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Structured particles in the thermoplastics

Structured particles in the thermoplastics. Joong-In Kim Bayer Corporation Plastics, Technology Oct. 6th, 2000. Emulsion Short Course Yonsei University. Contents. Role of structured particles in thermoplastics Toughening mechanism ABS / HIPS Structure property relationship

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Structured particles in the thermoplastics

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  1. Structured particles in the thermoplastics Joong-In Kim Bayer Corporation Plastics, Technology Oct. 6th, 2000 Emulsion Short Course Yonsei University

  2. Contents • Role of structured particles in thermoplastics • Toughening mechanism • ABS / HIPS • Structure property relationship • Role of emulsion • Structured particles C. Bucknall in Polymer blends, edited by D. Paul et al.

  3. Falling Dart Impact Test Izod Impact Test Measuring ductility of thermoplastics C. Bucknall in Polymer blends, edited by D. Paul et al.

  4. Ductility increase Small addition of the structured rubber particles improves impact strength significantly Role of structured particles Impact strength drop of PC Thick specimen Sharp notch Continuous Mass Emulsion B.S. Lomabardo et al., J. Appl. Polym. Sci., 54, 1697 (1994)

  5. Toughening mechanisms - ABS/HIPS • Crazing • Cavitation • Shear yielding • Wu’s theoretical model C. Bucknall in Polymer blends, edited by D. Paul et al.

  6. Fracture Mechanisms How do we know the mechanisms?

  7. Fracture Mechanisms Let’s break it !!! Are you CRAZ... ?

  8. Aha, Cavities!!! Fracture Mechanisms

  9. TEM of the fractured surface (HIPS) Crazing (large rubber particles) J. Stabenow and F. Haaf, Die Ange. Makro. Chemie, 29, 1 (1973)

  10. Optimum RPS on HIPS Toughening D. Cook et al. J. App. Polym. Sci., 48, 75 (1993) J. App. Polym. Sci., 44, 505 (1992)

  11. TEM of the fractured surface (ABS) Crazing / Cavitation J. Stabenow and F. Haaf, Die Ange. Makro. Chemie, 29, 1 (1973)

  12. Cavitation, not crazing Stress whitening due to cavitation, not crazing H. Breuer, F. Haaf, and J. Stabenow, J. Macromol. Sci., Phys., B14(3), 387 (1977)

  13. Optimum RPS on ABS Toughening D.J. Buckley Jr., Ph.D. Thesis, Cornell Univ. (1993)

  14. Fracture mechanisms on ABS Toughening Cavitation / Shear strain dominant No shear at large RPS (0.5 micron) Little crazing at small RPS D.J. Buckley Jr., Ph.D. Thesis, Cornell Univ. (1993)

  15. Rubber toughening mechanism Wu et al.: Interparticle distance model Critical rubber particle size for the brittle-tough transition at different rubber volume. S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  16. L d t Interparticle distance model • tc : Critical matrix ligament thickness • Independent of rubber volume and size • Characteristic of the matrix • Brittle-tough transition at tc S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  17. Interparticle distance model • Toughness: Matrix property t < tc : Shear yield, toughen t > tc : Brittle failure S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  18. Plane stress Plane strain Interparticle distance model Change in stress state and stress field overlap S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  19. Interparticle distance model • Critical rubber particle diameter for toughness dc = tc [ (p / 6 f r)1/3 - 1 ] dc : Max. diameter of the rubber particles for toughness tc : Critical ligament thickness f r : Volume fraction of the rubber particles S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  20. Schematics of particle dispersion and flocculation Interparticle distance model Connectivity of liagments (Rubber clustering) S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  21. t N Interparticle distance model • As the polydispersity, sg , increases; • the number of particles, n(sg), decreases • the average ligament thickness, t, increases • toughness decreases. S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)

  22. 26 Degree of dispersion on toughness F. Haaf et al., J. Sci. Ind. Res., 40, 659 (1980)

  23. K1c=2.67 K1c=2.55 K1c= 2.26 Degree of dispersion on toughness J. Qian, Ph. D. Thesis, Lehigh University (1994)

  24. Degree of Grafting on Dispersability 25% 40% 65% H. Breuer et al., J. Macromol. Sci., Phys., B14(3), 387 (1977)

  25. Improved toughness with clustering H. Keskkula et al., Poly. Eng. Sci., 30, 21, 1373 (1990)

  26. No sharp transition in ABS • No abrupt change due to increased crazing above tc. • Cavitation/Shear yielding and Crazing should be considered together D.J. Buckley Jr., Ph.D. Thesis, Cornell Univ. (1993)

  27. ABS toughening mechanisms • Toughening mechanisms ; Wu’s model Critical RPS for ductility Not dependent on rubber type Dependent on matrix characteristic (Inherent ductility) Uniform dispersion of small particles • Toughening mechanisms for ABS Rubber cavitation by small particles Crazing by large particles Optimum RPS Non uniform dispersion (Network structure)

  28. G = Gloss and gloss thermal stability • Gloss ; Surface appearance light reflected from the sample surface light reflected from a mirror surface • Gloss decreases with: increasing particle size increasing rubber clustering thermal history (time and temp) decreasing graft level F. Lednicky et al., Ange. Makro. Chemie, 141, 151 (1986)

