Reference Book
is able to separate the cellulose fibers. After the chips are screened for size,
they are put in a huge cooking kettle called digester.
Pulping:- There are two types of pulping methods namely chemical pulping
and mechanical pulping. Pulp made by chemical pulping is again divided into
two - sulphate pulp (using alkali) and sulphite pulp (using acid).
In the chemical pulping process, chemicals in the sealed, pressurised digester
break down in the lignin present in the cellulose fibers. The cellulose fibers
become pulp, a mass of soft, spongy matter. The pulp is blown into a pit
where the chemicals are washed away.
The mechanical pulpmaking process uses grinding wheels to reduce the logs
to fiber. Pulp with high opacity but relatively low strength is produced.
Treating the pulp :- Sizing chemicals are added to the pulp slurry to make the
paper more resistant to moisture. Resin and alum are added during this process.
Fillers like clay and titanium dioxide are added to improve a paper’s opacity,
brightness, softness and ink receptivity.
Dyes and pigments are added to produce coloured paper; bleaching makes the
pulp white.