Outline

1. Extrusion and folding models for the passage of pressure sensitive adhesive materials through slotted pressure screening devices in paper recycling Richard A. Venditti, Bradley E. Lucas, and Hasan JameelNorth Carolina State UniversityDepartment of Wood and Paper Science 7th Research Forum on Recycling September 27-29, 2004

2. Outline • Industrial screening results • Single slot findings (size, pressure, temperature • Qualitative PSA behavior in single slot • PSA characteristics and passage • Extrusion and folding models • Conclusions

3. Impact of Adhesive Contaminants on Paper Recycling • One adhesive label can generate about 4000 stickies particles during repulping • Stickies cost the paper industry almost $700 million per year due to downgrading of the product, mill downtime, and waste disposal* • Stickies deposit on the paper machine equipment and appear as dirt in the final product

4. Pressure Screening and Adhesive Contaminants Pressure screening considered to be the most effective method to remove adhesive contaminants Typical removal efficiencies are 50-80% for commercial pressure screens

5. Intense Forces in a Pressure Screen Break/Deform Adhesives: Decreases Screening Efficiency “Thousands of small particles generated” Pressure Screening Accepts +Rejects Shredding makes particles more 1-dimensional Feed

6. Removal Efficiency vs Particle Size for an Industrial Screen

7. Outline • Industrial screening results • Single slot findings (size, pressure, temperature • Qualitative PSA behavior in single slot • PSA characteristics and passage • Extrusion and folding models • Conclusions

8. Single Slot Device Top View 0.178 mm 6.35 mm Side View 0.356 mm WATER PI Vacuum WATER

9. Dominant Screening Variable: Particle Size SLOT Width = 0.175 mm

10. Secondary Significant Screening Variables: Pressure and Temperature *Typical Industrial Screening Pressures Cumulative Passage (%) Pressure Difference, kPa *Bliss, T., and Ostoja-Starzewski, M., 1997 Tappi Korea Recycling Symposium, pp. 1-17, 1997.

11. Outline • Industrial screening results • Single slot findings (size, pressure, temperature • Qualitative PSA behavior in single slot • PSA characteristics and passage • Extrusion and folding models • Conclusions

12. PE Film Passes

13. Acrylate PSA During Delta P RampPasses

14. Acrylate PSA During Delta P RampBall Blocked

15. Acrylate PSA During Delta P RampEnd Enters Only

16. Acrylate PSA During Delta P RampMiddle Enters Only

17. Commonly Observed Particle Passage Process indicates Increasing Pressure Difference

18. Outline • Industrial screening results • Single slot findings (size, pressure, temperature • Qualitative PSA behavior in single slot • PSA characteristics and passage • Extrusion and folding models • Conclusions

19. What Characteristics of the PSA Correlate with Passage? • Mechanical properties? • Surface characteristics? • Dimensions? It is already known that the general particle size was important.

20. Sample BA, % BA-EA, % Tack A, % Tack G, % BA 100 0 0 0 BA:A 60 0 40 0 BA:G 60 0 0 40 BA-EA 0 100 0 0 BA-EA:A 0 60 40 0 BA-EA:G 0 60 0 40 Materials • Commercial acrylic adhesive film • Commercial styrene-isoprene-styrene (SIS) • Base polymers (Union Carbide) • UCAR9165 (92% butyl acrylate, BA) • UCAR9175 (50% butyl acrylate and 50% 2-ethylhexyl acrylate, BA-EA) • Tackifiers from Akzo Nobel: • Snowtack 775A (Tack A) • Snowtack 780G (Tack G) • Manually mixed • Applied with coating rod onto litho paper • Dried • Each adhesive pulped separately with copy paper Table 1. Solids Concentrations of Base Polymers and Tackifiers in Adhesive Solutions.

21. Identification of PSA Characteristics that Impact Passage Modulus Yield Strain Yield Stress Contact Angle Glass Trans. Temp Length Width Thickness Area Volume • Analyzed several PSA compositions and characterized the materials • Performed screening expts • Performed a statistical analysis (SAS, analysis of variance) to determine which characteristics were most significant Statistical Analysis Significant Characteristics Lucas, Venditti and Jameel, Progress in Paper Recycling,13(2), 2004.

22. Measurement of the Physical Properties SIS Upper Rod Acrylate Adhesive 7.9 mm 0.45 mm Lower Rod Yield stress ( ) is the stress at which the stress-strain data becomes non-linear (deviates by 1%).

23. Sample Tg, oC Contact Angle, o Yield Strain, % Yield Stress, kPa Modulus, MPa BA -37 80 2.9 25 0.84 BA:A -20 67 0.78 3.0 0.38 BA:G -12 78 3.5 18 0.51 BA-EA -49 98 19 56 0.30 BA-EA:A -23 75 0.67 1.5 0.22 BA-EA:G -16 92 6.4 20 0.31 AC -28 80 0.86 6.0 0.69 SIS -27 92 3.1 44 1.4 Tack A 17 70 - - - Tack G 33 74 - - - Selected Properties of PSA Materials

24. Particle Passage vs Yield Stress Identification of PSA Characteristics that Impact Passage • The Yield stress alone explained 72% of the dependent variable (particle passage) • A model with yield stress + area + yield stress times area explained 90% of the dependent variable (particle passage) • This was motivation to investigate how these variables (yield stress and dimensions) mechanistically impacted passage. • Extrusion and Folding Models utilize yield stress and size Predicted Passage with YS, A, YS*A Model Lucas, Venditti and Jameel, Progress in Paper Recycling,13(2), 2004.

25. Identification of PSA Characteristics that Impact Passage Modulus Yield Strain Yield Stress Contact Angle Glass Trans. Temp Length Width Thickness Area Volume • Analyzed several PSA compositions and characterized the materials • Performed screening expts • Performed a statistical analysis (SAS, analysis of variance) to determine which characteristics were most significant • The statistical analysis results indicated that PSA yield stress and average area had the strongest correlation with % particle passage Statistical Analysis Yield Stress Area Lucas, Venditti and Jameel, Progress in Paper Recycling,13(2), 2004.

26. Outline • Industrial screening results • Single slot findings (size, pressure, temperature • Qualitative PSA behavior in single slot • PSA characteristics and passage • Extrusion and folding models • Conclusions

27. Objective • Evaluate the passage of PSA particles with respect to extrusion and folding models that involve the yield stress and dimensions of particles Bliss, T., and Ostoja-Starzewski, M., 1997 Tappi Korea Recycling Symposium, pp. 1-17, 1997.

28. Extrusion Model P1 Particle • Plastic yielding (permanent deformation) of a material through an opening • With two forces at opposite ends of the object, extrusion will occur at the following condition: P2 Wslot WPart LPart

29. P1 P2 Results of the Extrusion Model Yield stress of 15 kPa from slope is within the range of yield stresses of the PSA materials (1-60 kPa). Y = m X

30. P1 D=Tpart P2 Folding Model • Plastic yielding (permanent deformation) of a material through bending • Maximum load, WP, a centrally loaded simply supported beam can support: Wslot L=WPart b=LPart

31. Results of the Folding Model P1 P2 Slope of 30 kPa is within the range of the yield stresses of the PSA materials (1-60 kPa). Y = m X

32. Conclusions • The single slot device is a useful research tool • Simplicity is a limit and an advantage • Unambiguous results: size, pressure and temperature • PSA particles in the simplified single slot enviroment • Rotate, sections enter, pass/are blocked • Bending and folding mechanisms may both contribute to passage • According to general agreement of data and models • Scatter of data in models suggests a more complex mechanism