BLEACHING OF SECONDARY FIBER PULPS

Recycled Pulps from various fibre sources were treated with ozone (Z), sodium hypochlorite (H), peroxide (P), and sodium hydrosulphite (Y) b leaching stages. Included in the pulp furnishes were deinked ledger pu lps (one spiked with 30% coloured broke), a book furnish containing a large portion of groundwood, and two furnishes containing unbleached c hemical pulps. The best result was obtained with a ledger pulp contain ing some semi-bleached fibres. The ledger pulps responded as follows t o the various sequences in terms of brightness gain: ZY greater-than-o r-equal-to ZH > ZP The Z and Y stages removed the colour tint from pul p better than did a P stage. A secondary pulp with a high proportion o f mechanical pulp fibres or unbleached chemical pulp fibres did not re spond well to ozone or hypochlorite bleaching.