‘LUENCINGSTlCKlES FORMATION

~- Changes in mill chemistry drastically aftkt lab tests BY K. CATHIE, R. HAYDOCK AND I. DlAS

chemicals in clean systems. trolled carefully. Acrylate polymer was the main chemical component of the adhesive on the labels. This adhesive OEASUREMEHTtype was chosen as it is commonly To determine the factors influenc- found in mill deposits. ing stickies deposition, a test to mea- The test procedure involves two sure this feature had to be developed. polyester machine forming fab- The test had to fulfil several criteria; it rics which are inserted into aluminum had to be reproducible, sensitive to frames and counter-rotated in a stock changes in processing conditions and suspension at a speed of 60 rpm, Fig. 1. simulate mill situations. The stock suspension is maintained at Virgin fibre , artificially contam- 45 to 50°C to enhance sticky tack and inated with self-adhesive labels, was more closely simulate mill conditions. used to develop the test. The amount Stock consistency is 0.5%. At the end of and type of stickies present in the stock testing the wires are removed, rinsed suspension could therefore be con- and the stickies adhering to them

ELECTRIC MOTOR

RPM DISPLAY

GEARS (SIDE VIEW)

HIS PAPER OUTLINES research done to elucidate the funda- T mental factors influencing stick- ies formation and deposition. The work was carried out as part of a 22-month research project funded by the European Commission and indus- try. It was thought that from fundamen- tal studies examining why stickies are sticky in mill systems, new techniques for controlling or preventing sticky problems could be developed. Studies covered two areas: Development of a method to measure sticky deposition. Effect of variables and \ T392 4 PULP & PAPER CANADA 93:12 (1992) 157 numerous, larger, less tacky stickies pro- determined by weight or area. pulping stage on stickies deposition ', In the development of the test, tendency were evaluated using the duced by acid or neutral pulping would three variables were investigated; the deposition test, Fig. 1. be far easier to screen out of a paper method of sticky contamination mea- Pulping at a neutral or acid pH mill system. surements, test duration, and sticky resulted in little deposition on the fab- contamination level. rics irrespective of test pH, Table 11. @ALCIUM IONS Test reproducibility was improved Slightly more deposition occurred with with increased testing time to 30 min- these pulping pHs at an acid test pH. Calcium ions were found to have a utes. Interestingly, increasing the Test sensitivity is, however, reduced large effect on the deposition charac- amounts of the adhesive in the stock when deposition is so low. teristics of this sticky type. Sticky forma- resulted in a greater deposition of stick- The average size of stickies deposit- tion in this case was not assessed. Addi- ies on the fabrics, but an overall reduc- ed on the test fabrics was unaffected by tion of calcium chloride to the stock tion in removal efficiency. pH. Larger stickies produced on pulp- suspension to give a water hardness of Assessment of sticky deposition ing under neutral or acid conditions using area measurements via image did not adhere to the test fabrics. As analysis in comparison to weight mea- the test detects large stickies, this result surement gives additional information suggests again that stickies produced Pulping on the physical characteristics of stick- under alkaline conditions have the 30g softwood bleached kraft ies such as their size and surface fea- greatest tack and, therefore, deposition 30g hardwood bleached kraft tures. This was therefore chosen as the tendency. 0.29 adhesive (from self adhesive labels) measurement method for the rest of Differences in stickies formation 15 cm3 x 6g/L sodium hydroxide the work. and deposition under different pH (to adjust the pH to 10-10.5) regimes are thought to be due to two 3.0% consistency factors: @LEAN SYSTEMS Chemistry of the acrylate polymer Sticky deposition Effect of papermaking variables and adhesive; 0.5%consistency chemicals in clean systems: The role of Release of materials during disinte- 45-50" c different pH conditions, calcium ions gration, such as hemicelluloses. pH 9.5 and a wire-cleaning chemical in the cre- Both are likely to affect sticky char- ation of tacky sticky particles was acteristics at different pHs. Sticky formation assessed using virgin fibre pulp artifi- Alkaline pulping, practised by many Sommerville screen 0.15 mm cially contaminated with self-adhesive mills using waste paper, produces acry- slotted screen plate labels, as described in the earlier sec- late polymer stickies with the worst 20 minutes screening duration tion. Testing conditions are outlined in characteristics for removal. The less Table I. Effect of pH: The effect of pulping pH Number of stickv Darticles on sticky formation is well known. How- ever, its effect on tack and the effects of changes in pH through further stock preparation are not well documented. Changes in sticky characteristics through alterations in pulping and test pH were therefore assessed. Pulping pH The effect of alterations in pulping pH on the size and number of stickies formed was assessed by screen- ing the stock over a 0.15-mm-slotted screen plate and measuring the stickies by image analysis. Alkali Neutral Acid Pulping pH affected sticky forma- Pulping pH tion. Pulping at alkaline pH (10.5) pro- duced approximately four times as many sticky particles in contrast to acid pH, and neutral pH, Fig. 2. These stick- ies were also much smaller. Average size Area of sticky deposition ("-2) Mean size of sticky panicies (mm-2) of stickies produced at alkaline pH was

