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 mm 2 per particle 8
Assessing the quality of DIP • Quality objectives of recycled printing grade paper Parameter Specifications <150 mm 2 /m 2 Impurities <100 mm 2 /m 2 Stickies, hot melts 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 Disintegration Step 1: collection 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 Mill 4 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 110 o C 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 125 o C • 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 125 o C • 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, mm 2 area, mm 2 area, mm 2 particles particles particles 13.03 46 13.09 47 8.98 40 DIP ± 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 Total surface area, mm 2 Sample % error 1 scan 5 scans 10 scans 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 Total surface area, mm 2 Sample % 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
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