Development of Extrusion Instabilities and Surface Irregularities for Polymers and Filled Polymers

1. Development of Extrusion Instabilities and Surface Irregularities for Polymers and Filled Polymers D.Kalyon, E. Birinci and H. Gevgilili Stevens Institute of Technology October, 2002 12th Extruder and Continuous Mixers Users Group Meeting

2. Outline • We studied PDMS, HDPE and BAMO/AMMO-ETPE for wall slip behavior in steady torsional flow and development of surface irregularities in capillary flow • Compare with filled PDMS (10,20,40% by volume hollow glass spheres) and KCl Filled BAMO/AMMO.

3. Important points • Materials which do exhibit strong slip exhibit flow instabilities during extrusion commencing at the shear stress at which strong slip is observed. Incorporation of rigid particles at the right concentration eliminates all types of surface irregularities during extrusion. • Melt which does not exhibit strong slip for relatively high strains and shear rates does not exhibit surface irregularities in the same shear rate range. However, the incorporation of rigid particles introduces surface irregularities during extrusion.

4. Conclusion • It appears that the stability of stick or slip at the wall during extrusion governs the occurrence of surface irregularities. • It is not clear what controls the stability of the boundary condition.

6. HDA 601 high density polyethylene available from Exxon-Mobil Chemical Company Melt flow index=0.55 (according to ASTM D-1238) Density=0.933 g/cm3 (according to ASTM D-1505) • Polydimethylsiloxane (PDMS SE-30) manufactured by GE Silicones Density=0.98 g/cm3 at 30°C • A Thermoplastic Elastomer: BAMO-AMMO available from ATK Thiokol Propulsion

7. Structure of BAMO-AMMO Consisting of of 3, 3-bis (azidomethyl) oxetane, BAMO, which is a crystalline homopolymer and the soft block consisting of 3-azidometyl-3-metyloxetane, AMMO, which is an amorphous homopolymer, forming the soft block of this energetic thermoplastic elastomer

8. gׂ=70 s-1, t=0.1 s, g=7 Sample ejection from the gap gׂ=60 s-1 gׂ=50 s-1 gׂ=70 s-1 gׂ=23 s-1 gׂ=10 s-1 gׂ=5 s-1 gׂ=10 s-1, t=1 s, g=10 t=0 s, g=0 HDPE steady torsional flow

9. gׂ=70 s-1 gׂ=60 s-1 gׂ=25 s-1 gׂ=10 s-1 gׂ=50 s-1 gׂ=1 s-1 gׂ=0.1 s-1 HDPE steady torsional flow

10. gׂ=30 s-1 gׂ=40 s-1 gׂ=20 s-1 gׂ=5 s-1 gׂ=10 s-1 gׂ=2 s-1 gׂ=1 s-1 gׂ=0.1 s-1 gׂ=2 s-1, t=3.5 s, g=7 gׂ=40 s-1, t=0.15s, g=6 t=0 s, g=0 PDMS steady torsional flow

11. gׂ=30 s-1 gׂ=10 s-1 gׂ=5 s-1 gׂ=20 s-1 gׂ=2 s-1 gׂ=40 s-1 gׂ=1 s-1 gׂ=0.1 s-1 PDMS steady torsional flow, first normal stress difference

12. gׂ=200 s-1 gׂ=150 s-1 gׂ=100 s-1 gׂ=30 s-1 gׂ=10 s-1 gׂ=1 s-1 gׂ=0.1 s-1 BAMO/AMMO TPE steady torsional flow

13. Transducer overload gׂ=200 s-1 gׂ=150 s-1 gׂ=10 s-1 gׂ=100 s-1 gׂ=30 s-1 gׂ=1 s-1 gׂ=0.1 s-1 gׂ=0.05 s-1 BAMO/AMMO TPE steady torsional flow

14. Critical wall shear stress values at which strong wall slip is initiated in steady torsional flow • HDPE: • @ 170C tc=0.22 MPa • @ 190C tc= 0.22 MPa • @ 210C tc= 0.23 MPa • PDMS: • @ 10C tc= 0.067 MPa • @ 30C tc= 0.069 MPa • @ 50C tc= 0.068 MPa • No strong wall slip for BAMO/AMMO TPE for strains up to 20 even at shear rates as high as 200 s-1.

