The effect of DTPA and complementally bleaching on the optical properties of hornbeam and beech CMP pulps

In this research, beech and hornbeam chips were chosen randomly from the chips pile of Mazandaran Wood and Paper Industries and cooked under CMP conditions and pulps were prepared at the yield of 85%. The CMP pulps were separately bleached with hydrogen peroxide and sodium dithionite and 60 gr/m2 hand sheet were made. Then, a solution of 0.5 percent of DTPA was sprayed over a number of hand sheets. Then, their optical characteristics were measured and compared using TAPPI Standard test methods. The results of this study explored that following H2O2 bleaching brightness and greenness increased and opacity, absorption coefficient, K/S ratio and a* factor decreased. After complementally bleaching with sodium dithionite, the most part of optical properties improved. Following DTPA solution spraying on the surface of hand sheets, brightness, opacity and greenness improved and absorption coefficient, K/S ratio and a* factor decreased.  Among the different treatments, DTPA spray has a great effect in stability of brightness and increasing it durability against optical deterioration. Also, the complementally bleaching pattern in improving the optical properties of the paper obtained from hornbeam CMP pulp was more noticeable than that of beech.