METHOD FOR ALKALI TREATMENT OF PRINTED PAPER Russian patent published in 2011 - IPC D21C5/02 D21C9/10 

FIELD: chemistry.

SUBSTANCE: method involves repulping old paper stock in the presence of H₂O₂, NaOH and Na₂SiO₃. After repulping, the mass is held for 2 hours and floatation is carried out in the presence of sulphate soap as a surfactant in amount of 2% of the weight of absolutely dry fibre. The repulped stock is bleached with formamidine sulphinic acid taken in amount of 0.3-0.6% fo the weight of absolutely dry fibre at pH 8-9, temperature 65°C for 60 minutes.

EFFECT: high degree of whiteness of repulped stock while preserving mechanical properties.

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