the rotating metal discs of a refining is hard and rigid and this gives the sheet a limited degree machine. The heat and water vapour generated soften the of consolidation, high bulk (low density), resilience, dimen- lignin so the fibres can be separated. The pulp is screened sional stability, and stiffness. and cleaned and fibre clumps are reprocessed. The presence of lignin and the limited degree of consoli- Mechanical pulping results in a very high yield. About dation would make a sheet made solely from mechanical 95 % of the wood is converted to fibre. Mechanical fibre pulp relatively weak. The pulp retains the colour of the separation requires high levels of electric power, and some wood used and is of known natural composition and purity. of the energy is usually recovered and used as heat in the Refiner mechanical pulp (RMP) is a two-stage process in process. Washing Logs Chipping + of raw De- and Refiner barking defibration Bleaching Pulp to material washing board mill Bark for fuel or compost CONVEYORS Metering EXCESS CHIPS Screw RECIRCULATE WOOD Conveyors CHIP Preheater Preheater Preheater SILO REFINER CHIP WASHER AND DEWATERER BLEACHING REFINED FIBRE To screens and cleaners 28 Reference Manual | IGGESUND PAPERBOARD Fibre to board Chemical pulp characteristics solve 80–90 % of the lignin, allowing the fibres to separate This process preserves fibre length and the pure cellulose easily. develops a high degree of consolidation, both features that The sulphate process, which is used within Iggesund, give a very strong sheet. also permits efficient chemical recovery and energy utilisa- The fibre is flexible and soft, giving good creasing, emboss- tion. The fibre yield of unbleached chemical pulp relative to ing, and cutting properties and with low dust generation. wood is in the range of 50–65 %. The dissolved lignin and Bleached cellulose pulp has high whiteness, brightness, resins from the wood are used in internal energy generation. and light stability. This material has the highest purity and provides products with the best odour and taint neutrality. In the chemical process timber is first converted into wood chips. These are then cooked in chemical solutions to dis- Washing Logs Chipping Washing Oxygen De- Impreg- Continuous Diffusion + of raw and and delignifi- barking nation cooking bleaching Pulp to material washing straining cation board mill Chemical Bark recovery for energy fuel generation DEFIBRATION CHIPS O2 NaOH Modified continuous Pressure Double Oxygen delignification Final wash cooking diffuser wash straining PULP CIO2 CIO2 O2 NaOHH2O2 CIO2 CIO2 DIFFUSER BLEACHING IGGESUND PAPERBOARD | Reference Manual 29 Fibre to board Caustic soda/ High pressure steam sodium sulphide solution (white liquor) Chips + liquor IMPREGNATOR DIGESTER Chips Forward flow cooking Caustic Reverse soda/ flow sodium cooking sulphide solution (white liquor) Black liquor in recycle loop Wash liquor Impregnated chips Pulp (incl. liquor) 30 Reference Manual | IGGESUND PAPERBOARD Fibre to board Bleaching All these factors have technical and economic implications, All the varieties of pulp used in the manufacture of paper- not least of which is their environmental significance. board can be bleached to influence colour and purity. Whitening methods fall into three categories: Chemical pulp is brown in colour, the colour density • Bleaching by delignification using chlorine gas. This depending on the cooking process and degree of lignin approach has largely been replaced by processes with removal. While unbleached pulp may be used for some better environmental safeguards. The use of oxygen is purposes, such as corrugated board boxes, it is neces- being progressively introduced instead. sary to whiten the pulp for many graphical and packaging • Bleaching by oxidation using materials such as chlorine applications. dioxide, hydrogen peroxide or sodium hypochlorite. The whitening of pulp is called bleaching, though the • Bleaching by reduction using materials such as sodium process can take many forms depending on a number bisulphite. of factors. These include the degree of colour change If the pulp mill is integrated with paperboard manufac- required, choice of chemicals, method of treatment and ture, the pulp is pumped to intermediate storage facilities. whether coloured compounds are removed (delignifica- If the pulp is sold to the open market it is dried in sheets tion) or merely changed in colour. or by fluffing and drying in hot air. Market pulp is baled for shipment. IGGESUND PAPERBOARD | Reference Manual 31 Fibre to board Pulp (stock) preparation steel surface. A wet paperboard web will adhere to the cyl- If the pulp is bought in bales it is first mixed by agitation in inder surface and be progressively dried while at the same water in a large vessel known as a hydrapulper. All pulp, time achieving a very smooth board surface. This cylinder including the pulp which comes straight from the pulp mill is known as an MG (machine glazing) or Yankee cylinder. without drying, is then treated in various ways to prepare it for use on the paperboard machine. The processed pulp Surface sizing is referred to as “stock”. The consolidation properties of A starch solution can be applied to the paperboard surface fibre can be improved by mechanical processing – refining to improve strength and anchor surface fibres firmly in the – which modifies the surface structure of the fibre. Swelling sheet. Within Iggesund Paperboard the baseboard is sur- in water expands the fibres’ surface area, thereby increas- face sized prior to being coated. When board is surface ing their strength and ability to consolidate. sized a starch-based solution is applied to both sides of Additives such as internal sizing can be used to increase the product: this improves surface strength and anchors the water repellency of fibres, and retention aids to increase the fibres to the sheet.