In order to be recycled, polymers with different molecular masses, designed to be initially processed by different technologies such as thermoforming, injection or blow molding, are collected together. The melt viscosity of this material mixture will depend on the ratio of polymers having different molecular characteristics. The possibility of re-processing implies the use of higher range of temperature or the use of different additives to adjust the melt viscosity. In these conditions, the quality of recycled goods could be affected. This study presents the results obtained by differential scanning calorimetry analysis of some polypropylene-based samples coming from the real waste stream collection (conventional samples) as well as of selected polymers from this stream based on the processing technology and of different brand packages from each of the above-mentioned classified fractions. Based on the thermal data (Tm, Tc, ΔHm, ΔHc and the melting and crystallization curve characteristics), morphological features of the recycled polypropylene, such as crystallinity degree of the initial recycled and re-crystallized polymers (Xm, Xc), melting and crystallization rates (vm, vc), lamellae thickness, and number of tie molecules, were determined, and the prediction of the maximal Young’s modulus was made. This study evidenced that processing technology of the polymers in fresh state or as recycled material strongly influenced the product morphology and, as a consequence, the predicted mechanical properties. By comparing the conventional recycled polymers with the injection-molded mix of virgin polymers, the first one exhibited a lower crystallinity with about 22%, approximately the same lamella thickness, the crystals’ polydispersity higher with about 10% and the Young’s modulus lower with about 22%.
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We acknowledge the contribution of Erasmus + master student Alexandra Rusanescu, from Transilvania University of Brasov, Romania, and master student Emma P.A. van Bruggen, from Delft University of Technology, the Netherlands, which prepared the samples used in this study under the kind and competent supervision of Prof. Dr. Peter C. Rem, from Delft University of Technology, Civil Engineering and Geosciences Faculty.
Satilla C, Cafiero L, De Angelis D, La Marca F, Tuffi R, Vecchio Ciprioti S. Thermal and catalytic pyrolysis of a mixture of plastics from small waste electrical and electronic equipment (WEEE). Waste Manag. 2016;54:143–52.CrossRefGoogle Scholar
Costiuc L, Tierean M, Baltes L, Patachia S. Experimental investigation on the heat of combustion for solid plastic waste mixtures. Environ Eng Manag J. 2015;14(6):1295–302.CrossRefGoogle Scholar
Costiuc L, Baltes L, Patachia S, Tierean M, Lunguleasa A. Influence of reprocessing by melt-mixing and thermo-formation of polyolefin fractions, separated from wastes, on their calorific power. Bulg Chem Commun. 2018;50:165–71.Google Scholar
Stromberg E, Karlsson S. The design of a test protocol to model the degradation of polyolefins during recycling and service life. J Appl Polym Sci. 2009;112:1835–44.CrossRefGoogle Scholar
Blanco I, Siracusa V. Kinetic study of the thermal and thermo-oxidative degradations of polylactide-modified films for food packaging. J Therm Anal Calorim. 2013;112(3):1171–7.CrossRefGoogle Scholar
Zhang C, Yi X-S, Asai S, Sumita M. Morphology, crystallization and melting behaviors of isotactic polypropylene/high density polyethylene blend: effect of the addition of short carbon fiber. J Mater Sci. 2000;35(3):673–83.CrossRefGoogle Scholar
Varga J. Crystallization, melting and supermolecular structure of isotactic polypropylene. In: Karger-Kocsis J, editor. Polypropylene: structure, blends and composites. London: Chapmann&Hall; 1995. p. 56–115.CrossRefGoogle Scholar
Addink EJ, Beintema J. Polymorphism of crystalline polypropylene. Polymer. 1961;2:185–93.CrossRefGoogle Scholar
Phillips PJ, Mezghani K. Polypropylene, isotactic (polymorphism). In: Salamon JC, editor. The polymeric materials encyclopedy. Boca Raton: CRC Press; 1996. p. 6637–49.Google Scholar
Nitta KH, Takayanagi M. Role of tie molecules in the yielding deformation of isotactic polypropylene. J Polym Sci, Part B: Polym Phys. 1999;37:357–68.CrossRefGoogle Scholar
Nitta KH, Takayanagi M. Tensile yield of isotactic polypropylene in terms of a lamellar-cluster model. J Polym Sci, Part B: Polym Phys. 2000;38:1037–44.CrossRefGoogle Scholar
Wunderlich B. Thermal analysis of polymeric materials. Berlin: Springer; 2005.Google Scholar
Furushima Y, Nakada M, Murakami M, Yamane T, Toda A, Schick C. Method for calculation of the lamellar thickness distribution of not-reorganized linear polyethylene using fast scanning calorimetry in heating. Macromolecules. 2015;48(24):8831–7.CrossRefGoogle Scholar
Horváth Z. Correlation between molecular architecture and properties in semicrystalline polypropylene. PhD thesis, Published by Laboratory of Plastics and Rubber Technology, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, Budapest; 2014.Google Scholar
Horváth Z, Menyhárd A, Doshev P, Gahleitner M, Tranninger C, Kheirandish S, Varga J, Pukánszky B. Effect of molecular architecture on the crystalline structure and stiffness of iPP homopolymers: modeling based on annealing experiments. J Appl Polym Sci. 2013;130:3365–73.CrossRefGoogle Scholar
Menyhárd A, Suba P, László Z, Fekete HM, Mester ÁO, Horváth Z, Vörös G, Varga J, Móczó J. Direct correlation between modulus and the crystalline structure in isotactic polypropylene. Express Polym Lett. 2015;9:308–20.CrossRefGoogle Scholar
Molnár J, Jelinek A, Maloveczky A, Móczó J, Menyhárd A. Prediction of tensile modulus of semicrystalline polymers from a single melting curve recorded by calorimetry. J Therm Anal Calorim. 2018;134:401–8.CrossRefGoogle Scholar
Clark EJ, Hoffman JD. Regime lll crystallization in polypropylene. Macromolecules. 1984;17:878–85.CrossRefGoogle Scholar
Pukánszky B, Mudra I, Staniek P. Relation of crystalline structure and mechanical properties of nucleated polypropylene. J Vinyl Addit Technol. 1997;3:53–7.CrossRefGoogle Scholar