  29. Rubber particle size and Gloss ln G = ln Gm - D/Do Gm: matrix gloss F. Lednicky et al., Ange. Makro. Chemie, 141, 151 (1986)

  30. Gloss vs Toughness • Max. toughness at intermediate gloss (graft level) F. Lednicky et al., Ange. Makro. Chemie, 141, 151 (1986)

  31. Rubber Particle Clustering • Changes in physical properties Molding time and temperature A. Casale et al., Polym. Eng. Sci., 15, 286 (1975)

  32. Rubber Particle Clustering • Rubber particle size measurement • Stable rubber dispersion in a solvent • Joyce Loebl disk type centrifuge • Agglomeration Index Np= (Dw,c)3/(Dw,p )3 Dw,c = Clustered rubber particle size measured from the molded chip Dw,p = Primary rubber particle size measured from the pellet O.M. Chang et al., PMSE, ACS 71, Washington D.C., 739 (1994)

  33. Severe Molding Condition Mild Molding Condition Rubber Particle Clustering by Np O.M. Chang et al., J. Appl. Polym. Sci., 61, 1003 (1996)

  34. Effect of graft level on melt dispersion M. Huguet et al., Colloidal and Morphological Behavior of Block and Graft Copolymer, Plenum, NY, 183, (1971)

  35. Tough Cosmetic Gloss Toughness Toughness Gloss What kind of Thermoplastics ?

  36. Structure property relationships • Matrix structure • Interparticle spacing • Rubber particle size and size distribution • Rubber matrix compatibility • Large rubber particles and internal occlusions • Cross-linking of the rubber phase • Graft level • Structure of the graft latex C. Bucknall in Polymer blends, edited by D. Paul et al.

  37. Rubber matrix compatibility - thermal expansion C. Bucknall in Polymer blends, edited by D. Paul et al.

  38. AN mismatch on Dispersability 2.5% 11.5% 17.5% 22.5% H. Kim et al., Polymer, 31, 5, 869 (1990)

  39. Max. Toughness of ABS (Fixed SAN graft) H. Kim et al., Polymer, 32, 8, 1447 (1991)

  40. Continuous mass particles Emulsion particles Bimode rubber particles Optimum properties balance C.R. Bernal et al, J. Appl. Polym. Sci., 58, 1 (1995)

  41. Bimode Large Small Bimode rubber particles • Synergistic increase of toughness L. Morbitzer et al., J. Appl. Polym. Sci., 20, 2691 (1976) F. Fowler et al., Polymer, 28, 1703 (1987) & J. Appl. Polym. Sci., 35, 1563 (1988)

  42. Role of Emulsion Technology What you want is what you get !!! Adjust the process parameters to control the structures for the optimum properties

  43. Core Shell Raspberry Sandwich-like Inverted C/S Hemisphere Occlusions Half moon Engulfing Morphologies of Graft Latex Particles

  44. Graft Morphology Control • Thermodynamic Process parameters • Rubber composition • Rubber particle size • Rubber level • Surfactant (Interfacial tension) • Kinetic Process parameters • Initiator type, level, and charging method • Cross-link density of rubber • Monomer metering time • Reaction Temperature • Chain transfer agent

  45. Graft Degree and Graft Density Graft Degree (gd); Ratio between the weight of grafted polymers and the weight of the particles Graft density (s); Number of polymer per unit area of the particles s = gd D rpNA/6Mg D : Diameter of the particles rp: Density of the particles NA : Avogadro’s number Mg : Molecular weight of the grafted polymer Thickness of the grafted polymer t = (D/2) [ (1 + gd rp / rg) 1/3 - 1 ]

  46. Storage Modulus (G’) at second plateau vs graft density Master Curve of the Storage Modulus (G’) for ABS (170 nm, 10% PB) Critical Degree of Grafting Aoki, Macromolecules, 20, 2208 (1987) Aoki et al, Macromolecules, 29, 6656 (1996)

  47. Grafting Degree and chain conformation Under grafting: (gd < gd,c) Mushroom conformation, The particle surface is not well covered. Agglomeration of the particles Optimum grafting: (gd gd,c) The thickness of graft layer equivalent to two radius of gyration. The particles are just well covered and protected Over grafting: (gd > gd,c) Brush conformation, The particle surface is well covered. Matrix chains are expelled from the grafted layer and causes agglomeration Bertin et al, Polym Eng. Sci., 35, 17, 1394 (1995)

  48. Particle size effect on Critical Grafting Critical Grafting for bimodal particle size Effect of particle size on Critical Grafting Bimodal particle size case: Minimum modulus at the same as the small particles Dominated by the small particles Bertin et al, Polym Eng. Sci., 35, 17, 1394 (1995)

  49. Matrix MW on Critical Grafting Matrix Composition on Critical Grafting Rubber level on Critical Grafting Effect of matrix properties on Critical Grafting Critical Degree of Grafting Independent of rubber content and matrix properties Controlled mainly by the particle size and size distribution Bertin et al, Polym Eng. Sci., 35, 17, 1394 (1995)

  50. Optimum graft shell thickness M. Huguet et al., Colloidal and Morphological Behavior of Block and Graft Copolymer, Plenum, NY, 183, (1971)

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