Comparative Study on the Rheological Properties of PS/PP–CaCO3 and PS/PP–Walnut Shell Blends

(Rama AL Jobarani, Douaa Alsaeed, Fawaz Deri and Mhd. Hassan Alkurdi )

---

Abstract

This study presents a comparative rheological analysis of polystyrene/polypropylene (PS/PP 20/80) blends filled with either calcium carbonate (CaCO3) or walnut shell powder at 8 and 12 wt.% loadings. Rheological properties were investigated using a capillary rheometer at temperatures ranging from 190°C to 220°C. The results demonstrate that adding CaCO3 significantly increases shear stress, apparent viscosity, and flow activation energy (up to 12.9 kJ/mol), enhancing rigidity but impairing processability. In contrast, walnut shell composites exhibited a lubricating effect, reducing viscosity by 15–20%, increasing the melt flow index, and lowering the flow activation energy, thereby promoting easier flow. This is attributed to the thermal softening of lignocellulosic components. The optimal balance for processability was achieved with 8% walnut shell at 220°C, while 12% CaCO3 is recommended for applications requiring higher stiffness. These findings underscore the potential of walnut shell as a sustainable, processability-enhancing filler, presenting a clear trade-off between improved flow and mechanical reinforcement.
KEYWORDS
Agricultural waste, capillary rheometry, melt viscosity, polymer composites, processability enhancement, shear thinning

PDF

References

Ak, B. (1994). Composites reinforced with cellulose-based fibers. Progress in Polymer Science, 19(2), 221–74. DOI: 10.1016/0079-6700(94)90040-X.
Al-Kateb, H., Wassouf, H. and Al-Dairi,F. (2023). Study the effect of temperature and shear stresses on flow behavior Polylactic acid - polystyrene (PLA/PS) molten mixture. Tishreen University Journal of Research and Scientific Studies - Basic Sciences Series, 45(6), 61–73. 
Arzumanova, N.B. (2021). Polymer biocomposites based on agro waste: Part III. Shells of various nuts as natural filler for polymer composites. New Materials, Compounds and Applications, 5(1), 19–44. 
ASTM International. (2013). Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer (ASTM D1238-13). ASTM international.
Barnes, H.A., Hutton, J.F. and Walters, K. (1989). An Introduction to Rheology. Elsevier.
Dealy, J.M. and Wang, J. (2013). Melt Rheology and Its Applications in the Plastics Industry. Springer Science and Business Media. 
 Faruk, O., Bledzki, A.K., Fink, H.P. and Sain, M. (2012). Biocomposites reinforced with natural fibers: 2000–2010. Progress in Polymer Science, 37(11), 1552–96. DOI: 10.1016/j.progpolymsci.2012.04.003. 
Fazeli, M., Mukherjee, S., Baniasadi, H., Abidnejad, R., Mujtaba, M., Lipponen, J. and Rojas, O.J. (2024). Lignin beyond the status quo: Recent and emerging composite applications. Green Chemistry, 26(2), 593–630. DOI: 10.1039/D3GC03596G.
Fu, S.Y., Feng, X.Q., Lauke, B. and Mai, Y.W. (2008). Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites. Composites Part B: Engineering, 39(6), 933–61. DOI: 10.1016/j.compositesb.2008.01.002.
Huo, Y., Groeninckx, G. and Moldenaers, P. (2007). Rheology and morphology of polystyrene/polypropylene blends with in situ compatibilization. Rheologica Acta, 46(4), 507–20. DOI: 10.1007/s00397-006-0158-3.
Kloziński, A., Lewandowski, K., Mirowski, J., Barczewski, M. and Jakubowska, P. (2023). Rheological properties of polypropylene composites with calcium carbonate under high shear rates. Polimery, 68(7–8), 403–12.  DOI: 10.14314/polimery.2023.7.3. 
Kuram, E. (2022). Advances in Bio-Based Polymers and Composites: Processing and Applications. In A. Khan (Ed.), Polymer Science and Technology. Elsevier. 
Landel, R.F. and Nielsen, L.E. (1993). Mechanical Properties of Polymers and Composites. (2nd ed.). CRC Press. 
Lee, I.Y., Roh, H.D., Oh, S.Y. and Park, Y.B. (2023). Advanced condition-based self-monitoring of composites damaged area under multiple impacts using Monte Carlo based prognostics. Polymer Testing, 123(n/a), 108024. DOI: 0.1016/j.polymertesting.2023.108024 
Macosko, C.W. (1994). Rheology: Principles, Measurements, and Applications. Wiley-VCH 
Mohamad B.I., Hussein Y.H. and Rafi M.J. (2020). Preparation and Mechanical Characterization of Basalt Fabric, Epoxy, and Silicon Dioxide Composite Materials. Scientific Journal of King Faisal University: Basic and Applied Sciences, 21(2), 167–71. DOI: 10.37575/b/sci/0007
Montfort, J.P., Marin, G., Arman, J. and Monge, P. (1978). Capillary flow of filled polypropylene: Apparent and true values. Polymer Engineering and Science, 18(5), 391–8.  DOI: 10.1002/pen.760180509.
Paul, D.R. and Bucknall, C.B. (2000). Polymer Blends: Formulation and Performance (Vol. 1). John Wiley and Sons. 
Pukanszky, B. (1990). Influence of interface interaction on the ultimate tensile properties of polymer composites. Composites, 21(3), 255–62. DOI: 10.1016/0010-4361(90)90259-U.
Rothon, R.N. (2003). Particulate-Filled Polymer Composites (2nd ed.). Smithers Rapra Publishing. 
Rudolph, N. and Osswald, T.A. (2014). Polymer Rheology: Fundamentals and Applications. Carl Hanser Verlag. 
Rueda, M.M. (2017). Rheology and Processing of Highly Filled Materials, PhD Thesis, Université de Lyon.
Tanner, R.I. (2000). Engineering rheology (2nd ed.). Oxford University Press. 
Tsegaye, B., Ström, A. and Hedenqvist, M.S. (2023). Thermoplastic lignocellulose materials: A review on recent advancement and utilities. Carbohydrate Polymer Technologies and Applications, 5(n/a), 100319. DOI: 10.1016/j.carpta.2023.100319. 
Utracki, L.A. and Wilkie, C.A. (2002). Polymer Blends Handbook. (Vol. 1). Kluwer Academic Publishers.
Wang, Y., Zhang, X., Li, J. and Chen, Y. (2015). Dynamic extrusion rheology of polypropylene filled with calcium carbonate. Polymer Composites, 36(8), 1450–7. DOI: 10.1002/pc.23052.