The Breakage of Pressure Sensitive Adhesive Contaminants in
The Breakage of Pressure Sensitive Adhesive Contaminants in Paper Recycling Operations Brad Lucas Advisors: Dr. R. A. Venditti and Dr. H. Jameel North Carolina State University 2000 TAPPI Pulping Conference
Stickies Impact Stickies are the greatest challenge in recycling operations l Stamps, labels, envelopes, etc. are the source of adhesive material in wastepaper l Repulping the wastepaper breaks down the adhesive material into stickies l One adhesive label can generate about 4000 stickies particles l
Outline Background l Objective l Results l Conclusions l Future Work l
Background l l Screening, in general, is considered to be the most effective way to remove adhesive contaminants Various researchers have found removal efficiencies of adhesive contaminants ranging from -14 to 83% using pressure screens
Previous Pilot Plant Stickies Screening Research at NCSU Overall stickies removal efficiencies ranged from 39 to 72% depending on the reject rate l Negative removal efficiencies occurred for small particles in the pressure screen due to breakage of large particles l Heise et. al. found that the probability of disintegration of large particles increased with consistency l Lucas, B. E. , Venditti, R. A. , and Jameel, H. , Analysis of Stickies Removal Using Pilot Plant and Laboratory Screening Devices, in press Tappi Journal, 2000.
Screen Removal Efficiency vs. Particle Size and Reject Rate
Shear Stress in a Pressure Screen l l l Pressure screens are second only to the fan pump in shear stress for the wet end of the paper machine High shear forces can occur due to movement of the foil across the pulp mat formed on the face of the screen plate Shear forces also occur when material is passing through the slots
Objective of the Study: l To determine the effect of shear conditions on the breakage of adhesive particles l Approach: Study the breakage of adhesive particles in a well-controlled high shear pulp mixer
Experimental Procedure Copy Paper with Adhesive Labels (1% by wt. ) Samples Pilot Plant Pulper 10% K, 45 C, 20 min 80 OD lbs. Quantum High Shear Mixer 3 liters Handsheets Dyeing/ IA
High Shear Mixer Experiments l Full Factorial Design Experiment with a Center Point was conducted
Dyeing of Handsheets for Stickies Contrast Enhancement handsheet Morplas Blue - Heptane Dye Solution
Increased Contrast of Stickies after Dyeing and Rinsing Undyed Dyed
Question: l Was our method sensitive to changes in the stickies particles due to the independent variables studied? l Approach: Compare the number of particles in 1 m 2 (and average particle size) for the samples treated under different shear conditions.
Handsheets from Different Shear Conditions Untreated Low Conditions High Conditions
Number of Particles in 1 m 2 vs. Shear Conditions
Average Particle Size vs. Shear Conditions
Stickies Size Distribution Untreated and Treated (Low Conditions)
Stickies Size Distribution Untreated and Treated (High Conditions)
Question: l Which variables were most significant for breakage of adhesive particles in the high shear mixer? l Approach: statistical analysis and modeling of the four independent variables.
Statistical Analysis and Modeling l Independent Variables n Consistency, Time, Temperature, Rotor Speed n All interactions l Dependent Variables n PPM, Number of Particles in 1 m 2, and Average Particle Size Pareto Analysis l Modeling Procedures l n GLM, Maximum R, Backward
Pareto Chart for Number of Particles in 1 m 2
Pareto Chart for Average Particle Size
Statistical Model to Predict Number of Particles in 1 m 2 = 3218 + 8. 636*Consistency - 17. 80*Time + 15. 89*Temperature + 2. 694*Consistency*Time + 0. 3235*Time*Temperature l R 2 = 0. 86 l
Statistical Model to Predict Average Particle Size, mm 2 = 1. 012 - 0. 03197*Consistency - 0. 0007241*Time - 0. 004725*Temperature l R 2 = 0. 61 l
Predicted vs. Actual Number of Particles in 1 m 2
Predicted vs. Actual Average Particle Size
Question: l What is the relationship between breakage and each of the significant variables? l Approach: Vary each of the significant variables while keeping the other variables constant.
Consistency Experiment Consistency: 1, 3, 4. 5, 6, 9, 10. 5, 12, 14% l Time: 165 seconds l Initial Temperature: 35 o. C l Rotor Speed: 1500 rpm l
Number of Particles in 1 m 2 vs. Consistency
Average Particle Size vs. Consistency
Shear Stress for Pulp Suspensions Newtonian fluid t = m(du/dy) l Bingham fluid t = ty + m(du/dy) ty = a. Cb, b > 2 m = d. Ce, e > 2 l
Consistency Conclusions As the consistency increases, the number of particles in 1 m 2 increases (average particle size decreases) l Breakage of adhesive particles is significant at consistencies greater than 6% l At consistencies greater than 6%, breakage increases with consistency l
Temperature Experiment Initial Temperature: 25, 35, 55, and 75 o. C l Consistency: 7. 5% l Time: 165 seconds l Rotor Speed: 1500 rpm l
Number of Particles in 1 m 2 vs. Initial Temperature
Average Particle Size vs. Initial Temperature
Effect of Initial Temperature on Particle Sizes
Temperature Conclusions As the initial temperature increases, the number of particles in 1 m 2 increases (average particle size decreases) l As the initial temperature increases, the particle size distribution is shifted toward smaller particles l
Time Experiment Time: 0, 30, 60, 90, 120, 150, 180, 360 sec l Consistency: 10% l Initial Temperature: 35 o. C l Rotor Speed: 1500 rpm l
Number of Particles in 1 m 2 vs. Time
Average Particle Size vs. Time
Overall Conclusions Consistency, time, and initial temperature significantly affect breakage of stickies l Rotor speed was not found to be significant l At consistencies greater than 6%, breakage increases with consistency l
Implications of Results In a recycling operation, processes that have high shear, consistency and temperature will break adhesive particles l Such conditions should be avoided before adhesive particles are removed l Reductions in the consistency of the fiber mat on the screen basket are expected to reduce breakage and increase screening efficiency l
Future Work Evaluate benign and non-benign adhesives in the high shear mixer l Calculate and compare the forces in the pressure screen and in the high shear mixer l Determine the effect of particle size on breakage of adhesive particles l
Acknowledgements Ecosynthetix l SCA Corporation l Apogee Systems l Boise Cascade l
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