Experiments and analysis of stress-induced stiffening of a polypropylene

Document Type : Original research

Author

New materials research laboratory, New Borg El Arab city Alexandria, Egypt

Abstract

Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization and thus can lead to an unexpected solidification. This study explores how flow fields influence the crystallization behavior of PP. A controlled-stress rheometer was used to investigate the effect of short shear stress steps on crystallization kinetics. The results revealed that applying a stress step significantly increased the rate of crystallization compared to a non-stressed sample. This acceleration is attributed to the stress-induced orientation of macromolecules, which promotes nucleation. Furthermore, longer durations of applied stress led to a faster increase in viscosity, indicating a higher nucleation density with increasing stress exposure. A mastercurve approach validated the consistency of the model describing the stress-crystallization relationship. The calculated parameter relating to nucleation density confirmed a linear increase with stress duration, allowing estimation of the nucleation rate during shear.

Keywords

Main Subjects

References

  1. Mollova A, Androsch R, Mileva D, Gahleitner M, Funari SS (2013) Crystallization of isotactic polypropylene containing beta-phase nucleating agent at rapid cooling. Eur Polym J 49: 1057-1065 [CrossRef]
  2. Mileva D, Tranchida D, Gahleitner M (2018) Designing polymer crystallinity: An industrial perspective. Polym Cryst 1: 1–16 [CrossRef]
  3. Maddah HA (2016) Polypropylene as a promising plastic: A review. Am J Polym Sci 6: 1–11 [CrossRef]
  4. Pantani R, Speranza V, Coccorullo I, G Titomanlio (2002) Morphology of injection moulded iPP samples. Macromol Symp 185: 309–326 [CrossRef]
  5. Gloger D, Rossegger E, Gahleitner M, Wagner C (2020) Plastic drawing response in the biaxially oriented polypropylene (BOPP) process: polymer structure and film casting effects. Journal of Polymer Engineering 40: 743-752 [CrossRef]
  6. Pantani R, Speranza V, Titomanlio G (2001) Relevance of mold-induced thermal boundary conditions and cavity deformation in the simulation of injection molding. Polym Eng Sci 41: 2022-2035 [CrossRef]
  7. Houichi H, Maazouz A, Elleuch B (2015) Crystallization behavior and spherulitic morphology of poly(lactic acid) films induced by casting process. Polym Eng Sci 55: 1881–1888 [CrossRef]
  8. Pantani R, Titomanlio G (2001) Description of PVT behavior of an industrial polypropylene–EPR copolymer in process conditions. J Appl Polym Sci 81: 267–278 [CrossRef]
  9. Hieber CA (2002) Modeling/simulating the injection molding of isotactic polypropylene. Polym Eng Sci 42:1387–1409 [CrossRef]
  10. Iozzino V, De Santis F, Volpe V, Pantani R (2018) PLA-Based Nanobiocomposites with Modulated Biodegradation Rate. In: Advances in Bionanomaterials, pp 51-60 [CrossRef]
  11. De Santis F, Volpe V, Pantani R (2017) Effect of molding conditions on crystallization kinetics and mechanical properties of poly (lactic acid). Polym Eng Sci 57: 306–311 [CrossRef]
  12. Caelers HJ, Govaert LE, Peters GW (2016) The prediction of mechanical performance of isotactic polypropylene on the basis of processing conditions. Polymer 83: 116-128 [CrossRef]
  13. Speranza V, Sorrentino A, De Santis F, Pantani R (2014) Characterization of the polycaprolactone melt crystallization: Complementary optical microscopy, DSC, and AFM studies. Sci World J 2014: 720157 [CrossRef]
  14. Billon N, Castellani R, Bouvard JL, Rival G (2023) Viscoelastic properties of polypropylene during crystallization and melting: Experimental and phenomenological modeling. Polymers (Basel) 15: 3846 [CrossRef]
  15. Pantani R, Speranza V, Titomanlio G (2014) Evolution of iPP relaxation spectrum during crystallization. Macromol Theory Simul 23: 300–306 [CrossRef]
  16. Roy D, Audus DJ, Migler KB (2019) Rheology of crystallizing polymers: The role of spherulitic superstructures, gap height, and nucleation densities. J Rheol 63: 851-862 [CrossRef]
  17. Pantani R, Speranza V, Titomanlio G (2015) Simultaneous morphological and rheological measurements on polypropylene: Effect of crystallinity on viscoelastic parameters. J Rheol 59: 377-390 [CrossRef]
  18. Speranza V, Liparoti S, Pantani R, Titomanlio G (2019) Hierarchical structure of iPP during injection molding process with fast mold temperature evolution. Materials 12: 12030424 [CrossRef]
