The production of wood pulp

HideShow resource information
  • Created by: emb98
  • Created on: 20-05-16 14:58

Mechanical Pulp:

-The logs of coniferous trees are saturated with water and de-barked. 

- The wood is ground down, which softens the ligin, and the mechanised forces separate the fibres to form 'groundwood pulp'. 

- This pulp is screened to accept 1-2mm 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 with peroxide or sodium hydroxide. 

 -This is the most widely used method in the UK for producing wood pulp. 

Chemical pulp:

- After de-barking, the hard- and softwood logs are cut into 2cm chips along the grain. 

- These are pounded into fragments and screened. 

- The resulting pulp is stored and treated with either an acid or and alkali to break down the lignin. 

- Most chemical pulp is made by the alkaline kraft process, or sulphate process, which uses caustic soda and sodium sulphate to 'cook' the wood pulp. 

- 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. 

- Manufacturers blend a variety of…


No comments have yet been made

Similar Design & Technology: Graphics resources:

See all Design & Technology: Graphics resources »See all Materials resources »