Ink detachment, fragmentation and alkali darkening during pulping - PowerPoint PPT Presentation

Ink detachment, fragmentation and alkali darkening during pulping of ONP/OMG. Part II. Effects of sodium sulphite. Luc Lapierre, Diane Pitre and Gilles Dorris 8 th Research Forum on Recycling 25 September 2007, Niagara ON 1

During repulping of ONP:OMG, high pH in the pulper increases the… • darkening of mechanical fibres – Requires peroxide and sodium silicate to counteract • Increases cost of deinking (5-15 $/T) • fragmentation of large stickies – Removal by screens is less efficient • release of COD • sensitivity to flexo-printed papers – Water-based inks become more dispersed – More prone to irreversible deposition in lumen • acid addition before paper machine (neutralization) 2

Lowering the pH in the pulper can lead to many advantages • How to transition from alkaline to neutral chemistry ? 3

Replacing (sodium hydroxide + peroxide) by sodium sulphite Alkaline pulping (pH 10-10.5): Neutral pulping (pH 7-8): • • 0.8% NaOH (varies seasonally) 1-2% sulphite (varies seasonally) Bleaching Deflaking, ink dislodging – – Alkaline darkening – • 1.1% H 2 O 2 (varies seasonally) Bleaching – • 1.8% Silicate • 0.5-2% Silicate Slow down peroxide decomposition – Reduces ink fragmentation – / increases ink agglomeration Reduces bound ink – • • 0.2% surfactant blend Proprietary additive(s) 4

Isolate effect of sulphite is not straightforward • Aqueous sulphite solution is alkaline – Difficult to differentiate effect of pH from Sulphite • pH varies with pulping time – Initial pH ? – Final pH ? • Solution: pulping in buffered solutions – Fixed Ca concentration – No surfactant – No bleaching agent 5

Experimental : Buffers • 7.4 , 8.0, 9.4 and 11.0 • When adding ONP:OMG, – 7.4 � 7.4 – 8.0 � 8.0 – 9.4 � 9.0 – 11.0 � 9.8 • When adding ONP:OMG + sulphite – 8.0 � 8.2 6

Furnish is 70:30 mixture of newspapers and magazines • Printed ONP:OMG – ONP: Journal de Montréal – OMG: LWC magazine • Unprinted NP:MG – UNP: Unprinted Journal de Montréal – UMG: Close match to printed LWC 7

Pulping • 625 g • 10% consistency • 50°C • 60 ppm Ca +2 8

Measurement: Total ink • 3.42 g pad from standard British sheet machine • Addition of an ink retention aid (alum + cationic polyacrilamide) • Leads to relative ERIC values (ISO opacity > 0.97) 9

Measurement: Bound ink (undetached + redeposited) Time � � � � Time � � � � Hyperwashing, then 1.2 g handsheet 10

Reminder: in part I JPPS, 32(3):150-155 (2006) • Pulping ONP:OMG in different buffers • 60 ppm of Ca +2 • Nothing else added – No soap/surfactant – No bleaching agent 11

Total ink after pulping Decrease in ink fragmentation 7.4 ERIC after pulping (ppm) 1200 8.0 1000 9.1 10.3 800 600 0 2 4 6 8 10 Time of pulping (min) 12

Total ink after 3 min. of pulping vs. pH ERIC after 3 m inutes of pulping 1000 • Rapid decrease 900 (ppm ) • Start leveling off at around 800 pH 8.5 700 7 8 9 10 11 pH in pulper 13

Bound ink after pulping Decrease in bound ink 160 160 ERIC after pulping and ERIC after pulping and Minimum at around hyperwashing (ppm) hyperwashing (ppm) 3 minutes 7.4 130 130 8.0 9.1 100 100 10.3 70 70 0 0 2 2 4 4 6 6 8 8 10 10 Time of pulping (min) Time of pulping (min) 14

15 • Linear vs. pH Bound ink after 3 min. of pulping decrease ERI C after 3 m inutes of pulping and after hyperwashing (ppm ) 110 70 90 7 8 pH in pulper 9 10 11

ISO brightness after pulping Curve at pH 10.3 is 45 45 not following the expected order ISO brightness after pulping (% ) ISO brightness after pulping (% ) 44 44 9.1 43 43 8.0 10.3 42 42 ALKALINE DARKENING ! 41 41 7.4 40 40 0 0 2 2 4 4 6 6 8 8 10 10 Time of pulping (min) Time of pulping (min) 16

