Assessment of Methods for the Measurement of Macrostickies in Recycled Pulps

Bruce Sitholé & Denise Filion

10/17/2007 www.fpinnovations.ca 1 Outline

• Classification of stickies • Assessing quality of DIP • How are stickies measured • Evaluation of different methodologies – Their merits and demerits

2 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)

3 Classification of stickies

• More commonly classified into 2 broad classes: – Macrostickies – Microstickies • Later, also classified into: –Macro –Micro – Colloidal

4 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

5 Classification of stickies

• Microstickies – Particles 100-1 µm range – Sources • Small adhesives particles • Coating binders • Ink resins

6 Classification of stickies

• Colloidal – Particles below 1 µm – Particles of insoluble wood resin, SBR, PVA, latexes, emulsified oils

7 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

8 Assessing the quality of DIP

• Quality objectives of recycled printing grade paper

Parameter Specifications Impurities <150 mm2/m2 Stickies, hot melts <100 mm2/m2 Brightness >62% ISO Filler <10%

9 Assessing the quality of DIP

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

10 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

11 Measurement of stickies

Pulp sample

Step 1: collection Disintegration

Screening (150 or 100 µm)

Collect on filter paper or screen

Coating, pressure, Blotter, couch, Copy paper, Step 2: transfer temperature brushing laminator

Manual counting, Step 3: measurement Image analysis

12 Measurement of stickies

• Significant differences in the details of the three steps • Therefore, we evaluated the pros and cons of the methods

13 Objective

• Evaluate the different methodologies • Recommend which one(s) to use for evaluating the quality of recycled pulps

14 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 15 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

16 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

17 Our approach

• Samples analysed by the same personnel in one laboratory • Helps in assessing the merits and demerits of the different methodologies

18 Samples

Site Type of Fibre source Amount mill of sample Mill1 DIP ONP/magazine (70:30) 25 g OD

Mill2 news ONP (100%) 50 g OD

Mill3 tissue MOW 50 g OD

Mill4 paper OCC 25g OD recycled board

19 Methods used

• TAPPI T277 • Total count • Stickies count • Wet specimen • Blue dye • Lamination • Transparency film • Reference method – Manual observation and counting

20 Sample preparation

• Collection step – Pulmac Masterscreen

21 Analysis

Characterization of macrostickies

Physical properties (tacky, gooey, powdery, etc)

Quantification

Scanner (number/area of particles)

22 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.

23 Methods used: Total count • Collect rejects on white filter paper, dry overnight at room temperature • Laminate filter paper • Scan and analyse by image analysis.

24 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

25 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

26 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

27 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

28 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

29 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.)

30 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

31 Image analysis • Software: Image-Pro Plus • Calibrated using image of ruler • Accuracy checked using calibration plate (Micro-Scanner, Paprican)

32 Image analysis: Micro-Scanner

33 Results • Different scanners Sample HP scanner A HP scanner B AGFA scanner

Total Number Total Number Total Number surface of surface of surface of area, mm2 particles area, mm2 particles area, mm2 particles

DIP 13.03 46 13.09 47 8.98 40 ±2.23% ±5.21% ±1.74% ±3.20% ±0.28% ±2.5%

Cleaner 288.35 841 283.10 834 187.32 815 rejects ±3.30% ±0.86% ±2.03% ±0.52% ±0.07% ±0.28%

34 Results • Reproducibility of scanning measurements

Sample Total surface area, mm2 1 scan 5 scans 10 scans % error

DIP 13.01 13.012 13.45 1.7 Cleaner 269.62 277.67 284.23 2.6 rejects Number of particles 1 scan 5 scans 10 scans % error

DIP 45 46 49 4.5 Cleaner 825 831 836 0.66 rejects

35 Results • Effect of location on the scanner

Sample Total surface area, mm2 % error top middle bottom DIP 13.18 13.15 13.25 0.39 Cleaner 284.62 282.55 283.37 2.6 rejects Number of particles top middle bottom % error

DIP 47 46 49 4.5 Cleaner 837 842 842 0.34 rejects

36 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

37 Results: DIP sample 60000

55000

50000

45000

40000

35000

30000 Number

25000 ## particlesparticles per per kg kg 20000

15000

10000

5000

3960 11248 1856 111480 976 38472 528 2690 4696 0 Method 1 Method 2 Method 3 Method 4A Method 4B2 Method 5 Method 6 Method 7 Method 8 S Voith Total BTB Dye Stone Aquan-Yuen + HM

9000

8000

7000

2200

2000

1800

1600 Area 1400

1200

1000 Area, mm²/kg mm²/kgArea, Area, 800

600

400

200 578 1279 3327716 108 1684 92 641 579 0 Method 1 Method 2 Method 3 Method 4A Method 4B2 Method 5 Method 6 Method 7 Method 8

38 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

39 Results: further testing • DIP sample

Total surface Number of area of particles/kg Methods contaminants, pulp mm2/kg area % error Number % error TAPPI 992 13 3124 16 Stickies count 401 17 2028 10 Transparency 798 20 3528 18 Reference 567 28 2950 0.5

40 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

41 Results: further testing • Tissue sample

Total surface Number of area of particles/kg pulp Methods contaminants, mm2/kg area % error Number % error TAPPI 1957 29 4724 21 Stickies count 246 25 1908 22 Transparency 261 11 1136 14 Reference 273 3 5910 5

42 Results: tissue sample

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

43 Results: further testing • 100% OCC mill

Total surface area Number of of contaminants, particles/kg pulp Methods mm2/kg area % error Number % error TAPPI 6,671 12 25,160 15 Stickies 271,779 5 843,611 3 Transparency 42,954 64 169,097 58 Reference n/a n/a 26,120 n/a

44 Results: 100% OCC mill

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

45 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

46 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.

47 Thank you for your attention!

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