10/17/2007 www.fpinnovations.ca 1

Assessment of Methods for the Measurement of Macrostickies in Recycled Pulps

Bruce Sitholé & Denise Filion

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Outline

• Classification of stickies• Assessing quality of DIP• How are stickies measured• Evaluation of different methodologies

– Their merits and demerits

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Classification of stickies

• Doshi and Dyer classified stickies by physical and chemical properties– Chemistry (PSA, hot melts, or both)– Screening (macro and micro)– Behaviour (viscoelastic and rigid)– External factors (primary and secondary)– Association (bound to fibres and free)– Compatibility (recycle-compatible & recycle-

incompatible)– Visibility (visible and sub-visible)

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Classification of stickies

• More commonly classified into 2 broad classes:– Macrostickies– Microstickies

• Later, also classified into:– Macro– Micro– Colloidal

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Classification of stickies

• Macrostickies– Solid particles resulting from incomplete

disintegration during repulping– Particle size exceeds 100 µm– Can be removed by coarse screening– Major sources

• Hot melts, PSAs

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Classification of stickies

• Microstickies– Particles 100-1 µm range– Sources

• Small adhesives particles• Coating binders• Ink resins

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Classification of stickies

• Colloidal– Particles below 1 µm– Particles of insoluble wood resin, SBR,

PVA, latexes, emulsified oils

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Assessing the quality of DIP

• Variable and mill specific• Commonly assessed by amount and

size of particles• Acceptable pulps

– 10 or less particles per 100 g OD pulp– Maxim size of 0.4 mm2 per particle

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Assessing the quality of DIP

• Quality objectives of recycled printing grade paper

<150 mm2/m2

<100 mm2/m2

>62% ISO<10%

ImpuritiesStickies, hot meltsBrightnessFiller

SpecificationsParameter

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Assessing the quality of DIP

• It is evident that macrostickies define the quality of DIP recycled printing papers

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How are they measured?

• Literature review and discussions with mill personnel show large variety in methods used

• The methods are based on three principles– Collection– Transfer– Measurement

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Measurement of stickiesPulp sample

Disintegration

Screening(150 or 100 µm)

Collect on filter paper or screen

Coating, pressure,temperature

Blotter, couch,brushing

Copy paper,laminator

Manual counting,Image analysis

Step 1: collection

Step 3: measurement

Step 2: transfer

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Measurement of stickies

• Significant differences in the details of the three steps

• Therefore, we evaluated the pros and cons of the methods

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Objective

• Evaluate the different methodologies• Recommend which one(s) to use for

evaluating the quality of recycled pulps

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Previous work• Doshi et al (2003) compared four

methods for measuring macrostickies• Model and real samples were analysed

by 4 labs– Black ink method– INGEDE method– Enzyme digestion method– Blue dye method

• All methods used image analysis– Average # and size of contaminants

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Previous work

• Conclusion– considerable variations in actual values

of stickies area reported by the participating groups

• Not surprising due to significant differences in the methods used to measure the concentration of macrostickies

– excellent linear correlation among all methods for both laboratory as well as mill samples

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Previous work

• Conclusion– Any one of the methods was

suitable for monitoring stickies content

– But one could not compare actual values from the different labs as they may vary significantly

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Our approach

• Samples analysed by the same personnel in one laboratory

• Helps in assessing the merits and demerits of the different methodologies

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Samples

25 g OD

50 g OD

50 g OD

25g OD

ONP/magazine (70:30)

ONP (100%)

MOW

OCC

DIP

news

tissue

paperrecycled

board

Mill1

Mill2

Mill3

Mill4

Amount of sample

Fibre sourceType of mill

Site

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Methods used

• TAPPI T277• Total count• Stickies count• Wet specimen• Blue dye• Lamination• Transparency film• Reference method

– Manual observation and counting

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Sample preparation

• Collection step– Pulmac Masterscreen

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Analysis

Physical properties

Quantification

Scanner

Characterization of macrostickies

(tacky, gooey, powdery, etc)

(number/area of particles)

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Methods used: TAPPI T277

• Collect rejects on a black filter paper• Place coated paper on top of the rejects• Sandwich filter paper and coated paper

between two blotters• Heat and press for 10 min • Wash to remove other material • Cover with silicon release paper: heat

and dry• this transfers the silicone onto the stickies to

make them more visible for image analysis.• Eliminate fibres prior to scanning and

image analysis.

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Methods used: Total count• Collect rejects on white filter paper, dry

overnight at room temperature• Laminate filter paper • Scan and analyse by image analysis.

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Methods used: Stickies count• Collect rejects on white filter paper• Place blotter on top, press with couch roll

and remove• Place second blotter on the rejects and

press with couch roll• Dry both blotters (with rejects) at 110oC for

exactly five minutes• Use paint brush to remove other materials• Place transparency film on top of each

blotter• Scane and analyse by image analysis

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Methods used: Wet specimen

• A black palette with uniform flat surface• Wet specimen is rolled with a soft roller to

remove the air formed between it and the palette

• A shallow box with a transparent bottom that is placed on the image analysis glass

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Methods used: Blue dye

• Disintegrate, 1.2 g handsheets• Couch, discard second wet blotter, replace

by a third one to protect the handsheet• Dry• Apply the blue dye to the backside of the

blotter• Evaporate heptane solvent in the dye • Peel dyed handsheet, scan, image

analysis

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Methods used: Lamination

• Collect rejects on white filter paper• Dry• Place facedown on white copy paper• Place another copy paper on the filter

paper to make a protective pocket• Pass twice through a laminator at 125oC • Staple a transparency film onto the copy

paper with the contaminants • Scan, image analysis

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Methods used: Transparency film

• Collect rejects onto a white filter paper• Place wet filter paper, stickies side down,

on image side transparency• Place blotter paper on top • Sandwich filter paper, transparency, and

blotter into paper folder• Pass sandwiched sheets, twice through

laminator set at 125oC• Remove blotter and filter paper, allow

transparency to air-dry• Protect transparency with another

transparency, scan, image analysis

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Methods used: Reference method

• Collect rejects on a white filter paper• Place another filter paper on top of the

rejects• Dry by heating and pressing • Examine each filter paper under a low-

power stereo microscope with aid of a needle

• Manually count contaminants, classify into– the different classes (stickies, hot melts,

plastics, others.)

