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

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Ink detachment, fragmentation and alkali darkening during pulping of ONP/OMG. Part II. Effects of sodium sulphite.

Luc Lapierre, Diane Pitre and Gilles Dorris 8th Research Forum on Recycling 25 September 2007, Niagara ON

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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)

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Lowering the pH in the pulper can lead to many advantages

How to transition from

alkaline to neutral chemistry ?

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Replacing (sodium hydroxide + peroxide) by sodium sulphite

Alkaline pulping (pH 10-10.5):

0.8% NaOH (varies seasonally)

– Deflaking, ink dislodging – Alkaline darkening

1.1% H2O2 (varies seasonally)

– Bleaching

1.8% Silicate

– Slow down peroxide decomposition

0.2% surfactant blend

Neutral pulping (pH 7-8):

1-2% sulphite (varies seasonally)

– Bleaching

0.5-2% Silicate

– Reduces ink fragmentation / increases ink agglomeration – Reduces bound ink

Proprietary additive(s)

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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

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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

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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

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Pulping

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

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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)

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Measurement: Bound ink (undetached + redeposited)

Time Time

Hyperwashing, then 1.2 g handsheet

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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

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9.1

Total ink after pulping

600 800 1000 1200 2 4 6 8 10

Time of pulping (min) ERIC after pulping (ppm)

7.4 8.0 10.3

Decrease in ink fragmentation

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700 800 900 1000 7 8 9 10 11 pH in pulper ERIC after 3 m inutes of pulping (ppm )

Total ink after 3 min. of pulping

vs. pH
Rapid

decrease

Start

leveling off at around pH 8.5

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8.0

Bound ink after pulping

70 7.4 9.1 10.3

70 100 130 160 2 4 6 8 10 Time of pulping (min) ERIC after pulping and hyperwashing (ppm) 100 130 160 2 4 6 8 10 Time of pulping (min) ERIC after pulping and hyperwashing (ppm)

Decrease in bound ink Minimum at around 3 minutes

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70 90 110 7 8 9 10 11 pH in pulper ERI C after 3 m inutes of pulping and after hyperwashing (ppm )

Bound ink after 3 min. of pulping

vs. pH
Linear

decrease

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ISO brightness after pulping

40 8.0 9.1 10.3 7.4

40 41 42 43 44 45 2 4 6 8 10 Time of pulping (min) ISO brightness after pulping (% ) 41 42 43 44 45 2 4 6 8 10 Time of pulping (min) ISO brightness after pulping (% )

Curve at pH 10.3 is not following the expected order ALKALINE DARKENING !

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ISO brightness after hyperwashing

51 52 53 54 55 56 2 4 6 8 10 Pulping time (min) ISO brightness after pulping and hyperwashing (% )

7.4 8.0 9.1 10.3

51 52 53 54 55 56 2 4 6 8 10 Pulping time (min) ISO brightness after pulping and hyperwashing (% )

Plot of ISO brightness at 3 minutes vs. pH At pH 8, best compromise between maximizing ink detachment and minimizing alkali darkening

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52 53 54 55 56 7 8 9 10 11 pH in pulper

I SO brightness after 3 m inutes of pulping and after hyperwashing (% )

ISO brightness after 3 minutes of pulping followed by hyperwashing

No surfactant

added in pulper

Highest ISO bright.

near pH 8

The more the pH

deviates from 8, the more chemical needed to regain brightness

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Part II : Effect of sulphite

Since pH 8 is optimal for brightness, we

decided to test suphite in buffer at pH 8

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Total ERIC after pulping vs. pulping time

700 800 900 1000 1100 1200 2 4 6 8 10 Time, min ERIC AP, ppm

pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

700 800 900 1000 1100 1200 2 4 6 8 10 Time, min ERIC AP, ppm

pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

Reduces ink fragmentation

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80 120 160 200 2 4 6 8 10 Time, min ERIC AW, ppm

pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

80 120 160 200 2 4 6 8 10 Time, min ERIC AW, ppm

pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

Bound ERIC after pulping vs. pulping time

Improves ink detachment

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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

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40 41 42 43 44 45 2 4 6 8 10 Pulping time ISO brightness AP, % pH 8.2 (buffer + sulphite) pH 8.0 (buffer only) 40 41 42 43 44 45 2 4 6 8 10 Pulping time ISO brightness AP, % pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

ISO brightness after pulping vs. pulping time

1.9 2.5

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52 53 54 55 56 2 4 6 8 10 Time, min ISO brightness AW, %

pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

52 53 54 55 56 2 4 6 8 10 Time, min ISO brightness AW, %

pH 8.2 (buffer + sulphite) pH 8.0 (buffer only)

ISO brightness after hyperwashing and pulping

vs. pulping time

1.9 2.5

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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

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Repeated experiments with Unprinted newspaper and Unprinted magazine

Used the same buffers
Compare with 2% sulphite + 2% silicate

– Unbuffered, final pH of 8.3

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ISO brightness AP vs. pulping time

57 59 61 63 2 4 6 8 10 Pulping time (min.) ISO brightness AP, %

7.0 7.8 9.0 9.8 Fully deflaked pulp Sulphite + silicate (pH 10.0 8.3)

57 59 61 63 2 4 6 8 10 Pulping time (min.) ISO brightness AP, %

7.0 7.8 9.0 9.8 Fully deflaked pulp Fully deflaked pulp Sulphite + silicate (pH 10.0 8.3)

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ISO brightness after 10 min. of pulping

vs. pH at 10 min.

56.5 58.5 60.5 62.5 6.5 7.5 8.5 9.5 10.5

pH in repulper ISO brightness AP, %

2% sulp. + 2% sil. Buffers Tap water 2% silicate NaOH

4.2

56.5 58.5 60.5 62.5 6.5 7.5 8.5 9.5 10.5

pH in repulper ISO brightness AP, %

2% sulp. + 2% sil. Buffers Tap water 2% silicate NaOH

4.2

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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

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Acknowledgements

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