Wood Pulp

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Mechanical Pulp

  • Logs of coniferous trees (pines etc.) are saturated with water and de-barked.
  • The wood is ground down to soften the lignin.
  • Mechanical forces seperate the fibres to form 'ground wood pulp'. 

Paper made from this process can only be used for low-grade paper such as newspaper. 

  • The pulp is bleached with peroxide or sodium hydroxide to whiten it and give it a slightly better quality. 

ADVANTAGES

-Bleaching adds value    -Well suited for 'bulk' grades of paper (newspapers and packaging boards)

-The process uses the whole of the log except for the bark ( 90% yield) 

DISADVANTAGES 

-Paper can yellow when exposed to bright lights due to high lignin content. 

- Lower strenght characteristics.

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Chemical Pulp

  • The wood is debarked and cut into chips along the grain. 
  • These chips are pounded into fragments and screened.
  • This pulp is stored and treated  with either an acid or an alkali to break down the lignin. 

ADVANTAGES 

-Higher quality wood pulp produced with longer and stronger fibres that have less impurities.

-'Chlorine-free' disposable products.    -Waste lignin can be reused.

DISADVANTAGES

-Lower yield than mechanical methods as the lignin is dissolved from the fibres.

-Has to be imported (no chemical pulp is produced in the UK) 

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Waste Pulp

  • Recycled paper and board used for waste pulp is often used for lower grade paper - it's strength, colour and durability is not as good as virgin fibres.
  • Waste pulp is mixed with virgin fibres to make better quality papers as fibres become shorter and weaker. 

ADVANTAGES 

-Makes use of recycled papers - a sustainable resource.

-Well suited for bulk grades of paper (newsprint, tissue, board packaging) 

DISADVATNAGES

-Cannot always be recycled as the pulp loses quality and more virgin pulp will need to be added. 

-Doesn't save any more energy than other methods.

-Requires processing and additives to achieve a good quality. 

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