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Evaluation of the different methods• To facilitate processing, a DIP sample was

first evaluated using all the methods• Three most promising ones were then

selected for further testing on the rest of the pulp samples

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Image analysis• Software: Image-Pro Plus• Calibrated using image of ruler• Accuracy checked using calibration plate

(Micro-Scanner, Paprican)

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Image analysis: Micro-Scanner

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Results• Different scanners

815±0.28%

187.32±0.07%

834±0.52%

283.10±2.03%

841±0.86%

288.35±3.30%

Cleanerrejects

40±2.5%

8.98±0.28%

47±3.20%

13.09±1.74%

46±5.21%

13.03±2.23%

DIP

Number of

particles

Total surface

area, mm2

Number of

particles

Total surface

area, mm2

Number of

particles

Total surface

area, mm2

AGFA scannerHP scanner BHP scanner ASample

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Results

0.66836831825Cleaner rejects

4.5494645DIP

% error10 scans5 scans1 scanNumber of particles

2.6284.23277.67269.62Cleaner rejects

1.713.4513.01213.01DIP

10 scans5 scans1 scan % errorTotal surface area, mm2Sample

• Reproducibility of scanning measurements

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Results• Effect of location on the scanner

0.34842842837Cleaner rejects

4.5494647DIP

% errorbottommiddletopNumber of particles

2.6283.37282.55284.62Cleaner rejects

0.3913.2513.1513.18DIP

bottommiddletop % errorTotal surface area, mm2Sample

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Results

• Reproducibility of the scanning measurements– Placement of sample on scanner does not

affect the data generated– Scanner generates very reproducible data

irrespective of the number of scans

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Results: DIP sample

578 1279 332 108 1684 92 641 5790

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

7000

8000

9000

Method 1 Method 2 Method 3 Method 4A Method 4B2 Method 5 Method 6 Method 7 Method 8

Are

a, m

m²/k

g

7716578 1279 332 108 1684 92 641 5790

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

7000

8000

9000

Method 1 Method 2 Method 3 Method 4A Method 4B2 Method 5 Method 6 Method 7 Method 8

Are

a, m

m²/k

g

7716

3960 11248 1856 111480 976 38472 528 2690 46960

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Method 1Voith

Method 2Total

Method 3BTB

Method 4A Method 4B2 Method 5Dye

Method 6Stone

Method 7Aquan-Yuen

Method 8 S+ HM

# pa

rticl

es p

er k

g

3960 11248 1856 111480 976 38472 528 2690 46960

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Method 1Voith

Method 2Total

Method 3BTB

Method 4A Method 4B2 Method 5Dye

Method 6Stone

Method 7Aquan-Yuen

Method 8 S+ HM

# pa

rticl

es p

er k

g

Number

Area

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Results: DIP sample• Total count

– Measures total # of contaminants– Particles that are not macrostickies also

counted• Wet specimen (4A)

– Gave unrealistic results (25X larger than reference method)

– Particles that are not macrostickies also counted

• TAPPI & Transparency methods– Results very close to reference method

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Results: further testing

0.5295028567Reference 18352820798Transparency10202817401Stickies count 16312413992TAPPI

% errorNumber% errorarea

Number of particles/kg

pulp

Total surface area of

contaminants, mm2/kg

Methods

• DIP sample

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Results: DIP sample

• Significant differences in surface areas of contaminants– Reflection of different drying procedures– Methods that require pressure induce

deformation• TAPPI method agrees well with the

reference method in number of particles

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Results: further testing

559103273Reference 14113611261Transparency22190825246Stickies count 214724291957TAPPI

% errorNumber% errorarea

Number of particles/kg pulp

Total surface area of

contaminants, mm2/kg

Methods

• Tissue sample

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Results: tissue sample

• Stickies count and transparency methods– Best results in agreement with reference

method

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Results: further testing

n/a26,120n/an/aReference 58169,0976442,954Transparency3843,6115271,779Stickies1525,160126,671TAPPI

% errorNumber% errorarea

Number of particles/kg pulp

Total surface area of contaminants,

mm2/kgMethods

• 100% OCC mill

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Results: 100% OCC mill

• TAPPI method gives results similar to those of the reference method

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Conclusions

• TAPPI method results are comparable to manual reference method– Therefore, image analysis using this

method is acceptable for rapid measurement of macrostickies

• There is no correct method to measure areas of contaminants– Therefore, evaluation of stickies should not

be based on area but on number of particles

• Contrast between background and contaminants is a big problem in image analysis

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Conclusions

• Image analysis does not work well on highly contaminated samples collected on 100 µ m screens– Particles hidden under fibres and shives– Best to use 150 µm screen

• If interested in evaluating contaminants, beside macrostickies, use Table X as a guide to method of choice.

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Thank you for your attention!