Abstract:
Wheat straw is a non-wood agricultural residue which serves as an excellent fibrous
source for pulp and paper industry. In the present work, TCF bleaching sequences
were developed for indigenous variety of AS/AQ wheat straw pulp. Different
chemicals such as acid, oxygen, oxone, dithionite, alkali and hydrogen peroxide were
optimized in different stages and sequences at varying doses of bleaching agents and
reaction conditions. Multistage TCF bleach sequences i.e., AOOxPP*, AOOxEP,
AOOxYP, AO′Ox′P′ are resulted from various optimization trials during the study. It
was very promising to find out that cellulose remained protected whereas most of the
residual lignin was removed during the process. Most of the hemicelluloses were
washed away during bleaching. However, it is quite evident from the pulps’ sugar
analysis that only a small fraction of hemicelluloses remained intact in the bleached
pulp which is important in fiber preparation and its bonding during papermaking
process. Similarly, hexenuronic acid was also removed during successive stages of
bleaching that may be the causes of reduction in fiber strength, brightness and
brightness stability. The results also revealed that the developed bleaching sequences
are effective and selective to fully bleach the pulp with brightness gain greater than
80% ISO without deteriorating its fibre characteristics such as kappa number,
viscosity, strength and brightness stability etc. A considerable reduction in effluent
load with reduced toxicity and zero AOX level shows the advantage of process over
chlorinated bleaching processes. Thus the study provides enough evidence to fill the
gap between producing quality products and requirements for a healthy environment
using TCF bleaching sequences.