15. D=0.375” 45°angle D L The angle of convergence was varied between 15, 45 and 75 degrees.

16. Conclusions • The shear stress at the onset of catastrophic failure of the no-slip condition in steady torsional flow coincides with onset of flow instabilities in capillary flow • TPE which does not exhibit strong slip up to high strains (20) and strain rates (200 s-1) in steady torsional flow also does not exhibit flow instabilities in capillary flow

17. Conclusions • The critical shear stress at the point of catastrophic failure of the no-slip condition is temperature independent for PDMS and HDPE. • Results emphasize the central role played by wall slip in the development of the flow instabilities

18. What happens to development of surface irregularities in extrusion flow when we fill these polymers with rigid fillers?

19. 1,000,000 100,000 CORRECTED SHEAR STRESS, Pa 10,000 0.01 0.10 1.00 10.00 -1 CORRECTED SHEAR RATE, s KCl filled BAMO/AMMO TPE

20. PDMS + Glass Sphere(10% by vol.) Mixture Corrected Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Diameters

21. D=0.098 g = 10 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

22. D=0.098 g = 20 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

23. D=0.098 g = 40s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

24. D=0.0591 g = 45 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

25. D=0.0591 g = 45 s-1 D=0.098 g = 40s-1 D=0.0591 g = 91 s-1 D=0.0328 g = 53 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

26. D=0.0591 g = 45 s-1 D=0.098 g = 40s-1 D=0.098 g =98 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

27. D=0.0591 g = 45 s-1 D=0.098 g = 40s-1 D=0.0591 g = 182 s-1 D=0.0328 g = 53 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

28. D=0.0591 g = 45 s-1 D=0.098 g = 40s-1 D=0.0591 g = 454 s-1 D=0.0328 g = 53 s-1 PDMS + Hallow Sphere Glass Particles ( 10% by vol.) Mixture

29. g= 40 s-1 g= 10 s-1 PDMS + Glass Sphere(10% by vol.) Mixture Step Rate Experiment

30. PDMS + Glass Sphere(10% by vol.) Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Angle

31. a = 15° g = 18s-1 a = 45° g = 18s-1 a = 75° g = 18s-1 PDMS + Glass Sphere(10% by vol.) Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Angle

32. a = 45° g = 45s-1 a = 15° g = 45s-1 a = 75° g = 45s-1 PDMS + Glass Sphere(10% by vol.) Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Angle

33. a = 75° g = 90s-1 a = 45° g = 90s-1 a = 15° g = 90s-1 PDMS + Glass Sphere(10% by vol.) Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Angle

34. a = 75° g = 181s-1 a = 15° g = 181s-1 a = 45° g = 181s-1 PDMS + Glass Sphere(10% by vol.) Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Angle

35. a = 15° g = 454s-1 a = 45° g = 454s-1 a = 75° g = 454s-1 PDMS + Glass Sphere(10% by vol.) Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Angle

36. PDMS + Glass Sphere(20% by vol.) Mixture Corrected Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Diameters

37. g= 40 s-1 PDMS + Glass Sphere(40% by vol.) Mixture

38. PDMS + Glass Sphere Mixture Corrected Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Loaded Material

39. PDMS + Glass Sphere Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Loaded Material

40. PDMS + Glass Sphere Mixture Apparent Shear Stress vs. Apparent Shear Rate Behavior Comparison of Different Loaded Material

41. Conclusion • It appears that the stability of stick or slip at the wall during extrusion governs the occurrence of surface irregularities. • It is not clear what controls the stability of the boundary condition.

42. Acknowledgement • We acknowledge with gratitude the support of TACOM/ARDEC, NSWC/IH, BMDO/IST (ONR), DARPA, PBMA and various companies including Unilever, Duracell, Henkel-Loctite, GPU, and MPR which made this investigation possible.