Is Thiourea Dioxide Suitable for Pulp and Paper Applications?

Direct Answer

Direct Answer Suitable, and pulp and paper is one of the earliest industrial applications of thiourea dioxide.

Main uses

• Reductive post-bleaching of deinked pulp to raise brightness and remove shade
• Reductive bleaching of mechanical pulp and CTMP
• Decolourisation of coloured recovered paper

Why it suits papermaking

• Reductive bleaching acts on chromophoric groups only. It does not delignify, so yield is not materially reduced, which suits high-yield mechanical pulping systems particularly well
• The end products are urea and sodium sulphate, with no heavy metals and no chlorinated compounds
• Compared with sodium dithionite it is safer to store and transport, which is a practical advantage for a mill that charges chemicals frequently

Key differences from textile processing

Textile reduction clearing and paper deinking and bleaching are entirely different systems: consistency, pH, temperature, time and the measures of success all differ. Paper is judged on brightness in % ISO, ERIC, dirt count, fibre yield and effluent COD, not on fastness or colour difference.

Process reference points

These are screening starting points; the actual figures have to be established for the specific furnish and line.

Bottom line

Suitable and well established for reductive bleaching in papermaking, but it has to be trialled against paper-industry measures rather than a textile recipe.

Sources

1. US3384534A, Bleaching of wood pulps with thiourea dioxide（对绝干浆用量范围与白度提升数据），https://patents.google.com/patent/US3384534A/en
2. US5958184A, Process for producing thiourea dioxide（还原当量质量比、碱中水解式、木浆与脱墨浆等当量漂白实施例），https://patents.google.com/patent/US5958184A/en
3. The effect of bleaching reagents on bleachabilities of DIP and environmental loads，KTAPPI 47(1), 2015，DOI 10.7584/ktappi.2015.47.1.066