- 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.
-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)
-Paper can yellow when exposed to bright lights due to high lignin content.
- Lower strenght characteristics.
- 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.
-Higher quality wood pulp produced with longer and stronger fibres that have less impurities.
-'Chlorine-free' disposable products. -Waste lignin can be reused.
-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)
- 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.
-Makes use of recycled papers - a sustainable resource.
-Well suited for bulk grades of paper (newsprint, tissue, board packaging)
-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.