Title
Hydrogen peroxide bleaching of deinked pulp
Authors
NISHI K. BHARDWAJ and KIEN LOI NGUYEN

Received November 10, 2025
Published Volume 60 Issue 5-6 May-June
Keywords deinked pulp, hydrogen peroxide bleaching, brightness, scattering coefficient, absorption coefficient

Abstract
This research study focused on the impacts of some crucial process variables on the single-stage hydrogen peroxide bleaching of recycled deinked pulp. The impacts of hydrogen peroxide and sodium hydroxide doses, temperature, retention time, pulp consistency, and sodium silicate addition were analyzed systematically. The results obtained indicated that an increase in the dose of peroxide increases the brightness and reduces absorption; however, excess doses result in yield loss, without improving the performance further. Sodium hydroxide is vital for the activation of peroxide, with an optimal range of 1.50–2.00% leading to maximum brightness and higher doses promoting alkaline darkening. Temperature and time have high impact on the bleaching performance; optimal values of 70 °C and 3 h retention give the best combination of brightness and yield. Pulp consistency of medium (10.00%) value is the most advantageous for achieving effective use of chemicals, in contrast to lower and higher consistencies. The addition of sodium silicate (2.00– 3.00%) stabilized peroxide, increased scattering effect, and prevented ink redeposition. Overall, the optimization of chemicals and process variables considerably improves the brightness and optical characteristics of recycled deinked pulp. Single-stage peroxide bleaching of recycled deinked pulp yielded pulp brightness of 65.00% ISO, with a yield of 95.20%.