ISO brightness after hyperwashing At pH 8, best compromise between maximizing ink detachment and minimizing alkali darkening 56 56 ISO brightness after pulping ISO brightness after pulping 55 55 and hyperwashing (% ) and hyperwashing (% ) 8.0 54 54 7.4 53 53 9.1 52 52 Plot of ISO brightness 10.3 at 3 minutes vs. pH 51 51 0 0 2 2 4 4 6 6 8 8 10 10 Pulping time (min) Pulping time (min) 17

ISO brightness after 3 minutes of pulping followed by hyperwashing • No surfactant 56 I SO brightness after 3 m inutes of pulping added in pulper and after hyperwashing (% ) • Highest ISO bright. 55 near pH 8 • The more the pH 54 deviates from 8, the more chemical 53 needed to regain brightness 52 7 8 9 10 11 pH in pulper 18

Part II : Effect of sulphite • Since pH 8 is optimal for brightness, we decided to test suphite in buffer at pH 8 19

Total ERIC after pulping vs. pulping time 1200 1200 pH 8.0 (buffer only) pH 8.0 (buffer only) 1100 1100 ERIC AP, ppm ERIC AP, ppm 1000 1000 pH 8.2 (buffer + sulphite) pH 8.2 (buffer + sulphite) 900 900 800 800 Reduces ink fragmentation 700 700 0 0 2 2 4 4 6 6 8 8 10 10 Time, min Time, min 20

Bound ERIC after pulping vs. pulping time Improves ink detachment 200 200 ERIC AW, ppm ERIC AW, ppm pH 8.0 (buffer only) pH 8.0 (buffer only) 160 160 120 120 pH 8.2 (buffer + sulphite) pH 8.2 (buffer + sulphite) 80 80 0 0 2 2 4 4 6 6 8 8 10 10 Time, min Time, min 21

Effect of sulphite on ERIC • ERIC values are lower with sulphite – Reduces ink fragmentation – Improves ink detachment • 60% of the benefit due to the sulphite only – 40% due to pH 22

ISO brightness after pulping vs. pulping time 45 45 ISO brightness AP, % ISO brightness AP, % pH 8.2 (buffer + sulphite) pH 8.2 (buffer + sulphite) 44 44 1.9 43 43 42 42 2.5 41 41 pH 8.0 (buffer only) pH 8.0 (buffer only) 40 40 0 0 2 2 4 4 6 6 8 8 10 10 Pulping time Pulping time 23

ISO brightness after hyperwashing and pulping vs. pulping time pH 8.2 (buffer + sulphite) pH 8.2 (buffer + sulphite) 56 56 ISO brightness AW, % ISO brightness AW, % 55 55 1.9 2.5 54 54 53 53 pH 8.0 (buffer only) pH 8.0 (buffer only) 52 52 0 0 2 2 4 4 6 6 8 8 10 10 Time, min Time, min 24

Sodium sulphite … • Reduces the extent of alkali darkening and provides a bleaching benefit • Slightly reduces ink fragmentation and improves ink detachment – Changes in rheological properties – Pulp slurry becomes less viscous – Reduces shear forces on ink – Reduces ink break-up and redeposition Presence of ink masks the “bleaching” benefits 25

Repeated experiments with Unprinted newspaper and Unprinted magazine • Used the same buffers • Compare with 2% sulphite + 2% silicate – Unbuffered, final pH of 8.3 26

ISO brightness AP vs. pulping time Fully deflaked pulp Fully deflaked pulp Fully deflaked pulp 63 63 Sulphite + silicate (pH 10.0 � 8.3) Sulphite + silicate (pH 10.0 � 8.3) ISO brightness AP, % ISO brightness AP, % 61 61 7.0 7.0 59 59 7.8 7.8 9.0 9.0 9.8 9.8 57 57 0 0 2 2 4 4 6 6 8 8 10 10 Pulping time (min.) Pulping time (min.) 27

ISO brightness after 10 min. of pulping vs. pH at 10 min. 2% sulp. + 2% sil. 2% sulp. + 2% sil. 62.5 62.5 Buffers Buffers Tap water Tap water 2% silicate 2% silicate ISO brightness AP, % ISO brightness AP, % NaOH NaOH 4.2 4.2 60.5 60.5 58.5 58.5 56.5 56.5 6.5 6.5 7.5 7.5 8.5 8.5 9.5 9.5 10.5 10.5 pH in repulper pH in repulper 28

Conclusion Addition of sodium sulphite in the repulper… • Increases brightness of ONP:OMG – Gains will depend on pH and ERIC – At 2% dosage and ERIC ≈ 200 ppm, gains of 3.0±0.5 % are expected • Seems to reduce ink fragmentation and to increase ink detachment – Effect is small – Mechanism: reduced viscosity of pulp slurry • Reduces shear forces on ink • Reduces ink break-up and redeposition 29

Acknowledgements • Paprican Member Companies 30