Pulping Paperboard

two principal methods extracting fibres sources are:

chemical pulping uses chemical solutions convert wood pulp, yielding around 30% less mechanical pulping; however, pulp made kraft process has superior strength
thermo mechanical pulp two-stage process results in high yield of wood fibres @ expense of strength.

bleaching

pulp used in manufacture of paperboard can bleached decrease colour , increase purity. virgin fibre pulp naturally brown in colour, because of presence of lignin. recycled paperboard may contain traces of inks, bonding agents , other residue colors grey. although bleaching not necessary end-uses, vital many graphical , packaging purposes. there various methods of bleaching, used according number of factors example, degree of colour change required, chemicals chosen , method of treatment. there 3 categories of bleaching methods:

bleaching delignification using chlorine gas, method has been largely replaced procedures gentler environment such use of oxygen replacement chlorine gas.
bleaching oxidation using chemicals such chlorine dioxide, hydrogen peroxide or sodium hypochlorite.
bleaching reduction using chemicals such sodium bisulphite.




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