Materials, components and processes

Materials, components and processes

1. Materials

   • Paper and board
     • The production of wood pulp
       • Mechanical pulp
         • Logs of coniferous trees are saturated with water and de-barked. The wood is ground down, softening the lignin, and the mechanised forces separate the fibres to form 'ground wood pulp'. This pulp is screened to accept 1-2 mm pieces, with larger pieces being re-circulated for additional screening. The resulting pulp can only be used for low-grade paper such as newspaper, so the pulp is bleached.
       • Chemical pulp
         • After de-barking, the hard- and softwood logs are cut into 2 cm chips along the grain. These are pounded into fragments and screened. The resulting pulp is stored and treated with either an acid or an alkali to break down the lignin. Most chemical pulp is made by the alkaline kraft process, or sulphate process. The amount of fibre produced is lower than with mechanical methods, but the fibres are longer, stronger and contain fewer impurities.
       • Waste pulp
         • Recycled paper and board used for waste pulp is often used for lower grades of paper, as its strength, durability and colour are not as good as virgin fibres. Waste pulp is often mixed with virgin fibres to produce better quality papers as fibres become shorter and weaker and lose their papermaking qualities.