20 The Carton Packaging Fact File THE PULPING PROCESS 4 The Carton Packaging Fact File 21 KEY FACTS Cellulose fibre makes up 40% - 45% of wood. Fibres are separated from wood and from waste paper and board by pulping When wood is pulped by Pulp produced from wood chemical processes, the by chemical processing is remaining wood components brown in colour. The bleaching are used to provide energy. process results in a chemically About 50% of the energy pure, white, pulp. Bleaching used world-wide by the processes today do not paper and board industry use chlorine gas and do not is from this naturally produce toxic waste products sustainable source Fibres in wood can also be separated by mechanical processes. The cellulose fibres in recovered paper and board are separated by agitation in water 22 The Carton Packaging Fact File THE PULPING PROCESS CHEMICAL PULP PRODUCTION DIAGRAM cooking washing oxygen delignification pine or birch timber logs chips pulp final diffuser washing bleaching washing energy generation chemical recovery Different pulping processes is then screened and cleaned and any for pulping and for both pulp for wood (virgin fibre) remaining fibre clumps are reprocessed. and cartonboard manufacture in and recovered paper/board integrated mills. (recycled fibre) Wood chips may be preheated with steam to assist the refining process What is meant by bleaching? What is wood pulp? in which case the pulp is known as Chemically separated fibres are Wood pulp is cellulose fibre separated “thermomechanical pulp” or TMP, and frequently bleached in the pulp mill to from wood by “pulping”. Cellulose fibre when limited chemical pretreatment is remove the last traces of lignin and any makes up 40-45% of the dry weight of also applied it is called “chemi- other residual material. Bleached pulp is wood. The rest comprises lignin, a thermomechanical pulp” or CTMP. white in appearance and pure cellulose hard brittle material which binds the in content even though individual fibres together, hemicelluloses and small The colour of mechanical pulp is the fibres are colourless and translucent. amounts of wood resins. same as that of the wood from which it is derived. Using the option of chemical Bleaching is no longer carried out with Fibres in spruce and pine are ribbon treatment reduces the amount of lignin chlorine gas. Today the most widely used shaped. In dimensions they are and this results in lighter coloured pulp. process is ECF (elemental chlorine free). approximately 3-4mm long and 30µm In principle this treatment is a type of This replaces chlorine with successive wide. They are called “long” fibres to bleaching and the chemical treatment treatments of oxygen, hydrogen distinguish them from the “short” fibres can be varied depending on the level peroxide and chlorine dioxide. found in birch, which are approximately of whiteness and degree of lignin The by-products are simple and 1.0-1.5mm in length. reduction required. harmless and identical with compounds which occur naturally What is mechanical pulp? What is chemical pulp? in sea water. The first process in pulping wood is to In chemical pulping, debarked logs are remove the bark, which is then either chipped and treated with chemicals Another process is known as TCF used as a horticultural product or as a under heat and pressure. This process (totally chlorine free) where the source of energy in the mill. dissolves the resins which bind the fibres chemicals used are oxygen and together in the wood. There is a choice hydrogen peroxide. Mechanical pulping simply means that of chemical process. The Kraft, or fibre separation is achieved by subjecting Sulphate, process is by far the more Is bleaching necessary? the wood to crushing/grinding widely used nowadays because of its Whilst the use of bleached chemically pressure. The wood may be in the ability to process all the commonly separated fibre is not necessary for all form of logs, in which case the pulp is used species of wood and its high grades of paper and board, it is used known as “groundwood pulp”, or it rate of chemical recovery. when specific appearance and may first be converted into small chips performance needs have to be approximately 25mm square and The Sulphite process also dissolves the achieved. When used in cartonboard known as “refiner mechanical pulp”. non-fibrous components of the wood. bleached fibres provide strength and The heat generated softens the lignin In both processes the non-fibrous durability, particularly when used in the and results in fibre separation. The pulp components are used to provide energy external layers. Bleached chemical The Carton Packaging Fact File 23 MECHANICAL PULP PRODUCTION refining spruce timber logs wood chips washing process bleaching wood pulp cleaning pulp has a white appearance. Fibre separation is achieved by Combined heat and power generation When used as a surface layer in the mechanical agitation in water. is used in 90% of European mills. The manufacture of cartonboard it can Pulp made in this way is known