0.3 mm*. Stickies of 0.57 mm2 and 0.76 - mm2 were produced at neutral and 0.8 acid pHs respectively. - 0.6 Using data from this test, Fig. 2, and 30 the deposition results, Table 11, it - 20 0.4 appears that stickies formed under alka- - line conditions were also more tacky. 1C 0.2 Up to 28% of stickies formed under I .* alkaline conditions adhered to the 0 -10 polyester test fabrics. Only a maximum 0 30 60 eo 120 of 20% of those formed under acid con- Water Hardness (PPd ditions, and 11% of those produced * Sticky deposition -tSticky size under neutral conditions, deposited on I the fabrics. Testing pH: Changes in pH after the

158 PULP 81PAPER CANADA 93:12 (1992) 4 T393 only 30 parts per million (ppm), become more tacky, either by contami- decreased subsequent sticky area nation of the stock system or due to a @ONCLUEIONS deposited on the test fabrics by approx- residue of the cleaning chemical on the imately 7076, Fig. 3. fabric. This work has shown that the forma- Changes in sticky deposition were The chemical reduces the surface tion and deposition characteristics of accompanied by changes in particle charge characteristics of the fabric. stickies are highly complex. Many inter- size. Mean sticky size was doubled by the addition of calcium chloride to 30 ppm water hardness. Water hardness at the pulping stage, Pulping Test Number of Area of sticky Average rather than at tack testing determined PH PH sticky particles deposition (mm2) sticky size ("2) sticky deposition. Reduction in sticky deposition on Alkali Alkali 135 29.1 0.2 the fabrics is thought to be due to the Alkali Neutral 99 24.5 0.2 calcium ions neutralizing the negative Alkali Acid 99 25.0 0.3 charges on the sticky particles causing them to agglomerate. These larger par- Neutral Alkali 2 0.3 0.2 ticles then do not adhere due to the Neutral Neutral 6 1.9 0.3 hydrodynamics of the system, reduction Neutral Acid 15 4.6 0.3 in available surface area or reduction in charge, all of which lessen their affinity Acid Alkali 3 0.3 0.1 for the polyester fabrics. Alternatively, Acid Neutral 8 1.9 0.2 the reduction in deposition may be due Acid Acid 13 5.0 0.3 to the 'hardness' of the adhesive. Calci- um could cause acid groups to crosslink, which might reduce tack. Although the deposition potential of this sticky type is reduced by the pres- Wire cleaning agent Area of sticky deposition ("2) ence of calcium ions, the presence of larger sticky particles could cause Water 21.9 problems other than deposition, for example, dry end breaks, printing blan- Paraffin-basedchemical 40.4 ket contamination, etc. @LEANING AGENTS Tissue mills sometimes experience a sudden build-up of stickies on their forming fabrics after 40r-----J the use of proprietary cleaners. The question was therefore raised whether 30 t these cleaners influence sticky forma- tion or deposition characteristics. A paraffin solvent-based wire cleaner lot applied to the polyester test fabrics - before testing had a dramatic effect on 0 6 10 16 sticky deposition. The area of stickies Time (minuted adhering to the test fabrics with adhering +Chnln@ CI*lW +Control stickies was increased by SS%, Table 111. To assess whether this effect was due to changes in the fabric's surface or the stickies themselves, the paraffin solvent- based cleaning agent was added direct- R6sumO: Cette communication d6crit les recherches menkes dans le but de mieux com- ly to the stock suspension. A small prendre les facteurs fondamentaux influenCant la formation et le6 d6pBts de particules col- amount of the chemical (1 mL in 12 lantes. litres of stock at 0.5% consistency) increased deposition by 30%. Abstract: This paper outlines research done to increase understanding of the fundamen- Additionally, after cleaning with the tal factors influencing stickies formation and deposition. A laboratory method developed to chemical and rinsing, if the fabrics are evaluate sticky tack is described. Results obtained from the use of this apparatus to evaluate counter-rotated in a stock suspension the effect of different papermaking chemicals and variables on sticky formation and deposi- containing no stickies before tack test- tion under laboratory conditions are highlighted. ing, the effect on sticky tack is reduced. As this time is extended deposition is Reference: CATHIE, K., HAYDOCK, R., DIAS, I. Understanding the fundamental factors reduced, but not the level of the con- influencing stickies formation and deposition. Pu& Paper Can 93(12): T392-395 (Dec.1992). Paper presented at the 1991 Research Forum on Recycling of the Technical Section, CPPA, trol, Fig. 4. The effect of the chemical is at Toronto, Ontario, on October 29 to 31, 1991. Not to he reproduced without permission. therefore not easily reversed. Manuscript received September 3, 1991. Revised manuscript approved for publication by the The increase in deposition tendency Review Panel June 12, 1992. of this type of sticky in the presence of the chemical therefore appears to be Keywords: ADHESIVES, FORMATION, DEPOSITION, VARIABLES, CLEANERS, TEST due to either of the following reasons: METHODS, WASTE , PAPER MAKING, SIMULATION, EQUIPMENT. The chemical causes stickies to

