| abstract |
In this process, the conventional alkaline deinking chemistry or the more recent near-neutral sulphite chemistry, both used industrially for processing old newspapers and old magazines is replaced by a bleaching chemical of the phosphine or phosphonium salt-types, effective over a broad range of pH, from acidic to alkaline. In this new application, the bleaching chemical can be added directly in the pulper where it is used in conjunction with nonionic, cationic and/or anionic surfactants, with and without sodium silicate. It can also be added at other points of the deinking process such as the dump chest or in any holding tank or bleaching tower located before or after ink removal steps. It was discovered that this new class of bleaching chemicals was more effective as a bleaching agent than sodium sulphite, currently used in the near-neutral deinking process; however ink fragmentation and redeposition that take place in the pulper at near-neutral conditions and that are aggravated by this new class of compounds preferably have to be minimized otherwise the brightness benefit will be masked. Final brightness of wood-containing fibers approached that obtainable with the conventional alkaline process that uses a mixture of sodium hydroxide, sodium silicate, hydrogen peroxide and surfactants. |