as CHP process provides savings in fuel be printed, varnished, coated and recycled pulp, recycled fibre, consumption of the order of 30-35% laminated to achieve the required recovered fibre, waste paper compared with conventional means of appearance. fibre or, simply, secondary fibre. power production and distribution. Bleached cellulose fibre is chemically What energy sources are used in Why is water used in pulping? pure so that it is suitable for the the production of pulp, paper and Water is used in mechanical and packaging of many products in either cartonboard? chemical pulping to separate, process direct contact or in close proximity. Chemical pulping results in a and transport primary or virgin fibres, i.e. This is particularly important where by-product which is used as an fibres made directly from wood. Water products are flavour or aroma sensitive. energy source for pulping and, where is also used in the recycling of fibres appropriate, bleaching. In integrated from recovered paper and board. What is meant by the AOX level? mills, where paper or board is AOX is a measure of the organic made at the same site, the wood After use the water is treated to meet chlorine material in the discharge from a by-products also provide energy in the the local regulations and returned to pulp mill operating a bleaching process. form of electricity and steam, for the nature. There is a trend to use less Though the levels discharged from manufacturing process. This energy water and, even to close water systems mills in Europe are extremely low as a source is, therefore, renewable and in virgin pulp mills, thereby reducing result of the process changes which sustainable. It accounts for around the demand and the environmental have been made AOX is not a measure 50% of the energy consumed in pulp, impact of water use. CEPI has stated of environmental impact. This is paper and cartonboard manufacture. that water consumption in European because the measurement does not mills has been reduced by a third in give any indication of the types, and Mechanical and fibre recycling both the course of a recent 10 year survey. hence the toxicity, of compounds which use energy to separate the fibres. are present. The compounds present This energy may be generated on-site today are simple, harmless compounds or supplied from external sources. with no adverse environmental effects. For on-site generation, several mills have installed combined heat and What is recycled pulp? power (CHP) plants which are much Recycled pulp is pulp made from more efficient compared to power paper and board, including stations supplying a national grid. cartonboard and carton waste, which The energy source is most likely to be has been used and then recovered by fossil fuel based (oil, coal or natural waste collection schemes. gas) although, depending on the location, hydroelectric, nuclear, wind or biofuel sources may also be used. 24 The Carton Packaging Fact File RECYCLED PULP PRODUCTION waste paper bales hydrapulper fibre cleaning board board at mill separation in water machine What are the advantages of How is used paper and board cartonboard made from virgin fibres? selected for recycling as Cartonboard made from primary, cartonboard? or, virgin, fibres is generally whiter, Used paper and board is selected for smoother and has a less pronounced recycling according to the quality of surface structure than cartonboard the fibre. This depends on the type of made mainly from recycled fibres. fibre and how the fibre was processed It can be up to 25% lighter for the previously - whether mechanically or same strength and therefore reduce chemically, bleached or unbleached and the overall weight of the carton. whether it has already been recycled. Fibres made directly from wood are Fibre quality will also be significantly more “consistent”. This consistency influenced by the way the paper or means that cartonboard made from board was recovered and the ways virgin fibre readily meets the needs of in which it was printed, converted food and pharmaceutical packaging and used. and wherever the products packed have sensitive flavours and aromas. How is the quality of recovered paper and board graded? What are the advantages of Recovered paper and board is graded cartonboard made from recycled according to the definitions listed by fibres? CEPI and BIR published in 1999. Cartonboard made from recycled fibre utilises valuable recovered waste This describes 57 grades of recovered paper and board which would paper and board. The list includes otherwise be discarded into landfill several cartonboard grades. sites or disposed of by other means. It differentiates the waste in terms of the type of cartonboard, which takes Energy and material resources were into account the fibre composition, invested in the paper or board when it the extent of the print coverage, was first made and hence recovering whether it is of post consumer or and recycling as fibre is therefore an industrial/commercial origin and efficient use of those resources.