PULP & PAPER CANADA 93:12 (1992) 159 \ T394 !

related variables contribute to the problem. The work has also illustrated the problems associated with laboratory A Natural studies related to mill conditions. Sim- ple changes in mill chemistry, for example water hardness, appear to have a drastic effect on stickies when Evolution in examined in the laboratory. Careful consideration of mill conditions must be observed in studies to assess sticky Engineering behavior.

Excellence+ OCKNOWLEDGEMENTS~~ The authors acknowledge the finan- cial assistance of the CEC and individu- Experience. Excellence, Enthusiasm. All are al sponsoring companies. Technical qualities that have helped Neill and Gunter assistance from sponsoring companies was also invaluable. Additional help grow into one of Eastern Canada’s foremost and advice came from Betz Ltd., the design and consulting engineering companies. industrial partner of this project. We have become an important resource Sponsoring companies included: Beloit Gorp., USA; Betz Ltd., England; for the as a result of our Bridgewater Paper Company, England; expertise in such critical areas as Instrumentation Compania Manufacturers De Papeles Y Cartones, Chile; Garden State Paper and Controls, Air Emissions, Energy Generation Co., USA, Grace Dearborn Ltd., Eng- and Solid Waste Management. land; Henkel-Nopco Ltd., England; The recent acquisition of Owen Washbum James River Corporation, USA; Kao Corporation GmbH, USA; Kao Corpo- Associates Ltd., environmental specialists, is ration, Japan; Kimberly Clark Ltd., representative of our determination to meet the England; Nippon Kakoh Seishi-KK, increasingly complex needs of the Industry. Japan; Noranda Technology Centre, Canada; Reedpack Ltd. (now SCA Through advanced technology, skilled Aylesford Ltd.), England; Stephenson professionals and a dedication to creating innov- Bros Ltd., England; Tokai Pulp Co Ltd., Japan; United Paper Mills, Finland. ative solutions to unique problems, Neill and Gunter has naturally evolved into a company renowned for engineering excellence. REPRINTS of articles AJi!dL&GbW%Z& and technical Design Consulting Engineers and papers Fredericton, NB (506) 452-7000 Dartmouth, NS (902) 434-7331 are available. Scarborough, ME (207) 883-3355 Call us.

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160 PULP & PAPER CANADA 93:12 (1992) 4 T395