  19. Volpe V, De Filitto M, Klofacova V, De Santis F, Pantani R (2018) Effect of mold opening on the properties of PLA samples obtained by foam injection molding. Polym Eng Sci 58: 475–484 [CrossRef]
  20. Viana JC, Cunha AM, Billon N (2002) The thermomechanical environment and the microstructure of an injection moulded polypropylene copolymer, Polymer (Guildf) 43: 4185–4196 [CrossRef]
  21. Vietri U, Sorrentino A, Speranza V, Pantani R (2011) Improving the predictions of injection molding simulation software, Polym Eng Sci 51: 2542–2551 [CrossRef]
  22. Pantani R, Speranza V, Titomanlio G (2001) Relevance of crystallisation kinetics in the simulation of the injection molding process, Int Polym Proces 16: 61–71 [CrossRef]
  23. Derakhshandeh M, Mozaffari G, Doufas AK, Hatzikiriakos SG (2014) Quiescent crystallization of polypropylene: Experiments and modeling, J Polym Sci Pol Phys 52: 1259–1275 [CrossRef]
  24. Xu J, Srinivas S, Marand H, Agarwal P (1998) Equilibrium Melting Temperature and Undercooling Dependence of the Spherulitic Growth Rate of Isotactic Polypropylene. Macromolecules 31: 8230-8242 [CrossRef]
  25. Hieber CA (1995) Correlations for the quiescent crystallization kinetics of isotactic polypropylene and poly(ethylene terephthalate). Polymer (Guildf) 36: 1455-1467 [CrossRef]
  26. Sorrentino A, Pantani R (2009) Pressure-dependent viscosity and free volume of atactic and syndiotactic polystyrene. Rheol Acta 48: 467-478 [CrossRef]
  27. Zhong G-J, Yang S-G, Lei J, Li Z-M (2024) Flow-induced polymer crystallization under pressure and its engineering application in “structuring”. Macromolecules 57: 789-809 [CrossRef]
  28. R. Pantani, A. Sorrentino (2005) Pressure effect on viscosity for atactic and syndiotactic polystyrene, Polym Bull 54: 365-376 [CrossRef]
  29. Hamad FG, Colby RH, Milner ST (2015) Onset of flow-induced crystallization kinetics of highly isotactic polypropylene. Macromolecules 48: 3725-3738 [CrossRef]
  30. Nie C, Peng F, Cao R, Cui K, Sheng J, Chen W, Li L (2022) Recent progress in flow‐induced polymer crystallization. J Polym Sci 60: 3149-3175 [CrossRef]
  31. Speranza V, De Santis F, Pantani R (2024) Effect of isothermal shear flow on morphology evolution of an isotactic polypropylene, Polymer (Guildf) 295: 126752 [CrossRef]
  32. De Santis F, Pantani R, Titomanlio G (2016) Effect of shear flow on spherulitic growth and nucleation rates of polypropylene. Polymer (Guildf) 90: 102-110 [CrossRef]
  33. Boutaous M, Bourgin P, Zinet M (2010) Thermally and flow induced crystallization of polymers at low shear rate. J Nonnewton Fluid Mech 165 (2010) 227-237 [CrossRef]
  34. Roozemond PC, van Drongelen M, Verbelen L, Puyvelde VP, Peters GWM (2014) Flow-induced crystallization studied in the RheoDSC device: Quantifying the importance of edge effects. Rheol Acta 54: 1-8 [CrossRef]
  35. Custódio FJMF, Steenbakkers RJA, Anderson PD, Peters GWM, Meijer HEH (2009) Model development and validation of crystallization behavior in injection molding prototype flows. Macromol Theory Simul 18 (2009) 469-494 [CrossRef]
  36. Zhou YG, Shen CY, Liu CT, Li Q, Turng LS (2010) Computational modeling and numerical simulation of flow-induced crystallization kinetics during injection molding of polyethylene terephthalate. J Reinf Plast Compos 29: 76-85 [CrossRef]
  37. Tanner RI, Qi F (2005) A comparison of some models for describing polymer crystallization at low deformation rates, J Nonnewton Fluid Mech 127: 131–141 [CrossRef]
  38. Volpe V, Foglia F, Pantani R (2021) Flow-induced crystallization of a Poly(Lactic acid): Effect of the application of low shear rates on the polymorphous crystallization. Polymer (Guildf) 229: 123997 [CrossRef]
  39. Ma Z, Steenbakkers RJA, Giboz J, Peters GWM (2011) Using rheometry to determine nucleation density in a colored system containing a nucleating agent, Rheol Acta 50: 909-915 [CrossRef]
  40. Koscher E, Fulchiron R (2002) Influence of shear on polypropylene crystallization: morphology development and kinetics, Polymer (Guildf) 43: 6931-6942 [CrossRef]
  41. Boutaous M, Bourgin P, Zinet M (2010) Thermally and flow induced crystallization of polymers at low shear rate, J Nonnewton Fluid Mech 165: 227-237 [CrossRef]

Files

History

  • Receive Date: 05 May 2024
  • Revise Date: 31 May 2024
  • Accept Date: 05 June 2024
  • First Publish Date: 06 June 2024

Share

How to cite

Statistics