The straw ammonium sulfite pulp is completely free from chlorine-based bleaching agents

Abstract

This paper investigates the completely chlorine-free bleaching of rice straw ammonium sulfamate pulp, with a focus on the OAP bleaching process workflow.

Experimental results demonstrate that during the OAP bleaching process, the optimal conditions for conventional oxygen-alkali bleaching are: pulp concentration 10%, alkali dosage 3%, oxygen pressure 0.6 MPa, temperature 80°C, duration 80 min, and magnesium sulfate content 0.5%. Post-bleaching measurements showed a white degree increase from 43.3% ISO to 55.2% ISO, a potassium permanganate value decrease from 7.8 to 5.7, a yield of 90.56%, and ash content of 21.57%. The optimal sulfuric acid pretreatment conditions were: pulp concentration 5%, H₂SO₄ 1.5%, temperature 65°C, duration 40 min. Post-treatment properties included a white degree of 55.7% ISO and a potassium permanganate value of 4.8. For hydrogen peroxide supplementary bleaching, the optimal parameters were: H₂O₂ 4%, NaOH 2%, temperature 80°C, duration 80 min, DTPA 0.2%, MgSO₄ 0.05%, and Na₂SiO₃ 3%. Experimental results indicated a white degree of 66.4% ISO, a yield of 91.02%, and a potassium permanganate value of 2.9.